Fluid-structure Coupling Effect Research Articles

Design of flexible sensor for wind pressure monitoring of stay cables

Strong winds can make a bridge’s cable-stayed cables produce violent vibrations, leading to fatigue of the cable-stayed cables and damaging the cable-stayed bridge’s structure. Accurately and effectively obtaining data on the wind loads applied to the cable-stayed cables is important for assessing the cable-stayed cables’ health. The existing sensing elements for detection include diffusion silicon piezoresistive sensor, strain gauge, and other rigid sensors. However, most of them present such disadvantages as rigidity, difficult to fit the curved surface, high cost and low sensitivity. And it cannot be directly installed on the surface of the cable. In this paper, a conductive hydrogel flexible pressure sensor based on TA/CB@PDMS was developed, using carbon black (CB) as the main conductive medium, with good electrical conductivity, high sensitivity (0.65 kPa−1) and excellent tensile properties (210% tensile breakage). Meanwhile, a salt permeation method (Soak the sensor in LiBr solution) was used to effectively inhibit the sensor’s water from being evaporated and frozen. Its substrate incorporates tannic acid to increase the sensor’s adhesion so that it adheres well to the diagonal cable’s surface. In this paper, the wind speed variation around the diagonal cable and the force distribution on the surface with considering the fluid-structure coupling effect are analyzed by ANSYS WORKBECH finite element simulation. Wind tunnel experiments simulate the sensor’s force response when the inclined cable is subjected to different wind speeds, and the detection accuracy reaches 96.17%. The results show the sensor developed in this paper can realize accurate wind pressure detection of the inclined cable. This study provides a new method for wind pressure detection and health inspection of diagonal cables.

Mechanical response analysis of the wide-chord hollow fan blade considering the fluid–structure interaction

The aero-engine wide-chord hollow fan blade with a cavity stiffener structure can effectively reduce the weight and greatly increase the rotational speed. However, during the high-speed rotation process of the hollow fan, there is a strong coupling effect between the solid domain of the blade and the incoming air. This effect leads to a certain deformation of the rotor blade, which has a large impact on the structural strength of the blade. Aiming at the problem of the fluid–structure interaction in its operation, the finite-element method was used to simulate the two-layer structure of the TC4 titanium alloy wide-chord hollow fan blade. The centrifugal force and fluid–structure coupling effect were considered when carrying out the research on the structural mechanical characteristics of the blade. The results show that the maximum equivalent stress of the blade considering the fluid–structure coupling effect is 508 MPa at the rotational speed of 2,900 r/min, which is approximately 18% higher than the maximum stress when only the centrifugal force is considered. This phenomenon indicates that the effect of aerodynamic force on the blade stress cannot be ignored. The stress concentration area of the blade is located in the third stiffener from the leading edge and near the root of the blade, and the aerodynamic force has a more significant effect on the radial stress distribution of the blade. Further analysis of the equivalent stress distribution along the blade tip direction shows a trend of first increasing and then decreasing. The maximum equivalent stress appears at a distance of 30 mm up to the bottom of the stiffener.

Study on Earthquake Failure Mechanism and Failure Mode of Cable-Stayed Pipeline Bridge Considering Fluid–Structure Coupling

To investigate the failure mode of the cable-stayed pipeline bridge under seismic loading, this study focuses on an oil and gas cable-stayed pipeline bridge as the research subject. A full-scale finite element calculation model of the structural system is established using ANSYS Workbench 14.0 software, considering the stress characteristics and structural properties of the oil and gas pipeline. Additionally, a fluid–structure coupling effect finite element model is developed to account for the influence of medium within the pipeline. The analysis includes evaluating deformation, stress, strain, and other responses of the oil and gas pipeline subjected to seismic waves from different directions. The results indicate that the overall damage in the pipeline is consistent with maximum deformation, stress, and strain, concentrated at both the inlet/outlet ends and side spans; however, variations exist in terms of seismic damage depending on wave directionality. Furthermore, by considering interactions between various components within the oil and gas cable-stayed pipeline bridge’s structural system during strong earthquakes, this study analyzes failure mechanisms caused by the support–pipeline interaction as well as excessive displacement-induced failure patterns in bridge towers. Finally, a proposed failure mode for pipe bridge systems resulting from longitudinal slip between supports and pipelines, along with excessive displacement of bridge towers, is presented.

