Fluid-structure Model Research Articles

Characterization of coal fines generation: A micro-scale investigation

Coal fines are commonly generated as by-product during coalbed methane production mainly due to the interaction of coal with inseam water flow. A portion of the created coal fines may settle and plug the coal cleats and hydraulic fractures due to the gravity and coal pore size constraint. This could result in the reduction of coal permeability and blockage of coalbed methane wells or gas drainage boreholes. Despite the increasing awareness of the importance of understanding coal fines, limited research has been carried out on the characterization of coal fines creation. This study aimed to numerically characterize the generation process of coal fines in micro-scale coal cleats. The Scanning Electron Microscopy (SEM) images for a coal sample from Bulli Seam of the Sydney Basin in Australia were obtained and analysed to determine the actual cleat geometries and the characteristics of coal fines distribution. Then a fully coupled fluid-structure numerical model was developed to identify the creation process of coal fines at micro-scale. The impact of pertinent production conditions on coal fines generation was studied, including production pressure drawdown, temperature, coal fines Young's modulus and strength. The SEM images revealed that the particle size distributions of the coal fines in the examined cleats were in the order of hundreds of nanometres to several microns. The results of the numerical studies showed the coal fines production increased with pressure build-up, and decreased with increasing coal fines strength with more sensitivity compared with pressure. Critical values for production pressure drawdown were obtained, above which failure area began to expand; threshold values were also determined, below which remarkable reduction of coal fines production was achieved. Coal cleat geometry plays an important role in determining coal fines production. It was noted that exposed microstructures, cleat elbow regions and micro-fracture tips are more likely to generate coal fines. Based on these findings, guidance can be provided on the control of production conditions to mitigate coal fines issue, and new insight into where and how coal fines are created by inseam water flow can be achieved.

The analysis of flow characteristics in multi-channel heat meter based on fluid structure model

In this paper, a fluid structure interaction (FSI) model is used to study the internal flow field and the measurement performance of a multi-channel flow meter. The RNG k – ɛ turbulent model and the finite element model are used separately in the fluid domain and the structure domain to obtain the meter factor K and the deformation of the structure. The meter factor K of the flow meter is obtained through the FSI model at temperatures of 20°C, 50°C and 80°C. The calculated results show the thermo expansion of the structure can significantly influence the measurement performance of the flow meter. The meter factor of the flow meter is also measured experimentally, and the comparison between the experimental results and the calculated results shows the validity of the fluid-structure interaction model. In order to reduce the measurement error, the meter factor K should be modified as the water temperature changes.

Simulation of aortic valve dynamics during ventricular support.

Existing commercially-used left ventricular assist devices (LVADs) make no attempt to automatically detect the aortic valve condition in their control methods to optimize ventricular assistance. An important design goal for LVADs is the ability to reliably and accurately detect aortic valve (AV) states during heart pump support that can cause harmful effects on AV structure and function. In this paper, we have investigated the correlation between AV performance and LVAD motor current as well as speed set points, simulating aortic valve blood flow, pressure, pump flow and LV mechanics using a simplified two-dimensional fluid-structure interaction finite-element model of AV dynamics.

Stochastic identification of the structural damage condition of a ship bow section under model uncertainty

A accurate, quantifiable means of assessing structural damage condition are paramount for maintaining the structural integrity of ship hull forms. Toward this end, precise knowledge of the location and magnitude of any imperfections (i.e. geometric imperfections in the form of denting and corrosion patches) must be determined, along with concomitant uncertainties accompanying such predictions. The current paper describes a non-contact approach to identifying and characterizing such imperfections within the submerged bow section of a representative ship hull. By monitoring the pressure field local to the acoustically excited hull section, it is shown how the resulting data can be used to identify the parameters describing the structural damage field. In order to perform the identification, a fluid–structure model that predicts the spatio-temporal pressure field is required. A Bayesian, reversible jump Markov chain Monte Carlo approach is then used to generate the imperfection parameter estimates and quantify the uncertainty in those estimates. This approach is particularly appealing as it does not allow for the damage model to be explicitly known a priori. Convergence of the Markov chains is assessed, and estimates of the Monte Carlo standard error (MCSE) are provided.

