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A new time domain methodology for Computational Aeroacoustics (CAA) is proposed. The time domain wave packet (TDWP) method employs a temporally compact broadband pulse for acoustic sources. As the radiation and transmission of acoustic waves of all frequencies within the numerical resolution are embedded in the propagation of the wave packet, acoustic solution of the full spectrum become available at once. In addition, it becomes possible to separate the acoustic and instability waves in shear flows in the time domain wave packet method due to the compactness of the wave packet. The instability waves can further be suppressed by a source filtering technique, applied after the acoustic wave packet has propagated through the shear layers. Details on the source filtering technique used in the paper are presented. The TDWP method has been validated using a CAA Benchmark problem. The TDWP method is also applied to the NASA/GE Fan Noise Source Diagnostic Test (SDT) exhaust radiation problem.

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Accelerated life testing (ALT) is an effective way to assess the lifetime of a product. Due to the complex nature of its testing profile, it is difficult to carry out temperature cycling ALT. This paper establishes a modified Norris-Landzberg model as acceleration model, and proposes the optimum design method of temperature cycling ALT. First, the FEA method is used to study the influence of temperature cycling profile parameters on the thermal fatigue life of 63Sn-37Pb solder joints. Then, a modified Norris-Landzberg model is proposed by introducing ramp time and dwell time with an added weight value. Finally, the temperature cycling ALT is regarded as a special multi-stress ALT to study its optimum design method. The uniform design theory is used to determine the combined mode. The optimum model is established with the objective of minimizing the asymptotic variance of the estimation of median lifetime under normal use conditions, and the simulation example shows the workability of the proposed method.Keywords: temperature cycling ALT, 63Sn-37Pb, Norris-Landzberg model, optimum design, uniform design.Introduction. Accelerated life testing(ALT) is a test process that subjects a product to conditions that are excess of its normal usage. ALT allows for the collection of extensive failure data over a short time period that can be used to extrapolate and predict lifetime and reliability of products under normal conditions. Currently, ALT technology is an effective way to predict the life expectancy of product, and has been widely recognized in both academia and industry [1]. However, most of previous ALT research has focused on "constant" stress types, such as high-temperature and voltage. It is still unclear how to apply alternating stress types, such as temperature cycling, during ALT.In practice, many products are mainly subjected to alternating stress during service processing. For example, most on-orbit satellite devices are subject to the temperature cycling stress because of the alternating effects of light and shadow areas. The service environment of aircraft components can be seen as a temperature cycling environment, which is composed of ground parking -takeoff (low tropospheric temperature) -smooth flight (high temperature environment caused by aerodynamic heating) -and landing (low tropospheric temperature). In the process of temperature cycling, the differing thermal expansion coefficients of different materials could lead to thermal fatigue failure. Therefore, it is not effective to only conduct ALT at constant high temperature stress due to different failure mechanisms, and temperature cycling stress should be used in ALT for the products whose main failure mode is thermal fatigue.Very little research has been conducted on temperature cycling in ALT. Cui [2] carried out a temperature cycle accelerated reliability testing for electronic device packaging, and the Coffin-Manson model and Weibull analysis were used to determine the activation energy related to the crack failure mechanism, which could be u...