Numerical simulation study of the fluid-structure coupling effects of Kármán vortex street on airfoil motion with varying thickness

This paper examines the fluid-structure interaction of rigid and passive motion of airfoils with different thicknesses in the Kármán vortex street at low Reynolds numbers through numerical simulations. Five NACA airfoils with varying thicknesses (8%, 12%, 16%, 20%, and 24%) were investigated regarding their fluid-structure interaction in the Kármán vortex street. These airfoils were positioned downstream along the centerline of a D-shaped cylinder. Employing a six-degree-of-freedom method, their passive motion was simulated, and the motion grid was generated using the elastic deformation method and local grid reconstruction technique. The analysis included examing alterations in the flow field and forces acting upon airfoils of varying thicknesses in both fixed and released states. The outcomes demonstrate that an increase in airfoil thickness amplified the traction force exerted on the airfoil within the Kármán vortex street, consequently yielding higher lateral force and torque. In the released state, the airfoil exhibited forward motion towards the D-shaped cylinder and deviated from the suction region of the Kármán vortex street due to the influence of lateral force. The study unveils that airfoils of suitable with appropriate thickness, such as NACA0012, achieved an improved equilibrium between forward speed and lateral displacement, thereby covering a more extensive forward distance. These findings provide valuable insights for the designing robotic fish that utilize vortex streets under low-flow conditions.

Forced response analysis of the rotor blade rows with the ROM-based aeroelastic model

Forced response is one of the aeroelastic problems which lead to the blade damage. The energy method based on the hypothesis of a conventional travelling wave model and direct numerical simulation are used usually to analyze the problem. However, energy method cannot cover the fluid-structure coupling effect, while numerical simulation needs large computational cost. A rapid method, based on the reduced order model (ROM), is developed to analyze the forced response of the rotor blades. The unsteady aerodynamic force acting on blades is divided into two parts according to the source. One part is due to the blade vibration. An unsteady aerodynamic force model is built to simulate it and then an aeroelastic model is built by coupling the structural equation. The other part is due to rotor-stator interaction (RSI), which is regarded as the excitation of the aeroelastic model. Then the forced response of the rotor blade rows is transferred to calculate the response of the aeroelastic model under the RSI excitation, which requires one to two orders of magnitude less computational time than direct numerical method and could study the effect of the structural parameters conveniently. Results show that the effect of fluid-structure coupling is crucial to the low-mass-ratio structure. Besides, the structural frequency is not exactly coincident with the excitation frequency when the response amplitude reaches its peak.

A fluid–structure interaction model for large wind turbines based on flexible multibody dynamics and actuator line method

With higher demand of affordable electricity and rapid development of wind turbine technology, scale of wind turbines has been upsizing. As a consequence, blades grow longer and slender. Large geometrically nonlinear deformation and vibration of the blades lead to more challenges in the structural design. In the aerodynamic analysis, traditional blade element momentum theory cannot predict the complicated behavior of these modern blades while fully resolved Navier–Stokes equation methods cost much time modeling and refinement. To overcome these challenges, this paper proposes a new numerical method to analyze turbine aeroelastic performance and fluid–structure interaction based on flexible multibody dynamics and large eddy simulation with anisotropic actuator line method. By comparing the results with various existing numerical methods, we show that the newly proposed method can effectively predict the performance of the wind turbine, such as deformation and power output. We find that blade flexibility poses noticeable impact on the performance of large scale turbines in normal working conditions. The location of nascent vortex is postponed by blade deflection. The max difference between rigid and flexible blades in downstream velocity distributions reaches 10% and occurs at a radial distance around 0.55D. The new method also takes the fluid–structure coupling effect and momentum interaction into consideration and eliminates the non-physical oscillations caused by uncoupled methods. Also, blades deflection and vibration are found to accelerate momentum exchange, which facilitates the wake recovery process. Furthermore,compared to the rigid-blade model, the turbulent kinetic energy obtained by the newly developed flexible-blade model is higher in the low-frequency region, in which large-scale vortices develop and the turbulent mixing effect is strong. This paper is expected to provide a framework for researchers and technology developers to design or estimate the performance of modern large wind turbines.

