Fluid-solid Coupling Problem Research Articles

Finite Element Method-Peridynamics Coupled Analysis of Slope Stability Affected by Rainfall Erosion

Rainfall is a pivotal factor resulting in the cause of slope instability. The traditional finite element method often fails to converge when dealing with the strongly nonlinear fluid–solid coupling problems, making it impossible to fully analyze the sliding process under the state of slope instability. Therefore, this paper uses the coupling of peridynamics (PD) and the finite element method (FEM) to propose a data exchange mode between the seepage field and the deformation field. The influencing factors of fine particle erosion during rainfall are further considered. According to the damage mechanism of the slope sliding process to the original structure of the soil, a modified erosion constitutive relationship is proposed, which takes into account the destructive effect of plastic deformation on coarse particles. Then, the influence of rainfall duration, rainfall intensity, erosion, and initial saturated permeability coefficient on slope stability was simulated and analyzed. This paper provides a novel concept for slope stability analysis and safety evaluation under rainfall conditions.

Water and mud inrush dynamics process simulation by using coarse-grained CFD-DEM method

Water and mud inrush disaster is a typical fluid-solid coupling problem, and its forecasting and prevention can reduce human and economic losses. In this work, a coarse-grained discrete element method and computational fluid dynamics model based on bonded particles is employed to investigate an inrush disaster happened in Foshan Metro Line 2. It's shown that the current model can simulate beam bending, and the differences from the analytical solution are 7% and 5% in deflection and maximum axial stress. This study also suggests that two-way coupling is in superior agreement with field observation than one-way coupling. The water pressure is highly influential as it increases from 0.15 MPa, 0.25 MPa, 0.35 MPa to 0.45 MPa inrush occurrence time varies from 28.0 s, 11.5 s, 7.5 s to 5.0 s, respectively. The current model is capable of simulating water and mud inrush, and may provide a framework for investigating this disaster in complex engineering scenarios.

A super-real-time three-dimension computing method of digital twins in space nuclear power

Digital twins (DTs) have attracted widespread attention in academia and industry in recent years. It can accurately reflect the physical world in real-time, enabling online monitoring, control, and prediction operations. Their foundation is super-real-time computing and high data representation capabilities. However, current DTs do not achieve 3D super-real-time computing. This study proposes a novel 3D computational method for solving fluid–solid coupling problems in a super-real-time. The method is based on a mixed solution framework that combines traditional numerical methods with deep learning operators. Specifically, the method employs multi-core CPU parallel acceleration to solve the solid equations while leveraging the computing power of GPU to solve the fluid equations. The fluid–solid coupling is achieved through information exchange between the GPU and the multi-core CPU. In addition, the proposed method introduces a new deep learning operator framework based on the DeepONET. The framework is accompanied by a database structure that facilitates model training and validation and a loss function that guides the training. The space nuclear reactor, an improved TOPAZ-II system, was selected to demonstrate its feasibility. Four non-training transient conditions were simulated to test the generalization performance. The results show that the proposed method achieves an average error between the calculated results and reference values below 2.5%, with the average error of thermodynamic parameters below 1.5%. The average deviation between system parameter peak values during the transient process and the reference value was less than 5 s. The result meets the acceptable error level and satisfies the super-real-time requirements with a time acceleration ratio of approximately 1.17, which is 60 times faster than traditional numerical methods. The results demonstrate the accuracy and efficiency of the proposed method for DT.

Numerical Modeling of Pumping-Induced Earth Fissures Using Coupled Quasi-Static Material Point Method

Pumping-induced earth fissuring is a typical fluid–solid coupling problem involving fracture evolution. Despite recent advances in the numerical modeling of earth fissures, a holistic approach capable of predicting their evolution and understanding their behavior from fracture mechanisms is absent. This paper presents a coupled numerical method based on the framework of the material point method (MPM) and fracture mechanics for the process-oriented simulation of pumping-induced tensile earth fissures. In this method, fissure behavior is driven by the real-time stress field affected by soil consolidation. After an earth fissure initiates in the region of maximum tensile stress, it propagates in the direction of the maximum circumferential stress around the fissure tip. The great scale difference between a fissure tip and the entire model is addressed with an adaptive refinement strategy. Through the simulation of a physical model experiment reproducing pumping-induced earth fissures with the presence of a bedrock ridge, the complete fissuring process, including initiation, propagation, and arrest, is presented. The simulated fracture time (24 h after drainage), location (directly above the bedrock ridge), final length (165 mm), and morphology evolution (from straight to zigzag) of the main fissure basically were in agreement with the experimental results. The stress intensity factors (SIFs) around fissure tips, which are important fracture parameters that have not been discussed in existing earth fissure analyses, also are captured during the fissure growth. The proposed method quantifies the inhibition of geostatic stress fields in earth fissure development and correlate fissure morphology with the stress field at a fissure tip.

