Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1

Lithium ion batteries (LIB) are widely applied to energy storage systems, like electric vehicles, ships. While limited reserves of lithium and cost of lithium enforced to explore new materials. Hence, Low cost and abundance of sodium has made Sodium ion batteries (SIBs) an attractive alternative for energy storage. Li ion replacement with Na ion will not require change of design in present LIBs, except change of cathode material (based on Na) and respective electrolyte. But the challenge exists to develop sodium cathode with good electrochemical performance and excellent thermal stability. Therefore, various crystal structure for sodium cathode material were explored to meet these challenges. Among cathode materials, pyrophosphate family represented high theoretical capacity due to existence of two sodium ions in a repeating unit. In this report we synthesized mixed pyrophosphate cathode, Na2Fe1/2Mn1/2P2O7, via simple solid state process. The precursors, Na2CO3 (Aldrich), (NH4)2HPO4 (Aldrich), FeC2O4.2H2O (Aldrich) and MnC2O4.2H2O (Aldrich), were mixed in stoichiometric ratio and extensively grinded in mortar and pestle. The fine powder was subjected to heat treatment under inert atmosphere at 350 °C, cooled, grinded and then annealed in inert atmosphere at 600 °C for 6 hours. The compositional and structural analyses confirmed the formation of a crystalline pure phase. The optimization of operation temperature, time and atmosphere (inert); and the formation of mixed component systems (i.e., incorporation of more than one transition metal) not only lead to single phase mode but also tune the voltage potential for high energy density. The X-ray diffraction (XRD) data of as-synthesized Na2Fe1/2Mn1/2P2O7 was indexed to a triclinic structure. This triclinic structure has open framework which facilitated diffusion of Na-ions during charging and discharging. Thermogravimetric Analysis (TGA) showed negligible weight loss (∼5%) when heated to 550 °C, indicating decent thermal stability of the material and differential thermal Analyses (DTA) hardly observed any endothermic or exothermic peak. Carbon coating of Na2Fe1/2Mn1/2P2O7 was proceeded to impregnate electrical conductance in the material. SEM images showed the difference between pristine Na2Fe1/2Mn1/2P2O7 and carbon coated Na2Fe1/2Mn1/2P2O7. The carbon coated Na2Fe1/2Mn1/2P2O7 was, then, casted on aluminum to prepare cathode. The casted material (cathode) was dried at 70 °C under vacuum for two hours. The materials was then assembled into coin cell as a cathode in the glove box. The electrochemical measurements confirmed that Na2Fe1/2Mn1/2P2O7 is electrochemically active at room temperature. It showed a single-phase reaction during cycling. This single phase reaction is changed by the Na environment through a change in Na/Vacancy ordering. The Na2Fe0.5Mn0.5P2O7 cathode represented discharge capacity of 80 mAh/g at C/20 in the voltage range of 2.0 to 4.5 V. The average redox potential was observed to be approximately 3.2 V (vs. Na/Na⁺). The capacity retention of Na2Fe0.5Mn0.5P2O7 is 84% over 90 cycles. Between first charge capacity and second charge capacity, Na2Fe0.5Mn0.5P2O7 cathode showed a difference of 5mAh/g only. This employs that sodium based mixed iron-manganese pyrophosphate (Na2Fe0.5Mn0.5P2O7) cathode has increased occupancy. The rate capability of Na2Fe0.5Mn0.5P2O7 shows 70% retention from 0.05 C to 0.5 C. Synthesis of Na2Fe1/2Mn1/2P2O7 in nanometric size may result in further improvement in its electrochemical performance.

Environmental conditions such as irradiance, temperature, humidity and dust accumulation have impact on PV performance and reliability. In this paper, we will focus on the effect of temperature and how to mitigate this effect by using passive cooling approach.

Qatar is rich with solar irradiance favored for photovoltaic; however, the high temperature (a module temperature of 50°C was measured during summer months) has a negative impact on the power output of a PV module. Operation of solar PV systems under extremely high temperatures and high humidity in hot climates represents one of the major challenges to guarantee higher system's reliability. Therefore, thermal management in hot climates is crucial for reliable application of PV systems, as it has a potential to increase the efficiency and life expectancy and to stabilize the output power characteristics.

Apart from that, dust accumulation on PV module is known to be also as one of the challenges that affect the PV power output. Due to the difference in ambient temperature between day and night, water condensation on PV modules was observed. Dust accumulated on a PV module together with water condensation may cause a thick layer of mud that is difficult to be removed. In this paper, we will show that, condensation of water on the cell surface during night can be prevented by maintaining the temperature of solar PV panels above the dew point during night.

Application of Phase Change Materials (PCM) for passive or combined active-passive cooling systems offers various options for adequate thermal management solutions. The present research focuses on utilization of PCM for passive thermal management of solar systems. Passive cooling can be realized by integration of PCM layers with the back side of PV panels. Passive cooling use the high temperature differences between day and night in arid desert regions, due to sky radiation in the night. The high thermal capacity of PCM accumulates coolness during night to keep the PV cells at a moderate temperature during the day. This also can help maintaining the PV panel temperature well above the dew point to prevent condensation during day and night, thereby avoiding mud formation on the panel surface. In some instances, active cooling may still be needed during peak solar radiation hours around noon time in summer, however integration of PCM can also reduce significantly the pumping power required to circulate the cooling medium as well as the external thermal/cool storage size and cost.

Although PCM provides high energy storage density and nearly isothermal behavior around the phase change temperature, they suffer from low thermal conductivity, which limits the power density during charging and discharging. The low thermal conductivity of a PCM can be increased by combining them with highly conductive heat transfer structures. One advanced option is the application of cellular materials like metal fibers, which allow a significant enhancement of the PCM absorber thermal conductivity by more than 100 times. Hence it is proposed to hybridize PCM with cellular metallic matrices to enhance the thermal conductivity and provide a practical solution for easy encapsulation and integration with the PV panels.

The main focus of this study is therefore to explore the effect of utilization of PCM based cooling elements incorporating cellular metallic heat conducting structures on the thermal behavior of solar PV panels.

Preliminary laboratory experimental investigations have been carried out to characterize the thermal resistances between the PV panel and the PCM matrix absorber using different coupling mechanisms attached to the backside of PV panels. The coupling mechanisms include mechanical clamping, adhesive bonding, and double side thin and thick adhesive tapes. Based on the measured data, design recommendations for the desired performance will be discussed. The outcomes of the laboratory experimental investigations provide important input parameters that are needed in numerical analysis and design optimization of such systems under weather conditions in Qatar and elsewhere.

