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Understanding how the pressure level affects the efficiency of liquid piston gas compression is essential for a greater applicability of the technology in compressed air energy storage. To explore the impacts, compression starting at three different initial pressure levels (1, 2, 3 bar) with a pressure ratio of 2 is performed, and how isothermal compression efficiencies are affected depending on the initial pressures is analyzed. Under the experimental conditions, higher initial pressure leads to lower isothermal efficiency. Air dissolution during the compression is also investigated because the chamber is a pressure-varying and a liquid-containing environment, where the gas solubility changes during the process. Evaluating the dissolution is critical as it affects the energy output when the compressed air is expanded to regenerate the energy. The changes in the air mass and the retrievable volume of the air after expansion are quantified based on Henry’s law. For a compression at higher pressure, because the air solubility is proportional to pressure, a greater reduction in the air mass and volume percentages is expected. This trend of the mass decreasing with the pressure level leads to less energy output than the originally intended output when the stored energy is retrieved in a discharging process.

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

A knee assistive device can serve a large number of people to overcome muscle weakness due to aging and perform normal functional activities of the knee joint. The objective of this paper is to study the effectiveness of a knee brace to aid with normal functions and reduce muscle forces at different walking speeds. The study uses two major muscle groups, rectus femoris (RF) and biceps femoris (BF), for the muscle force study. The Electromyography (EMG) signal was recorded at 3 different walking speeds (slow, normal, fast) under both brace-assisted and normal walking conditions. EMG signals were processed and converted into muscle activation signals and finally used for muscle force calculation. The amount of assistance to each muscle group at different walking speeds was derived and analyzed to see the effectiveness of a knee brace. The knee brace was seen to have provided additional support for motion generation. However, the amount of support is found to be speed-dependent and has a different effect on different muscle groups. At slower speed, the BF muscle was seen to work against the brace, while it was not the case for the RF muscle group.

One of the challenges in designing an Ocean Compressed Air Energy Storage (OCAES) system is achieving efficient compression and expansion of air. The rise of temperature during air compression results in significant loss of energy which leads to low storage efficiency. In this study, temperature abatement in liquid piston compressor using spray injection and metal wire mesh are investigated experimentally to improve storage efficiency. Water spray at different injection pressures and metal wire mesh of different surface areas and volumes were tested for heat dissipation inside the compression chamber. Results indicated that the water spray injection is useful to reduce the final temperature from 334 K to as low as 297 K for compression of air from atmospheric pressure to about 250 KPa when the injection pressure is 60 psi. For the more effective metal wire mesh among the inserts tested in this study, temperature abatement to a final temperature of 308K was observed. Compared to wire mesh inserts alone, the simultaneous use of the inserts and spray injection resulted in enhanced temperature abatement. Compared with spray injection method alone, temperature abatement improvement was observed when inserts of sparse density were used along with spray injection. Although wire mesh inserts distract the contact of water droplets with hot air, the simultaneous use of the two methods resulted in an increased effective surface area because the surface area added by the inserts is larger than the surface area lost by the droplets coming to contact with the inserts. When inserts with more compacted structures are used, the temperature abatement was less than the spray injection alone. This seems to suggest that the contact surface lost by the droplets is more significant than the extra surface area added by the inserts. Since the geometries of mesh inserts used in this study are different from each other, temperature increase patterns at certain pressure levels are compared. Clearly, spray injection improves compression efficiency to 95% from the base 80% efficiency of liquid piston compressor. This work uniquely highlights the further development of efficient air compression using spray injection and metal wire mesh.

The use of liquid pistons is a promising approach for attaining efficient near-isothermal compression. One of the key factors affecting the efficiency of a liquid piston compressor is heat transfer. Understanding the heat transfer mechanism during compression is crucial for the design and development of an efficient liquid piston compressor. In this paper, heat transfer in the liquid piston compressor is studied experimentally for air compression. An analytical model is presented based on a thermal resistance circuit. Experiments are performed using compression chambers of different materials for a compression ratio of 2.05–2.35 with various stroke times of compression. It is observed that the rate of heat transfer increases with faster stroke time of compression. However, a faster compression process requires a higher compression work and results in a higher air temperature. The convective heat transfer coefficient of air decreases rapidly as compression proceeds and approaches a steady value towards the end of compression. Thermal resistance analysis for compression with different chamber materials indicates that convective thermal resistance of air has a significant contribution in the total thermal resistance. During the initial phase of compression, the high conductivity of the chamber material helps improve the overall heat transfer coefficient; however, it has a marginal effect during the later phase of compression. An isothermal compression efficiency of 84–86% is observed with the liquid piston.

