A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based ...A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based on the three-dimensional equation of heat transfer through a fluid element is created to predict the viscous heating in the fluid damper under shock conditions. A comprehensive experimental program that investigates the problem of viscous heating in the fluid damper under different shock conditions is conducted on the shock test machine to validate the analytical expression. Temperature histories for the fluid within the damper at two locations, the annular-oriflce and the-end-of stroke of the damper, are recorded. The experimental results show that the theoretical model can offer a very dependable prediction for the temperature histories in the damper for increasing input velocity. The theoretical model and experimental data both clearly indicate that the viscous heating in the damper is directly related to the maximum shock velocity input and the pressure between the two sides of the piston head.展开更多
A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater ex...A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater explosion environments in laboratory as well as increase the testing capability of shock test machine. In order to produce the required negative shock pulse in the given time duration, four hydraulic actuators are utilized. The model is then used to formulate an advanced feedforward controller for the system to produce the required negative waveform and to address the motion synchronization of the four cylinders. The model provides a safe and easily controllable way to perform a ＂virtual testing＂ before starting potentially destructive tests on specimen and to predict performance of the system. Simulation results have demonstrated the effectiveness of the controller.展开更多
Individuals’risk attitudes play an important role in economic decision making and policy evaluation,particularly in the midst of unprecedented uncertainty caused by the COVID-19 pandemic.We adopt a multiple-price-lis...Individuals’risk attitudes play an important role in economic decision making and policy evaluation,particularly in the midst of unprecedented uncertainty caused by the COVID-19 pandemic.We adopt a multiple-price-list elicitation method with real money incentives to measure precisely individuals’risk attitudes at different stake levels and the extent to which they are affected by personal and social shocks following the COVID-19 outbreak in China.We find that subjects who had previously experienced negative personal shocks are more risk-averse at medium and large stakes but more risk loving at very small stakes.For our sample,COVID-19 has no significant impact on risk attitudes,as it is more likely to be regarded as a social shock.The result indicates that the impact of COVID-19 on individual risk attitudes is not as influential as expected,unless the individual’s personal life is affected directly.展开更多
基金Chinese Navy Warship Research Center(No.05131-1046)
文摘A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based on the three-dimensional equation of heat transfer through a fluid element is created to predict the viscous heating in the fluid damper under shock conditions. A comprehensive experimental program that investigates the problem of viscous heating in the fluid damper under different shock conditions is conducted on the shock test machine to validate the analytical expression. Temperature histories for the fluid within the damper at two locations, the annular-oriflce and the-end-of stroke of the damper, are recorded. The experimental results show that the theoretical model can offer a very dependable prediction for the temperature histories in the damper for increasing input velocity. The theoretical model and experimental data both clearly indicate that the viscous heating in the damper is directly related to the maximum shock velocity input and the pressure between the two sides of the piston head.
文摘A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater explosion environments in laboratory as well as increase the testing capability of shock test machine. In order to produce the required negative shock pulse in the given time duration, four hydraulic actuators are utilized. The model is then used to formulate an advanced feedforward controller for the system to produce the required negative waveform and to address the motion synchronization of the four cylinders. The model provides a safe and easily controllable way to perform a ＂virtual testing＂ before starting potentially destructive tests on specimen and to predict performance of the system. Simulation results have demonstrated the effectiveness of the controller.
文摘Individuals’risk attitudes play an important role in economic decision making and policy evaluation,particularly in the midst of unprecedented uncertainty caused by the COVID-19 pandemic.We adopt a multiple-price-list elicitation method with real money incentives to measure precisely individuals’risk attitudes at different stake levels and the extent to which they are affected by personal and social shocks following the COVID-19 outbreak in China.We find that subjects who had previously experienced negative personal shocks are more risk-averse at medium and large stakes but more risk loving at very small stakes.For our sample,COVID-19 has no significant impact on risk attitudes,as it is more likely to be regarded as a social shock.The result indicates that the impact of COVID-19 on individual risk attitudes is not as influential as expected,unless the individual’s personal life is affected directly.
