Numerical Simulation Techniques Research Articles

Modelling non-ideal detonations in commercial explosives

Highly non-ideal explosives usually react expressively below their ideal velocities of detonation. In these cases, dimensional effects and product heterogeneities become important to proper model their respective detonation state. Although Direct Numerical Simulation (DNS) techniques can provide a complete and exact solution for this problem, their actual computation cost are still not practical for industrial applications. In order to minimize these constrains, a simplified two-dimensional steady non-ideal detonation model for cylindrical stick explosives is presented. Based on an ellipsoidal shock shape approach (ESSA), the proposed model combines the quasione-dimensional theory for the axial flow solution with the unconfined sonic post-flow conditions at the edge of the explosive. Once calibrated, the model offers the possibility to predict the non-ideal detonation state for any charge diameter, resulting in a full mapping of the diameter-effect curve of the explosive. In addition, the effect of the inert confiner on the detonation flow is calculated by coupling a mechanistic confinement approach with the ESSA model. Thus, the proposed engineering approach is used to model the main properties of one of the most common ammonium nitrate-based explosive used in mining and quarrying industries, including the complete axial flow solution.

Simulated Study and Surface Passivation of Lithium Fluoride-Based Electron Contact for High-Efficiency Silicon Heterojunction Solar Cells

Numerical simulation and experimental techniques were used to investigate lithium fluoride (LiFx) films as an electron extraction layer for the application of silicon heterojunction (SHJ) solar cells, with a focus on the paths toward excellent surface passivation and superior efficiency. The presence of a 7 nm thick hydrogenated intrinsic amorphous silicon (a-Si:H(i)) passivation layer along with thermally evaporated 4 nm thick LiFx resulted in outstanding passivation properties and suppresses the recombination of carriers. As a result, minority carrier lifetime (τ eff) as well as implied open-circuit voltage (iVoc) reached up 933 μs and iVoc of 734 mV, accordingly at 120 °C annealing temperature. A detailed simulated study was performed for the complete LiFx based SHJ solar cells to achieve superior efficiency. Optimized performance of SHJ solar cells using a LiFx layer thickness of 4 nm with energy bandgap (Eg) of 10.9 eV and the work function of 3.9 eV was shown as: Voc = 745.7 mV, Jsc = 38.21 mA cm−2, FF = 82.17%, and η = 23.41%. Generally, our work offers an improved understanding of the passivation layer, electron extraction layer, and their combined effects on SHJ solar cells via simulation.

Technique of numerical simulation of wave processes in a heterogeneous hydrate-containing porous medium

A technique for numerical simulation of wave propagation in a hydrate-containing porous medium consisting of layers with different properties is proposed. The method is based on a mathematical model previously developed by the authors, which considers the difference between the velocities and pressures of the skeleton and fluid, and the McCormack finite difference method. A computer implementation of the model was performed, and preliminary calculations were carried out, which showed the efficiency of the proposed methodology. The possibility of applying this approach to the numerical solution of the problem of propagation and reflection of pressure waves in a layered hydrate-containing porous medium is shown.

A Flux Based Approximation to Simulate Coupled Hydromechanical Problems for Mines with Heterogeneous Rock Types Using the Material Point Method

Advances in numerical simulation techniques play an important role in helping mining engineers understand those parts of the rock mass that cannot be readily observed. The Material Point Method (MPM) is an example of such a tool that is gaining popularity for studying geotechnical problems. In recent years, the original formulation of MPM has been extended to not only account for simulating the mechanical behaviour of rock under different loading conditions, but also to describe the coupled interaction of pore water and solid phases in materials. These methods assume that the permeability of mediums is homogeneous, and we show that these MPM techniques fail to accurately capture the correct behaviour of the fluid phase if the permeability of the material is heterogeneous. In this work, we propose a novel implementation of the coupled MPM to address this problem. We employ an approach commonly used in coupled Finite Volume Methods, known as the Two Point Flux Approximation (TPFA). Our new method is benchmarked against two well-known analytical expressions (a one-dimensional geostatic consolidation and the so-called Mandel-Cryer effect). Its performance is compared to existing coupled MPM approaches for homogeneous materials. In order to gauge the possible effectiveness of our technique in the field, we apply our method to a case study relating to a mine known to experience severe problems with pore water.