Ocean renewable energy resources are intermittent and a large scale energy storage is needed for their optimal utilization. Ocean compressed air energy storage (OCAES) system is promising large-scale energy storage for integration of ocean energy with the electric grid. In OCAES, energy is stored in the form of compressed air in an underwater storage device. In this paper, modeling and design of various components in the OCAES system is presented. Furthermore, design specifications and efficiencies of the various components in the 2MWh storage system at 500 m ocean depth are evaluated. Design of compressor/expander is crucial for high efficiency and sensible component sizing. Tread-off between the polytropic index and stroke time should be addressed in the compressor/expander design. Compressor/expander volume can be divided into a large number of liquid piston cylinders to achieve high efficiency. Higher ocean depth of the air storage system decreases storage volume requirement but affects roundtrip efficiency. The roundtrip efficiency of OCAES can be significantly improved by designing compressor/expander operating under near-isothermal conditions.

Intermittent nature of power from renewable energy resources demands a large-scale energy storage system for their optimal utilization. Compressed air energy storage systems have the potential to serve as long-term large-scale energy storage systems. Efficient compressors are needed to realize a high storage efficiency with compressed air energy storage systems. Liquid piston compressor is highly effective in achieving efficient near-isothermal compression. The compression efficiency of the liquid piston can be improved with the use of heat transfer enhancement mechanism inside the compression chamber. In this study, a novel heat transfer enhancement technique using metal wire mesh is experimentally tested in a liquid piston compressor to improve compression efficiency. Metal wire meshes of aluminum and copper materials and different wire diameters along with various stroke times of compression are considered in the experimental design. A distinctive Archimedean spiral form of metal wire mesh is considered to facilitate heat transfer in the axial and radial direction inside the compression chamber. Experiments are conducted for the compression of air from the atmospheric pressure to about 280 kPa pressure at various stroke times of compression. Results show that the peak air temperature was reduced by 26–33 K with the use of metal wire mesh inside the liquid piston compressor. Both the materials are observed to be equally effective for temperature abatement. The use of metal wire mesh in liquid piston shifts the compression process towards the near-isothermal conditions. Furthermore, the isothermal efficiency of compression is evaluated to assess the potential for efficiency improvement with this technique. The metal wire mesh was observed to improve the isothermal efficiency of compression to 88–90% from the base efficiency of 82–84%. A 6–8% improvement in efficiency was observed at faster compression strokes signifying the efficacy of metal wire mesh to accomplish an efficient compression with a high power density.

Utilization of intermittent ocean energy resources can be improved by integrating them with an energy storage system. Ocean compressed air energy storage (OCAES) is a promising large-scale energy storage system in the proximity of ocean energy resources. Efficient compressors and expanders are needed to achieve a high roundtrip efficiency of OCAES systems. In this paper, the development of an efficient liquid piston compressor is discussed. Heat transfer enhancement techniques such as aqueous foam and spray cooling are tested in a liquid piston compressor to achieve a highly efficient near-isothermal compression. It is observed that both aqueous foam and spray cooling are highly effective in abating the rise of air temperature during compression and improve the isothermal efficiency of compression. The use of aqueous foam in a liquid piston compressor shows an isothermal efficiency up to 91% whereas spray cooling results in an isothermal efficiency up to 96%. Efficiency analysis of liquid piston based OCAES systems with aqueous foam and spray cooling indicate the potential improvement of 4-14% in roundtrip efficiency of OCAES with the use of aqueous foam and 10-20% improvement with the spray cooling.

