Numerical Simulation Tools Research Articles

Theoretical and Numerical Study on Electrical Resistivity Measurement of Cylindrical Rock Core Samples Using Perimeter Electrodes

The estimation of hydraulic and mechanical properties of bedrock is important for the evaluation of energy-related structures, including high-level nuclear waste repositories, hydraulic fracturing wells, and gas-hydrate production wells. The hydraulic conductivity and stress–strain curves of rocks are conventionally measured through laboratory tests on cylindrical samples. Both ASTM standards for hydraulic conductivity and compressive strength involve the use of the planar bases of a cylindrical sample. Hence, an alternative test method is required for the simultaneous measurement of hydraulic conductivity and stress–strain curves. This study proposes a novel electrical resistivity estimation method using two perimeter electrodes for the estimation of hydraulic properties. The theoretical background for the perimeter electrode setup is derived and the COMSOL MultiPhysics® finite element numerical simulation tool is employed to verify the derived theoretical equation. The accuracy of the numerical simulation tool is first validated by simulating the ASTM standard testing method for electrical resistivity. The electrical resistance values derived from the theoretical equation and numerical simulation are compared for different electrical resistivity and electrode radius. The assumed equidistant, circular equipotential surface results in a theoretical lower bound for the measured electrical resistance in the cylindrical specimen. The introduction of a phenomenological distortion factor to correct for the theoretical equipotential surface results in a good fit with the numerical simulation results. The effects of electrode length and equivalent strap electrodes were investigated to assess the applicability of the suggested method for laboratory testing. Consequently, this study presents an effective alternative theoretical assessment method for the lower bound electrical resistivity of cylindrical rock core samples under confining conditions when the installation of base electrodes is infeasible.

Towards Numerical Simulation Tool of Motion Solid Particles in Fluid Flow

We present here a numerical method to compute the motion of rigid particles in fluid flow with a non-elastic impact law. Many methods have been proposed recently and different strategies have been used to compute such flows. Our motivation is the handling of the non-overlapping constraint in fluid-particle direct simulations. Each particle is treated individually and the Navier-Stokes equations are solved for the moving fluid by Fluent code which is based on the Finite Volume Method. The contact-handling algorithm, which is implemented in a research C ++, is based on the projection of the velocity field of the rigid particles over the velocity field of the fluid flow. The method consists of imposing a constraint on the velocity field of the particles, as a guarantee that at each time step the calculated particle velocity field belongs to an eligible velocity field of the fluid. In this case study, an Uzawa algorithm has been applied.

The 2020 glacial lake outburst flood at Jinwuco, Tibet: causes, impacts, and implications for hazard and risk assessment

Abstract. We analyze and reconstruct a recent glacial lake outburst flood (GLOF) process chain on 26 June 2020, involving the moraine-dammed proglacial lake – Jinwuco (30.356∘ N, 93.631∘ E) in eastern Nyainqentanglha, Tibet, China. Satellite images reveal that from 1965 to 2020, the surface area of Jinwuco has expanded by 0.2 km2 (+56 %) to 0.56 km2 and subsequently decreased to 0.26 km2 (−54 %) after the GLOF. Estimates based on topographic reconstruction and sets of published empirical relationships indicate that the GLOF had a volume of 10 million cubic meters, an average breach time of 0.62 h, and an average peak discharge of 5602 m3/s at the dam. Based on pre- and post-event high-resolution satellite scenes, we identified a large debris landslide originating from western lateral moraine that was most likely triggered by extremely heavy, south-Asian-monsoon-associated rainfall in June 2020. We back-calculate part of the GLOF process chain, using the GIS-based open-source numerical simulation tool r.avaflow. Two scenarios are considered, assuming a debris-landslide-induced impact wave with overtopping and resulting retrogressive erosion of the moraine dam (Scenario A), as well as retrogressive erosion without a major impact wave (Scenario B). Both scenarios are in line with empirically derived ranges of peak discharge and breach time. The breaching process is characterized by a slower onset and a resulting delay in Scenario B compared to Scenario A. Comparison of the simulation results with field evidence points towards Scenario B, with a peak discharge of 4600 m3/s. There were no casualties from this GLOF, but it caused severe destruction of infrastructure (e.g., roads and bridges) and property losses in downstream areas. Given the clear role of continued glacial retreat in destabilizing the adjacent lateral moraine slopes and directly enabling the landslide to deposit into the expanding lake body, the GLOF process chain can be plausibly linked to anthropogenic climate change, while downstream consequences have been enhanced by the development of infrastructure on exposed flood plains. Such process chains could become more frequent under a warmer and wetter future climate, calling for comprehensive and forward-looking risk reduction planning.

