Finite Element Numerical Simulation Research Articles

Stokesian processes : inferring Stokes flows using physics-informed Gaussian processes

We develop a probabilistic Stokes flow framework, using physics informed Gaussian processes, which can be used to solve both forward/inverse flow problems with missing and/or noisy data. The physics of the problem, specified by the Stokes and continuity equations, is exactly encoded into the inference framework. Crucially, this means that we do not need to explicitly solve the Poisson equation for the pressure field, as a physically meaningful (divergence-free) velocity field will automatically be selected. We test our method on a simple pressure driven flow problem, i.e. flow through a sinusoidal channel, and compare against standard numerical methods (Finite Element and Direct Numerical Simulations). We obtain excellent agreement, even when solving inverse problems given only sub-sampled velocity data on low dimensional sub-spaces (i.e. 1 component of the velocity on 1D domains to reconstruct 2D flows). The proposed method will be a valuable tool for analyzing experimental data, where noisy/missing data is the norm.

Resistive switching modulation by incorporating thermally enhanced layer in HfO2-based memristor.

Oxide-based memristors by incorporating thermally enhanced layer (TEL) have showed great potential in electronic devices for high-efficient and high-density neuromorphic computing owing to the improvement of multilevel resistive switching. However, research on the mechanism of resistive switching regulation is still lacking. In this work, based on the method of finite element numerical simulation analysis, a bilayer oxide-based memristor Pt/HfO2 (5 nm)/Ta2O5 (5 nm)/Pt with the Ta2O5 TEL was proposed. The oxygen vacancy concentrates distribution shows that the fracture of conductive filaments (CF) is at the interface where the local temperature is the highest during the reset process. The multilevel resistive switching properties were also obtained by applying different stop voltages. The fracture gap of CF can be enlarged with the increase of the stopping voltage, which is attributed to the heat-gathering ability of the TEL. Moreover, it was found that the fracture position of oxygen CF is dependent on the thickness of TEL, which exhibits a modulation of device RS performance. These results provide a theoretical guidance on the suitability of memristor devices for use in high-density memory and brain-actuated computer systems.

Experimental and Numerical Study on the Low Velocity Impact Behavior of ABR Pipe

The low velocity impact load on pipes during transportation, construction and operation will cause pipeline damage and lay hidden dangers for the safety of pipeline engineering. To study the low velocity impact performance of pipes made of acrylate polymer blended with polyvinyl chloride resin for water supply (ABR), 20 sets of specimens with different heights and different masses of drop hammer were carried out to study the mechanical properties of ABR pipes. Based on the impact time curve, the energy dissipation capacity and impact peak value of ABR pipe specimens were analyzed, and the empirical calculation formula of impact force peak based on the test data is obtained by the dimensional analysis method, with a relative error ranging from −7.8% to 4.1%. Moreover, the finite element numerical simulation of ABR pipe specimens subjected to impact load is carried out, and the strain development law and failure mode of the pipe under low-speed impact load are analyzed. Therefore, the calculation formula of peak impact force and failure mode proposed in this paper can provide safety assessment methods for pipeline engineering designers and constructors.

An Intelligent Monitoring System for the Force Characteristics of Floating Bollards in a Ship Lock

Due to the large scale of navigation ships, the fast speed of entering the lock, and the irregular mooring and the complicated flow conditions in the lock chamber, it is common for the floating bollards of the lock to suffer structural damage or even failure due to the overloaded mooring force. However, the traditional cable load measurement method cannot offer real-time feedback on force characteristics of floating bollards, making it difficult to accurately judge its service status. To this end, according to the floating bollard structure type and load condition of a representative ship lock project in China, this paper determines the theoretical model parameters of a floating bollard load response based on three-dimensional finite element numerical simulation test data and constructs a modified load response model of floating bollards. On this basis, an intelligent floating bollard monitoring system based on big data, internet, and cloud services is developed to intelligently perceive real-time floating bollard force characteristics and monitor the long-term service status. Relying on a representative ship lock in China, a field test of the floating bollard intelligent monitoring system is carried out. The relative error between the calculated values via the model (i.e., system exhibition results) based on the numerical results and the field-measured values is within 15%. This result verified the accuracy and effect of the monitoring system. This research supports the establishment of the digital perception monitoring platform for ship lock facilities and improves the automation level of ship lock operation and management as well as overall risk prevention and control capabilities.

