Fluid-structure Interaction Phenomena Research Articles

Experimental and numerical investigation on the hydroelastic response of barge and KVLCC2 ship

In this paper, the hydroelasticity of two segmented ship models (Barge and KVLCC2) is investigated by experimental and numerical methods. A two-way Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) coupled method is adopted and further validated its accuracy against experimental results. The current approach emphasizes the overall convergence between two solvers, maintaining a strongly coupled manner to comprehensively address the fluid-structure interaction phenomenon, including the added mass effect. A series of experiments of a segmented Barge and KVLCC2 under various wave conditions were firstly conducted. The motions of the models are measured and the displacement Response Amplitude Operators (RAOs) are calculated. The CFD-FEA coupled method is demonstrated in agreement with experimental results by comparing the numerical prediction with the tank test results in terms of motion, affirming the validity and robustness. Finally, the hydroelastic response is discussed and investigated.

Coupled fluid-structure simulation of a flapping wing using free multibody dynamics software

AbstractComputer simulations offer invaluable insights into fluid-structure interaction phenomena, increasing our understanding of complex behaviors within fluid flows and enabling predictions of consequential effects. This paper explores flapping wing simulation using an original toolchain based on free software. The structural domain is modeled using multibody dynamics, interfaced with arbitrary fluid dynamics solvers through a general-purpose multiphysics coupling library. The proposed toolchain is validated against benchmark models, demonstrating its effectiveness in various applications. Our study, inspired by experimental ones, applies this coupling to investigate the hydroelastic behavior of a flexible wing. Wing motion characteristics, structural properties, and convergence criteria are analyzed through numerical simulations. While achieving appreciable agreement with experimental data on wing motion ratios, challenges in dealing with large displacements have been identified. Nonetheless, the present study provides valuable insights into fluid-structure interactions, laying the groundwork for future refinements in computational modeling techniques and advancing the understanding of bio-inspired flight mechanisms.

Modified Overset Method in OpenFOAM for Simultaneous Motion and Deformation: A Case Study of a Flexible Flapping Foil

The influence of wing deformation in animal propulsion and motion is an intriguing phenomenon that has contributed to a growing interest in biomimetics in both academia and industry. The study focuses on developing a robust numerical tool for analyzing the motion of biological systems in fluid flows, crucial to understanding fluid-structure interaction (FSI) phenomena. The research introduces a new mesh deformation solver, dynamicOversetZoneFvMesh, designed to address limitations in OpenFOAM's conventional Overset method. This solver enables the application of both rigid body motion and deformation at specified patches within certain zones, allowing for more complex motion scenarios. Through meticulous verification, parallelization, validation, and mesh convergence studies, the modified Overset solver's reliability is confirmed. Two cases are examined: a rigid-body flapping foil and a flexible foil with leading-edge deformation. Results demonstrate the adapted solver's proficiency in managing complex fluid dynamics and accommodating simultaneous motion and deformation. Furthermore, the study reveals that leading-edge flexibility improves the power extraction efficiency of flapping foils, aligning with previous literature. Overall, the research lays the foundation for advancing FSI simulations and opens avenues for addressing previously challenging problems in the field.

Characterizing vibrations and associated wake structures of tandem square cylinders at different angles of incidence

