Numerical Analysis Model Research Articles

SPH-based Numerical Modelling and Performance Analysis of a Heaving Point Absorber Type Wave Energy Converter with a Novel Buoy Geometry

SPH-based Numerical Modelling and Performance Analysis of a Heaving Point Absorber Type Wave Energy Converter with a Novel Buoy Geometry

Hybrid Analytical-Numerical Modeling of Surface Geometry Evolution and Deposition Integrity in a Multi-Track Laser-Directed Energy Deposition Process

Abstract Modeling multitrack laser-directed energy deposition (LDED) is different from single-track deposition. There is a temporal variation in the deposition geometry and integrity in a multitrack deposition, which is not well understood. This article employs an analytical model for power attenuation and powder catchment in the melt pool in conjunction with a robust fully coupled metallurgical-thermomechanical finite element (FE) model iteratively to simulate the multitrack deposition. The novel hybrid analytical–numerical approach incorporates the effect of preexisting tracks on melt pool formation, powder catchment, geometry evolution, dilution, residual stress, and defect generation. CPM 9V steel powder was deposited on the H13 tool steel substrate for validating the model. The deposition height is found to be a function of the track sequence but reaches a steady-state height after a finite number of tracks. The height variation determines the waviness of the deposited surface and, therefore, the effective layer height. The inter-track spacing (I) plays a vital role in steady-state height evolution. A larger value of I facilitates faster convergence to the steady-state height but increases the surface waviness. The FE model incorporates the effects of differential thermal contraction, volume dilation, and transformation-induced plasticity. It predicts the deposition geometry and integrity as a function of inter-track spacing and powder feed rate. The insufficient remelting of the substrate or the preceding track can induce defects. A method to predict and mitigate these defects has also been presented in this article.

Slenderness limit for reinforced ultra-high-performance concrete columns

The use of ultra-high-performance concrete (UHPC) allows for much smaller cross-sections compared to conventional reinforced concrete columns, which may make reinforced UHPC (R-UHPC) columns more susceptible to slenderness effects. Currently, there is no guideline in design standards for the slenderness limit of R-UHPC columns. This paper, therefore, attempts to develop a design provision for determining the slenderness limit of R-UHPC columns. Firstly, a numerical analytical model was proposed for predicting the load-deflection of R-UHPC columns under eccentric loading, which was validated by comparing its predictions with available experimental results from the available literature. Based on the validated model, a parametric study was then conducted to determine the key parameters affecting the slenderness limit of R-UHPC columns. It was found that the slenderness limit corresponding to the 5% strength reduction was sensitive to the ultimate compressive strain of UHPC, the tensile strength of UHPC, and the reinforcement ratio. On this basis, a design equation for the slenderness limit of R-UHPC columns in single curvature was statistically derived. Additionally, the slenderness limit for R-UHPC columns in non-sway frames was also proposed in a convenient form for design procedures.

Transforming Landslide Prediction: A Novel Approach Combining Numerical Methods and Advanced Correlation Analysis in Slope Stability Investigation

Landslides cause significant economic losses and casualties worldwide. However, robust prediction remains challenging due to the complexity of geological factors contributing to slope stability. Advanced correlation analysis methods can improve prediction capabilities. This study aimed to develop a novel landslide prediction approach that combines numerical modeling and correlation analysis (Spearman rho and Kendall tau) to improve displacement-based failure prediction. Simulations generate multi-location displacement data sets on soil and rock slopes under incremental stability reductions. Targeted monitoring points profile local displacement responses. Statistical analyses, including mean/variance and Spearman/Kendall correlations, quantified displacement-stability relationships. For the homogeneous soil slope, monitoring point 2 of the middle section of the slope showed a mean horizontal displacement of 17.65 mm and a mean vertical displacement of 9.72 mm under stability reduction. Spearman’s rho correlation coefficients ranged from 0.31 to 0.76, while Kendall’s tau values ranged from 0.29 to 0.64, indicating variable displacement–stability relationships. The joint rock slope model had strong positive total displacement correlations (Spearman’s and Kendall’s correlation ranges of +1.0 and −1.0) at most points. Horizontal and vertical displacements reached mean maxima of 44.13 mm and 22.17 mm, respectively, at the unstable point 2 of the center section of the slope. The advanced correlation analysis techniques provided superior identification of parameters affecting slope stability compared to standard methods. The generated predictive model dramatically improves landslide prediction capability, allowing preventive measures to be taken to mitigate future losses through this new approach.

