Efficient Numerical Model Research Articles

Efficient numerical model for sediment transport on vortex ripple bed in wave-induced oscillatory flow

Sediment motion on rippled bed under wave action plays an important role in coastal landforms, but the application of traditional numerical model is limited by large computational work or bottom sediment condition due to unsteady effects. A single-phase model is proposed to maintain low computation and high accuracy for the vortex structure development and suspended sediment motion on vortex rippled bed in wave-induced oscillatory flow. The 2D bottom sediment condition takes into account the acceleration effect and asymmetric boundary layer development under nonlinear waves as well as the sediment phase-lag. The particle inertia and wake flow around sediment particle are considered in sediment turbulence, and the SST k-ω turbulence model which is suitable for inverse pressure gradient flow on rippled bed is selected to close the Reynolds stress. The single-phase model well predicts the velocity on vortex ripples, periodic concentration at fixed points and vertical distribution of averaged sediment concentration. The results show qualitative formation, development and ejection of vortex, and demonstrate quantitative development of vortex center, radius and strength in symmetric and asymmetric flows. In addition, the model well performs the development of sediment cloud referring to vortex structure.

An efficient monolithic multiscale numerical manifold model for fully coupled nonlinear saturated porous media

This paper presents an efficient monolithic computational homogenization model for transient nonlinear hydro-mechanical analysis within the framework of Numerical Manifold Method (NMM). The proposed model is on the same theoretical basis as the FE2 method. The scale transitions are achieved through the extended Hill-Mandel theorem so that the microscopic fluid and solid dynamic effects are fully incorporated. The two-scale simulations are solved in a monolithic manner and the microscopic problems of all macroscopic integration points are decoupled from each other to prevent size of the system of equations from soaring to exceedingly large. By conveying microscale unbalanced forces and tangent operators to the macroscale level, the micro- and macroscale problems are solved in the same Newton loop such that unnecessary microscopic iterations based on estimated macroscopic variables in the conventional nested homogenization m are avoided. By solving benchmark numerical examples, the proposed model proves to be capable of capturing transient hydro-mechanical responses accurately. Moreover, in contrast to the conventional nested homogenization model, the proposed model saves around 40% of computational costs for nonlinear hydro-mechanical analysis. Using the framework of numerical manifold, the presented model can be easily extended to multiscale analyses involving complex boundaries, interfaces and fractures.

Flow simulation in 3D fractured porous medium using a generalized pipe-based cell-centered finite volume model with local grid refinement

The presence of fractures in porous media strongly influences the fluid flow behavior. This work presents an efficient and simple numerical model to address the hydrodynamic behavior of complex fractured porous media, aiming at balancing computational efficiency and accuracy. Fractures are mapped to a set of cells having implicit aperture, where local grid refinement (LGR) is adopted around the fracture to improve accuracy with lower computational burden. The fluid flow in the matrix, fracture, and exchange between fracture-matrix, are described by a generalized equivalent pipe-network model. The numerical scheme and implementation are verified against established numerical solutions. Results show that this method is efficient in capturing main phenomena of the fluid transport in fractured porous media, without sacrificing computational accuracy. Heterogeneous and anisotropic features of fluid flow are well captured. Particularly, the convergence of the LGR is in a higher order than the global grid refinement (GGR). This model also provides great flexibility in handling a multitude of fracture input data, e.g., planar fractures obtained from statistical data and non-planar fractures from digital images represented with point clouds. Balancing computational accuracy and efficiency, this method provides an effective approach for simulating flow transport in fracture porous medium.

