The course of shock response of warship cannot be exactly analyzed by traditional Fourier trans-form because of its obvious character of non-stationary and non-linearity. In this paper, the short time Fourier transform (STFT) is used to analyze the time-frequency variation of impact response. This method can exactly represent the frequency evaluative character of impact response of the shipbuilding structure and ship’s equipment. The results of this study can provide the technical support for the detailed analy-sis of warship anti-shock rule and the investigation of limit impact load.

An integrative dynamic model for the ship hull and the shipboard equipment dynamic response due to far field underwater explosion is developed. The model incorporates the Dynamic Design Analysis Method (DDAM) into the Taylor Plate Theory, and enables the shipboard equipment dynamic response analysis to be performed more efficiently. The model is formulated by assuming the ship hull to be a flat plate with an N-mass deck and shipboard equipment attached to the hull. A one-dimensional analysis is used to represent the explosion wave in water. The pressure wave is assumed to be a decaying exponential function. The model can predict the ship hull and the shipboard equipment shock response based on the underwater explosion charge weight, stand off distance, the Ship's Tonnage, principal dimensions, approximate ship hull structure and shipboard equipment mass and support stiffness parameters. The analytical results based on the model are compared to that of scaled ship model underwater explosion experiment results. In general, the spectrum values of the hull motion are similar in shape and magnitude to the experiment.

Blast wave is numerical simulated based on FCT method. According to the comparative analysis, taking Henrych empirical formula as a standard, FCT method is more accuracy than Godunov method. Moreover, it has been found that the numerical accuracy is insufficient when the distance is small, it is necessary to develop and modify the numerical method continuously.

The filtering frequency of shock response is difficult to study due to its obvious features of transient and non-linearity in course of shock response of a warship.So far,there is no standard or uniform method of choosing filtering frequency for anti-shock study.The specific analysis method and criterion were provided here by taking impulse information variation of shock response as the basis of choosing filtering frequency.The shock response filtering frequencies of a shipbuilding structure and an equipment were analyzed with the proposed method.The results showed that the shock response filtering frequencies are same for the same part of the shipbuilding structure with different balst distances,but they are different for the same part of the ship equipment with different explosion distances.

Experiments were conducted where the underwater bubble oscillates between two boundaries, a free surface and a horizontal rigid wall. The motion features of both the bubble and the free surface were investigated, via the consideration of two key factors, i.e., the non-dimensional distances from the bubble to the two boundaries. To support the investigation, experiments were conducted in the first place where the bubble oscillates near only one of the two boundaries. Then the other boundary was inserted at different positions to observe the changes in the motion features, including the types, maximum speed and height of the water spike and skirt, the form and speed of the jets, and bubble shapes. Correspondence is found between the motion features of the free surface and different stages of bubble oscillation. Intriguing details such as gas torus around the jet, double jets, bubble entrapment, and microjet of the water spike, etc., are observed.

A numerical model for simulating the underwater explosion of bottom charge was established using the hydrodynamics analysis software,and the underwater explosion process was numerically simulated to obtain the law of its shock wave propagation.For the underwater explosion of a bottom charge,the shock wave propagation complies with the law of exponential decay.The bottom affected the shock wave propagation.Mach wave was formed due to the reflective wave catching up with the incident wave at the gauge points which were close to the explosion point on the bottom.For the points near the bottom their incident wave was strengthened or weakened by the shock wave or the rarefaction wave reflected from the bottom.

A method was proposed to estimate the dynamic strength of fiber reinforced concrete specimen with the non-ideal end-surfaces. Finite element modeling was used to simulate the specimen with two prescribed concaves. The numerical results show that the corrected compression stresses at the ends of specimen are identical with that in the main part of specimen, in which the axial compression stress is uniform and the highest. A steel fiber-reinforced concrete (SFRC) with the fiber volume fraction of 3% was tested to demonstrate the feasibility of the method. The variance of the compression strength was decreased from 22.64 MPa to 10.95 MPa using the proposed method. The experimental results show that the method can effectively correct the dynamic strength measurements of the steel fiber-reinforced concrete.

