Search

Recently, the phenomenon of tail-sustained swaying of the 160 km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody's vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

Accidental burst of hydrogen pipeline can generate highly destructive blast wave, highlighting the importance of predicting the blast wave intensity for industrial safety and protection. However, current methods for predicting overpressure fail to consider the coupling effect between the blast wave and dynamic rupture. Therefore, a fluid-structure-rupture coupling model is constructed to address this limitation. The accuracy of the model is verified through a comparison of fracture morphology, crack propagation, and internal pressure decay between the simulation and experimental results. On this basis, the effects of dynamic rupture on blast wave formation and propagation, overpressure decay histories, and peak overpressure are investigated. Results indicate that the traditional CFD method tends to overestimate the peak overpressure in the near field while underestimating it in the middle and far fields. Furthermore, it is discovered that the blast waves from bursts of hydrogen pipelines with different diameters exhibit a consistent decay law under the same burst pressure by defining dimensionless distance and peak overpressure. Accordingly, the dimensionless blast curve is proposed for predicting overpressure from hydrogen pipeline burst with diameters ranging from 250 mm to 1000 mm and burst pressures ranging from 4 MPa to 12 MPa. The results can serve as a reference for the accurate and fast evaluation of blast wave intensity from hydrogen pipeline burst. • The proposed model effectively couples the dynamic rupture and blast wave. • Propagation of blast wave from hydrogen pipeline burst is quantitatively depicted. • Previous methods underestimate the peak overpressure in the middle and far fields. • Blast curve is developed to improve the prediction accuracy of peak overpressure. [ABSTRACT FROM AUTHOR]

With the trend towards larger and lighter designs of wind turbines, blades are progressively being developed to have longer and more flexible configurations. Under standstill conditions, the separated flow induced by a wide range of incident flow angles can cause complex aerodynamic elastic phenomena on blades. However, classical momentum blade element theory methods show limited applicability at high angles of attack, leading to significant inaccuracies in wind turbine performance prediction. In this paper, the geometrically accurate beam theory and high-fidelity CFD method are combined to establish a bidirectional fluid–structure coupling model, which can be used for the prediction of the aeroelastic response of wind turbine blades and the analysis of fluid–structure coupling. Aeroelastic calculations are carried out for a single blade under different working conditions to analyze the influence of turbulence, gravity and other parameters on the aeroelastic response of the blade. The results show that the dominant frequency of the vibration deformation response in the edgewise direction is always the same as the first-order edgewise frequency of the blade when the incoming flow condition is changed. The loading of gravity will make the aeroelastic destabilization of the blade more significant, which indicates that the influence of gravity should be taken into account in the design of the aeroelasticity of the wind turbine. Increasing the turbulence intensity will change the dominant frequency of the vibration response in the edgewise direction, and at the same time, it will be beneficial to the stabilization of the aeroelasticity response. [ABSTRACT FROM AUTHOR]

Currently, cranes used at sea are insufficient in efficiency. Accordingly, a floating multi-robot coordinated towing system is proposed to meet offshore towing needs. However, the towing robot is prone to overturning because of the system's utilization of rope-driven robot flexibility and its floating attributes in fluid environments. First, the kinematics and dynamics of the towing system are analyzed through coordinate transformations and hydrodynamic theory. Subsequently, physical modeling of the towing system is conducted, with an emphasis on analyzing the system's fluid-structure coupling properties, supplemented by illustrative examples. Finally, the stability of the floating robot is assessed based on ship stability theory, encompassing analyses of the rope tension effects, size and shape of the floating base, and external environmental factors influencing system stability. Results show that the special shape of the floating base is beneficial in reducing water resistance and improving the stability of the floating robot in the flow field. The results provide a good basis for the system structural design and application. [ABSTRACT FROM AUTHOR]

The ureteral pain caused by kidney stones has long tormented humans and seriously affected their quality of life. However, currently, in clinical practice, due to the lack of quantitative analysis of the interaction between kidney stones and ureters, urologists are unable to develop precise personalized treatment and pain relief plans for different patients. In response to this issue, small-sized kidney stones were taken as an example and to analyze the interaction behavior between small-sized kidney stones entering the ureteral lumen and the ureter with a fluid-structure coupling finite element method based on the coupled Eulerian-Lagrangian (CEL) algorithm. With the established ureteral pain model, the ureteral pain caused by small-sized kidney stones was quantitatively studied. The finite element analysis results indicate that, when the stone diameter is smaller than the inner diameter of the ureter, the stone will dynamically contact the ureter under peristalsis of the ureter wall, causing dynamic stress on the inner wall of the ureter. The stone moving speed will increase with the peristaltic amplitude of the ureteral wall, but the contacting probability between the stone and the ureter will decrease, and the contacting stress on the ureteral wall will decrease as well. The stress results were input into the ureteral pain model to calculate the corresponding central transmission neuron cell membrane potential. The model results show that, the change in the pain level over time was similar to the trend of dynamic stresses over time. In the case of alternating stress changes, the pain level would not decrease below the pain threshold as the stress drops to 0, showing inconformity between the pain level and the stress level. The results can be combined with existing medical imaging technologies in clinical practices, as well as big data and artificial intelligence technologies in the field of computer science. The research provides a theoretical basis for personalized and accurate diagnosis of the condition of stone patients, quantitative evaluation of patient pain levels, and the development of personalized treatment plans for precise medical clinical strategies. [ABSTRACT FROM AUTHOR]

The coupling relationship between the deformation field, the diffusion field, and the seepage field is an important factor in fluid transport mechanisms in the long-term coalbed methane (CBM) exploitation process. A mathematical model of gas–water two-phase fluid–structure coupling in a double-porosity medium in coal reservoirs is established in this paper. Taking Hancheng Block, a typical production block in Qinshui Basin, as the geological background critical desorption pressure, reservoir permeability anisotropy is considered in the model. COMSOL Multiphysics (COMSOL_6.0) was used to create the model. The accuracy and rationality of the model were verified by comparing field production data with the results of the simulation. Using the simulation, the influence law of various reservoir geological characteristics parameters (Langmuir strain constant, ratio of critical desorption pressure to reservoir pressure of coal seam (CDPRP), elastic modulus, initial water saturation, Langmuir pressure, etc.) on CBM productivity, reservoir pressure, and permeability ratio was discussed, and a thorough analysis of the factors affecting productivity was obtained using the orthogonal test method. The findings of this study indicate that the change in permeability is the result of the superposition effect of many factors. Different stages of drainage have different primary regulating factors. Rock skeleton stress has a consequence on coal matrix permeability in the early drainage stage, and coal matrix shrinkage is primarily impacted in the later drainage stage. Besides the initial water saturation, other reservoir geological parameters (e.g., CDPRP, Langmuir volume, Langmuir strain constant, elastic modulus) have a strong relationship with productivity. When the value of coal geological parameters increases, the degree of productivity release is higher (as the initial water saturation increases, the production decreases correspondingly). Different coal and rock parameters have varying levels of impact on the drainage stage of CBM wells. The influences of the CDPRP, Langmuir volume, Langmuir strain constant, and elastic modulus on gas production are mainly concentrated in the initial and intermediate drainage stages and begin to fall off during the last drainage stage. Per the multi-factor analysis, the main coal–rock parameters affecting the productivity release are the Langmuir strain constant, followed by the CDPRP and other parameters. The analysis findings can offer theoretical guidance for CBM well selection and layer selection and enhance the block's overall CBM development level. The improved productivity prediction model for CBM, which is based on fluid–structure coupling theory, can offer a new technical benchmark for CBM well productivity prediction. [ABSTRACT FROM AUTHOR]

