Two-way Fluid-structure Interaction Method Research Articles

Tip clearance influence on hydrodynamic performance and pressure fluctuation of a composite ducted propeller using a two-way FSI method

With the development of advanced materials, composite materials have been studied by researchers over the world to make them more applicable to many applications, especially in the marine industry. As an important component of marine vehicles, propellers have been studied over decades to achieve the goals of increasing hydrodynamic performances and structural properties. However, traditional marine propellers manufactured with metallic materials have many limits. Therefore, the use of composite material to improve the performances of the propeller has become a research hotspot since their great structural performances and material damping properties can improve the comprehensive performance of the propellers such as increased hydrodynamic performances and reduced pressure fluctuation characteristics. The ducted propeller is a typical marine propulsor, which has a tip clearance between the blade tip and the inner face of the duct that can cause a complex fluid flow around the blades and influence the performance of the propeller. In this research, the tip clearance influence on hydrodynamic performance and pressure fluctuation of a composite ducted propeller compared with a metallic equivalent is calculated using a two-way fluid-structure interaction (FSI) method. The results indicate that the use of composite materials with a proper stacking sequence on the ducted propeller blade with a smaller tip clearance size corresponding to GSR = 0.417 can achieve good hydrodynamic properties for the propeller, and it has a significant inhibiting effect on pressure fluctuations on the blade surface.

Influence of Tip Speed Ratio on the efficiency of Savonius wind turbine with deformable blades

Improving machines efficiency and searching for their new applications are the main topics in the development of the renewable energy industry. In the case of Savonius type wind turbines, the works aim at the improvement of aerodynamic performance. The CFD simulations of a turbine equipped with deformable blades showed a significant positive impact of this enhancement on the machine aerodynamic efficiency. Previously, the investigation was carried out for a TSR (Tip Speed Ratio) equal to 0.8, typically recognized as the point of maximal efficiency for conventional Savonius wind turbines with rigid blades. However, the continuously altering shape of blades during their rotation can influence the optimal TSR. Therefore, the efficiency of the deformable blade turbine was investigated in a wide range of TSR. In this paper, the previously developed quasi-2D model with a two-way Fluid-Structure Interaction method was employed to obtain turbine efficiency characteristics as a function of TSR. The maximum power coefficient Cp was achieved at TSR = 0.9. Obtained characteristic was compared with data for a conventional rigid blades turbine, gathered with a comparable sliding mesh model.

Structural design of the composite blades for a marine ducted propeller based on a two-way fluid-structure interaction method

Compared to metal materials, fiber-reinforced composites have many advantages such as higher specific strength, higher specific stiffness, lighter weight, better damping performance, and better design ability. By reasonably choosing the material and arranging the stacking sequence, the directional stiffness properties of composite laminates can be tailored to match the actual needs. Hence, the effects of the laminate type on the performance of the composite ducted propeller in both hydrodynamic and structural are analyzed in this paper. The two-way fluid-structure interaction (FSI) method is applied to the composite ducted propeller, whose hydrodynamic performance is compared with the metallic one. The efficiency, deformation, stress, failure and pitch angle properties are compared with different laminate types under various working conditions. Moreover, a parameter optimization method is proposed to obtain the most suitable laminate type for the composite ducted propeller with the optimum hydrodynamic performance and structural properties. The research results can provide references for the design of composite ducted propellers.

