Fluid-structure Coupled Analysis Research Articles

Aerodynamic and Structural Assessment of Floating Wind Turbine Rotor Under Varying Tilt Angle

Predicting the aerodynamic performance of floating offshore wind turbines (FOWTs) proves challenging due to platform motion induced by waves. The effect of wind and waves results in a six-degree-of-freedom motion of the platform, directly influencing turbine performance. Understanding the impact of specific degrees of freedom (DOF) motions on aerodynamics and structural response is crucial for effective wind turbine design. This research examines the impact of rotor tilt on both aerodynamic performance and structural response. The investigation employs computational fluid dynamics (CFD) analysis and mapping aerodynamic loads onto the finite element (FE) mesh for structural analysis. The study employs a comprehensive 3D simulation, utilizing the moving reference frame (MRF) method for the NREL 5 MW reference wind turbine CFD simulations. It explores different rotor tilt angles (5°, 10°, 15°, and 20°) encountered by offshore structures during their operation and examines their impact on aerodynamic performance. Predicted aerodynamic loads were mapped onto the blade FE mesh using the radial basis function (RBF) interpolation technique and solved using the open-source FE solver CalculiX. The analysis shows that the turbine performance is relatively unaffected up to a tilt angle of 10°. However, further increase in rotor tilt angle adversely impacts turbine performance, leading to notable reductions in thrust and power output. The fluid-structure coupled analysis provided insights into the deformations and stresses experienced by the turbine blade, indicating a notable increase in flap-wise displacement for larger tilt angles, while edge-wise displacement is not as significantly affected. The maximum stress location on the blade generally correlates well with actual observations.

Analysis of vibration response characteristics of composite pipeline based on finite element method

In order to ensure the good stability of the composite pipeline under fluid dynamic loads, finite element analysis method was applied to simulate and calculate the modal characteristics under dry and wet mode conditions. According to the working principle and structural characteristics of composite pipelines, the model was parameterized and simplified to improve computational efficiency and convergence. The modal testing platform is constructed, consisting of a combination of pipeline structure and pipeline support structure. The movement direction of the slider is limited by the guide rail used, allowing the horizontal section of the branch to move only along its own pipeline axis direction. The fluid structure coupling analysis technology was applied to obtain the vibration mode and spectral response results of the composite pipeline, which was verified through an experimental platform. The research results indicate that the natural frequency in wet mode was about 16 % lower than that in dry mode. In addition, it could be proven that the simulation scheme had good computational accuracy, with a maximum error of 9.2 %.

A new 3D plastoelastohydrodynamic lubrication model for rough surfaces

Plastoelastohydrodynamic lubrication of rough surfaces (R-PEHL) is a cutting-edge area of research in interface fluid-structure coupling analysis. The existing R-PEHL model calculates the elastic-plastic deformation of rough surface by the Love equation in a semi-infinite space smooth surface, which deviates from the actual surface. Therefore, it is an innovative work to study the exact solution of elastic-plastic deformation of rough surface and its influence on the solution results of R-PEHL model. In this paper, a new contact calculation model of plastoelastohydrodynamic lubrication (PEHL) with three-dimensional (3D) rough surface is proposed by integrating numerical method of EHL and finite element method. The new model eliminates an original error introduced by the assumption of semi-infinite space in contact calculation, providing wide applicability and high accuracy. Under the given rough surfaces and working conditions, the study reveals that: (1) the oil film pressure calculated by the new model is lower than that of the smooth surface in semi-infinite space by 200–800 MPa; (2) the Mises stress of the new model is 2.5%–26.6% higher than that of the smooth surface in semi-infinite space; (3) compared with the semi-infinite space assumption, the rough surface plastic deformation of the new model is increased by 71%–173%, and the local plastic deformation singularity may appear under the semi-infinite space assumption; (4) the plastic deformation caused by the first contact cycle on the rough surface of the new model accounts for 66.7%–92.9% of the total plastic deformation, and the plastic deformation of the semi-infinite space accounts for 50%–83.3%. This study resolves the contradiction between the smooth surface assumption and the rough surface in the existing R-PEHL model, establishing a solid logic foundation for the accurate solution of R-PEHL model.