Αn efficient numerical model for the simulation of debonding of adhesively bonded titanium/CFRP samples induced by repeated symmetric laser shocks

ABSTRACT Novel engine fan blades are made of 3D woven composite materials and incorporate a protective metallic layer at the leading edge. The end-of-life of such structures involves complicated disassembly and recycling processes. In this paper, laser-shock is being investigated as an environmentally friendly disassembly method. In this context, symmetric laser-shock experiments that have been conducted in a previous work using a time delay between the shots have been proven successful for debonding initiation and propagation as they manage to effectively focus the tensile stress field developed by the shock waves at the bondline. In this paper, a numerical model simulating the symmetric laser-shock disassembly of titanium/CFRP specimens has been developed using the LS-Dyna explicit FE code. The aim is to give a deeper insight into the physical mechanisms and to optimize the experimental process. To simulate the behavior of the titanium part, the Johnson-Cook material model in combination with Grüneisen equation of state has been employed, while for the composite part a progressive damage material model incorporating high-strain rate effects has been used. The bondline between the two parts has been modeled using cohesive zone elements. To obtain tensile and shear elastic and strength properties at high strain rates for the composite damage model, tension and punch shear Split-Hopkinson Bar tests have been conducted. The numerical results correlate well with back-face velocity profiles obtained from single sided laser shock experiments and with debonding patterns in the adhesive, observed in electron microscopy images, induced by symmetrical laser shock experiments. After the validation, the numerical model has been used successfully to simulate a larger disassembly process composed of 16 consecutive shots.

Volume of fluid based modeling of thermocapillary flow applied to a free surface lattice Boltzmann method

Thermocapillary flow, also termed as thermal Marangoni convection, is an important material transport mechanism in many technical processes. Thus, it has to be considered in the corresponding simulations. In this work, a novel numerical model for the implementation of thermocapillary flow into a volume of fluid based free surface lattice Boltzmann method is presented. It is based on the idea of discretizing the surface normal vector in accordance to the discretization scheme of the velocity space. This approach is used to interpolate the temperature at the surface and to calculate the local surface gradients.The result is a simple and efficient numerical model, which is able to calculate the Marangoni stress along a liquid surface with sufficient accuracy and without the need to explicitly reconstruct the interface. We show that the Marangoni stress can readily be incorporated into a free surface lattice Boltzmann model by adjusting the boundary condition at the surface. In doing so, no additional forcing scheme has to be applied.In order to verify the presented model, it is tested using several simulation setups. As the lattice Boltzmann method is particularly suitable for complex geometries, a special attention is paid to the behavior at curved surfaces. Additionally, a simple test case for thermocapillary flow that can be regarded as a modified version of the Couette flow problem, is presented.

Numerical study of an industrial burner to optimise NOx emissions and to evaluate the feasibility of hydrogen-enriched fuel

Reducing NOx emissions from industrial burners is a significant concern due to their harmful environmental and human health impact. A computationally efficient numerical model was developed and validated using a detailed GRI 3.0 chemistry mechanism to simulate the combustion process and precisely predict the NOx emissions from industrial burners. The numerical model was implemented to reduce NOx emissions by varying the burner's primary to secondary air mass flow ratio. An optimum nozzle diameter was proposed to abate NOx emissions by a factor of 0.845. A feasibility study on the optimised burner was conducted by blending up to 50% hydrogen by volume with natural gas by maintaining the same burner power output. Results showed that the burner exhibited similar flame characteristics until 40% hydrogen was added to natural gas. A 41.8% increase in NO and a 76.8% decrease in CO emissions were observed by enriching natural gas with 50% hydrogen.

Development of an efficient numerical model for two-phase flows in air-lift pumps and its application to deep-sea mining

Air-lift pump system has been selected as a potential application to convey the Rare-Earth mud in deep-sea mining processes due to the superior reliability and schematic simplicity. It is a major focus of current research to study the behavior and mechanism of the two-phase flow. Based on the drift flux model and modified Akawa pressure drop equation, mathematical model controlling the numerical simulation of two-phase flow within air-lift pump system is proposed and constructed. Comparison with experimental data concerning steady and unsteady two-phase flows in vertical pipes shows the high precision of the model. Combing with the robustness test results, it can be found that the present model can accurately predict the maximum flow rate of the two-phase flow at the outlet of the gas lift pump, as well as the average gas and liquid flow rates of the two-phase flow at the outlet in both steady and unsteady states. On this basis, several operation laws of the deep-sea mining airlift pump were studied. The relationship between input and output in the mining process is established and the output of the gas lift pump system is predicted. It is found that changing the position of the injected gas, the time for the two-phase flow in the vertical pipe to reach dynamic equilibrium varies equiprimordially. And changing the maximum amount of gas injected, the time required to reach dynamic equilibrium shows a symmetric relationship with the volume fraction after dynamic equilibrium. A series of laws closely related to the prediction of rare earth mud at the outlet of gas-lift pumps in deep-sea mining are investigated to be proposed for subsequent studies.

