Fluid Domain Research Articles

Numerical Approach for The Evaluation of Hemodynamic Behaviour in Peripheral Arterial Disease: A Systematic Review

Reduced blood flow to the lower extremities causes peripheral arterial disease (PAD), which is caused by atherosclerotic plaque in the arterial wall. If this impairment is not treated, it will result in severe vascular diseases like ulceration and gangrene. Previous research has shown that while evaluating the pathology of the peripheral artery, the assumption of the model geometry significantly impacts the uncertainty of the stenosis area. However, more work needs to be done to understand the interaction between mechanical better and flow conditions in the peripheral artery using a separate computer model of the cardiovascular system. This paper reviews the numerical approach on pre- and post-treatment of hemodynamic behavior in peripheral arterial disease (PAD). The goal of this study was to thoroughly examine the most recent developments with the application of computational studies in PAD from 2017 to 2022. While FSI investigation highlights the behavior of both the fluid and structure domains (blood and artery) during the numerical analysis of blood flow, CFD simulations primarily focus on the fluid domain (blood) behavior. Out of 92 research publications, 19 were appropriate for this assignment. This thorough study divides the publications into the categories of CFD, and FSI approaches. The results were then reviewed in accordance with the wall characteristic, analytical method, geometry, viscosity models, and validation. This paper summarizes the parameters of geometrical construction, viscosity models, analysis methods, and wall characteristics taken into consideration by the researchers to identify and simulate the blood flood flow in the stenosis area. These parameters are summarised in this study. Additionally, it could offer systematic data to help future studies produce better computational analyses.

A synthetic theory to integrate and explain the causes of the Flynn effect: The Parental Executive Model

The Flynn effect is one of the most interesting puzzles in psychology. Measured intelligence increased worldwide for a century, primarily in the fluid domain. Some increases may be flattening and/or reversing. Around 20 theories have been developed to explain the Flynn effect; most have empirical or conceptual weaknesses, though they also have strengths and face validity. The role of parents has been given only slight attention in past theorizing. We propose a new synthetic theory, the Parental Executive Model (the PEM) that integrates, organizes, and takes advantage of most previous theories. To structure our paper, we begin with a description of synthetic theories, and how to evaluate them (which has unique and difficult challenges). Following, we review the Flynn effect, and briefly summarize the new theory. Next, recent research is reviewed suggesting the value of re-conceptualizing the location of the Flynn effect to focus on families, and parents. Following, we describe the PEM, which states that parents – and teachers, authors, friends, etc. – use their agency to manage children's intellectual growth. The PEM posits that many (not all) parents subjectively optimize their children's intellectual outcomes, taking advantage of some subset of available resources – nutrition, education, technology, health care, etc. Cross-generational momentum occurs as parenting improves across generations. Prior research motivating the PEM is reviewed, and methods to evaluate the PEM are discussed. Finally, one recent empirical evaluation of the PEM is reviewed, that the cognitive home environment has been improving over time.

Large-Amplitude Steady Solitary Water Waves with Constant Vorticity

This paper considers two-dimensional steady solitary waves with constant vorticity propagating under the influence of gravity over an impermeable flat bed. Unlike in previous works on solitary waves, we allow for both internal stagnation points and overhanging wave profiles. Using analytic global bifurcation theory, we construct continuous curves of large-amplitude solutions. Along these curves, either the wave amplitude approaches the maximum possible value, the dimensionless wave speed becomes unbounded, or a singularity develops in a conformal map describing the fluid domain. This is stronger than what one would expect from a straightforward generalization of existing results for periodic waves. We also show that an arbitrary solitary wave of elevation with constant vorticity must be supercritical. The existence proof relies on a novel reformulation of the problem as an elliptic system for two scalar functions in a fixed domain, one describing the conformal map of the fluid region and the other the flow beneath the wave.