Fluid–Structure Coupled Analysis of Maneuver Load Alleviation on a Large Transport Aircraft

Fluid–structure coupled simulations are performed for quasi-steady pitching maneuvers of a large transport aircraft with a load alleviation system consisting of trailing edge flaps and droop noses at the leading edge. For the fluid part of the simulation, a RANS approach is used, whereas the structural simulation is based on a linear modal model. The selected maneuvers are located on the lift boundary of the maneuver envelope at maximum load factor, as not only are the structural loads high here, but also redistributing lift for load alleviation is especially challenging as the wing is close to stall. For a target value of 33% reduction in wing bending loads, which is derived from the CS-25, the effects of applying load alleviation on wing loads, deformations, and aircraft maneuverability are investigated. It is found that the desired reduction of wing bending loads can be achieved for all maneuvers considered, while controlling the torsional moment turns out to be more difficult. A loss of maneuverability due to load alleviation is observed for only one of the maneuvers, while for the other maneuvers, maneuverability could even be increased. To assess the influence of the elasticity of the wing, additional simulations of the rigid wing are carried out and compared with the elastic results. Finally, other potential applications of the considered flap system are also explored. Here, for example, a cruise drag reduction of up to 1.8% is possible by adjusting the spanwise lift distribution.

Structural Response Analysis for Multi-Linked Floating Offshore Structure Based on Fluid–Structure Coupled Analysis

Recently, offshore structures for eco-friendly energy, such as wind and solar power, have been developed to address the problem of insufficient land space; in the case of energy generation, they are designed on a considerable scale. Therefore, the scalability of offshore structures is crucial. The Korea Research Institute of Ships & Ocean Engineering (KRISO) developed multi-linked floating offshore structures composed of floating bodies and connection beams for floating photovoltaic systems. Large-scale floating photovoltaic systems are mainly designed in a manner that expands through the connection between modules and demonstrates a difference in structural response with connection conditions. A fluid–structure coupled analysis was performed for the multi-linked floating offshore structures. First, the wave load acting on the multi-linked offshore floating structures was calculated through wave load analysis for various wave load conditions. The response amplitude operators (RAOs) for the motions and structural response of the unit structure were calculated by performing finite element analysis. The effects of connection conditions were analyzed through comparative studies of RAOs and the response’s maximum magnitude and occurrence location. Hence, comparing the cases of a hinge connection affecting heave and pitch motions and a fixed connection, the maximum bending stress of the structure decreased by approximately 2.5 times, while the mooring tension increased by approximately 20%, confirmed to be the largest change in bending stress and mooring tension compared to fixed connection. Therefore, the change in structural response according to connection condition makes it possible to design a higher structural safety of the structural member through the hinge connection in the construction of a large-scale multi-linked floating offshore structure for large-scale photovoltaic systems in which some unit structures are connected. However, considering the tension of the mooring line increases, a safety evaluation of the mooring line must be performed.

Study on the impact of the perforated floating breakwater on coastal bridge with box-girder superstructure under two-dimensional focused waves

The advantages of Floating Breakwater encompass its adaptability to varying water depths and tidal ranges, as well as its economic viability, mobility, and ease of installation. However, limited research has been conducted on the wave damping performance of floating breakwaters on the box-girder superstructure of coastal bridges during extreme wave conditions. In this study, a two-dimensional numerical model was established using the RANS equations and SST k-ω turbulence model in OpenFOAM. The breakwater was constrained by mooring forces, with linear elastic deformation, and underwent horizontal, vertical, and torsional movements under the action of ocean waves. The validity of the numerical model was confirmed by comparing it with existing numerical simulations and experimental data. The study examined influential factors, including the cross-sectional shape, submergence depth, and spacing of the floating breakwater, with a specific emphasis on the dimensions of the upper and lower openings for perforated breakwaters. Combined with attenuation rates and fluid-structure coupling analysis, the wave damping performance of the floating breakwater on the box-girder superstructure of coastal bridges under extreme wave conditions was evaluated. The research results demonstrate that the perforated floating breakwater, with Cs = 0.75, L = 10 m, and upper opening B1 = 0.1 B and lower opening B2 = 0.4 B, maximizes the wave damping performance on the box-girder superstructure of coastal bridges, which holds crucial significance for studying wave attenuation and disaster prevention on the box-girder superstructure of coastal bridges.