Longitudinal seismic response of shield tunnel: A multi-scale numerical analysis

Developing a rational and efficient numerical model to analyze the longitudinal earthquake response of shield tunnel has become a hot topic in the field of underground structure seismic research in recent years. Based on the idea of scale coupling, this study proposed a multi-scale numerical model that can capture the dynamic response of ring joint in the vulnerable part of shield tunnel precisely. In this multi-scale model, the non-focused part of structure is described by the Timoshenko beam & nonlinear spring, while the focused part is described by the three-dimensional “refined ring joint”. The multi-scale model is subsequently utilized to calculate the longitudinal seismic response of the shield tunnel through a typical site with a soft-hard stratum junction. In addition, the influence of earthquake wave parameters on the seismic response of the tunnel structure is also discussed in this study. Some inspiring conclusions are as follows. The dynamic response of the shield tunnel rises dramatically near the soft-hard stratum interface because of the non-uniform deformation of the soil in that area. Strong earthquake waves (with high PGA or PGV) may cause nonlinear increase in the opening deformation of a ring joint and the yielding of several joint bolts. Under high intensity seismic load, the service state of joint bolts varies widely, and the damage is concentrated in one region of the ring joint.

A unified section-based restoring force model for reinforced concrete coupling beams based on the XGBoost model: Establishment, validation and application

To enhance the seismic performance of reinforced concrete (RC) coupling beams, improved reinforcement details such as diagonal layout and high-performance concrete including fiber reinforced concrete (FRC) as well as engineered cementitious composites (ECC) are widely investigated and applied. Despite the numerous experimental studies on various reinforced concrete coupling beams, there is still a lack of unified, efficient and accurate numerical model applicable to all kinds of concrete and reinforcement layouts, leading to difficulty in numerical study and proper design of coupling beams and coupled shear walls. In this study, a database containing 180 reinforced concrete coupling beam specimens is first set up. Then the key mechanical indexes of test curves including the peak load, peak beam rotation, yielding beam rotation and softening beam rotation are predicted using the trained XGBoost models. The feature importance and partial dependence of different independent variables are analyzed. Based on the predicted results, the skeleton curves of the section-based restoring force model can be obtained. Besides, a new hysteretic rule for the restoring force model which can account for the pinching effect, strength and stiffness degradation is proposed. The proposed model is then implemented in ABAQUS 2017 software, of which the accuracy and applicability are validated by twelve coupling beam specimens with different concrete materials and reinforcement layouts. Finally, a coupled shear wall specimen is simulated to quantitatively and thoroughly evaluate the effects of key indexes of the coupling beams on the seismic performance of the coupled shear wall structures.

Reduced order 1 + 3D numerical model for evaluating the performance of solar borehole thermal energy storage systems

This study presents a computationally efficient numerical model for solving the fluid flow and heat transfer phenomena in co-axial boreholes heat exchangers arranged on a rectangular grid (N × N) drill hole pattern. Such systems of boreholes are an integral component of a Solar-Borehole Thermal Energy Storage System for seasonal thermal storage application. The numerical model couples a one-dimensional fluid flow and convective heat transfer model in the heat exchanger with a three-dimensional model of conductive heat transfer in the strata. In addition to solving mass and heat transfer in borehole systems, it integrates a solar thermal collector system and building dynamic thermal load to design a Solar- Borehole Thermal Energy Storage system for a 182-unit residential apartment building. Simulation also considers and evaluates the conductive, convective, and radiative thermal losses of the system. The model is validated using experimental data from a coaxial borehole heat exchanger and compared to the results of a commercial finite volume solver for multiple co-axial boreholes. The computational cost of developed numerical model is reduced by a factor of 194 compared to a commercial finite volume solver. Solar- Borehole Thermal Energy Storage system simulation is performed for a period of five years considering hourly fluctuations in solar irradiance and building dynamic thermal energy demand. Parametric study is performed on depth and spacing of boreholes, and mass flowrate in the solar thermal collectors. It is found that a system of 100 boreholes, each 100 m deep, linked to 674 solar thermal collectors can provide the heating for the building with a total thermal demand of 5600 GJ per year.

