In this work, the combination of vibration loading and thermal cycle effects on the fatigue properties of a solder joint in a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) discrete was investigated. The fatigue mechanism under each loading mode was individually analyzed, and then according to the incremental damage superposition approach, the simultaneous effects were thoroughly studied. Under thermal cycling, the creep behavior of the solder is linked to the fatigue life. In fact, the creep accumulated strain in each thermal cycle has a straight relation to the failure time of solder joint. The origin of stress/strain in the assembly is owing to the sharp difference between coefficients of thermal expansions of the components in the electronic package. Regarding the vibration loading, the root mean square of peeling stress as a widely acceptable failure indicator was used to evaluate the vibration effects on the fatigue life. It is determined that the maximum stress is concentrated at the corner of solder layer. This result was similar to the outcomes of thermal cycling. The results also indicated that the combination of thermal and mechanical loadings accelerates the failure of the solder joint of the power MOSFET. Furthermore, the experimental and simulation studies showed similar results and approved the crack initiation at the corner of solder layer.
The flapping foil hydrokinetics turbine is a new method to generate energy from incoming flow field. The numerical simulations have been performed computationally by using two-dimensional unsteady Reynolds-averaged Navier–Stokes equations. It was found that the maximum energy efficiency reached about 35.2% when the reduced frequency was 0.11; at this time, the foil experienced a light dynamic stall and two opposite-sign vorticities were shed from the foil per half of the cycle. This report also studied the energy extraction performance of flapping foil device and the correlation between the foil kinematic parameters and the flow fields around it at actual operating Reynolds number comprehensively. In addition, the vortex variation and the pressure coefficient distribution along the foil’s surface were used to demonstrate the mechanism of flapping foil energy generation turbine. The creation and shedding of the leading edge vortex played the critical role in energy transformation between the flow fluid and energy harvesting systems. Therefore, if the timing of the leading edge vortex generation and shedding is controlled, the energy extraction efficiency can be increased considerably.
Analytical methods are described that were developed to undertake the pump manifold calculations for hydraulic air compressors (HACs) where multiple pumps are installed in parallel configurations. The procedures are fast and exact and were developed for design optimization and control tasks which, although described in the specific context of HACs, are also applicable to more general pumping systems. The proposed method uses a recursive/iterative procedure to establish the pump curve equivalent to the pump combination so that the design performance of the system can be assessed for any value of externally attached hydraulic resistance. The technique is verified against a numerical method applied to the same problem, but where the external hydraulic resistance must be completely specified for a solution. Losses at convergent and divergent wyes, which are required to create the parallel pump manifold arrangements, are found to be significant factors in establishing the overall energy efficiency of the pumping system. With efficient pump manifold arrangements designed, a so-called binary pumping scheme is explained, where individual pumps in the manifold can be activated (1) or deactivated (0) so that the pumping system flow can be reduced with good turn-down ratios while ensuring that the best efficiency point (BEP) efficiency of the system is maintained (exemplified with 4:1 or 25%).
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