Study On Similarity Laws Of Dynamic Response For Structures Under Blast Load In Cabin

Test on a scale-down model is an effective approach to predict the dynamic response of full scale structure under blast loadings.A better understanding of the dynamic response of a steel plate subjected to blast loading would help design the ship structures with enhanced blast resistance and increase the level of safety for personnel and structures in increasingly threatening environments.A suitable similarity relationship,which takes parameters of confined blast load and dynamic response of strcurure into consideration,is the key to codunct the scale-down model test.Based on dimensional analysis,a similarity criteria for the salce-down and prototype confined blast loaded plate is presented and verified exprimermentally and numerically.The works of the present thesis are as follows:(1)Based on the similarity theory,appropriate parameters and primary dimensions are selected.Then,in dimensional analysis,the Buckingham ?-theorem is used to derive the similarity relations for the internal explosion load and the dynamic responses of stiffened plates under internal explosion.The proposed similarity relation of internal explosion load indicates that the prototype cabin and model cabin with the same kind of charge and the same initial state of gas will experience the same pressure history when the charge mass of TNT is scaled by the cubic of the geometry scale factor,time is scaled by the geometry scale factor.The proposed similarity relation of dynamic response of structures imply that under the same internal blast loading,the displacement scale factor and the velocity scale factor is the same as the geometry scale factor,and the acceleration scale factor is the inverse of the geometry scale factor.(2)The experiments of prototype and scaled model of plates and stiffened plates are designed according to the similarity relation.The experimental results of shock wave and quasi-static pressure verify the similarity relation proposed for the internal explosion load.The experimental results of structural response are recorded with DIC(Digital Image Correlation)system.However,when it comes to the displacement of structures,the results indicate the displacements of prototype and scaled model specimens do not satisfy the similarity relation for the dynamic response of stiffened plates.Further analysis was carried out in this paper.(3)The afterburning energy of TNT detonation products enhances the blast loads evidently.The internal explosion pressures of TNT in both nitrogen and air atmosphere are compared by experiments.It is found that the contribution of afterburning energy to the quasi-static pressure is twice that of detonation energy when the ratio of charge mass to the volume of cabin is relatively small.With the increase of charge volume ratio,the contribution of afterburning energy to the quasi-static pressure decreases gradually.To simulate the blast pressure in cabin,a method is proposed to take the afterburning energy into account.The reliability of this internal blast load simulation method is verified by comparing the numerical results with the experimental data.The numerical simulation of the structural response is carried out by using the proposed internal blast load simulation method.The comparison between the simulation results and experimental results further verifies the reliability and accuracy of the simulation method in calculating the structural response.(4)The validated calculation method is used to carry out the numerical calculation of prototype and scaled model tests respectively.The influencing factors of structural response similarity are analyzed by comparing simulation results.The results show that the effect of boundary constraints on the dynamic response of the structure is significant.In order to analyze the influence of boundary distortion,numerical experiments on dynamic response of specimens with different geometry scale factors are carried out under fixed boundary constraints,the result of which verify the correctness of the similarity relation of structural response derived in this paper.