Effects of outrigger configuration on trimaran stability in longitudinal waves

A trimaran has excellent characteristics of transverse stability and less resistance because of its unconventional multiple slender hull form. However, the multi-hull configuration potentially triggers parametric roll due to the periodical fluctuation of metacentric height. In this study, an efficient numerical model was established to investigate the effects of the outriggers on trimaran stability in longitudinal waves, based on Froude-Krylov assumption and hydrostatic assumption. Then, the relationship between the metacentric height of the trimaran and the outrigger position was discussed, and the influence of heave/pitch motion responses on the wave stability of the trimaran was evaluated. Furthermore, a method of predicting the stability zone was proposed and checked by numerical simulation based on computational fluid dynamics. The relationship between the outrigger position and the potential risk of the parametric roll was analyzed by the obtained stability zones. It was found that the decrease in the outrigger displacement ratio and the increase in the clearance can significantly raise the risk of parametric roll of a trimaran.

Identification and Investigation of Extreme Events Using an Arbitrary Lagrangian–Eulerian Approach With a Laplace Equation Solver and Coupling to a Navier–Stokes Solver

AbstractIncreased deployment of offshore wind turbines is seen as an important pathway to increase green renewable energy production. Improved and rapid identification of extreme events and evaluation of hydrodynamic loads due to such events is essential to reduce the cost of energy production. Numerical modeling to pre-screen sea states and to identify the crucial events to prioritize model tests will make a major contribution to reduce design times and costs for such structures. In this effort, a highly efficient and nonlinear numerical model based on the Laplace equations is used to generate undisturbed wave kinematics. Such a simulation is used to identify extreme wave events in a sea state realization, and further, the wave loading due to such events are evaluated using Morison formula. Events screened in this manner can then be transferred to a high-resolution model such as a Navier–Stokes equation-based solver to investigate the hydrodynamics in detail. The implementation and application of such an approach in the open-source hydrodynamic model REEF3D is presented in this work.

The Influence of Gravitational Stiffening and De-stiffening on Nonlinear Dynamic Behavior of Vertical Beams with Cracks

ABSTRACT Dynamics of vertically oriented blades is an important topic of research as it replicates the physical behaviour of several real-time applications such as horizontal axis wind turbine blades. It is observed that available literatures explaining the effects of gravity on the dynamic behaviour of vertical beams/blades did not focus on the various operational adversities such as geometric nonlinearities, possibilities of crack initiation due to adverse conditions. Therefore, in present study, an attempt is made to capture reverberations of gravity on cracked vertical blades including geometric nonlinearity. A computationally efficient numerical model for nonlinear dynamic analysis of vertically oriented cracked blades is developed. Efficacy of proposed model is verified by several case studies. Subsequently, parametric investigation is performed for combined effects of crack and gravity on the dynamic response. Crack and gravity dominant regions based on slenderness ratio are identified for the first time . Furthermore, influence of nonlinearities on such behaviour provides useful insights to anticipate the mechanics of the dynamic behaviour of a vertical cracked cantilever beam. Proposed work may be useful for developing a robust vibration-based condition monitoring for a given application which involves hanging beams with a possibility of crack such as rotor blades.

