Fluid-structure Coupling Method Research Articles

Design optimization and numerical verification of adaptive composite blades for hydro-turbine

In this paper, an adaptive composite blade is designed based on the composite mechanics and bending torsion coupling theory, and the blade structure is optimized by a multi-parameter and multi-objective optimization method. Furthermore, the dynamic interaction between the flow and structure domain during the bend-twist coupling process was also studied by the two-way fluid-structure coupling method to verify the hydrodynamic performance and structural performance of the optimized blade. The results show that the multi-parameter and multi-objective optimization method is suitable for the design of composite blades. The optimized blade has better hydrodynamic performance and structural performance, manifesting a higher energy utilization and less concentrated stress.

Ventilation structure design and heat transfer analysis of 3.3MW permanent magnet direct drive wind generators

For megawatt permanent magnet direct drive wind generator, with the increase of its power level, the insulation of the motor may be threatened by the increase of operating temperature, which may also lead to the irreversible demagnetization of permanent magnets. To solve this problem, a radial forced ventilation cooling structure was designed and established in this paper, based on a 3.3MW, 12rpm external rotor surface mount permanent magnet motor. The coupling relationship between electromagnetic field and temperature field is reasonably considered by iterative simulation method, and the temperature field and fluid flow are analyzed based on fluid–structure coupling method. The results show that the ventilation structure designed in this paper has a certain cooling effect and can meet the needs of its safe and stable operation. It has a certain reference significance for the cooling system design of megawatt permanent magnet direct drive wind generator.

On the safety threshold of trains running on Sichuan-Tibet Railway bridges under the influence of floating ice

To investigate the running safety threshold of trains on the Sichuan-Tibet Railway bridges under the floating ice impact loads, a train-track-bridge dynamics model is established based on the theory of the train-track-bridge dynamic interaction and the design method of tuned mass damper (TMD), which uses the fluid-structure coupling method to calculate the floating ice impact loads. Taking a 5 × 32 m typical simply-supported beam bridge on the Sichuan-Tibet Railway as an example, the critical train speeds corresponding to floating ice impact loads of varying intensity are evaluated, and the effect of TMD on the running safety of the trains under extreme ice loads is investigated. The results show that the fluid effect has a significant influence on the impact loads of ice hitting the bridge pier, which cannot be ignored in the calculation. The ice impact intensities significantly reduce the train's safe speeds. Under the action of floating ice impact loads, the TMD attached to the bridge can effectively reduce the train's derailment factor and wheel unloading rate. The greater the TMD mass ratio, the more pronounced the vibration control effect.

Research on the Flow-Induced Stress Characteristics of Head-Cover Bolts of a Pump-Turbine during Turbine Start-Up

Nowadays, pump-turbine units have to experience multiple start-stops every day to balance the power production and consumption on the grid. During the transient process of turbine start-up, the hydraulic forces applied to the head-cover would change dramatically and induce high-level stresses on the head-cover bolts. As key components of large hydraulic turbine units, the head-cover bolts are subjected to tens of thousands of tonnes of hydraulic excitation force during operation. Special attention should be paid to the design of the head-cover bolts of large hydraulic pump-turbine units because these units have high water heads and high hydraulic excitation forces. Therefore, the safe design of the head-cover bolts is extremely important to maintain the operational safety of the whole unit. This paper investigates the flow-induced stress characteristics of the head-cover bolts during turbine start-up in a large prototype pump-turbine unit. A complete 3D fluid model and a corresponding 3D structural model, including the head-cover bolts of the pump-turbine unit, were created. The fluid–structure coupling method was used to calculate the structural stresses caused by fluid flow during turbine start-up. The pressure files during turbine start-up calculated by the CFD tool were transferred and mapped to the finite element model of the structural components of the pump-turbine unit. Subsequently, the flow-induced stress characteristics of the head-cover bolts were numerically simulated. The simulation results showed that the hydraulic excitation force on the head-cover bolts increased significantly during turbine start-up, and the displacement and the stress distributions of different head-cover bolts were not uniform. The calculation methods and conclusions in this paper can also be applied to evaluate the flow-induced stress characteristics of head-cover bolts for similar hydraulic pump-turbine units.

