Mesh Regeneration Research Articles

Optimisation of open pit slope design considering groundwater effects using particle swarm optimisation and scaled boundary finite element method

Slopes are a crucial structures in open pit mines. Their design has implications on the economic, safety and environmental operation of the mining industry. Designing stable slopes can be challenging due to the complexities introduced by the stratigraphy and hydrology of the strata. With rising commodity costs and inflation rates, mining operating costs are increasing. Reducing operational costs is necessary for mining industries to remain competitive. While steepening the pit slope can decrease stripping materials and save money, it also increases the risk associated with slope surges. Therefore, optimising slopes is crucial for both financial and safety reasons. Numerical models such as the finite element method experience challenges in mesh generation of heterogeneous systems characterised by varying material properties and stratigraphies. Moreover, the need for repetitive geometry update necessitates recursive mesh regeneration that increases the computational burden. Moreover, previous slope optimisation studies focus solely on dry conditions. To consider the complex condition of hydrology along with heterogeneity in the soil stratigraphy, this study develops an optimisation procedure by combining the particle swarm optimisation algorithm and the scaled boundary finite element with an image-based meshing technique to optimise slopes with groundwater and achieve the desired factor of safety (FoS). The method changes the slope design parameters and the phreatic surface of groundwater simultaneously, considering user-defined parameters while iteratively re-meshing the optimisation processes. Several cases are presented, demonstrating the optimisation of bench width, bench angle, backfill parameters, and groundwater pumping levels.

Optimising shapes of multiple pin fins in a microchannel using deep reinforcement learning and mesh deformation techniques

The utilisation of advanced pin fin designs in microchannels is useful for enhancing cooling efficiency. Advancements in machine learning and processing power have sparked interest in shape optimisation techniques. This research employs a novel framework that integrates Deep Artificial Neural Networks and Reinforcement Learning with a Computational Fluid Dynamics (CFD) solver to optimise multiple pin fin shapes within a microchannel. By incorporating Radial Basis Function interpolation and Proximal Policy Optimisation alongside FLUENT, acting as the CFD environment, the reinforcement learning agent adeptly explores the design space to enhance the thermohydraulic performance factor (TPF), aiming to maximise Nusselt number while minimising pressure loss. Unlike previous heat transfer optimisation studies, which typically required mesh regeneration at each step, the proposed framework could bypass the meshing step and alter the geometry directly by relying on the RBF interpolation technique to deform the mesh directly. Three distinct scenarios investigated in this study are uniform deformation of all pin fins, deformation of all pin fins arranged in two rows, and individual deformation of each pin fin. Extensive simulations, exceeding 90,000 different cases, demonstrate that although the optimisation process for the individual deformation of each pin fin requires more iterations compared to others, it surpasses them in terms of TPF improvement. Notably, significant improvements are achieved, such as a 49 % enhancement in Nusselt number and a 33 % reduction in pressure drop, culminating in an impressive 63 % increase in TPF compared to the initial geometry.

Fixed-matrix regenerators optimization with wire mesh screens using entropy generation minimization method

The thermodynamic efficiency of a wire mesh fixed matrix regenerative heat exchanger mainly depends on the regenerator’s heating performance and losses. This paper aims to increase the effectiveness and decrease the pressure loss of static regenerators with wire mesh screens as packing geometry. The entropy generated for several combinations of mesh screens is calculated by using the entropy generation minimization method (EGM), and this method helps in finding the right combination with the minimum entropy generation. The study aims to minimize entropy generation by dividing the conventional uniform mesh regenerator pack length into multiple zones by accommodating different combinations of wire mesh screens. For the sample flow condition, it is observed that 3.94 × 103 W/K entropy is generated by uniform mesh, and from 68 hybrid mesh combinations, 80–120–200 generated 2.11 × 103 W/K. By balancing pressure loss and thermal efficiency, the potential of EGM-based optimization is underscored during this study, which improves the regenerator’s performance.

