Simulation Of Underwater Explosion Research Articles

An enhanced interface-sharpening algorithm for accurate simulation of underwater explosion in compressible multiphase flow on complex grids

In underwater explosion simulations, the accuracy is critically affected by numerical diffusion and the quality of the computational grid. An enhanced interface-sharpening algorithm, based on the five-equation model and an anti-diffusion source term, is proposed to simulate the strongly compressible multiphase flow with an arbitrary number of phases in underwater explosions. To enhance the precision of interface and maintain computational stability on nonuniform and unstructured grids, an adaptive factor algorithm and a continuous interface capture function are developed. Furthermore, a redesigned fractional step method incorporating a special iteration stop criteria is proposed to solve the volume fraction equation. A pressure–density cutoff model is used to calculate the mixture density at the saturation pressure to account for the effect of cavitation. The quadratic monotone upstream-centered scheme for conservation laws reconstruction scheme and the improved advection upstream splitting method (AUSM+-up) flux scheme are also adopted to compute the flux across the grid interfaces. The overall computational framework is constructed upon a density-based explicit finite volume method. To assess the accuracy and robustness of the proposed numerical model, four representative test cases were chosen. The results reveal that the model refines the phase interface, adeptly capturing the complexities inherent in underwater explosion scenarios with both precision and efficiency across a diverse array of conditions.

SPH numerical simulation of peak pressure in near-field underwater explosion with moving boundary method using virtual particles

A new moving boundary method using virtual particles in smoothed particle hydrodynamics is designed and applied to numerical simulation of underwater explosion. The wave structure in underwater explosion was semi-analyzed, which provides references for the understanding of numerical results in various dimensions. The results show that the boundary point between the near-field and middle-field, with the specific distance R/a = 6, is a demarcation point in the wave structure. Piecewise power fitting computational results in the near-field underwater explosion are in good agreement with the numerical results.

Application of Six Equation Compressible Multifluid Model For the Numerical Simulation of Under-water Explosion

A two phase, six-equation compressible multifluid formulation, three-dimensional code is developed. In this paper, numerical simulation of underwater explosion near a free surface is presented as an application of the code developed. The flow structures and the processes are unsteady. Finite volume method is used for spatial discretization with HLLC scheme with second order accuracy for flux computation. Explicit, classical four stage Runge-Kutta method is used for temporal discretization. The main focus is to study the wave travel and capture the physics when a high-pressure high temperature gas explosion happens in water near to the free surface.

Investigation on the cavitation and atomization characteristics of multiphase fluids in underwater explosion near a free surface

The characteristics of cavitation and atomization induced by underwater explosion near a free surface have been investigated by the multiphase fluid model based on two-fluid phase transition. This numerical method can provide the phase transition between liquid and its vapor phases during shock wave and rarefaction wave propagation at any time in underwater explosion. The detailed density, pressure, vapor, and liquid phases of volume fraction contours in cavitation and atomization zones can be obtained. The phase transition model was first used to quantitatively research the phenomenon of vapor liquefaction after shock wave propagation in initial water containing different trace amounts of vapor. Then the contribution of phase transition to the formation of cavitation and atomization in underwater explosion was investigated through a shock tube test and two typical underwater explosion cases. It is found that the phase transition effect between the vapor and liquid phases contributes more than 60% to the formation of the cavitation zone. Two charges under two different water surface conditions have been investigated by comparison with the case of a single charge. We can conclude that it is very necessary to introduce the phase transition model into the simulation of underwater explosion, which can provide details of the flow field in the cavitation and atomization zones that cannot be obtained by the one-fluid cavitation model.

A pressure-dependent adaptive resolution scheme for smoothed particle hydrodynamics simulation of underwater explosion

For promoting numerical efficiency in smoothed particle hydrodynamics (SPH) simulation of underwater explosion, a pressure-dependent adaptive resolution scheme (PARS) is proposed. The approach involves dividing computation domain into several regions of different resolution and automatic splitting or merging particles in these regions. Methods are established for identifying resolution regions and for adapting particle resolutions, so that the wave front and the zone with sharp pressure variation is dynamically covered in the region of the highest resolution. Numerical examples are present to demonstrate that the proposed technique can reduce significantly the number of particles and computing time to produce solutions of adequate accuracy. The main features of shockwave propagation can be well captured using much less particles. For large scale or 3D problems, the technique can be decisive for completing a numerical simulation. Numerical examples also testified that the proposed PARS is robust and effective in capturing the complicated phenomena of wave interferences and interaction between shock wave and solid barrier.