Stress Coupling Analysis and Failure Damage Evaluation of Wind Turbine Blades during Strong Winds

Blades in strong wind conditions are prone to various failures and damage that is due to the action of random variable amplitude loads. In this study, we analyze the failure of 1.5 MW horizontal axis wind turbine blades. The computational fluid dynamics unsteady calculation method is used to simulate the aerodynamic load distribution on the blade. Fluid–structure coupling methods are applied to calculate the blade stress. The results show that the equivalent stress of the blade is the largest when the azimuth angle is 30°, and the maximum equivalent stress is 20.60 MPa. There are obvious stress peaks in six sections, such as r/R = 0.10 (the span length of blade/the full length of the blade = 0.10). The frequency of damage that is caused by the stress in each area of the blade is determined based on the blade damage. The frequency of gel coat cracking in the blade tips and leaves is 77.78% and 22.22%, respectively, and the frequency of crack occurrence is 87.75%, 10.20% and 2.05%, respectively. By combining the stress concentration area and the damage results, the cause of blade damage is determined, which can replace the traditional inspection methods and improve the inspection efficiency.

A simulation study on stress-seepage characteristics of 3D rough single fracture based on fluid-structure interaction

This paper expounds on the process of deformation and seepage field change of single coarse fracture under normal stress and puts forward a numerical simulation framework based on fluid-structure coupling method to reasonably link contact deformation of fracture surface with seepage field change. The geometric model of a three-dimensional rough single fracture surface with controllable JRC is established based on the random surface generation method. The numerical test model of radiation flow of single fracture in rough rock is constructed, which is consistent with the laboratory test. Through carrying out numerical simulation tests of different JRC and normal stress conditions, this paper discusses the phenomenon and intrinsic nature of the influence of JRC on fracture seepage characteristics. The increase in eddy current intensity and eddy current area ratio is the inherent characteristics of the seepage field characteristics after JRC increases. With the rise of energy loss, the macroscopic seepage flow decreases. In addition, with the advantage of the fluid-structure interaction method, the fracture deformation characteristics under different normal stresses are reflected by the ratio of the contact area. The correlation among fracture surface deformation, velocity vector, and seepage pressure are analyzed. Finally, the cubic polynomial correlation between gap width ratio and contact area ratio is established and verified. It is of positive significance to quantify the influence of coarse single fracture contact ratio on deformation-seepage coupling characteristics under normal stress.

Prestressed Modal Analysis of Wind Turbine Blade Considering Fluid-solid Coupling

Wind turbine blade is a kind of slender elastic body structure, which is prone to vibration and deformation during operation, seriously affecting the smooth operation of wind turbine. Taking the 1.5MW wind turbine blade as the research object, the three-dimensional shell model of the blade is established based on Solidworks, and the composite material layer design of the blade is carried out in ANSYS ACP. The stress and deformation of the blade in the flow field are studied based on the fluid structure coupling method. The first six natural frequencies and modes of the blade are obtained by taking the stress of the structural field as the prestress of the modal analysis. The results show that flapping and shimmy are the main vibration forms of the blade. When resonance occurs, the fluctuation of the blade in the flapping direction is the largest, and the maximum stress appears near the blade root.

Effect of COPD on respiratory function investigated by a fluid-structure coupled method for lung deformation and airway flow

Effect of COPD on respiratory function investigated by a fluid-structure coupled method for lung deformation and airway flow

Study on Vibration and Heat Transfer Performances of a Modified Elastic Tube Bundle Heat Exchanger

Based on the bi-directional fluid-structure coupling method, the vibration and heat transfer performances of a modified elastic tube bundle heat exchanger are studied. The vibration frequency and amplitude of tube bundle are compared between different directions and tube row spacing. Furthermore, the Nusselt number of tube bundle are studied in vibrational and non-vibrational cases. The numerical results represent that the vibration amplitude of tube bundle is the largest in the z direction, which is 7.25 times that in the y direction (direction of the smallest amplitude). In the calculation scope, the vibration frequency and amplitude promote with tube row spacing. From 50 mm to 90 mm spacing, the vibration frequency and amplitude increase by 21.88% and 10.65%, respectively. The Nusselt number under the fluid-induced vibration increases up to 11.67% compared with non-vibration. Besides, the Nusselt number of tube bundle in the middle part is lower than that at the two ends. Within 50-90 mm interval, the enhanced heat transfer effect rises along with tube row spacing. The rising rate of the Nusselt number increases by 52.4%. in the range of computation.