Numerical analysis of the post-installation consolidated response of skirted foundations

The effect of the installation process on the subsequent foundation consolidation response requires assessment when the preload is initially applied. In the framework of effective stress, the influence of large soil deformations during penetration is analysed in this study using a comparison of results from large deformation finite element (LDFE) analysis based on periodic mesh regeneration (Ritss technique) and a 'wished-in-place' small strain finite element (SSFE) model. The LDFE results demonstrate that considerations of the skirt penetration and soil plug bulge lead to different soil excess pore pressure and void ratio change distributions from that of the SSFE analysis, thereby affecting the foundation settlement and consolidated bearing capacity. The normalised fully consolidated undrained bearing capacity grows linearly with the preload ratio for preloads higher than the penetration resistance, and the capacity obtained from the LDFE is higher. The settlement ratio and the proportion of partially consolidated to fully consolidated capacity gain can be represented as a hyperbolic function of a revised dimensionless time factor. The methods integrated in this study can be used to predict the increase in the vertical undrained capacity of skirted foundations after consolidation, accounting for installation effects in engineering practice.

Enhancing alpha solar stirling engine performance with regenerator

Nowadays, as traditional fossil energy sources are in decline, renewable energy sources are being actively sought, and the use of renewable energy is receiving widespread attention. The Dish engine solar power plant is vital in using solar energy. The Stirling engine is the fundamental element of the power plant, responsible for energy conversion. And the internal regenerator has an essential influence on the engine's performance. Hence, this paper focuses on the analysis and improvement of the regenerator. Heat transportation determines its efficiency, while the regenerator is the core component. An efficient Stirling engine cannot occur without a high-quality regenerator. This paper uses simulation experiments to explore the impact of various materials on the regenerator's performance. By comparing the regenerator performance of filled copper foam and stainless-steel mesh, it was found that the copper foam regenerator had a faster start time, while the stainless-steel mesh regenerator had a higher thermal capacity. After this conclusion, an optimized regenerator is designed, filled with different materials at each end according to the material properties. After simulations, it can be concluded that this enhancement improves the regenerator's performance, increasing the Stirling engine's overall efficiency.

Multidimensional numerical simulation of thermodynamic and oscillating gas flow processes of a Gifford-McMahon cryocooler

Abstract The Gifford-McMahon cryocoolers are considered to be prominent candidates for the cooling of high-temperature superconducting magnets, liquefaction of permanent gases, helium recondensation in magnetic resonance imaging machines, cooling of superconducting quantum interference device, etc. In this paper, multi-dimensional numerical simulation is performed to visualize the oscillating heat and fluid flow processes that happen in a mechanically driven GM cryocooler. Influence of the ideal gas equation and real gas equation of states on the cooling behaviour is explained. The minimum achievable refrigeration temperature of a uniform mesh regenerator is compared with a multi-mesh regenerator. It is noticed that a multi-mesh regenerator produces a lower refrigeration temperature as compared to a uniform mesh regenerator. In addition to this, a one-dimensional simulation is conducted and results are compared with multi-dimensional numerical simulation. The no-load temperature value calculated by the one-dimensional model and multi-dimensional model with ideal gas is lower than that of real gas equations. Additionally, the refrigerating capacity calculated by the one-dimensional model and multi-dimensional model with the ideal gas equation is higher than those of the real gas equation of state.

Quadtree SBFEM and optimization based forward and inverse interval analysis for PCM-integrated walls

Interval model is employed to describe the uncertain behavior of phase change materials (PCM) integrated walls. A numerical model is developed for the forward interval analysis, by which the interval bounds of thermal response, such as the temperature on the inner wall and the degree of phase change of PCM, can be estimated when materials and environmental parameters are interval variables. This model integrates the advantages of the quadtree-scaled boundary finite element method (quadtree SBFEM), the Legendre polynomial surrogate (LPS), interval model, and optimization method, to gain a comprehensive benefit of convenient mesh regeneration, reliable bounds estimation, and the alleviation of heavy computational burden in the optimization process. On the other side, a numerical model is presented for the inverse interval analysis, by which the interval bounds of material parameters can be identified when the intervals of measurement of temperature and the degree of phase change of PCM are provided, and the impact of nosy data is taken into account. This model may be enlightening for a deeper investigation of inverse interval analysis of PCM-integrated walls since no attention seems to have been paid to this issue. In terms of computing accuracy, computational cost, and numerical examples are provided to elucidate the effectiveness of proposed approaches, and satisfactory results are achieved in both forward and inverse interval analysis.