Beside the laboratory experimental work, theoretical analysis to optimize the properties of the PCM matrix absorber for application of solar PV systems in Qatar has been carried out. The simulation model has been developed using homogenization based on volume averaging techniques and interpenetration continua approach. Due to complexity of the underlying transport phenomena, solution of highly nonlinear coupled system of equations with moving boundaries is required as a function of space and time. Hence, numerical modeling and optimization of large scale PCM storage is both challenging and computationally expensive. However, in engineering systems microscopic details are neither easy to be captured nor needed, instead, the macroscopic aspects are much more interesting. Therefore, dealing with a large-scale PCM storage, a fundamental question arises as how to bridge the computational scale and reduce the problem to a simple one. A simplified modeling approach and numerical procedures shall be proposed to determine the macroscopic transport and time history of the PCM temperature field in a PCM thermal storage. The model is fairly general to be applied as a design and optimization tool for thermal energy storage and thermal management systems. Preliminary results of the numerical simulation shall be presented and discussed.

Due to similarity of climatic conditions in the GCC, the solution can be easily adapted to suit other countries in the Gulf. The fibrous porous structure can be manufactured using wastes of metals processing such as in manufacturing aluminum profiles. PCM candidates with low temperature and desired thermo-physical properties, such as paraffin waxes, are abundantly available with reasonable cost. Further cost reductions for manufacturing of PCM matrix absorbers can be achieved by integration with the PV support structure. This an important part of the ongoing research in collaboration with local industry partners in Qatar in order to produce these systems locally on a commercial scale effectively with lower costs. Preliminary analysis shows that the passive thermal management can increase both instantaneous conversion efficiency by 3–5%, while it can considerably increase the life span of PV modules and reduces maintenance and cleaning costs. These factors hold a great promise for supporting the economic viability of passive thermal management using PCM matrix absorbers. However, detailed technoeconomic analysis will be elaborated within the framework of this project and will be published later.

The main target of membrane technologies such as the Ultrafiltration (UF), Nanofiltration (NF) and Reverse osmosis (RO) is to produce better filtration and separation of organic and inorganic substance from water as well as for longer life of the membrane. The phase inversion method is a well-known method to fabricate UF, NF and RO membranes for different application. The UF membrane is widely used in separation of macromolecules from solution as pretreatment stage with higher efficiency in hybrid process. The UF membrane made by pure polymer showed low flux, which affect on process performance of separation. The Polysulphone (PSF) is the most common polymer used in UF membrane which a hydrophobic material is making its surface prone to fouling due to adsorptive mechanism. This limitation of UF membranes have been solved by blended with nanoparticles incorporated membranes which showed significant enhancement on permeability, surface hydrophilicity, mechanical properties and other properties such as the selectivity. The main objective of this study to modify of UF membrane by blended with new composite nano-material for higher rejection of salt and organic substances. The graphene-zinc iron oxide composite as new nano-material was synthesized by sol gel method at low temperature of preparation. The composite was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) to show the structure, morphology and particle size of nanoparticles. Thermal decomposition was determined using thermogravimetric–differential scanning calorimetry (TGDSC). The results showed that cubic system of zinc iron oxide nanoparticles with 8 nm of crystal size was obtained using XRD. The morphology using TEM showed zinc iron oxide composite graphene as layer of nanoparticles with size lower than 10 nm which confirmed the XRD results. The novel synthesized of zinc iron oxide nanoparticles embedded in graphene incorporated into polysulfone (PSF) with 0.5 wt. % loading which significant impact on the UF membrane properties was investigated. The effect of composite additive on membrane properties was investigated in terms of permeability, hydrophilicity (contact angle), zeta potential, porosity and pore size. However, the membrane cross section, surface, EDX and mapping were also analyzed using FESEM include EDX analyzer. This composite incorporated PSF showed significant improvement in terms of surface hydrophilicity with reduction of about 25% (reduce contact angle from 82 to 62°). This improvement confirms by increasing the zeta potential values and surface negatively charge of blended PSF with composite compared to pure PSF membrane. The permeability results showed that significant increased more than two times compared to pure PSF membrane. The phenomenon of permeability increasing was attributed to increase of porosity of blended membrane which becomes lower resistance of water permeation. Generally, the rate of pore production has been reported directly affected by rate of solvent and non-solvent exchange in phase inversion process. However, higher rejections of organic substances such as the dyes and humic acid as well as the salt such as Sodium sulfate (Na2SO4) were maintained using UF at low pressure. This enhancement affects on time and load of process especially when hybrid with Nanofiltration (NF) which can increase of membrane life and reduce of overall process cost. The results of this study will have bigger impact in the future for different application including for water treatment and desalination.

With around 60–80% of electricity used for air conditioning, and around 99% of potable water production being supplied by desalination plants, sustaining life in Qatar, as well as GCC and hot arid countries around the world, is uniquely energy intensive.

As District Cooling Plants (DCPs) have a potential to reduce energy consumption and CO2 emissions, Qatar and GCC are continuously shifting paradigm towards adoption of DC plants to satisfy the rapidly growing demand in all sectors. However, DC plants usually rely on wet cooling towers for disposing the excess heat to the ambient. Thus the heat disposal is accompanied by considerable loss of fresh water, a common problem in hot arid countries with highest demand for air cooling and also relies on costly and energy intensive desalination processes for securing fresh water supply. In addition to this, evaporative cooling devices and wet cooling towers can spread humidifier fever, a serious health risk with similar symptoms as mild influenza, and Legionella, which can be deadly. Hence huge evaporation loss in densely populated urban centers in Qatar and GCC is an imperative environmental issue which necessitates effective and practical solutions.

This study presents an invention, which involves an innovative process called the “SELF-SUSTAINABLE DISTRICT COOLING AND DESALINATION (SSDD)”. The patented solution is directed to construct a totally new concept for maximization of water and energy use efficiency in district cooling plants in hot arid countries while preserving the environment. The system couples district cooling plants with polishing of treated sewage effluents (TSE) using hybrid reverse osmosis and thermal desalination technologies with the district cooling plant. The desalination process is equipped with a zero liquid discharge (ZLD) system to achieve full recovery of the TSE resource and eliminate the common environmental problem related to brine disposal. The invention closes the water and energy circuits in DC plants, which considerably enhances the overall water and energy efficiencies.

The techno-economic analysis of the SSDD technology has revealed a breakthrough in the technology in terms of reducing energy consumption by 20–30% and water consumption by more than 50%. Considering, for instance, a planned capacity of 1.6 million refrigeration ton DCPs to be added in Qatar by 2022, the SSDD can save up to 200,000 m³/day evaporation losses and 650 MW of electrical power together with elimination of water distribution power needed for pumping potable water from desalination plants to the DCPs. The total energy saving corresponds with 3.5 Million ton reduction of CO2 emissions and more than 1.5 Billion QAR/year excluding the environmental benefits. Considering the ambitious development plans of other GCC states, the SSDD technology may play a significant role in achieving sustainable development goals not only in the region but also worldwide. Thus it holds a great promise for energy and water securities as well as combating global climate change.

The new RO/ZLD concept can be used for applications other than DC, e.g. waste water treatment and reuse, aquifer recharge, football stadia, irrigation for the Qatar National Food Security Program (QNFSP). Moreover, this process can be applied around GCC, Middle East and North Africa (MENA) as well as other hot parts of the world.