Under the action of the flow field force and the constraint reaction force of the negative rotor and the positive rotor, the twin screw compressor shell will produce vibration, which will affect the life of the parts and produce noise. The rotors restraint reaction force is calculated by fluid-structure coupling method. The shell inherent frequency is solved by modal analysis, and the shell resonance is analyzed during the rotors meshing process. On this basis, the flow field force and rotor constraint reaction force are used as the compressor shell vibration excitation sources, and the vibration response of the compressor shell under the action of excitation force is studied. The research results can provide some reference for the optimized design of compressor shell structure. [ABSTRACT FROM AUTHOR]

Coupled fluid-structure-rupture model was developed to evaluate the blast field from X65 hydrogen pipeline burst. Johnson-Cook material model was implemented considering the high strain rates of material at crack tips. Internal hydrogen decompression, outer blast wave generation and propagation, and dynamic rupture of pipeline were simulated simultaneously and validated with experiments. Results demonstrated that the crack primarily ran axially at an average speed of about 120 m/s, while the maximum speed was about 200 m/s. Due to the dynamic growth of rupture opening, the outer blast wave experienced a process of first form and then strengthened by subsequent compression waves. This makes the maximum peak overpressure along the jetting direction appears at a certain standoff distance above rupture. The blast overpressures along the jetting direction were compared and discussed with those from traditional CFD method, TNT equivalence method and Baker-Tang blast curves. It was found the effective volume to calculate the burst energy needs to be further studied. Also, new blast curves were required for quick and rational estimation of blast overpressure from hydrogen pipeline burst. • Coupled fluid-structure-rupture method offers improvements of hazards assessments. • Flow behavior and dynamic rupture of pipeline were well coupled together. • Maximum peak overpressure appears at a certain standoff distance above rupture. • New blast curves are needed to estimate blast overpressure along jetting direction. [ABSTRACT FROM AUTHOR]

The wings of birds exhibit multi-degree-of-freedom motions during flight. Among them, the flapping folding motion and chordwise passive deformation of the wings are prominent features of large birds in flight, contributing to their exceptional flight capabilities. This article presents a method for the fast and accurate calculation of folding passive torsional flapping wings in the early design stage. The method utilizes the unsteady three-dimensional panel method to solve the aerodynamic force and the linear beam element model to analyze the fluid–structure coupling problem. Performance comparisons of folding flapping wings with different kinematics are conducted, and the effects of various kinematic parameters on folding flapping wings are analyzed. The results indicate that kinematic parameters significantly influence the lift coefficient, thrust coefficient, and propulsion efficiency. Selecting the appropriate kinematic and geometric parameters is crucial for enhancing the efficiency of the folding flapping wing. [ABSTRACT FROM AUTHOR]

Marine risers typically experience nonlinear vibration failure problems caused by the ocean vortex excitation force. To resolve this, the Hamilton variational principle is applied to establish a vortex-induced vibration (VIV) model for a flexible riser. A wake oscillator model is employed to simulate the vortex-induced forces of cross flow (CF) and inline flow (IL) and their coupling, considering the effect of top tension and internal flow on the riser. The VIV model is solved by combining the Newmark–β and Runge–Kutta methods and then verified by comparing the calculation results of the proposed vibration model with data in published literature. Based on the foregoing, the effects of uniform flow, top tension, and shear flow on the VIV behaviour of risers with a large aspect ratio are systematically investigated. Moreover, the VIV characteristics are identified. First, the results demonstrate that, when the top tension is 10 t, the IL vibration is 0.73 Hz and the CF vibration is 0.36 Hz, which shows that the IL vibration is twice as high as the CF vibration. Moreover, the amplitude of the latter is between 7 and 21 times that of the former, which are respectively 0.018 and 0.12 m. Second, the shear velocity and top tension also have considerable influence on the IL vibration under shear flow. Third, the CF vibration has a frequency-locking effect under shear flow and uniform flow conditions. The IL vibration exhibits a frequency-locking effect under uniform flow and a multifrequency effect under shear flow. The study led to the formulation of a theoretical method for safety evaluation and a practical approach for effectively improving the service life of marine risers. [ABSTRACT FROM AUTHOR]

The flutter of the linear compressor valve plate is the main factor that affects the working life and performance of the compressor. Because the flutter of the valve plate will aggravate the fatigue failure of the valve plate and affect the stability of the mass flow through the valve plate. In order to study this problem, this paper uses a three-dimensional fluid-structure interaction (FSI) model to simulate the opening and closing process of the exhaust valve of a linear compressor. This method can effectively predict valve plate flutter and valve plate reflux. Based on the FSI model, the influence of compressor working pressure ratio and piston operating frequency on valve flap vibration period and valve flap return was studied. According to the simulation results, an empirical correlation between the predicted valve plate flutter period and the piston operating frequency is obtained. [ABSTRACT FROM AUTHOR]

In this study, a developed co-simulation method, which couples 1D-fluid and 3D-structural models, has been utilised to simulate wear in a hydraulic percussion unit. The effect of wear is generally detrimental on performance and lifetime for such units, but can also cause catastrophic failure and breakdown, requiring a total overhaul and replacement of core components. One experiment of standard straight impact was performed to investigate the tolerance against seizure. The percussion unit was operated at successively increasing operating pressures, and the level of wear was registered at each step, until seizure occurred. The co-simulation model was used to replicate the running conditions from the experiment to simulate the structural response to be used as input for the wear routine to calculate the wear depth. The wear pattern from the simulations corresponds well to the wear pattern from the experiment. Further, the effect of a misaligned impact on wear development was also studied, as this is a loading situation that typically occurs for hydraulic percussion units. The study demonstrates that the simulation method used has a potential for simulating wear and predicting seizure in hydraulic percussion units. [ABSTRACT FROM AUTHOR]

Transient processes that occur in pumped storage power plants can cause high-pressure conditions, which in turn can result in vibrations in the pump–turbine structure and even damage to structural components. It is therefore crucial to research the transient process of the large pump–turbine units and the flow-induced vibrations of the structural components. The three-dimensional flow field and structural field models of a high-head prototype pump–turbine were constructed to study its flow characteristics and structural characteristics under the turbine start-up. Calculations and analyses were performed on the pressure variation and the flow-induced stress concentrations of the pump–turbine during start-up in turbine mode. The simulated pressure distributions during the turbine start-up were mapped onto the finite element calculation model of the structures of the pump–turbine to calculate the flow-induced stress concentrations. This study provides a reference to improve the design and operation of high-head prototype pump–turbines based on the findings of the flow and structural characteristics. [ABSTRACT FROM AUTHOR]