A novel artificial neural network-based interface coupling approach for partitioned fluid–structure interaction problems

This paper presents a novel interface technique employing Artificial Neural Networks (ANN) for efficient data transfer between incompressible fluid and deformable solid domains in a partitioned fluid–structure interaction (FSI) framework. Governing differential equations (GDE) with potential flow assumptions are solved to obtain pressure values at computational nodes in the fluid domain. Pressure values are then used to train an ANN-based model to interpolate pressure loads for application at non-collocated nodes on the solid boundary. Both finite element method (FEM) and meshfree element free Galerkin (EFG) formulations are used to calculate the solid deformation. Proposed methodology is applied to solve a two-dimensional (2D) unidirectional flow problem, consisting of a flexible cantilever beam immersed in a laminar, steady, and inviscid fluid. Overwhelming mathematical intricacies of computational solvers are avoided for the sake of simplistic interface treatment, flux transfer and associated phenomena. Dedicated partitioned solvers are developed for both solid and fluid domains, which are individually benchmarked for established problems from the literature. The presented ANN-based interpolation scheme provides an alternative to higher-order polynomial algorithms at the interface boundary. The proposed scheme is simple to employ, computationally efficient, and offers competitive accuracy as well as stability.

Numerical investigation of forced convection flow characteristics on hydrophobic surface with nanofluid

In the present study, the flow resistance and heat transfer characteristics of nanofluid flowing through the channel with hydrophobics surfaces are investigated based on mixture multiphase model. A new model is built to exhibit the comprehensive performance of four structured hydrophobic surfaces under different parameters, and one structure with best thermos-hydraulic performance is chosen for the next step. Then, the Al2O3–water nanofluid is added to fluid domain and the flow characteristics is discussed in detail. The results show that the square posts structure has the best comprehensive performance. The overall performance of hydrophobic surfaces has been greatly improved after adding nanofluid, due to the slip-velocity produced by hydrophobic surface and increased fluid thermal conductivity by nanofluid. In addition, the value of performance evaluation criterion is steadily improved as the contact angle and volume fraction are both increasing, which can be increased to 20%, compared with smooth plate, due to the combined effect of hydrophobic surface and nanofluid.

A high-order finite difference method with immersed-boundary treatment for fully-nonlinear wave–structure interaction

In order to predict nonlinear wave loading on marine structures, a fully nonlinear higher-order finite difference based potential flow solver with all boundary conditions treated by an immersed boundary method has been developed in this paper. The solver adopts high-order finite difference schemes for the spatial derivatives and a 4th order Runge–Kutta method for time stepping. Test cases of forced oscillation of a cylinder in an infinite fluid domain are first studied, which reveal the advantage of the acceleration potential method in terms of wave load computation. Then a wave generation problem using a piston type wave maker is tested. Special attention is paid to the intersection point between the free surface and the body surface, and a scheme which best meets the accuracy and stability requirements is suggested from several proposals. A novel hyperviscosity filter, which works for both uniform and non-uniform grids, is introduced to stabilize the time-domain solution of the wave maker problem. Finally, a forced heaving cylinder on the free surface is considered, and the nonlinear wave loads on the cylinder are analyzed and compared to benchmark results.

Corrected ALE-ISPH with novel Neumann boundary condition and density-based particle shifting technique

It is well-known in the Smoothed Particle Hydrodynamics (SPH) community that correction in the gradient and Laplacian operators have the potential to drastically increase the accuracy of the method at the expense of computational stability. This paper proposes a stable implementation of such corrections in all derivative operators to the Arbitrary Lagrangian Eulerian incompressible SPH (ALE-ISPH) method, in addition to a novel Neumann boundary condition (BC) applied directly on the velocity (as opposed to traditional BCs where the constraint is applied on the acceleration). In this way, the pressure is solved for both water and wall particles simultaneously, leading to a pressure field that obeys non-penetration BC and divergence-free at the same time. Furthermore, to stabilize the method, we have developed a novel density-based particle shifting technique (PST), specifically designed to deal with incompressible fluids. In this formulation, the numerical density is given as one of the most critical constraint variables. As a result, the proposed density-based PST can maintain the fluid's overall volume for the whole simulation. In addition, it also provides numerical stability as it prevents particle clustering and leads the fluid domain to an isotropic composition. First, we verified the proposed corrected formulation with the novel Neumann BC for both non-penetration and non-slip conditions with the simulation of hydrostatic pressure and Poisenuille flow, respectively. Then, we tested the proposed density-based PST with the rotating square patch problem with results comparable to previous studies. Lastly, we verified the proposed method for the dam break with an obstacle test, a highly dynamic problem.