Optimal utilization of renewable energy resources needs energy storage capability in integration with the electric grid. Ocean compressed air energy storage (OCAES) can provide promising large-scale energy storage. In OCAES, energy is stored in the form of compressed air under the ocean. Underwater energy storage results in a constant-pressure storage system which has potential to show high efficiency compared to constant-volume energy storage. Various OCAES concepts, namely, diabatic, adiabatic, and isothermal OCAES, are possible based on the handling of heat in the system. These OCAES concepts are assessed using energy and exergy analysis in this paper. Roundtrip efficiency of liquid piston based OCAES is also investigated using an experimental liquid piston compressor. Further, the potential of improved efficiency of liquid piston based OCAES with use of various heat transfer enhancement techniques is investigated. Results show that adiabatic OCAES shows improved efficiency over diabatic OCAES by storing thermal exergy in thermal energy storage and isothermal OCAES shows significantly higher efficiency over adiabatic and diabatic OCAES. Liquid piston based OCAES is estimated to show roundtrip efficiency of about 45% and use of heat transfer enhancement in liquid piston has potential to improve roundtrip efficiency of liquid piston based OCAES up to 62%.

This paper focuses on the deployment and evaluation of a separated pitch control at blade tip (SePCaT) control strategy for large megawatt (MW) wind turbine blade and explorations of innovative blade designs as a result of such deployment. SePCaT configurations varied from five to thirty percent of the blade length in 5 percentage increments (SePCaT5, SePCaT10, SePCaT15, SePCaT20, SePCaT25, and SePCaT30) are evaluated by comparing them to aerodynamical responses of the traditional blade. For low, moderate, high, and extreme wind speed variations treated as 10, 20, 30, and 40 percent of reference wind speeds, rotor power abatement in region 3 of the wind speed power curve is realized by feathering full length blade by 6, 9, 12, and 14 degrees, respectively. Feathering SePCaT30, SePCaT25, SePCaT20, and SePCaT15 by 14, 16, 26, and 30 degrees, respectively, achieves the same power abatement results when compared to traditional blade at low wind speeds. Feathering SePCaT30, SePCaT25, and SePCaT20 by 18, 26, and 30 degrees on the other hand has the same effect at high wind speeds. SePCaT30 feathered to 26 and 30 degrees has the same abatement effects when compared to traditional blade at high and extreme wind speeds.

Ocean compressed air energy storage (OCAES) is a promising large-scale energy storage concept. Different types of OCAES viz. - Diabatic, adiabatic and isothermal are possible based on the handling of heat in the system. In diabatic OCAES, compressed air is cooled in a cooler and heated using external heat source before transport to the expander. In Adiabatic OCAES, heat from the compressed air is stored in a thermal energy storage (TES) and reused to reheat compressed air before sending it to the expander. In Isothermal OCAES, air is compressed and expanded isothermally which results in the least compression work and highest expansion work. These OCAES configurations are assessed using exergy analysis in this paper. The exergy efficiency of individual components, exergy flow and overall efficiencies of diabatic, adiabatic and isothermal OCAES are presented. Results show that adiabatic OCAES shows improved efficiency over diabatic OCAES by storing thermal exergy of compressed air in TES and isothermal OCAES shows significantly higher efficiency over adiabatic and diabatic OCAES.

Near-isothermal compression is desired to achieve high efficiency in many compressor applications. Low heat transfer characteristic of conventional compressors is a major bottleneck in attaining a near-isothermal compression. A high heat transfer rate is possible with an injection of a large number of water droplets using a spray nozzle inside the compression chamber. In this paper, the effectiveness of spray injection to achieve near-isothermal compression is investigated experimentally in a liquid piston compressor for a compression ratio of about 2.5. Parametric investigations are performed by varying injection pressures of spray from 10 psi (69 kPa) to 70 psi (483 kPa), using different spray nozzle angles (60°, 90°, and 120°), and by changing the stroke time of compression. It is observed that water spray injection is highly effective in abating the air temperature rise during the compression process. The pressure-volume plots indicate a significant reduction in the compression work, and they approach near-isothermal compression with spray at higher injection pressures. The isothermal efficiency of compression consistently increases with an increased injection pressure of spray and reaches up to 95% at the highest injection pressure studied (70 psi). Furthermore, the spray nozzle angle marginally affected the isothermal efficiency with a 1–4% improvement with the use of a 60° nozzle angle over a 120° spray angle at all injection pressures. Also, comparable isothermal efficiencies are observed for compression with different stroke times between 3 and 5 s especially at higher injection pressures which highlight the efficacy of spray injection in attaining a high power-density along with high efficiency. Overall, with an optimized spray design, water spray injection can achieve a highly efficient near-isothermal compression in liquid piston.