• Proposition of a symmetrization method based on fixed interface transformation for coupled fluid-structure problems. • Physical interpretation of the critical parameter in Felippa's symmetric formulation. • Definition of a modal criterion developed from modal parameters to ensure the response accuracy of reduced model. • A general reduction strategy for coupled fluid-structure models based on symmetric formulation and double modal synthesis. This paper presents a symmetric formulation combined with component mode synthesis to analyze coupled fluid-structure problems. First, the symmetric formulations for coupled fluid-structure problems are revised. Then, based on these reviews, a symmetrization method based on fixed interface transformation and substructuring method is proposed. Afterwards, one of Felippa's formulations has been subsequently re-established by applying the proposed transformation matrix. In addition, the modal amplitude of branch modes has been proposed as a mode truncation criterion with regard to the forced response calculation of reduced models. Finally, the proposed symmetric formulation combined with component mode synthesis has been applied to a coupled fluid-structure problem to analyze the coupled vibration characteristics, the simulation results of which have shown the efficiency of the proposed strategy. [ABSTRACT FROM AUTHOR]

Peridynamics provides a new model and method for describing material failure and fracture development. In this study, a three‐dimensional peridynamic fluid–solid coupling model of hydraulic fracture propagation was established. The model considered the effective stress and transverse isotropic characteristics of shale and was used to simulate the propagation of the hydraulic fracturing of bedding shale. The damage evolution influence on the fracture propagation behavior, as well as the interactions between the fractures and bedding, were investigated through a simulation. The damage evolution had discontinuous characteristics. In addition to the incomplete damage zone adjacent to the complete damage zone, there were nonadjacent and incomplete damage zones. The fracture and propagation of hydraulic fractures followed the same trends of damage evolution. Moreover, the simulation and related experimental results confirmed the existence of a large amount of mesodamage in the region far from the fracture, and the concept of "remote damage" in hydraulic fracturing was proposed. Finally, the damage evolution of the propagating fractures and bedding was simulated. The simulation showed that bedding hinders the propagation of main fractures in the height direction but promotes the complexity of fracture propagation. Overall, this study provides a new theoretical understanding and research ideas for an in‐depth understanding of hydraulic fracture geometry and the accurate calculation of Stimulated Reservoir Volume. [ABSTRACT FROM AUTHOR]

After increasing the train speed, the wheel-rail coupling effect is intensified, as is the coupling effect between the train and the surrounding air, which causes the severe vibration of the train. Considering this problem and taking the high-speed train as the object of this study, a method for the coupling of aerodynamics and vehicle dynamics is proposed. Its validity is then demonstrated by the results of field tests and moving model experiments. On this basis, the fluid–structure coupling characteristics of a high-speed train passing through a tunnel are studied, as well as the effects of different coupling methods and track irregularities. The obtained results demonstrate that the interaction between the tail car and the surrounding air is significant. In the tunnel and at its exit, the lift and the car body acceleration significantly change, especially when the coupling of aerodynamics and vehicle dynamics, as well as the vertical and lateral track irregularities, are simultaneously imposed. When the head car travels out of the tunnel, the lift of the middle and tail cars both dramatically will change. It is deduced that the fluid–structure interaction has a significant effect on the swing phenomenon of the tail car. This phenomenon is the result of the combined effects of aerodynamics and track irregularities. The different frequencies of the lateral displacement for each car body, except the frequencies of the car bodies themselves, are mainly determined by vertical track irregularities. [ABSTRACT FROM AUTHOR]

In the construction of water-rich tunnels, the curtain grouting method is often used to reinforce the surrounding rock for water blocking. Therefore, the displacement and stress fields of the surrounding rock of the tunnel after being reinforced by the curtain grouting method for a deep buried tunnel with rich water should be accurately described. Based on the theory of fluid-solid coupling, a mechanical model of the tunnel curtain grouting is established, and the displacement and effective stress of the surrounding rock are deduced. Then, with a deep-buried tunnel on the Dali-Ruili Railway as the engineering background, six reinforcement schemes are calculated using the established mechanical model, and the influence of the shear modulus and elastic coefficient of the surrounding rock on the field change of displacement and stress are discussed. The accuracy of the mechanical model is verified by comparing with the results of numerical simulation and field monitoring. The research results show that the mechanical model can be used to calculate the displacement and effective stress of the surrounding rock of the tunnel constructed by the curtain grouting method; the larger shear modulus and elastic coefficient can restrain the displacement of the surrounding rock, but will increase the radial and circumferential directions of the surrounding rock effective stress. [ABSTRACT FROM AUTHOR]

Summary: 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. [ABSTRACT FROM AUTHOR]

This study conducts a numerical simulation investigation on the flow field characteristics and fluid-elastic instability of the spatially bent tube structure in the intermediate heat exchanger (IHX) of a fast reactor. The inherent frequencies of the unique structure of the IHX spatially bent tube are calculated by using the wet modal method. They are employing Computational Fluid Dynamics (CFD) in conjunction with a fluid-structure coupling model, establishing an elastic tube model. Considering the bundle concentric circles arrangement, the "transition" arrangement is selected as the model to simulate the fluid-elastic instability. By the analysis of critical flow velocity, displacement, and the main vibration direction, the results indicate that the fluid-elastic instability of the tube bundle with a transition arrangement is mainly manifested by more severe vibrations in the bent tube segment. The instability flow velocity in the straight tube segment, ranging from 4.64 to 4.84 m/s, is greater than the instability flow velocity of 2.85 m/s in the bent tube segment. This study provides theoretical support for the design and operation of the intermediate heat exchanger in fast reactors, offering references for considering tube bundle arrangement and fluid-elastic instability in engineering practice. [ABSTRACT FROM AUTHOR]

Supersonic parachute plays a crucial role in Mars exploration missions. The disk-gap-band (DGB) parachute he been used in all the successful Mars exploration missions. The parachute is fabricated from different porous fabric materials, and the fabric permeability is an important design and performance parameter, now it has been proved that the fabric permeability of porous canopy has important effects on the complicated flow fields around the parachute and in turn effects the nonlinear deformation and aerodynamic performances of the flexible canopy. However, till now, the influence mechanism of fabric permeability on the fluid-structure interaction mechanism and aerodynamic performance of supersonic flexible porous parachute in the inflation process still remain unknown. Therefore, in this study, a fluid-structure coupling method was used to numerically simulate the inflation process of disk-gap-band parachute with different fabric permeability (i.e., different fabric materials), and the effect of fabric permeability on the aerodynamic performance of disk-gap-band parachute was also analyzed. The results showed that the fabric permeability has a significant effect on the inflation process of DGB parachute with different fabric materials. During the inflation process, the oscillation angle and drag coefficients of the parachute both gradually decreased with the increase of fabric permeability, while the stability performance of the parachute became more complicated. Furthermore, it was also found that the influence of fabric permeability was different under subsonic and supersonic conditions. The K5836-3 fabric used as canopy material has better stability under subsonic conditions, and the 42105 fabric material has the best stability under supersonic conditions. [ABSTRACT FROM AUTHOR]