A study on the computational hemodynamic and mechanical parameters for understanding intracranial aneurysms of patients with hypertension and atrial fibrillation

ObjectiveIntracranial aneurysms of patients with comorbidities like hypertension and atrial fibrillation have elevated rupture risk. Besides, the height and width of the aneurysm sacs are also essential features for pre-operative planning. However, clinicians still use only medical images and aspect ratios to identify which aneurysm has a higher risk of rupture. The rupture risk assessment often remains incomplete for lack of crucial insights. Therefore, the implication of a computational study on aneurysm diagnosis is analyzed in this study. MethodHere, the two-way fluid-structure interaction method is used to reproduce these effects of clinical conditions and geometry on aneurysms. Wall shear stress, oscillatory shear index, total deformation, and other parameters are calculated. ResultsThe wall shear stress (WSS) is the stress exerted by the wall on the fluid in a direction on the local tangent plane. The WSS inside a larger aneurysm decreases by around 50% compared to the aneurysms with a lower aspect ratio, indicating higher potential growth and rupture risk. However, the maximum pressure during systole for the aneurysm with the highest aspect ratio is 33% lower than the second-largest one during atrial fibrillation because of its unusual geometry. Although these hemodynamic parameters can be used to identify the effects of the size and shape of the aneurysms, they cannot completely depict the impact of the medical conditions. On the other hand, structural parameters like effective stress and total deformation successfully show the influence of size, hypertension, and atrial fibrillation on the aneurysm walls. The time-averaged wall deformation for the largest aneurysm is 1.3 and 2 times higher than the medium and smallest aneurysms, respectively. Moreover, compared to the normal condition, the total deformation at the aneurysm sac walls is 4–8% more for atrial fibrillation and 25–33% more for hypertension. A similar observation is made for the time-averaged value of effective stress exerted on the aneurysm walls, another parameter used to assess the rupture risk of aneurysms. Most importantly, these computational results align with previous clinical studies on patients with hypertension and atrial fibrillation. ConclusionBased on these observations, it is certain that to understand the impact of the comorbidities of the patients with intracranial aneurysms, results obtained from the structural analysis are required alongside hemodynamic parameters.

Numerical Validation of the Two-Way Fluid-Structure Interaction Method for Non-Linear Structural Analysis under Fire Conditions

Fire accidents on ships and offshore structures lead to complex non-linear material and geometric behavior, which can cause structural collapse. This not only results in significant casualties, but also environmental catastrophes such as oil spills. Thus, for the fire safety design of structures, precise prediction of the structural response to fire using numerical and/or experimental methods is essential. This study aimed to validate the two-way fluid-structure interaction (FSI) method for predicting the non-linear structural response of H-beams to a propane burner fire by comparison with experimental results. To determine the interaction between a fire simulation and structural analysis, the Fire-Thermomechanical Interface model was introduced. The Fire Dynamics Simulator and ANSYS Parametric Design Language were used for computational fluid dynamics and the finite element method, respectively. This study validated the two-way FSI method for precisely predicting the non-linear structural response of H-beams to a propane burner fire and proposed the proper time increment for two-way FSI analysis.

Strain-life estimation of the last stage blade in steam turbine during low volume flow conditions

Based on the elastic-plastic analysis, the local strain-life of the last stage of steam turbine under the low volume flow conditions is predicted. Considering the unsteady flow steam force and local high temperature of blade, the three-dimensional transient flow field, strain distribution and stress distribution of the last stage blade are calculated by the two-way fluid structure interaction method. Under low volume flow conditions, the temperature of blade tip increases with the decrease of volume flow. In addition, the self-excited unsteady frequency of rotor -stator clearance vortex is obtained at 90% span. According to the distribution of maximum equivalent stress on the rotor blade surface, three dangerous points are identified, which are located at the blade tip of the pressure surface (DP1), 90% span of the suction surface (DP2) and the trailing edge at the blade root of the pressure surface (DP3). With the decrease of volume flow, the equivalent stress and strain range of dangerous points increase, so the strain- life of dangerous points decreases. Among them, the strain-life of DP2 is the shortest at case3 condition. The strain response frequency of DP2 is consistent with the self-excited unsteady frequency of rotor -stator clearance vortex, which proves that it is necessary to consider the unsteady steam flow force in strain-life calculation. This study provides theoretical guidance for the safe operation time of the steam turbine under low volume flow conditions.