Aeroelastic analyses of functionally graded aluminium composite plates reinforced with graphene nanoplatelets under fluid-structural interaction

This study presents a comprehensive investigation on functionally graded (FG) graphene reinforced aluminium cantilever rectangular plates under aerodynamic loads. Two-way loosely coupled fluid structure interaction (FSI) is implemented by coupling finite element analysis (FEA) and computational fluid dynamics (CFD). FEA models are developed using FG graphene nanoplatelets (GPL) reinforced aluminium composite structures with different GPL distribution patterns. Fluid domain is modelled using finite volume method and FSI module is then used to connect FEA with the CFD code. The simulation results of FSI indicate that the maximum stress of the plate can be efficiently reduced with satisfactory aerodynamic performance after aeroelastic tailoring, depending on specific GPL distribution patterns. It is shown that in conjunction with aeroelastic tailoring technique, the composite plate can achieve optimized structural and aerodynamic performance. The present results of the FG graphene reinforced aluminium plates offer useful design guideline for their applications as the structural components in aeronautical fields.

Analysis of Circulation Characteristics and Heat Balance of High-Speed Rolling Bearing under Oil-Air Lubrication

Aiming to solve the problem of oil-air lubrication failure caused by the high working temperature of high-speed rolling bearings, this study proposes a method, based on the theory of gas-solid two-phase flow and bearing tribology, of predicting the dynamic temperature rise of nonlinear high-speed rolling bearings under oil-air lubrication conditions. The accuracy of the fluid–structure coupling model is verified by comparing the temperature rise test results of angular contact ball bearing at different speeds. The characteristics of oil-air lubrication circulation and the relationship between the lubrication parameters and the heat balance of the high-speed rolling bearings have been studied. The results show that the gas supply pressure of the system has a significant influence on the continuity and fluctuation of the oil film in the oil pipe nozzle. The initial rise in temperature of the inner and outer rings of the bearing and the fluid domain has a speed threshold value, and the temperature increases linearly with the bearing speed. With the increase in the oil supply and lube oil viscosity of the system, the temperature rise of the outer ring of the bearing increases first, then decreases, and finally increases again. There is an optimal oil supply 5.5 mL and optimize viscosity 68 cSt for the bearing in the work condition.

On aerodynamic force computation in fluid–structure interaction problems — Comparison of different approaches

This paper is interested in the numerical approximation of a two-dimensional fluid–structure interaction problem. A special attention is paid to the numerical realization of aerodynamic force (AF) calculations. Three different AF computations within finite element method framework are described and compared. First, the extrapolation of fluid stress tensor components from the interior of the fluid domain is the most straightforward method; however, this approach is of lower theoretical accuracy due to the explicit computation of velocity gradient. Second, the local reconstruction method applied on the velocity gradient is based idea of the least square fit of the gradients evaluated at finite element centroids from local patch. Third, the weak reformulation technique using the weak formulation of the fluid flow problem leads to the expression of AF in an integral form. As it avoids direct velocity gradient computation it is of higher accuracy compared to previous methods.The experimental convergence of all mentioned methods for the drag and lift coefficients is tested on the benchmark of a static cylinder in a cross-flow and further extended to the case with prescribed motion of the cylinder. Further, two FSI simulations compare the transferred energy from the fluid to the structure for the case of structure vibrations submerged in the viscous fluid and also for the flow-induced structural vibrations. The critical inlet velocity of flutter instability is determined and it is shown that for a given numerical setting the choice of AF computation can lead to the different FSI behavior.