Numerical analysis of biothermal-fluids and cardiac thermal pulse of abdominal aortic aneurysm.

Abdominal aortic aneurysms are serious and difficult to detect, conditions can be deadly if they rupture. In this study, the heat transfer and flow physics of Abdominal Aortic Aneurysm (AAA) were discussed and associated with cardiac cycle to illustrate the cardiac thermal pulse (CTP) of AAA. A CTP and infrared thermography (IRT) evaluation-based on AAA and abdomen skin surface detection method was proposed, respectively. Infrared thermography (IRT) is a promising imaging technique that may detect AAA quicker and cheaper than other imaging techniques (as biomarker). From CFD rigid-wall and FSI Analysis, the transient bioheat transfer effect resulted in a distinct thermal signature (circular thermal elevation) on the temperature profile of midriff skin surface, at both regular body temperature and supine position, under normal clinical temperature. However, it is important to note that thermography is not a perfect technology, and it does have some limitations, such as lack of clinical trials. There is still work to be done to improve this imaging technique and make it a more viable and accurate method for detecting abdominal aortic aneurysms. However, thermography is currently one of the most convenient technologies in this field, and it has the potential to detect abdominal aortic aneurysms earlier than other techniques. CTP, on the other hand, was used to examine the thermal physics of AAA. In CFD rigid-wall Analysis, AAA had a CTP that only responded to systolic phase at regular body temperature. In contrast, a healthy abdominal aorta displayed a CTP that responded to the full cardiac cycle, including diastolic phase at all simulated cases. Besides, the findings from FSI Analysis suggest the influence of numerical simulation techniques on the prediction of thermal physics behaviours of AAA and abdominal skin surface. Lastly, this study correlated the relationship between natural convective heat transfer coefficient with AAA and provided reference for potential clinical diagnostic using IRT in clinical implications.

Comparison of Numerical Simulation Techniques of Ballistic Ceramics under Projectile Impact Conditions

This article presents an analysis of the effectiveness of available numerical techniques in mapping the characteristic behavior of ballistic ceramics under projectile impact conditions. As part of the work, the ballistic tests were performed on the layered ceramic/steel composite armor and tested with the 7.62 × 39 mm, armor-piercing incendiary (API) BZ projectile. The experimental tests were then mapped using computer simulations. In numerical analyses, four different techniques were used to describe cubic ceramic tiles Al2O3 placed on the ARMOX 500T steel backing plate, i.e.,: the Finite Element Method without Erosion (FEM), Finite Element with erosion (FEM + Erosion), Smoothed Particles Hydrodynamics (SPH) and a hybrid method that converts finite elements to SPH particles after exceeding the defined failure criteria (FEM to SPH conversion). The effectiveness of the individual methods was compared in terms of quality (mapping of characteristic phenomena occurring during the penetration process), quantity (bulge height of the backing plate) and time needed to complete the calculations. On the basis of the results of the experiments and numerical simulations, it was noticed that the most accurate reproduction of the phenomenon of ballistic impact of AP projectiles on ceramic/steel composite armor can be obtained by using a hybrid method, incorporating the conversion of finite elements into SPH particles. This method should be used in cases where accuracy of the results is more important than the time required to complete the calculations. In other situations where the purpose of the calculation is not to determine, for example, the exact value of penetration depth but only to observe a certain trend, the FEM method with defined erosion criteria (variant 2), which is more than 10 times faster, can be successfully used.

Prediction of Conformance Control Performance for Cyclic-Steam-Stimulated Horizontal Well Using the XGBoost: A Case Study in the Chunfeng Heavy Oil Reservoir