Hardware-in-the-loop simulations of a railway pantograph with a finite element periodic catenary model

The pantograph-catenary dynamic interaction problem is addressed by Hardware-in-the-Loop (HIL) tests to simulate the dynamic interaction between a numerical model (the catenary) and a physical device (the pantograph). The real-time simulation requires a computationally efficient numerical model and an on time and accurate transference of the response to the pantograph, for which a Periodic Finite Element Model (PFEM) of the catenary is considered. Firstly because of the acceptable computation time required to solve it, makes it suitable for real-time simulations and, secondly, its ability to allow for the delay caused by the transfer of the numerical model response. The catenary PFEM we used considers the non-linear behaviour of the dropper slackening, leading to highly accurate HIL test results, which were validated up to a frequency of 25 Hz.

Two-dimensional models for waterflooding induced hydraulic fracture accounting for the poroelastic effects on a reservoir scale

This work focuses on the developing of a computationally efficient numerical model for a waterflooding induced planar hydraulic fracture in a poroelastic medium. In particular, under certain assumptions it is possible to decouple the fully coupled model into poroelastic reservoir and purely elastic fracture subproblems. Further, the general 3D problem formulation for a planar fracture is reduced to two dimensions for early time plane strain fracture and late time constant height fracture. Noticeably, the division of the problem into two subproblems allows us to use the displacement discontinuity approach for the fracture related part, and finite element method for the reservoir related part. The latter is especially important for the constant height fracture, which cannot be modeled using exclusively the finite element approach in two dimensions. The algorithm is benchmarked against the available analytical solutions, as well as compared to other numerical codes. The developed numerical method is used to study the influence of the heterogeneous pore pressure and the corresponding stress for different waterflooding fracturing situations. We consider the cases with both injection and production wells operating nearby. With the presence of such wells, the fracture growth becomes asymmetrical and both the well type and location are important. The qualitatively different fracture behavior is observed for various cases. Other numerical examples include the simulation of a step-rate test as well as investigation of the possibility of fracture control by altering the injection rate.

Entropy Generation and Thermal Radiation Analysis of EMHD Jeffrey Nanofluid Flow: Applications in Solar Energy.

This article examines the effects of entropy generation, heat transmission, and mass transfer on the flow of Jeffrey fluid under the influence of solar radiation in the presence of copper nanoparticles and gyrotactic microorganisms, with polyvinyl alcohol-water serving as the base fluid. The impact of source terms such as Joule heating, viscous dissipation, and the exponential heat source is analyzed via a nonlinear elongating surface of nonuniform thickness. The development of an efficient numerical model describing the flow and thermal characteristics of a parabolic trough solar collector (PTSC) installed on a solar plate is underway as the use of solar plates in various devices continues to increase. Governing PDEs are first converted into ODEs using a suitable similarity transformation. The resulting higher-order coupled ODEs are converted into a system of first-order ODEs and then solved using the RK 4th-order method with shooting technique. The remarkable impacts of pertinent parameters such as Deborah number, magnetic field parameter, electric field parameter, Grashof number, solutal Grashof number, Prandtl number, Eckert number, exponential heat source parameter, Lewis number, chemical reaction parameter, bioconvection Lewis number, and Peclet number associated with the flow properties are discussed graphically. The increase in the radiation parameter and volume fraction of the nanoparticles enhances the temperature profile. The Bejan number and entropy generation rate increase with the rise in diffusion parameter and bioconvection diffusion parameter. The novelty of the present work is analyzing the entropy generation and solar radiation effects in the presence of motile gyrotactic microorganisms and copper nanoparticles with polyvinyl alcohol-water as the base fluid under the influence of the source terms, such as viscous dissipation, Ohmic heating, exponential heat source, and chemical reaction of the electromagnetohydrodynamic (EMHD) Jeffrey fluid flow. The non-Newtonian nanofluids have proven their great potential for heat transfer processes, which have various applications in cooling microchips, solar energy systems, and thermal energy technologies.