Geometric deformation prediction of a centrifugal impeller considering welding distortion and fluid-structure interaction

An impeller serves in a centrifugal fan, pushes the surrounding air and in turn reacts on itself. The fluid-to-structure response and part welding distortion during the fabrication and working processes will cause the impeller to deform and reduce fan performance. This work develops a numerical simulation approach and focuses on two essential factors: welding distortion and distortion induced by fluid to structure interaction. The research target was an impeller comprising five thin-plate curved fillet joints, and its total distortion was predicted using the proposed approach. First, the structure of the impeller was modeled with solid elements, and each welded local joint's welding distortion was measured with a modified inherent strain method. A one-way fluid-structure coupling analysis carefully examined the distortion induced by Fluid-Structure Interaction (FSI) from the fluid medium and coupling surfaces. Then, an interpolation method was conducted to compute the welding and FSI distortion contours using a simple structural analysis. To determine the inherent strain in a curved and non-curved fillet joint, a detailed transient analysis by the Thermal Elastic Plastic (TEP) Finite Element Method (FEM) and their welding distortion, plastic strain distribution, and inherent deformation are discussed. The welding and flow field tests both agree with the simulation results, confirming the modified inherent strain method and relevant FSI results. Thus, the developed approach can provide a suitable reference for controlling distortion in welded fans and related fluid machinery.

Numerical analysis of vibration response of elastic tube bundle of heat exchanger based on fluid structure coupling analysis

Abstract A tube bundle heat exchanger is a typical heat exchange equipment that exchanges heat between two fluids with different temperatures. Through this equipment, one fluid can be cooled down and another fluid can be heated up to meet their respective needs. The equipment is widely used in chemical, petroleum, pharmaceutical, energy, and other industrial sectors, and is one of the indispensable and important equipments in chemical production. To improve the heat transfer performance and service life of the heat exchanger, a numerical analysis of the vibration response of the elastic tube bundle in the heat exchanger based on fluid–structure coupling analysis is proposed. Using the weak coupling method of fluid–structure coupling, the vibration response of multiple rows of elastic tube bundles induced by shell side fluid in a heat exchanger with different tube row spacing and different tube row numbers is studied numerically, and the effects of shell side fluid and tube side fluid on the vibration response of elastic tube bundles are compared and analyzed. The results show that the maximum relative error of monitoring point amplitude is 43.36% when H = 40 mm and 10.17% when H = 70 mm. For connection IV, the maximum relative error of monitoring point amplitude is 31.71% when H = 40 mm and 24.08% when H = 70 mm. This is because when H is small, the interaction between rows of tube bundles is strong, so the amplitude changes violently with the number of the tube bundle. The step-by-step calculation strategy of rough calculation and actuarial calculation proposed in this article can greatly reduce the calculation time and improve the calculation efficiency.

Analysis of Fluid-Structure Coupling Vibration Characteristics of Pipeline Transporting Bubbly Fluid Medium: With Application to Luxury Passenger Ship Life Area Pipeline

When pipelines are transporting bubbly fluid medium, due to the coalescence and breakage behaviours of the bubbles, the pressure distribution at the wall is not uniform and the structure response is more complex. The bubbly beverage pipeline in the life area of the luxury passenger ship is a typical scene of the pipeline transporting bubbly fluid medium. In this paper, the two-way fluid-structure coupling analysis is carried out on such a scene with the aid of ANSYS software and the PBM model is introduced to characterize the dynamic properties of bubbles. At the same time, the accuracy of this calculation method is verified by the scaling experiment. On this basis, the response of the pipeline under the excitation of bubbly fluid is calculated for different inlet velocities and gas volume fractions, and the effectiveness of common vibration damping measures is evaluated. The result shows that the addition of bubbles to the fluid medium has a significant effect on the distribution of the flow field in the pipeline during transport, and the vibration acceleration values of the pipe wall also increase significantly. This method enables accurate simulation of the vibration characteristics of bubbly fluid medium pipelines.