Quantum-Driven Energy-Efficiency Optimization for Next-Generation Communications Systems

The advent of deep-learning technology promises major leaps forward in addressing the ever-enduring problems of wireless resource control and optimization, and improving key network performances, such as energy efficiency, spectral efficiency, transmission latency, etc. Therefore, a common understanding for quantum deep-learning algorithms is that they exploit advantages of quantum hardware, enabling massive optimization speed ups, which cannot be achieved by using classical computer hardware. In this respect, this paper investigates the possibility of resolving the energy efficiency problem in wireless communications by developing a quantum neural network (QNN) algorithm of deep-learning that can be tested on a classical computer setting by using any popular numerical simulation tool, such as Python. The computed results show that our QNN algorithm can be indeed trainable and that it can lead to solution convergence during the training phase. We also show that the proposed QNN algorithm exhibits slightly faster convergence speed than its classical ANN counterpart, which was considered in our previous work. Finally, we conclude that our solution can accurately resolve the energy efficiency problem and that it can be extended to optimize other communications problems, such as the global optimal power control problem, with promising trainability and generalization ability.

Seismic wave modeling in vertically varying viscoelastic media with general anisotropy

Seismic anisotropy, wave attenuation, and dispersion are critical phenomena of wave propagation in real media. Full-wavefield modeling of wave behavior in such media plays an important role in investigating dynamic features of the earth’s interior and in full-waveform inversion of anisotropic parameters and velocity dispersion. We have developed a numerical scheme to model the full-waveform response from a point source in a vertically varying viscoelastic medium of arbitrary anisotropy. The method is implemented in the frequency domain, so the complexity of anelasticity and anisotropy can be described by a complex elastic stiffness matrix and frequency-dependent moduli can also be readily incorporated. In our scheme, we solve the elastodynamic equations for general anisotropy through finite-element method in the frequency-wavenumber domain and we use the stiffness reduction method to suppress reflections from artificial boundaries along the depth direction. A nonuniform 2D Fourier transform strategy is developed to reconstruct the spatial-domain counterparts from the wavenumber-domain solutions. The time-domain responses are then obtained by taking inverse fast Fourier transform with respect to frequency. We validate the method by comparing the numerical results with the exact solutions for a homogeneous transversely isotropic model and a two-layered model. In the application example, we further proved the feasibility and generality of the scheme using an attenuative, dispersive model with velocity and attenuation anisotropy. Our scheme enjoys significant advantages in incorporating various viscoelastic/dispersive behaviors and general anisotropy, and thus provides a useful tool for numerical simulation of dynamic responses in practical application.