Pipes can be subjected to external transient impacts such as accidental collision, which affects the safe operation of storage and transportation systems for liquid hydrogen. Fluid–structure coupling calculation for a pipe under external transient impact is performed, and the flow characteristics of liquid hydrogen in the pipe are analyzed. The pipe deforms and vibrates when suffering from external transient impact. Liquid hydrogen pressure in a cross-section plane increases along the pipe deformation direction. Additionally, external transient impact enhances the disturbance of liquid hydrogen near the pipe wall. The increased flow resistance and the energy induced by the deformed pipe both affect the flow of liquid hydrogen, and contribute to the fluctuated characteristics of liquid pressure drop. In addition, the phase state of liquid hydrogen remains unchanged in the pipe, indicating that little of the induced energy is transformed into the internal energy of liquid hydrogen. The work provides theoretical guidance for the safe operation of liquid hydrogen storage and transportation systems. [ABSTRACT FROM AUTHOR]

Diffuser is a key component of aero-engine compressor, which has an important impact on its performance, efficiency and operating conditions. In order to solve the problem of poor rigidity and easy deformation of insulating sleeve structure in the process of electrochemical trepanning, the optimization method of insulating sleeve rigidity is proposed, strengthening rib is designed at the free end of insulating sleeve, and the fluid structure coupling simulation comparative study under different strengthening rib shapes and sizes is carried out. When the two ends of strengthening rib are round, the width b = 2 mm and the distance from the bottom h = 6 mm, the maximum deformation is reduced by 88.3% compared with the structure without strengthening rib. The experimental research of electrolytic machining is carried out. The stable machining with cathode feed rate of 1.4 mm/min is realized, and the machining stability and efficiency are significantly improved. The effectiveness of the rigidity optimization method of insulating sleeve is verified. [ABSTRACT FROM AUTHOR]

During the load rejection transient process of the prototype pump turbine units, the pressure fluctuations of the entire flow passage change drastically due to the rapid closing of guide vanes. The extremely unsteady pressure distribution in the flow domains including the crown chamber and the band chamber may cause a strong vibration on the stationary structures of the unit and result in large dynamic stress on the head cover, stay ring and bottom ring. In this paper, the numerical fluid dynamic analysis of the entire flow passage of a reversible prototype pump turbine during load rejection was performed. The flow characteristics in the runner passage, crown chamber, band chamber, seal labyrinths and balance tubes are analysed. The corresponding unsteady flow-induced dynamic behaviour of the head cover, stay vanes and bottom ring was investigated in detail. The analysed results show that the total deformation of the inner edge of the head cover closed to the main shaft is larger than that of other stationary structures of the unit during the load rejection. The maximum stress of the stay ring is larger than that of the head cover and the bottom ring and the maximum equivalent stress is located at the fillet of the stay vane trailing edge. The fluid–structure coupling calculation method and the analysed results can provide guidance for the design of stationary components of hydraulic machinery such as pump turbines, Francis turbines and centrifugal pumps with different heads. [ABSTRACT FROM AUTHOR]

In this paper, through finite difference and finite element coupling algorithms with structured grid, the fluid–structure coupling problems of the pressure of the fluid as well as stress and strain of the heterogeneous porous medium under the initial pressure of MPa magnitude are calculated, respectively. The porous medium is a cavity cylinder with fractal characteristics. The parameters of porosity, elastic modulus and Poisson's ratio of porous media with different fractal dimensions (D = 2. 3 , 2.4 and 2.5) are obtained by theoretical calculation. Through theoretical derivation, the amplitude of WM function is expressed by the fractal parameter porosity, which can predict the uneven characteristics caused by the nonuniformity of pore size distribution after explosion. The results show that with the increase of fractal dimensions, the porosity increases, and both the elastic modulus and the Poisson's ratio decrease. The Poisson's ratio has a linear relationship with porosity, which is well consistent with the modified formula in the literature. Under the same initial pressure, the stress and strain values of the material without fractal characteristics are much larger than those of the material with fractal feature which has an obvious fluctuation by extracting the average values. It indicates that the fractal porous media with rough surface can effectively reduce the pressure wave peak at the wall surface, and reduce the size of the stress and strain concentrations to prevent the vibration of the cylinder. As expected, if the initial pressure increases with an equal fractal dimension, the stress and strain values of the fluid–structure coupling will increase too. When the initial pressure is equal, the peak value of pressure in wall decreases gradually with the increase of fractal dimension, and the stress and strain values also decrease. [ABSTRACT FROM AUTHOR]

To satisfy the growing electricity demand, continuous and stable hydropower conversion is particularly critical in tidal power station operation. In the above industrial application, multiphase vortices will be formed, and they suck air and floating items into the flow tube, thus causing irregular pulsation that affects turbine performance. Due to nonlinear characteristics of gas-liquid coupling transfer, dynamic modeling and transition behavior of the multiphase vortex-induced vibration have improtant difficulties. This paper conducts a fluid-structure mechanic optimization model with the dynamic mesh technology to investigate multiphase vortex-induced vibration (MVIV) dynamic behaviors and reveal the internal relation between displacement responses and multiphase flow states. The fluid-induced vibration sensing platform is developed to validate MVIV transition behaviors, and a wavelet packet signal analyzing approach is adopted to acquire energy-spectrum distribution regularities of the vibration distortion state. Results show that the presented optimization modelling strategy can well obtain the MVIV transition behaviors and energy transfer mechanism. The flow flux can control the Ekman transfer intensity, and vibration energy waves take on various frequency components at the critical penetration state. Moreover, impulse energy components and structure evolution properties of high-frequency bands can be utilized to recognize the MVIV distortion peak. It can supply theoretical guidance and technology support for hydropower conversion. • A fluid-structure mechanic optimization modelling and solution method is presented. • The MVIV dynamic behaviors at the critical penetration states are revealed. • Energy distribution regularities are obtained by the wavelet packet analyzing approach. [ABSTRACT FROM AUTHOR]