Study on Separation Characteristics of Nozzles with Large Expansion Ratio of Solid Rocket Motors

In order to study the flow characteristics of a nozzle with large expansion ratio and its influence on the force on the nozzle, ground cold flow test research and a fluid–structure coupling simulation analysis were carried out (maximum expansion ratio ε = 30.25). The variation and pulsation characteristics of the pressure near the measuring point area and the inlet pressure were obtained through experiments. Through the analysis of the peak-to-peak value and average value, it was found that the average pressure after separation increases by 90%, but the peak-to-peak value increases by about five times, indicating that the pressure fluctuation after separation is much larger than before separation. The separation flow field under cold flow conditions was simulated using the CFD commercial calculation software Fluent to verify the correctness of the numerical calculations. The fluid–structure coupling analysis was carried out on a large expansion ratio (maximum expansion ratio ε = 48) full-scale nozzle, and the structural deformation characteristics of the nozzle under the separation conditions were studied. The research results show that flow separation occurs in the nozzle with a large expansion ratio under ground conditions. Before the separation point, the pressure pulsation on the nozzle wall is small, and the turbulent pulsation effect is weak. After the separation point, the pressure pulsation increases, and the turbulent pulsation effect is enhanced. When the total pressure decreases, the separation area of the nozzle increases, and the separation flow field presents a strong asymmetry. Reducing the total inlet pressure by half resulted in approximately 50 times the lateral load. Under the combined influence of the ground conditions and low total pressure, the large lateral load caused by the asymmetry of the separation flow field will cause the deformation of the nozzle structure to increase by 5.5 times. This research provides an important reference for the design and experiment of nozzles with a large expansion ratio.

Optimization and characteristic analysis of screw rotor of a twin-screw pump

In order to reduce the leakage between the teeth of the twin-screw pump and improve the working performance, it is necessary to reduce the clearance between the teeth; In this paper, the end face profile equation of A-type screw rotor is derived by coordinate transformation method, the end face profile is generated based on MATLAB software, and the cusp and curve of the profile are optimized by arc transition method; The changes of pressure field and velocity field in the fluid domain of screw rotor before and after optimization are analyzed by finite element method; Taking the twin-screw pump as the research object, the fluid-structure coupling analysis and calculation of the master and slave screw rotors are carried out. The modal analysis of the screw without prestress and under the action of prestress is carried out respectively. Through the simulation calculation, the first six modal vibration shapes of the screw are taken, and the results of the two different states are compared. The results show that when the working pressure difference is 2 MPa, the maximum pressure after optimization increases by 1 % compared with that before optimization. With the continuous increase of center distance, the maximum pressure of flow field fluctuates slightly up and down; The maximum velocity after optimization is 3.5 % lower than that before optimization. The comparison results show that the frequency of the screw rotor increases with the increase of the modal order of the screw rotor without prestress. The frequencies of the second and third orders are similar, and the amplitudes of the first and fourth orders are similar. After the fluid-structure coupling force is applied, the change trends of the modal frequencies of each order are basically the same, but the magnitudes of the frequencies and amplitudes change. The amplitude of the main and driven screw rotors under the fluid-structure interaction decreases rapidly in the third-order vibration mode and is lower than the amplitude without prestress.

Dynamic Coupling Analysis on Thermo–Chemo–Mechanical Field and Fluid–Structure Interaction for Aero-Engine Turbine Blade with Functional Gradient Thermal Barrier Coatings

In this study, an extended layerwise/solid-element (XLW/SE) method is developed for the thermo–chemo–mechanical (TCM) coupling problem of an aero-engine turbine blade with thermal barrier coatings (TBCs). The method consists of two parts, the extended layerwise (XLW) method and the three-dimensional (3D) solid-element (SE) method, which are adopted to formulate the governing equations of TBCs and substrate, respectively. Then, according to the compatibility conditions of displacement, temperature, concentration and internal force equilibrium at the TBCs/substrate interface, the governing equation of the final blade structure is assembled. Through a time integration, the dynamic responses of displacement, temperature and concentration can be calculated. In addition, the fluid–structure coupling analysis is conducted by using COMSOL. The nonuniform thermal load is imported into the XLW/SE method to calculate the mechanical response of blade structure. Finally, the corresponding computing program is compiled with C++. In numerical examples, the TCM coupling analysis is conducted on the blade structure with and without interfacial debonding and delamination damages. To validate the effectiveness of the proposed method, the dynamic TCM responses of the XLW/SE model is compared with those of a 3D elastic model generated by COMSOL, which shows that the two models are in good agreement.