Simulating advance distance in border irrigation systems based on the improved method of characteristics

Improving the simulation accuracy of the advance distance based on the method of characteristics is essential to develop numerical solutions for simulating surface irrigation. Instead of volume balance in the traditional method of characteristics (T-MC), the position of critical flow is determined to simulate the advance distance in the improved method of characteristics (I-MC), which is used in border irrigation systems with rapid variation in inflow discharge in the current research. Specifically, the zones of both subcritical and supercritical flow were firstly distinguished to determine the position of the critical flow point, which was also the upstream boundary of the wetting front region, and then the advance distance was calculated by applying the diffusive wave equation in the wetting front region. The results showed that the I-MC accurately simulated the advance distance with high determination coefficients (0.984-0.998) and low errors (root mean square error of 0.35-1.56 min and coefficient of residual mass of 0.01-0.06), which performed much better than the T-MC. The I-MC provided a suitable and simple numerical simulation tool to improve the establishment of numerical surface irrigation models. Keywords: border irrigation, numerical solution, advance distance, method of characteristics DOI: 10.25165/j.ijabe.20211403.5877 Citation: Liu K H, Jiao X Y, Guo W H, Salahou M K, Gu Z. Simulating advance distance in border irrigation systems based on the improved method of characteristics. Int J Agric & Biol Eng, 2021; 14(3): 156–162.

Analytic Design of Segmented Phase Grating for Optical Sensing in High-Precision Alignment System.

Ultra-precision measurement systems are important for semiconductor manufacturing processes. In a phase grating sensing alignment (PGA) system, the measurement accuracy largely depends on the intensity of the diffraction signal and its signal-to-noise ratio (SNR), both of which are associated with the grating structure. Although an equally segmented grating structure could increase the signal of a high odd order, it could also strengthen the signals at the zeroth and even orders which are the main contributors of stray light. This paper focuses on the practical problem of differently responding diffraction orders but in one grating structure. An analytical relationship has been established between the diffraction efficiency and the segment structure of phase grating. According to this analytic model, we then propose a design method to increase the diffraction signal at high odd orders and, meanwhile, to decrease it at the zeroth and even orders. The proposed method provides a fast and effective way to obtain the globally optimal grating structure in the valid scope. Furthermore, the design examples are also verified by means of numerical simulation tool–rigorous coupled-wave analysis (RCWA) software. As a result, the proposed method gives insight into the diffraction theory of segmented grating and the practical value to greatly improve the design efficiency.

Design of substrate integrated waveguides based on nanowires: Numerical guidelines

AbstractA thorough study of the parameters influencing the operation of devices based on nanowired alumina substrate is presented. The basic structures are realized by growing metallic nanowires inside alumina porous substrate. The control of the areas wherein growth occurs allows building of various microwave devices supported on the filled template. The performances of these devices depend on the material parameters and topology/geometry in presence. These devices have the particularity to combine nanoscale, through the use of nanowires, and millimeter scale that is characteristic of microwave devices and their associated operating wavelength. The gap between the two‐scale ranges implies that analytical models and numerical simulation tools have to be combined to modelize and design performant microwave devices, such as Nanowired Substrate Integrated Waveguides (NSIWs) devices that are the subject of the paper. A deep parametric analysis of the properties and operation of the basic NSIW is presented and is followed by the illustration of two designs: a simple NSIW line, and an EBG NSIW filter.

Prediction of Anisotropic Elastoplastic Instability with Rice’s Criterion in Plane Compression

Objectives: The main objective of this work is the development of a mechanically coherent framework for the implementation of numerical simulation tools for sheet metal forming processes. The work at hand is part of a study of the mechanical behaviour of metallic materials subjected to large elastoplastic deformations during channel-die testing and a study of the mechanisms that limit their formability and cause their instability. We analyse the effect of induced rotation on the appearance of plastic instability predicted by Rice’s criterion. Methods: At the beginning, an adequate modelling of the mechanical behaviour of metals in large elasto-plastic deformations using the formalism in rotational referential is made. Then, a prediction of plastic instabilities is developed using Rice’s bifurcation criterion. Indeed, the integration of the law of anisotropic elastoplastic behaviour is presented in a three-dimensional kinematics framework in order to write the deformation tensor as a superior triangular matrix, with Hill’s anisotropic yielding function, using Runge Kutta’s method to integrate the obtained equations. Findings: we were able to show that Rice’s criterion can be used for any kind of material and that this criterion is effective in predicting what happens in metals. It predicts shear-band bifurcation in a continuous plastic medium. Hill’s criterion is suitable for what is weakly anisotropic. The model described above represents a good mathematical framework for analysing the behaviour of materials and plastic instability. Novelty: This study allows to apply Rice’s criterion in the case of a channel-die compression test, so as to locate plastic instability and see the appearance of shear bands for all types of materials; it demonstrates that the initial rotation of the material influences the appearance of shear-bands during a test simulating rolling. Keywords: Elastoplastic; Large deformations; Anisotropy; Plastic instability; Localisation