Numerical Investigation of Stratified Slope Failure Containing Rough Non-Persistent Joints Based on Distinct Element Method

To address the critical issue of slope stability in jointed rock masses with complex and rough structural planes, a rough joint network model using the Fourier transform was proposed and applied to the Shilu open pit mine. The on-site structural plane survey results were combined with MATLAB and PFC2D to establish numerical models for slope stability analysis considering both linear-jointed and rough-jointed rock slopes. By comparing the slip body and fracture distribution, it was found that the rough-jointed slope was stabler than the linear-jointed slope. In addition, the fracture patterns and slip displacement were significantly influenced by the inclination and undulation of the bedding planes. Slip failure patterns occurred when the angle of inclination was set at 60°. The joints played a crucial role in inducing the shear strength of slope rock masses, and the slide area was mainly observed in the shallow slope surface for inclination angles of 0° and 45°, and in the middle deep area for 60° and 90°. These results demonstrated the importance of considering rough non-persistent fractures when developing a new numerical model for slope failure modes.

Numerical analysis of a poroelastic cartilage model: Investigating the influence of changing material properties in osteoarthritis

Several changes occur in both the cartilage's material properties and anatomical structure as osteoarthritis progresses. Unlike most numerical studies that solely consider individual changes, our study aimed to understand the impact on cartilage mechanics by considering the combined effect of material properties and cartilage thickness varied with osteoarthritis progression. In total, 3 three-dimensional finite element models, representing the intact, early, and late osteoarthritis conditions, were developed to simulate a load-bearing area in the knee. The articular cartilage was modelled as fluid-saturated linear biphasic poroelastic to incorporate solid-fluid interaction. All models underwent prolonged creep (50 N) and relaxation (0.3 mm) analyses for 600 s. In the early stage of osteoarthritis, the tibial cartilage demonstrated an overall stiffer behaviour attributed to cartilage swelling despite decreased stiffness at the material level. On the other hand, in the late stage of osteoarthritis, the decrease in cartilage thickness led to increased knee deformation. Additionally, increased permeability resulted in accelerated fluid exudation across all osteoarthritis models, and the elevation in void ratio further intensified fluid pressure within the cartilage to a higher magnitude. Furthermore, these changes collectively influenced both the magnitude and distribution of the outcomes. A holistic understanding of the material properties altered in osteoarthritis may contribute to a better understanding of the mechanical performance of cartilage during disease progression.

Exploring seismic resilience in frame structures through advanced numerical modeling and dynamic nonlinear analysis of recycled aggregate concrete

This study developed an advanced three-dimensional spatial model to examine the behavior of Recycled Aggregate Concrete (RAC) frame structures using sophisticated nonlinear beam-column fiber elements. It thoroughly investigates the dynamic properties such as natural frequency, vibration modes, and stiffness of RAC structures and conducts a detailed nonlinear dynamic analysis focusing on acceleration, displacement, drift, and hysteresis curves. The seismic resilience of RAC structures, especially inter-story drift under various seismic intensities, was evaluated and compared with Natural Aggregate Concrete (NAC) structures by adjusting the concrete material model parameters in the finite element framework. The accuracy of the numerical model was validated against shaking table tests, showing that RAC and NAC structures comply with structural damage criteria across seismic phases from 0.066 g to 1.170 g. The findings suggest RAC structures are as seismically resilient as NAC ones, making them suitable for earthquake-prone areas.

