The effects of impact positions(offset ratios)on the dynamic behaviors of Q235 steel thin-walled cylindrical shells under lateral impacts by foam projectiles were explored with finite element software ABAQUS/Explicit.Based on existing experimental results,the accuracy of the finite element model was validated,and the model was employed to conduct a comparative analysis of the dynamic deformation evolution,the deflec-tions at mid-points of the impact region on the impact and rear sides,and the final deformation modes of the cylindrical shell under different offset ratios.The results show that,the deflections at the mid-point of the im-pact region on the impact side are consistent with the impact direction,while those on the rear side are in the opposite direction;the asymmetric deformation mode of the cylindrical shell becomes more pronounced as the offset ratio increases.Subsequently,the effects of constraint types,initial momentums,and length-to-diameter ratios on the impact resistance of the cylindrical shell under offset lateral impact were studied.The comparisons indicate that,regardless of the constraint type or the initial momentum,an increase in the offset ratio will re-duce the absolute values of the deflections at the mid-point of the impact region on both sides,which will also slow down the transition process of deflections at the mid-point of the impact region on the rear side from in-dentation to bulging,under the influence of the length-to-diameter ratio.This enhancement mechanism is pri-marily attributed to the significant improvement of the constraining effect of boundary conditions on the cylin-drical shell as the offset ratio increases.
The conventional methods of digital image edge detection include Canny algorithm,Sobel algorithm,Prewitt algo-rithm,etc.On the basis of studying the calculation principle of the conventional methods of image edge detection,a digital image edge detection algorithm is proposed,which includes the preliminary extreme edge matrix calculation of the image,the suppres-sion calculation of the Otsu threshold and the extension calculation of the edge.The feasibility of the proposed algorithm is veri-fied by comparing the image edges extracted by the proposed algorithm with the image edges extracted by the conventional algo-rithms.The proosed algorithm and the corrventional methods are used to detect the edge of the engine nozzle burning flame im-age.The results show that the Sobel algorithm and the Prewitt algorithm the edge of a small amount of flame,the Canny algo-rithm provides the large outline of the flame,and the proposed algorithm provides a large amount of flame detail edge informa-tion.Because the edge of the combustion flame is an important feature of combustion,the proposed algorithm is more suitable for the depth analysis of the digital image edge of the nozzle burning flame,and provides a new method for the nozzle burning flame analysis.
A cold kerosene hot air two-phase cylindrical rotating detonation combustor with nozzles with convergence ratios of 4.81 and 3.60 was studied by numerical simulation and experiments.The commercial CFD software were used to simulate and analyze the empty cylindrical rotating detonation combustor with a convergent nozzle.With the help of the ground test bench,the experimental study of a ramjet rotating detonation engine under the condition of high total enthalpy incoming flow was carried out,and the pressure signals of the isolation section,detonation combustor,and nozzle throat were obtained.The results show that when the nozzle with a small throat area is used in the rotating detonation combustor,the wave velocity is slightly increased.In the simulation,the wave velocity is increased from 1 891 to 1 899 m/s,while in the test,it is increased from 1 670 to 1 686 m/s.Increasing the convergence ratio leads to an increase in total pressure,combustion efficiency,and fuel specific impulse along the way.However,changing the convergence ratio of the converging nozzle will cause the positive shock wave at the end of the isolation section to move forward,thus stable working margin decreases.
To study the effect of inflow entrained non-condensable gas on cavitating flow inside the inducer,a series of experiments are performed based on the visualization experimental platform.The macroscopic performance,cavita-tion development and cavitation instabilities of the inducer pump with different inlet gas volume fractions are investi-gated.It is found that the head breakdown occurred earlier at larger inlet gas volume fractions.Additionally,the non-condensable gas is entrained in leakage flow vortices and backflow vortices,resulting in significant extensions of leak-age flow vortex cavities and backflow vortex cavities,under larger inlet non-condensable gas entrained condition.With small cavitation numbers(Φ=0.083,σ=0.090,and Φ=0.071,σ=0.068),the non-condensable gas provides extra cavitation compliance to the cavity and therefore suppresses the cavitation surge.
Liquid rocket engines are used as the main propulsion system for Chinese space transportation,which offer the most spacecraft launch for space activities.During the rigorous working conditions,such as high pressure,high temperature,high rotational speed and strong vibration environment,structural strength of engine and its components have become momentous technical problems to be solved in the engine development process.Structural strength problems began with the preliminary design stage of project operated throughout the product full life cycle and ended with completing the launch missions.However,many uncertainties and profound problems,including structural de-sign,loads and serving environments,materials,manufacturing process,test measure,destructive evaluation,test verification process and strength assessment,caused the structural strength to become an important factor that af-fected the safety and reliability of engine.Therefore,taking the structural strength as fundamental starting point,the aforementioned essential problems and elements in structural strength design,test verification process of liquid rocket engines were summarized and analyzed,and research ideas for structure strength design system exploration and the new engine pre-research were proposed and discussed in this paper.