Численное моделирование многостадийных бимолекулярных фотореакций в жидкости: алгоритмы и программные средства

In this paper we consider the tools for numerical simulation of multistage bimolecular photoreactions assisted by diffusive mobility of reactant molecules in viscous solutions. To describe these processes, the differential encounter theory (DET) is extended to account for the coherent dynamics of certain degrees of freedom (for example, electronic spins of reactants and intermediates). The model involves diffusion of reactants in solution and multistage/multichannel physicochemical processes proceeding both at the level of individual molecules and encounter complexes. Algorithms for numerical solution of model equations are proposed, which are related to evaluation of evolution operators. The algorithm for computing the quantum propagator for the density matrix based on the Trotter splitting is presented. A software package for simulation of multistage photoreactions has been developed using the suggested numerical approaches. The structure of the key software components is presented, examples of the program model construction are presented. A software testing has been carried out, showing good correspondence between the numerical results and exact solutions of the model equations in certain particular cases. As an example, a photoreaction with participation of 9,10-dimethylanthracene and 1,3-dicyanobenzene in acetonitrile solution has been considered, and basic procedures for configuring and simulating multistage bimolecular photoprocesses are shown. An importance of coherent description of the electronic spin evolution at the radical stage is shown.

Effect of Different Forms of Periodic Piecewise Linear Forces on Duffing Oscillator

The paper highlights the effect of different forms of periodic piecewise linear forces in the ubiquitous Duffing oscillator equation. The external periodic piecewise linear forces considered are Triangular, Hat, Trapezium, Quadratic and Rectangular. With the aid of some numerical simulation tools such as bifurcation diagram, phase portrait and Poincare´ map, the different routes to chaos and various strange attractors are found to occur due to the applied forces. The effect of an ε-parametric control force in the Duffing system is also analyzed. To characterize the regular and chaotic behaviours of this system, the maximal Lyapunov exponent is employed.

Additive manufacturing for thermal management applications: from experimental results to numerical modeling

Recently, Additive Manufacturing (AM) of metal components has opened new frontiers in heat transfer applications, going beyond the capabilities of conventional technologies. Despite the great design freedom offered by AM, when dealing with metals, there are a few issues that should be considered to exploit the great capabilities of this manufacturing technology. In fact, the surface roughness of the components is expected to affect the performance of the devices, which can be remarkably different from the ones simulated with computer codes. This paper presents a critical analysis of the accuracy of the numerical tools to simulate the fluid flow behaviour inside channels obtained via AM, showing the major limitations of the standard approaches to accurately predict the pressure drops in straight and complex channels. Three different copper channels of growing complexity were built via SLM (Selective Laser Melting) and then they were experimentally tested to evaluate the predictive abilities of the numerical model. The results revealed that the surface roughness deeply affects the fluid flow, thus the numerical models need to be calibrated to become reliable design tools. The proposed procedure can be considered the first attempt in this direction and allows for a proper integration of the AM with the numerical simulation tools to boost the design capabilities of SLM technology.