A dynamic large-deformation particle finite element method for geotechnical applications based on Abaqus

In this paper, the application of Abaqus-based particle finite element method (PFEM) is extended from static to dynamic large deformation. The PFEM is based on periodic mesh regeneration with Delaunay triangulation to avoid mesh distortion. Additional mesh smoothing and boundary node smoothing techniques are incorporated to improve the mesh quality and solution accuracy. The field variables are mapped from the old to the new mesh using the closest point projection method to minimize the mapping error. The procedures of the proposed Abaqus-based dynamic PFEM (Abaqus-DPFEM) analysis and its implementation in Abaqus are detailed. The accuracy and robustness of the proposed approach are examined via four illustrative numerical examples. The numerical results show a satisfactory agreement with published results and further confirm the applicability of the Abaqus-DPFEM to solving dynamic large-deformation problems in geotechnical engineering.

Geometric parameterization of unit cell configurations for reduced basis approximation

To facilitate rapid yet accurate multiscale homogenization, we formulate geometric mapping schemes that effectively handles the fiber radius changes of a unit cell to dispense with mesh regeneration. To further expedite unit cell analysis involving fiber radius variation, we integrate the formulated geometric transformations into reduced basis analysis using an empirical interpolation method. For demonstration, we examine the proposed geometric parameterization strategies with the linear elastic analyses of square and hexagonal unit cells under tension and shear loads, respectively. Overall, reduced basis analyses combined with the devised geometric mappings are found more efficient than the corresponding finite element analyses while producing insignificant errors.

IMFREE: A versatile software tool for modelling machining processes with particle methods

The current state-of-the-art for the simulation of machining process is the application of the FEM (finite element method). Nevertheless, the cost of FEM analyses for such problems is high due to their complex multi-physics nature, mesh regeneration issues, and small time-length scales. In contrast, particle methods are an alternative numerical approach well-suited for large deformations as in material's chip formation. In this work, the key features and simulation capabilities of iMFREE are presented, which is a massively parallel and robust particle-based code for machining simulations developed at the ETH Zürich. Various applications of iMFREE are shown, where the efficiency is demonstrated in orthogonal cutting simulations for the optimisation of material removal rates, a chip formation study, the inverse identifications of friction law parameters and material constitutive law parameters. Further, the applicability to single and multiple grain grinding simulations of Ti6Al4V and silicon is shown.

Experimental study on regenerative effectiveness and flow characteristics of parallel-plate regenerator in Stirling engine

Regenerator is the critical component of the Stirling engine. Its performance directly affects the efficiency of the whole engine. The heat transfer and flow characteristics of the parallel-plate regenerator (PPR) are experimentally investigated, and the influences of material and geometric parameters on regenerative effectiveness and pressure drop are obtained. The results show that the axial heat conduction will reduce the regenerative effectiveness of the PPR. The higher the thermal conductivity of the plate, the lower the regenerative effectiveness. Larger plate thickness and smaller plate length will also increase the axial heat conduction loss. The PPR shows good flow characteristics. The comparative experiment with the wire mesh regenerator shows that its friction coefficient is much lower than that of the wire mesh regenerator. Through the comprehensive index NPH/NTU defined as the ratio of number of pressure heads (NPH) to number of transfer units (NTU), the overall performances of PPR and wire mesh regenerator are compared. The results show that the PPR has better working performance. To reduce the adverse effect of axial heat conduction on the PPR, the optimization experiment was carried out by segmenting the regenerator into several sections. The results show that the regenerative effectiveness of the segmented PPR is increased by 20%, while the increase of pressure drop is within an acceptable range.

A Novel Embedded Domain Decomposition Method for Electromagnetic Simulation of Structures in Inhomogeneous Medium

A novel embedded domain decomposition method (EDDM) is proposed to simulate electromagnetic scattering from structures in an inhomogeneous medium. In this method, the inhomogeneous medium (e.g., layered substrate) is set as the background subdomain, and the integrated structures (e.g., metallic/dielectric components) with properly defined buffer regions (BRs) are set as the embedded subdomains, where the meshes of two can be completely independent and arbitrarily overlapping. The major contribution of this work lies in the following three aspects. First, to allow for arbitrary inclusion of the embedded subdomains in an inhomogeneous background subdomain, an adaptive BR method is developed. The self-coupling equation is rederived to ensure the consistency of the BR and the inhomogeneous background, and a new mutual-coupling equation is introduced to account for the material and/or conductor differences. Second, the boundary element method (BEM) accelerated by the multilevel fast multipole algorithm (MLFMA) is utilized to truncate the finite-element region so that the computation capability can be enhanced and the extra air box setting of the background subdomain in the original EDDM can be avoided. Third, for structure adjustments such as translations and rotations, we further propose an inherited calculation to avoid mesh regeneration and repeated computation of the self-coupling and preconditioning matrices and also reduce the iteration counts and solution time. Numerical examples have shown the accuracy, robustness, and efficiency of the proposed method.