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Considering the shock-resistance threshold of equipment on board as the important base for ship shock-resistance design and assessment,a finite element model of marine gearbox was established to get the characteristic of shock-resistance threshold.The shock-resistance threshold was analyzed using endurable stress method.Results indicate that endurable stress method is a direct and effective computational method for getting shock-resistance threshold of marine equipment.The shock-resistance threshold of marine gearbox is related to the peak value of acceleration and pulse width of input load.

Considered many non-linear contact relationships between the main components in diesel,a time domain simulation method was applied to assessment its shock response.In the assessment,some modeling principles of complex mechanical systems,such as diesel,were given.Also,the finite element models of main components in V6 diesel were established,and then,their shock response characteristics were analyzed in time-domain on the basis of BV043/85 criterion.The stress responses of main components showed the shock vulnerability spots,and the motion response and results of oil film on bearing indicated the work ability.Theanalysis results show that the assessed diesel meet BV043/85 standard on impact security level of A-grade equipments.

In this paper,ship pipeline vibration reduction optimization was studied.An optimization process and analysis method based on ANSYS was studied.Based on the single beam model,the response of the shockwave of the pipes was simulated with various boundary conditions,different numbers of pipe clamps,and several directions of the constraint.A reduced beam model was established based on the reduced model of the starboard diesel generator's vent-pipes.An analysis and optimization method was provided for complex pipes.Considering different numbers of the pipe clamps,the model's response to a shock wave was analyzed in the case of shock load,sine load,and a fixed constraint.The position of the pipe clamps was optimized for the minimum displacement when the shock response was obviously improved.The best position of the pipe clamps was obtained from thorough analysis.The response and displacement were improved due to the same shockwave.

The basic theory of the extended Fourier amplitude sensitivity test method was introduced and the parametric model of a piping system on the main engine of a ship was built by using ANSYS-APDL software. The procedure for applying the extended Fourier amplitude sensitivity test method to computing the sensitivities of the model was programmed by use of MATLAB software. The sensitivity analysis indicated that the key factors influencing the shock response of the piping system are the thickness of the pipe, the rigidity of the elastic hanger, the lumped mass and its position, and the position of the elastic support; the method and the conclusions obtained can be used in the optimal shock-resistant design of a piping system.

The frequency domain analysis of marine equipment anti-shock capacity is a common engineering evaluation method.A finite element model of a diesel was established,and modified using the modal tests of its main components.According to GJB1060.1-91,the shock load of the computation model was cletermined based on the DDAM method.Then,its shock response was analyzed under each shock load.The results indicated that the frequency domain analysis of marine equipment anti-shock capacity is an effective evaluation method,and this diesel model meets the requirement of the GJB.

The problem of underwater explosion near free surface is a dynamic process involving multi-medium and transient nonlinearity.The dominant difficulty is how to trace the moving interface between different medium.The level-set technique is adopted herein to capture the time-dependent changes of the free surface and the moving interface of explosive gaseous product and water.To simulate compressible-fluid flow in which discontinuous shocks are present,the high-resolution method of Total Variation Diminishing(TVD) scheme is used.A numerical method has been first developed for numerical simulation of 2-D underwater explosion near free surface.The method is then extended to account for the interaction of fluid and a rigid structure present in water.The non-reflection boundary condition technique developed by Thomson is finally employed for considering the infinite flow field.

A new concept product——Anti-Shock Layer(ASL)——was developed to isolate the underwater non-contact explosion loads and ship radiated noise.Ship resistance was taken into account while a naval ship was coated with ASL.Numerical simulation of three-dimensional viscous flow fields over the ship model was processed by solving Reynolds-Averaged Navier-Stokes(RANS) equations with an RNG turbulence model and the finite volume method.A type of time domain boundary element method based on Green's theorem was used to compute the wave making resistance of the ship model.At the same time,a resistance contrast test between ship models coated with and without ASL was carried out at the towing tank.The numerical test results show that the ship resistance is almost the same at low speed and increases less than 1% at high speed as a result of wave making resistance when a ship is coated with ASL.The comparison between numerical and experimental data shows that the demonstrated numerical method is feasible and reliable.