Efficient simulation of flame acceleration and deflagration-to-detonation transition in smooth pipes

Evaluation of accident scenarios including flame acceleration and deflagration-to-detonation transition (DDT) in chemical plant piping systems increases the need for an efficient numerical simulation tool capable of dealing with this phenomenon. In this work, a hybrid pressure-density-based solver including deflagrative flame propagation as well as detonation propagation is presented. The initial incompressible acceleration stage is covered by the pressure-based solver until the flame velocity reaches the fast flame regime and transition to the density-based solver is done. The deflagration source term is formulated in terms of a turbulent flame speed closure model incorporating various physical effects crucial for flame acceleration at low turbulence conditions (Katzy and Sattelmayer, 2018). Modelling of the detonation source term is based on a quadratic heat release function (Hasslberger, 2017). The presented numerical approach is validated in terms of DDT locations and pressure data from Schildberg (2015) as well as recently completed flame tip position measurements. For this purpose, H2/O2/N2 mixtures ranging from 25.6 vol-% H2 to 29.56 vol-% H2 in two different pipe geometries are considered. The focus of the current work is on predicting the DDT location correctly and good agreement is observed for the investigated cases.

Optimal sizing of Solar Home Systems: Charge controller technology and its influence on system design

Solar Home Systems are a promising solution to enable access to affordable, reliable, sustainable, and modern energy for non-electrified areas, especially in the Global South. In this study, the influence of the charge controller technologies Maximum Point Tracker (MPPT) and Pulse Width Modulation (PWM) on the optimal system design and system performance is analyzed. Therefore, a multi-objective optimization that minimizes the number of days with Power-Cut-Offs and the Levelized Cost of Electricity for three Solar Home System sizes and three sub-saharan locations is conducted. Cost savings of the MPPT controller are in the range of 4.0% to 8.6% compared to the PWM controller. This is achieved by a reduction of the optimal installed photovoltaic peak power by 31.2% to 38.6% and the battery capacity by 2.8% to 8.8%. A sensitivity analysis shows the high robustness of cost savings regarding a variation in solar irradiance, load profile, and charge controller investment costs. Therefore, MPPT charge controllers are a promising solution even for the smallest Solar Home System sizes to reduce system costs compared to PWM controllers. The applied numerical simulation tool is open-source to enhance openness and transparency in modeling studies.

Numerical prediction of process-dependent properties of high-performance Ti6Al4 in LS-DYNA

In modern manufacturing processes such as hot forming or additive manufacturing, the workpiece material undergoes very complex thermomechanical load cycles. The local mechanical properties in the component are process-dependent and the result of the different micro-structure evolution mechanisms in the material. Numerical process simulation tools aim to include more and more of these mechanisms in order to improve the accuracy of the simulations. The mechanical strength of high-performance materials such as Ti-6Al-4V depends on microstructural parameters, which are influenced by the temperature and strain histories. This contribution puts forward an implementation of a new generalized internal variables material model *MAT_GENERALIZED_PHASECHANGE in LS-DYNA. The evolution of internal variables such as phase fractions, grain size and dislocation densities can be predicted by evolution equations, and combined with yield stress models taking the contribution of the phases, grain sizes (Hall-Petch effect), and the dislocation density into account to predict the resulting mechanical properties of the processed material. The benefits of the implementation in the commercial software LS-DYNA is the possibility to solve complex coupled problems. For example, the new material law can be used to simulate hybrid manufacturing processes like forging and an additional additive manufacturing process, where changes in microstructure are highly coupled and important for the part properties.

Experimental Investigation of Damage and Failure Mechanisms of Polymer-Metal Joints assembled by Self-Piercing Riveting

The increased use of polymer-based material in the manufacturing of vehicles structures makes critical the management of multi-material interfaces, and hence the issue of polymer-metal joining. It has been demonstrated in the literature that for large-scale manufacturing, self-piercing riveting (SPR) represents a reliable alternative technique to conventional resistance spot welding (RSW). However, the riveting operation induces, by nature, damages to the joint composite layer due to the steel rivet crossing it. In this study, the damage of the SMC thermoset material during SPR process has been experimentally investigated. Moreover, the influence of the riveting velocity as a major SPR process parameter on the composite layer damage has been identified. Eventually, the failure mechanisms of the polymer-metal joint resulting from failure under lap-shear and pure tension loadings were studied with the support of the numerical simulation tool.