Performance optimization of a free piston stirling engine using multi-section regenerators based on the response surface methodology

In this paper, a TD-Sage model of a beta-type free piston Stirling engine (β-FPSE) is put forward, which combines thermodynamic-dynamic model with the Sage model. Considering the inhomogeneous distribution of thermal penetration depth, multi-section wire mesh regenerators are proposed to enhance the performance of the FPSE based on the response surface methodology (RSM) and desirability approach. The quadratic regression models of power and efficiency are derived based on the analysis of variance, and the maximum deviation between prediction values from RSM model and actual values from Sage model is less than 5%. The interactive effects of the factors are analyzed and the available energy loss (AE loss) analysis is presented to interpret the mechanism of improvement. The optimal design parameters of two- and three-section regenerators are obtained. Moreover, the maximum output power is obtained when the AE loss of the regenerator is minimized. Compared with the optimal single-section regenerator, the optimal two-section regenerator that consists of meshes with mesh number of 60# (50%) and 80# (50%) improves the power and efficiency by approximately 3.6% and 5.8% respectively. The optimal three-section regenerator that consists of meshes with mesh numbers of 60# (43%), 80# (25%), and 90# (32%) improves the power and efficiency by approximately 4.1% and 6.7%, respectively.

Analysis and Experiment of Heat Transfer Performance of Straight-Channel Grid Regenerator

The design of heat transfer performance of regenerator is the key technology of Stirling machine and is of great significance to ensure the operation efficiency of equipment. In this study the temperature difference between the two ends of regenerator at room temperature is less than 50K. This paper attempts to study the heat transfer performance of the straight channel grid regenerator at room temperature and verify its accuracy. At first, a straight-channel grid regenerator was designed in this study by analyzing the influence of structural parameters on the regenerator in order to reduce the flow resistance loss. The Pore Scale method and Representative Elementary Volume methods were combined to analyze the heat transfer characteristics of the grid regenerator. Compared with the wire mesh regenerator under the same condition, the straight-channel grid regenerator’s flow resistance could reduce by 96.2%. When the length-diameter ratio is 2:1 and the porosity is between 0.4 and 0.5, the heat transfer performance of the grid regenerator is satisfactory when it is applied in Stirling heat pump at room temperature. Then, A segmented variable porosity grid regenerator was designed based on the grid regenerator, and its performance was proved to be better than that of the grid regenerator. Finally, the two regenerators were developed based on additive manufacturing technology, and a single blow experiment platform was built. The experimental results fit well with the simulation results, with the maximum error being less than 1.5%. The experimental results prove the correctness of the model, which lays a foundation for the subsequent analysis of the periodic heat transfer characteristics of the straight-channel grid regenerator.

Investigation of regenerator mesh characteristics for a pulse tube cryocooler

An investigation of regenerator mesh characteristics on a Pulse tube cryocooler’s performance is conducted using Sage V11 software. The cryocooler operates between temperatures of 300 K and 80 K. The components of the cryocooler are free piston linear compressor, aftercooler, regenerator, pulse tube, warm heat exchanger, and inertance tube- bounce space as the phase shifter. The performance of the regenerative cryocoolers depends on the regenerator. The regenerator of this cryocooler consists of a stack of stainless steel meshes. In this paper, a comparison of regenerator stainless steel meshes with mesh number #200, #300, #400, #500 and its combinations were analysed. To choose the best multi mesh combination, the length of the individual meshes is varied so that the total length of the regenerator is unchanged. The performance was analysed based on the Coeffcient of Performance of cryocooler for single mesh type and mesh combinations (combination two) at acceptor temperature of 80 K. The maximum performance with single mesh was with #400 mesh with COP of 6.12%. The cryocooler’s maximum Coeffcient of Performance was with the combination of #400 and #500 meshes in the regenerator. The best multi mesh combination gave 4.071 W cooling power with an input power of 61.92 W with a COP of 6.57%. There was an improvement of 7.26% with the use of multiple mesh regenerator.