Two-phase flow is typically found in several industrial applications, such as in the production and transportation of oil and gas in the petrochemical industry, in the catalytic cracking and microreactors in the chemical industry, and in nuclear reactor cooling pumps. Measurement of two-phase flow features is usually necessary and has been done in several ways, including pressure probes, resistive sensors, gamma-ray, wire-mesh sensor and many others. However, these are either intrusive or invasive techniques, which might be of challenging application in industrial environments, or rely on a hazardous radioactive source. Vibration-based measurement of two-phase flow in pipes stands out as a non-invasive/non-intrusive approach and, consequently, multiphase-flow induced vibration in pipes has receiving increasing attention in recent years. In this work, the dynamic behaviour of a horizontal tube conveying an intermittent two-phase gas-liquid flow is investigated based on indirect approaches. The phenomenon of fluid–structure coupling is investigated using acceleration and pressure measurement. Moreover, the bubble size distribution is estimated from high-speed camera images and a deep learning model for image segmentation, along with its spectral content and time modulation. Focus is given at frequency bands around the cut-on frequencies of the circumferential wave modes of the pipe. An approach based on the estimation of frequency response function of the pressure and vibration at the liquid slug and elongated bubble is proposed, such that the coherence function can be used as quantitative measure of the coupling. Two experimental conditions with intermittent flow are investigated as representative cases. It is shown that there is a great vibration amplification at the cut-on frequencies of circumferential wave modes in pipes due to the corresponding structural wave and pressure coupling. Consequently, the frequency of passage of bubble can be estimated from the demodulation of vibration response filtered at the cut-on modes. The experimental results pave the way for innovative vibration-based measurement approaches. [Display omitted] • Vibration is induced at higher frequencies by two-phase fluid slug flow. • Circumferential pipe wave modes couple with fluid acoustic modes. • Bubble size distribution produces a broadband frequency sound excitation. • Vibration measurements can be used to extract void fraction features. [ABSTRACT FROM AUTHOR]

The gas-liquid coupled vortex flow (GCVF), as a complex physical phenomenon, has been encountered in some sustainable productions, such as chemical cleaner production, continuous steel pouring processes, and energy conversion in the tidal power plant. Its critical penetrating state recognition is essential to improve sustainable production efficiency and equipment lifetime. Due to the gas-liquid coupling transport and fluid nonlinear excitation, the state recognition oriented to the GCVF critical penetrating still faces significant challenges. To address the above matter, a fluid-structure coupling modeling and solution method based on the level set and residue theorems is put forward to obtain the GCVF-induced vibration evolution mechanism at the critical penetrating state. A wavelet packet-based signal processing method is proposed to obtain the evolution law of the peak component of the GCVF-induced vibration. Research results found that the proposed modeling and method can better reveal the GCVF dynamic evolution regularities in the critical penetrating state. The GCVF-induced vibration exhibits energy peak and complex nonlinear pulse characteristics in the critical penetrating process. The relevant research work can provide multi-source sensing data support for the research and development of a fluid-induced vibration detection system, laying the foundation for sustainable metallurgy production, chemical cleaner extraction, and hydroelectric energy conversion. • A fluid-structure mechanic model is built to reveal critical penetrating evolution mechanism. • A displacement response solution method is presented to acquire the GCVF vibration laws. • A wavelet packet processing method is proposed to discuss penetrating energy attributes. [ABSTRACT FROM AUTHOR]

In order to study the natural vibration characteristics and vibration modes of different types of gates under the fluidstructure coupling effect with different openings, the plane escape gate and a radial gate in spillway tunnel are taken as the research objects, the finite element analysis software ANSYS is used to establish the modal and carry out modal analysis. The results show that due to the influence of additional mass, the natural frequencies of the plane gate and the radial gate decrease compared with the waterless condition and gradually increase with the gate opening process, but change oppositely with the modal order; the low-order frequencies of the radial gate are closer to the main frequency of the flow fluctuation resulting in high probability of resonance compared with that of the plane gate; the upper and lower structures of plane gate are easy to obviously vibrate while the lower structures and the arms of radial gate are easy to obviously vibrate. [ABSTRACT FROM AUTHOR]

Fluid‐structure coupling is the main cause for the vibration of fluid‐conveying pipelines, and fluid‐solid coupling vibration of fluid‐conveying pipelines is a "typical dynamic problem." The present paper analyzes the dynamic characteristics and dynamic response of the elbow with simultaneous dual‐thread analysis, aiming to clarify the dynamic change law of pipe vibration induced by gas‐liquid two‐phase flow in the elbow. It can be concluded that the characteristics of the slug flow developed from the interphase instability mechanism have been captured in the volume of fluid (VOF) method. The dynamic evolution information of different two‐phase flow patterns is often accompanied by complex self‐similarity, but has different complex structures, chaotic characteristics, and dynamic behaviors. The unique modal frequencies of each order are applied to the elbow to obtain different exclusive mode shapes. The evolution of the flow pattern is related to the increase in the wave height, and the wave amplitude often depends on the gas‐liquid superficial velocity. The superficial liquid velocity is more sensitive to the influence of flow pattern formation and vibration than that of gas. [ABSTRACT FROM AUTHOR]

The nonlinear dynamics of the drilling string system is studied, and the fluid-structure coupling dynamic equation of the drilling string system is established. With the Galerkin truncation method, a set of partial differential equations are diverted into ordinary differential equations. Numerical simulation is carried out by using the Runge-Kutta integration method and the effects of parameters such as pulsating frequency, pulsation amplitude and mass ratio on the dynamic characteristics of the drilling string system are investigated. The results show that there are various dynamic behaviors for the model in different parametric excitation such as periodic motion, quasiperiodic motion, chaotic motion and jump discontinuous phenomenon. Besides, the path from chaotic motion to periodic motion is in the form of period-doubling inverse bifurcation, and the support stiffness can cause a certain change in the inherent characteristics of the system, which has a complex impact on the nonlinear dynamic behavior of the system. [ABSTRACT FROM AUTHOR]

Prestressed concrete cylinder pipe (PCCP) is widely used in hydraulic engineering. The bell‐and‐spigot joint is a weak point along a PCCP pipeline, since damage of joint can affect the operation of the whole pipeline. In this paper, a three‐dimensional numerical model of buried PCCP, considering the simulation of rubber gasket in bell‐and‐spigot joint is established. The fluid–structure coupling of PCCP is accomplished using the Mesh‐based parallel Code Coupling Interface (MpCCI), where the pipe and the surrounding soil are characterized in the software ABAQUS, and the pressurized water is modeled in the software FLUENT. The force and rotation angle at joints of PCCP under different conditions, including surcharge load, loading location, cover depth, and internal pressure, are analyzed. It is shown that the rotation angle of joint exceeds the allowable value, when the surcharge load is greater than 180 kPa. Compared with the effect of surcharge load, the offset distance (i.e., distance between the loading position and the pipe axis) has a greater influence on the development of horizontal displacement and rotation angle. As the offset distance increases, both the horizontal displacement and rotation angle at joints increase first, and they decrease after the peak. [ABSTRACT FROM AUTHOR]