Dynamic response and acoustic characteristics of composite hydrofoil under cavitation-induced vibration

Nonconstant characteristics of cavitating flow can cause adverse effects, including vibration, noise, and cavitation. With the application of composite materials, the vibration and deformation of hydrofoils are becoming increasingly obvious, and the fluid–solid coupling problem is becoming very important. Herein, the cavitating flow field of National Advisory Committee for Aeronautics 0012 hydrofoil composed of bronze alloy and composite material is numerically investigated. The hydro-elastic response of a hydrofoil is obtained via a fluid–structure coupling method under a tight coupling strategy. The Schnerr–Sauer model is used to describe the cavitation process, and the large eddy simulation method is used to solve the turbulence problem. Additionally, the finite element method is used to determine the structural deformation. A comparison of the numerical calculation results of the fluid–solid acoustic coupling under two operating conditions shows that the composite materials can suppress the sheet cavitation attached to the hydrofoil suction surface and the tip leakage vortex (TLV) cavitation and can decrease the flow field pressure pulsation and increase the lift-to-drag ratio of the hydrofoil. Additionally, the composite material significantly improves the wake field turbulence, reducing the turbulence intensity and integration scale, and nearly eliminates the large-scale vortex. Moreover, the composite material changes the vortex structure evolution at the gap flow field, results in smoother TLV development, and enhances the flow field velocity gradient effect. Finally, the monitoring of the flow noise radiation characteristics shows that the composite material effectively reduces the sound pressure level of the self-noise and far-field radiation noise.

Mixed EHL Problems: An Efficient Solution to the Fluid–Solid Coupling Problem with Consideration of Elastic Deformation and Cavitation

For transient mixed Elastohydrodynamic lubrication (EHL) problems, a novel solution is required to predict friction loss and wear in sliding or rolling parts. However, existing solutions have numerous limitations. In general, the lower the oil film thickness is, the more serious the non-linear problem is. This paper presents an efficient solution to tackle the non-linearity of the mixed EHL problem. The elastic deformation in the fluid–solid iteration coupling problem is divided into two parts: One is induced by the hydrodynamic pressure. This part of the deformation is obtained by the unsteady EHL-FBNS (Fischer–Burmeister–Newton–Schur) solver by considering both mass-conserving cavitation and elastic deformation. The other part of the deformation is introduced by the asperity contact pressure. It can be obtained by the Newton–Raphson method. After some limited iterations, the mixed EHL problems can be solved by evaluating the residual total pressure (including hydrodynamic pressure and asperity contact pressure). The proposed methodology was validated against the results from the published literature and applied to characterize the tribological performance of point contact with moving texturing. It appears that the developed method can be effectively used for tracking the tribological behavior of friction pairs.

Generalized finite difference method based meshless analysis for coupled two-phase porous flow and geomechanics

This paper applies GFDM to analyze coupled two-phase flow and geomechanics for the first time, to our knowledge, is also the first meshless solver for two-phase fluid-solid coupling problems in porous media. Firstly, the implicit GFDM-based discrete schemes of the hyperbolic two-phase flow equation and elliptic stress equilibrium equation coupled by Biot's poroelastic theory are derived. Then the nonlinear solver based on Newton's method is used to solve the fluid pressure, water saturation, and displacement at each node simultaneously. Two technical details are found critical to the implementation of this method. The one is using different radii of the node influence domain to discretize the flow equation and the stress equilibrium equation respectively, and the other one is the selection criterion of the two radii of the node influence domain, which improves the implementation flexibility of the multi-physics coupling calculation, reduces the dissipation error of the calculation results of the convection-dominated water saturation distribution, and ensure a low computational cost. Several numerical test cases are implemented to analyze the computational efficiency and accuracy, and illustrate that GFDM can achieve good computational performance in case of regular domains, irregular domains, and different point clouds.Overall, this work may provide an important reference for building a GFDM-based general-purpose numerical simulator for multi-physics flow problems in porous media.