Simplified Aeroelastic Model for Fluid Structure Interaction between Microcantilever Sensors and Fluid Surroundings.

Fluid-structural coupling occurs when microcantilever sensors vibrate in a fluid. Due to the complexity of the mechanical characteristics of microcantilevers and lack of high-precision microscopic mechanical testing instruments, effective methods for studying the fluid-structural coupling of microcantilevers are lacking, especially for non-rectangular microcantilevers. Here, we report fluid-structure interactions (FSI) of the cable-membrane structure via a macroscopic study. The simplified aeroelastic model was introduced into the microscopic field to establish a fluid-structure coupling vibration model for microcantilever sensors. We used the finite element method to solve the coupled FSI system. Based on the simplified aeroelastic model, simulation analysis of the effects of the air environment on the vibration of the commonly used rectangular microcantilever was also performed. The obtained results are consistent with the literature. The proposed model can also be applied to the auxiliary design of rectangular and non-rectangular sensors used in fluid environments.

Effectiveness of eye armor during blast loading.

Ocular trauma is one of the most common types of combat injuries resulting from the interaction of military personnel with improvised explosive devices. Ocular blast injury mechanisms are complex, and trauma may occur through various injury mechanisms. However, primary blast injuries (PBI) are an important cause of ocular trauma that may go unnoticed and result in significant damage to internal ocular tissues and visual impairment. Further, the effectiveness of commonly employed eye armor, designed for ballistic and laser protection, in lessening the severity of adverse blast overpressures (BOP) is unknown. In this paper, we employed a three-dimensional (3D) fluid-structure interaction computational model for assessing effectiveness of the eye armor during blast loading on human eyes and validated results against free field blast measurements by Bentz and Grimm (2013). Numerical simulations show that the blast waves focused on the ocular region because of reflections from surrounding facial features and resulted in considerable increase in BOP. We evaluated the effectiveness of spectacles and goggles in mitigating the pressure loading using the computational model. Our results corroborate experimental measurements showing that the goggles were more effective than spectacles in mitigating BOP loading on the eye. Numerical results confirmed that the goggles significantly reduced blast wave penetration in the space between the armor and the eyes and provided larger clearance space for blast wave expansion after penetration than the spectacles. The spectacles as well as the goggles were more effective in reducing reflected BOP at higher charge mass because of the larger decrease in dynamic pressures after the impact. The goggles provided greater benefit of reducing the peak pressure than the spectacles for lower charge mass. However, the goggles resulted in moderate, sustained elevated pressure loading on the eye, that became 50-100% larger than the pressure loading experienced by the unprotected eye after 0.2 ms of impact of blast wave, for lower as well as higher charge mass. The present model provides fundamental insights of flow and pressure fields in the ocular region, which helps to explain the effectiveness of the eye armor. Since the measurements of these fields are not trivial, the computational model aids in better understanding of development of PBI.

Fluid Structure Modelling of Blood Flow in Vessels.

This paper describes the capabilities of fluid structure interaction based multi-physics numerical modelling in solving problems related to vascular biomechanics. In this research work, the onset of a pressure pulse was simulated at the entrance of a three dimensional straight segment of the blood vessel like circular tube and the resulting dynamic response in the form of a propagating pulse wave through the wall was analysed and compared. Good agreement was found between the numerical results and the theoretical description of an idealized artery. Work has also been done on implementing the material constitutive models specific for vascular applications.

Desarrollo de un sistema de apoyo a la decisión para optimizar el comportamiento de barcos de vela

In this paper, the conception and design of a new monitoring system for a racing yachts rig is presented. The sensors developed are able to process the measured strain data, by applying artificial neural networks (ANN) algorithms, and then evaluate the load acting on an element and identify the direction of the action of that force. This way, it is possible to identify the actual operating conditions of the yacht rig. The required data for ANN training is generated from the results obtained from different finite element method (FEM) computational models of the device. Furthermore, during the design phase of the system, different experimental campaigns were carried out. The experimental tests were designed to serve as proof of concept, as well as to validate the different procedures used in the system development and application.The developed monitoring system is wireless, low-intrusive and easily adaptable to any yacht configuration.This work also presents the integration of the monitoring system into a coupled fluid-structure computation model for the sails and rig of a boat. The resulting system is an efficient tool for evaluating performance and decision support in the adjustment of a sailboat rig.