Research on the Reflection Characteristics of the Shock Wave Boundary in the Numerical Simulation of Underwater Explosion

A two-dimensional axisymmetric model of the underwater explosion is established in this paper. After verification by empirical formula, the variation law of the reflection coefficient of the shock wave with different boundary sizes under different boundary conditions is studied. The results show that the peak pressure of the near-field shock wave is relatively close to the empirical formula. The calculated value of the far-field shock wave peak pressure is smaller than the empirical value, and refining the mesh can make the near-field shock wave peak pressure closer to Cole’s empirical formula; when the “Flow-out” boundary condition is set, with the increase of the proportional boundary size, the boundary pressure decreases and the reflection coefficient increases. When the proportional boundary size reaches 5, the reflection coefficient of the boundary is the same as that without the “Flow-out” boundary, which is close to 90%.

Application of the Sub-Sea Analysis (SSA) capability in numerical simulation of underwater explosion

In order to solve the problem that LS-DYNA fluid-solid coupling algorithm is not suitable for remote underwater explosion simulation and improve calculation efficiency, the numerical simulation of remote underwater explosion is carried out for the subsea analysis function in LS-DYNA. The dynamic response process of ship hull girder under underwater explosive load is analyzed by comparing it with the general software AUTODYN numerical simulation. The method reflects the loading process of underwater explosion load on structure to a certain extent. The calculation speed is fast, but the accuracy is not high and the error of bubble pulsation process is large.

Finite element-finite volume simulation of underwater explosion and its impact on a reinforced steel plate

Finite element-finite volume simulation of underwater explosion and its impact on a reinforced steel plate

SPH-BEM simulation of underwater explosion and bubble dynamics near rigid wall

A process of underwater explosion of a charge near a rigid wall includes three main stages: charge detonation, bubble pulsation and jet formation. A smoothed particle hydrodynamics (SPH) method has natural advantages in solving problems with large deformations and is suitable for simulation of processes of charge detonation and jet formation. On the other hand, a boundary element method (BEM) is highly efficient for modelling of the bubble pulsation process. In this paper, a hybrid algorithm, fully utilizing advantages of both SPH and BEM, was applied to simulate the entire process of free and near-field underwater explosions. First, a numerical model of the free-field underwater explosion was developed, and the entire explosion process–from the charge detonation to the jet formation–was analysed. Second, the obtained numerical results were compared with the original experimental data in order to verify the validity of the presented method. Third, a SPH model of underwater explosion for a column charge near a rigid wall was developed to simulate the detonation process. The results for propagation of a shock wave are in good accordance with the physical observations. After that, the SPH results were employed as initial conditions for the BEM to simulate the bubble pulsation. The obtained numerical results show that the bubble expanded at first and then shrunk due to a differences of pressure levels inside and outside it. Here, a good agreement between the numerical and experimental results for the shapes, the maximum radius and the movement of the bubble proved the effectiveness of the developed numerical model. Finally, the BEM results for a stage when an initial jet was formed were used as initial conditions for the SPH method to simulate the process of jet formation and its impact on the rigid wall. The numerical results agreed well with the experimental data, verifying the feasibility and suitability of the hybrid algorithm. Besides, the results show that, due to the effect of the Bjerknes force, a jet with a high speed was formed that may cause local damage to underwater structures.

Continuous simulation of the whole process of underwater explosion based on Eulerian finite element approach

Underwater explosion is an extremely complex hydrodynamic problem and it is always divided into two stages and studied individually, i.e., shock wave stage and bubble motion stage. Actually underwater explosion is a continuous process and there are intensive interactions between the two stages in some cases, e.g. underwater explosion in the vicinity of the wall. In this paper, the Eulerian finite element formulation considering the fluid compressibility is applied to continuously simulate the process of underwater explosion based on the subroutine of ABAQUS. Firstly, the governing equation and its solution by the operator splitting approach are discussed. Then the free-field underwater explosion is continuously simulated, including shock wave propagation and the bubble expansion, contraction, collapse, jet and rebound. The applicability and reliability of this method are discussed by comparing with experimental results from Klaseboer [5]. Furthermore, the traditional treatments of the simulation initialized at the bubble motion stage are discussed. Finally, the underwater explosion near wall is investigated regarding the interactions of shock wave and bubble motion and the importance of the continuous simulation of underwater explosion on the bubble motion characteristics is summarized.