Abstract

The present paper evaluates the composite risk of anthropogenic and climate change on the future water status in Jordan during the period 2030–2050. The projected water status in the country is evaluated based on the more likely population growth and climate change scenarios. The most likely figure for the population of Jordan, excluding refugees from neighboring countries, in 2040 would be ∼15 million people. Given this likely projection, though conservative, annual water needs for the domestic sector alone are expected to be between 700 and 800 million m³, with the current level of water consumption. A rise in near surface air temperature by 2 °C and a drop in total precipitation by 15%, as projected by most Global Circulation Models, would diminish renewable water resources in the mountainous region by ∼ < /AσΣETHιγηλιγητ>25–40%, being more severe as aridity increases.

1. Introduction

There is almost a consensus among earth scientists that the buildup of greenhouse gases in the atmosphere is leading to a global warming. Documented evidence suggests that global temperature observed over continental and marine regions has been rising for the past several decades (IPCC, 2007). The increased air temperature will intensify the hydrological cycle due to increased water vapor release into the atmosphere. Recent unprecedented severe meteorological events such as large scale torrential rains in many parts of the world and the recurrent tropical cyclones invading the southern parts of the Arabian Sea could be cited as a strong evidence of a global climate change. A climate change towards warmer conditions is expected to increase precipitation over the Arabian Peninsula due to the northward extension of the Monsoon Trough which will enhance the Red Sea Trough during the transitional periods, Fall and Spring.

There is almost a consensus among most GCM that a global warming will be most severe in the eastern Mediterranean, with a significant drop in precipitation and a large temperature rise (Zhang et al., 2005; IPCC, 2007; Kelley et al., 2012). Model results suggest that near surface air temperature will increase by 2–3.5 °C following an equivalent doubling of Carbon Dioxide in the atmosphere (Kelley et al., 2012). The projections for precipitation amount, its temporal distribution and variability are not as certain. Due to the northward retreat of the polar front during the winter months, however, the eastern Mediterranean is expected to experience less cyclogenic activities, and as such less winter storms, leading to a precipitation decline (Schulz et al., 2008). It is also projected that the timing and frequency of precipitation in this region will be more erratic, less frequent but more intense. Statistical evidence show a strong reduction in the number of rainy days with precipitation in excess of one mm day-1.

Population growth adds another negative dimension to the water crisis. This includes more water demands for the domestic, agricultural, tourism, and industrial sectors. Additionally, increased population causes severe deterioration to surface and underground water quality through large scale land use changes, release of large volumes of waste, gaseous and liquid effluents and solid waste disposal. It is clear that anthropogenic and natural forcings work hand in hand to adversely impact Jordan's limited water resources. As such, two operational questions need to be answered:

1- What is the near future water needs in the country?,

2- What is the water availability for the near future following a climate change?

Answering these two questions adequately is essential for a better assessment of the relative impacts of climate change and population growth on water availability, demands, and stress during the near future. This projection can be used to minimize the potential risks of the projected climate change and population growth.

2. Current water availability in jordan

Around 70% of precipitation in Jordan falls in the winter months, December through February, due mainly to cyclogenic activities; the other 30% fall in the transitional periods. Average annual precipitation in the country ranges from a ∼600 mm in a small enclave in northwestern Jordan to less than 5 mm near the Saudi borders (Fig. 1). Additionally, this area receives large quantities of solar radiation year around due to persistently clear skies triggered by large scale subsidence. The combination of scanty precipitation along with a large global radiation enhances direct evaporation and substantially limits blue water availability. The average annual renewable water resources in Jordan are estimated at about 800–850 million cubic meters (M m³) (Ministry of Water and Irrigation, Jordan, 2015).

There is observational evidence that precipitation in the country is declining; Fig. 2 shows a time series of precipitation in two stations, one in northern Jordan during the period, 1945 through 2005, and the other one in central Jordan, Rabbah in the Karak Plateau. Both linear regression and Mann-Kendall non-parametric tests reveal that annual precipitation in all stations in the country is declining.

3. Future population

The population of Jordan experienced a large growth during the past 60 years due to natural growth and as a result of political conflicts. The population of the country, however, swelled by about 20 times during the past 60 years. The invasion of Iraq caused a mass movement of Iraqis towards Jordan. The current civil war in Syria paints another unpleasant, in fact very gloomy, portrait of the population dynamics in Jordan, with current population close to 11 million people.

The population growth was paralleled by a similar increase in irrigated agriculture. The area of irrigated lands in the Jordan Valley increased from ∼15 thousand hectares in the early 1960's to ∼38 thousand hectares in 2011. Likewise, irrigated agriculture in the desert region increased from virtually nil in the early 1970's to ∼17 thousand hectares in 2008 (Ministry of Water and Irrigation, 2012). The substantial increase in the irrigated agricultural land caused further demands on freshwater. The availability of irrigation water will shrink in the near future, however, because of growing demands on this resource from other sectors, mainly the domestic sector. The future water status in the country would indeed look quite bleak should population growth continues unabated and a climate change towards warmer and/or drier conditions prevail in the near future.

4. Future Water Needs

Official figures provided by the Ministry of Water and Irrigation, Jordan (2015) indicated that current domestic freshwater supply is ∼150 liters per person/day, which gives a total annual freshwater need of 370 M m³. Nowadays, with only 7.5 million inhabitants (excluding fresh refugees), most households in Jordan receive a specified amount of water during the summer months, and domestic water is supplied once (few hours) per week. Renewable water resources in the country were not enough to meet the water demands, and as such non-renewable fossil freshwater resources have been intensively exploited during the past several decades. These measures have caused steady drop in the level of underground aquifers and resulted in poor water quality. The Dissi Project, conveying fossil water is expected to provide freshwater for several decades before it dries up completely.

Projections based on future population growth scenarios indicate that annual domestic water needs alone will range from a minimum of 550 M m³ to a value close to 1100 M m³ by 2050. A more likely figure would probably be between 700–800 M m³. Thus, renewable freshwater resources of the entire country will barely meet domestic water needs even without a climate change.

Currently, the agricultural sector accounts for about 65% of total freshwater consumed in Jordan (MWI, 2015). Paradoxically, the amount of water allocated for irrigation must drop in the near future because of demands by relatively more needy sectors, the domestic one in

particular. Based on population growth alone, it is obvious that the future water status in the country looks quite bleak even without a climate change. Should the climate of the eastern Mediterranean become warmer and/or drier or both, the country will face a serious, probably tragic, freshwater dilemma in the very near future which will ultimately lead to economic, social and political unrest. The anticipated climate change will seriously influence the future water crisis in Jordan.