Assisted airflow can cause the deformation of canopy leaf for the wide transport channel of droplets in the air-assisted spray. The uniformity of droplet deposition can be enhanced in the crop canopy. In this study, a mathematical model of cotton leaf deformation was established under the action of assisted airflow using fluid-structure coupling and parameter identification. Firstly, the petiole and leaf surface samples of cotton were collected to obtain the size parameters. A three-point bending was selected to calculate the elastic modulus of petiole and leaf surface. The moisture content of the petiole and leaf surface was measured during drying at 105 ℃. The results showed that the median elastic modulus of leaf surface was 46.5 MPa, where 95% confidence interval was [28.5, 64.5] MPa, whereas the median elastic modulus of petiole was 244.6 MPa, where 95% confidence interval was [215.5, 273.69] MPa, while the average moisture content of petiole was 87.2%, where 95% confidence interval was [82.5%, 91.9%], and the average moisture content of leaf surface was 80.7%, where 95% confidence interval was [72.3%, 89.1%]. Then, a bidirectional fluid-structure coupling model was established to characterize the deformation process of cotton leaf. The deflection data were obtained in four monitoring points, including the middle and end of the petiole, as well as the center and tip of leaf surface. A high-speed camera was used to carry out the deformation test of cotton leaf with assisted airflow. The deflection test data of monitoring points were captured to verify the coupling model with the maximum simulation error of 9.9%. Furthermore, an orthogonal test was performed on experimental factors, including the assisted airflow speed, leaf inclination angle, elastic moduli of petiole and leaf. A significant order of experimental factors was obtained: wind speed, elastic modulus, leaf inclination angle. Finally, a mathematical model of cotton leaf deformation was constructed using the nonlinear least square. A trust-region iterative was used to obtain the identification parameters. A systematic evaluation was made on the performance of the mathematical model for cotton leaf deformation. The mean absolute percentage error (MAPE) of petiole deflection was 5.13%, and the MAPE of main vein deflection was 10.43%. It was found that the bending deformation of cotton leaf mainly occurred at the junction of petiole and leaf surface in the assisted airflow, where the leaf surface basically kept flat with the relatively small curvature. A quantitative analysis was made to obtain the initial parameters of blade inclination and dynamic variation in the frontal area of cotton leaf at different airflow speeds. The frontal area of cotton leaf decreased monotonously with the increase of airflow speed, when the inclination angles of cotton leaf were 0° and 10°. At the inclination angles of 20° and 30°, the frontal area of cotton leaf increased first and then decreased as the airflow speed increased. It infers that the canopy density can increase under the inappropriate assisted airflow. This finding can provide a sound reference to understanding the dynamic changes of cotton canopy density, further optimizing spraying parameters in the air-assisted spray [ABSTRACT FROM AUTHOR]

To meet the stringent size and noise requirements for hydraulic pumps used in submarines, an embedded tri-screw pump is proposed. The pump is embedded in the core of the servo motor to form a new servo motor pump. This paper first presents the embedded triscrew pump, as well as the cross-section profile design and parameter equations of the driving and driven screws. Velocity and pressure field distributions as well as changes in internal pressure and shear stress inside the embedded tri-screw pump with different radial and interlobe clearances were investigated using computational fluid dynamics. Furthermore, screw deformation under multi-field coupling was analyzed. In contrast to torque or fluid pressure acting alone, under the fluid-solid coupling effect, screw deformation and stresses are inversely proportional to the rotational speed of the pump and directly proportional to the power and output pressure. The simulation and experimental results were consistent for various outlet pressures and rotational speeds. Radial clearance of the screw has a more significant influence on leakage than inter-lobe clearance and therefore, more impact on the volumetric efficiency of the pump. [ABSTRACT FROM AUTHOR]

The reciprocating piston seals are crucial parts in the hydraulic system, which are widely used in aerospace and military industry. A direct fluid–structure coupling method with high efficiency is proposed for solving the transient elaso-hydrodynamic-lubrication problem in the hydropneumatic suspension reciprocating piston seal system. A detailed three-dimensional fluid–structure coupling model is built using finite element discretization. Material tests are carried out to obtain the parameters of the third-order Ogden constitutive model of the rubber O-ring. The sealing performance and friction force of the sealing system are analysed for different piston speed. The critical speed from mixed lubrication to full-film lubrication is obtained. Three different micro-asperity geometries on cylinder surface are researched for their influence on piston sealing and lubrication performance. [ABSTRACT FROM AUTHOR]

Based on the 2D fluid-structure coupling theory, the wind-induced vibration responses of transmission lines across 2 close hills were calculated. Both the load on the wire by the mountain wind and the surface wind pressure change caused by wire vibration with its influence on the flow field were considered. Firstly, the correctness of the method was verified in comparison with the existing literature results. Then, the numerical wind tunnel model for the transmission line across 2 close hills was established. The average wind speed characteristics of the canyon and mountain pass topography as well as the distribution characteristics of the corresponding wind pressure were analyzed. The distributions of aerodynamic coefficients and vertical displacements were analyzed. The numerical results show that, in the transient wind field, the acceleration effect of the mountain pass is more significant than that of the canyon, and the acceleration ratio at the middle of the line is more important. The distribution of wind pressure around the wire is also inconsistent due to the influence of different topographic wind fields. Under the canyon topography, the distribution of wind pressure around the wire is stable with time. Under the mountain pass topography, the wind pressure around the wire fluctuates with time. The smaller the distance between the 2 hills is, the greater the variation range of the resistance coefficient time history curve will be, so is the change of wind pressure. The updraft under the mountain pass topography makes the wire subject to greater lifting force and vertical wind deviation. [ABSTRACT FROM AUTHOR]

In order to reduce the weight and improve aerodynamic characteristics, the new aircraft generally adopts lightweight composite materials and high-aspect-ratio layout. Such the structural layout aircraft will produce large nonlinear aeroelastic deformation under the action of aerodynamic loads. Due to the anisotropy of the composite, the composite ply angle of wing skin has a great influence on the elastic deformation of the high-aspect-ratio wing. In order to study the influence of the ply angle on the nonlinear static aeroelastic wing deformation, based on CFD/CSD unidirectional fluid-solid coupling, the structural deformation and stress of high-aspect-ratio composite wing were numerically solved. The wing deformation along the lift direction was taken as the optimization target. The structure strength was taken as the constraint. The ply angle for the composite skin of the high-aspect-ratio composite wing was optimized by the Screening method. The optimization results show the nonlinear static aeroelastic deformation of the wing in the lift direction is reduced by 39.1%. The maximum stress of the wing beam and rib is reduced by 39.0%. The maximum Tsai-Wu failure factor of the wing skin is reduced by 47.1%. [ABSTRACT FROM AUTHOR]

Vibration in pipeline system is a usual occurrence in industrial equipments. A transient fluid-structure coupling method, with data exchange between fluid and structure, is used in this paper to study the pipeline self-excited vibration under the interaction between pipe structure and internal airflow. The coupling method is based on large eddy simulation and dynamic mesh. Structured grids are used to make the displacements of grid nodes accurately calculated at each time step. The results of transient calculation show that when there is no external excitation and the given inlet mass flow rate is constant, the vibration and the pressure fluctuation of pipeline will occur, and the frequencies are close to the natural frequencies of structure and the acoustic frequencies. Furthermore, the higher the pressure inside the pipeline, the more intense the vibration and pressure fluctuation of the pipeline. By comparison of the experimental and numerical results, it is suggested that the calculation results of fluid-structure coupling are consistent with the practical situation, which indicates that the coupling method is effective and reasonable, and may be used in engineering practice. [ABSTRACT FROM AUTHOR]