Efficiency of gas compression can be significantly improved by achieving isothermal compression. A high heat transfer rate in the compression chamber is desired to achieve the isothermal compression process. A large surface area and a high heat transfer coefficient of aqueous foam can be used to achieve a significantly high heat transfer rate in the compression chamber. In this study, a novel heat transfer enhancement technique using aqueous foam is investigated in a compressor for achieving near-isothermal compression. Experiments are performed with the use of aqueous foam generated inside a liquid piston compressor. The volume of aqueous foam in the compression chamber, the air flow rate for foam generation, and various foam generator designs are considered in this parametric investigation. It is observed that the use of aqueous foam in the compression chamber is highly effective in reducing air temperature during the compression process. A higher volume of aqueous foam in the compression chamber leads to a significant increment in isothermal efficiency, however, with higher variability. The higher variability in efficiency is due to the higher cyclic variation of the temperature profiles during compression. A compression chamber completely filled with aqueous foam shows a 4–8% improvement in the efficiency for a compression ratio of 2.5. Moreover, several foam generator designs were tested to identify if there is any dependency of cyclic variability on foam generator design parameters. The results show some promise on optimizing the design to reduce the variability. Overall, the heat transfer enhancement using aqueous foam is effective in achieving an isothermal efficiency up to 92% compared to 86% for the no-foam case in a liquid piston compressor.

Previous work concerning ocean compressed air energy storage (OCAES) systems has revealed the need for an efficient means for compressing air that minimizes the energy lost to heat during the compression process. In this paper, we present analysis, simulation, and testing of a tabletop proof-of-concept experiment of a liquid piston compression system coupled with a simulated OCAES system, with special attention given to heat transfer issues. An experimental model of a liquid piston system was built and tested with two different materials, polycarbonate and aluminum alloy, used for the compression chamber. This tabletop liquid piston system was tested in conjunction with a simulated OCAES system, which consisted of a hydrostatic tank connected to a compressed-air source from the wall to mimic the constant hydrostatic pressure at ocean depth experienced by the air stored in an actual OCAES system. Good agreement was found between the experimental and numerical studies and demonstrated that the heat transfer characteristics of a liquid piston compression process are effective in reducing the increase in air temperature that occurs during the compression process. The results also suggest that it may be possible to achieve a near-isothermal process with a fully optimized liquid piston compression system.

This paper investigates the impact of deploying control surfaces on a model 5 MW offshore wind turbine blade. The wind turbine blade is modeled in 3D based on NREL's 5 MW wind turbine and incorporates varying airfoil shapes and structural twist along the blade length. Lift and aero-dynamic moment at various angle of attack settings are simulated and analyzed. Partial span-wise trailing-edge 3D control surfaces are modeled, simulated and analyzed at various control angles. Results depict the onset of stall around 22 degrees and a larger lift gain versus 10–15 degrees for standard 2D airfoils. Mid-flap controller enhances lift by a factor 2 and mitigates moment a factor of around 7 while end-flap controller enhances lift by a factor of around 1.024 and mitigates moment by a factor of around 2. The results and comparisons obtained serve as one of many instruments for gauging, designing, analyzing, and optimizing wind turbine systems.

This paper analyses a novel heat transfer enhancement technique that can be used in compressors to limit the temperature rise during compression. This technique is based on the injection of external high-pressure gas into the chamber during the compression process. The impact of different factors on the effectiveness of this technique has been studied using experimental and computational methods. In the first set of trials, the location and angle of injection of the external air was varied. It was observed that the heat transfer coefficient governing the heat transfer rate from the chamber varied greatly with change in location and angle of injection. In the second set of experiments, the source pressure of the injected gas was varied from 100.66 kPa to 551.58 kPa. It was observed that the temperature rise of air in the chamber was reduced with an increase in source pressure. Additionally, the increase in chamber pressure was steeper in the higher source pressure cases. In the third set of experiments, the injection profile of the injected gas was varied. This parameter did not greatly impact the effectiveness of external gas injection. In the last set of experiments, the time of initiation of injection was varied. Earlier injection had a positive impact on reducing the temperature rise in the chamber. However, the pressure in the chamber was seen to increase more rapidly in the runs with early injection. Considering that these factors could have a positive/negative impact on the temperature and pressure in the chamber (work required for compression), it may be required to optimize the injection of external high-pressure gas depending on the application.