5. Projected climate change impact

A climate change in the eastern Mediterranean will impact water resources in at least three ways: 1) reduces blue water availability due to increase direct evaporation from soils, 2) intensifies irrigation water demands, and 3) increases evaporation losses from dams and open water canals. The impact of climate change on the available water resources in Jordan is investigated using a water balance model with a temporal resolution of one day. The model is run over the mountainous areas of Jordan where around 65% to 70% of blue water is generated (Oroud, 2015). A detailed description of the model is presented elsewhere (Oroud, 2008; 2011). Figure 4 shows the linkage between annual blue water availability and annual precipitation as calculated by the daily model. Conservative calculations show that a 2 °C temperature increase along with a 15% reduction in precipitation decreases water availability, on average, by ∼ 25%–40% depending on the level of aridity, being more sever as in more arid regions. This means that renewable water resources in the country following a warmer, drier climate will probably be between 500–650 M m³ by 2050. This conclusion is commensurate with those presented by other investigators (e.g., IPCCk 2007; Margane et al. 2008; Suppan et al. 2008; Giorgi and Lionello, 2008; Kelley et al., 2012).

Irrigation water needs under current climate conditions and following a climate change were simulated for the Jordan Valley using a spatially distributed daily model. Following a climate change, the irrigation water needs will increase by around 15%. This is equivalent to 40 to 50 M m³ of extra irrigation water needed to maintain the irrigation water demands in the Jordan Valley at the current land use regime.

References

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Margane A., et al., 2008, Water resources protection efforts in Jordan and their contribution to a sustainable water resources management. In F. Zereini and H. Hotzl (eds) Climatic Changes and Water Resources in the Middle East and North Africa, Springer, pp. 325–345.

Kelley, C., et al., 2012, Mediterranean precipitation climatology, seasonal cycle and trend as simulated by CMIP5, Geophysical Research Letters, 39, DOI: 10.1029/2012GL053416

Oroud, I. M., 2008. The impact of climate change on water resources in Jordan. In: F. Zereini and H. Hotzl (eds) Climatic Changes and Water Resources in the Middle East and North Africa, Springer, pp 109–123.

Oroud, I. M., 2012a, The relative impacts of climate change on water resources in Jordan, in: National Security and Human Health Implications of Climate Change (H. Fernando et al., eds.), DOI 10.1007/978-94-007-2430-3-31, Springer Science.

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Buildings represent one of the most significant sources of negative impacts to the natural ecosystems on which Qatar's inhabitants health and environmental quality depend. The market has identified Qatar as one of the busiest construction areas in the world (Ibrahim 2011), While rapid economic development, population growth, and construction boom are positive indicators of growth, they may also present issues related to the negative impact on the socio-environmental components of cities. Such is the case of the Gulf Cooperation Council (GCC) countries where increasing economic prosperity has led to a surge in tall building construction and a sense of competition to erect the tallest skyscrapers in the world (Mahgoub and Abarra 2012).

While tall buildings are a source of national pride and cultural identity enabled by economic prosperity, they pose several challenges to integrate with the urban fabric of the city while also having a tremendous environmental impact. Tall buildings are especially massive consumers of energy (Ali and Armstrong 2008). They are the dominant elements in urban architecture due to their scale and purpose, and should be the focus of sustainable design. With large number of towers constructed and to be constructed in Al Dafna and West Bay areas of Doha, these buildings affect different aspects of the built and urban environment, i.e., city image, traffic, urban spaces and physical conform. Therefore, more architectural design strategies have to be planned well ahead in order to tackle the issues of sustainability and adaptability to climate change and to foster sustainable built environment in the state of Qatar.

With Qatar slated to host a ‘zero carbon’ World Cup in 2022, Qatar Green Building Council (QGBC) has set up a group to foster green infrastructure as a national resource. Qatar is utilizing Leadership in Energy and Environmental Design (LEED) and the Global/Qatar Sustainability Assessment System (GSAS/QSAS) to this end. Furthermore, shortages in raw materials between 2013 and 2017 are expected to challenge the construction sector, as the period is expected to be the peak for the sector. Therefore, the sector will have to bridge the gap during this period by mutual agreements with the companies in Saudi Arabia and the UAE (QCB 2012).

The objectives of this paper are as follows: 1- to Identify sustainability metrics for tall buildings with focus on construction materials and methods used in Qatar; 2- Explore existing literature and identify analogies in optimization consistent with design variables; 3- to examine sustainability of construction materials used in Qatar by utilizing software which is based on currently available databases to perform life cycle assessment.

To meet the objectivess described above, the currently available software platforms to perform life cycle analysis of building materials were explored. A commercial software, SimaPro, which utilizes the environmental impact database Ecoinvent, was chosen for its flexibility in defining custom mix designs for concrete, as well as database information on steel and many other building materials. With SimaPro, a sustainability model for concrete and steel was developed which reflects the environmental implications of manufacture of materials in Qatar as appropriate. Quantitative results from the model for the sustainability of constituents of building materials were extracted, to form the basis of sustainability metrics in the forthcoming tall building topology optimization protocol.

Furthermore, Blanco-Carrasco et al (2010) outline reduced use of Portland cement, increased use of alternate cementitious materials, and reduced water use to improve the sustainability of the concrete industry in Qatar. Using structural models and the SimaPro model, ultra-high performance concrete was explored as a potential solution for all these problems, to be applied in the gravity/lateral structural components of Qatar tall buildings. In addition to identifying a novel material which fits well with the current tall building designs of the region, the process of examining the structural and environmental improvements from using ultra-high performance concrete has resulted in the formation of a procedure to compare multiple materials used in Qatar.

This paper is a result of a funded research project by QNRF, entitled “Multi–Objective Tall Building Topologies – Optimizing for Structural Performance, Economy, and Sustainability” and a jointly collaboration between researchers from Qatar University, Virginia Tech, Johns Hopkins University, Optim Design Inc, and MZ & Partners.

“This research/publication was made possible by a National Priority Research Program NPRP award [NPRP- 7 - 1518 - 2 – 549] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the author(s).”