Seismic Response of Cable-Stayed Spanning Pipeline Considering Medium-Pipeline Fluid–Solid Coupling Dynamic Effect

With the aim of determining the influence of the fluid–structure coupling dynamic effect of the oil and gas transmission medium and pipeline on the seismic response, an oil pipeline supported by a cable-stayed spanning structure was taken as the study object. Kinetic equations taking into account the action of oil and gas medium were studied, and a finite element model structure considering the additional-mass method and the fluid–structure coupling effect were established separately. In addition, the mechanism of the oil–gas–pipeline coupling action on the seismic response of pipeline structure was analyzed, and the results were obtained. The results show that the pipeline has a minimal seismic response at the abutment location, the seismic response gradually increases along the abutment to the main tower, and the seismic response reach is maximized at about one-fifth of the bridge platform. The seismic response of the oil and gas pipeline model structure using the additional-mass method is generally more significant than that based on the fluid–solid coupled dynamic model; moreover, the maximum displacement response differs by about 24%, and the maximum acceleration response differs by approximately 30%, indicating that the oil and gas medium has a certain viscoelastic damping effect on the seismic response of the oil pipeline, which provides a reference for the seismic response calculation theory and analysis method of cable-stayed spanning oil pipelines.

Study on dynamic response characteristics of radial steel gate under rare earthquake considering fluid structure coupling effect

The water resources in southwest China is abundant and the seismicity is strong, so it is necessary to study the dynamic response and safety of hydraulic structures under rare earthquake. Taking a typical radial steel gate as an example, a three-dimensional numerical model considering the interaction between water and gate during the earthquake is established. The accuracy and applicability of the model are verified by comparing with the measured results of the dynamic response of Zipingpu dam during the Wenchuan earthquake. Thereafter, the dynamic displacement and stress, and resonance frequency of the radial gate under the rare earthquake of two wave types are analyzed. The water-structure coupling effect has a great influence on the seismic dynamic response of the radial steel gate. The calculated result of the dynamic response of the gate considering the fluid-structure coupling effect is significantly larger than that of the specification, and the maximum ratio of the two is more than 2.27 times. Under the action of EI wave, the peak value of dynamic stress response is at the bottom of the panel, and the maximum value of resonance frequency (about49.13 Hz) is located in the middle and lower part of the panel. Under the action of far-field wave, the peak area of dynamic displacement response of the gate is basically the same as that under the action of EI wave, while the maximum value of some measuring points is only half of the maximum value under the action of EI wave. However, the resonance frequency is significantly greater than that of EI wave, the maximum value reaches 65.24 Hz, which appears at the top of the gate. The dynamic response of the gate structure caused by two different wave types of earthquakes is not completely consistent. The comprehensive consideration of different wave types is of significance for the structural design and safety evaluation of the radial steel gate in the earthquake-prone areas.

Improved frequency-domain Spectral Element Method for vibration analysis of nonuniform pipe conveying fluid

The well-known Spectral Element Method (SEM) has a broad application in vibration analysis for various configurations, such as flat plates, beams and straight pipes. Considering the fluid–structure coupling effects in variable cross-section, it has one limitation in dealing with the nonuniform pipes conveying fluid. In the present work, an improved frequency-domain SEM (IFSEM) is proposed for the analysis of the nonuniform fluid-conveying pipes by introducing structural wave propagation. In the IFSEM, the wave propagation coefficient plays a critical role to construct the equivalent dynamic stiffness, improving the analysis accuracy and efficiency. And there is a rule that the propagation coefficients are mainly related to the pipe diameter, flow rate and hydrodynamic pressure. A Simplification is put forward to obtain these coefficients in advance, which can significantly facilitate the vibration analysis. Finally, the IFSEM is validated through several numerical examples and the results show that it can analyze the vibration of the liquid-conveying nonuniform pipes efficiently and accurately.

The effects of submergence depth on energy harvesting from the VIV of a four-cylinder oscillator with rigid connection

