Numerical Simulation Program Research Articles

Planning of Electric Public Transport System under Battery Swap Mode

Applying battery electric buses (BEBs) in the city is a good means to reduce the increasing greenhouse gas emissions and crude oil dependence. Limited by the driving range and charging time, battery swap station seems to be the best option for battery electric buses to replenish energy currently. This paper presents a novel method to plan and design an electric public transport system under battery swap mode, which comprised of battery electric buses, routes, scheduling, battery swap station, etc. Thus, new routing and scheduling strategies are proposed for the battery electric bus fleets. Based on swapping and charging demand analysis, this paper establishes an algorithm to calculate the optimal scales of battery swap station, including scales of battery swapping system, battery charging system and battery packs, and power capacity of output. Regarding the case of Xuejiadao battery swap station serving 6 BEB routes in Qingdao, China, a numerical simulation program is established to evaluate the validity of our methods. The results reflect that our methods can optimize the system scales meeting an equivalent state of operation demand. In addition, sensitivity analyses are made to the scales under different values of battery capacity and charging current. It suggests that the scales and cost of battery swap station can be effectively reduced with the development of power battery manufacture and charging technology in future.

Impacts of SO2 gas impurity within a CO2 stream on reservoir rock of a CCS pilot site: Experimental and modelling approach

In order to evaluate chemical impacts of SO2 impurity on reservoir rock during CO2 capture and storage in deep saline aquifers, several batch reactor experiments were performed on laboratory scale using core rock samples from the pilot CO2 injection site in Heletz. In this experiment, the samples were exposed to pure N2(g), pure CO2(g), and CO2(g) with an impurity of 1.5% SO2(g) under reservoir conditions for pressure and temperature (14.5 MPa, 60 °C). Based on the set-up and the obtained experimental results, a batch chemical model was established using the numerical simulation program TOUGHREACT V3.0-OMP. Comparing laboratory and simulation data provides a better understanding of the rock-brine-gas interactions. In addition, it offers an evaluation of the capability of the model to predict chemical interactions in the target injection reservoir during exposure to pure and impure CO2. The best match between the geochemical model and experimental data was achieved when the reactive surface area of minerals in the model was adjusted in order to calibrate the kinetic rates of minerals. The simulations indicated that SO2(g) tends to dissolve rather quickly and oxidizes under a kinetic control. Hence, it has a stronger effect on the acidity of the brine than pure CO2(g) and as a result, increased mineral dissolution and caused the precipitation of sulfate and sulfide minerals. Ankerite, dolomite, and siderite, the most abundant carbonates in the sandstone rock sample, are subject to stronger dissolution in the presence of SO2 gas. The performed simulations confirmed a slower dissolution rate for ankerite and siderite than for dolomite. The model reproduced the precipitation of pyrite and anhydrite as observed in the laboratory. The dissolution of dolomite observed in the batch reaction test with pure N2 is assumed to be due to slight contamination with oxygen and modelling supported this. The inclusion of SO2 increased the porosity over that of the pure CO2 case, and is thus considered to increase the permeability and injectivity of the reservoir as well. Exposure to SO2 also increased the concentration of trace elements. The calibrated kinetic parameters determined in this study will be used to model the injection and long-term behavior of CO2 at the Heletz field site, and may be used for similar geologic reservoirs.

Meshless method simulation and experimental investigation of crack propagation of CBM hydraulic fracturing

For simulating CoalBed Methane (CBM) hydraulic fracturing using 3-D meshless method, this paper analyzed the hydraulic fracturing mechanism and cracking form for coal rock and established the geometric and mathematical models of hydraulic fracturing propagation in coal rock in terms of the Hillerborg model on crack opening displacement theory. With the theoretical basis of hydromechanics, the formulas for calculating hydraulic pressure inside the fracture by numerical simulation were deduced from the analysis on this fluid-structure interaction problem. The geometric and mathematical models established above were described by 3-D meshless Galerkin (EFG, Element-Free Galerkin) method and compiled into the numerical simulation program using VB and FORTRAN programming language to simulate the fracture propagation for an actual coal rock sample with a drilling hole as an example. Then the physical simulation experiment of hydraulic fracturing propagation of coal seam was conducted on the same coal rock sample. Through the direct observation with naked eyes and detection by advanced instruments of ESEM and Micro-CT, the shape and parameters of cracks on the surface of and inside the coal rock sample were achieved, which indicated that experimental results are reasonably consistent with numerical simulation results.

