The search for more sustainable energy to match the growing energy demand begins with finding more dispatchable resources such as solar energy. As one of the promising solar technologies, concentrated solar power (CSP) has a full capacity to store thermal energy for extended operation. Nevertheless, some key components in CSP systems usually face extreme environment, such as uneven solar flux, cyclic thermal expansion, structural degradation on the solar absorber tubes in a Concentrated Solar Power Tower (CSPT) Plant. In this study, we applied Multiphysics simulation to explore the benefits of introducing optimized fins for heat transfer enhancement and uniform temperature distribution, the goal is to improve the thermal efficiency of such advanced solar absorber tubes. The results of this study can supply design guidance for the manufacturing process of absorber tubes, and eventually can benefit the solar energy community for the next generation of molten salt based CSP system.

The knowledge of temperature and emissivity of the receiver are both critical for a solar tower power plant, in order to guarantee an efficient operation of the thermal receiver on the one hand, while monitoring any degradation of the receiver coating on the other hand. To make these measurements, a new thermographic system is currently being developed, using a multispectral camera working in the short wavelength infrared spectrum. This system applies the principle of ratio thermography, using a couple of narrow bandpass filters centered on atmospheric water absorption bands, at 1.4 and 1.9 µm, to reduce the influence of solar reflections on the measurement signal, making it sensitive to atmospheric conditions. In this thesis, a batch simulation approach is used to identify boundary atmospheric and operating conditions necessary to achieve temperature errors below 2 %, minimizing the influence of solar reflection. Furthermore the influence of atmospheric parameters on the sensitivity of ratio thermography is analyzed, in particular the validity of the gray body assumption. It is shown that the atmosphere has a critical influence on the measurement accuracy. A humid atmosphere and/or high zenith angle is necessary for making accurate measurements. Furthermore only receiver temperatures above 450◦C could be measured for the current system configuration, regardless of atmospheric conditions. Assuming negligible solar reflections, the validity of the gray body assumption is shown to be sensitive to the precipitable water vapor. A model based atmospheric compensation is therefore required to further improve the accuracy of ratio thermography.

Parabolic solar trough receivers are used to collect heat via the mean of a heat transfer fluid. This component is one among a myriad of the Concentrated Solar Power (CSP) devices. Parabolic troughs reach high temperatures around 400 ºC. improving the Parabolic Solar Trough's receiver with an IR selective coating will increase the heat transfer absorbed by the heat transfer fluid and reduce the radiative heat loss. Thus, optimizing the receiver will ameliorate the efficiency of the electrical production for a CSP. The parabolic solar receiver existing in industry currently are made of stainless steel with no specific coating for IR solar rays spectrum selection. Therefore, the heat transferred through the absorber is limited to certain light spectrum. Furthermore, numerous receivers proposed are made from materials that contaminates their optical properties when oxidized such as aluminum [1]. The heat transfer and optical analysis of the PTC are essential to optimize and understand its performance under high temperatures and reduce the heat loss. In this paper, our focus is on presenting a super-lattice IR selective coating to minimize the radiative heat loss. Making use of the power of metamaterials to confection optical properties that are inexistent in nature, the coating will serve to maximize the tube's reflectance above 70% in the IR. Not only does the selective coating enhance the optical properties of the receiver, but also it ensures performance stability for high temperatures.