Qatar is the biggest exporter of liquefied natural gas, LNG, in the world and is a main oil-producing member of The Organization of Petroleum Exporting Countries, OPEC. A fossil fuel-based industry emerged around the ports of Ras Laffan and Mesaieed, Qatar's industrial cities, perusing industrial diversity and maximising the huge fossil fuel reserves that serve as the primary feedstock for the industrial sector. LNG, crude oil, and petroleum products has given Qatar a per capita GDP that ranks among the highest in the world with the lowest unemployment. This also has given Qatar a per capita CO2 emissions among the highest in the world. A recent report from The World Health Organisation, stated that the capital of Qatar, Doha, is one of the world's most polluted cities and its air ranked the 12th highest average levels of small and fine particles which are particularly dangerous to health [1]. The people and wise leadership of Qatar recognizes the significance of the problem and made environmental development one of the four pillars of Qatar National Vision 2030. The vision places environmental preservation for Qatar's future generations at the forefront. Qatar Carbonates and Carbon Storage Research Centre is an example demonstrating Qatar's commitment to preserve the envioronment by investigating and implementing key technologies such as carbon capture and storage (CCS) to address the next step in climate change. CCS in deep saline aquifers is an important process for CO2 reduction on industrial scales. The aim of CCS is to safely sequester CO2 generated from stationary sources, such as power-plants, into aquifers and depleted oil reservoirs. It is considered a valuable option to reduce greenhouse gases and has been proposed as a practical technology to tackle climate change [2–4]. The importance of CCS as a key option to mitigate CO2 emissions and combat climate change has been highlighted also in a report by the International Energy Agency (IEA) and suggests that CCS could contribute to a 17% reduction in global CO2 emissions by 2035 [5]. Previously, carbon dioxide injection into the subsurface has mainly been used for enhanced oil recovery (EOR) purposes. That gave rise to Carbon capture, utilization and storage (CCUS) processes in mature oil reservoirs where CO2 is first used to enhance oil recovery and then ultimately stored in the reservoir. The incremental hydrocarbon recoveries associated with CCUS make it more attractive to implement compared to CCS. It have significant energy, economic and environmental benefits and is considered an important component in achieving the widespread commercial deployment of CCS technology. Residual trapping of CO2 through capillary forces within the pore space of the reservoir is one of the most significant mechanisms for storage security and is also a factor determining the ultimate extent of CO2 migration within the reservoir. Observations and modelling have shown how capillary, or residual, trapping leads to the immobilisation of CO2 in saline aquifer reservoirs, limiting the extent of plume migration, enhancing the security and capacity of CO2 storage [6,7]. In contrast, carbonate hydrocarbon reservoirs are characterised by a mixed-wet state in which the capillary trapping of nonpolar fluids have been observed to be significantly reduced relative to trapping in rocks typical of saline aquifers unaltered by the presence of hydrocarbons [8,9]. There are, however, no observations characterising the extent of capillary trapping that will take place with CO2 in mixed-wet carbonate rocks, the same rock type found in Qatar's subsurface geological formations and many other giant oil reservoirs in the Middle East that hold most of the oil in the world [10, 11]. Experimental tests of CO2 and brine in carbonate rocks at reservoir conditions are very challenging due to the complex and reactive nature of carbonates when dealing with corrosive fluids pair of CO2 and brine. In this study, we compare residual trapping efficiency in water-wet and mixed-wet carbonates systems on the same rock sample before and after wettability alteration by aging with oil mixture of Arabian medium crude oil. The experimental work was conducted using a state of the art multi-scale imaging laboratory (core and pore scale) developed at Imperial College London designed to characterise reactive transport and multiphase flow, with and without chemical reaction for CO2-brine systems in both sandstone and carbonate rocks at reservoir conditions [12]. The flow loop included stir reactor to equilibrate rock with fluids, high precision pumps, temperature control, the ability to recirculate fluids for weeks at a time and an x-ray CT scanner and micro x-ray scanner for in situ saturation monitoring. The wetted parts of the flow-loop are made of anti-corrosive material that can handle co-circulation of CO2 and brine at reservoir conditions with the ability to preserve the rock sample from reacting to carbonic acid. We report the initial-residual CO2 saturation curve and the resulting parameterisation of hysteresis models for both water-wet and mixed-wet systems. A novel core-flooding approach was used, making use of the capillary end effect to create a large range in initial CO2 saturation in a single core-flood. Upon subsequent flooding with CO2-equilibriated brine, the observation of residual saturation corresponded to the wide range of initial saturations before flooding resulting in a rapid construction of the initial residual curve. Observations were made on a single Estaillades limestone core sample. It was made first on its original water-wet state, then were measured again after altering the wetting properties to a mixed-wet system. In particular, CO2 trapping was characterized before and after wetting alteration so that the impact of the wetting state of the rock is observed directly on both core and pore scales. A carefully designed wettability alteration programme was designed in this study to replicate a mixed-wet carbonate system similar to those found in Qatari oil reservoirs. At the pore level, oil can precipitate asphaltene and other heavy components after long exposure with the rock changing the wetting state of the surface to oil-wet. A mixture of the evacuated crude oil with an organic precipitant, n-heptane, was used to deposit a stable oil-wet film. The precipitant substituted some of the evaporated and oxidised light hydrocarbon originally existed in the crude and deposited asphaltene to generate a stable strongly oil-wet film layer. Filtration experiments were carried out to sensibly precipitate enough asphaltene for a stable and strong oil-wet film without over precipitating and causing fine migration that can damage the core sample. The weight fraction of asphaltene precipitated with different fractions of crude-precipitant mixtures were measured. The diluent consisted of toluene as the solvent and heptane as the precipitant. 40 ml of the diluent was thoroughly mixed with 1 ml of Arabian Medium crude oil at 11 different precipitant/solvent volume ratios ranging from 0–100% at 10% increments and then left in the dark for 48 hours to allow the system to come to equilibrium. The mass of precipitated asphaltenes was measured in each mixture by vacuum filtration using a 0.45 micron polytetrafluoroethylene hydrophobic filter paper (Millipore) and evaporation of any remaining liquid oil from the filter paper. No asphaltene was precipitated at low precipitant volume fraction and only above the onset of precipitation, a linear relationship was seen between the wt% precipitated asphaltenes and the volume % of the precipitant in the mixture. The onset for asphaltene precipitation for an oil mixture of Arabian Medium crude oil and heptane alone without solvent was calculated at the onset using the volume fractions of the components with the mixing rule. The sample's wettability was altered to a mixed-wet using the appropriate oil mixture as measured using the filtration test and the oil was then removed from the sample by CO2 enhanced oil recovery injected above the minimum miscibility pressure. This allowed for producing unique dataset and a great complement to the more theoretical analysis. That is if we make a surface oil-wet (to water), how does it behave in the presence of a gas. Here we show that residual CO2 trapping in mixed-wet carbonate rocks characteristic of hydrocarbon reservoirs is significantly less than trapping in water-wet systems characteristic of saline aquifers. We found that in the native water-wet state of the carbonate sample, the extent of trapping of CO2 and N2 were indistinguishable, consistent with past studies of trapping and multiphase flow properties in water-wet sandstones [13, 14]. After alteration of the wetting state of the same rock sample with oil, the residual trapping of N2 was reduced compared to the amount in the pre-altered rock. Surprisingly, the trapping of CO2 was reduced even further. The unique results were complemented with pore scale observations to investigate the balance of interfacial tensions and contact angles in three-phase flow. Our results show that one of the key processes for maximising CO2 storage capacity and security is significantly weakened in hydrocarbon reservoirs relative to saline aquifers. We anticipate this work to highlight a key issue for the early deployment of carbon storage – that those sites which are economically most appealing as initial project opportunities are the very locations in which the contribution of capillary trapping to storage security will be minimised. This should serve as a starting point for modelling studies to incorporate the reduced impact of capillary trapping on CO2 injection projects using hydrocarbon reservoirs.