Prediction of tensile behavior of compression therapeutic biomedical materials by mesoscale laid-in loop model

Tubular laid-in weft-knitted compression (LWC) therapeutic materials have been extensively applied in medical clinic treatment and daily healthcare management. Limited studies have explored the mechanical mechanisms through the numerical analytical models for the development and performance prediction of laid-in fabrics. This study developed the three-dimensional (3D) finite element (FE) laid-in loop model to simulate and predict the tensile behaviors of LWC materials based on the determination of geometric models and investigation of yarn mechanical properties. Through the constructed FE mesoscale models with various physical-mechanical characteristics of inlay yarn materials, it was found that the ground yarns and inlay yarns played distinct roles in producing tensile stresses under the course and wale direction of stretching strains. These tensile stresses determined the selection of yarn materials for controlling the tension of laid-in knitted fabrics in end applications. Then, the interfacial pressure dosages exerted by LWC materials were quantitively obtained based on the simulated Young's moduli values and modification of Laplace's Law model. The accuracy and acceptability of proposed mechanical laid-in models (mean error: 10.22 %) and pressure prediction models (mean error: 14.70 %) were validated by the comparative studies. The simulation methods and results created a visual tool for dynamically illustrating the tensile behaviors and predicting pressure performances of the elastic therapeutic materials in functional material design of biomedical compression textiles.

Design and Analysis Method of Piezoelectric Liquid Driving Device with Elastic External Displacement.

In piezoelectric drive, resonant drive is an important driving mode in which the external elastic force and electric drive signal are the key factors. In this paper, the effects of the coupling of external elastic force and liquid parameters with the structure on the vibrator resonance frequency and liquid drive are analyzed by numerical simulation. The fluid-structure coupling model for numerical analysis of the elastic force was established, the principle of microdroplet generation and the coupling method of the elastic force were studied, and the changes in the resonant frequency and mode induced by the changes in the liquid parameters in different cavities were analyzed. Through the coupled simulation and calculation of the pressure and deformation of the cavity, the laser vibration measurement test was carried out to test the effect of the vibration mode analysis. The driving model of the fluid jet driven by the elastic force on the piezoelectric drive was further established. The changing shape of the fluid jet under different elastic forces was analyzed, and the influence law of the external elastic force on the change in the droplet separation was determined. It provides reference support for further external microcontrol of droplet motion.

Research on the hydraulic support face guard mechanism and coupling characteristic of rib spalling in large mining heights

In view of the problem of poor coupling adaptability and easy rib spalling of coal wall in large mining height comprehensive mining, based on the effective inhibition effect of face guard mechanism on coal wall spalling, the structural characteristics and bearing capacity of different structural forms of the face guard mechanism are compared and analyzed. According to the surrounding rock adaptability of the face guard mechanism, established a numerical analysis model for rigid-flexible coupling of the face guard mechanism under different spalling forms. In order to accurately simulate the stress state of the protective mechanism, a variable stiffness spring damping system is used to replace the hydraulic cylinder. The load-bearing performance and response characteristics of the face guard mechanism under rib spalling coupling conditions were analyzed by applying uniform normal load and impact load to the face guard. The findings indicated that, the integral-type face guard mechanism has a better effect on suppressing rib spalling. When the face guard mechanism bears the static load of the coal wall, the entire response process of the face guard jack can be divided into three stages: initial support, increasing resistance bearing, constant resistance bearing; both the impact load position and the coupling state of the rib spalling will affect the characteristics of force transmission at the face guard mechanism’s hinge point, the hinge point between the extensible canopy and the primary face guard is most sensitive to biased load. The research results can provide reference for optimizing the face guard mechanism of large mining height hydraulic support and improving the reliability of coal wall support.

A rigorous theoretical and numerical analysis of a nonlinear reaction-diffusion epidemic model pertaining dynamics of COVID-19

The spatial movement of the human population from one region to another and the existence of super-spreaders are the main factors that enhanced the disease incidence. Super-spreaders refer to the individuals having transmitting ability to multiple pathogens. In this article, an epidemic model with spatial and temporal effects is formulated to analyze the impact of some preventing measures of COVID-19. The model is developed using six nonlinear partial differential equations. The infectious individuals are sub-divided into symptomatic, asymptomatic and super-spreader classes. In this study, we focused on the rigorous qualitative analysis of the reaction-diffusion model. The fundamental mathematical properties of the proposed COVID-19 epidemic model such as boundedness, positivity, and invariant region of the problem solution are derived, which ensure the validity of the proposed model. The model equilibria and its stability analysis for both local and global cases have been presented. The normalized sensitivity analysis of the model is carried out in order to observe the crucial factors in the transmission of infection. Furthermore, an efficient numerical scheme is applied to solve the proposed model and detailed simulation are performed. Based on the graphical observation, diffusion in the context of confined public gatherings is observed to significantly inhibit the spread of infection when compared to the absence of diffusion. This is especially important in scenarios where super-spreaders may play a major role in transmission. The impact of some non-pharmaceutical interventions are illustrated graphically with and without diffusion. We believe that the present investigation will be beneficial in understanding the complex dynamics and control of COVID-19 under various non-pharmaceutical interventions.

