Systematic Numerical Simulations Research Articles

Combined effects of pores and cracks on the effective thermal conductivity of materials: a numerical study

Porous solids are commonplace in engineering structures and in nature. Material properties are inevitably affected by the internal inhomogeneity. The effective thermal conductivity of porous materials has been and remains to be a subject of extensive research. Less attention has been devoted to thermal conductivity impacted by internal cracks. This study is devoted to theoretical analyses of the combined effects of pores and cracks on the effective thermal conductivity. Systematic numerical simulations using the finite element method are performed based on two-dimensional models, with periodic distributions of internal pores and cracks. The parametric investigations seek to address how individual geometric layout can influence the overall thermal conduction behavior. In addition to circular pores and isolated cracks, angular pores with cracks extending from their sharp corners are also considered. It is found that both isolated cracks and cracks connected to existing pores can significantly reduce the effective thermal conductivity in porous materials. Since it is much easier to microscopically detect internal pores than thin cracks, care should be taken in using the apparent porosity from microscopic images and density measurements to estimate the overall thermal conductivity. Quantitative analyses of the detailed geometric effects are reported in this paper.

(De)hydration Front Propagation Into Zero‐Permeability Rock

AbstractHydration and dehydration reactions play pivotal roles in plate tectonics and the deep water cycle, yet many facets of (de)hydration reactions remain unclear. Here, we study (de)hydration reactions where associated solid density changes are predominantly balanced by porosity changes, with solid rock deformation playing a minor role. We propose a hypothesis for three scenarios of (de)hydration front propagation and test it using one‐dimensional hydro‐mechanical‐chemical models. Our models couple porous fluid flow, solid rock volumetric deformation, and (de)hydration reactions described by equilibrium thermodynamics. We couple our transport model with reactions through fluid pressure: the fluid pressure gradient governs porous flow and the fluid pressure magnitude controls the reaction boundary. Our model validates the hypothesized scenarios and shows that the change in solid density across the reaction boundary, from lower to higher pressure, dictates whether hydration or dehydration fronts propagate: decreasing solid density causes dehydration front propagation in the direction opposite to fluid flow while increasing solid density enables both hydration and dehydration front propagation in the same direction as fluid flow. Our models demonstrate that reactions can drive the propagation of (de)hydration fronts, characterized by sharp porosity fronts, into a viscous medium with zero porosity and permeability; such propagation is impossible without reactions, as porosity fronts become trapped. We apply our model to serpentinite dehydration reactions with positive and negative Clapeyron slopes and granulite hydration (eclogitization). We use the results of systematic numerical simulations to derive a new equation that allows estimating the transient, reaction‐induced permeability of natural (de)hydration zones.

Estimating Bethe roots with VQE

Abstract Bethe equations, whose solutions determine exact eigenvalues and eigenstates of corresponding integrable Hamiltonians, are generally hard to solve. We implement a Variational Quantum Eigensolver approach to estimating Bethe roots of the spin-1/2 XXZ quantum spin chain, by using Bethe states as trial states, and treating Bethe roots as variational parameters. In numerical simulations of systems of size up to 6, we obtain estimates for Bethe roots corresponding to both ground states and excited states with up to 5 down-spins, for both the closed and open XXZ chains. This approach is not limited to real Bethe roots.

Flow Analysis of Centrifugal Compressor using ANSYS

Abstract: The aerodynamic and structural designs of the impeller are vital to the functioning of the entire compressor stage in centrifugal compressors. In contrast to previous years, there has been a greater demand for industrial centrifugal compressors to operate with greater efficiency and operational range. Although the efficiency of low-pressure-ratio centrifugal compressors has nearly achieved its maximum, intermediate and high-pressure ratio machines still lag behind the state-of-the-art in terms of efficiency. Maintaining maximum efficiency while extending the working range is a challenging task in centrifugal compressor design. Furthermore, a single design must be usable globally due to product globalisation, even in the face of technological disparities and variances in electricity frequency of up to 10 percent in some nations. Often operating at different rotational speeds, centrifugal compressors add another layer of complexity to the impeller structural design. A full-3D impeller design that is optimised for both structural integrity and aerodynamic performance is shown in this study .For air conditioning systems of the future, centrifugal compressor performance must be improved. This research focusses on systematic numerical simulation, a computationally efficient method of optimising centrifugal compressor performance. ANSYS simulations are used in conjunction with a thorough literature review on the aerodynamic behaviour of materials used in centrifugal compressors. For the purpose of performing flow simulations under subsonic circumstances with suitable boundary conditions and grid independence checks, geometric modelling was completed using CATIAV5R22 and imported into ANSYS. Tests were conducted using various aluminium materials and mass flow rates, and enhanced efficiency findings were confirmed by comparison with experimental data. Materials Processing and Characterisations is in charge of peer review.