Higgs compositeness in Sp(2N) gauge theories – Determining the low-energy constants with lattice calculations

As a first step towards a quantitative understanding of the SU(4)/Sp(4) composite Higgs model through lattice calculations, we discuss the low energy effective field theory resulting from the SU(4) → Sp(4) global symmetry breaking pattern. We then consider an Sp(4) gauge theory with two Dirac fermion flavours in the fundamental representation on a lattice, which provides a concrete example of the microscopic realisation of the SU(4)/Sp(4) composite Higgs model. For this system, we outline a programme of numerical simulations aiming at the determination of the low-energy constants of the effective field theory and we test the method on the quenched theory. We also report early results from dynamical simulations, focussing on the phase structure of the lattice theory and a calculation of the lowest-lying meson spectrum at coarse lattice spacing.

Effect of Reynolds number on supercritical helium axial compressor rotors performance in closed Brayton cycle

Supercritical helium has been considered as an ideal working fluid in a number of design studies for closed Brayton cycle due to its thermal properties. But the low density level of supercritical helium, the characteristics of the small flow channel in the turbomachine and the variable working condition method of the system determine that the compressor may run at low Reynolds number. In this paper, the influence of Reynolds number on supercritical helium compressor rotor is investigated under different conditions by numerical simulation program. Effects of specific heat ratio on Reynolds number sensitivity of supercritical helium compressor rotor are also investigated by comparing the calculated results of different working fluids. Special attention is paid to the relationship between properties of working fluids and efficiency. Then, the equations of efficiency and total pressure ratio for different working fluids are established. The results show that the Reynolds number sensitivity of supercritical helium compressor rotor decreases with the increase of tip clearance and increases with the increase of the specific heat ratio.

The matching design of electromagnetic parameters for obtaining excellent microwave-absorption properties by numerical simulation method

Currently, most of microwave-absorption work has focused on the theoretical formula and design rules of microwave absorber in broadband absorption at low frequencies, especially below 6 GHz. In this work, the detailed matching relation of complex permeability, permittivity, absorber thickness, and microwave-absorption properties were studied by setting up the numerical simulation program of microwave absorption according to the transmission-line theory based on cyclic algorithms. By which, the reason why most materials possess weak microwave-absorption performances below 6 GHz was explained, and the methods how to design desired absorbers utilizing the matching relation were also introduced. The concept presented here is suitable and applicable for a tuned microwave-absorber, which is useful while designing a low frequency absorber.

Optical Modeling of Ultrathin Silicon Solar Cells with PC1D

We show that the optical diffusion model embedded in the numerical simulation program PC1D systematically underestimates light‐generated currents in thin textured Si solar cells. The demonstration exploits the exact analytical solution to minority‐carrier transport in uniformly doped regions and the fact that, at the first pass of internal light, the average optical propagation angle, θ, with respect to the device normal is determined by surface texture. We provide a simple correction procedure to remove the aforementioned systematical error. One can so reliably model with PC1D the optical performance of textured thin devices at standard Lambertian regimen (θ = 60° at all wavelengths, λ) that starts at either the first or the second pass of trapped light. We exploit such a possibility to scrutinize with PC1D a reported non‐standard Lambertian optical model, where θ varies with λ.

Numerical simulation of crack growth in piezoelectric structures by BEM

In this paper, a dual boundary element computer program is developed for numerical simulation of a crack propagating in piezoelectric plates under a combined quasi-static electric and mechanical loading. To determine the crack growth path, two fracture criteria are taken into account: the maximum of hoop stress intensity factor (HSIF) and hoop mechanical strain energy release rate (HMERR). By using the displacement extrapolation method, these fracture parameters of any small kinked crack branch are obtained and validated by comparing with the available analytical results. The critical fracture loads for some test specimens are numerically analyzed based on the maximum HMERR fracture criterion. Different electrical boundary conditions on the crack faces are considered and checked with the experimental data. Finally, one crack or a pair of cracks propagating in infinite or finite piezoelectric plates is numerically simulated. The influences of the loading conditions, the anisotropic fracture toughness and the interaction between the cracks on the crack growth paths are also studied. The comparisons with the exiting finite element results show the accuracy and efficiency of the present BEM program for numerical simulation of crack growth in piezoelectric materials.