Finite element computations were conducted to investigate the transverse vibrations of three identical tandem square cylinders and the associated wake patterns at a Reynolds number Re = 150. The reduced velocities ranged from U*=3 to 20, and the angles of incidence were set at α=0°, 22.5°, and 45°. The streamwise gaps for these three α were Lx=5H, 3.8H, and 3.5H, respectively, where H represents the projected dimension of the cylinder normal to the freestream. The mass ratio of the cylinders was fixed at m*=2, and damping was neglected to allow the cylinders to attain maximum amplitudes. In the presence of primary vortices being shed from all three cylinders, the upstream cylinder at α=22.5° and 45° exhibits three distinct vibration regimes: initial excitation and upper and lower response regions. On the other hand, due to interaction with the upstream vortices, the two downstream cylinders display four response regions. In the case of α=0°, the dynamic response of the upstream cylinder appears in only two regimes, but with a higher peak amplitude compared to α=22.5° and 45°. Vibration and shedding frequencies closely synchronize with the natural frequency of the spring-mass system in the second regime, leading to high amplitude oscillations for the most upstream cylinder with α=22.5° and 45°. The third response regime for the two downstream cylinders is associated with the lock-in phenomenon. In α=0° and 22.5° configurations, the shedding mode is 2S in all response regimes, while at α=45°, the shedding mode shifts to P + S during the second regime. Up to the second regime, lift and vortex forces are in-phase with the cylinder's oscillation for α=0° and 22.5°, but they go out of phase beyond that. In the case of α=45°, although lift remains in-phase with the displacement in the second regime, the vortex force is found to be out of phase. This study is expected to enhance the understanding of fluid–structure interaction phenomena involved in multiple structures and can aid in the design of stable structures in civil engineering, offshore engineering, and development of energy harvesting devices.

Effect of slug characteristics on the nonlinear dynamic response of a long flexible fluid-conveying cylinder

Hydrocarbon flows in a marine riser may appear in multiple phases with varying flow patterns, among which, slug flows are known to exhibit complex flow characteristics due to fluctuations in multiphase mass, velocities, and pressure changes. Bulk of the literature concerning internal single and two-phase flow induced vibrations have largely focused on the use of a linearized tension beam model. In this study, the fluid-structure interaction phenomena of a submerged long flexible cylinder conveying two-phase slug flows is investigated taking into account the geometric and hydrodynamic nonlinearities. A semi-empirical theoretical model which consists of nonlinear structural equations of coupled out-of-plane, in-plane and axial structural motions is presented for the analysis and prediction of two-phase slug flow induced vibrations (SIV). The model includes equations involving centrifugal and Coriolis forces to capture mass variations in the slug flow regime. A numerical space-time finite difference approach combined with a frequency domain analysis is used for analyzing the highly nonlinear three-dimensional responses. The model assumes constant geometric properties across the span of the cylinder and utilizes an idealized slug unit concept, wherein slug properties are considered to be fully developed and undisturbed by pipe oscillations. Model validations are performed through comparisons with published experimental internal flow-induced vibration results. Parametric study captures the effects of several key slug characteristics on the vibration responses of a fluid-conveying cylinder. The results demonstrate amplitude-modulation response, mean displacements, three-dimensional cylinder displacements due to geometric nonlinear couplings and the influence of internal flow velocities. Higher dominant modes and oscillation frequencies were observed when the cylinder experiences large amplitude motions at specific slug formations. A new dimensionless parameter is introduced to predict scenarios of high amplitude oscillations for long flexible cylinders carrying two-phase slug flows.

Response of flexible structures to air-blast: nonlinear compressibility effects in fluid–structure interaction

This paper presents a coupled model that considers the nonlinear compressibility effect in fluid–structure interaction (FSI) during air-blast loading on flexible structures. In this coupled model, structural behaviour is idealized as a linear single-degree-of-freedom mass-spring-damper system whereas nonlinear fluid compressibility is considered by applying Rankine–Hugoniot jump conditions across a moving plate. The surrounding fluid medium is modelled with an ideal gas equation and hence, this model can be applied for FSI analysis with relatively strong shocks (reflection coefficient of up to 8). The nonlinear compressibility of the fluid medium at the backside of the plate is also considered in this coupled formulation and its effects on the structural responses are examined. Moreover, the negative/underpressure phase of the reflected wave profile, which is typically neglected in a decoupled model, is also considered in the proposed model and its influence on the structural response is also investigated. The study reveals that the nonlinear compressibility of fluid medium significantly influences the coupled FSI phenomena, especially in flexible lightweight structures. Numerical examples are presented to highlight the implications of the nonlinear compressibility effect in FSI on the reflected pressure profile and the response of flexible structures. Parametric dependencies of response on structural mass and natural frequency are examined thoroughly and a response spectrum is obtained. It is envisaged that the lightweight protective structure design under higher blast intensity may benefit from this study.