The Research of Maneuverability Modeling and Environmental Monitoring Based on a Robotic Dolphin.

In this study, the C-turning, pitching, and flapping propulsion of a robotic dolphin during locomotion were explored. Considering the swimming action required of a three-dimensional (3D) robotic dolphin in the ocean, we propose a maneuverability model that can be applied to the flapping motion to provide precise and stable movements and function as the driving role in locomotion. Additionally, an added tail joint allows for the turning movement with efficient parameters obtained by a fluid-structure coupling method. To obtain a mathematical model, several disturbance signals were considered, including systematic uncertainties of the parameters, the perpetually changing environment, the interference from obstacles with effective fuzzy rules, and a sliding mode of control. Furthermore, a combined strategy of environment recognition was used for the positional control of the robotic dolphin, incorporating sonar, path planning with an artificial potential field, and trajectory tracking. The simulation results show satisfactory performance of the 3D robotic dolphin with respect to flexible movement and trajectory tracking under the observed interference factors.

Analysis on Aerodynamic Stability of Blades by an Efficient Fluid–Structure Coupling Method

AbstractPoor calculation efficiency is a major issue in the investigation of time-domain aerodynamics of turbomachinery bladings by fluid–structure coupling. In this work, a numerical methodology f...

MULTI-FIELD COUPLING EFFECT AND SIMILARITY LAW OF FLOATING ICE BREAK BY VEHICLE LAUNCHED UNDERWATER

Fluid structure coupling effect and dynamic load characteristics are the important basis of the safety evaluation of the vehicle in the process of underwater launching and floating ice break. In this paper, the main control parameters which influence the dynamic load and the stress at the head of the vehicle, as well as the similarity law, are obtained by dimensional analysis. Based on the LS-DYNA fluid structure coupling method, the numerical simulations for underwater launched vehicle impacting with floating ice have been conducted, and the load characteristics of the vehicle under the conditions of different impact velocities, different ice thicknesses and different ice sizes are obtained. The simulated results show that, the higher the initial velocity of the vehicle is, the greater the distinction of the influence of different ice targets on the overload and the stress at the head of the vehicle is, which is mainly due to the different destruction of different ice targets under the strong water impact generated by the underwater motion of the vehicle in the early stage. For the infinite ice sheet, when its thickness is more than 3 times the vehicle diameter, the penetration into the ice appears stable at the later stage, the rigid body acceleration and the stress at the head of the vehicle are only related to the penetration velocity and the dynamic mechanical properties of the ice; for the thinner ice target, the higher the velocity of the vehicle is, the smaller the stress at its head is. This is because the early damage of the ice under the water impact generated by the higher speed motion of the vehicle is more serious, the ice layer is easy to crack and bulge, resulting in the smaller stress at the vehicle head. For the broken ice whose radial dimension is 6 times the vehicle diameter, when its thickness is also greater than 5 times the vehicle diameter, the influence on the vehicle motion is almost the same as that of the infinite ice sheet; when its thickness is less than 3 times the diameter of the vehicle, the ice size effect can be ignored only when the vehicle velocity is low. In addition, by comparing the influence of broken ice and infinite ice on the vehicle motion, it can be observed that, the thicker ice got less damage by the water impact at the early stage, thus the influence of broken ice and infinite ice are basically the same; while the thinner ice is seriously damaged by the water impact, resulting in little influence of broken ice and infinite ice on the vehicle motion; only for the ice targets with medium thickness, their damage degrees are related to the radial size under the condition of the higher vehicle velocity, for instance, when the initial vehicle velocity is 40 m/s, there is a great damage difference between the two kinds of ice targets with dimensionless thickness 3 at the early stage, which leads to a significant difference in the influence on the vehicle motion at the later stage.

Effect of Stiffness on Flutter of Composite Wings with High Aspect Ratio

High aspect ratio wing (HARW) structures will deform greatly under aerodynamic loads, and changes in the stiffness will have a great impact on the flutter characteristics of such wings. Based on this, this paper presents an effective method to determine the effect of the stiffness on the flutter characteristics of HARWs. Based on the calculation theory of the mechanical profile of thin-walled structures, the torsional stiffness and bending stiffness of the wing are obtained through calculation. We use the fluid-structure coupling method to analyze the flutter characteristics of the wing, and we use our research results based on the corotational (CR) method to perform structural calculations. The load is calculated using a computational fluid dynamics (CFD) solver. The results show that, compared with the original wing, when the bending stiffness and torsional stiffness of the wing along the spanwise direction increase by 8.28% and 5.22%, respectively, the amplitude of the flutter decreases by approximately 30%. Increasing the stiffness in the range of 0.4 to 0.6 Mach has a greater impact on the flutter critical velocity, which increases by 12.03%. The greater the aircraft’s flight speed is, the more severe the stiffness affects the wing limit cycle oscillation (LCO) amplitude.