Numerical and experimental studies of energy harvesting driven by vortex-induced vibration (VIV) are currently focused on arranging the energy-captured structure in a uniform incoming flow at a certain depth, ignoring the effect of the free surface on VIV. The fluid–structure coupling effect can be enhanced when a column-group structure with rigid connection is arranged under uniform flow, which is helpful for the structure to concentrate hydrokinetic energy from low-velocity water flow. In this paper, a staggered arrangement of a four-cylinder oscillator with rigid connections is proposed as the energy converter, and the fluid–solid interaction numerical method is carried out to simulate the VIV of the four-cylinder structure under single-phase flow and free surfaces. In U* = 2–16 (flow velocity U = 0.16–1.28 m/s), the results of the energy harvesting magnitude, efficiency, and density of the four-cylinder oscillator under the arrangement depth ratios S* = 2, S* = 3, S* = 4, and S* = 5 are compared with the results obtained in the single-phase flow. It was found that the column-group structure has a broader resonance range of VIV in single-phase flows than a single cylinder and can capture more hydrokinetic energy concentratedly from low-velocity flow. The VIV responses of the four-cylinder oscillator are suppressed at low submergence depths with a narrower resonance range, and its captured energy is reduced. In contrast, at high submergence depth ratio S*, the VIV responses are not suppressed obviously by the free surface. The magnitude of captured energy, energy-harvesting efficiency, and density of the four-cylinder structure are basically consistent with the results obtained in single-phase flow at S* = 5.

Numerical Analysis of Flow-Induced Vibration of Deep-Hole Plane Steel Gate in Partial Opening Operation

Hydraulic steel gates are the core adjustment mechanism for water conservancy projects, the safety of which is related to the safety of the entire water conservancy project. In this study, the issue of flow-induced vibration under the influence of pulsing water pressure when the deep-hole plane steel gate construction is partially opened is investigated using a numerical calculation approach of CFD–CSD coupling. The time-history pulsating pressure loads of each part are first determined by tracking the upstream, bottom, and downstream pulsating water pressure loads under partially open operation conditions of the gate. The impact of the water in front of the gate on the natural vibration mode and frequency of the gate is then investigated based on the analysis of the dry/wet modes of the gate structure. Additionally, the hydrodynamic load is applied to the finite element model of the gate structure while taking into account the fluid–structure coupling effect, and the results of the gate flow-induced vibration response are obtained. Three typical local opening relative openings are chosen, with the operating state of the design water head (Hs = 70 m) of a deep-hole plane steel gate as an example. According to the analysis’s findings, the gate’s natural vibration frequency is greatly lowered under the influence of the water in front of it, and its amplitude increases by 50%. The pressure value pressing on the gate changes dynamically as it is partially opened and discharged. The maximum dynamic displacement value and the maximum dynamic stress value of the gate both appear in the middle and lower part of the gate under the condition of partial opening, and both occur when the relative opening is e/H = 0.125. The maximum displacement value is 3.43 mm, and the maximum stress value is 161 MPa. The maximum dynamic displacement and dynamic stress of each gate component steadily decrease with an increase in the relative openness. The gate dynamic response analysis approach described in this research can serve as a guide for hydraulic engineering design.

Feasibility study of percussion–acoustic‐based void identification for underwater concrete

Concrete has been widely used in underwater structures. However, accidental voids near the concrete protective layer may weaken the bearing capacity of the structures and can even lead to severe disasters. Therefore, it is necessary to develop an efficient and convenient method for quantitatively identifying voids in concrete and guaranteeing structural safety. A percussion–acoustic method is commonly used to identify voids in concrete exposed to air, owing to its high efficiency and low-cost. Nevertheless, its feasibility for underwater concrete remains questionable, owing to the complexity of the underwater environment. To address this limitation, this study conducted experimental and theoretical studies by using a percussion–acoustic-based method to identify voids in underwater concrete while considering the fluid–structure coupling effect. The results demonstrate that the frequency characteristics of percussive sound pressure underwater are significantly different from those in air and are determined by the void scopes and depths. Accordingly, this study provides a potentially applicable method for evaluating the voids in underwater concrete.

Study on the energy dissipation mechanism of the pyramidal lattice sandwich panel subjected to underwater explosion

The energy dissipation mechanism of a pyramidal lattice sandwich panel subjected to underwater explosion (UNDEX) is studied. Firstly, a three-layer pyramidal lattice sandwich panel with a dimension of 500 mm × 500 mm × 120 mm was fabricated by welding. The deformation mode of the pyramidal lattice sandwich panel subjected to UNDEX is revealed through an experiment. Furthermore, the deformation process of the front and back plates, interlayer sheets, and pyramidal lattices is demonstrated by simulation. The energy absorbed by every component is attained according to simulation results. Finally, the theoretical solution of the dynamic response of the experiment model in the stage of fluid-solid coupling, lattice collapse, and whole deformation is presented. Simulation and theoretical results are consistent with experimental results. Theoretical analysis shows that the advantage of the pyramidal lattice sandwich panel in the resistance to UNDEX is that the fluid-structure coupling effect could be controlled by strength design of the pyramidal lattice. The impulse transmitted to the experiment model could be considerably attenuated to 54.97% of the incident impulse, which is more efficient than the reported literature. This research could support the protection of ship structures subjected to UNDEX.