Fluid-structure interaction characteristics between natural gas fluid and tubing string in high-pressure high-temperature high-production gas wells

The transient internal flow in high-pressure high-temperature high-production (three-high) gas wells may bring about serious fluid-structure interaction (FSI) between natural gas fluid and tubing string. Then, fatigue failure, wear and leakage of tubing string can easily be caused to threaten the wellbore safety and integrity. However, it is difficult to directly adopt the existing FSI model owing to particularity environment of the three-high gas wells. Based on water hammer, FSI and Timoshenko beam theory, a mathematical model expounding FSI phenomenon of the three-high gas wells is established by Poisson, friction and junction coupling, which considers unsteady friction effect, centrifugal and Coriolis force to make FSI characteristics more consistent with the engineering practice. Then, the improved method of characteristics (MOC) is applied into combination solution of the model. Later, the model and solution method is verified by comparing the results with different reference's ones respectively. On this basis, the effects of shut-in time, well depth position, unsteady friction on FSI characteristics are analyzed and discussed systematically. The calculation results are shown that shut-in time and well depth position have a more significant influence on FSI characteristics in three-high gas wells. In addition, FSI characteristics under action of unsteady friction decay faster, the time of the peak value also is delayed accordingly, and cumulative attenuation and cumulative delayed time of FSI characteristics increases with decrease of shut-in time. The FSI model, solution method proposed in this paper and results can provide theoretical basis and reference for the research on FSI and the formulation of shut-in operation for three-high gas wells, and even for highly deviated or horizontal gas wells.

Nonlinear WEC modeling using Sparse Identification of Nonlinear Dynamics (SINDy)

Modeling oscillating surge wave energy converter (OSWEC) systems to accurately predict their behavior has been a notoriously difficult challenge for the wave energy field. This is particularly challenging in realistic sea states where nonlinear WEC dynamics are common due to complex fluid-structure interaction, breaking waves, and other phenomena. Common modeling techniques for OSWECs include using potential flow theory to linearize the governing equations and ease computations, or using CFD to solve the full Navier-Stokes equations coupled with rigid body motion. However, both of these options have significant limitations. Potential flow theory breaks down in realistic sea conditions where nonlinear WEC dynamics are present, and CFD is often too computationally expensive for many applications such as real-time state prediction and optimal control, two areas of active research in the wave energy field. In particular, OSWEC dynamics are dominated by diffractive and viscous forces, often making common assumptions and linearization approximations (including small-body approximations) unreasonable, and CFD computationally intractable.
 To bridge this gap in modeling methods, we propose using Sparse Identification of Nonlinear Dynamics (SINDy) to build nonlinear reduced-order models (ROMs) that describe OSWEC behavior in response to large-amplitude regular waves. SINDy is an equation-free, data-driven algorithm that identifies dominant nonlinear functions present in system state dynamics using a library of nonlinear functions created from time series measurement data. The result is an ordinary differential equation (ODE) in time that can be solved from an initial condition to model and predict time behavior of the states. SINDy is parsimonious, meaning it uses a sparsity-promoting hyperparameter with the goal of only including the minimum number of terms to capture dominant dynamics, resulting in interpretable and generalizable results that are not overfit to the data. Using the discovered ROMs and integrating in time, not only can SINDy provide time series models and future state predictions of OSWEC dynamics, it can also give insights into which variables are critical in describing the underlying dynamics of the state. 
 In this study, we use SINDy to describe the nonlinear dynamics of a lab-scale OSWEC in a wave tank subjected to large-amplitude regular waves. We use nonlinear simulation data to generate kinematic, force, and torque data and use it as input to SINDy to identify ODEs that describe the measurement variables in time. We then integrate the ODEs to recreate the time series as well as predict future system behavior. We directly compare the resulting time series to the original data input to assess the accuracy of the SINDy model. We also interpret the dominant terms in the ODEs to gain insight on underlying mechanisms of the observed nonlinearity.
 Early results show SINDy is a promising tool for modeling nonlinear OSWEC dynamics. We are able to build ROMs for variables such as angular kinematics and the moment about the hinge that generate an accurate recreation of data measurements. We found strong dominance in cubic and quintic terms of the ROMs, suggesting higher-order nonlinearities in the system dynamics. These findings inspire future work in identifying underlying mechanisms driving nonlinearity.