The Fluid-structure Coupling Analysis of Steel-Wire-Reinforced Flexible Pipe Under Inner Fluid Pressure Impact

Identifying dynamic characteristics of the fluid filled steel-wire-reinforced flexible pipe is vital in controlling the pipe vibration. A direct fluid-structure coupling method based on finite element analysis is proposed and validated by modal simulation of an oil filled T-shape pipe. An innovative way of modeling steel-wire-reinforced rubber pipe is put forward. The modeling method is validated by modal test of the water-filled pipe. The 2nd Mooney-Rivlin constitutive model is used for the rubber material. Transient dynamic simulations of a bending steel-wire-reinforced pipe filled with water under step and sine-shape pressure impact are performed for the first time. Different fluid turbulence models are used to evaluate the influences on pipe vibration. The dynamic characteristics of the water filled flexible pipe is researched under different fluid pressures. The vibration peak frequencies of the water-filled pipe under various impact excitations coincide well with the fluid-structure coupling modes of the pipe.

Research on Contact Explosion Response of Reinforced Concrete Slab

In order to compare the contact explosion response of reinforced concrete in the air to that under the water, a FEM model based on multi-material fluid-structure coupling method is constructed to simulate the responses and failure process of two-way reinforced concrete slabs under contact explosion. The model is verified by fellow tests, then used to calculate dynamic responses and damage conditions of two-way reinforced concrete slabs subjected to underwater contact explosion and air contact explosion. It is found that the local destruction area of the slab subjected to underwater contact explosion roughly turned into a circle, while it turned into a rhombus for air contact explosion. Nonetheless, the damage of the reinforced concrete slab subjected to underwater explosion is more serious.

Numerical study on swirl cooling flow, heat transfer and stress characteristics based on fluid-structure coupling method under different swirl chamber heights and Reynolds numbers

In this study, a three-dimensional swirl cooling model coupled with high temperature mainstream cascade channel and blade leading edge solid region is established to simulate the flow, heat transfer and stress characteristics. The fluid-structure coupling model is utilized to analyze the interaction of external mainstream, solid blades and swirl cooling air. Six different swirl chamber heights are selected to explore the optimal height which is the most beneficial to gas turbine blade operation. Finally, influences of coolant chamber inlet Reynolds number on swirl cooling performance are discussed in detail. Results show that the temperature distribution of blade solid region is highly related to swirl cooling effect. Compared with aerodynamic load, the thermal load behaves more significant effects for blade stress conditions. As the swirl chamber height increases, the swirl cooling heat transfer performance gradually decreases, and the flow resistance also gradually decreases. The comprehensive heat transfer factor is introduced to evaluate the swirl cooling overall performance. When swirl chamber height is 19 mm, it has higher heat transfer capacity and lower flow resistance, and the comprehensive heat transfer factor is the highest. The Reynolds number has a strong influence on heat transfer performance. In order to avoid high aerodynamic losses, the Reynolds number should be selected appropriately.

Investigation of Temperature Transient Response Characteristics of Ceramic Fuel Rod of Open-Cycled Reactor

To investigate the effects of the fuel material property on the temperature safety response characteristics of the new-designed open-cycled reactor with the air as the coolant, the geometric model of the annular fuel rod is built. The parameter model is developed based on the properties of the three types of ceramic material of nuclear fuel including the Uranium dioxide (UO2), Uranium carbide (UC) and Uranium nitride (UN). The temperature transient response rule of the three kinds of fuel rods at the cases of reactor power step increase is obtained based on the fluid-structure coupling method. The temperature transient response characteristics of three types of ceramic fuel rods open-cycled reactor are analyzed. The numerical results reveal that the peak fuel temperature and the average fuel temperature increase significantly with the step increasing reactor power. The response time of the fuel rod with UC is the longest. The peak fuel temperature and the temperature difference of the fuel rod with UO2 are the highest. The relative results can lay the theoretical foundation for the fuel material selection, structure design and the safety analysis of the open-cycled reactor.