Stability analysis for laminar separation flutter of an airfoil in the transitional flow regime

Laminar separation flutter (LSF) is a type of aeroelastic instability phenomenon characterized by small-amplitude low-frequency pitching oscillations of the airfoil. The present study aims to gain insight into the intrinsic dynamics of LSF via data-driven stability analysis. The proposed data-driven approach relies on the autoregressive with exogenous input (ARX) technique to design reduced-order models (ROMs) of unsteady aerodynamics in a state-space format. First, high-fidelity full-order numerical simulations of the LSF phenomenon are performed using the incompressible Unsteady Reynolds-Averaged Navier–Stokes equations and the Shear-Stress Transport k−ω turbulence model with Low-Reynolds-number correction. The calculated LSF responses show good agreement with previous experimental data in the literature. Then, linear stability analysis (LSA) of the aeroelastic system is carried out to reveal the underlying fluid-structure interaction mechanism. The LSA model is developed by coupling the ROM with the structure motion equation. LSA results indicate that the LSF phenomenon is primarily caused by the instability of the structure mode (SM), which is induced by the mutual repulsion effect between one static fluid mode (FM) and the SM. The presence of laminar separation near the trailing-edge of the airfoil can significantly reduce the stability of the static FM, which ultimately strengthens the fluid-structure coupling effect and leads to LSF. We would like to emphasize that LSF is essentially different from other flow-induced vibration phenomena, such as transonic buffeting of an airfoil and vortex-induced vibration of bluff bodies, for which the instabilities are triggered by the coupling between one dynamic FM and the SM. Finally, the effects of the mass ratio, structural damping ratio, and freestream turbulence intensity on the aeroelastic system are also investigated.

Application of the deep neural network to predict dynamic responses of stiffened plates subjected to near-field underwater explosion

For quick prediction of nonlinear elastic-plastic responses of stiffened plates subjected to near-field underwater explosion (UNDEX), a machine learning algorithm was adopted, and two deep neural network (DNN) models composed of three hidden layers were trained based on data collected by a detailed finite element (FE) model. Firstly, a DNN model with the charge mass, the stand-off distance, and thicknesses of the plate and stiffeners as input variables was constructed to predict final plastic deformations of the stiffened plate, and influences of the optimizer, activation function, and under fitting and over fitting on the results were discussed. Then, a more complicated DNN model, which adopts the plastic deformations as another input variable and contains more neurons in hidden layers, was constructed to predict non-uniformly distributed effective plastic strain nephograms. Finally, the first DNN model with more neurons was used to predict the nonlinear displacement-time curves of the plate. By comparing with results obtained by LS-DYNA program, it is found that DNN can accurately estimate dynamic responses of the stiffened plate considering fluid-structure coupling effects, geometric and material nonlinearities. More importantly, the DNN models can capture the strain concentration at the boundary and the oscillation of the displacement-time curves.

Sound transmission loss of an inertant metamaterial plate submerged in moving fluids

This article presents the sound transmission loss of an inertant metamaterial plate submerged in moving fluids. The metamaterial plate is constructed by resonators of two-degree-of-freedom and a homogeneous plate. The moving fluids in which the metamaterial plate is submerged, are represented by external mean flow. In the subwavelength scale, the effective medium approach is used to develop explicit formulae for defining the sound transmission loss of the inertant metamaterial plate. The correlation mechanisms between sound insulation and the structural and fluid parameters of the model are as follows: (a) Due to the translational and rotational motions of the attached resonators interacting with the host plate, the metamaterial plate may create two sound transmission loss peaks; (b) the metamaterial plate's inertance design is capable of pushing the sound transmission loss peaks to a lower frequency range. The frequency gap between the two sound transmission loss peaks can be narrowed by moving the spring distances closer to the centroid of the attached mass; (c) the moving fluids have a significant influence on the sound transmission loss due to fluid-structure coupling and aerodynamic damping effect, despite the fact that the external mean flow in the transmitted field has a greater impact on the sound transmission loss than the moving fluids in the incident field.