An elaborate numerical model with progressive damage and failure and fluid-structure coupling was developed to study the crack propagations of tubes under hydrogen static and detonation loads. The numerical model was verified with experiment in terms of crack behaviors and fracture patterns. The tube responses, crack propagations, pressure histories, crack lengths and speeds as well as the energy storages were obtained and analyzed in detailed. It was found the static load case has higher stored energy inside the tube, which causes the larger crack length and speed, as well as the severer bending deformation of tube. The forward crack first run faster under detonation load, but it will be caught up by the backward crack in the late period. The crack growths are incremental under both types of loads. However, the crack growth under detonation load has certain regular patterns, where the oscillating crack speed has a dominant frequency that can be calculated by the proposed formula. Moreover, the quantitative relationship between detonation load speed and the incremental crack growth length was revealed, which is fundamentally and practically useful. • Crack propagations under hydrogen static and detonation loads are compared. • Incremental crack growth under detonation load has a regular pattern. • Static load case has higher stored energy and symmetrical crack behaviors. • Relation of detonation load speed and incremental crack growth length is revealed. [ABSTRACT FROM AUTHOR]

With a validated fluid-structure-fracture coupling approach, this paper studied the dynamic response and crack propagation of pre-flawed square tube under internal hydrogen-oxygen detonation. Fracture of tube was judged by a bivariate failure criterion derived from the underlying failure mechanism at high strain rate conditions. A programed burn approach based on the CJ theory was applied to simulate gaseous detonation. The coupling between detonation wave and tube was realized by penalty contact algorithm with an improved contact stiffness calculation formula. It was demonstrated that the peak pressure at tube edge is 29% higher than that at the middle of tube face. The dominant crack driving force comes from the specific vibration and deformation modes of square tube, where the deformed round section of tube corresponds to the maximum stress wave that travels behind the flexural waves on the tube. Above mechanism makes the backward cracks branch or turn before the forward cracks and the speeds of front and back branch cracks comparable to each other, which is opposite or different from the cases of round tubes. The crack behaviors with different initial flaw locations and detonation pressures were summarized and identified in detail. The forward crack speed can be up to 900 m/s, while the backward crack speeds are generally 65%–85% of above and the branch cracks run at about 100 m/s. In addition, the crack speed has a certain increase immediately after crack branching or turning. Among the three initial flaw location cases, the tube with initial flaw at the middle of face is most resistant to crack propagation under internal detonations. • The coupled fluid-structure-fracture approach captures crack extension effectively. • The deformed round section of square tube corresponds to the max. stress wave. • Backward cracks branch or turn before forward cracks for square tubes. • Crack speed has a certain increase immediately after crack branching or turning. • Tube with initial flaw at middle of face has strongest resistance against fracture. [ABSTRACT FROM AUTHOR]

Highlights • Experimental validation of a co-simulation approach for hydraulic percussion units has successfully been conducted. • Very good correlation to the experimental data was found. • Elastic bodies were successfully used for a correct representation of the stress wave propagation in the structural components. • A parameter study confirms that a correct response is obtained from a parameter change in the simulation model. Abstract In this study, a previously developed co-simulation approach has been adopted to simulate the responses of an existing hydraulic hammer product. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of the hydraulic hammer. The simulation model was validated against four experiments with different running conditions. The corresponding set-ups were analysed using the co-simulation method in order to evaluate the overall responses. A parameter study was also performed involving the working pressure and the restrictor diameter, with the objective to validate that a parameter change in the simulation model will affect the input and output power in the same direction as in the experiments. The experimental responses used in the validation were time history data of fluid pressure, component position and acceleration, and structural stresses. The experiments result in high frequency and high amplitude excitations of the hydraulic hammer and thus require a model with a high resolution of the model dynamics. The conclusion of the validation is that the simulation model is able to replicate the experimental responses with high accuracy including the high frequency dynamics. The favourable outcome of the validation makes the described co-simulation approach promising as an efficient tool for a wide range of other applications where short time duration mechanisms need to be studied. [ABSTRACT FROM AUTHOR]

Abstract In the design of the scale reduced model of the new generation reusable re-entry capsule, the supersonic stabilizing parachute should be applied to avoid the failure of the main parachute due to the uncertainty of the space capsule's attitude. Compared with the inflation technology during the subsonic process, special attention should be paid to the aerodynamic heating loads during the inflation process at supersonic speeds. In this manuscript, the inflation process of the supersonic stabilizing parachute is numerically studied by adopting the fluid–structure coupling method. The three-dimensional compressible Reynolds Averaged Navier–Stokes (RANS) equations are simulated and Menter's shear stress transport (SST) turbulence model is applied. Also, we study the aerodynamic heating loads of the stabilizing parachute by conducting numerical simulations at a typical reentry trajectory point. Results suggest that the wake of the capsule increases the temperature of the flow field remarkably. Also, the inner faces of the parachute encounter severer heating loads than the outer faces, and the severest heating load appears at the first horizontal parachute belt. [ABSTRACT FROM AUTHOR]

The swirling motion of blood flow is a widespread physiological flow phenomenon in the human body. The probability of cardiovascular and cerebrovascular diseases could be effectively reduced by swirling blood flow. In this study, first we proposed a new integrated vascular model with spiral folds on the inner wall. Based on the model, fluid-solid coupling simulation analyses of blood and blood vessels were performed. The results indicate that the spiral folds cause the swirling flow. This model provides new insights that may be of use for developing methods to generate swirling flow. Second, we discussed the specific effects of different fold parameters' characteristics on swirling flow. We found that increasing the pitch or cross-sectional area enhanced the swirling flow, specifically increasing cross-sectional diameter by 0.2 mm, wall shear stress by about 2 mm Hg, and deformation by about 0.2 µm. Finally, we proposed a new method to prepare an integrated artificial blood vessel based on the heteromorphic channel co-extrusion method; the inner wall of this blood vessel had a spiral fold structure and was micron scale in width. This study offers important guidance for the design of interventional treatments involving swirling flow. [ABSTRACT FROM AUTHOR]

A fast mesh deformation method for propeller flow is developed based on the elastic solid method. The flow field of a propeller is assumed to be fulfilled with a kind of pseudo elastic solid which does not influence the flow. The vibration equation for the propeller blade-pseudo elastic solid system is derived. During fluid-structure coupling, the nodal displacement for the blade and the flow mesh is computed by modal superposition of the first several modes. Fluid-structure coupling is performed for a highly skewed propeller. The computing time for the dynamic mesh by the present method is about 0.017% of the computing time by the existing elastic solid method. The computing time for the fluid-structure coupling using the present method is 52% less than the computing time by the existing elastic solid method. [ABSTRACT FROM AUTHOR]

The aeroelasticity (especially the aerothermoelasticity) of the high-speed aircraft is raising more and more attention in recent years. First of all, this paper summarizes the recent progress of the aeroelasticity problems according to different numerical methodologies. Then, based on the problems emerging in engineering practice, the thermal aeroelastic problems of high-speed vehicles are divided into issues related to thermal aeroelasticity of the aircraft and the thermal aeroelasticity of the inner runners, and their research status and future development are discussed. Particularly, the aerothermoelasticity problems related to the engine (including the panel flutter inside the ramjet engine and the aeroelasticity of the rocket engine nozzle) are investigated in detail and the significance of this issue in future work is pointed out. [ABSTRACT FROM AUTHOR]