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This dissertation presents the results of a detailed physical and hydrogeophysical study of two soil-filled sinkholes mantled by ancient New River fluvial terrace deposits. Research was performed at the Virginia Tech Kentland Experimental Farms in Whitethorne, Virginia, USA between fall 2003 and spring 2007, and focused on characterizing infiltration, deep drainage, and recharge through soil-filled sinkholes. Using hydrogeophysical methods, the spatial and temporal distribution of soil moisture was modeled and potential recharge was quantified in two soil-filled sinkholes. Access-tube time domain reflectometry (TDR) was used to derive one-dimensional (1-D) soil moisture profiles. During access-tube installation, 470 soil samples were obtained from depths between 0.3 and to 9.0 m and characterized both physically and chemically. Using these data, a TDR calibration method was developed. Physio-chemical, TDR moisture, and 1-D electrical resistivity tomography (ERT) data were used to derive a numerically optimized form of Archie's Law which was used to convert ERT measurements into volumetric soil moisture. These results led to development of 2-D ERT-derived distributions of soil moisture in three transects across the two sinkholes in two terraces. Potential recharge was quantified using time-series ERT data with comparison to modeled cumulative potential evapotranspiration (PET) and cumulative precipitation between May 17 and October 9, 2006. The patterns of ERT-derived potential recharge values compared well with those expected from PET and precipitation data. Over the monitoring period from late spring to early fall during this study, results showed that a period of intense rain followed by a 31-day period of consistent rain, in which the rate of precipitation was equal to or exceeded PET, were the only periods in which significant amounts of potential recharge occurred (from 19 to 31% of cumulative precipitation during the study). Spatial distributions of ERT-derived moisture clearly revealed that significant amounts of infiltration occurred on sinkhole flanks and bottoms. Runoff during periods of intense rain flowed to the topographically lowest point in the sinkholes where it infiltrated and resulted in localized zones of enhanced infiltration and potential recharge to the water table. / Ph. D.

This research presents a simplified framework for the analysis of deployable trusses using the concentrated strain approach and uses it to provide key insights into the many design decisions to be made in the development of concentrated strain architectures. The framework uses Euler Column Theory to derive closed form solutions to estimate truss performance. The results are compared to a classical solution and shown to give similar results. A range of strut and hinge hierarchy choices are considered. Trusses composed of solid rods with rectangular flexures are shown to have significant axial and bending stiffness reductions due to the smaller cross-sectional areas and lower modulus of the flexures. Trusses composed of tubes are less sensitive to this because the flexure cross-sectional area does not dramatically change from that of the tube. A hinge material metric that properly weights flexure strain and modulus is presented to provide a basis for the comparison and selection of proper hinge materials. However, based on this metric, new materials with higher folding failure strain and higher modulus are needed. Finally, a concentrated strain deployable truss of solid rods was designed, manufactured, and tested. A truss performance index for column loading was used to compare this system with a distributed strain ATK-ABLE GR1 coilable boom system and an articulated ATK-ABLE SRTM boom system. It was demonstrated that the concentrated strain approach has the potential to achieve a higher linear compaction ratio and truss performance index for mass efficient deployable trusses than the distributed strain approach and the articulated approach. / Ph. D.

京都大学 / 新制・論文博士 / 博士(医学) / 乙第13636号 / 論医博第2327号 / 新制||医||1074(附属図書館) / (主査)教授 川上 浩司, 教授 森本 尚樹, 教授 安達 泰治 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