Energy optimization of a micro-CHP engine using 1-D and 3-D modeling

This research focused on utilizing numerical simulation tools to improve the performance of a micro-CHP engine. The engine was developed at West Virginia University by screening candidate technologies and implementing those which were balanced between practicality and cost. The engine was a 34-cc, two-stroke engine which was modified to operate on low-pressure direct injection of natural gas combined with resonant intake and exhaust systems. This engine served as a baseline engine design. A 1-D simulation was developed and trained based on the baseline engine geometry and experimental data collected from laboratory experiments. After verifying the 1D model with measured data from the baseline configuration, a genetic algorithm approach was used to optimize the exhaust resonator design such that the fuel efficiency was maximized. Based on simulation outcomes, a new exhaust resonator was fabricated and tested. The experimental results showed an 8.3% improvement in brake thermal efficiency (BTE) compared to the baseline design. The test results of the optimized exhaust design were used in a 3-D CFD cold flow model to optimize the spark plug location to exploit charge stratification. The 3-D simulations suggested an alternative spark plug location, which was then applied on the engine and improved results were verified with additional experimental operation. The experimental results showed relative increase in BTE of 5.7% and a 4% decrease in total unburnt fuel compared to the original spark location.

Complex Dynamics in a Memristive Diode Bridge-Based MLC Circuit: Coexisting Attractors and Double-Transient Chaos

This paper uncovers some striking and new complex phenomena in a memristive diode bridge-based Murali–Lakshmanan–Chua (MLC) circuit. These striking dynamical behaviors include the coexistence of multiple attractors and double-transient chaos. Also, period-doubling, chaos, crisis scenarios are observed in the system when varying the amplitude of the external excitation. Numerical simulation tools like phase portrait, cross-section basin of attraction, Lyapunov spectrum, bifurcation diagrams and time series are used to highlight the complex dynamical behaviors in the memristive system. Further, practical realizations of the circuit both in PSpice and real-laboratory measurements match well with the observed numerical simulations.

A numerical performance study of a fixed-bed reactor for methanol synthesis by CO2 hydrogenation

Synthetic fuels are needed to replace their fossil counterparts for clean transport. Presently, their production is still inefficient and costly. To enhance the process of methanol production from CO2 and H2 and reduce its cost, a particle-resolved numerical simulation tool is presented. A global surface reaction model based on the Langmuir-Hinshelwood-Hougen-Watson kinetics is utilized. The approach is first validated against standard benchmark problems for non-reacting and reacting cases. Next, the method is applied to study the performance of methanol production in a 2D fixed-bed reactor under a range of parameters. It is found that methanol yield enhances with pressure, catalyst loading, reactant ratio, and packing density. The yield diminishes with temperature at adiabatic conditions, while it shows non-monotonic change for the studied isothermal cases. Overall, the staggered and the random catalyst configurations are found to outperform the in-line system.

Modelling damping in piezoceramics: A comparative study

Abstract The progress in numerical methods and simulation tools promotes the use of inverse problems in material characterisation problems. A newly developed procedure can be used to identify the behaviour of piezoceramic discs over a wide frequency range using a single specimen via fitting simulated and measured impedances by optimising the underlying material parameters. Since there is no generally accepted damping model for piezoelectric ceramics, several mechanical damping models are examined for the material identification. Three models have been chosen and their ability to replicate the measured impedances is evaluated. On the one hand, the common Rayleigh model is considered as a reference. On the other hand, a Zener model and a model using complex constants are extended to model the transversely isotropic material. As the Rayleigh model is only valid for a limited frequency range, it fails to model the broadband behaviour of the material. The model using complex constants leads to the best fit over a wide frequency range while at the same time only adding three additional parameters for modelling damping. Thus, damping can be assumed approximately frequency-independent in piezoceramics.