Analysis of interpolar air motion coherence and heat transfer under different asymmetric rotor yoke ventilation duct structures of the pumped storage power machine

Large-capacity per pole and high current density in the rotor lead to the high heat load per unit volume of the excitation winding. In order to improve cooling efficiency on the heat exchange surface and the axial uniformity of the rotor excitation winding temperature, the asymmetric yoke ventilation duct structures with four different widths are proposed along both sides of the pole axis. However, the structure of yoke ventilation duct with different width not only affect motion coherence of interpolar air at different axial positions, but also produce two adjacent interpolar air motion difference. Consequently, it is essential to study the flow rate distribution, motion law and motion difference of interpolar air for the accurate temperature field analysis of the rotor excitation winding. Taking a Xiangshuijian pumped storage machine with rated capacity of 277.8MVA (generator condition)/ 286.4MVA (motor condition) and rated speed of 250 rpm as an example, based on the multiple frames of reference model, the fluid-structure coupling analysis is performed in the solution domain by the finite volume method. The obtained numerical results of excitation winding average temperature are validated using the temperature measured data under the operation conditions of rated power generation, 80% power generation and rated pumping.

Fluid-Structure Coupling Analysis of a Pump-turbine unit during the Pump Shutdown Transient Process

Hydropower is a major renewable clean energy and is widely used worldwide. The reversible pump-turbine unit of the pumped-storage power station is able to work in two main operating modes as required by the power grid: turbine-mode for power generation and pump-mode for power storage. In order to absorb unstable energies such as wind and solar energy and improve the quality of the electricity, reversible pump-turbines need to frequently change operating conditions, and experience more start-stops under different operating modes in a short period. The unstable flow during these transient processes will lead to high-level stresses on the structural components of the pump-turbine units. Therefore, it is of great engineering and academic significance to study the flow characteristics and structural characteristics of the unit during the transient processes. This paper has established a numerical calculation model for a prototype reversible pump-turbine unit, has carried out the CFD calculations of the pump-turbine fluid domains during the pump shutdown transient process, and has analysed the corresponding structural dynamic characteristics of the stationary components of the unit with the fluid-structure coupling method. The pressure variation trend of the spiral case outlet during pump shutdown has the same trend as that of the spiral case domain, and the guide vane flow domain. The maximum flow-induced deformation and stress of the stationary structures have a strong correlation with the axial thrust values of the head cover. The maximum deformation occurs at the inner edge of the head cover, and the maximum stress appears in the fillet of the stay vane leading edge. An increase in the number of shutdowns will result in a higher real risk of fatigue damage to the stay vanes. The conclusions obtained are of great value for safe operation, field condition monitoring, fault diagnosis, and predictive maintenance of the pump-turbine units.

Thermal—Fluid—Structure Coupling Analysis of Flexible Corrugated Cryogenic Hose

Thermal—Fluid—Structure Coupling Analysis of Flexible Corrugated Cryogenic Hose

Experimental and Numerical Study on the Performance of Double Membrane Wing for Long-Endurance Low-Speed Aircraft

Flexible membrane structure is generally used as wing skin for long-endurance low-speed aircraft, such as solar aircraft, to control the structure weight within the allowable range. Predictably, the elastic deformation of the membrane under complex loads will cause uncertain impacts on the aerodynamic performance. The existing research indicates that the deformation of the membrane wing is helpful to improve the aerodynamic characteristics. However, most of the research objects are non-thickness membrane wings. In this paper, wind tunnel experiments are performed on double membrane wings. The experiment results indicate that the membrane deformation behavior is related to the surface curvature distribution and will change the camber and thickness of the airfoil. The deformation has little effect on lift but has a significant effect on drag and pitching moment. On this basis, a high-precision fluid structure coupling analysis method for the wider range of research is introduced. The numerical analysis indicates that the deformation can delay the stall angle by 1°. Furthermore, based on the numerical results, suggestions on prestress setting during membrane skin laying are provided, and the numerical simulation results of two flexible skin wings are compared. The research results of this paper provide a scientific basis for the aerodynamic design and analysis of long-endurance low-speed aircraft.

Calculation Model of Mechanical and Sealing Properties of NiTi Alloy Corrugated Gaskets under Shape Memory Effect and Hyperelastic Coupling: Two Sealing Properties.