Simulation-based personal fatality risk assessment due to the fragmentation hazard

In the military and chemical industry, modeling the fragmentation hazard field is of great significance in conducting the fatality risk assessment and calculating the safety distance for person. Although the ballistic methodology achieves the simulation of fragmentation flight trajectory, the acquisition of accurate initial projection data of fragmentation is a challenge. By coupling continuum-discontinuum element method and particle discrete element method, the fragmentation power algorithm is established, which achieves the integrated simulation of the initial projection data of fragmentation and the flight process of fragmentation. First, continuum-discontinuum element method is adopted to simulate the detonation products-driven fragmentation acceleration process by introducing the explosive detonation model, which achieves the acquisition of initial projection data of fragmentation. Then, the particle discrete element method is adopted to simulate the flight trajectory and power data of fragmentation. Based on the numerical and experimental result, the accuracy of fragmentation power algorithm is verified. In conjunction with the personal vulnerability model, a systematic numerical simulation framework is established to conduct the simulation-based personal fatality risk assessment when the metal-cased munition detonates accidentally, and the results indicate that the personal fatality risk due to the fragmentation becomes severer with the increase of munition curvature.

Numerical simulations of the optical properties of SiO2@Au core–shell nanoparticles: The effect of geometrical parameters on the tunability and sensitivity of their plasmon response

Based on systematic numerical simulations, the effect of geometrical parameters of SiO2@Au core-shells (nanoshells) on the tunability and sensitivity of their optical response was elucidated. The surface plasmon resonance (SPR) of nanoshells experiences a blueshift-redshift crossover with the increase in shell thickness, and this phenomenon is ascribed to the competition between the two effects, that is, the hybridization effect dominated in the thin shells and the retardation effect dominated in the thick shells. The relative strength of absorption/scattering in the extinction spectra and the relative strength of dipolar/multipolar modes can be selectively tuned by controlling the total volume of nanoshells. The sensitivity of the SPR peak wavelength to the shell thickness is primarily dependent on the core-to-shell ratio; the higher this ratio is, the larger the sensitivity. The tailorable properties of nanoshells make them promising and well-suited platforms in various applications.

Indentation of an elastic arch on a frictional substrate: Pinning, unfolding, and snapping.

In this study, we investigate the morphology and mechanics of a naturally curved elastic arch loaded at its center and frictionally supported at both ends on a flat, rigid substrate. Through systematic numerical simulations, we classify the observed behaviors of the arch into three configurations in terms of the arch geometry and the coefficient of static friction with the substrate. A linear theory is developed based on a planar elastica model combined with Amontons-Coulomb's frictional law, which quantitatively explains the numerically constructed phase diagram. The snapping transition of a loaded arch in a sufficiently large indentation regime, which involves a discontinuous force jump, is numerically observed. The proposed model problem enables a fully analytical investigation and demonstrates a rich variety of mechanical behaviors owing to the interplay among elasticity, geometry, and friction. This study provides a basis for understanding more common but complex systems, such as a cylindrical shell subjected to a concentrated load and simultaneously supported by frictional contact with surrounding objects.