An improved MPS-DEM numerical model for fluid–solid coupling problem in nuclear reactor

Compared with the grid method, the moving particle semi-implicit method (MPS) has prominent advantages in capturing the phase interface and avoiding grid distortion at the interface. However, MPS method is not particularly effective in dealing with the fluid–solid coupling problems including the interaction between discrete solid elements. Therefore, the PArticle method software for Nuclear reactor thermal hyDraulic Analysis (PANDA) is developed based on the MPS method and coupled Discrete Element Method (DEM) by introducing the idea of multiphase flow into the MPS-DEM coupling method. In this paper, the model is validated by reappearing the phenomena of DKT(drafting, kissing, and tumbling), and the problems of the slide of dry granular material and the underwater landslide are simulated as well. The numerical results are in good agreement with the experimental results, and the relative error of the leading edge distance is less than 6.12%. Finally, numerical simulation is carried out by taking molten pool accumulation in sereve accident of nuclear reactor as an example, which further confirms the good application prospects of PANDA in engineering problems.

A new mixed finite element method for a swelling clay model with secondary consolidation

In this paper, we propose a new mixed finite element method for a swelling clay model with secondary consolidation, which is a process of the volume of saturated clay decreasing with time after the completion of primary consolidation. To better describe the multi-physics processes underlying in the original model, we firstly reformulate the swelling clay model with secondary consolidation by introducing a new variable to transform the fluid-solid coupling problem to a fluid coupled problem. Then we give the PDE analysis to prove the existence and uniqueness of the weak solution. And we design a fully discrete time-stepping scheme to use mixed finite element method with P2−P1−P1 element pairs for the space variables and backward Euler method for the time variable, give the stability analysis and the optimal convergence order error estimates. Finally, we show some numerical examples to verify the theoretical results and significant effect on the displacement of the secondary consolidation term.

Simulation of interacting elastic sheets in shear flow: Insights into buckling, sliding, and reassembly of graphene nanosheets in sheared liquids

In liquid-based material processing, hydrodynamic forces are known to produce severe bending deformations of two-dimensional (2D) materials such as graphene. The non-linear rotational and deformation dynamics of these atomically thin sheets is extremely sensitive to hydrodynamic particle-particle interactions. To investigate this problem, we developed a computational model of the flow dynamics of elastic sheets suspended in a linear shear flow, solving the full fluid-solid coupling problem in the two-dimensional, slender-body, Stokes flow regime. Both single and pairs of sheets in close proximity are analyzed. Despite the model being two-dimensional, the critical non-dimensional shear rate yielding single-particle buckling is comparable in order of magnitude to that reported for fully three-dimensional, disk-like sheets. For pairs of interacting sheets, hydrodynamic interactions lead either to parallel sliding or bending, depending on the value of an elasto-viscous number based on particle length. For sufficiently low bending rigidity or large shear rates, large deformations of initially stacked sheets lead to sheet reattachment after separation, unlike for the rigid case. A peeling-like dynamics where lubrication provides a viscous bonding force is observed for sheet pairs when one of the two sheets is more rigid than the other. Practical implications for graphene processing and exfoliation are discussed.

Numerical simulation and flow noise computation during transient launching process of torpedo in deep-sea simulator

The transient launching process of a torpedo in a deep-sea simulator is a complex nonlinear fluid–solid coupling problem. Complex problems, such as projectile movement and gap flow, must be dealt with in the numerical computation. The launching channel is usually simplified to reduce computational cost, which affects the accuracy of the simulated flow field and acoustic computation results. The complete inner structure of the launching channel was retained in the numerical computations in this study to make the computation results much realistic. The spring mesh method and the radial basis function method were applied to update the mesh for the projectile movement, and a fine simulation was conducted on the launching flow field. The computation results related to torpedo movement were validated based on the test results, and the evolution of each flow structure in the deep-sea simulator was analysed. Based on the simulated flow field, acoustic computations were completed using the acoustic analogy method, and the acoustic characteristics, e.g. the propagation direction and sound source contribution of the launching noise, were analysed.

Extensions of the two-phase double-point material point method to simulate the landslide-induced surge process

Landslide-induced surges, as a complex type of fluid-solid coupling problem, are widespread in mountain regions and cause disastrous consequences. In order to reproduce the entire process of landslide-induced surge, by taking full advantage of material point method (MPM) in simulating large deformation of soil and gravity-driven flow of water, the two-phase double-point material point method (TPDP-MPM) was extended: a new algorithm handling the boundary without setting boundary particles was proposed. The classical submarine block-induced surge test and sand column collapse experiment were numerically simulated by the MPM and verified the effectiveness of the program. After that, the multiphase coupling process of Lituya Bay landslide-induced surge was simulated and verified the reliability of the TPDP-MPM code, which have achieved parallel computing by making use of OpenMP model. By comparing the results of numerical simulation with the model experiment, the two-phase double-point material point method can well simulate the starting, propagation, run-up and reflux stage of landslide-induced surge. Moreover, the extension mechanism of landslide-surge disaster chain in both time and space is revealed from the perspective of energy. This study provides a reliable tool for the analysis and assessment of landslide-induced surge disasters.