Research on Gas Flow in Vertical Fissure Field of Coal Mine Goaf

The gas in the goaf of a coal mine is difficult to extract compared to the gas in the roadway. Studying the flow pattern of gas in the goaf fracture field is of great significance for optimizing gas extraction measures and ensuring coal mine production safety. Taking a coal mining face in Shaanxi Province, China as the research object, a mathematical model of gas flow was constructed. Through finite element numerical simulation, the pressure and velocity distribution of gas in the goaf fracture field were obtained, and the influence of vertical fracture field on gas flow was analyzed. The research results provide a theoretical basis for coal mine gas control.

Thermo-electro-elastic coupled modeling and simulation of functionally graded piezoelectric structures

Compared with the composite materials, the functionally graded materials can not only provide better specific stiffness but also reduce the risk of layered damage. Therefore, the graded distribution forms have become the development trend of advanced structures. An efficient finite element (FE) modeling method and numerical simulation of plate and shell with nonlinear temperature gradient coupling are developed based on the FOSD hypothesis for thermo-electro-elastic coupled functionally graded piezoelectric material (FGPM) integrated with smart structures in this paper. The constitutive model for thermo-electro-elastic coupled FGPM is derived. Assuming that the temperature gradient distribution changes secondarily through the thickness, two nonlinear physical models for temperature change are constructed. Based on the FOSD hypothesis, the multi-field coupled FE equation of plate and shell is derived. The accuracy of the present FE model is verified by the commercial calculation structures. The parametric simulation of FGPM shells is carried out based on the FE model.

An elastoplastic constitutive model for municipal solid waste (MSW) incorporating solid particle compression and fibrous reinforcing effect

The failures in municipal solid waste (MSW) landfills could result in considerable ecological as well as social problems. Numerical simulations are widely employed to analyze MSW deformation and stability. These methods require an appropriate stress-strain characterization of MSW, which is crucial. Different from soils, the extremely complicated constituents of MSW contain a large number of fibrous reinforced and particle compressible materials. The findings of numerous tests suggest that the fiber reinforced phase and the basic phase are solely responsible for determining the mechanical properties of MSW. On the basis of the double-phase assumption, a new plastic potential function of MSW is developed considering that the reinforcement of fibrous materials only relates to plastic shear strain and the particle compression only affects plastic volumetric strain. According to the associate flow rule, a constitutive model based on elastoplasticity is developed for MSW. The strain hardening behaviour of MSW is well predicted by the model, and this behaviour is in good agreement with experimental evidence. Effects of confining pressure and fibre content are modelled, together with the mechanical and deformation behaviour of MSW. The accurate calculation of effective stresses is obtained through considering the MSW particle compression under the undrained conditions. Parametric investigations calibrate the model and show its properties by comparing them to data from triaxial tests. Moreover, incorporating the proposed model, finite-element numerical simulation was conducted, and the results of finite-element numerical simulation were compared with field monitoring results.

Effect of Train Vibrations on the Dynamic Response of a Multi-Span Double-Curved Brick Arch Thin-Shell Factory of Changleyuan

