Study on a Nonlinear Dynamic Model and Its Parameters Determination Method for Half-Sine Programmer

A nonlinear dynamic model for describing shock response of half-sine programmer in shock test is constructed, in which many important factors in half-sine programmer such as size, hard nonlinearity, damping and initial impact velocity are considered, based on the damped Duffing equation, and the empirical static stiffness and shock stiffness calculation formulas of cylindrical rubber isolator. The shock pulse of half-sine programmer is measured and calculated by using shock test machine and Runge-Kutta method. Taking the minimum determination coefficient between the calculated and the measured shock pulse as the optimization objective, the parameters in the present model are determined by using quantum genetic algorithm (QGA), and meanwhile the extreme capacity in the present model for describing the dynamic behavior of half-sine programmer under shock excitations can also be verified. Experiments were implemented with drop shock test machine. The experimental results show that the present model is precise and efficient, and the prediction errors of pulse peaks and pulse widths were all below 5%, the waveform fitting errors between the calculated and the measured pulses are all less than 15%. The present results are helpful for designing the half-sine programmer.

Impact Tests in an Air-Water Mixture

Experimental impact tests were performed using a shock machine and aerated water by means of an air-bubble generator. High speed shock test machine allows carrying out tests of impact on water (slamming). This machine permits to stabilise velocity with a maximal error equal to 10% during slamming tests. The air volume fraction in the bubble was measured by optical probe technique. The present work is aimed at quantifying the effects of the aeration on the hydrodynamic loads and pressures during the entry of a rigid body at constant speed in an air-water mixture. The impact tests were conducted with a rigid pyramid for an impact velocity equal to 15 m.s−1 and for two average void fractions, 0,46% and 0,84%. The reduction of the impact force and pressure due to aeration has been confirmed by these experiments.