A three-dimensional numerical well-test model for pressure transient analysis in fractured horizontal wells with secondary fractures

During oil and gas reservoir development, multi-stage horizontal wells (MFHWs) and hydraulic fracturing techniques can effectively increase estimated ultimate recovery. However, there still lacks an understanding of the three-dimensional (3D) pressure transient behaviors of multi-stage fractured horizontal wells with secondary fractures. To narrow this gap, a three-dimensional numerical well-test model based on a discrete fracture model and unstructured tetrahedral grids is developed to study the pressure transient behaviors of MFHWs with secondary fractures. The pressure transient solutions of MFHWs with secondary fractures have been demonstrated by model verifications. The results show that the proposed model can accurately capture the complex transient flow around fractures, including early radial flow that is not easily captured by two-dimensional numerical well test models. The proposed model classifies the flow regimes of a MFHW as: wellbore storage and skin effects, early radial flow, bilinear flow, linear flow, elliptical flow, pseudo radial flow, and pseudo-boundary dominated flow. It is found that the fracture geometry has a relatively large effect on the shape of the pressure derivative curve in this work. The hydraulic fracture half-length has the greatest impact on the pressure transient behaviors of the MFHW, followed by fracture height and secondary fracture half-length, as found in this study. Additionally, fracture parameters are evaluated, and actual well testing data are interpreted, taking into account the fracture height. This work is meaningful to understand the three-dimensional pressure transient behaviors of MFHWs with secondary fractures.

Numerical analysis of age-structured HIV model with general transmission mechanism

In this paper, we discuss the numerical representation of the linearly implicit Euler method for an age-structured HIV infection model with a general transmission mechanism. We first define the basic reproduction number of the continuous model, and present the stability results of the equilibriums. For the numerical process, we establish the solvability of the system and the non-negativity and convergence of numerical solutions. In the analysis of the long-term dynamical behavior, this paper mainly focus on the existence of the infection equilibrium determined by the numerical reproduction number R0Δt. To overcome the difficulty caused by the complexity of epidemic transmission mechanisms, the 1-order convergence analysis of numerical basic reproduction numbers R0Δt is implemented by using the properties of the fundamental solution matrix. By a comparison principle, we show that the disease-free equilibrium is globally asymptotically stable if R0Δt<1. Moreover, for R0Δt>1, a unique numerical endemic equilibruim exists, which converges to the exact one, is locally asymptotically stable. Hence, numerical processes visually represent the dynamic properties of nonlinear age-structured HIV models. Finally, some numerical experiments demonstrate the verification and the efficiency of our results.

Experimental and numerical investigation of hysteretic earthquake behavior of masonry infilled RC frames with opening strengthened by adding rebar-reinforced stucco

Adding a reinforced stucco layer to the masonry infill walls is a preferred method for strengthening RC frame system structures with an easy-to-apply method that does not require a long time, is economical, and does not require detailed and extensive workmanship. However, no research has been discovered as a result of the extensive literature review that investigates the effects of masonry-infilled RC frames strengthened with a reinforced stucco layer on the seismic performance of openings that must be due to architectural requirements such as doors, windows, installations, and similar ventilation systems. As a result, an experimental study was planned to investigate the effects of the dimensions and location of the opening in the masonry infill walls on the performance of the strengthening method with the reinforced stucco layer. The applied strengthening method increased the ultimate load capacity, initial stiffness, and energy dissipation capacity values of reinforced concrete frames with masonry infill walls by 83%, 226%, and 62%, respectively, but resulted in a 38% decrease in displacement-ductility ratios. The study found that the openings in the masonry infill walls harm the performance of the strengthening technique by adding a rebar-reinforced stucco layer and decreasing the success level. When the opening size increased, and the opening was located at the corner of the masonry wall, the performance of the applied strengthening technique was negatively affected and decreased. Furthermore, nonlinear numerical analyses of the experiments conducted as part of the study were performed using ABAQUS finite element software. The numerical analysis results were compared to the experimental results. It has been determined whether numerical analysis models are compatible with experimental results.