Conformance control is an effective method to enhance heavy oil recovery for cyclic-steam-stimulated horizontal wells. The numerical simulation technique is frequently used prior to field applications to evaluate the incremental oil production with conformance control in order to ensure cost-efficiency. However, conventional numerical simulations require the use of specific thermal numerical simulators that are usually expensive and computationally inefficient. This paper proposed the use of the extreme gradient boosting (XGBoost) trees to estimate the incremental oil production of conformance control with N2-foam and gel for cyclic-steam-stimulated horizontal wells. A database consisting of 1000 data points was constructed using numerical simulations based on the geological and fluid properties of the heavy oil reservoir in the Chunfeng Oilfield, which was then used for training and validating the XGBoost model. Results show that the XGBoost model is capable of estimating the incremental oil production with relatively high accuracy. The mean absolute errors (MAEs), mean relative errors (MRE) and correlation coefficients are 12.37/80.89 t, 0.09%/0.059% and 0.99/0.98 for the training/validation sets, respectively. The validity of the prediction model was further confirmed by comparison with numerical simulations for six real production wells in the Chunfeng Oilfield. The permutation indices (PI) based on the XGBoost model indicate that net to gross ratio (NTG) and the cumulative injection of the plugging agent exerts the most significant effects on the enhanced oil production. The proposed method can be easily transferred to other heavy oil reservoirs, provided efficient training data are available.

Nonlinear evolution of Kinetic Alfvén Wave and the associated turbulence spectra in laser produced plasmas and laboratory simulation of astrophysical phenomena

This investigation presents the nonlinear interplay between pump wave (Kinetic Alfvén Wave (KAW)) and low-frequency ion acoustic wave (IAW) in the magnetized plasma. The model is developed by taking into account the ponderomotive nonlinearity associated due to the pump KAW. The coupled dimensionless equations (pump and IAW) are solved by adopting numerical simulation technique. The deduced results give the localization and filamentary structures of KAW, which eventually become chaotic with the evolution of time. The fundamental physics governing the dynamics of these two waves is influenced by the plasma beta () parameter; thereby affecting the nature of nonlinearity, dispersive properties and magnetic field amplification. The saturated spectra are analogous to that observed for many astrophysical scenarios for low (Chatterjee et al 2017 Nat. Commun. 8 15970) and high beta (White et al 2019 Nat. Commun. 10 1758; Tzeferacos et al 2017 Phys. Plasmas 24 041404) plasma. This theoretical model outlining the nonlinear interaction can be imperative in understanding the dynamics of magnetic field amplification in various astrophysical scenarios.

Heat transfer model of the front-end capillary heat exchanger of a subway source heat pump system

The use of metro source heat pumps can help alleviate the deterioration of the subway thermal environment and convert the “waste heat” into a valuable resource for heating aboveground buildings. At present, this technique represents a highly effective energy-saving method to control the thermal environment in subway tunnels. In this study, the front-end capillary heat exchanger (CHE) of the subway source heat pump system of a demonstration project in Qingdao was considered as the research object. Considering a CHEthat was installed in a multilayer circularcomposite medium, a fluid-thermal coupled heat transfer model was established by combining theoretical analyses and numerical simulation techniques. A module pertaining to the CHE was implemented on the TRNSYS platform based on the corresponding fluid-thermal coupled heat transfer model. The field test results for the performance of the subway tunnel CHE system were compared with the simulation results of the module. The maximum and average relative errors were 9.3% and 3.5%, respectively. The verification results indicated that the developed simulation module is highly accurate and can satisfy the requirements of practical engineering applications. Based on the validated module, the influence of three typical design factors (inlet water temperature, flow velocity and type of surrounding rock) on the heat transfer performance of CHE was analyzed. This study can provide a theoretical basis for the design and operation optimization of front-end CHEs of metro source heat pump systems.

Fused Filament Fabrication Process: A Review of Numerical Simulation Techniques.

Three-dimensional printing (3DP), also known as additive manufacturing (AM), has rapidly evolved over the past few decades. Researchers around the globe have been putting their efforts into AM processes improvement and materials development. One of the most widely used extrusion-based technology under AM processes is Fused Deposition Modeling (FDM), also known as Fused Filament Fabrication (FFF). Numerical simulation tools are being employed to predict the FFF process complexities and material behavior. These tools allow exploring candidate materials for their potential use in the FFF process and process improvements. The prime objective of this study is to provide a comprehensive review of state-of-the-art scientific achievements in numerical simulations of the FFF process for polymers and their composites. The first section presents an in-depth discussion of the FFF process’s physical phenomena and highlights the multi-level complexity. The subsequent section discusses the research efforts, specifically on numerical simulation techniques reported in the literature for simulation of the FFF process. Finally, conclusions are drawn based on the reviewed literature, and future research directions are identified.