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Krevor, S., Blunt, M., Benson, S., Pentland, C., Reynolds, C., Al-Menhali, A., Niu, B., 2015. “Capillary trapping for geologic carbon dioxide storage -From pore scale physics to field scale implications”. International Journal of Greenhouse Gas Control, Volume 40, Pages 221–237, ISSN 1750–5836, http://dx.doi.org/10.1016/j.ijggc.2015.04.006.

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Non-Linear loads such as Compact Fluorescent lamps (CFLs), Light Emitting diodes (LEDs),Solid state voltage regulators, and variable speed electric drives are increasingly being added tothe domestic, residential and industrial power network. These light sources and other house-hold appliances using power electronic converters are termed as non-linear loads and they introduce distortion in the power network by generating harmonics in the current, leading to poor power quality [1 − 4]. Power quality issues are now becoming a major concern because of several reasons: a) Increasing dependence on electrical supply and even small disruption or interruption are not bearable because it can halt the modern lifestyle, b) new modern electrical equipment are highly sensitive to the power quality and c) the power electronic components such as variable speed drives and switched mode power supplies poses new disturbance challenges to the electrical supply network [5 − 7]. Power quality standards such as IEEE 519 is proposed to: a)assure that the electric supply company should deliver clean electric power to the consumers, b) assure that the electric supply company can protect electrical equipment from excessive voltage stress, overheating and loss of operational life of equipment. The IEEE 591 standard is in place that puts a limit on the allowed harmonic distortion of 3% on individual harmonic components and 5% on total harmonic distortion (THD). This standard is of utmost importance on the present day situation due to increasing non-linear loading. Although the distortion limits are not applied to specific equipment, however, with a high penetration of non-linear loads, it is likely that some harmonic suppression may be necessary [8 − 12]. The power quality problem is a distortion in the voltage waveform of the power source which is deviation from sine wave. Another power quality problem is a change in the amplitude from an established reference level. Other disturbance can be caused by harmonics in the current. With increasing the number of harmonics generating devices in a power system network, the problem of their impact on the performance of system components like induction motors needs is becoming a serious problem that need further consideration. It is well known that approximately 60–70% of loads in all over the world are motor loads. Most of the motors used in the world are three-phase induction motors. However, single-phase induction motors are major load in a domestic or residential setup. The modern day home uses large number of house hold appliances that uses different kind of single-phase motors as given in Table 1. A power network is shown for a domestic house in Fig. 1. Mix of loads are connected across the line. The effects of increasing non-linear loads in residential setting can be significant especially on single-phase motors connected to the same line. This paper investigate the effect of increasing distortion in the supplied voltage on the performance of single-phase induction motor behavior. Firstly the effect of increasing distortion in the applied voltage waveform on stator current is investigated. It is found that increasing a small %age of 3rd harmonic in the applied stator voltage significantly increases the 3rd harmonic component in the stator current. When voltage is pure sine wave, the current contains 1.7% 3rd harmonic. When the stator voltage is injected with 2.5% of 3rd harmonic the resulting current contain 11% 3rd harmonic. Hence it is concluded that current harmonic content is strongly dependent on the harmonic content in the stator voltage waveform. A Matlab/Simulink model is developed with single-phase capacitor start machine. The procedure adopted is as follows:

• Pure sine wave is applied to a capacitor start single-phase induction motor.

• Distorted supply is produced from inverter using appropriate PWM scheme and supplied to a capacitor start single-phase induction motor Non-linear loads such as CFLs and LEDs are emulated using thyristor based converter.

The thyristors are switched at different firing angle in order to vary the harmonic content in the supply voltage. The behavior of single-phase induction motor under distorted voltage conditionis recorded. The setup shown in Fig. 2 is consist of a single phase capacitor start induction motor supplied with PWM Converter. The motor is rated for 110V rms, 1500 rpm and 0.5 HP. The reference of the converter is generated by adding 3rd and 5th harmonic component to the fundamental component. The loads are switched in this order: Fig. 2. Single-phase induction machine (capacitor start) setup. a) At t = 0, the controlled rectifier with thyristor switching at 30° is turned on. This rectifier will always be on. The current drawn from the supply is analyzed for harmonic components. Each harmonic component contribution becomes input for reference generation for PWM Inverter. b) At t = 2 Sec, the controlled rectifier with thyristor switching at 60° is turned on. Now we have two controlled rectifier connected to the same ac supply. The resultant current is analyzed for harmonic component contribution. c) At t = 4 Sec, the controlled rectifier with thyristor switching at 90° is turned on. d) At t = 6 Sec, the controlled rectifier with thyristor switching at 120° is turned on. Efficiency estimation, a) The output of the system is calculated by multiplying load torque with the motor speed (in rad/sec). b) The input of the system is calculated by extracting P, Q, S from the bridge output voltage and current drawn by the motor from the block as shown below in Fig. 3. Efficiency computation of a single-phase capacitor start machine. c) Fundamental frequency, 3rd harmonic and 5th harmonic power is estimated by using the above block. The resultant power is calculated as: d) With the resultant absolute power drawn from the system, efficiency is calculated as: The simulation results are presented in Fig. 4–6. Ripple is seen in the current, torque and speed when voltage is distorted. The FFT of stator current (main winding) is shown in Fig. 7. Strong 3rd harmonic current is seen and also 5th harmonics.Sinusoidal Supply: Fig. 4. Single-phase IM behavior when pure sine wave is applied. Supply from a single-phase Inverter with Fundamental frequency (50 Hz) only: Fig. 5. Single-phase IM behavior when supplied from a DC/AC inverter. Supply from a single-phase Inverter with Fundamental, third and fifth harmonic: Fig. 6. Single-phase IM behavior when supplied from a DC/AC inverter with distorted waveform Fig. 7. Harmonic spectrum of stator current under distorted voltage source. Different powers are measured and shown in Fig. 8 for pure sine-wave supply and distorted voltage supply to a single-phase capacitor start induction machine. It is observed that the requirement of active, reactive and apparent power increases and efficiency decreases with the increase in the voltage distortion.

Acknowledgment

This publication was made possible by UREP grant # [17-061-2-017] from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.

References

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[3] M.K. Richard, P.K. Sen, “Compact Fluorescent Lamps and Their Effect on PowerQuality and Application Guidelines”, IEEE Industry Applications Society Annual Meeting (IAS), pp. 1–7, 2010.

[4] C. Keyer, R. Timens, F. Buesink, F. Leferink, “DC pollution of AC mains due tomodern compact fluorescent light lamps and LED lamps”, Int. Symposium on Electromagnetic Compatibility (EMC EUROPE), pp. 632–636, 2013.

[5] A.M. Eltamaly, “Power quality considerations of heavy loads of CFL on distribution system” IEEE Int. Symposium on Industrial Electronics (ISIE), pp. 1632–1638, 2011.

[6] Kesharvani, S.K.; Singh, A.; Badoni, M., “Conductance based fryze algorithm for improving power quality for non-linear loads,” in Signal Propagation and Computer Technology (ICSPCT), 2014 International Conference on, vol., no., pp. 703–708, 12–13 July 2014.