Numerical and semi-empirical models for the stress analysis of flexible pipes tensile armors terminations within end-fittings

The tensile armors of flexible pipes are typically terminated in two configurations, i.e., hook and pigtail, essential to guarantee the tensile armors’ anchorage in the pipe's end-fitting. However, despite its importance for the secure operation of flexible pipes, few works have dealt with the mechanical analysis of these terminations. Hence, this work proposes numerical and semi-empirical models to study the stresses induced on them by operational and extreme loading. Two- and three-dimensional finite element (FE) models are initially proposed, and their advantages and limitations in estimating local stiffness, stresses, and associated failure modes are highlighted. The initial analyses indicated that the two-dimensional model underestimated the terminations’ stiffness, while the detailed three-dimensional model required significant computational effort. However, a simplified three-dimensional model achieved the best compromise between accuracy and computational effort. In common, all models indicated that the hook termination failure is due to a pullout mechanism, while the pigtail induces the tensile armor steel rupture. After that, the simplified three-dimensional model was employed to conduct a parametric study involving several physical and geometric characteristics of the terminations. The importance of these parameters was evaluated using the Design of Experiment (DoE) technique, leading to semi-empirical equations to predict the maximum stresses induced in the terminations due to an axial load imposed on the tensile armor. Finally, the semi-empirical equation obtained for the hook termination was verified using previously presented full-scale experimental test results, showing good agreement.

Development of structural type-based physical vulnerability curves to debris flow using numerical analysis and regression model

Urbanization has significantly increased the risk of debris flows to houses located at mountain boundaries, particularly in South Korea, where urban centers are surrounded by mountains. The degree of damage to a house strongly depends on the structural rigidity of the building, even when exposed to the same hazard intensities. However, the structural characteristics of buildings are usually disregarded in vulnerability assessments. In this study, vulnerability curves were proposed for three different structural types of buildings: brick masonry, light-weight steel frame, and wood structures, using numerical and regression analyses. A total of 22 debris flow events from 2011 to 2020 and 63 cases of damage to unreinforced structures were collected and analyzed. Back analysis of the debris flows was performed using Flow-R, and the impact pressure acting on each structure was calculated. Three different vulnerability curves were proposed using various linear and nonlinear regression analyses; the Avrami equation provided the highest statistical significance. The vulnerability curves of three different structures were similar for the slight damage range. However, over the slight damage range, the wood structure was the most vulnerable at a given hazard intensity, whereas the brick masonry structure was the least vulnerable. Validation was performed using data from recent debris flow events, revealing precise damage level predictions for 9 out of 11 buildings. Compared with previous research, the degree of damage at the same hazard intensity was found to be significantly dependent on the structural type. The developed vulnerability curve for each unreinforced structure can be used as key data for vulnerability and risk assessments.

Numerical modeling and dynamic response analysis of an integrated semi-submersible floating wind and aquaculture system

Floating wind turbines (FWT) are facing the challenges of high cost of energy. Integrating floating wind with offshore aquaculture cages presents a mutually beneficial approach to address cost concerns and maximize overall benefits. This study introduces and numerically models an integrated system, encompassing a self-designed semi-submersible FWT coupled and an aquaculture cage (FWT + AC). Comprehensive, fully coupled aero-hydro-servo-elastic-mooring models for this integrated system are established. Subsequently, the numerical model of the FWT is validated against wave basin model tests. The research further discusses the coupled dynamic response characteristics of the integrated system for both the FWT with and without the aquaculture cage. The results highlight that integrating aquaculture cages leads to an increase in the mean surge response by up to 12.6%, while significantly reducing pitch motion by as much as 7.69% under combined wind, wave, and current conditions. Moreover, the mean mooring loads, particularly for line 4 which faces the direction of wind, wave, and current, do not exhibit an increase of more than 15%. This integration not only enhances the stability of wind power generation under different wind degree, but also minimally impacts the average power generation efficiency, showing a variation of only about 2% under rated wind speed. The findings provide beneficial theoretical support for the design of the integrated FWT + AC system, demonstrating the potential of such integrated systems in promoting offshore sustainable development and enhancing wind energy utilization efficiency.