A simplified method to consider hydrodynamic effect in oblique vessel-bridge collisions

The hydrodynamic effect in vessel-bridge collisions is either directly omitted or considered by the constant added mass (CAM) method in current studies. However, the high-resolution fluid-structure interaction (FSI) simulations indicate that the hydrodynamic effect plays an important role and cannot be adequately captured by the CAM method, particularly for oblique vessel-bridge collisions. On the other hand, the FSI simulations are time-consuming and have a high requirement for computational resources. For these reasons, a simplified analysis method was developed in this study to consider the hydrodynamic effect of vessel collision with bridge structures. In the developed method, mechanics of full 6-DoF ship maneuvering were established using several matrices to replace the explicit fluid domain of the FSI models, while the added mass method was adopted for the impacted pier to account for the hydrodynamic effect. Several collision scenarios were performed to compare the developed method with the FSI simulation and the CAM analysis. It was found that the proposed method is superior to the CAM method in terms of considering the hydrodynamic effect of vessel-bridge collisions, and its required computational cost can be significantly saved in comparison with the FSI model. From the perspective of calculation efficiency and accuracy, the proposed method is more suitable for the analysis and design of vessel-bridge collision in engineering practice than the FSI simulation and the CAM analysis.

An arbitrary Lagrangian–Eulerian method for fluid–structure interactions due to underwater explosions

Purpose This study aims to evaluate blast loads on and the response of submerged structures. Design/methodology/approach An arbitrary Lagrangian–Eulerian method is developed to model fluid–structure interaction (FSI) problems of close-in underwater explosions (UNDEX). The “fluid” part provides the loads for the structure considers air, water and high explosive materials. The spatial discretization for the fluid domain is performed with a second-order vertex-based finite volume scheme with a tangent of hyperbola interface capturing technique. The temporal discretization is based on explicit Runge–Kutta methods. The structure is described by a large-deformation Lagrangian formulation and discretized via finite elements. First, one-dimensional test cases are given to show that the numerical method is free of mesh movement effects. Thereafter, three-dimensional FSI problems of close-in UNDEX are studied. Finally, the computation of UNDEX near a ship compartment is performed. Findings The difference in the flow mechanisms between rigid targets and deforming targets is quantified and evaluated. Research limitations/implications Cavitation is modeled only approximately and may require further refinement/modeling. Practical implications The results demonstrate that the proposed numerical method is accurate, robust and versatile for practical use. Social implications Better design of naval infrastructure [such as bridges, ports, etc.]. Originality/value To the best of the authors’ knowledge, this study has been conducted for the first time.

Neural-network-based fluid–structure interaction applied to vortex-induced vibration

In this paper, a fluid–structure interaction (FSI) solver with neural-network-based fluid-flow prediction is proposed. This concept is applied to the problem of vortex-induced vibration of a cylinder. The majority of studies that are concerned with fluid-flow prediction using neural networks solve problems with fixed boundary. In this paper, a convolutional neural network (CNN) is used to predict unsteady incompressible laminar flow with moving boundary. A deformable non-Cartesian grid, which traces the boundary of the fluid domain, is used in this paper. The CNN is trained for oscillating cylinder with various frequencies and amplitudes. The dynamics of the elastically-mounted cylinder is modelled using a linear spring–mass–damper model and solved by an implicit differential scheme. The results show that the CNN-based FSI solver is capable of capturing the so-called lock-in phenomenon for the problem of vortex-induced vibration of a cylinder and the quantitative behaviour is similar to the results of the CFD-based FSI solver. Moreover, the CNN-based FSI solver is two orders of magnitude faster than the CFD-based FSI solver and the speedup is expected to be even greater on larger problems.