[7] Pattnaik, M.; Kastha, D., “Power quality improvement in a speed sensorless stand-alone DFIG feeding general unbalanced non-linear loads,” in Renewable Power Generation Conference (RPG 2014), 3rd, vol., no., pp.1–6, 24–25 Sept. 2014.

[8] Sharma, R.; Singh, A.; Jha, A.N., “Performance evaluation of tuned PI controller for power quality enhancement for linear and non linear loads,” in Recent Advances and Innovations in Engineering (ICRAIE), 2014, vol., no., pp. 1–6, 9–11 May 2014.

[9] Singh, A.; Baredar, P., “Power quality analysis of shunt active power filter based on renewable energy source,” in Advances in Engineering and Technology Research (ICAETR), 2014 International Conference on, vol., no., pp. 1–5, 1–2 Aug. 2014.

[10] Priyadharshini, K.M.; Srinivasan, S.; Srinivasan, C., “Power quality disturbance detection and islanding in micro grid connected distributed generation,” in Computational Intelligence and Computing Research (ICCIC), 2014 IEEE International Conference on, vol., no., pp. 1–6, 18–20 Dec. 2014.

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[12] Ejlali, A.; Arab Khaburi, D., “Power quality improvement using non linear-load compensation capability of variable speed DFIG based on DPC-SVM method,” in Power Electronics, Drive Systems and Technologies Conference (PEDSTC), 2014 5th, vol., no., pp. 280–284, 5– Feb. 2014.

Drilling in deeper formations and in high pressure and high temperature (HPHT) environments is a new frontier for the oil industry. Fifty years ago, no one would have imagined drilling in more than 10,000 feet of water depth like we do today. However, more issues need to be researched, tested, and studied in order to maintain a good drilling efficiency as deeper depths are drilled. One of these issues is the great effect that drilling at HPHT conditions has on the behavior of drilling fluids. The goal of this research was to study fluid loss properties of water based mud and its effect on permeability under HPHT dynamic conditions utilizing advanced laboratory equipment that allows for wide ranges of pressure and temperature. Filtration tests were performed at both ambient and HPHT conditions. After several laboratory evaluations of fluid loss additives available in the market, Polysal HT was found to be the most effective in reducing the fluid loss of the water based mud for both static and dynamic tests at HPHT conditions. It is economically designed to be saturated in salt and other brine system. An additive that encapsulates particles with protective polymer coating as colloid. Drilling fluid stabilizer especially in drilling hydratable shale and a remarkable effectiveness in wide range make up water (high saline and high hardness). The fluid loss behavior of the mud and the characteristics of the filter cake produce dare the basic factors that need to be considered when determining mud treatment. A detailed workflow of experiments using equipment from OFITE HPHT Fluid Apparatus with differential pressure of 500 psi under 230 °F with 2.5” filter paper (30 minutes) as well as OFITE Permeable Plugging Tester with 1,200 psi differential pressure @ 230 °F using a ceramic disc were conducted. Also tests were conducted using the Low Temperature- Low Pressure API Filter Press at 100 psi @77 °F with 3.5” filter paper for the purpose of comparison. Drilling fluid behavior should be studied and researched in order to get better drilling efficiency and less fluid losses. This topic has been for years the subject of research and many laboratory studies. Most of these studies focused on the methods and parameters involved in the study of drilling fluid characteristics. Mud can act unexpectedly under HPHT conditions and testing its properties at these conditions produces results that differ from those obtained from testing under static conditions. Drilling fluids' interaction with the spacer fluid is also critical. Krueger found out that the API filter loss tests (standard and high pressure) shouldn't be considered accurate when testing for the losses in mud that has viscosity reducers under dynamic conditions. He also studied the quantities of dynamic fluid loss in water based muds when adding substances to the drilling fluid such as CMC, starch, polyacrylate, and viscosity reducers. He found that–in dynamic system-starch and viscosity reducers were the most useful additives. However, when using API fluid test, the results deduced that CMC, starch and polyacrylate were the most beneficial additives. So he deduced that industry was paying so much on the API filter loss test (standard or at high temperature high pressure) expecting it to be accurate, instead of focusing on the dynamic filtration tests (at HPHT) whose results were more accurate since their conditions were very similar to the reservoir conditions. This is an experimental study of the impact of having HPHT reservoirs on the drilling fluids loss. Three different cases will be studied at different conditions. An API Filtration and fluid loss equipment will be used in order to test the mud capacity to withhold its filtrates under the HTHP as well as from static to dynamic condition. Experiment #1 consist of low pressure, low temperature conditions. The second one is at HTHP using static model. Finally, the last experiment will also be at HTHP conditions but using a dynamic model. Fluid loss models (beyond the conventional such as viscosity, gel strength, yield point and so forth) will then be compiled. The Polysal HT, a modified starch that serve as the fluid loss control additive along with Bentonite and Polypac UL will generally do the job. Roodhart stated that the commonly used 30 minutes API filtration test was inadequate especially in dynamic conditions. Also, he concluded that the range for fluid data testing (1,000 psi [7-MPa] differential) was lacking and deficient. Shadravan and Amani investigated the HPHT challenges in drilling and completions. Lee et al. researched the rheological properties of an extreme HPHT drilling fluids. Amani et al. compared the rheological properties of oil based and water based drilling fluids under HPHT conditions. Shadravan et al. looked at the possibility of fluid loss in underbalanced situations. Bland et al. mentioned that there were many parameters that need to be taken into consideration while designing and monitoring drilling fluids for HPHT conditions. These parameters included pressure and temperature effects on hydraulic calculations (while drilling under HPHT conditions at large depths, mud is subjected to high pressures and temperatures for long period of time) and PVT behavior of the base fluid (where the usual conditions considered by industry in fluid PVT measurements ranged from 15 psi per 750 °F to 20,000 psi/350 °F, but this range was exceeded while drilling under HPHT conditions). In addition, drilling efficiency was affected greatly by HPHT conditions where the use of additives like barite to increase the mud weight for such conditions caused lower drilling efficiency where the percentage of dispersed solids increased. This has many disadvantages (like decreasing hydraulic and cutting efficiency) during drilling high compressive formations under HPHT conditions. Elkatatny and Nasr-El-Din studied the formation of filter cake under static and dynamic conditions. They deduced that the same filtrate quantity was formed during dynamic and static conditions. However, dynamic conditions' spurt volume exceeded that under static conditions and when the filtration process reached an end, the part of the filtrate near to the drilling fluid had zero porosity and permeability. Further results by the CT scan proved that ceramic disk properties (like permeability and porosity) varied significantly during filtration and this should be taken into account during filter cake calculation. Properties of water based drilling fluids under HPHT dynamic testing conditions that can be measured include spurt loss, quality of plugging, total fluid loss, and cake formation thickness. Crespo et al. looked at some fluid loss related problems such as formation fracture, lost circulation, and well-control problems as a result of surge and swab pressures for yield-power-law drilling fluids. As the results show, permeability is proportional to the flow rate per unit cross sectional area. This can be translated into pore throats in subsurface rock. Therefore, the greater the pore size through which the fluid is going to flow at a constant flow rate, the higher the capacity of the fluid to flow and therefore its permeability. It can be deduced that as the concentration of the Polysal HT increased, less and less filtrate was lost into the formations. Same results were obtained from the low temperature low pressure API test where smaller filtrate volume was obtained as the concentration of the used Polysal HT increased. Thus, water based mud under HTHP conditions undergoes many changes in its main parameters like spurt loss, fluid loss, and filter cake thickness. Fluid loss control additives are therefore required in order to handle these changes and maintain the required properties of the used drilling fluid where Polysal HT was the required additive in this case. Dynamic as well as static API filtration tests should be performed before choosing the best additive. Numerous trials has been set up to test the fluid loss effectivity of the mud used in drilling but a very limited resources targeted the HTHP course due to its collaborative safety and productivity concerns, they call it “Drilling in the Dark” (a time to time check of properties).