Shock response underwater explosive of piping system on ship is analyzed by simulation and experiment. This conclusion can be gained: The maximum of acceleration response between simulation and experiment is within 30%; The maximum of strain response between simulation and experiment is within 30% too; With the distance between the mine and ship expanding, the maximum of shock displacement decreases; With the distance between the mine and ship expanding, the maximum of shock stress also decreases. But the position of the shock stress is commonly at the bend. The result between simulation and experiment proves that the shock response underwater explosive of piping system on ship can be computed by ANSYS code and the method gives a base of the structural anti-shock optimization design of piping system on ship.

As the operations platform in the sea war, combatant vessels were inevitably attacked by underwater weapons and the structures of ship and the shipboard equipments usually suffered serious damage. It is very necessary to predict a virtual shock environment of underwater explosions in order to design the optimal protective structures of ship and enhance the capacity of ship's impact resistance. So the tandem shaped charge was taken as the research object and the whole process of tandem warhead underwater explosion was simulated by using Ansys-Autodyn, and the basic characteristics and interaction laws were also analyzed in order to provide reliable explosive Loading for the ship-shock environments.

Various shock waves in time domain were translated into shock response spectrums(SRS).It was found that the peak acceleration value of 10ms triangular shock wave is equal to the acceleration value on the isoline of SRS.Accordingly,10ms triangular shock wave was suggested as the standard input load for anti-shock performance analysis of equipment.By virtue of the software of ABAQUS6.7,the flexible multi-body and anti-shock analysis model of the whole engine,including the backbone,was established.The shock simulations of a V6 type diesel were carried out under rated condition and standing condition respectively.The simulation results indicate that the shock response characteristic of diesel engine is nonlinear.The stress response under rated condition added with a shock is not the simple superposition of the shock stress under standing condition plus the working stress under rated condition.The strength of crankshaft,cylinder block,flywheel housing and block support should be checked through shock simulation.

The motion of a rotor can be decomposed into forward whirls and backward whirls. This approach is referred to as whirl analysis or whirl transform.It reveals the relationship between motion of a rotor and forces applied more evidently,therefore this method is widely applied to diagnosing problems in rotating machinery.4 theorems about rotation vibration were established.Theorem 1 states that,an elliptical orbit of a rotor can always be decomposed into a forward whirl and a backward whirl.The area of the elliptical orbit is equal to the absolute value of the difference between the area of the forward whirl and that of backward whirl.Theorem 2 is associated with the circumference of an elliptical orbit and its forward whirl and backward whirl.Theorem 3 states that,the forces applied to a rotor can also be decomposed into forward whirl force and backward whirl force.The forward whirl force can only perform work on the forward whirl but not on backward whirl;vice versa,the backward whirl force can only perform work on the backward whirl but does not on the forward whirl.Theorem 4 states that the work performed by forward whirl force is equal to the dot product of forward whirl force and the displacement of rotor in the forward whirl,similarly the work performed by backward whirl force is equal to the dot product of backward whirl force and the displacement of rotor in backward whirl.The theorems are applied to determine the work performed by unbalance,viscous damping and restoring forces due to skew symmetric stiffness.The results are identical with those obtained from traditional dynamics.However it is found that,when ωyΩωx,as |r-||r+|,the skew symmetric stiffness will act as a stabilizing force suppressing backward whirl of a rotor.

A method of considering the multiple points' excitations, multiple peak values, and multiple phases of shock load of computing the shock response of pipeline system is presented on the condition that the impulsive environment is undetermined. Utilizing the mentioned loading method, the shock response of pipeline of a ship is analyzed by ANSYS code. Comparing with the analysis not considering the differences of excitations, peak values, and phases, the result is beneficial to the shock resistance design of the pipeline system on ship.