The dynamic characteristics of a multi-span double-curved brick arch thin-shell factory of Changleyuan in Baoji City and the dynamic response to train vibration load were studied using field dynamic tests and finite-element numerical simulations, and a vibration evaluation of the thin-shell factory was carried out. The results showed that the first-order frequency of the thin-shell factory was 6.24 Hz in the horizontal direction (east–west) and 9.31 Hz in the vertical direction. Moreover, it was established that the horizontal vibration is the overall vibration of the factory, while the vertical vibration is the individual vibration of the double-curved brick arch. In addition, the self-oscillation frequency obtained from the numerical simulation results was greater compared with the field measurements, with a maximum error rate of 7.14%. Both in acceleration and velocity, the vertical vibration for each measurement point was larger than the horizontal vibration, and the farther away from the railroad, the smaller the vibration. The vibration of the velocity at the bottom of the arch was almost the same as that at the top of the arch, while the acceleration vibration at the bottom of the arch was significantly larger than that at the top of the arch, with an average amplitude of 40.64%. For every 20 km/h increase in train running speed, the average increase in vertical acceleration amplitude, vertical velocity amplitude, horizontal acceleration amplitude, and horizontal velocity amplitude for each measurement point of the thin-shell factory was 35.4%, 29.8%, 23.7%, and 12.5%, respectively. When v = 150 km/h, the maximum velocity amplitude for each measurement point of the thin-shell factory was 1.163 mm/s, which is less than the security specification limit of 2.5 mm/s, such that the security of the thin-shell factory meets the requirement, and the maximum horizontal velocity amplitude was 0.272 mm/s, which is close to the integrity specification limit of 0.27 mm/s, such that the integrity of the thin-shell factory just exceeds the requirement; so it is suggested that train running speeds should not exceed 150 km/h and that the thin-shell factory needs to strengthen the monitoring and protection of its integrity.

Study on the forming characteristics of polytetrafluoroethylene/copper jet with different preparation processes

In this paper, PTFE/Cu composite material for liner is taken as the research object, and the preparation process and jet forming characteristics of PTFE/Cu composite liner are studied. The liners were prepared by extrusion molding, molded sintering and hot-pressing sintering. Due to different preparation processes, different microstructures of the liner can occur, including defects such as pores and microcracks, resulting in different strength and density of the liner, leading to differences in the forming characteristics of the jet. Therefore, the forming process of the jet was simulated by the finite element numerical simulation software. It was found that there was obvious radial expansion effect in the head of the jet, but with the increase of density, the radial expansion effect was weakened, and the jet velocity decreased gradually. The strength and densification of the shaped charge liner prepared by different processes were different. The densification of the molded sintering liner was generally better than that of the other two kinds of shaped charge liners. As a result, the velocity of the jet formed by the molded sintering liner is always the highest, with a numerical simulation velocity of 6642 m/s and an experimental velocity of 6534.7 m/s. The second is the jet of the hot-pressing sintering liner and the lowest velocity is the jet of the extrusion molding cover, with a numerical simulation velocity of 6482 m/s, while the experimental velocity is only 6397.9 m/s. The jet velocity measured by the pulse X-ray experiment was compared with the velocity of the numerical simulation, and the error was within 2.96%, which verifies the accuracy of the numerical simulation.

Influence of Structure and Geometry on the Compressive Deformation Behavior of Macadamia Integrifolia and Bertholletia Excelsa Shells: A Validated Finite Element Simulation Study

Macadamia (Macadamia integrifolia) and Brazil nuts (Bertholletia excelsa) have an impressive mechanical resistance. To better understand the key structural features and foam‐like deformation behavior, mechanical compression tests coupled with numerical finite element simulations are performed. Models with different degrees of structural complexity highlight the effects of geometry where even small changes strongly influence the stress distribution and deformation behavior. Circumferential tensile stresses play a vital role in the failure process. Voids or vascular bundles in the shell wall redistribute stresses and bolster the overall strength of structures by preventing early crack propagation. The void arrangement has the potential to inspire the design of lightweight materials with strategically incorporated porosity, leading to improved mechanical performance. Linear elastic models, despite their oversimplification, are valuable for gaining crucial insights about the influence of geometry. The mechanical behavior is further influenced to different extents by isotropy and orthotropy. The distinctive architecture of nutshells offers valuable insights into the design of composite structures with controlled failure, capable of withstanding high compression loads combining foam‐like behavior and fibrous layers.