Modelling and Simulation using Finite Element Method of Surface Acoustic Wave Biosensor for Gas Detection Application

A surface acoustic wave (SAW) sensor detects changes in physical properties such as mass and density on its surface. Compared to other types of sensors, SAW sensor have a good stability, high selectivity and sensitivity, fast response, and low-cost. On the other hand, to design and optimize a SAW biosensor requires a long process including time and cost using conventional methods. Therefore, numerical simulation and computational modelling are useful and efficiently conduct analysis for the SAW biosensor. In this paper, a numerical simulation technique is used to analyse the SAW device sensitivity for the application of gas detection. The SAW biosensor can detect very small mass loading by changing its sensor resonance frequency. The two-dimensional (2D) device model is based on a two-port SAW resonator with a gas sensing layer. We made two design of SAW biosensor device with frequency of 872 MHz and 1.74 GHz. A gas with vary concentration from 1 to 100 ppm were used to determine the change of the device resonance frequency. As a result, the high frequency (1.74 GHz) device, shows that the resonance frequency is shifted larger than to the low frequency (872 MHz) device. In addition, the high frequency device offers five times more sensitivity than the low frequency device. By changing the sensor design, the sensor characteristics such as sensitivity can be altered to meet certain sensing requirements. Numerical simulation provides advantages for sensor optimization and useful for nearly representing the real condition.

Methodology to estimate the modulus of elasticity of parts manufactured by FFF/FDM combining finite element simulations and experimental tests

Due to the manufacturing characteristics “layer by layer” of Additive Manufacturing processes (AM) such as Fused Filament Fabrication (FFF) or Fused Deposition Modelling (FDM) techniques, the manufactured parts exhibit anisotropic behaviour, and therefore it is complex to estimate their mechanical response. Consequently, finite element (FE) modelling of the performance of this kind of additive parts can be time-consuming, especially for implicit algorithms. For this reason, in this work, a proposal of simplified FEM model is presented to reduce the computation time but keeping accurate results, when predicting the modulus of elasticity of FDM parts. The methodology is based in a combination of experimental and numerical simulation techniques. A FEM model is developed using the commercial finite element software Abaqus/Standard. The parameters considered in this study are the percentage of infill (25, 50 and 75%) and the construction orientation (XYZ). Tensile tests were performed following the guidelines specified in the standards UNE-EN ISO 17296-3 and UNE-EN ISO 527-2. The comparison of the elastic behaviour obtained by both experimental and simulation techniques allowed to adjust the simulation parameters, resulting in a simplified FE model. The methodology presented can be used as a prediction tool to analyse the tensile mechanical behaviour of this kind of samples.

EDUCATIONAL EFFECTIVENESS OF A VIRTUAL DESIGN STUDIO ON ZERO-ENERGY BUILDING DESIGNS: THE CASE OF THE U.S. SOLAR DECATHLON DESIGN CHALLENGE

ABSTRACT Ongoing global architectural agendas span climate change, energy, a carbon-neutral society, human comfort, COVID-19, social justice, and sustainability. An architecture studio allows architecture students to learn how to solve complicated environmental issues through integrated thinking and a design process. The U.S. Department of Energy’s Solar Decathlon Design Challenge enables them to broaden their analytic perspectives on numerous subjects and strengthen their integrated thinking of environmental impacts, resilience, sustainability, and well-being. However, the unprecedented impact of the global COVID-19 pandemic transformed the physical studio-based design education system into an online-based learning environment. Mandatory social distancing by the global COVID-19 pandemic restricted interactive discussions and face-to-face collaborations for the integrated zero-energy building design process, which requires features of architecture, engineering, market analysis, durability and resilience, embodied environmental quality, integrated performance, occupant experience, comfort and environmental quality, energy performance, and presentation. This study emphasizes the educational effectiveness of virtual design studios as a part of the discourse on architectural pedagogy of zero-energy building (ZEB) design through integrated designs, technological theories, and analytic skills. The survey results of ten contests show educational achievement with over 90% of the highest positive tendency in the categories of embodied environmental quality and comfort and environmental quality, whereas the positive tendency of educational achievement in the categories of integrated performance, energy performance, and presentation were lower than 70%. The reason for the low percentage of simulation utilization and integrated performance was the lack of a proper understanding of and experience with ZEB simulations and evaluations for undergraduate students. Although VDS is not an ideal pedagogical system for the iterative design critique process, it can support the learning of the value of architectural education, including integrative design thinking, problem-solving skills, numerical simulation techniques, and communicable identities through online discussions and feedback during the COVID-19 pandemic.