Simulation of motor current waveform as an index for aortic valve open-close condition during ventricular support.

Monitoring of aortic valve (AV) opening and closure during heart pump support by a left ventricular assist device (LVAD) is crucial in preventing adverse events such as thrombus formation near the AV. In preventing adverse events such as thrombus formation near the AV. In this paper, simulations of LVAD motor current waveform were undertaken to evaluate its suitability for ascertaining aortic valve status. A two-dimensional fluid-structure interaction finite-element model is presented to predict AV closure during LVAD outflow, useful in the development of a pump speed controller.

Efficient modal dynamic analysis of flexible beam–fluid systems

This paper proposes an efficient simplified method to determine the modal dynamic and earthquake response of coupled flexible beam–fluid systems and to evaluate their natural vibration frequencies. The methodology developed extends available analytical solutions for mode shapes and natural vibration frequencies of slender beams with various boundary conditions to include the effects of fluid–structure interaction. The proposed method is developed for various beam boundary conditions considering lateral interaction with one or two semi-infinite fluid domains. Numerical examples are provided to illustrate the application of the proposed method, and the obtained results confirm the importance of accounting for fluid–structure interaction effects. We show that the developed procedure yields excellent results when compared to more advanced coupled fluid–structure finite element solutions, independently of the number of included modes, beam boundary conditions, and number of interacting fluid domains. The proposed simplified method can be easily implemented in day-to-day engineering practice, as it constitutes an efficient alternative solution considering the fluid–structure modeling complexities and related high expertise generally involved when using advanced finite elements.

Influence of cavitation on the hydroelastic stability of hydrofoils

This work numerically examines the effect of turbulent and cavitating flow on the hydroelastic response and stability of a hydrofoil. A cantilevered, rectangular, chordwise rigid hydrofoil is modeled as a 2-degrees-of-freedom structure for its spanwise bending and torsional flexibilities. The fluid flow is modeled with the incompressible, Unsteady Reynolds Averaged Navier–Stokes equations using an eddy-viscosity turbulence closure model that is corrected for the presence of cavitation, and with a transport equation based cavitation model. The results show that, in general, massive cavitation tends to: (i) reduce the mean lift, (ii) increase the mean drag, (iii) lower the mean deformations, and (iv) delay static divergence, while unsteady sheet/cloud cavitation promotes flow induced vibrations. Such vibrations and load fluctuations could be as large as (and even greater than) the mean values for cases with unsteady cavitation, so dynamic and viscous fluid–structure models are needed to simulate flexible hydrofoils in cavitating flows. In general, the flow induced vibrations, and hence the drag force, are higher with decreasing stiffness. For small leading edge partial cavitation, increasing foil flexibility increases the maximum cavity length and reduces the cavity shedding frequency; however, the influence of foil flexibility is limited for cases where the maximum cavity length is near or beyond the foil trailing edge, because of the relocation of the center of pressure at the elastic axis, near the mid-chord. The results show that the mean deformations are generally limited by stall, and by the quasi-steady linear theory predictions at the fully-wetted and supercavitating limits. Furthermore, frequency focusing can occur when the cavity shedding frequency is near the fundamental system resonance frequencies, and broadening of the frequency spectrum can occur due to excitation of the sub-harmonics and/or modulation induced by the fluctuating cavities, if the cavity shedding frequency is away from the fundamental system resonance frequencies.

