An efficient ghost-cell immersed boundary method (GCIBM) for simulating turbulent flows in complex geometries is presented. A boundary condition is enforced through a ghost cell method. The reconstruction procedure allows systematic development of numerical schemes for treating the immersed boundary while preserving the overall second-order accuracy of the base solver. Both Dirichlet and Neumann boundary conditions can be treated. The current ghost cell treatment is both suitable for staggered and non-staggered Cartesian grids. The accuracy of the current method is validated using flow past a circular cylinder and large eddy simulation of turbulent flow over a wavy surface. Numerical results are compared with experimental data and boundary-fitted grid results. The method is further extended to an existing ocean model (MITGCM) to simulate geophysical flow over a three-dimensional bump. The method is easily implemented as evidenced by our use of several existing codes.

A Ghost-Cell Immersed Boundary Method for Flow in Complex Geometry

The immersed boundary method is a methodology for dealing with boundary conditions at fluid–fluid and fluid–solid interfaces. The immersed boundary method has been attracting growing attention in t...

https://journals.sagepub.com/doi/pdf/10.1177/0954406219842606

Recent trends and progress in the immersed boundary method

This study aims to develop an adaptive mesh refinement (AMR) algorithm combined with Cut-Cell IBM using two-stage pressure–velocity corrections for thin-object FSI problems. To achieve the objectiv ...

https://www.tandfonline.com/doi/pdf/10.1080/19942060.2019.1652209

Thin and sharp edges bodies-fluid interaction simulation using cut-cell immersed boundary method

A novel geometry-adaptive Cartesian grid based immersed boundary–lattice Boltzmann method for fluid–structure interactions at moderate and high Reynolds numbers

Abstract High-speed water entry is a transient hydrodynamic process that is accompanied by strongly compressible flow, free surface splash, cavity evolution and other nonlinear hydrodynamic phenomena. To address these problems, a novel fluid–structure interaction (FSI) scheme based on the immersed boundary method is proposed which is suitable for strongly compressible multiphase flows. In this scheme, considering the multiphase interfaces at the immersed boundary, an improved immersed boundary method for effectively suppressing the non-physical force oscillation is proposed. Additionally, a quaternion-based six degrees of freedom motion system is used to describe rigid body motion, and the multiphase flow Eulerian finite element method is applied as the fluid solver. Using analytical solutions, experimental data and literature data, the accuracy and robustness of the FSI scheme are validated. Finally, the high-speed water entry of the slender body with different noses is investigated, and the hydrodynamic loads including the axial and normal drag forces and the bending moment are extensively discussed. The hydrodynamic load and motion trajectory are determined by the nose configuration. The tail slamming phenomenon is the primary focus, and it is revealed that its formation is primarily related to the pitch moment formed at the stage of crossing the free surface. Tail slamming also causes violent impact loads, especially bending moments, which may cause slender projectiles to break off. Finally, to combine the features of the flat and hemispherical noses, the water entry of the projectile with a truncated hemispherical nose is simulated and discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/643D4FA2733CAFF86BABE373E2E47937/S0022112023001209a.pdf/div-class-title-investigation-of-hydrodynamics-of-water-impact-and-tail-slamming-of-high-speed-water-entry-with-a-novel-immersed-boundary-method-div.pdf

Investigation of hydrodynamics of water impact and tail slamming of high-speed water entry with a novel immersed boundary method

An immersed boundary method for fluid–structure interaction with compressible multiphase flows

Rocket-towed systems are commonly applied in specific aerospace engineering fields. In this work, we concentrate on the study of a rocket-towed net system (RTNS). Based on the lumped mass method, the multibody dynamic model of RTNS is established. The dynamic equations are derived by the Cartesian coordinate method and the condensational method is utilized to obtain the corresponding second order ordinary differential equations (ODEs). Considering the elastic hysteresis of woven fabrics, a tension model of mesh-belts is proposed. Through simulation in MATLAB, the numerical deploying process of RTNS is acquired. Furthermore, a prototype is designed and flight tests are conducted in a shooting range. Ballistic curves and four essential dynamic parameters are studied by using comparative analysis between simulation results and test data. The simulation acquires a good accuracy in describing average behaviors of the measured dynamic parameters with acceptable error rates in the main part of the flight and manages to catch the oscillations in the intense dynamic loading phase. Meanwhile, the model functions well as a theoretical guidance for experimental design and achieves in predicting essential engineering factors during the RTNS deploying process as an approximate engineering reference.

/pdf/dynamic-modeling-simulation-and-flight-test-of-a-rocket-3v8pxbvd33.pdf

Dynamic Modeling, Simulation, and Flight Test of a Rocket-Towed Net System

The projection angles of fragments from a cylindrical casing filled with charge initiated at one end

Cylindrical casing filled with charge under eccentric point initiation is a kind of velocity enhanced warhead (VEW). The initial velocity distribution of fragments from VEW is a key issue in the field of explosive technology. Most of the formulas existed can predict the fragment velocity distribution from VEW with a single eccentric initiation point, but the fragment velocity distribution of the VEWs with double symmetric eccentric initiation points is not studied well. In this paper, a new formula is established to predict the radial distribution of the fragment velocities from VEW under double symmetric initiation points. Not only the maximum velocity gains, but also the velocity gains with azimuth angle can be calculated using this formula. The formula applies a correctional function in consideration of both the angle 2ϕ between the two symmetric initiation points and the ratio of the mass charge to that of metal casing β. Finally, the X-ray experiments were conducted to verify the formula established in this paper, and the predictions agree well with the experimental data. According to the comparisons between the calculated results from the formula and the published data, the formula also shows good agreement.

Fragment Velocity Distribution of Velocity Enhanced Warhead under Double Symmetric Initiations

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Papers

An immersed boundary method for fluid–structure interaction with compressible multiphase flows

Dynamic Modeling, Simulation, and Flight Test of a Rocket-Towed Net System

The projection angles of fragments from a cylindrical casing filled with charge initiated at one end

Fragment Velocity Distribution of Velocity Enhanced Warhead under Double Symmetric Initiations