Study on the Influence of Sudden Change of Water Level on High Fill Canal Segment

Extreme conditions will cause the water level of high fill canal segment to change suddenly, which will affect the velocity and pore pressure of the slope. In this paper, numerical method is used to study the influence of water level sudden change on seepage characteristics of high fill canal segment. HyperMesh software is used to establish the finite element model of typical high fill canal segment under complex foundation conditions. Through the combination of secondary development program and fluid-structure coupling calculation method, the fluid structure cou-pling effect of canal under sudden change of water level is analyzed in ABAQUS. The results show that when the water level changes suddenly, the pore pressure below the free water surface and the velocity near the free surface will be greatly affected.

Development and Optimization of Vehicle Systems for Improved Road Noise and Prediction Using Vehicle System Model in an Autonomous Vehicle Application

<div class="section abstract"><div class="htmlview paragraph">As autonomous vehicles with electric propulsion technology are introduced to the market, the customer expectations may change significantly compared to the conventional ownership models. It is expected that the customers' focus while commuting will shift from driver related to non-driver related tasks and, as a result, more isolation from the environment may be required. Among the many challenges in noise, vibration and harshness (NVH) for an autonomous-electric vehicle, the expectation is that road noise and component noise will require the most amount of development and refinement efforts. As such, a major focus on structure-borne road noise must be considered early in the vehicle development phase to avoid either costly changes late in the program or dissatisfied customers in the market. In order to minimize the amount of structure-borne noise transmission through the body and chassis systems, a vehicle system model for virtual road noise development has been developed at Zoox with close collaboration across vehicle integration, computer-aided engineering (CAE), and tire supplier teams. Vehicle system models for road noise development are generally limited by the tire models used, which are often too simplified and limiting with respect to virtual efforts for system optimization. This paper will review the application of spindle forces and their estimation, an advanced tire-wheel model in a vehicle system model, the proceeding vehicle system analysis, and synthesis of road noise. The tire-wheel model includes the structural dynamic properties of both the tire and wheel with the centrifugal, gyroscopic, fluid-structure coupling and preload effects while the vehicle system model includes vibro-acoustics properties of chassis, powertrain, body and interior systems. A review of other work in the area of road noise excitation methods and application in a vehicle system model will be given, a description of the advanced tire-wheel system model and its application will be introduced, and system optimization will be highlighted. The inclusion of the advanced tire-wheel system model and close collaboration across teams enabled a high level of correlation with experimental tests from 20-400 Hz.</div></div>

PORE-SCALE SIMULATION OF MULTIPHASE FLOW CONSIDERING THERMO-HYDRO-MECHANICAL COUPLING EFFECT IN POROUS MEDIA

Researches on the thermo-hydro-mechanical (THM) coupling effect in porous media from the perspective of pore-scale is of great significance for the study of enhanced oil recovery, nuclear storage, and geological sequestration of CO2. In order to study the migration of oil resources in porous media in the deep oil reservoir, we used a combined method to realize the THM process occurring in porous media. The Darcy-Brinkman-Biot method was applied to simulate the THM process and the calculation of thermal stress was achieved by adding the Duhamel-Neumann thermoelastic stress to the model. A water-oil two-phase flow process considering THM coupling effect in porous media was then realized. The model has simulated flow of multiphase fluid in the pore space by solving the Navier-Stokes equations and calculated flow of the fluid in the rock matrix by solving the Darcy equation. The two processes were coupled with a series of momentum exchange equations to obtain the displacement of solid particles, thus realizing the fluid-solid coupling effect. On this basis, a heat transfer model was added to numerical model to consider the influence of temperature field on the two-phase flow process. Temperature field acts on the matrix in the form of thermoelastic stress to realize the THM coupling process. Based on the model, we simulated the flow process of water-oil two-phase fluid in a two-dimensional porous media model. The results have shown that: (1) the direction of thermal stress was opposite to that generated by fluid-structure coupling effect, which made the total stress smaller than that under the fluid-structure coupling effect; (2) the porosity of the model increased with the increase of temperature, however, when the injection temperature difference reached 150 K, the porosity no longer increased significantly; (3) with the increase of temperature, the relative permeability of the water phase increased and the equal-permeability point shifted to the left.

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.