A Nonisothermal Fluid-Structure Interaction Analysis on the Piston/Cylinder Interface Leakage of High-Pressure Fuel Pump

In this paper, a nonisothermal fluid-structure interaction mathematical model for the piston/cylinder interface leakage is presented. Full account is taken of the piston eccentricity, elastic deformations of the piston pair, the nonisothermal flow in the interface, and the physical properties of the fluid such as the pressure-viscosity and temperature-viscosity effects. The numerical method for the solution of the model is given, which can simultaneously solve for the fluid pressure distribution and leakage rate in the interface. The model is validated by comparing the calculated leakage rates with the measurements. Results show the good accuracy of the model. The impacts of parameters such as the piston diameter, the initial clearance between the piston pair, and the piston velocity on the leakage rate are discussed. Some of the conclusions provide good guidance for the design of high-pressure fuel pumps.

On well-posedness and small data global existence for an interface damped free boundary fluid–structure model

We address a fluid–structure system which consists of the incompressible Navier–Stokes equations and a damped linear wave equation defined on two dynamic domains. The equations are coupled through transmission boundary conditions and additional boundary stabilization effects imposed on the free moving interface separating the two domains. Given sufficiently small initial data, we prove the global-in-time existence of solutions by establishing a key energy inequality which in addition provides exponential decay of solutions.

Stochastic identification of imperfections in a submerged shell structure

Accurate predictions of the buckling load in imperfection sensitive shell structures requires precise knowledge of the location and magnitude of any geometric imperfections in the shell (e.g. dents). This work describes a non-contact approach to identifying such imperfections in a submerged shell structure. By monitoring the acoustic pressure field at discrete points proximal to a shell structure excited by a cyclic membrane (i.e. in-plane) loading, it is noticed that parameters, describing small scale denting, can be identified. In order to perform the identification, a fluid-structure model that predicts the spatio-temporal pressure field is required. This model is described in detail and includes the predicted effects of the imperfection on the observations. A Bayesian, Markov chain Monte Carlo approach is then used to generate the imperfection parameter estimates and quantify the uncertainty in those estimates. Additionally: for cases involving the occurrence of an unknown number of dents, reversible jump Markov chain Monte Carlo (RJMCMC) methods are employed in this work.

CO2 Pipeline Integrity: Comparison of a Coupled Fluid-structure Model and Uncoupled Two-curve Methods

One challenge in CCS is related to the prevention of running-ductile fracture in CO2-carrying pipelines. Commonly used tools for ensuring crack arrest in pipelines hinge mainly on semi-empirical models, which may not be appropriate for CO2 transport since they have been developed and fitted for natural gas and older pipeline materials, and due to an assumed decoupling of the fluid decompression and fracture propagation phenomena. In this paper, we apply a coupled fluid-structure model to a case with pure dense liquid CO2 in a modern high-toughness steel pipeline, and compare the results one would obtain from directly applying the uncoupled models to the same case without any re-fitting to test data. For this case, the coupled model indicates that a significantly thicker pipeline wall may be required to prevent running-ductile fracture than what is predicted by the uncoupled models. Therefore, using the uncoupled models for such cases might not be conservative.

A fluid–structure model coupling the Navier–Stokes equations and the Lamé system

We study a fluid–structure system describing the motion of an elastic solid inside an incompressible viscous fluid in three dimensions. The motion of the solid is described by the Lamé system of linear elasticity and the fluid obeys the incompressible Navier–Stokes equations in a time-dependent domain. At the fluid–solid interface, natural conditions are imposed, continuity of the velocities and of the Cauchy stress forces. The fluid and the solid are coupled through these conditions. By this interaction, the fluid deforms the boundary of the solid which in turn influences the fluid motion. We prove the existence and uniqueness of local strong solutions by rewriting the coupled system in Lagrangian variables and by using the method of successive approximations. Our analysis relies on new regularity results for the linearized coupled system. In particular, if u˜ is the Lagrangian velocity of our system, we have to estimate separately Pu˜ and (I−P)u˜, where P is the Leray projector for the fluid model. Moreover, we prove new hidden regularity results for the Lamé system, that we are able to establish only in the case when the interface, in the reference configuration, between the fluid and the solid is flat. Due to this restriction, the model is completed by periodic boundary conditions in two directions. The other results may be transposed to more general configurations.