Surface roughness effect on cylinder vortex-induced vibration at moderate Re regimes

The marine riser is the key equipment connecting the floating platform with the seabed wellhead, and the vortex-induced vibration (VIV) is the main cause of its fatigue damage, which contains complex and substantial dynamics content. Marine risers are operated for a long time. As time goes by, marine organisms will attach on the marine riser surfaces, thus significantly affect their surface roughness of the riser. The increased surface roughness makes the dynamic characteristics of the riser VIV more abundant and complex, including jumping, multi-frequency vibration, broadband vibration, resonance and other dynamic contents. In this study, based on the bidirectional fluid-structure coupling method of computational fluid dynamics (CFD) and computational structure dynamics (CSD), the modified model of rough wall velocity gradient is introduced, and the calculation program of a rough cylinder wall velocity gradient is compiled and embedded into the numerical calculation program of a smooth cylinder VIV to construct the numerical calculation program of a rough cylinder VIV. The program is used to study effects of various key parameters, including surface roughness, and inflow velocities, on the vibration response characteristics, dynamic characteristics, wake vortex shedding patterns and vibration trajectories of a rough cylinder. The differences of VIV characteristics are systematically studied to reveal the nonlinear dynamic behavior of a rough cylinder VIV, such as jumping, multi-frequency vibration, resonance, etc. The influence mechanism of surface roughness on a cylinder VIV is explored to provide a scientific theoretical basis and a practical engineering method for vibration control of a rough marine riser.

Vibration characteristics of marine riser groups considering the coupled action of cross-flow and in-line

Fluid-induced vibration (FIV) prediction is an important prerequisite work in wear and fatigue analysis of multi-wellhead marine risers in deepwater operation condition. A two-way fluid-structure coupling method (CFD/CSD) is used to establish a numerical model vibration of the marine riser groups, taking into account the interaction between two physical fields of fluid-structure, the combined effects of ocean eddy-induced force and wave-induced force. The model is solved numerically by ANSYS Workbench and Fluent software and verified preliminarily by a classical example in literature in which considering vibration response of a single riser. The effects of number, spacing, and arrangement of risers on the vibration response characteristics of marine riser groups are analyzed by established mode. It is found that with the increase of the number of risers, the vibration of the front risers is mainly cross-flow (CF), while the vibration of the rear risers is mainly in-line (IL). Therefore, the influence of incoming flow should be taken into account in the front risers, and the disturbance of wake should be taken into account in the rear risers. With the increase of the distance between risers, the interaction between risers groups affects CF and IL. The critical spacing of the interaction is between 3.5D and 4D. The arrangement of marine risers mainly affects the CF vibration of risers, especially the upstream and downstream risers. The research results can provide theoretical support for the design and vibration control of multi-wellhead marine risers.

Deformation and vibration analysis of compressor rotor blades based on fluid-structure coupling

Under the influence of aerodynamic and rotational load, deformation and vibration could occur to rotor blades of axial compressor, which may cause fatigue fracture, and threaten the exist of tip clearance because it is the assurance of operation safety by separating the rotor from the case. The overall performance will be deteriorated by the change of blade shape due to the deformation and vibration. Three different materials, titanium alloy, aluminum alloy and stainless steel are compared quantitatively under various operating conditions by fluid-structure coupling method. First the CFD method is validated by experimental data, the obtained pressure distribution on blade surface is exerted to the structure as boundary condition, then deformation characteristic and the corresponding maximum equivalent stresses are analyzed, at last vibration modal is analyzed and resonance points, the main reason for the vibration-induced failure, are predicted by Campbell diagrams. The results show that deformation increases with rotation speed and outlet pressure; the aluminum alloy has the largest deformation of the three materials. The equivalent stress of the blade is mainly caused by rotation, large stress regions are often near the blade root. The tip clearance of rotor blades can be reduced by deformation in the radial direction, for titanium and aluminum alloy blade, the maximum stretched length of blade at 100% rotation can account for 30% of the designed tip clearance. Centrifugal loading is the main reason for the increase of natural frequency while the increased amplitude with rotation speed is extremely small compared to the first order natural frequency.