In concentrated solar power (CSP) stations, large arrays of mirrors which are capable of changing its orientation are used to reflect the incident solar energy to a stationary receiver kept at a distance. Such mirrors are often called as heliostats. The receiver contains a heat absorbing medium like molten salt. By absorbing the thermal energy reflected from thousands of heliostats, the temperature would reach around 6000C and the heat can be used in thermal power plants to generate steam and thus run a turbine to produce electricity. One of the biggest advantages of CSP over conventional energy harvesting from Sun is that it can generate electricity during night for long hours of time from the thermal energy stored during daytime. This eliminates the usage of batteries or any other energy storing methods. The conversion efficiency is also high in CSP due to the high temperature achieved. With prior knowledge of the station coordinates, viz., the latitude and longitude, the day of the year and time, the direction or the path of sun can be fully determined. Typically, the sun's motion is tracked by the azimuth-elevation (Az-El) or the target-aligned configuration heliostats. In both these approaches, the mirror needs to be moved about two axes independently using two actuators in series with the mirror effectively mounted at a single point at the centre. This arrangement causes the mirror to deform in presence of gusty winds in a solar field which results in loss of pointing accuracy. Typically a beam error of less than 2-3 mrad is desirable in a large solar field and this value also includes other sources of loss of pointing accuracy like gravity and wind loading. In order to prevent this, a rigid support frame is required for each of the heliostats. In this work, two three degree-of-freedom parallel manipulators, viz., the 3-UPU wrist and 3-RPS, have been proposed to track the sun in central receiver systems. The main reasons for choosing a parallel manipulator as heliostat are its desirable characteristics like large load carrying capacity, high accuracy in positioning the mirror and easy to obtain the inverse kinematics and convenient for real time control. The proposed parallel manipulators support the load of the mirror, structure and wind loading at three points resulting in less deflection and thus a much larger mirror can be moved with the required tracking accuracy and without increasing the weight of the support structure. The algorithm for sun tracking is developed, extensive simulation study with respect to actuations required, variation of joint angles, spillage loss and leg intersection has been carried out. Using FEA, it is shown that for same sized mirror, wind loading of 22 m/s and maximum deflection requirement (2 mrad), the weight of the support structure is between 15% and 60% less with the parallel manipulators when compared to azimuth-elevation or the target-aligned configurations. A comprehensive study on stroke minimization of prismatic joints is carried out. It is found that a stroke of 700 mm is required for a 2 m x 2 m heliostat at Bangalore when the farthest heliostat is at a distance of 300 m from the tower. Although, there is an extra motor required to track the sun, the 3-RPS manipulator is better than the conventional methods if the mirror area per actuator criteria is taken into consideration. Prototypes of the Az-El and 3-RPS heliostats were made with a mirror size of 1 m x 1 m. A PID controller implemented using MATLAB-Simulink and a low cost, custom made motor driver circuit is used to control the motion of the 3-RPS heliostat. The algorithm developed is tested on the prototype by tracking a point marked on the wall of the lab space and is found to have a tracking error of only 7.1 mrad. Finally, the actual sun tracking is carried out on the roof of a building reflecting the sun-light to a wall situated 6.72 m above and a distance of 15.87 m from the heliostats. The images are captured at various instances of time from 11:30 a.m. to 3:30 p.m. on October 15th and November 10th, 2016, tracking errors are quantified and it is demonstrated that the proposed 3-RPS parallel manipulator can indeed work as a heliostat in concentrated solar power plants.

<p>Ni-based superalloys continue to exert themselves as the industry standards in high stress and highly corrosive/oxidizing environments, such as are present in a gas turbine engine, due to their excellent high temperature strengths, thermal and microstructural stabilities, and oxidation and creep resistances. Gas turbine engines are essential components for energy generation and propulsion in the modern age. However, Ni-based superalloys are reaching their limits in the operating conditions of these engines due to their melting onset temperatures, which is approximately 1300 °C. Therefore, a new class of materials must be formulated to surpass the capabilities Ni-based superalloys, as increasing the operating temperature leads to increased efficiency and reductions in fuel consumption and greenhouse gas emissions. One of the proposed classes of materials is termed refractory complex concentrated alloys, or RCCAs, which consist of 4 or more refractory elements (in this study, selected from: Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) in equimolar or near-equimolar proportions. So far, there have been highly promising results with these alloys, including far higher melting points than Ni-based superalloys and outstanding high-temperature strengths in non-oxidizing environments. However, improvements in room temperature ductility and high-temperature oxidation resistance are still needed for RCCAs. Also, given the millions of possible alloy compositions spanning various combinations and concentrations of refractory elements, more efficient methods than just serial experimental trials are needed for identifying RCCAs with desired properties. A coupled computational and experimental approach for exploring a wide range of alloy systems and compositions is crucial for accelerating the discovery of RCCAs that may be capable of replacing Ni-based superalloys. </p> <p>In this thesis, the CALPHAD method was utilized to generate basic thermodynamic properties of approximately 67,000 Al-bearing RCCAs. The alloys were then down-selected on the basis of certain criteria, including solidus temperature, volume percent BCC phase, and aluminum activity. Machine learning models with physics-based descriptors were used to select several BCC-based alloys for fabrication and characterization, and an active learning loop was employed to aid in rapid alloy discovery for high hardness and strength. This method resulted in rapid identification of 15 BCC-based, four component, Al-bearing RCCAs exhibiting room-temperature Vickers hardness from 1% to 35% above previously reported alloys. This work exemplifies the advantages of utilizing Integrated Computational Materials Engineering- and Materials Genome Initiative-driven approaches for the discovery and design of new materials with attractive properties.</p> <p> </p> <p><br></p>