Numerical and Experimental Analysis of the Oil Flow in a Planetary Gearbox

The circular layout and the kinematics of planetary gearboxes result in characteristic oil flow phenomena. The goal of this paper is to apply a new remeshing strategy, based on the finite volume method, on the numerical analysis of a planetary gearbox and its evaluation of results as well as its validation. The numerical results are compared with experimental data acquired on the underlying test rig with high-speed camera recordings. By use of a transparent housing cover, the optical access in the front region of the gearbox is enabled. Different speeds of the planet carrier and immersion depths are considered. A proper domain partitioning and a specifically suited mesh-handling strategy provide a highly efficient numerical model. The open-source software OpenFOAM® is used.

On the use of Hermit-type WLS approximation in a high order continuation method for buckling and wrinkling analysis of von-Kàrmàn plates

The aim of this work is to develop an efficient numerical model for bifurcation analysis within the Föppl–von-Kàrmàn plate theory. This model consists in adapting the High Order Continuation Method (HOCM) with a Hermit-type Weighted Least Square (WLS) method. The collocated Hermit-type technique allows to approximate the binding unknowns and their derivatives. Furthermore, a new implementation of boundary conditions is developed by using the normal boundary derivatives of the main field unknowns to overcome the edge vertex’s nodes normal issues related to the strong formulation boundary value problem. The HOCM has an adaptative step length which is very efficient and performed especially for bifurcation problems. By this way, we are able to detect precisely the critical buckling and wrinkling loads for very thin membranes with fewer degrees of freedom and less CPU time. A comparison between the proposed approach with analytical solution, Finite Element Method (FEM), and Element-Free Galerkin (EFG) method is illustrated in some numerical results that demonstrate the accuracy and robustness of the proposed approach.

Reliability of toe-nail connections in a gable roof houses under uplift wind loads

The latest devastating hurricanes have caused considerable damage to light frame wooden houses. The detachment of the roofs because of the high uplift wind loads is one of the typical damages. This detachment often occurs at the contact connections in between the roof trusses and the walls of the houses. For several decades, toe-nail connections, which are poor in uplift resistance, have been used in those contacts. The purpose of this paper is to develop an efficient numerical model for performing reliability assessment of wooden roofs under uplift wind loads taking into account the statistical variability in both the load–deflection curve of toe-nails and the uplift wind load. The model utilizes a three-dimensional semi-analytical solution previously developed to predict the behaviour and failure of wood roofs under spatially variable uplift loads. The random characteristics of the toe-nails were calculated based on experimental results found in the literature and were statistically simulated using a beta distribution. The randomness of the wind speed was evaluated using a normal distribution. A full-scale gable roof was considered as a case study to determine the probability of roof failure at different wind speeds, Monte Carlo simulations along with the semi-analytical model were used to obtain the fragility curve based on two different criteria. It was found that beyond a mean wind velocity of 32 m/s, the probability of roof failure increases rapidly.

Nonlinear air dynamics of a surface effect ship in small-amplitude waves

In many existing works, the seakeeping motions and air dynamics of a surface effect ship (SES) were assumed to be linear under small-amplitude waves (wave amplitude to wave length ratio ≤ 5%) to enhance the computational efficiency. However, according to SES model test results, it was found that even in small-amplitude waves, the fluctuating air cushion pressure shows significantly nonlinear effects. To precisely reveal this distinctive feature, the origin of nonlinearity was carefully investigated and the air leakage was considered as the main source of nonlinearity based on mathematical analysis in this paper. The reason is that the variance of clearance height under seals is comparable to the clearance height at equilibrium state in small-amplitude waves, which makes the air leakage area intermittently equal to zero without any harmonic variance. Therefore, an efficient partial nonlinear numerical model for the SES dynamics was proposed by combining a linear frequency-domain hydrodynamic model based on the efficient 2.5D methods with a nonlinear time-domain air dynamic model. The nonlinear parts of numerical results from the partial nonlinear model, including the fluctuating air pressure and midship accelerations, agree well with experimental results. The results demonstrate the effectiveness of the partial nonlinear model on the SES seakeeping performance prediction, and confirm that its nonlinearity mainly originates from the air leakage.