Tightness and stability evaluation of salt cavern underground storage with a new fluid–solid coupling seepage model

The effects of operating pressure and ground stress on the seepage parameters (permeability and porosity) of surrounding rock and stability and tightness of salt cavern have been investigated, and a method is proposed for safe operating pressure classification. In previous works, the analysis of stability and tightness of salt caverns were mostly carried out independently, and few studies have considered the interaction between them. However, when used as a storage space for natural gas, petroleum and brine, there are many fluid–solid coupling problems in salt cavern underground storages. To address these problems, we establish a fluid–solid coupling seepage model based on the relationships between pressure, rock deformation and seepage parameters, and apply it to actual engineering. The coupling analysis results show that the relationship between shrinkage displacement of salt cavern and operating pressure is an exponential function with negative correlation, while the relationship between seepage range of a salt cavern and the operating pressure is a power function with positive correlation. Therefore, the effects of operating pressure on the stability and tightness of salt caverns are diametrically opposite. The seepage range of gas in surrounding formations gradually increases with time, and eventually tends to become stable. Under an operating pressure of 12 MPa and after operating for 30 years, the maximum seepage range and shrinkage displacement of the studied salt cavern are 99.72 m and 1.86 m, respectively. Hence the stability and tightness of this salt cavern meet the requirements of the regulations in China, and a gas leakage accident will not occur in this storage during operation. The seepage parameters of the surrounding formation increase with operating time of gas storage, and the increase in permeability is larger than that of porosity. The research results can provide reference and guidance for safe operation and parameter design of salt cavern underground storage.

Fast Algorithm for Heating Injection Mold by Water

This paper puts forward a fast algorithm for heating injection mold by water accordance with these problems that the computing is enormous to simulate heating injection mold and there is a limitation for velocity of hot water that it should not be too larger otherwise simulating algorithm will be failure. The method does the similarity transformation to construct similarity model whose solution is the same with the mathematics model for the problem of heating injection mold by water, and the simulation time will be reduced greatly at the precondition of keeping precision using the similarity model. The first step of similarity transformation is time similarity transforming for the fluid governing equation describing the moving of hot water in the time area, i.e., actual heating time area for mold heating is transformed to heating time area of similarity model while keeping spatial domain unchanged. Meanwhile it does the same transformation for the heat conduction governing equation in the time area, also keeping spatial domain unchanged. In this way the similarity model of the origin mathematics model for fluid-solid coupling problem of heating mold by water is obtained. Simulating the similarity model could obtain mold temperature field after heating fast. The paper shows that the fast algorithm has good application value through examples.

Wavelet Element Modelling for Inviscid Fluid-Solid Coupling Problem based on Partitioned Approach.

To provide a simple numerical formulation based on fixed grids, a wavelet element method for fluid–solid modelling is introduced in this work. Compared with the classical wavelet finite element method, the presented method can potentially handle more complex shapes. Considering the differences between the solid and fluid regions, a damping-like interface based on wavelet elements is designed, in order to ensure consistency between the two parts. The inner regions are constructed with the same wavelet function in space. In the time and spatial domains, a partitioned approach based on Jacobi iteration is combined with the pseudo-parallel calculation method. Numerical convergence analyses show that the method can serve as an alternative choice for fluid–solid coupling modelling.

A Numerical Study on Hydraulic Fracturing Problems via the Proper Generalized Decomposition Method

The hydraulic fracturing is a nonlinear, fluid-solid coupling and transient problem, in most cases it is always time-consuming to simulate this process numerically. In recent years, although many numerical methods were proposed to settle this problem, most of them still require a large amount of computer resources. Thus it is a high demand to develop more effificient numerical approaches to achieve the real-time monitoring of the fracture geometry during the hydraulic fracturing treatment. In this study, a reduced order modeling technique namely Proper Generalized Decomposition (PGD), is applied to accelerate the simulations of the transient, non-linear coupled system of hydraulic fracturing problem, to match this extremely tight response time constraint. The separability of the solution in space and time dimensions is studied for a simplifified model problem. The solid and flfluid equations are coupled explicitly by inverting the solid discrete problem, and a simple iterative procedure to handle the non-linear characteristic of the hydraulic fracturing problem is proposed in this work. Numeral validation illustrates that the results of PGD match well with these of standard fifinite element method in terms of fracture opening and fluid pressure in the hydro-fracture. Moreover, after the off-line calculations, the numerical results can be obtained in real time.