Numerical and experimental study of a nearby solid boundary and partial submergence effects on hydrofoil added mass

The influence of the boundary conditions on the added mass of a NACA0009 cantilever hydrofoil has been numerically and experimentally investigated. The study has been focused on the effects of a lateral solid wall close to the hydrofoil tip side and of a partially wetted vertical hydrofoil at different levels with the free surface parallel to the span. A detailed fluid–structure model has been built for both cases and a modal analysis has been carried out. The numerical three first natural frequencies have been used to calculate the added mass coefficients. These coefficients have been compared with the results of the analogous experiments carried out by means of an onboard excitation and response system based on piezoelectric patches. The obtained results are in reasonable good agreement with experimental data. The proximity of a lateral solid wall provokes an increase of the added mass experienced by the hydrofoil which can be approximated by a 2nd order polynomial function for both bending and torsion modes. On the other hand, the increase of the added mass with the level of partial submergence is found to be dependent on the relative displacements of the hydrofoil submerged part and hence on the mode shape.

Fluid–Structure Interaction-Based Biomechanical Perception Model for Tactile Sensing

The reproduced tactile sensation of haptic interfaces usually selectively reproduces a certain object attribute, such as the object's material reflected by vibration and its surface shape by a pneumatic nozzle array. Tactile biomechanics investigates the relation between responses to an external load stimulus and tactile perception and guides the design of haptic interface devices via a tactile mechanism. Focusing on the pneumatic haptic interface, we established a fluid–structure interaction-based biomechanical model of responses to static and dynamic loads and conducted numerical simulation and experiments. This model provides a theoretical basis for designing haptic interfaces and reproducing tactile textures.

3D Numerical Simulation on Thermal Flow Coupling Field of Stainless Steel During Twin-Roll Casting

The surface crack and lateral crack of the AISI 304 stainless steel thin strip produced by twin-roll casting were observed. The temperature at the center of outlet during twin-roll-casting process was determined by infrared thermometer. In order to avoid the surface cracks of the casting strip, the thermal flow coupling field of AISI 304 stainless steel during twin-roll-casting process was simulated by a 3D fluid-structure coupling model. According to the simulation result, the effect of the casting speed on thermal flow field was analyzed and the process parameters were optimized. Moreover, by studying heat flux curves, the heat transfer mechanism between molten pool and roll was analyzed. The results show that, with the increase of the casting speed, the temperature of the molten pool increases and the solidification point moves toward the outlet. Meanwhile, the whirlpool above gets larger. Based on the solidification front position, the optimized process parameters are 1500 °C and 0.37 m/s. The heat transfer mechanism between molten pool and roll contains direct contacting heat transfer and air gap heat transfer.

Biomechanical comparison between mono-, bi-, and tricuspid valve architectures.

An understanding of the relationship between venous valve architecture and associated fluid and solid mechanical forces will undoubtedly advance prosthesis design and treatments. The objective of the current study was to compare three valve architectures (mono-, bi-, and tricuspid) and the implications of these designs on the fluid and solid mechanics of the valve leaflets. The hypothesis is that the bi-cuspid valve has the lowest mechanical cost, defined as the ratio of leaflet wall stress and fluid wall shear stress (WSS), forthe venous environment as compared with mono- and tricuspid valves. To address this hypothesis, fully coupled, two-way fluid-structure interaction computational models were developed and simulated for the three types of valves. The numerical simulations showed that the mean fluid WSS of the bicuspid valve was generally higher than the tri-cuspid valve, which was further higher than the monocuspid valve. The mean leaflet wall stress of the bicuspid valve was lower than the tricuspid valve, which was further lower than the monocuspid valve. Therefore, the mechanical cost, which was defined as solid wall stress/fluid WSS, of the bicuspid valve was the lowest. The lower mechanical cost may be a reason why the bicuspid valve is the dominant design in the venous system. This knowledge provides guidance for the design ofnovel venous prosthetic valves and may shed light on venous valve disease when the architecture of the valve is altered.