Deposition mechanism of ceramic reinforced metal matrix composites via cold spraying

Understanding the mechanism underlying metal matrix composites (MMCs) in cold spraying is critical to fabricate innovative MMC coatings and deposits with tailored microstructures and excellent mechanical performance. In this work, we propose a systematic numerical simulation framework combined with experimental observations to reveal the co-deposition mechanism of cold-sprayed metal/ceramic MMCs. The finite element modeling results and experimental validation found some critical conclusions regarding the deposition mechanism. The modeling results show that most of alumina particles are significantly fractured in Inconel718/alumina coating in contrast to aluminum/alumina coating. This fact suggests that the critical fragmentation velocity (CFV) of ceramic particles is dependent on the hardness of the metal substrate/matrix. Ceramic particles are more prone to fracture when co-deposited with metals having high hardness. Moreover, the simulation results also indicate that the rebounded alumina particles or fragments are possibly captured by incoming metal particles and trapped into MMCs. Since intact alumina particles are barely seen in composites, especially when co-deposited with hard metals, it can be concluded that direct ceramic particle deposition significantly relies on fragmentation. In addition, secondary fragmentation plays a key role in the metal-ceramic co-deposition process. The particles that have completed the impact process may be subjected to secondary fragmentation in the form of new cracks and fragmentation due to the impact by following metal and ceramic particles.

Hydrodynamic effects and water environment improvement of topographic reconstruction in shallow lakes

This paper focuses on a typical shallow lake, Lake Changdanghu, which is subject to frequent hydrodynamic disturbances and suspended sediment deposition, resulting in reduced water clarity and the degradation of the grass-type ecosystem. Using a combination of long-term systematic observations and numerical simulations, the impact of terrain modification on the hydrodynamic characteristics of Lake Changdanghu and its resulting environmental improvements are systematically analyzed. The results indicate that there is a significant correlation between the wind wave intensity, suspended solids concentration of the water, and water clarity. The artificial shoal project effectively reduces the local wind wave intensity, increases the water area of the weak waves, and alters the flow structure and transport path of the lake. The wave reduction effect of the artificial shoal significantly improves the transparency of the local water, especially under high wind wave conditions, with a 60% increase in the sheltered area, significantly improving the physical habitat environment. Additionally, the flow resistance and guidance roles of the artificial shoal concentrate the impact of the poor water quality of the inflow in a local area, reducing its adverse effects on the main body of the lake. Our research demonstrates that for shallow lakes, the water transparency can be improved, the physical habitat conditions for aquatic vegetation can be enhanced, and grass-type ecosystems can be gradually restored through artificial intervention and vegetation recovery projects by reducing the wave energy, flow resistance, and guidance through the construction of artificial shoals. This approach achieves long-term maintenance of eutrophication control and water quality improvement in shallow lakes.

Experimental and numerical study on wet steam flow metering overreading characteristics in venturi tube

The precise measurement of wet-steam flow is of great importance in various industrial systems, including nuclear reactors, oil and gas transportation, and cogeneration systems. However, the measurement accuracy of wet-steam flow can be affected by overreading (OR) when using venturi meters. This paper presents a systematic numerical simulation using the DPM model and an experimental study on the characteristics of overreading in wet-steam flow metering. The experiments are carried out on a two-phase flow liquid and steam platform. Firstly, the OR characteristics of a venturi structure with fixed dimensions (a throttling ratio of 0.6, a divergence angle of 15°, and a venturi diameter of 20 mm) are quantitatively analyzed at different flow rates (0.14-0.32 kg/s) and qualities (ranging from 0.14 to 0.90). It is found that the Lockhart-Martinelli parameter (XLM) plays a more significant role than the gas Froude number (Frg) in determining the overreading (OR) characteristics of a venturi under a given temperature, pressure, and venturi structure. Secondly, a venturi overreading prediction model based on XLM is proposed, and its ability to predict overreading for larger mass flow rates and venturi diameters is verified by numerical simulation data. As evaluated through numerical simulation data, the proposed model’s maximum relative error and average deviation are below 15% and 10%, respectively. This study provides valuable insights into developing an overreading model for industrial applications under large flow and venturi diameter conditions.

Atomic soliton transmission and induced collapse in scattering from a narrow barrier

We report systematic numerical simulations of the collision of a bright matter-wave soliton made of Bose-condensed alkali-metal atoms through a narrow potential barrier by using the three-dimensional Gross–Pitaevskii equation. In this way, we determine how the transmission coefficient depends on the soliton impact velocity and the barrier height. Quite remarkably, we also obtain the regions of parameters where there is the collapse of the bright soliton induced by the collision. We compare these three-dimensional results with the ones obtained by three different one-dimensional nonlinear Schrödinger equations. We find that a specifically modified nonpolynomial Schrödinger equation is able to accurately assess the transmission coefficient even in a region in which the usual nonpolynomial Schrödinger equation collapses. In particular, this simplified but very effective one-dimensional model takes into account the transverse width dynamics of the soliton with an ordinary differential equation coupled to the partial differential equation of the axial wave function of the Bose–Einstein condensate.