Torsional vibrations experienced by drill strings can be detrimental to drilling operations. With a goal of understanding torsional vibrations experienced by drill strings and determining means to attenuate undesired vibrations, the authors have studied the effect of adding a sinusoidal modulation to a constant rotation speed of a drill string. A combination of modeling, analysis, and experiments is used to explore the influence of this rotation input modulation on the system response. The drill string is modeled as a modified Jeffcott rotor, which is described by a system with three degrees of freedom. Considering the case of forward whirling of a rotor in continuous contact with a stator, the equations of motion are reduced to a single degree-of-freedom nonlinear oscillator describing the torsional motions. In order to understand the fast time scale and slow time scale components of the motion, the method of direct partitions of motions is used to determine an approximate response to the nonlinear oscillator. The obtained results of the analysis illustrate that with the sinusoidal modulation of the rotor drive speed, the equivalent torsion stiffness can be enhanced and the character of the friction force at the contact can be made smooth. The analyses helps bring forth the stabilizing influence of the added sinusoidal input to the rotor drive speed. Over the considered parameter ranges, the numerical results obtained with the full three degree-of-freedom model and the reduced single degree-of-freedom model are found to be in agreement with each other. Furthermore, the results from these models are found to compare well with those obtained by using the method of direct partition of motions. Experiments with a laboratory scale drill-string arrangement are to be carried out to validate the analytical and numerical findings and further explore the effectiveness of the drive speed modulation on the rotor dynamics.

Introduction

Slender rotating structures are used in many engineering applications. Drill strings are long rotating slender structures, which are used in drilling operations. A schematic of a rotary drill rig is shown in Fig. 1 (e.g., Liao, Balachandran, Karkoub, and Abdel-Magid, 2011). Drill strings experience different types of vibrations (axial, torsional, and lateral vibrations) that may lead to detrimental failures of a drilling system. Drill-string vibrations have attracted the attention of many researchers, and many models have been developed to understand them. Since drill strings have a large length-to-diameter ratio, typically, the first torsional natural frequency and first lateral natural frequency are close to each other. This frequency proximity and the nature of the system allows for coupling and energy transfer between the associated vibration modes. Here, as a step towards developing further understanding, a drill string is modeled as an extended planar Jeffcott rotor with gravity acting normal to the rotor. Due to the planar motions, no gyroscopic effects are considered. The extended model, which was earlier considered in the work of Vlajic, Liu, Karki, and Balachandran (2014), is shown in Fig. 2. The model is described with three degrees of freedom (DOF), namely, x and y to account for lateral motions, and theta to account for torsional motion. A large number of research efforts have focused on controlling drill-string vibrations by using different feedback control algorithms, which need measurements along the drill string. In this work, the authors propose a different control approach to mitigate whirling motions during continuous rotor-stator contact. This can be compared to a situation of a drill string being in continuous contact with the borehole. The approach is open loop in implementation and this approach is based on adding a high frequency input to the drive speed of the drill string. Given the open-loop nature, the method does not depend on any measurements along the drill string or rotary table, which could be attractive for a practical stand point. Although the current focus is on motions of a rotor with continuous stator contact, it is planned to study stick-slip and non-contact cases in the future.

System Modeling, Studies, and Results

As previously mentioned, the drill string is modelled as a Jeffcott rotor with three DOF. Proceeding along the lines of the group's prior work (Vlajic, Liu, Karki, and Balachandran, 2014), after some approximations for the continuous rotor-stator contact case, the 3 DOF system is reduced to a single second-order nonlinear differential equation governing the torsional motion. In Fig. 3, for a representative case with a constant drive speed, the torsional state histories obtained for the full model and the reduced model are plotted. It is noted that the final state of the motion is captured quite well. To further analyze the response during forward whirling, the reduced-order model was nondimensionalized and an approximate solution was obtained by using the method of direct partitions. This method allows one to separate slow scale motions from fast scale motions. As discussed, in the group's prior work, this method can be useful to examine whirling motions. The results obtained by directly integrating the full model as well as the reduced-order model have been compared with that obtained by using the method of direct partitions of motions. It is seen that the perturbation analyses is able to provide an approximate solution that compares well with the numerical results obtained through direct integrations. Next, this analysis is used to examine the influence of the addition of secondary frequency component. It is seen that the addition of the secondary frequency, a high-frequency one, helps smooth out the friction coefficient variation with respect to the relative speed at contact. This is found to have a beneficial effect on the motion and helps suppress large-amplitude torsional motions. Stability analysis was also conducted to examine this effect.

Concluding Remarks

A study has been conducted to examine the influence of sinusoidal modulation of rotor drive speed in a system, wherein the rotor experiences continuous stator contact. A single degree of-freedom reduced model is developed to study the torsion response and it is found that the addition of a high frequency input can be beneficial in attenuating rotor motions. This is believed to be useful for developing open-loop control schemes for attenuating forward whirling motions of drill strings. Results obtained from a lab scale experimental arrangement will be used to examine the effect of this drive speed modulation further and they will be reported in the conference presentation. Future studies could build on the current effort to examine cases of backward whirling. Acknowledgment: The authors would like to gratefully acknowledge the support received from the Qatar National Research Fund for NPRP Project 7-083-2-041, to pursue this collaborative work between the University of Maryland, College Park, MD, USA and Qatar University, Doha, Qatar.

References

1. Liao, C.-M., Balachandran, B., Karkoub, M., and Abdel-Magid, Y., Drill-String Dynamics: Reduced-Order Models and Experimental Studies, ASME Journal of Vibration and Acoustics, Vol. 133, 2011, pp. 041008-1-041008-8.

2. Vlajic, N., Liu, X., Karki, H., and Balachandran, B., Torsion Oscillations of a Rotor with Continuous Stator Contact, International Journal of Mechanical Sciences, Vol. 83, pp. 65 − 75, 2014.