Numerical simulation of underwater explosion near air–water free surface using a five-equation reduced model

Underwater explosion phenomena is a complicated problem, however, it has different and important applications. This type of explosion includes strong shock waves with generation of low pressure cavitation׳s zone and deformable interfaces. The main objective of this article is simulation of interaction of shock wave with interface of two-phase gas–liquid flow and capturing the complicated interface generated from explosion. For this reason, a five equations reduced model is considered with using a new cavitation model including gravity force effect. From the numerical point of view, a Godunov method was applied using HLLC solver. By using MUSCL-Hancock strategy, second order accuracy is achieved. To verify the developed computer code, a one dimensional shock tube test case and two test cases including one dimensional cavitation in open tube and a two dimensional underwater explosion where its experimental results can be found in the related literature are used for comparison to justify the obtained results. The comparison of the results confirms an excellent accuracy of the numerical results. The proposed new cavitation model, on the other hand, is capable of calculating low pressures and simulating the dynamic creation and evolution of the bulk cavitation below the free surface.

Numerical Simulation of Underwater Explosion Based on Material Point Method

Underwater explosive load calculation and numerical simulation is the key issues of the design of underwater conventional weapons and protection of ships and submarine. Underwater explosion involves strong nonliner problems and multi-material coupling problems. The method of underwater explosion calculation base on the material point method (MPM) is presented. The MPM takes the advantages of the both Euler and Lagrangian methods and overcomes the shortcomings of them. The problems in the underwater explosive simulation such as large deformation, moving material interfaces and deformable boundaries can be solved effectively by the MPM. At last, blast wave produced by TNT exploding under similar infinite water region is computed. The calculated results are in good agreement with the results of empirical formula of Cole and SPH. The simulation results show that the MPM is an effective tool for underwater explosion calculation.

Numerical simulation of underwater explosion loads

Numerical simulation of TNT underwater explosion was carried out with AUTODYN software. Influences of artificial viscosity and mesh density on simulation results were discussed. Detonation waves in explosive and shock wave in water during early time of explosion are high frequency waves. Fine meshes (less than 1,mm) in explosive and water nearby, and small linear viscosity coefficients and quadratic viscosity coefficients (0.02 and 0.1 respectively, 1/10 of default values) are needed in numerical simulation model. According to these rules, numerical computing pressure profiles can match well with those calculated by Zamyshlyayev empirical formula. Otherwise peak pressure would be smeared off and upstream relative errors would be cumulated downstream to make downstream peak pressure lower.

929 SS400円筒内での水中爆発に対するSPH法を用いた数値解析(OS-9G,OS-9 メッシュフリー/粒子法)

929 SS400円筒内での水中爆発に対するSPH法を用いた数値解析(OS-9G,OS-9 メッシュフリー/粒子法)

Smoothed particle hydrodynamics for numerical simulation of underwater explosion

Underwater explosion arising from high explosive detonation consists of a complicated sequence of energetic processes. It is generally very difficult to simulate underwater explosion phenomena by using traditional grid-based numerical methods due to the inherent features such as large deformations, large inhomogeneities, moving interface and so on. In this paper, a meshless, Lagrangian particle method, smoothed particle hydrodynamics (SPH) is applied to simulate underwater explosion problems. As a free Lagrangian method, SPH can track the moving interface between the gas produced by the explosion and the surrounding water effectively. The meshless nature of SPH overcomes the difficulty resulted from large deformations. Some modifications are made in the SPH code to suit the needs of underwater explosion simulation in evolving the smoothing length, treating solid boundary and material interface. The work is mainly focused on the detonation of the high explosive, the interaction of the explosive gas with the surrounding water, and the propagation of the underwater shock. Comparisons of the numerical results for three examples with those from other sources are quite good. Major features of underwater explosion such as the magnitude and location of the underwater explosion shock can be well captured.