Research on Water Invasion Mode and Water Control Counter Measures of Geological MX Gas Reservoir

The MX gas reservoir is a typical carbonate gas reservoir and there are three types of water production characteristics in producing wells during the development process: fast rising type, slow rising type and stable type. The overall water invasion mode is dominated by the edge water invasion mode, with four types of water invasion modes including bottom water cone type, edge water finger type, edge water tongue type and native movable water tongue type. In this paper, numerical simulation techniques are used to investigate water management countermeasures for MX gas reservoirs based on the dynamic identification of water invasion. The results show that, after optimisation of the drainage and water control plans, the gas reservoir can produce steadily until the end of 2025 at a recovery rate of 3.06%, extending the time of steady production by about 9 months. In view of the relatively uniform advancement of fracture water channel and edge water into the interior of the gas reservoir, it is feasible to adopt active drainage and edge water control measures respectively to reduce the risk of water intrusion in the gas reservoir and ensure stable gas production.

Flexural buckling resistance of rectangular welded box section columns

AbstractApplication of high strength steel (HSS – S420 and higher steel grades) is growing nowadays in the civil engineering praxis due to the numerous advantages compared to the normal strength steel (NSS – S235‐S355). The accurate consideration of the flexural buckling resistance of HSS structures is highly important in the design. Higher yield strength indicates the applicability of smaller cross‐sections, which might be more sensitive for stability problems. The purpose of the current study is (1) to investigate the flexural buckling behaviour of HSS welded rectangular box section columns and (2) to propose a reliable column buckling curve.Residual stress in steel structural elements have significant influence on the flexural buckling behaviour of welded box section columns. This phenomenon causes that hot‐rolled, cold‐formed and welded sections have different flexural buckling behaviour and resistance. Previous research results of the authors proved that different buckling curves can be used for HSS or NSS welded square box section columns. Research is continued and extended to the investigation of rectangular box sections, which significantly increase the applicability of the design proposals. The buckling resistances for NSS and HSS rectangular welded box section columns are determined by using deterministic numerical simulation technique for a wide range of relative slenderness and steel grades. Based on the simulation results buckling curves are proposed for all the analysed steel grades and aspect ratios.

Thrust Characteristics of Ducted Propeller and Hydrodynamics of an Underwater Vehicle in Control Motions

A numerical technique to simulate the hydrodynamic behavior of ducted propellers attached to an underwater vehicle traveling under the mutually interacting flow fields of the vehicle and the propellers is proposed; the hydrodynamic performance of the propellers and the hydrodynamic loading on the main body of the vehicle when it is in different kinds of motion is investigated numerically. In the research, 3D geometric models of the duct, propeller, and main body of the vehicle are first constructed according to their geometrical features. A computational fluid dynamics (CFD) technique based on the hybrid algorithm of dynamic mesh-nested sliding mesh is applied to solve the Navier–Stokes equations that govern the fluid motion around the duct, propeller, and main body of the vehicle when it is in motion. These equations are solved numerically with the CFD code Fluent. With the proposed numerical simulation technique, the hydrodynamic characteristics of the thrusts generated by the ducted propellers and the loading on the main body in the vehicle system under the mutually interacting flow fields are observed. The results of our numerical simulation indicate that the hybrid algorithm of dynamic mesh-nested sliding mesh can simulate multiple degrees of freedom of motion in underwater vehicle systems. In different motion states, the main body exerts a significant influence on the investigated flow fields; during the vehicle motions, negative wakes are formed on both sides of the main body, which lead to a decrease in the thrusts generated by the propellers on both sides. The thrust of the middle propeller is greater than that of the normal single one because of the obstructing effect in the tunnel caused by the main body.