Thermoelectric cooler with embedded teardrop-shaped milli-channel heat sink for electronics cooling

Thermoelectric coolers (TECs) offer a site-specific, on-demand, and solid-state thermal management solution for on-chip electronics cooling. To maximize their cooling performance, it is essential to integrate an effective heat exchanger, such as microchannels, on the TEC’s hot side. However, traditional microchannel heat sinks pose challenges, including the necessity for high-cost equipment and the manifestation of deleterious parasitic contact thermal resistance with the TEC. Recent studies have demonstrated the superior performance of teardrop-shaped microchannels compared to their conventional counterparts, yet their effectiveness at the milli-scale remains unexplored. In this work, through systematic numerical simulations across nine milli-channels with distinct variable cross-sections, we propose a teardrop-shaped milli-channel heat sink designed for fabrication through cost-effective mechanical machining. The optimized teardrop-shaped milli-channel exhibits a superior overall thermo-hydraulic performance evaluation factor (PEC) of approximately 1.8 with respect to its rectangular cross-sectional counterpart. Furthermore, we seamlessly embed the designed milli-channel heat sink into the substrate of the TEC to mitigate the parasitic contact thermal resistance. Measurements on the TEC embedded with the teardrop-shaped milli-channel heat sink show that the cold end temperature reaches a minimum value of −18.6 °C at an optimal input electrical current of 3.5 A and an inlet coolant flow velocity of 0.2 m/s. This temperature represents an improvement of approximately 3.5 °C and 4.4 °C compared to the TEC with an attached teardrop-shaped milli-channel and a conventional water block heat sink, respectively, under identical operating conditions. Additionally, a prototype TEC cooling system with the embedded teardrop-shaped milli-channel for high-power field-effect transistor (FET) cooling is demonstrated. Operating at an input electrical current of 3.5 A and an inlet flow velocity of 0.6 m/s, our proposed TEC cooling system achieves a steady-state working temperature of 51.3 °C for the FET at a high heat flux of 75 kW/m2, outperforming the TEC with an attached teardrop-shaped milli-channel and a conventional water block heat sink by approximately 1.4 °C and 2 °C, respectively.

Surface gravity wave-induced drift of floating objects in the diffraction regime

Floating objects will drift due to the action of surface gravity waves. This drift will depart from that of a perfect Lagrangian tracer due to both viscous effects (non-potential flow) and wave–body interaction (potential flow). We examine the drift of freely floating objects in regular (non-breaking) deep-water wave fields for object sizes that are large enough to cause significant diffraction. Systematic numerical simulations are performed using a hybrid numerical solver, qaleFOAM, which deals with both viscosity and wave–body interaction. For very small objects, the model predicts a wave-induced drift equal to the Stokes drift. For larger objects, the drift is generally greater and increases with object size (we examine object sizes up to $10\,\%$ of the wavelength). The effects of different shapes, sizes and submergence depths and steepnesses are examined. Furthermore, we derive a ‘diffraction-modified Stokes drift’ akin to Stokes (Trans. Camb. Phil. Soc., vol. 8, 1847, pp. 411–455), but based on the combination of incident, diffracted and radiated wave fields, which are based on potential-flow theory and obtained using the boundary element method. This diffraction-modified Stokes drift explains both qualitatively and quantitatively the increase in drift. Generally, round objects do not diffract the wave field significantly and do not experience a significant drift enhancement as a result. For box-shape objects, drift enhancement is greater for larger objects with greater submergence depths (we report an increase of $92\,\%$ for simulations without viscosity and $113\,\%$ with viscosity for a round-cornered box whose size is $10\,\%$ of the wavelength). We identify the specific standing wave pattern that arises near the object because of diffraction as the main cause of the enhanced drift. Viscosity plays a small positive role in the enhanced drift behaviour of large objects, increasing the drift further by approximately $20\,\%$ .