Comparison of acoustic-structure based one-way FSI and two-way FSI

In the numerical simulation of flow-induced vibration using two-way fluid-structure interaction (TW-FSI) method, it is usually limited by mesh deformation, and consumes a lot of computing resources. These problems can be avoided by adopting acoustic-structure based one-way FSI (ASOW-FSI) approach. The purpose of this work is to explore the applicability of ASOW-FSI, and to analyze the similarities and differences between the two dynamic response analysis methods. A series of numerical calculations are carried out for the elastically mounted rigid cylinder at low Reynolds number. By systematically comparing the results calculated by these two methods, we found that ASOW-FSI can accurately predict the response in the range of partial reduced velocity, even closer to the experimental results than TW-FSI method. The main reason for the difference between the two methods in the whole reduced velocity range is that the ASOW-FSI method can not predict the “lock-in”. Finally, the mechanism of “lock-in” in vortex-induced vibration (VIV) is analyzed by forced oscillation. The results show that the structural vibration has the ability to dominate the vortex shedding under certain conditions. If the natural mode of the structure is excited at this time, “lock-in” will occur.

Research on inflation and floating-up process of unmanned underwater vehicle based on collaborative simulation technology

For solving the problem of unmanned underwater vehicle (UUV) recovery, a multidisciplinary collaborative simulation method is proposed to simulate the inflatable deployment of an annular airbag and the motion of an UUV: a) a deployment dynamic model of the underwater airbag is established, the volume expansion rate curve of the airbag during the inflatable deployment process based on the control volume algorithm is obtained, and the accuracy of the model is verified by experiments; b) under the condition of a constant volume expansion rate of the airbag, a hydrodynamic model that couples the six-degree of freedom rigid body motion and the local deployment of the airbag is established, and calculations are performed using a custom program. The simulation method is used to study the effects of the ‘stop’ water depth on the motion characteristics of the vehicle, and the accuracy of the calculations is verified via the two-way fluid-structure interaction method. According to the calculation results for the effective deployment volume of the airbag and the motion curve of the centre of mass of the underwater vehicle, the ultimate floating depth of the vehicle can be predicted, which provides a reference for engineering implementation.

Grouting Process Simulation Based on 3D Fracture Network Considering Fluid–Structure Interaction

Grouting has always been the main engineering measure of ground improvement and foundation remediation of hydraulic structures. Due to complex geological conditions and the interactions between the grout and the fractured rock mass, which poses a serious challenge to the grouting diffusion mechanism analysis, fracture grouting has been a research hotspot for a long time. In order to throw light on the grout diffusion process in the fractured rock mass and the influence of grout on the fracture network, and to achieve more realistic grouting numerical simulation, in this paper a grouting process simulation approach considering fluid–structure interaction is developed based on the 3D fractured network model. Firstly, the relationship between fracture apertures and trace lengths is used to obtain a more realistic value of fracture aperture; then a more reliable model is established; subsequently, based on the 3D fracture network model, different numerical models are established to calculate fluid dynamics (grout) and structure deformation (fractured rock mass), and the results are exchanged at the fluid–structure interface to realize the grouting process simulation using two-way fluid-structure interaction method. Finally, the approach is applied to analyze the grouting performance of a hydropower station X, and the results show that the grouting simulation considering fluid–structure interaction are more realistic and can simultaneously reveal the diffusion of grout and the deformation of fracture, which indicates that it is necessary to consider the effect of fluid–structure interaction in grouting simulation. The results can provide more valuable information for grouting construction.