Numerical Study on the Water Entry of a Freely Falling Unmanned Aerial-Underwater Vehicle

The unmanned aerial–underwater vehicle (UAUV) is a new type of vehicle that can fly in the air and cruise in water and is expected to cross the free water surface several times to perform continuous uninterrupted observation and sampling. To analyze the hydrodynamic and motion characteristics of the vehicle, the whole water-entry process of a multi-degree-of-freedom UAUV with various velocity and pitch angle was investigated through a Reynolds-averaged Navier–Stokes method. The computational domain was meshed by trimmer cells. The relative movement between the vehicle and fluid domain was simulated using moving reference frame overset mesh to delineate the interaction region around vehicle body. To reduce the computational cost, adaptive mesh refinement and adaptive time-stepping strategy were used to capture the slamming pressure accurately with reasonable computational effort. First, convergence study is considered. Simulations of the vehicle with various initial velocities and different pitch angles were performed. The variable physical properties were analyzed, and detailed results through the time-varying force and velocity were shown. Initial velocity and pitch angle are found to significantly influence hydrodynamic behavior, including the time-varying force, while thickness ratio has a great impact on added mass and pressure. The results show that higher entry velocity results in greater peak vertical force. The transverse hydrodynamic characteristics for oblique water entry of the vehicle with varies pith angle are quite different.

Unsteady and three-dimensional computational fluid dynamics modelling of scroll expander for low-grade waste heat recovery transcritical carbon dioxide micro-scale power system

Recent developments in the field of renewable energy have led to a renewed interest in low-grade heat (< 500 K). The low-grade heat is widely wasted by the lack of efficient heat recovery technologies. It is also limited by the system size, which defines as the micro to small-scale (< 50 kW). Although ORC based unit has been implemented in this field, the CO2 based waste heat recovery units can be more capable in the size construction. The performance of the expander plays a vital role in the system’s efficiency. Thus, the current paper provides thermodynamic and CFD analysis of a scroll expander regarding a micro-scale T-CO2 recovery system (< 10 kW) with a 400 K low-grade heat source. In the current CFD model, all the fluid domains were constructed by structural mesh. It also successfully integrated with the thermodynamic table to simulate two-phase T-CO2. This model can be the first scroll expander model for T-CO2 power system and gap the bridge of utilising the scroll machinery in this field. The CFD methodology was successfully validated by the new-built testing platform and previous data. The energy performance of T-CO2 and ORC (R123) based scroll expanders are compared by isentropic and exergy efficiency. The results showed that isentropic and exergy efficiencies of T-CO2 were 7% and 14% higher than the R123. It also identified higher irreversibilities of T-CO2 by the exergy of the working fluids. The pressure and temperature distributions identified the over-expansion and reversed flow characteristics, and the pressure imbalance of the initial expansion chambers denoted the reversed flow.

Coupling edge-based smoothed finite element method with incompressible smoothed particle hydrodynamics for thermal fluid structure interaction problems

Numerical simulation of thermal fluid structure interaction (TFSI) problems with incompressible flows is one of the most challenging topics in computational fluid dynamics. In this paper, the recently developed edge-based smoothed finite element method (ES-FEM) is coupled with incompressible smoothed particle hydrodynamics (ISPH) for modeling TFSI problems, where the fluid domain is simulated by ISPH and the structure domain is simulated by ES-FEM method. A ghost particle based algorithm to couple the ES-FEM elements and ISPH particles is applied to implement the modeling of TFSI problems. The numerical simulation of TFSI problems using the ES-FEM-ISPH coupling method under pure Lagrangian scheme is very attractive because it can naturally handle the moving interface and free surface. The effectiveness of the ES-FEM-ISPH coupling method developed in this paper is verified by a number of numerical simulation examples with TFSI problems. From the obtained numerical results, we can conclude that the ES-FEM-ISPH coupling method is effective to simulate TFSI problems.

Exact radiation boundary conditions to determine the complex wavenumber of an underwater acoustic leaky wave antenna.

