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1. A Fluid-Structure Coupled Computational Model for the Certification of Shock-Resistant Elastomer Coatings

   https://doi.org/10.1115/OMAE2020-18501  

   Ma, Wentao; Zhao, Xuning; Wang, Kevin (August 2020, ASME 2020 39th International Conference on Ocean, Offshore and Arctic Engineering)

   null (Ed.)

   Abstract Shock waves from underwater and air explosions are significant threats to surface and underwater vehicles and structures. Recent studies on the mechanical and thermal properties of various phase-separated elastomers indicate the possibility of applying these materials as a coating to mitigate shock-induced structural failures. To demonstrate this approach and investigate its efficacy, this paper presents a fluid-structure coupled computational model capable of predicting the dynamic response of air-backed bilayer (i.e. elastomer coating – metal substrate) structures submerged in water to hydrostatic and underwater explosion loads. The model couples a three-dimensional multiphase finite volume computational fluid dynamics model with a nonlinear finite element computational solid dynamics model using the FIVER (FInite Volume method with Exact multi-material Riemann solvers) method. The kinematic boundary condition at the fluid-structure interface is enforced using an embedded boundary method that is capable of handling large structural deformation and topological changes. The dynamic interface condition is enforced by formulating and solving local, one-dimensional fluid-solid Riemann problems, which is well-suited for transferring shock and impulsive loads. The capability of this computational model is demonstrated through a numerical investigation of hydrostatic and shock-induced collapse of aluminum tubes with polyurea coating on its inner surface. The thickness of the structure is resolved explicitly by the finite element mesh. The nonlinear material behavior of polyurea is accounted for using a hyper-viscoelastic constitutive model featuring a modified Mooney-Rivlin equation and a stress relaxation function in the form of prony series. Three numerical experiments are conducted to simulate and compare the collapse of the structure in different loading conditions, including a constant pressure, a fluid environment initially in hydrostatic equilibrium, and a two-phase fluid flow created by a near-field underwater explosion. 

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2. Shock-induced bubble collapse near solid materials: effect of acoustic impedance

   https://doi.org/10.1017/jfm.2020.810  

   Cao, S.; Wang, G.; Coutier-Delgosha, O.; Wang, K. (January 2021, Journal of Fluid Mechanics)

   null (Ed.)

   The fluid dynamics of a bubble collapsing near an elastic or viscoelastic material is coupled with the mechanical response of the material. We apply a multiphase fluid–solid coupled computational model to simulate the collapse of an air bubble in water induced by an ultrasound shock wave, near different types of materials including metals (e.g. aluminium), polymers (e.g. polyurea), minerals (e.g. gypsum), glass and foams. We characterize the two-way fluid–material interaction by examining the fluid pressure and velocity fields, the time history of bubble shape and volume and the maximum tensile and shear stresses produced in the material. We show that the ratio of the longitudinal acoustic impedance of the material compared to that of the ambient fluid, $$Z/Z_0$$ , plays a significant role. When $$Z/Z_0<1$$ , the material reflects the compressive front of the incident shock into a tensile wave. The reflected tensile wave impinges on the bubble and decelerates its collapse. As a result, the collapse produces a liquid jet, but not necessarily a shock wave. When $$Z/Z_0>1$$ , the reflected wave is compressive and accelerates the bubble's collapse, leading to the emission of a shock wave whose amplitude increases linearly with $$\log (Z/Z_0)$$ , and can be much higher than the amplitude of the incident shock. The reflection of this emitted shock wave impinges on the bubble during its rebound. It reduces the speed of the bubble's rebound and the velocity of the liquid jet. Furthermore, we show that, for a set of materials with $$Z/Z_0\in [0.04, 10.8]$$ , the effect of acoustic impedance on the bubble's collapse time and minimum volume can be captured using phenomenological models constructed based on the solution of Rayleigh–Plesset equation. 