Bolted flange connections are commonly used in process industries. Their sealing performance is greatly affected by the gasket. In this paper, a NiTi alloy corrugated gasket was simulated to reveal its sealing performance, considering the gasket surface roughness, shape memory effect and superelastic effect. A fluid–structure coupling analysis method that takes the real surface morphology of the gasket contact zone was proposed, and a leakage rate prediction model was established. The results showed that NiTi shape memory effect could enhance the sealing reliability in service and lower the leakage rate. The leakage rate of the NiTi alloy corrugated gasket is positively correlated with the internal pressure of the medium and the roughness of the sealing surface. The prediction model of the NiTi alloy corrugated gasket leakage rate has good reliability with an average error of about 16.81% compared with the simulation.

Analysis of grasping deformation of textile fabric based on fluid structure coupling

The grasping transfer deformation of textile fabrics is the primary problem faced by textile production automation. During the automatic transfer process of textile fabrics, due to its own flexibility, large deformations are brought about, which leads to the problem of overlapping folds before the fabric is formed. In this paper, the end gripper composed of non-contact Bernoulli suction cups is used to adsorb and transfer the textile fabric, and the fluid structure coupling analysis method is used to calculate the adsorption force under different inlet pressures by using the macroscopic continuous model of the end effector adsorbing the fabric. The fluid structure coupling adsorption model is established, and the effects of the number and layout of suction cups and different inlet pressure on the deformation of flexible fabric during clamping are analyzed and studied. The deformation effect of the end effector in the process of transferring fabric is verified by simulation and visual experiment. The results show that the optimal working parameters of the end effector obtained by fluid structure coupling simulation are consistent with the test. When the end effector adopts five suction cups and the air inlet pressure is 0.3 MPa, the deformation is the smallest. This study provides a new method to solve the problem of automatic grasping and transfer of textile fabrics, and provides technical support for improving the automation level of garment industry.

Head-Cover vibration investigation of a Prototype Reversible Pump-Turbine Unit during Start-up in Pump mode. Part I: Fluid dynamic analysis

Reversible pump-turbine units of pumped storage power stations can generate power in turbine mode and store electric energy in pump mode for load balancing of the electric power grid. During the start-up transient process in pump mode of a reversible pump-turbine, the flow pattern and the pressure distribution in the flow channel change dramatically with the increasing opening angle of guide vanes. The unsteady pressure of the flow passing channel can cause severe vibration on the head-cover, bottom ring, and other stationary structures around the impeller. In this paper, a coupled 1D/3D co-simulation approach is developed to investigate the pressure distribution characteristics of the flow field during the start-up transient process in pump mode for a large prototype reversible pump-turbine unit. The entire model of flow channel from spiral casing to draft tube is constructed and the flow characteristics of key fluid fields such as spiral casing, stay vanes, guide vanes, impeller, and draft tube are analyzed. The simulation results show that under the condition of minimum guide vane opening the flow is insufficient and vortices occur on the impeller blades. The pressure distribution results of the flow channel from 3D fluid dynamic analysis during the start-up transient process in pump mode are exported as boundary conditions for the subsequent fluid-structure coupling analysis of the head-cover vibration investigation.

Fluid-structure coupling analysis of a pressure vessel-pipe-safety valve system with experimental and numerical methods

Pressure vessel-pipe-safety valve (PVPSV) is a commonly used combination in the industrial pressure systems. For the design optimization purpose, an in-depth investigation on the working mechanism of such a combination is essential. To this end, experimental and numerical analysis were performed in this paper. For measuring, an experimental test rig is specially designed and built, thereby dynamic tests were performed. The results indicate that the set-pressure of the safety valve and the valve spring stiffness have significant influence on the dynamics of the PVPSV. Upon certain operating conditions, the safety valve responds in unstable manners, e.g., flutter or chatter. To compensate the tests, a high-fidelity 2-D axis-symmetric system-level Computational Fluid Dynamics (CFD) model is used. The simulation results show that both the damping coefficient and the connecting pipe length have great influence on the dynamics of the PVPSV system. A PVPSV system with a small damping coefficient and/or a long connecting pipe is more likely to exhibit dynamic instability. Finally, combining the results of experiments and numerical simulations, a large enough net disc force coupled with insufficient kinetic energy loss of valve moving parts are considered to be the root cause of unstable operations of the PVPSV system.