A finite element numerical simulation analysis of mine direct current method’s advanced detection under varied field sources

Ensuring the safety of coal mine production requires accurate forecasting of coal road heading faces in advance. Because of its high resistance to electromagnetic interference, the mine direct current (DC) method has been widely utilized in the advanced detection and prediction of coal mines. The layout of the field source significantly influences the detection outcomes obtained through this method. In this study, a variety of full-space three-dimensional geoelectric models were established based on the fundamental principle of DC resistivity, and the response features of geological anomalies located in various positions in front of a roadway were studied under different field source conditions using finite element numerical simulation. The electrical response characteristics were analyzed with the electrodes positioned in different directions and two-point to seven-point current sources located on the floor and side of the roadway, respectively. The electrical response of the geological anomalies was characterized with varying positions of the multi-point current source in the roadway and the pole distance of the power supply electrode. Furthermore, the electrical response characteristics of the mine DC method in advanced detection were compared for geological anomalies placed differently across the entire space. The results indicate that the response effect of the geological anomaly in front of the roadway is greater when the field source is placed on the shorter side of the roadway cross-section, with the number of field sources showing a positive correlation with the product of the pole distance and low-resistance amplitude. In advanced detection by DC method, the existence of geological anomalies on the side will affect the recognition of anomalies in front of the roadway.

Approximate semi-analytical technique based on eigenfunction expansion for phase change heat transfer in a cylindrical body contained within a thick multilayered annular wall

Phase change heat transfer occurs commonly in thermal management and energy storage problems. Most literature in this direction assumes direct contact between the phase change material (PCM) and the heat source/sink. However, in practical problems, the PCM is often enclosed within a non-melting wall. This work presents an approximate eigenfunction expansion-based analysis of inwards phase change propagation in a cylindrical PCM encapsulated in a multilayer annular wall. The model accounts for imperfect thermal contact between layers. The transient temperature distribution is determined by solving a transient multilayer thermal conduction problem. Evolution of the phase change front is determined by inserting the temperature distribution into the interfacial energy conservation equation. Results are shown to agree with past work for special cases of the general problem considered here. Good agreement with both experimental and numerical data from past work, and with finite-element numerical simulations is demonstrated. The role of key non-dimensional parameters on phase change characteristics, including total time to melt/freeze is quantified. Ranges of non-dimensional numbers in which the approximate method offers good accuracy are determined. This work extends the state-of-the-art of phase change modeling, with potential applications in energy storage, nuclear engineering, oil/gas transport, and in mass transport problems.

A Wearable Device for Upper Limb Rehabilitation and Assistance Based on Fluid Actuators and Myoelectric Control

Wearable exoskeleton solutions for upper limb rehabilitation or assistance, particularly for the hand area, have become increasingly attractive to researchers, proving to be effective over time in treating hand movement impairments following various neurological diseases. Our aim in the present work is to design a wearable exoskeleton device for active hand rehabilitation/assist control based on myoelectric signal (EMG) capture from forearm muscles, which is easy to wear by the user, comfortable, lightweight, and relatively inexpensive to make. The actuators use two different lengths to increase biocompatibility with the anatomy of the hand, and PneuNets fluid actuators are used. Their design to meet force and bending requirements was based on finite element numerical simulations, and the actuators were designed based on a clear design methodology to achieve the best possible quality. Tests on healthy subjects show that the EMG-based control strategy meets the needs of rehabilitation/assistive hand therapy, finding a comfortable and easy-to-use device. Future directions will focus on developing the device to meet rehabilitation needs for the entire upper limb and integrating the device into virtual reality (VR) through immersive devices.