Numerical Investigations of Stirring Induced Flow on Solidification and Interface Behavior in Continuous Casting Mold With Bifurcated Nozzle

Abstract Electromagnetic stirring (EMS) is a technique that has the potential to improve steel quality with fine microstructure by fragmentation of dendrites and enhancing the inclusion removal. The success of implementing the EMS lies in the selection of key input parameters such as position, frequency, and current density of the stirrer. In the present study, an integrated mathematical model consisting of liquid steel solidification and two phase interface is numerically developed with the use of EMS. The enthalpy porosity and volume of fluid (VOF) model are adopted for numerical modeling analysis of solidification and interface level fluctuation, respectively. The results reveal that on moving EMS downwards decreases the maximum magnetic field value, widens the mushy zone, and promotes the stability of the interface. Current intensity and frequency are seen to have the opposite effect on stirring intensity and interface fluctuation. With an increase in frequency, both stirring intensity and interface level fluctuations decrease while the high liquid fraction region increases. Moreover, current density enhances the swirling flow intensity and homogenizes the liquid fraction, thereby promoting equiaxed grain formation. Interface fluctuation is seen to increase with current density.

Salt dynamic changes between seawater and phreatic brine in muddy tidal flats under tidal influence

Evaporated salt accumulated on the surface of tidal flats is an important source of salt for supplying coastal phreatic brine resources. A clear understanding of the flux and process of evaporated salt recharge the shallow underground brine under tidal influence is a prerequisite for promoting the orderly development of coastal underground brine resources. This study established an in-situ numerical model for simulation analysis based on the results of ERT and hydrological parameter surveys conducted on muddy tidal flats on the south bank of Laizhou Bay to clarify the dynamic changes in salt transport between seawater and phreatic brine and to evaluate the recharge capacity of evaporated salt to phreatic brine. The results indicated that in the tidal flat on the sea side (from the “underground brine divide” to the sea) where evaporation is significant, the tidal effect can only periodically inhibit the loss of salt in phreatic brine, but cannot drive the effective accumulation of evaporated salt in the phreatic brine aquifer. During the flooding tide, a flow field from the tidal flat surface to the lower phreatic brine appeared in the aquifer. Salt from the burrows of the top layer entered the phreatic brine under the driving force of the flow field. These salt inputs only slowed the salt loss rate in the phreatic brine from 10.59 kg/h to 7.44 kg/h; During the ebb tide, when the seawater has not receded from the tidal flat, the direction of the groundwater flow field reverses from downward to upward and the driving force of water and salt migration disappears, the salt loss is inhibited in the phreatic brine, and the salt loss rate decreased rapidly to 0.95 kg/h. After the seawater receded from the tidal flat, the salt loss rate of the phreatic brine recovered to 9.89 kg/h, which was basically the same as the salt loss rate at the beginning of the flooding tide.

Numerical analysis of a mixed-dimensional poromechanical model with frictionless contact at matrix–fracture interfaces

We present a complete numerical analysis for a general discretization of a coupled flow–mechanics model in fractured porous media, considering single-phase flows and including frictionless contact at matrix–fracture interfaces, as well as nonlinear poromechanical coupling. Fractures are described as planar surfaces, yielding the so-called mixed- or hybrid-dimensional models. Small displacements and a linear elastic behavior are considered for the matrix. The model accounts for discontinuous fluid pressures at matrix–fracture interfaces in order to cover a wide range of normal fracture conductivities. The numerical analysis is carried out in the Gradient Discretization framework (see J. Droniou, R. Eymard, T. Gallouët, C. Guichard, and R. Herbin [The gradient discretisation method, Springer, Cham, 2018]), encompassing a large family of conforming and nonconforming discretizations. The convergence result also yields, as a by-product, the existence of a weak solution to the continuous model. A numerical experiment in 2D is presented to support the obtained result, employing a Hybrid Finite Volume scheme for the flow and second-order finite elements ( P 2 \mathbb {P}_2 ) for the mechanical displacement coupled with face-wise constant ( P 0 \mathbb P_0 ) Lagrange multipliers on fractures, representing normal stresses, to discretize the contact conditions.