In this paper, an ocean compressed air energy storage (OCAES) system is introduced as a utility-scale energy storage option for electricity generated by wind, ocean currents, tides, and waves off the coast of North Carolina. Geographically, a location from 40 to 70 km off the coast of Cape Hatteras is shown to be a good location for an OCAES system. Building upon existing compressed air energy storage (CAES) system designs, a conceptual design of an OCAES system with thermal energy storage (TES) is presented. A simple thermodynamic analysis is presented for an adiabatic CAES system which shows that the overall efficiency is 66%. In addition, finite element simulations are presented, which show the flow induced loads that will be experienced by OCAES air containers on the ocean floor. We discuss the fact that the combination of the buoyancy force and flow-induced lift forces (due to ocean currents) generates a periodic loading on the storage container and seabed, and how this presents engineering challenges related to the development of methods for reliably resisting these loads for decades in a corrosive environment. We also present a system, based on hydrolysis, which can be used for storing energy (in the form of oxygen and hydrogen gas) in containers on the ocean floor.

Intermittent ocean energy resources need energy storage system for their optimal utilization. Ocean compressed air energy storage (OCAES) is a promising way for a utility scale energy storage. In this paper, a liquid piston based ocean compressed air energy storage is analyzed for end-to-end efficiency. An analytical model for end-to-end efficiency based on efficiencies of individual components in the liquid piston based OCAES is presented. Numerical analysis based on the analytical model and experimental data is done using Monte Carlo simulations. End-To-End efficiency of the liquid piston based OCAES is observed to be highly dependent on the polytropic index of compression and expansion. End-to-End efficiency increases from 24% to 72% with decrease in polytropic index from 1.4 to 1. Experimentally observed polytropic index shows 45% end-to-end efficiency. Comparison of results with end-to-end efficiency of existing compressed air energy storage systems indicates that the isothermal liquid piston based OCAES shows significantly higher end-to-end efficiency.

This paper deals with a novel technique to curb the temperature raise during compression in a liquid piston compressor used in Ocean Compressed Air Energy Storage (OCAES) system. Hollow spheres made of various materials, viz. Silicon Carbide (SiC), High Density Polyethylene (HDPE), and Polypropylene (PP) were made to float on the top surface of the liquid column. It was observed that the temperature abatement in each of the three cases was very evident. The heat transfer does not depend on the material of the sphere, but the fact that there is a solid surface between water and air itself plays an important role along with the size of the sphere. The heat transfer per unit area from the simulation and the analytical model have been compared and the values are found to be very similar. Also, polytropic index of the compression process was evaluated in case without and with SiC spheres, and it was found to be closer to the isothermal index of 1 when the spheres are used.

In this paper, for the accurate estimation of the position and orientation of the UUV (unmanned underwater vehicle), an AHRS (Attitude Heading Reference System) was developed using the IMU (inertial measurement unit) sensor which provides information on acceleration and orientation in the object coordinate and the initial alignment algorithm and the E-KF (extended Kalman Filter). The initial position and orientation of the UUV are estimated using the initial alignment algorithm with 3-axis acceleration and geomagnetic information of the IMU sensor. The position and orientation of the UUV are estimated using the AHRS composed of 3-axis acceleration, velocity, and geomagnetic information and the E-KF. For the performance test of the orientation estimation of the AHRS, a testbed using IMU sensor(ADIS16405) and DSP28335 coded with an E-KF algorithm was developed and its performance was verified through tests.

This paper details a study performed on a new proposed twelve degree-of-freedom dual robot arm, which is very light but capable of handling heavy loads. The proposed robot arm has a higher value for the ratio of the load capacity/robot weight than conventional robot arms, which are actuated by motors with speed reducers, such as a harmonic drives, since it adopts a new type of robot actuator based on a closed chain mechanism. Because of the high value of the ratio of the payload capacity/robot weight, it can be used as a robot arm for mobile robots and for walking robots. Analyses of the design scheme and of the mechanism of the joint actuator used for the robot arm are presented. Also, the control system developed for the robot arm is introduced. The superior characteristics of the new proposed robot arm, handling heavy payloads with light weight links compared to industrial robots, are presented through carrying out various payload capacity tests. Since the robot arm is designed with light links, it has some deflections and these deflections of the links are analyzed using the Finite Element Method (FEM). The results of performance tests are presented to check the correctness of the FEM analysis and to demonstrate the actual capability of handling heavy payloads applied to the robot arm.