Characteristics of hydraulic fracture penetration behavior in tight oil with multi-layer reservoirs

The tight oil reservoirs of Fuyang and Gaotaizi in the Daqing Oilfield exhibit characteristics such as thin layers and distributed barriers, which pose challenges for maintaining drilling accuracy within the desired geological sweet spot. Hydraulic fracturing has emerged as the optimal method to connect production wells with target layers effectively. Understanding the behavior of hydraulic fracture propagation in multiple thin layers with significant differences in mechanical properties is crucial for assessing the extent of effective drainage. In this study, a finite element numerical simulation model incorporating cohesive elements is employed to investigate and quantify the effects of stress differences and rock mechanical parameters on fracture penetration. The results indicate that the stress difference between the reservoir and barrier layers plays a key role in controlling hydraulic fracture penetration and height. Moreover, the flow rate and viscosity of the fracturing fluid have a noticeable impact on fracture progression. Hydraulic fractures tend to propagate along the interface of layers with low flow rate and fluid viscosity, thereby hampering the penetration performance in those layers. To achieve a comparable penetrated fracture length in low permeability reservoirs, it is necessary to increase the volume of fracturing fluid in high permeability reservoirs. Furthermore, the barriers layers, which possess relatively weaker mechanical properties, can constrain the width development of hydraulic fractures. This limitation may result in the risk of excessive liquid without sufficient proppant (commonly known as “over liquid but no sand”). Therefore, appropriate measures should be implemented to increase the net pressure and avoid encountering this complex situation.

Study on seismic performance of green fiber-reinforced concrete shear wall

Reinforced concrete shear walls are widely used in civil engineering and it is necessary to study new environmental protection methods to improve its seismic performance.The green fibers (namely recycled steel fibers, collectively referred to as green fibers in this article) formed by cutting high quality steel wires extracted from waste tires and have good tensile, flexural, and yield strength.So the improvement effect of green fibers on the seismic performance of concrete shear wall is studied in this paper. Cyclic loading experiments are used to explore the seismic performance of plain concrete shear wall specimen, green fiber-reinforced concrete shear wall specimen mixed with green fibers 1.0 L (L is the length of shear wall, the same as below) and 1.5 L height and fiber volume ratio of 1.5%. The results show that with the addition of green fibers and the increases in incorporation height of green fibers, the ultimate bearingcapacity, ductility, and energy dissipation capacity of concrete shear wall specimens gradually increase. As the specimen increases the fiber incorporation height, the ultimate bearing capacity of the shear wall increases, and the ductility and energy dissipation capacity increase, and stiffness degradation of specimens gradually slows down. That is, the seismic performance of shear wall specimens is gradually improved. The error between the experimental values and calculated values obtained by the deduced calculation formula is within the allowable range. The results of Abaqus finite element numerical simulation are in good agreement with the experimental results. And through the numerical simulation of the other two specimens, it can be concluded that the flexural performance of green fiber-reinforced concrete shear wall specimens increases with the increases in fiber volume ratio and the decreases in axial compression ratio. This study can provide a reference for the research on the seismic performance of fiber-reinforced concrete shear wall and the application of steel wires extracted from waste tires in practical engineering.

Load carrying capacity of star‐battened angle members made of S460 steel in compression

AbstractLattice towers are extensively built in Europe and worldwide to serve power transmission purposes. Their members mainly consist of single angle profiles, while built‐up sections, such as star‐battened ones, are usually preferred for the strengthening of individual members or in case of very high compression loads. Recent upwards developments of the power grid requests also lead to the need to use high strength steels (HSS) for the design and construction of higher and heavier loaded steel lattice transmission towers. Within the present paper, investigations conducted on the bearing capacity of a star‐battened member made of two S460 L250×250×28 angles are presented, even if the conclusions may be extended to any angle size and steel grade.Firstly, a critical review of the current European normative documents (EN 50341, EN1993‐1‐3, prEN1993‐3) is made and the buckling resistance of the above‐mentioned member is evaluated. Secondly, the results of an experimental compression test performed on the studied member are presented; these results are complemented by a full non‐linear finite element numerical simulation. All the obtained results are finally compared and discussed.