Numerical analysis on stability of nuclear fuel plates with inlet support comb

Many nuclear research reactors use or are planned with cores containing flat-plate-type fuel elements. One of the problems of this fuel element design is the mechanical stability of the fuel plates. High-velocity coolant flowing through the narrow channels that separate the plates can cause large deflections of these plates leading to local overheating, structural failure or plate collapse. In particular, in real fuel elements and experimental tests, flow-induced deflections at the leading edge and along the length of the plates have been detected. Some authors have indicated that the use of a support comb removes the leading-edge static divergence, but it has been also suggested that, even with the comb, there are significant deflections away from the inlet.In this work, a fluid-structure interaction study is conducted to examine the effectiveness of using an inlet comb on the mechanical stability of fuel plates. The system consists of two fuel plates bounded by three-equal coolant channels. The pressure loadings caused by the fluid flow are calculated using a CFD model and the structural response of the plates and the support comb are determined by means of an FEA model. The two-way fluid-structure interaction method was employed for coupling the fluid and solid solvers.The results presented here show that the static divergence at the inlet end is effectively eliminated with the installation of a support comb. Nevertheless, the main contribution of this work is the detection of deformation of the plates along their length and that it was an increasing function of the fluid velocity in the channels. As a consequence, the flow channels could be constricted or completely closed, thus affecting the safe operation of the nuclear reactor. To the best of our knowledge, this is the first numerical analysis reported in the literature that models the fluid-structure interaction phenomenon of adjacent plates with the support comb located at the midpoint of their inlet end.

A numerical study on hemodynamics in the left coronary bifurcation with normal and hypertension conditions.

In this study, a three-dimensional analysis of the non-Newtonian blood flow was carried out in the left coronary bifurcation. The Casson model and hyperelastic and rigid models were used as the constitutive equation for blood flow and vessel wall model, respectively. Physiological conditions were considered first normal and then compliant with hypertension disease with the aim of evaluating hemodynamic parameters and a better understanding of the onset and progression of atherosclerosis plaques in the coronary artery bifurcation. Two-way fluid-structure interaction method applying a fully implicit second-order backward Euler differencing scheme has been used which is performed in the commercial code ANSYS and ANSYS CFX (version 15.0). When artery deformations and blood pressure are associated, arbitrary Lagrangian-Eulerian formulation is employed to calculate the artery domain response using the temporal blood response. As a result of bifurcation, noticeable velocity reduction and backflow formation decrease shear stress and made it oscillatory at the starting point of the LCx branch which caused the shear stress to be less than 1 and 2Pa in the LCx and the LAD branches, respectively. Oscillatory shear index (OSI) as a hemodynamic parameter represents the increase in residence time and oscillatory wall shear stress. Because of using the ideal 3D geometry and realistic physiological conditions, the values obtained for shear stress are more accurate than the previous studies. Comparing the results of this study with previous clinical investigations shows that the regions with low wall shear stress less than 1.20Pa and with high OSI value more than 0.3 are in more potential risk to the atherosclerosis plaque development, especially in the posterior after the bifurcation.

Investigations on static aeroelastic problems of transonic fans based on fluid–structure interaction method

Fan blades of high bypass ratio gas turbine engines are subject to substantial aerodynamic and centrifugal loads, producing the well-known phenomenon of blade untwist. Accurate fan blade shape prediction is very crucial for high-performance aero-engine. In order to investigate the effects of static aeroelastic deflections on aerodynamic performances, a time domain two-way fluid–structure interaction method was applied to simulate the deflection of NASA Rotor 67 fan blades under different operating conditions. This paper pays attention to the deviation of fan profile and aerodynamic performance due to the varying aerodynamic loads, especially for off-design conditions. The results show that the static aeroelastic deflection has a 1.8% impact on the total pressure ratio under near stall condition, and a 1.7% impact on the choke mass flow rate, relative to the cold configuration. Thus, the blade design in industrial practice should adopt a two-way fluid–structure interaction method to consider the influence of static aeroelastic problems on aerodynamic performance.