Experimental study on the effect of adaptive flaps on the aerodynamics of an Ahmed body

We perform wind tunnel tests on the turbulent flow around a square-back Ahmed to analyze the use of rear flexibly hinged parallel plates as a control strategy to reduce the drag in a self-adaptive manner under changing flow conditions. Those rigid flaps are able to rotate, adopting an angle, \ensuremath{\theta}. The observed fluid-structure interaction phenomena results in an important decrease of the drag coefficient of the original body, outperforming purely rigid flaps in aligned and yaw conditions. Additionally, hinged flaps are shown to interact with the reflectional-symmetry-breaking (RSB) modes, typically present in the wake of three-dimensional bodies.

Fluid structure interactions generated by an oblique shock impinging on a thin elastic panel

The flow structure coupling generated by an impinging shock boundary layer interactions (SBLI) flowfield over a rectangular panel is investigated. The impinging oblique shock is generated by an 8° shock generator placed incident to a Mach 2.5 flow. The shock strength is large enough to generate a mean separation that is nearly two-dimensional over the panel span. The panel is configured such that the panel oscillation amplitude is much smaller than the panel and incoming boundary layer thicknesses. This resulted in a weak coupling between the flowfield and structural response, and forms a relatively simpler configuration to study. Two multivariate measurement campaigns are performed to capture the mean and dynamic flowfield and panel response. The first campaign simultaneously measures the 2D panel surface pressure field, panel center-span deflection, and off-body velocity field at 10 Hz. The second campaign measures simultaneously the 2D panel surface pressure field and panel strain at two mid-span locations at 10 kHz. The acquisition rate is sufficient to resolve at least the first seven panel elastic models. These measurements provide comprehensive information about the fluid structure interaction (FSI) phenomenon from both aerodynamics and structural dynamics perspectives. Summarily, with the weak flow/structure interactions implemented in this study, there is no change in the mean separation size. However, the pressure fluctuations beneath the SBLI unit exhibit discrete elevations in the vicinity of different panel resonance mode frequencies. The greatest elevation pressure PSD occurs at the panel modes that overlaps with the separation bubble pulsation frequency band. Detailed coherence maps at and away from panel elastic modes and conditional statistics reveal critical insights into the mechanisms that cause the strengthening of the pressure fluctuations due to flow/structure coupling. It was found that the acoustic forcing by the cavity resonance has an important contribution to the dynamics of the surface pressure and panel oscillations.

Parametric model order reduction by machine learning for fluid–structure interaction analysis

An improved nonintrusive parametric model order reduction (pMOR) approach is proposed for the flow field interpolation regarding fluid–structure interaction (FSI) objects. Flow field computation using computational fluid dynamics (CFD) requires excessive computational time and memory. Nonintrusive and data-driven MOR schemes have been proposed to overcome such limitations. The present methodology is implemented by both proper orthogonal decomposition (POD) and a modified Nouveau variational autoencoder (mNVAE). POD attempts to reduce the number of degrees of freedom (DOFs) on the precomputed series of the full-order model parametric result. The reduced DOF yields parametrically independent reduced bases and dependent coefficients. Then, mNVAE is employed for the interpolation of POD coefficients, which will be combined with POD modes for parametrically interpolated flow field generation. The present approach is assessed on the benchmark problem of a two-dimensional plunging airfoil and the highly nonlinear FSI phenomenon of the limit cycle oscillation. The comparison was executed against other POD-based generative neural network approaches. The proposed methodology demonstrates applicability on highly nonlinear FSI objects with improved accuracy and efficiency.

