Modified Ghost Fluid Method Research Articles

Dynamic response of deformable structures subjected to shock load and cavitation reload

The dynamic response of deformable structures subjected to shock load and cavitation reload has been simulated using a multiphase model, which consists of an interface capturing method and a one-fluid cavitation model. Fluid–structure interaction (FSI) is captured via a modified ghost fluid method (Liu et al. in J Comput Phys 190: 651–681, 2003), where the structure is assumed to be a hydro-elasto-plastic material if subjected to a strong shock load. Bulk cavitation near the structural surface is captured using an isentropic model (Liu et al. in J Comput Phys 201:80–108, 2004). The integrated multiphase model is validated by comparing numerical predictions with 1D analytical solutions, and with numerical solutions calculated using the cavitation acoustic finite element (CAFE) method (Sprague and Geers in Shocks vib 7:105–122, 2001). To assess the ability of the multiphase model for multi- dimensions, underwater explosions (UNDEX) near structures are computed. The importance of cavitation reloading and FSI is investigated. Comparisons of the predicted pressure time histories with different explosion center are shown, and the effect on the structure is discussed.

A robust algorithm for moving interface of multi-material fluids based on Riemann solutions

In the paper, the numerical simulation of interface problems for multiple material fluids is studied. The level set function is designed to capture the location of the material interface. For multi-dimensional and multi-material fluids, the modified ghost fluid method needs a Riemann solution to renew the variable states near the interface. Here we present a new convenient and effective algorithm for solving the Riemann problem in the normal direction. The extrapolated variables are populated by Taylor series expansions in the direction. The anti-diffusive high order WENO difference scheme with the limiter is adopted for the numerical simulation. Finally we implement a series of numerical experiments of multi-material flows. The obtained results are satisfying, compared to those by other methods.

The accuracy of the modified ghost fluid method for gas–gas Riemann problem

Previous numerical tests have shown that the modified ghost fluid method (MGFM) [T.G. Liu, B.C. Khoo, K.S. Yeo, Ghost fluid method for strong shock impacting on material interface, J. Comput. Phys. 190 (2003) 651–681; T.G. Liu, B.C. Khoo, C.W. Wang, The ghost fluid method for compressible gas–water simulation, J. Comput. Phys. 204 (2005) 193–221] is robust and performs much better than the original GFM [R.P. Fedkiw, T. Aslam, B. Merriman, S. Osher, A non-oscillatory Eulerian approach to interfaces in multimaterial flows (the ghost fluid method), J. Comput. Phys. 152 (1999) 457–492]. In this work, a rigorous analysis is carried out on the accuracy of the MGFM when applied to the gas–gas Riemann problem. It is shown that at the material interface the MGFM solution approximates the exact solution to at least second-order accuracy in the sense of comparing to the exact solution of a Riemann problem. On the other hand, the results by the original GFM have generally no-order accuracy if the interface is not in normal motion.

The simulation of cavitating flows induced by underwater shock and free surface interaction

An underwater explosion near a free surface constitutes an explosive gas–water–air system with a shock and free surface interaction and the presence of bulk cavitation region. This paper applies a simplified modified ghost fluid method [T.G. Liu, et al., Comm. Comput. Phys. 1 (2006) 898] to simulate the explosive gas–water and water–air interfaces and an isentropic one-fluid cavitation model [T.G. Liu, et al., J. Comput. Phys. 201 (2004) 80] to describe and capture the unsteady cavitation just below the free surface. It is found that the proposed ghost fluid method can accurately simulate the gas–water/water–air compressible flows with the wave interaction at the interfaces and the deformation of the free surface. The isentropic one-fluid cavitation model, on the other hand, is capable of simulating the dynamic creation and evolution of the bulk cavitation below the free surface.

GHOST FLUID METHOD APPLIED TO COMPRESSIBLE MULTI-PHASE FLOWS

In this work, we show that the Ghost Fluid Method (GFM) has actually zero-order accuracy if the gas-liquid interface is not in normal motion initially. The modified GFM (MGFM) is found to overcome this problem well. Examples are given to support the present analysis and conclusions obtained, and the MGFM is then applied to simulate compressible fluid-structure interaction.

The ghost fluid method for compressible gas–water simulation

An analysis is carried out for the ghost fluid method (GFM) based algorithm as applied to the gas–water Riemann problems, which can be construed as two single-medium GFM Riemann problems. It is found that the inability to provide correct and consistent Riemann waves in the respective real fluids by these two GFM Riemann problems may lead to inaccurate numerical results. Based on this finding, two conditions are suggested and imposed for the ghost fluid status in order to ensure that correct and consistent Riemann waves are provided in the respective real fluids during the numerical decomposition of the singularity. Using these two conditions to analyse some of the existing GFM-based algorithms such as the original GFM [J. Comput. Phys. 152 (1999) 457], the new version GFM [J. Comput. Phys. 166 (2001) 1; J. Comput. Phys. 175 (2002) 200] and the modified GFM (MGFM) [J. Comput. Phys. 190 (2003) 651], it is found that there are ranges of conditions for each type of solution where either the original GFM or the new version GFM or both are unable to provide correct or consistent Riemann waves in one of the real fluids. Within these ranges, examples can be found such that either the original GFM or the new version GFM or both are unable to provide accurate results. The MGFM is also found to encounter difficulties when applied to nearly cavitating flow. Various examples are presented to demonstrate the conclusions obtained. The MGFM with proposed modification when applied to nearly cavitating flow is then found to be quite robust and can provide relatively reasonable results.