GPU based numerical simulation of core shooting process

Core shooting process is the most widely used technique to make sand cores and it plays an important role in the quality of sand cores. Although numerical simulation can hopefully optimize the core shooting process, research on numerical simulation of the core shooting process is very limited. Based on a two-fluid model (TFM) and a kinetic-friction constitutive correlation, a program for 3D numerical simulation of the core shooting process has been developed and achieved good agreements with in-situ experiments. To match the needs of engineering applications, a graphics processing unit (GPU) has also been used to improve the calculation efficiency. The parallel algorithm based on the Compute Unified Device Architecture (CUDA) platform can significantly decrease computing time by multi-threaded GPU. In this work, the program accelerated by CUDA parallelization method was developed and the accuracy of the calculations was ensured by comparing with in-situ experimental results photographed by a high-speed camera. The design and optimization of the parallel algorithm were discussed. The simulation result of a sand core test-piece indicated the improvement of the calculation efficiency by GPU. The developed program has also been validated by in-situ experiments with a transparent core-box, a high-speed camera, and a pressure measuring system. The computing time of the parallel program was reduced by nearly 95% while the simulation result was still quite consistent with experimental data. The GPU parallelization method can successfully solve the problem of low computational efficiency of the 3D sand shooting simulation program, and thus the developed GPU program is appropriate for engineering applications.

Modeling and simulation of efficiency droop in GaN-based blue light-emitting diodes incorporating the effect of reduced active volume of InGaN quantum wells

The efficiency droop of InGaN-based blue light-emitting diodes (LEDs) is analyzed using numerical simulations with a modified ABC carrier recombination model. The ABC model is modified to include the effect of reduced effective active volume of InGaN quantum wells (QWs) and incorporated into the numerical simulation program. It is found that the droop of internal quantum efficiency (IQE) can be well explained by the effect of reduced light-emitting active volume without assuming a large Auger recombination coefficient. A simulated IQE curve with the modified ABC model is found to fit quite well with a measured efficiency curve of an InGaN LED sample when the effective active volume takes only 2.5% of the physical volume of QWs. The proposed numerical simulation model incorporating the reduced effective active volume can be advantageous for use in the modeling and simulation of InGaN LEDs for higher efficiency.

Accuracy of Interpretation Methods for Deriving p–y Curves From Model Pile Tests in Layered Soils

Abstract Because of its simplicity and reasonable accuracy, the p–y-curve method is widely used for analyzing laterally loaded piles. The effectiveness of existing approaches for deriving p–y curves is case dependent; thus, a systematic assessment of these interpretation methods is necessary. This study compared p–y curves derived using four data interpretation methods. Instead of experiments, the numerical simulation program LPILE was used to produce hypothetical moment data for positions along a short pile in layered soil. The deduced p–y curves were compared with the “true” p–y curves used for numerical simulations to evaluate the accuracy of the interpretation methods. The comparison demonstrated that the cubic spline method and difference method were the best among the four considered methods for deriving p–y curves. However, the difference method generated a large resistance at the soil surface. Because of this error, the cubic spline method is the preferred method for deriving the response of a laterally loaded pile in layered soil. The results of this study will be useful for obtaining more accurate p–y curves from experimental data and for more effective planning of future experiments.

Numerical Simulation of the Forming Limit of Superplastic AZ31B Magnesium Alloy Sheet

Numerical simulation of superplastic forming limit of AZ31B magnesium alloy sheet was investigated. The damage evolution equation based on the law of the micro-damage evolution and statistical mechanics was derived, and damage characteristic parameters as well as the critical value of damage variable were identified to provide a theoretical ground on which the plastic forming technology of magnesium alloy sheet can be optimized. The theoretical prediction was made with the numerical simulation program, and the results were verified by experiments. The forming limit curve of the theoretical prediction drawn by numerical simulation was established by the basic adaptation of the forming limit curve based on the experimental data.

Simulations and experimental investigation of paint film leveling

The surface structure of a paint film is the result of the interplay of a variety of physical influences, e.g., the superposition of droplets during spray application, the surface tension-driven leveling, and the viscosity increase in the leveling phase. A numerical simulation program is presented that incorporates all the relevant mechanisms of paint film structure formation during and after spray application. The simulation program was validated by comparing simulations and leveling experiments. The influence of the initial film geometry and viscosity on the leveling behavior is demonstrated. For the investigations, model liquids and commercial paints with an increasing complexity of the physical properties were chosen: Newtonian flow behavior without solvent evaporation, Newtonian flow behavior with solvent evaporation, viscoelastic paints with non-Newtonian flow behavior. Four variants are proposed regarding how thixotropy can be measured and how a mathematical model can be created. The advantages and disadvantages of the variants with regard to the implementation of thixotropy in the simulations are listed. A method to predict the leveling behavior of thixotropic paints with simultaneous recovery of the viscous and elastic properties from rheological measurements using discrete relaxation time spectra is presented.