The Dakhov Salient is a small exposure of the preAlpine crystalline basement within Jurassic rocks at the northwestern termination of the Front Range of the Greater Caucasus (Fig. 1). Together with the southeastern Beskes and Sakhrai salients, the Dakhov Salient makes up a partly exposed northern framing of the Middle Paleozoic island-arc complex of the Front Range. Like crystalline rocks of the Blyb Salient at the southern framing of the island-arc complex, rocks of the Dakhov Salient are traditionally considered the pre-Paleozoic basement of the Front Range. The Dakhov Salient is mainly composed of pre-Alpine granitoids (primarily, granodiorites), which intrude metamorphic rocks exposed as a narrow band in the northern area. The Dakhov Salient is easily accessible, and ravines of the Belaya River and Syuk Creek are excellently exposed. Nevertheless, several essential aspects of the geology of the Dakhov Salient remain controversial. The age of host rocks is the most important issue. In the 1970s, the K–Ar dating of granitoids and metamorphic rocks of this salient yielded a Neoproterozoic value of 985–612 Ma [4, 5]. Since then, the Dakhov Salient has become a rare reference (in terms of geochronology) object in the Greater Caucasus. This salient is always mentioned for the substantiation of the pre-Paleozoic age of its metamorphic basement [1, 2]. However, there are grounds to doubt the reliability of the datings mentioned above [6]. We performed U–Pb geochronological investigation of one of the oldest components of the Dakhov Salient— metaaplite veins assigned to the symplectitic garnet amphibolites of the Belaya River canyon. We also carried out K–Ar dating of granodiorites intruding the metamorphic rocks. The Paleozoic Age of High-Pressure Metamorphic Rocks in the Dakhov Salient, Northwestern Caucasus: Results of U–Pb Geochronological Investigations

In this study, a convection cooling technique for handheld electronic devices is proposed and investigated. The technique uses bulk airflows generated by a vibrating cantilever beam actuated by a rotating imbalance motor. Analytic coupled physics modeling using an approximate integral method within laminar-flow boundary layers was used to analyze the proposed cooling technique. The cantilever beam and enclosure were designed based on the form factors of a typical handheld device. The bulk airflow cooling performances at various probe locations were investigated experimentally for low and high heating loads and numerically verified. The results indicate that a higher heating load of the heat source results in a larger temperature drop at the same convection rate. Also, for the probe locations away from the heat source and closer to the beam, the resulting temperature drops were relatively small despite a stronger velocity field generated by the beam. This is due first to the heat generated by the vibrating beam itself and second to a circulation of the air heated by the heat source to the rest of the regions in the enclosure. In general, a good agreement between experimental and numerical results was attained, even though a slight difference between two results exists. Overall, significant cooling was achieved by the proposed system. With a beam tip deflection of ±4 mm, nearly an 18-fold increase in the cooling performance was achieved compared to a natural convection case. Furthermore, the cooling performance continues to increase as the tip deflection of the cantilever beam increases. Thus, a cooling system using the bulk airflow generated by a vibrating cantilever beam has much potential as a feasible solution for electronic handheld devices.

A feasibility study on developing a small-scale thermoacoustic cooler based on form and size factors for a typical cell phone is presented. First, an approximate analytical model for the temperature difference was derived using the linear theory of thermoacoustics. Cooling performance could be reasonably predicted with the analytical model proposed in this study. Air and helium as the working gases and the operating frequencies of 3 kHz for air and 9.2 kHz for helium are considered within the scope of typical cell phone configurations. A stack as a core of thermoacoustic cooler is designed to accomplish the most effective performance based on normalized parameters. For the 57 mm thermoacoustic cooler operating at 3 kHz with air, the maximum temperature difference of 23.13 °C across the stack in the resonance cavity is achieved with a drive ratio of 2% with air as the medium and Mylar as a stack material. This temperature difference varies depending on the stack placement along the length of the resonance cavity, but the maximum difference was achieved when the center of stack is placed at around 7 mm away from the driver end. The drive ratio, which is proportional to the power required to produce the thermoacoustic effect, is shown to be directly related to the cooling performance achieved by thermoacoustic drivers. For example, while a drive ratio of 2% results in a temperature difference of over 20 °C at its maximum, a drive ratio of 0.2% causes a temperature difference less than 1 °C. This will be one of hardware issues to be considered in making commercially viable products. The possibility of omitting heat exchangers in the thermoacoustic cooler is investigated considering their manufacturing cost and the relatively minute improvement they bring to overall cooling for small-scale systems. The numerical result of the thermoacoustic cooling system based on design environment for low-amplitude thermoacoustic energy conversion (DeltaEC) is compared to the theoretical result. Discrepancies between the two results exist in the range of 10–15% mainly due to the limitation imposed by short stack considerations and the linear theory of thermoacoustics.