Heat transfer characteristics of water flow through a single rock fracture: The combined effects of shear and surface roughness

AbstractAn accurate understanding of the heat transfer of water through rock fractures is essential for the extraction and utilization of thermal energy from high‐temperature rock masses. A systematic numerical simulation based on the double‐rough‐walled model has been presented to investigate the shear effect on convective heat transfer in rough rock fractures. On the basis of the modified successive random additions algorithm, four different self‐affine surfaces were generated and utilized to establish the 3D double‐rough‐walled fracture models. The fluid flow and heat transfer were simulated by directly solving the Navier–Stokes equation and energy conservation equation, respectively. The combined effects of shear and surface roughness on the heat transfer were investigated. The results show that the heat within rough‐walled fractures transfers preferentially along the main fluid flow channels, and the areas of fast and slow thermal transmission fit well with the high‐ and low‐flow regions, respectively. As shear advances, the heat transfer coefficient firstly increases, then decreases slightly and finally stabilizes within a certain range, in which stabilization occurs earlier in fracture with a larger joint roughness coefficient. The effect of surface roughness on heat transfer shows an opposite trend during shearing. When the shear displacement is small, the enhancement effect of surface roughness that provides larger heat transfer areas dominates the heat transfer. As shear displacement continues to increase, this enhancement effect will be gradually weakened until the decreasing effect that bumps on the rough‐walled surface hinder the fluid flow dominates the heat transfer.

Enhancing the Efficiency of PM6:Y6 Bulk-Heterojunction Organic Solar Cells through SCAPS Simulation Optimization

Organic solar cell (OSC) is becoming a point of attraction in the solar cell industry due to their benefits, such as light weight, flexibility, low cost, semi-transparency, and easy fabricating methods. By replacing fullerene with non-fullerene acceptors like Y6, ITIC, PCBM, and ICBA, the power conversion efficiency (PCE) of OSCs has surpassed the 15% benchmark. Here, the proposed OSC structure includes an ITO front contact electrode, SnO2 electron transport layer (ETL), PM6:Y6 active layer, Cu2O hole transport layer (HTL), and Ag back contact electrode. Systematic numerical simulation of the above proposed OSC has been performed using a solar cell capacitance simulator (SCAPS)-1D (Version 3.3.09). The device improvement analysis has been carried out in steps by analyzing the ETL-HTL effect, selecting the optimum thickness of the active layer, and the optimum value of defect density. In the first step, a PCE of 24.60% was achieved, followed by an improvement to 27.55% with the optimized defect density value. The best PCE of 27.74% was achieved in the third step with an optimized active layer thickness, leading to high fill factor (80.56%), open-circuit voltage (0.9461 V), and short-circuit current density (36.188 mA/cm2). These simulated results promote an in-depth understanding of the optical and electronic properties of PM6:Y6 blend-based OSC and show the potential of NFA-BHJ OSCs as promising candidates for solar cells in the near future.

Track-bridge deformation relation and interaction of long-span railway suspension bridges subject to strike-slip faulting

During earthquakes, the long-span railway bridges crossing active faults are more vulnerable because of the combined effects of pulsed ground motions and surface dislocations. To study the track-bridge deformation and interaction of long-span railway suspension bridges crossing the strike-slip faults, the refined finite element model of a ballasted track-bridge-pile-soil coupled system was established using the nonlinear finite element software ANSYS/LS-DYNA. A detailed and systematic numerical simulation was conducted from the soil cracking and compression during the ground surface rupture, pile–soil interaction, and three-dimensional track constraints to track-bridge deformation relationships and interactions. One-dimensional wave propagation theory was employed to derive the ground motions on the bedrock according to ground surface-measured seismic records. The influences of the fault-crossing angle (FCA) and permanent ground rupture displacement (PGRD) on the seismic responses and track-bridge interaction were analysed by considering the pile–soil interaction and site response effect. A method for calculating the track curvature radius based on track deformation is presented to evaluate the running traffic conditions of the trains. Additionally, the stability of the ballast bed was estimated using the track-bridge relative displacement. The conclusions drawn can be applied in practical seismic design and train running safety assessment of long-span railway suspension bridges crossing the strike-slip faults.