Thermal characteristics and output power performances analysis of solar powered stratospheric airships

Thermal characteristics and output power performances are important factors to be considered in the design and operation of long endurance stratospheric airships. The thermal and output power models of stratospheric airships with solar array are established in this paper. Based on the models, a numerical simulation program is developed. The thermal and output power performances of a solar powered airship are simulated. The effects of solar array on the thermal performances of a stratospheric airship are discussed. The factors affecting the output power of solar cells are studied in detail. The results are conducive to understanding the thermal and output power behaviors of solar powered stratospheric airships.

An inverse modeling approach to obtain P–T conditions of metamorphic stages involving garnet growth and resorption

This contribution presents an approach and a computer program (GrtMod) for numerical simulation of garnet evolution based on compositions of successive growth zones in natural samples. For each garnet growth stage, a new local effective bulk composition is optimized, allowing for resorption and/or fractionation of previously crystallized garnet. The successive minimizations are performed using the Nelder–Mead algorithm; a heuristic search method. An automated strategy including two optimization stages and one refinement stage is described and tested. This program is used to calculate pressure–temperature ( P–T ) conditions of crystal growth as archived in garnet from the Sesia Zone (Western Alps). The compositional variability of successive growth zones is characterized using standardized X-ray maps and the program XMapTools. The model suggests that Permian garnet cores crystallized under granulite-facies conditions at T > 800 °C and P = 6 kbar. During Alpine times, a first garnet rim grew at eclogite-facies conditions (650 °C, 16 kbar) at the expense of the garnet core. A second rim was added at lower P (∼11 kbar) and 630 °C. In total, garnet resorption is modeled to amount to ∼9 vol% during the Alpine evolution; this value is supported by our observations in X-ray compositional maps.

TITAN2D를 이용한 제주도에서 발생 가능한 용암돔 붕괴에 의한 화쇄류 수치모의

본 연구에서는 제주도에서 화산분화에 의해 발생 가능한 화쇄류의 영향 범위를 파악하기 위하여 백록담 외륜산 외측 사면 8개 지점에서 새로운 용암돔이 발생하는 것을 가정하고 이 과정에서의 붕괴로 발생 가능한 화쇄류를 수치모의 하였다. 수치모의에는 TITAN2D 수치모의 프로그램을 사용하였다. TITAN2D프로그램에서 화쇄류 흐름의 속도를 제어하는 변수로 사용되는 내부마찰각과 층저마찰각 중 내부마찰각을 <TEX>$30^{\circ}$</TEX>, 층저마찰각을 <TEX>$20^{\circ}$</TEX>로 설정하였다. 붕괴되는 돔의 높이와 반경, 초기 붕괴 속도, 수치모의 시간 등을 선정하여 총 96개 시나리오에 대하여 수치모의를 실시하였다. 수치모의 결과 돔 붕괴에 의한 화쇄류는 최대 13.4 km까지 도달하여 한라산 정상부 및 제주시와 서귀포시까지 도달하는 것으로 나타났다. 본 연구를 통해 구축된 시뮬레이션 자료들을 이용하여 제주도의 화산 분화 시 발생 가능한 화쇄류의 피해범위 DB를 구축하고 이를 기반으로 재해도를 작성하여 화쇄류로 인한 피해를 최소화하는데 활용할 수 있을 것으로 기대된다. In order to determine the runout range of pyroclastic density currents on Jeju island, lava dome collapse on 8 locations of outer rim of Baekrokdam crater were simulated by TITAN2D numerical simulation program. We set parameters as internal friction angle as <TEX>$30^{\circ}$</TEX> and bed friction angle as <TEX>$20^{\circ}$</TEX> to control velocity of currents occurred by lava dome collapse. Then we set the height and radius of lava dome, initial speed of collapse and simulation times. And we carried out numerical simulations for a total of 96 scenarios. The result shows that the maximum runout distance was 13.4 km in case of lava dome collapse. This study can be used database for manufacturing of hazard map to minimize damages caused by pyroclastic density currents occurred on Jeju island.

Global and Local Cumulative Damage Models for Reinforced Concrete Structures Subjected to Monotonic, Cyclic, or Fatigue Loading

This paper deals with both global and local versions of an energetic analytical model to quantify the damage caused to reinforced concrete (RC) structures under monotonic, cyclic, or fatigue loading. The proposed model closely represents the damage to structures, and presents a damage index (DI) formulation for the RC members. The model is based on the cumulative energy absorbed by the structure. The data required to apply the model can be obtained either from numerical simulation or from experimental test. A computer program has been developed to simulate numerically the response of RC members under cyclic loading. In the program, the non-linear behavior of the materials and the structure involved are taken into account. The proposed numerical simulation model was verified by comparison with practical tests undertaken by other researchers on over 20 full-scale RC columns. The comparison demonstrates that the model provides a realistic estimation of the damage of the RC structural members. The comparison between values of the proposed DI calculated based on experimental test data and numerical simulation results shows that to calculate DI, it is not necessary to perform expensive experimental tests, employing a non-linear structural numerical simulation program is sufficient. The proposed DI is also compared to a damage model proposed by Meyer.