A transfer learning-physics informed neural network (TL-PINN) for vortex-induced vibration

Vortex-induced vibration (VIV) is a typical nonlinear fluid-structure interaction (FSI) phenomenon, which widely exists in practical engineering (such as flexible risers, bridges and aircraft wings). Conventional numerical simulation and data-driven approaches for VIV analysis often suffer from the challenges of computational cost and dataset acquisition. This paper proposed a physics-informed neural network (PINN) enhanced by transfer learning (TL) to study a VIV system (2D). The TL-PINN only used 1/2, 1/4 and 1/8 of the training set (for PINN model) to reconstruct the information of flow field and structure, but with the same prediction accuracy as PINN model. In addition, a stepwise iterative training strategy was proposed to train PINN model. The strategy can effectively reduce the dependence of neural networks on data sets, so as to reduce the training cost of PINN model. The results show that PINN with the stepwise iterative training strategy and TL-PINN can enhance learning efficiency and keep predictability without requiring a huge quantity of datasets. Based on the proposed method, limited and scattered label data from monitoring, numerical and experimental can be fused to realize the reconstruction and prediction of flow field and structure information. It can break the limitation of monitoring equipment and methods in practical projects, and promote the in-depth study of VIV.

A new monolithic design approach for topology optimization for transient fluid–structure interaction system

This study presents a new topology optimization method for transient coupled fluid–structure interaction (FSI) problems. The transient FSI problem is formulated using the monolithic design approach combining the design variables and the governing equations. This new approach allows for the possibility of considering the effect of transient FSI on topologically optimized layouts. Throughout this work, the analysis domain for the fluid and structure is modeled using the unified monolithic approach, in which the structure equation and the Navier–Stokes equation are coupled. With a fixed mesh and design variables assigned to each finite element, the governing equations as well as the involved material properties are interpolated. This modeling and analysis approach provides accurate solutions to the strongly coupled FSI system. An adjoint approach for calculating the transient sensitivity information and a gradient-based optimizer are used. Several numerical examples are solved to reveal the importance of considering the transient FSI. In addition, these examples demonstrate that the present approach can control transient FSI phenomena.

Elasto-capillary fluid–structure interaction with compound droplets

Computational modeling of elasto-capillarity, i.e., a fluid–structure interaction phenomenon where the solid deformation is driven by capillary forces at fluid–fluid interfaces has recently emerged as an important problem in computational mechanics. However, the high-fidelity simulation of elasto-capillary problems involving three immiscible fluids has remained unexplored. Here, we present a mathematical model and an algorithm to simulate elasto-capillary problems involving compound droplets. Such problems are of pivotal importance in pharmaceutical, biological and food industrial applications. We adopt a phase-field model described by the ternary Navier–Stokes–Cahn–Hilliard equations for the three immiscible fluids and a neo-Hookean model for the solid. We define a fluid–solid surface energy function, which determines the fluid–solid wettability and the tractions transmitted to the solid at the fluid–solid interface. We adopt a boundary-fitted approach for our fluid–structure interaction formulation and Isogeometric Analysis for the spatial discretization. To demonstrate the effectiveness of our computational model and algorithm, we perform elasto-capillary simulations involving various types of compound droplets.