Performance of the suspension method in large cross-section shallow-buried tunnels

Large cross-section tunnel construction induces ground surface settlements, potentially endangering both subterranean projects and nearby above-ground structures. A novel tunnel construction method, known as the suspension method, is introduced in this paper to mitigate surface settlement. The suspension method employs vertical tie rods to establish a structural connection between the initial tunnel support system and the surface steel beam, thereby exerting effective control settlements. To analyze the performance of the proposed method, systematic numerical simulations were conducted based on the practical engineering of Harbin Subway Line 3. The surface settlement and vault settlement characteristics during construction are investigated. The results show a gradual increment in both surface and vault settlement throughout the construction process, culminating in a stabilized state upon the completion of construction. In addition, compared to the double-side drift method and the Cross Diaphragm Method (CRD) method, the suspension method can obviously reduce the surface settlement and vault settlement. Moreover, the surface settlements and the axial force of tie rods were continuously monitored during the construction process at the trial tunnel block. These specific monitoring measurements are illustrated in comparison to numerical analysis results. The monitored results show great agreement with the numerical predictions, confirming the success of the project. This research can serve as a valuable practical reference for similar projects, offering insights and guidance for addressing ground surface settlements and enhancing construction safety in the domain of large cross-section tunneling.

A novel intramedullary nail design of intertrochanteric fracture fixation improved by proximal femoral nail antirotation

A proper and reliable fracture fixation is important for fracture healing. The proximal femoral intramedullary nail (IN), such as proximal femoral nail anti-rotation (PFNA) or Gamma nail, is widely used for intertrochanteric fracture fixation. However, it still suffers considerable stress concentrations, especially at the junction between the nail and the blade or lag screw. In this study, we propose a novel intramedullary nail design to enhance the intramedullary nail integrity by introducing a bolt screw to form a stable triangular structure composed of the nail, the lag screw, and the bolt screw (PFTN, Proximal femoral triangle nail). Systematic finite element numerical simulations were carried out to compare the biomechanical performances of PFTN and PFNA under both static and dynamic loads during the postures of ascending and descending stairs. The simulation results highlight the advantages of the proposed PFTN design with lower stresses, less stress concentration, and higher structure stability.

Unraveling the Potential Pathways for Improved Performance of EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98SnI2Br‐Based Solar Cells

This article comprehensively investigates the photovoltaic performance of a 3% GeI2‐doped ASnI2Br absorber in a solar cell. The cell features an inverted structure (fluorine‐doped tin oxide [FTO]/poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate [PEDOT:PSS]/absorber/C60/Ag) and utilizes EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98 as the A‐site cation (EDA for ethylenediamine; GA for guanidinium; FA for formamidinium). Through systematic numerical simulation and optimization, the photovoltaic performance of the solar cell is enhanced by sequentially optimizing several parameters: 1) absorber thickness and defect density, 2) conduction band offset at the ASnI2Br/C60 interface, doping of the electron‐transport layer (ETL), and its interface with the absorber, and 3) valence band offset at the PEDOT:PSS/ASnI2Br interface, and doping of the hole‐transport layer and its interface with the absorber. Additionally, the impact of series resistance (Rs) variation on device performance is investigated. Starting with an initial power conversion efficiency (PCE) of 4.86%, the systematic numerical optimization process elevates it to an impressive 18.55%. Furthermore, a final cell structure is proposed where C60 is replaced with indium‐doped tin oxide (ITO) as the ETL layer. This optimized FTO/PEDOT:PSS/absorber/ITO structure demonstrates a remarkable PCE of 18.68%. These findings hold significant promise for advancing tin‐perovskite solar cell technology.

Numerical Investigation on Hydrodynamic Characteristics and Drag Influence of an Open-Frame Remotely Operated Underwater Vehicle

Remotely operated underwater vehicles (ROVs) have been widely used in deep-sea resource exploitation and industrial engineering operations. To perform these tasks accurately in the deep-sea environment, stable motion control has become a key area of research on ROV systems, which has led to the importance of analyzing the hydrodynamic characteristic of ROVs. But a systematic methodology for analyzing the hydrodynamic characteristics of ROVs is still lacking nowadays. In this paper, systematic numerical simulation methods for analyzing hydrodynamic characteristics and shape optimization of a work-class ROV are conducted, and details of simulation procedures based on computational fluid dynamics are studied, which can be a foundation for robust controller design.