Underwater elastic leaky wave antennas (LWAs) steer acoustic energy as a function of frequency by exploiting fluid-solid coupling. LWAs present a modeling challenge due to complex radiation impedance on the waveguide surface that leads to changes in dynamic response. This work presents an approach to model underwater LWAs that considers an elastic unit cell surrounded by a fluid domain and includes a radiation boundary condition to simulate an open boundary. The model solves an eigenvalue problem for the complex-valued wavenumber given a specified frequency, forming an accurate representation for the free response of an elastic LWA in an underwater environment.

MHD flow of submerged jets behind the inlet disturbance

AbstractIn a broad variety of configurations in technology and industrial applications, the properties of liquid metal flows subjected to strong magnetic fields, are largely governed by the dynamics of coherent structures, known to settle several basic types, such as thin shear layers, forming near the walls or within the fluid domain, vortices extended along the field, or planar and round jets. In some cases, these structures are created by the design, like a submerged jet formed by a sudden expansion from the nozzle into a blanket channel, or jets formed behind some flow obstruction. In the other cases this may be due to instability and evolution of secondary structures, for example, descending and ascending jets appearing as a result of convective instability in blanket channels. In this study, we undertake an attempt to affect liquid metal flow via inlet disturbance formed by a simple rod placed along the magnetic induction lines. The disturbance can generate flat jets behind the rod and, furthermore, a sustainable flow of anisotropic vortical perturbations further downstream the flow. We seek to analyze the most important mechanisms of the flow dynamics and effects of magnetic field on the integral system properties of enhancing mixing, mass and heat transport for such flow. The most optimal regimes of vortex generation are found to be governed by the magnetic interaction parameter (Stuart number). The exact ratio of the optimal Stuart number is found to be in a range between 20 and 40, based on the channel double width as a characteristic size. The observed vortices attain quasi‐2D shape and exist at a length of dozens of duct calibers, being the strongest at higher flow rates. The obtained flow regimes and their turbulent properties are also found to resemble significant similarity to the results on quasi‐2D turbulence found in prior studies of channel and duct flows under spanwise magnetic field.

Finite Element Approach for Three-Dimensional Linearized Potential Equation with Application to Muffler Acoustic Attenuation Prediction

In this paper, a three-dimensional finite element method for solving the linearized potential equation (LPE) is implemented to predict the acoustic attenuation performance of mufflers in the presence of nonuniform flow. For accurate physical representations, the porous material is modeled as equivalent fluid with complex speed of sound and density while the background mean flow in fluid domain is captured by solving Reynolds-averaged Navier–Stokes equations. The treatment details for boundary integrals at different boundary conditions and expressions for transmission loss are presented. Good agreements of predicted and measured transmission loss of two reactive and a hybrid mufflers validated the present approach. Finally, the convective effect of nonuniform flow on the acoustic attenuation behavior of the hybrid muffler is examined numerically in detail.

Numerically modeling the sound absorption behavior of 3D printed fibrous absorbers

Recently, we have demonstrated the feasibility of using extrusion-based additive manufacturing methods to fabricate fibrous sound absorbers [1]. Here, we investigate the feasibility of predicting the sound absorption behavior of such structures by extracting their geometry-based transport properties using the hybrid, multiphysics modeling approach. The acoustical transport properties are calculated by modeling the fibrous unit cell and solving three boundary value problems over the representative elementary volume of the periodic fluid domain. Our results show that the absorption predictions obtained using the as-designed unit cell significantly differ from the experimental measurements obtained using conventional two-microphone impedance tube tests. Further investigations conducted using an optical microscope reveal that while the printed fiber diameter remains uniform over its central portion, the fiber diameter decreases drastically near the fiber root. Finally, we show that incorporating these geometrical differences within the model improves computational predictions and accounts for the deviations between the numerical and experimental absorption coefficients. [1] Johnston W, Sharma B. Additive manufacturing of fibrous sound absorbers. Additive Manufacturing. 2021 May 1;41:101984.