A new set of scaling relationships for DEM-CFD simulations of fluid–solid coupling problems in saturated and cohesiveless granular soils

The discrete element method (DEM) cannot effectively account for macroscale problems because of its high computational cost and time-consuming nature, especially for fluid–solid coupling problems. Therefore, a spatially scaled-down model, which should be established based on a set of scaling laws, is commonly employed to study the behaviors of the macroscale prototype. In the present study, various basic scaling relationships proposed by previous researchers for a scaled-down model are summarized first, as well as their limitations when they are used for DEM-CFD simulation of fluid–solid coupling problems in saturated and cohesiveless granular soils. Then, a new set of scaling relationships is proposed using a governing equation approach. Finally, a DEM-CFD model is established as an example analysis to study the feasibility and accuracy of the new scaling relationship present in this study for simulating fluid–solid coupling problems in saturated and cohesiveless granular soils. The results are analyzed in comparison with other scaling relationships, and the results indicate that the new set of scaling relationships is more reasonable and accurate than others.

Landslide‐generated wave hazard prediction based on multiphase flow model of DualSPHysics

AbstractBecause involving a large number of discrete particles interacting with water, simulating the fluid–solid coupling problem of landslide‐generated waves in a virtual environment is very difficult. This paper employs the DualSPHysics multiphase flow model to relatively easily simulate the dynamics of landslide‐generated waves in large scales. In addition, the simulation results are well visualized by the marching cubes algorithm. It is found that, when the factors of the landslide scale, the water length, and water depth are fixed, the initial maximum wave height decreases as the water width increases. After the water is squeezed by the falling slider, one‐way and two‐way propagations of the surge are generated under 2D and 3D conditions, respectively. In addition, under the true‐3D condition, although the initial swell generated is smaller than the 2D and quasi‐2D conditions, it will generate a large wave height during the climbing and undulation of the near shore. In the 2D condition, the surge generated is almost the largest. Therefore, when using the DualSPHysics multiphase flow model to predict the maximum wave height generated by landslide surges, a 2D simulation can be used to improve work efficiency.

Buckling Analysis on a Pipe Conveying Fluid under Two Stresses

Pressure pipes have broad applications in aviation, space flight, mechanical engineering, industrial and civil architecture etc. Instability destruction is their main failure mode. Firstly, in this paper, a complex fluid-solid coupling problem was simplified as a buckling problem of a pipe under two stresses which were along the pipe wall. The two stresses consisted of a compressive stress which was perpendicular to the pipe wall and a tangential stress which was parallel to the pipe wall. Secondly, the buckling performs of the pressured pipe were discussed by finite element analysis method under a working state and an off-working state, respectively. Some obtained conclusions were drawn as follows by the analysis in this paper.1). Provided the tangential stress is unchanged, by increasing compressive stress eigenvalue buckling critical load increases and nonlinear buckling critical load decreases.2). Provided the compressive stress is unchanged, when the direction of the tangential stress is same as that of the axial pressure, by increasing the absolute value of tangential stress the buckling critical load decreases; provided the compressive stress is unchanged, when the direction of the tangential stress is in the opposite direction of the axial pressure, by increasing the absolute value of tangential stress the buckling critical load increases.

Study on the multiphase fluid-solid interaction in granular materials based on an LBM-DEM coupled method

Fluid-solid coupling is a common phenomenon in the studies of granular materials, geotechnical engineering and so on. Based on a multiphase fluid model in the framework of lattice Boltzmann method (LBM) and the discrete element method (DEM), a multiphase fluid-solid coupling algorithm of LBM-DEM is proposed, where the coupling module is developed on the basis of two open-source codes, Palabos and Yade. The feasibility and accuracy of the algorithm are validated through three classical fluid-solid coupling examples: a single sphere settling in a fluid, a sphere falling into a fluid from the air and two spheres colliding with each other in fluid. Then two complex phenomena in geotechnical engineering, transient-state flow and debris flow, are simulated. The results indicate that the LBM-DEM coupled method has strong advantages in the numerical simulation of complex fluid-solid coupling problems. It can accurately reveal the fluid-solid interaction mechanisms, physical & mechanical behaviors and failure process at both macroscopic and mesoscopic scales. Furthermore, from the numerical simulation results, the process of debris flow can be divided into three stages: steady seepage stage, startup stage and flow stage of the fluid-solid mixture.