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3. Survival of the Fittest: Numerical Modeling of SN 2014C

   https://doi.org/10.3847/1538-4357/ac649d  

   Vargas, Felipe; De Colle, Fabio; Brethauer, Daniel; Margutti, Raffaella; Bernal, Cristian G. (May 2022, The Astrophysical Journal)

   Abstract Initially classified as a Type Ib supernova (SN), ∼100 days after the explosion SN 2014C made a transition to a Type II SN, presenting a gradual increase in the H α emission. This has been interpreted as evidence of interaction between the SN shock wave and a massive shell previously ejected from the progenitor star. In this paper we present numerical simulations of the propagation of the SN shock through the progenitor star and its wind, as well as the interaction of the SN ejecta with the massive shell. To determine with high precision the structure and location of the shell, we couple a genetic algorithm to a hydrodynamic and a bremsstrahlung radiation transfer code. We iteratively modify the density stratification and location of the shell by minimizing the variance between X-ray observations and synthetic predictions computed from the numerical model, allowing the shell structure to be completely arbitrary. By assuming spherical symmetry, we found that our best-fit model has a shell mass of 2.6 M ⊙ ; extends from 1.6 × 10 16 cm to 1.87 × 10 17 cm, implying that it was ejected ∼ 60/( v w /100 km s −1 ) yr before the SN explosion; and has a density stratification with an average behavior ∼ r −3 but presenting density fluctuations larger than one order of magnitude. Finally, we predict that if the density stratification follows the same power-law behavior, the SN will break out from the shell by mid-2022, i.e., 8.5 yr after explosion. 

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4. A Thermo‐Flow‐Mechanics‐Fracture Model Coupling a Phase‐Field Interface Approach and Thermo‐Fluid‐Structure Interaction

   https://doi.org/10.1002/nme.7646  

   Lee, Sanghyun; von_Wahl, Henry; Wick, Thomas (December 2024, International Journal for Numerical Methods in Engineering)

   ABSTRACT This work proposes a novel approach for coupling non‐isothermal fluid dynamics with fracture mechanics to capture thermal effects within fluid‐filled fractures accurately. This method addresses critical aspects of calculating fracture width in enhanced geothermal systems, where the temperature effects of fractures are crucial. The proposed algorithm features an iterative coupling between an interface‐capturing phase‐field fracture method and interface‐tracking thermo‐fluid‐structure interaction using arbitrary Lagrangian–Eulerian coordinates. We use a phase‐field approach to represent fractures and reconstruct the geometry to frame a thermo‐fluid‐structure interaction problem, resulting in pressure and temperature fields that drive fracture propagation. We developed a novel phase‐field interface model accounting for thermal effects, enabling the coupling of quantities specific to the fluid‐filled fracture with the phase‐field model through the interface between the fracture and the intact solid domain. We provide several numerical examples to demonstrate the capabilities of the proposed algorithm. In particular, we analyze mesh convergence of our phase‐field interface model, investigate the effects of temperature on crack width and volume in a static regime, and highlight the method's potential for modeling slowly propagating fractures. 

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5. Verification and convergence study of a spectral-element numerical methodology for fluid-structure interaction

   https://doi.org/doi.org/10.1016/j.jcpx.2021.100084  

   Xu, YiQin; Peet, Yulia T (March 2021, Journal of computational physics)

   A high-order in space spectral-element methodology for the solution of a strongly coupled fluid-structure interaction (FSI) problem is developed. A methodology is based on a partitioned solution of incompressible fluid equations on body-fitted grids, and nonlinearly-elastic solid deformation equations coupled via a fixed-point iteration approach with Aitken relaxation. A comprehensive verification strategy of the developed methodology is presented, including h-, p-and temporal refinement studies. An expected order of convergence is demonstrated first separately for the corresponding fluid and solid solvers, followed by a self-convergence study on a coupled FSI problem (self-convergence refers to a convergence to a reference solution obtained with the same solver at higher resolution). To this end, a new three-dimensional fluid-structure interaction benchmark is proposed for a verification of the FSI codes, which consists of a fluid flow in a channel with one rigid and one flexible wall. It is shown that, due to a consistent problem formulation, including initial and boundary conditions, a high-order spatial convergence on a fully coupled FSI problem can be demonstrated. Finally, a developed framework is applied successfully to a Direct Numerical Simulation of a turbulent flow in a channel interacting with a compliant wall, where the fluid-structure interface is fully resolved. 

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