We study the time-harmonic resonance of a finite-length elastic plate in a fluid in uniform flow confined in a duct. Although the resonance frequencies are usually real, the combined effects of plate elasticity and of a flow can create complex frequencies, different from the usual so-called scattering frequencies, corresponding to instabilities. We study theoretically the existence of instabilities versus several problem parameters, notably the flow velocity and the ratio of densities and of sound speeds between the plate and the fluid. A three dimensional volume in the parameters space is defined, in which no instability can develop. In particular it corresponds to a low enough velocity or a light enough plate. The theoretical estimates are validated numerically. [ABSTRACT FROM AUTHOR]

Highlights • A new type of PDMS check valve is presented in a supporting piezoelectric pump. • The flow rate of improved check valve is significantly increased. • Solves a series of problems that exist with regular PDMS bridge check valve design. • The modular pump design that allows the adjustment of the pump performance. Abstract A technique of check valve improvement for high frequency and high flow rate piezoelectric pumps is presented. By adding in a blocking edge over polydimethylsiloxane (PDMS) film check valve to modify their deformation pattern, 40%–300% flow rate enhancement and 5–6 kPa output pressure increment were achieved on a bench top testing platform. Experimental results show that the new valve is benefits to design a high efficiency and high outflow piezoelectric pump. [ABSTRACT FROM AUTHOR]

The multiple scattering of sound waves and the fluid-structure interaction should be taken into account to calculate the acoustic scattering of underwater elastic corner reflectors. The scattering acoustic field of underwater elastic corner reflectors in far field is simulated by using structure finite element method(FEM)/fluid indirect coupled boundary element method(IBEM). The influences of plate material and thickness, incident angle and the type of corner reflector on target strength and the scattering mechanism are analyzed when the incident wave frequency varies from 5.0 k Hz to 20.0 kHz. The results show that the scattering acoustic field of underwater elastic corner reflectors has a strong frequency characteristic. It varies with plate material and thickness, and incident wave frequency. The multiple scattering of sound waves has important contributions to the backscattering acoustic field of corner reflectors. The simulated results are in good agreement with the experimental results. The structure design and optimization method of corner reflectors are presented. [ABSTRACT FROM AUTHOR]

Abstract A coupled fluid-structure-fracture approach was presented to study the dynamic fracture of pre-flawed elbow pipes subjected to internal hydrogen-oxygen detonation. The initial flaw is located at the extrados, crown and intrados of the elbow, respectively. The hydrogen-oxygen detonation was modeled by a user-programed burn method based on the CJ theory. The fracture of elbow pipe was simulated by a validated bivariate failure criterion which was deduced based on the adiabatic shear failure mechanism of materials at high strain rates. Results demonstrate that the presented approach can capture the detonation wave propagation and the complex crack extension and branching effectively. It is found the peak pressure at extrados is 2.9 times larger than that at intrados, but the hoop stresses and effective strains at the three initial flaw positions are comparable with each other, even the average amplitude of hoop stress at intrados is higher than those at extrados and crown. The increase of detonation pressure can lead to crack branching and makes more cracks propagate simultaneously. The crack initiating at crown tends to turn and run to the intrados when passing the transition sections of elbow, while the crack initiating at intrados is expected to branch here. The average crack speeds for forward cracks are 100–300 m/s, while the speeds are 70%–90% of the above for backward cracks. The branch crack speeds are generally less than 40% of those before branching. Furthermore, the elbow pipes with initial flaw at intrados generally have the largest total crack length, while elbow pipes with initial flaw at crown have the strongest resistance against crack propagation. It is also suggested that local bucking is an important feature that takes place in dynamic fracture processes of elbow pipes. Highlights • Increase of detonation pressure can lead to earlier branching of cracks. • The forward crack speed is 100–300 m/s and backward crack speed is 0.7–0.9 of above. • Cracks running axially at crown tend to turn to the intrados at transition sections. • Elbow pipe with flaw at crown has strongest resistance against dynamic fracture. • Local buckling is an important feature in the dynamic fracture of elbow pipe. [ABSTRACT FROM AUTHOR]

In this paper, a graphical processing unit (GPU) implementation of adaptive particle refinement (APR) in the Smoothed Particle Hydrodynamics (SPH) framework is used to simulate the multi-phase flow and fluid-structure coupling problems. The multi-phase flow and fluid-structure coupling SPH models based on the Riemann solver are presented and the local particle refinement technique based on the axis-aligned square refinement pattern is adopted to split particles. A particle shifting technique constructing virtual fine particles (VFP-PST) is proposed to regularize the particle distribution for numrical accuracy and stability. To facilitate the device memory throughput efficiently, a dynamic resource management algorithm is used to implement GPU-accelerated adaptive particle refinement. Precision analysis shows the effect of the smooth length ratio of fine and coarse particles on numerical accuracy. Different tests have demonstrated that the proposed GPU-accelerated IAPR is accurate and stable and provides a promising approach to simulate the multi-phase flow and fluid-structure problems with low computational cost and comparable precision when compared with uniform particles. In order to improve numerical accuracy and save computation time in the applications of the SPH in large-scale or multi-scale problems, a GPU-accelerated adaptive particle refinement for multi-phase flow and fluid-structure coupling SPH is proposed in this paper. The novelty points are summarized as follows: • The multi-phase flow and fluid-structure coupling SPH model is developed with GPU-based adaptive particle refinement. • A particle shifting technique constructing virtual fine particles is proposed to regularize the particle distribution. • The dynamic resource management algorithm is proposed to implement the GPU-accelerated adaptive particle refinement. • Accuracy and stability of algorithm are analysed in detail using several multi-phase flow and fluid-structure coupling cases. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesters (PEHs) from fluid energy sources, particularly vortex shedding–induced vibrations, have received considerable attention in recent years. However, there still exists a common problem with these harvesters: the current optimum position of a vortex shedding–induced PEH located in the wake of a bluff body is commonly obtained through a series of experiments. This study proposes a theoretical model to determine the best position and demonstrate this mechanism. This theoretical model, which consists of fluid–structure and electromechanical couplings, is derived from the proposed PEH with a flapping sheet structure. The equivalent harmonic force in the fluid–structure coupling part caused by the vortexes on the flapping sheet is expressed by Bernoulli’s law and Lamb–Oseen vortex model. The system equations in the electro–mechanical coupling part are then obtained utilizing Euler–Bernoulli beam theory and an equivalent circuit model. This model was validated initially through the published data in the reference and then through the experimental results from a proposed PEH prototype. The optimum position of the PEH in the flow field is revealed by the analytical solution in numerical results and examined in experimental results. Moreover, the balanced match of fluid velocity and bluff body diameter can also contribute to the high–level system performance under the optimal load resistance. [ABSTRACT FROM AUTHOR]