Performance evaluation of sintered and stacked mesh regenerator for stirling cycle based LN2 plant

Performance evaluation of sintered and stacked mesh regenerator for stirling cycle based LN2 plant

A multi-objective optimisation study of trimaran hull applying RBF-Morph technique and integrated optimisation platform at two design speeds

ABSTRACT This paper presents an efficient optimisation method to improve the main hull of a trimaran ship, whilst proposing a computational fluid dynamics-based automated approach to reduce total resistance. A mesh-based method is introduced to modify a wave-piercing bow trimaran hull at two cruise and sprint speeds. Therefore, the problem pertains to a hydrodynamic multi-objective optimisation problem. Radial basis function-based mesh-morphing tool is implemented to alter the geometry at the mesh level. Mesh-morphing tool leads to elimination of geometry and mesh regeneration steps that consequently provides a shortcut for the designer's extrication from optimisation time and complexity of geometry modification. Ten global parameters accomplish expansion and contraction of the 10 sections, which are known as Magnification Factor. Optimisation results and design comparison illustrate the applicability and efficiency of the proposed technique. The results demonstrate 6.77% reduction in total resistance at cruise speed and 1.55% at sprint speed.

Influence of misalignment and spacing on the pressure drop through wire mesh Stirling engine regenerators

In order to obtain high Stirling engine efficiencies, pressure losses in the regenerator must be minimized. In this study, numerical methods are used to determine the influence of misalignment and spacing on the pressure drop through stainless steel wire mesh regenerators. Microscope images were taken to discover the average wire misalignment found in wire mesh regenerators, and it was found that regardless of the intended stacking arrangement, the average misalignment was 44%–49%. A 3-dimensional CFD model was validated against previous empirical results, and used to determine the effect of wire mesh misalignment on the pressure drop for steady flow through a regenerator. A new friction factor correlation equation was developed to include the effect of wire misalignment in the form of tortuosity. It was found that if a perfectly aligned regenerator was manufactured, Stirling engine designers could expect a 38%–45% decrease in pressure losses. The numerical model was also used to determine the influence of axial spacing on the pressure drop, and it was found to be dependent on the misalignment, with pressure loss reductions only being realized in highly misaligned cases. As a result of this study, Stirling engine designers can confidently disregard alignment and spacing when assembling wire mesh regenerators, and can more accurately calculate the expected pressure losses.

Experimental study of a free piston Stirling cooler with wound wire mesh regenerator

Free piston Stirling coolers have the advantages of high energy efficiency, environmental friendliness, wide cooling temperature range and easily-controlled cooling capacity, which is very attractive for deep-freezing applications. From the perspective of enhancing its competitiveness, here reports the use of wound wire mesh instead of the conventional stacked wire mesh to fill the regenerator, which brings low material waste, simplified manufacturing process and low flow resistance. In order to optimize the performance, a method of squeezing the bulges with variable heights into the mesh to adjust the porosity is used. A numerical model of cooler is first established to assist the system design, then experiments are done and compared with the simulation results. In the experiments, a coefficient of performance using wound wire mesh regenerator with a porosity of 72.7% is 0.8 at 102 W@-38 °C and 0.25 at 45 W@-80 °C, respectively. Though the comparison with stacked wire mesh regenerator shows that it leads to a relatively worse performance, the cooling performance is still comparable to that of vapor-compression refrigerators in the deep-freezing temperature region. Through further optimization, the application of wound wire mesh is promising.

An iterative method for optimal control of bilateral free boundaries problem

In this paper, a bilateral free boundaries problem is considered. This kind of inverse problems appears in the theory of semiconductors and multi‐phase problems. Using a shape functional and some regularization terms, an optimal control problem is formulated. In addition, we prove its solution existence. The first optimality conditions and the shape gradient are computed. With the finite element method, we write the discrete version of the optimal control problem. To design our proposed scheme, we based on the conjugate gradient, where we use the genetic algorithm to find the best initial guess for the gradient method. At each mesh regeneration, we perform a mesh refinement in order to avoid any domain singularities. Some numerical examples are shown to demonstrate the validity of the theoretical results and to prove the robustness and efficiency of the proposed scheme, especially to identify free boundaries with jump points.