Physical and numerical instabilities of radiatively cooling shocks in turbulent magnetized media

ABSTRACT We consider the influence of a fluctuating magnetic field on to the structure formation and instabilities of radiatively cooling blast waves. The study is based on an example of optically thin post-adiabatic supernova remnants (SNRs) in the homogeneous interstellar medium. By means of analytic estimations and full-scale multidimensional simulations, we investigate the roles of thermal, hydrodynamic (corrugation, pulsational, convective, Rayleigh–Taylor, linear and non-linear Vishniac) and numerical instabilities (‘carbuncle’ and grid-forced effects). It is found that of primary importance is the interplay of the thermal instability with quasi-regular and random components of the interstellar field. Bending fluctuations caused by the latter can be strongly amplified by non-linear Vishniac instability in the SNR regions where the regular component is almost normal to the shock. The instabilities driven by counter-directional pressure and density gradients are limited mostly to very narrow post-shock cooling layers, transient perturbations of the same short scales, and rather weakly magnetized environments. Some of these results can also be applied to radiative shocks separating optically thick media from thin or semitransparent ones. Several recommendations and requirements on numerical simulation techniques are formulated.

Simulation of DC surface flashover of epoxy composites in compressed nitrogen

To date, numerical simulation techniques for surface flashover are still under development. In this work, a DC surface flashover numerical simulation model is constructed based on a gas–solid coupling surface flashover theoretical model with a multilayered structure at the gas–solid interface. Considering the effects of solid, gas, and gas–solid interaction on surface flashover, bipolar charge transport in the solid surface layer, collision ionization in the gas phase layer, secondary electron emission, and gas adsorption in the gas surface layer are combined to calculate the surface flashover voltage. By initializing model parameters, surface charge transport dependent dc surface flashover voltages of epoxy composites in compressed nitrogen are calculated. The results indicate that the surface flashover voltage increases with surface deep trap level, deep trap density, shallow trap density, and carrier mobility; however, surface flashover voltage decreases with surface shallow trap level and surface charge density. To further investigate the effects of surface trap on surface flashover, a “U-shaped” curve is constructed to describe the relationship between surface flashover voltage and surface trap level by the simulation method which shows good agreement with experimental results. The simulation indicates surface flashover voltage of epoxy composites is influenced by surface deep and shallow traps in the solid surface layer—shallow traps mainly influence surface charge dissipation, while deep traps mainly influence electron emission on the solid surface. The value of Ptr/Pde is crucial for the dominating surface trap in surface flashover.

A process-based model and simulation system of dynamic change and spatial variation in large-scale terrestrial ecosystems

More attention has been paid to the monitoring, assessment, prediction, early warning and sustainable management of regional ecological environment and the changes of ecosystem state in recent years. It is an important scientific and technological task to develop quantitative methods and numerical simulation techniques for ecosystem modelling, and to construct the continental scale numerical simulator with the characteristics of multi-process coupling, multi-technology integration, and multi-objective application for stimulating research on ecosystem and global change and its resources, environment and disaster effects, based on the in-depth understanding of the components, processes, functions, patterns, and their interaction mechanism of terrestrial ecosystem. Here, we reviewed the current status and future direction of terrestrial ecosystem models, and discussed the conceptual framework of developing the simulation system of dynamic change and spatial variation in large-scale terrestrial ecosystems and its resource and environment effect, as well as basic issues on the function orientation and structure design of the simulation system, which would provide reference for constructing Chinese terrestrial ecosystem numerical simulator.

The Influence of Radial and Axial Gaps on Volumetric Efficiency of External Gear Pumps

The design of gear pumps and motors is focused on more efficient units which are possible to achieve using advanced numerical simulation techniques. The flow that appears inside the gear pump is very complex, despite the simple design of the pump itself. The identification of fluid flow phenomena in areas inside the pump, considering the entire range of operating parameters, is a major challenge. This paper presents the results of simulation studies of leakages in axial and radial gaps in an external gear pump carried out for different gap shapes and sizes, as well as various operating parameters. To investigate the processes that affect pump efficiency and visualize the fluid flow phenomena during the pump’s operation, a CFD model was built. It allows for a detailed analysis of the impact of the gears’ eccentricity on leakages and pressure build-up on the circumference. Performed simulations made it possible to indicate the relationship between leakages resulting from the axial and radial gap, which has not been presented so far. To verify the CFD model, experimental investigations on the volumetric efficiency of the external gear pump were carried out. Good convergence of results was obtained; therefore, the presented CFD model is a universal tool in the study of flow inside external gear pumps.