Forced convection in a narrow channel is investigated both numerically and experimentally. The flow field is established through the mechanism of acoustic streaming. This is accomplished by high frequency vibration of one of the channel walls, which is composed of a piezoelectric bimorph. In the numerical computations, the Navier-Stokes equations are decomposed into the acoustic equations and the streaming equations by the perturbation method. The acoustic field is first numerically obtained, which provides the driving force for the streaming field. The streaming field and the associated temperature field are then obtained numerically. Heat losses from a heat source are measured to determine the efficiency of this as a cooling method. The air-flow patterns in the channel between the heat source and the bimorph actuator are visualized using the particle tracking velocimetry. The visualization clearly shows that vortical streaming (acoustic streaming) can be induced by bimorph vibration, which enhances heat transfer between the heat source and the surrounding air. The temperature decreases obtained computationally and experimentally are in good agreement.

A prototype of a miniature cooling system for microelectronics using vibrating piezoelectric beam was proposed and constructed. The flow patterns and cooling effects of the system were investigated experimentally. The vibration characteristics of the piezoelectric beam were simulated by the finite element method. Cooling effects were measured in terms of the temperature drop of the heat source above the vibrating beam. The electric field applied on the piezoelectric beam and the gap between heat source and actuator were adjusted to find the best cooling result. A temperature drop of 25.9 °C from 92 °C can be observed for the heat source when operating at a certain condition, which indicates the feasibility of using the present miniature cooling system in small devices. The heat transfer performance of the cooling system was analyzed as well. The results show that the enhancement of heat transfer between the heat source and the beam can be up to 210% with the acoustic streaming generated by the beam vibration in the present experimental studies. The enhanced heat transfer can be attributed to the generation of vortical streaming by the vibrating beam which was also captured in the flow visualization experiments.

An analytical prediction of dynamic performance for piezoelectric bimorph structures was investigated. A damping ratio was assumed and employed to determine dynamic peak amplitudes at resonances by finding the frequency with of the peak amplitude. Finite element simulations were used to validate the proposed improvement strategy. Results show that the peak amplitude determination method is good enough to predict the dynamic performance of piezoelectric bimorphs. The effects of bonding layers were also analysed by both static and dynamic methods. The bonding influence can be minimized by selecting appropriate bonding materials and dimensions of structures.

The design of piezoelectric resonating structures was investigated for generating acoustic streaming which may be used for cooling microelectronic components. The vibration characteristics of different piezoelectric structures were simulated by the finite element method and validated with analytical approaches. Considering the product of resonance frequency and dynamic tip deflection as a performance merit, the effects of length and location of the actuators as well as the boundary conditions were analyzed for four different piezoelectric resonator designs. Results show that there exist optimal length and location of actuators on the passive structures.

In this study, an approach to obtain an accurate yet simple model for full-vehicle ride analysis is proposed. The approach involves linearization of a full car MBD (multibody dynamics) model to obtain a large-order vehicle model. The states of the model are divided into two groups depending on their effects on the ride quality and handling performance. Singular perturbation method is then applied to reduce the model size. Comparing the responses of the proposed model and the original MBD model shows an accurate matching between the two systems. A set of identified parameters that makes the well-known seven degree-of-freedom model very close to the full car MBD model is obtained. Finally, the benefits of the approach are illustrated through design of an active suspension system. The identified model exhibits improved performance over the nominal models in the sense that the accurate model leads to the appropriate selection of control gains. This study also provides an analytical method to investigate the effects of model complexity on model accuracy for vehicle suspension systems.