Tribological characteristics of piston rings in a single-piston hydraulic free-piston engine

PurposeA free-piston engine (FPE) is an unconventional engine that abandons the crank system. This paper aims to focus on a numerical simulation for the lubricating characteristics of piston rings in a single-piston hydraulic free-piston engine (HFPE).Design/methodology/approachA time-based numerical simulation program was built using Matlab to define the piston motion of the new engine. And a lubrication mode of piston rings was built which is based on the gas flow equation, hydrodynamic lubrication equation and the asperity contact equation. The piston motion and the lubrication model are coupled, and then the finite difference method is used to obtain the piston rings lubrication performances of the FPE. Meanwhile, the lubrication characteristics of the new engine were compared with those of a corresponding conventional crankshaft-driven engine.FindingsThe study results indicate that compared with the traditional engine, the expansion stroke of the HFPE is longer, and the compression stroke is shorter. Lubrication oil film of the new engine is thicker than the traditional engine during the initial stage of compression stroke and the final stage of the power stroke. The average friction force and power of the hydraulic free piston engine are slightly lower than those of the traditional engine, but the peak friction power of the FPE is significantly greater than that of the traditional engine. With an increase in load, the friction loss power and friction loss efficiency decrease, and with a decrease in equivalence ratio, the friction power loss reduces, but the friction loss efficiency decreases first and then increases.Research limitations/implicationsIn this paper, only qualitative analysis was performed on the tribological difference between conventional crankshaft engine and HFPE, instead of a quantitative one.Practical implicationsThis paper contributes to the tribological design method of HFPE.Social implicationsNo social implications are available now, as the HFPE is under the development phase. However, the authors are positive that their work will be commercialized in the near future.Originality/valueThe main originality of the paper can be introduced as follows: the lubrication and friction characteristics of the new engine (HFPE) were investigated and revealed, which have not been studied before; the effect of the HFPE’s special piston motion on the tribological characteristics was considered in the lubrication simulation. The results show that compared with the traditional crankshaft engine, the new engine shows a different lubrication performance because of its free piston motion.

Enhanced Robust Design Simulation and Application to Engine Cycle and Technology Design

Increased computing power has enabled designers to efficiently perform robust design analyses of engine systems. Traditional, filtered Monte Carlo methods involve creating surrogate model representations of a physics-based model in order to rapidly generate tens of thousands of model responses as design and technology input parameters are randomly varied within user-defined distributions. The downside to this approach is that the designer is often faced with a large design space, requiring significant postprocessing to arrive at probabilities of meeting design requirements. This research enhances the traditional, filtered Monte Carlo robust design approach by regressing surrogate responses of joint confidence intervals for metric responses of interest. Fitting surrogate responses of probabilistic confidence intervals rather than the raw response data changes the problem the engineer is able to answer. Using the new approach, the question can be better phrased in terms of the probability of meeting certain requirements. A more traditional approach does not have the ability to include confidence in the process without significant postprocessing. The process is demonstrated using a turboshaft engine modeled using the numerical propulsion system simulation (NPSS) program. The new robust design process enables the designer to account for probabilistic impacts of both technology and design variables, resulting in the selection of an engine cycle that is robust to requirements and technology uncertainty.

Research on Natural Element Method and the application to simulate metal forming processes

Abstract Due to the special characteristics of metal forming processes (i.e., large deformations, complex nonlinear, etc.), finite element method (FEM) often encounters the mesh distortion problem in simulating large and severe deformation metal forming processes. Once meshes become severely distorted, the whole simulation process cannot be continued unless the remeshing is used. Nevertheless, remeshing usually leads to not only the deterioration of computational precision but also the increase of time-consuming. To solve the problem, a meshless method known as natural element method (NEM) is introduced to analyze metal forming processes in the paper. The shape function of NEM is constructed by employing the natural neighbor interpolation method, and it has the high accuracy of the approximation. In addition, because the shape function possesses the Kronecker δ property like the FEM, the essential boundary conditions can be imposed directly. Therefore, the paper combines NEM with rigid/visco-plastic flow theory and applies it to simulate metal forming processes. Furthermore, a numerical analysis procedure is developed. A numerical example of metal forming processes is analyzed. The validity of the numerical simulation program is evaluated by comparing simulation results with those obtained by rigid/visco-plastic finite element method.