Flexible Wing of HALE UAV using Two-way Fluid Structure Interaction Method

Simulation of High Altitude Long Endurance (HALE) UAV wing using two-way fluid structure interaction (FSI) method is presented. To achieve its mission, the HALE wing was designed to have high aspect ratio. With longer wing span, the HALE UAV may produce less induced drag and lift-loss which caused by the decrease in wingtip vortex strength. However, the wing structure with longer span becomes more elastic that may yield large deformation when aerodynamic loads applied. This deformation influences flow characteristics at the surrounding of the wing causing the change of aerodynamic loads distribution on the wing. Subsequently, this new load provides a new deformation to the wing structure and vice versa. This interaction in a couple process called as fluid structure interaction (FSI) of the HALE wing was simulated using ANSYS 15.0 software. The unsteadiness and viscous flows at low speed are evaluated using the solution of time-dependent Reynolds Averaged Navier-Stokes (RANS) with SST k-ω turbulent model. In addition, multi-block structured grids are generated to provide more accurate viscous result and to anticipate negative volume of the mesh which may occur due to the wing deformation during simulation. Five different simulations with variation of material characteristics including Young’s modulus and Poisson’s ratio are carried out. The results include global aerodynamic characteristics at various material characteristics.

Flexible Wing of HALE UAV using Two-way Fluid Structure Interaction Method

Numerical simulation of flexible High Altitude Long Endurance Unmanned Aerial Vehicle (HALE UAV) wing using two-way fluid structure interaction (FSI) method is presented. The HALE wing is designed with high aspect ratio. This configuration intended to reduce the vehicle induced drag and reduces the lift-loss at wingtip which caused by wingtip vortex. But the structure of the wing itself becomes more elastic that be able to give large deformation when the aerodynamic loads applied. This deformation causes the change of aerodynamic loads distribution on the wing. Then this provides a new deformation to the wing structure and vice versa. This interaction in a couple process called as fluid structure interaction (FSI) will be simulated using ANSYS 15.0 software for HALE wing. The unsteadiness and viscous flows at low speed are evaluated using the solution of time-dependent Reynolds Averaged Navier-Stokes (RANS) with SST k-ω turbulent model. In addition, multi-block structured grids are generated to provide more accurate viscous result and to anticipate negative volume of the mesh which may occur due to the wing deformation during simulation. Five different simulations with variation of material characteristics including Young's modulus and Poisson's ratio are carried out. The results include global aerodynamic characteristics at various material characteristics.

Modal Analysis of Multi-Span Pipes Conveying Fluid Based on Three Different FSI Methods

The modal analysis of pipes conveying fluid considering the influence of Fluid-Structure Interaction (FSI) is always a topic in flow and solid mechanics fields worth study. Three methods of coupling, the direct FSI method, the one-way FSI method and the bidirectional FSI method, with the velocity’s influence on pipe system’s natural frequency were considered in this study. The results of pipe’s dynamic behavior indicate that the two-way FSI method can get a more reasonable result. Furthermore, when velocity changes in a small range far from critical velocity, velocity makes very little influence on system’s nature frequency. The result was compared with conclusion in the literature and very good agreement was found.

Determination of turbine runner dynamic behaviour under operating condition by a two-way staggered fluid-structureinteraction method

This paper presents the application of the two-way fluid-structure interaction method introduced by ANSYS to calculate the dynamic behaviour of a Francis turbine runner under operating condition. This time-dependant calculation directly takes into account characteristics of the flow and particularly the pressure fluctuations caused by the rotor-stator interaction. This formulation allows the calculation of the damping forces of the whole system implicitly. Thereafter, the calculated dynamic stress can be used for a fatigue analysis. A verification of the mechanical and fluid simulations used as input for the fluid-structure interaction calculation is first performed. Subsequently, a connection of these two independent simulations is made. A validation according to the hydraulic conditions is made with the measurements from the scale model testing. Afterwards, the static displacement of the runner under the hydraulic load is compared with the results of a classical static analysis for verification purposes. Finally, the natural frequencies deduced by the post-processing of the dynamic portion of the runner displacement with respect to time are compared with the natural frequencies obtained from a classical acoustic modal analysis. All comparisons show a good agreement with experimental data or results obtained with conventional methods.