Experimental Investigation on the Mechanism of Impeller Synchronous and Nonsynchronous Vibrations in an Industrial Centrifugal Compressor

Abstract Understanding of the fluid–structure interaction phenomena in centrifugal compressors is essential for the impeller structural integrity design. To enhance the understanding of blade vibration in a realistic flow environment, a single-stage centrifugal compressor representative of industrial architecture has been investigated experimentally. For deterministic synchronous vibrations, the response amplitudes at different operating lines are measured and compared. The fundamental relations between flow excitation and rotor modal resonance are established by pairwise strain gages from experimental perspective. Compared with the third mode, the impeller first bending mode shows traveling wave response characteristic only within the frequency band where two adjacent blades have the same resonant frequency. Besides, the impeller encounters unexpected nonsynchronous vibrations when operating near the flow instability boundary. Speed ramp tests show that the stall cell propagating speed increases along with the rotor rotational speed without changing the cell count. Response amplification is further measured when throttling the compressor into stall. Experimental findings point toward vaned diffuser rotating stall and the corresponding propagating pressure waves in circumference leads to the impeller vibration. The aerodynamic asymmetry of stall cells increases the possibility of aeroelastic coupling with the blade modes. These results contribute to an in-depth understanding of the aeroelastic phenomena in industrial centrifugal compressors. The observed nonsynchronous vibration is important for the aeroelastic design and also of great interest for numerical predictions near stall.

Design and evaluation of rotor blades for fluid structure interaction studies in wind tunnel conditions

Wind tunnel experiments with wind turbine models are a promising method for investigating fluid structure interaction (FSI) phenomena. However, the lack of suitable models that feature properly scaled blades and the complexity of aeroelastic and fluid dynamic measurements during turbine operation is challenging. In this paper, the design methodology for aeroelastically scaled blades which are intended for Model Wind Turbine Oldenburg (MoWiTO) 1.8 is presented. The scaling relations are formulated, initiating from the existing turbines’ design. Next, the manufactured blades are equipped on MoWiTO and are subsequently evaluated, during operation under gusty wind fields produced by an active grid. The tip deflection is recorded using an innovative photogrammetry setup. Simulations of an OpenFAST model, which has properties extracted from the scaling formulation, are used as reference. The recorded loads and blade deformations show similar dynamics, compared to the reference. These results prove the design successful, and the capability of measuring FSI phenomena in wind tunnel environment is showcased.

A high-order partitioned fluid-structure interaction framework for vortex-induced vibration simulation

Vortex-induced vibration (VIV) is a highly nonlinear fluid-structure interaction (FSI) phenomenon, and its accurate prediction remains challenging. In this study, we developed a high-order partitioned FSI framework towards accurate simulation of the VIV phenomenon. The focus is on simulating the two-way coupled interaction between a flexibly mounted rigid body and its surrounding fluids. In the FSI framework, a high-order computational fluid dynamics method, i.e., flux reconstruction/correction procedure via reconstruction, is utilized to simulate the unsteady compressible Navier–Stokes equations in the arbitrary Lagrangian Eulerian format on unstructured moving grids. A linearized fluid-solid Riemann solver is employed to weakly couple fluid dynamics and rigid-body dynamics on the fluid-solid interface, which can effectively mitigate the so-called added-mass instability. Time marching is conducted through either the linearly implicit Rosenbrock–Wanner method or the explicit strong stability preserving Runge–Kutta method. The high-order FSI framework is verified with a challenging VIV phenomenon, i.e., VIV of a zero-mass cylinder in viscous flows, and has been used to study two VIV-related problems, namely, the nonlinear energy sink and oscillating foil based energy harvesting mechanism.