On the Capacity of Beams with U Cross Section Subjected to Bending and Torsion

AbstractBeams with singly symmetric U cross sections are often subjected to bending about the strong axis and simultaneously to scheduled torsion, since the shear center is outside the section geometry. The member capacity of such sections, which is strongly influenced by effects of lateral torsional buckling, can therefore hardly be represented with the common design regulations based on reduction factors χLT of EN 1993‐1‐1. However, numerical approaches allow analyzing deeply the structural behavior of corresponding beams. In the present study, different numerical finite element simulations (GMNIA) including simplified numerical models based on the plastic zones theory are incorporated to determine member capacities and to derive corresponding reduction factors for simplified verifications. As the load‐bearing capacity of members susceptible to stability is strongly influenced by imperfections, the straightness according to manufacturing tolerances as well as approaches for the acquisition of structural imperfections (residual stresses) are considered in the numerical analyses. The investigations are carried out for selected structural systems with different sets of parameters, such as for the member lengths and cross section types. Concluding, a capacity curve is derived and compared to different reduction factors χLT specified in EN 1993‐1‐1.

Development of a software platform for bridge modal and damage identification based on ambient excitation

Modal and damage identification based on ambient excitation can greatly improve the efficiency of high-speed railway bridge vibration detection. This paper first describes the basic principles of stochastic subspace identification, peak-picking, and frequency domain decomposition method in modal analysis based on ambient excitation, and the effectiveness of these three methods is verified through finite element calculation and numerical simulation. Then the damage element is added to the finite element model to simulate the crack, and the curvature mode difference and the curvature mode area difference square ratio are calculated by using the stochastic subspace identification results to verify their ability of damage identification and location. Finally, the above modal and damage identification techniques are integrated to develop a bridge modal and damage identification software platform. The final results show that all three modal identification methods can accurately identify the vibration frequency and mode shape, both damage identification methods can accurately identify and locate the damage, and the developed software platform is simple and efficient.

A standard thermodynamic-based extension of the Modified Cam-Clay soil model and its applications

For mechanical behaviours of granular soils considered here (sands, silts and stiff clays), we propose a thermodynamic-based formulation which relies on the Modified Cam-Clay constitutive model. To this end, and in the framework of Generalized Standard Materials (GSM) framework, we introduce a free energy and a yield criterion (or equivalently a dissipation potential) which account for an isotropic nonlinear elastic behaviour and a volumetric hardening law. Based on available works with coupled hardening laws for von Mises plasticity, we propose for pressure-sensitive materials a new nonlinear deviatoric hardening preserving the well-known critical state existence.Taking advantage of the GSM framework, we establish an incremental variational formulation of the model whose solution obeys to a minimization principle. This has required an approximation of the incremental dissipation. The resulting equations are detailed for the use of an implicit resolution scheme with a standard Newton–Raphson algorithm. The constitutive model parameters are calibrated on a pool of experimental data on isotropic, shearing and triaxial tests on loose sand specimen. The investigations of the model responses allow to better predict the nonlinear regimes of soils specimen on monotonic and cyclic loading paths. Numerical finite element simulations finally underline the predictive capabilities of the model on structures.

Analysis of Arch Forming Factors of Shallow Buried Hard Rock Tunnel under Overlying Load

To investigate the arching effect of shallow buried hard rock tunnels under overlying load, the engineering scenario of a subway station on Qingdao Metro Line 6 is utilized. A large-scale tunnel loading model test is conducted, in conjunction with finite element numerical simulations, to analyze the impact of various overburden ratios on strata arching. The results show that: when the tunnel excavation span is certain, with an increase in the overlying rock mass, the stress diffusion process of the surrounding rock can be better accomplished to form the arch effect. This means that the thickness of the overburden of the tunnel determines whether or not the surrounding rock appears to have a stratified arch effect. When the tunnel overlying rock thickness is certain, the span of the tunnel determines the shape of the formation into an arch, that is, the curvature of the arch. The joint surface is an important factor in tunnel stability. When the overlying load increases to a certain value, the rock mass at the joint plane slips relatively, leading to the displacement phenomenon of the surrounding rock, which then affects the formation and shape of the formation arch.