Flexible cylinder flow-induced vibration

In this paper, we conducted a selective review on the recent progress in physics insight and modeling of flexible cylinder flow-induced vibrations (FIVs). FIVs of circular cylinders include vortex-induced vibrations (VIVs) and wake-induced vibrations (WIVs), and they have been the center of the fluid-structure interaction (FSI) research in the past several decades due to the rich physics and the engineering significance. First, we summarized the new understanding of the structural response, hydrodynamics, and the impact of key structural properties for both the isolated and multiple circular cylinders. The complex FSI phenomena observed in experiments and numerical simulations are explained carefully via the analysis of the vortical wake topology. Following up with several critical future questions to address, we discussed the advancement of the artificial intelligent and machine learning (AI/ML) techniques in improving both the understanding and modeling of flexible cylinder FIVs. Though in the early stages, several AL/ML techniques have shown success, including auto-identification of key VIV features, physics-informed neural network in solving inverse problems, Gaussian process regression for automatic and adaptive VIV experiments, and multi-fidelity modeling in improving the prediction accuracy and quantifying the prediction uncertainties. These preliminary yet promising results have demonstrated both the opportunities and challenges for understanding and modeling of flexible cylinder FIVs in today's big data era.

A numerical study on sloshing mitigation by vertical floating rigid baffle

Due to large hydrodynamic loads generated by the violent free surface flow, sloshing in partially filled tanks is an important phenomenon for the design of several offshore structures such as FPSO platforms, LNG carriers, crude oil carriers and, more recently, FLNGs. This study is focused on the numerical investigation of sloshing mitigation devices based on a floating baffle. For this purpose, the complex and highly nonlinear sloshing phenomenon is modeled and simulated using the Moving Particles Semi-Implicit (MPS) method, which is a fully-Lagrangian particle-based method for the simulation of incompressible flows widely applied to the study of fluid–structure interaction phenomena involving large free surface deformations, fragmentation and merging. As a reference for an in-depth discussion, the effectiveness of the equivalent fixed baffles placed at the bottom, the ceiling and mid-height of the tank were also studied. This work is divided into three parts: (1) the validation of the numerical method, (2) the study on the effect on sloshing of fixed baffles placed amid-tank and at different heights and (3) the investigation of the sloshing mitigation performance of floating baffles with a degree of freedom in the vertical direction of the tank. The effects of the floating baffles densities, which influence the draft of the baffles, on sloshing are investigated as well. The use of fixed baffles provided effective sloshing mitigation at the resonant frequencies for certain filling conditions depending upon the location of the baffle, but it might lead to even more violent flows in other filling conditions. On the other hand, the floating device presented sloshing mitigation for a larger range of filling conditions. Moreover, four different patterns of resonant motion of the floating baffle were identified and simple analytical estimations that could predict corresponding natural frequencies were proposed herein.

Coupling with the Embedded Boundary Method in a Runge-Kutta Discontinuous-Galerkin Direct Ghost-Fluid Method (RKDG-DGFM) Framework for Fluid-Structure Interaction Simulations of Underwater Explosions

Solution of near-field underwater explosion (UNDEX) problems frequently require the modeling of two-way coupled fluid-structure interaction (FSI). This paper describes the addition of an embedded boundary method to an UNDEX modeling framework for multiphase, compressible and inviscid fluid using the combined algorithms of Runge-Kutta, discontinuous-Galerkin, level-set and direct ghost-fluid methods. A computational fluid dynamics (CFD) solver based on these algorithms has been developed as described in previous work. A fluid-structure coupling approach was required to perform FSI simulation interfacing with an external structural mechanics solver. Large structural deformation and possible rupture and cracking characterize the FSI phenomenon in an UNDEX, so the embedded boundary method (EBM) is more appealing for this application in comparison to dynamic mesh methods such as the arbitrary Lagrangian-Eulerian (ALE) method to enable the fluid-structure coupling algorithm in the fluid. Its limitation requiring a closed interface that is fully submerged in the fluid domain is relaxed by an adjustment described in this paper so that its applicability is extended. Two methods of implementing the fluid-structure wall boundary condition are also compared. The first solves a local 1D fluid-structure Riemann problem at each intersecting point between the wetted elements and fluid mesh. In this method, iterations are required when the Tait equation of state is utilized. A second method that does not require the Riemann solution and iterations is also implemented and the results are compared.