Element Method Model Research Articles

An Energy-Based Discrete Element Modeling Method Coupled with Time-Series Analysis for Investigating Deformations and Failures of Jointed Rock Slopes

The discrete element method (DEM) can be effectively used in investigations of the deformations and failures of jointed rock slopes. However, when to appropriately terminate the DEM iterative process is not clear. Recently, a displacement-based discrete element modeling method for jointed rock slopes was proposed to determine when the DEM iterative process is terminated, and it considers displacements that come from rock blocks located near the potential sliding surface that needs to be determined before the DEM modeling. In this paper, an energy-based discrete element modeling method combined with time-series analysis is proposed to investigate the deformations and failures of jointed rock slopes. The proposed method defines an energy-based criterion to determine when to terminate the DEM iterative process in analyzing the deformations and failures of jointed rock slopes. The novelty of the proposed energy-based method is that, it is more applicable than the displacement-based method because it does not need to determine the position of the potential sliding surface before DEM modeling. The proposed energy-based method is a generalized form of the displacement-based discrete element modeling method, and the proposed method considers not only the displacement of each block but also the weight of each block. Moreover, the computational cost of the proposed method is approximately the same as that of the displacement-based discrete element modeling method. To validate that the proposed energy-based method is effective, the proposed method is used to analyze a simple jointed rock slope; the result is compared to that achieved by using the displacement-based method, and the comparative results are basically consistent. The proposed energy-based method can be commonly used to analyze the deformations and failures of general rock slopes where it is difficult to determine the obvious potential sliding surface.

Vehicle\u2013track\u2013tunnel dynamic interaction: a finite/infinite element modelling method

The aim of this study is to develop coupled matrix formulations to characterize the dynamic interaction between the vehicle, track, and tunnel. The vehicle–track coupled system is established in light of vehicle–track coupled dynamics theory. The physical characteristics and mechanical behavior of tunnel segments and rings are modeled by the finite element method, while the soil layers of the vehicle–track–tunnel (VTT) system are modeled as an assemblage of 3-D mapping infinite elements by satisfying the boundary conditions at the infinite area. With novelty, the tunnel components, such as rings and segments, have been coupled to the vehicle–track systems using a matrix coupling method for finite elements. The responses of sub-systems included in the VTT interaction are obtained simultaneously to guarantee the solution accuracy. To relieve the computer storage and save the CPU time for the large-scale VTT dynamics system with high degrees of freedoms, a cyclic calculation method is introduced. Apart from model validations, the necessity of considering the tunnel substructures such as rings and segments is demonstrated. In addition, the maximum number of elements in the tunnel segment is confirmed by numerical simulations.

Simulation analysis of mechanical properties of composite materials

Based on the technical study of a composite vertical tail, the mechanical properties of honeycomb sandwich structure at the leading edge of the composite were studied fundamental computational analysis. The stress calculation and modal analysis of sandwich beam/plate structure are carried out by using engineering algorithm and two finite element modeling methods. The comparative analysis of the results shows that the two modeling methods can effectively simulate the mechanical properties of composite sandwich structure. In the actual analysis of complex structures, a simple 2D shell element modeling method can be used for preliminary simulation analysis.

Manufacturing of cylindrical articles with a thick bottom and thin wall

The issue of increasing the efficiency of metal forming processes by combining the operations of drawing with thinning of the wall and extrusion in the manufacture of cylindrical articles having a thick bottom and thin wall. The ratio of height to diameter can vary from 1 to 10 and more. These are various connectins, adapters, unions, elements of cases, sleeves and other articles with a wall thickness less, than thickness of a bottom. Rolled sheet metal made of various grades of steel, brass, aluminum, titanium and other materials can be used as workpiece materials. The combination of drawing operations with wall thinning and extrusion at one working position allows to significantly expand the technological capabilities of metal forming, reduce the number of steps, improve the quality of articles. Compared to backward extrusion, the proposed technology provides a lower level of stress in the tool and workpiece, enabling to use less powerful hydraulic press equipment and significantly increase the durability of stamping equipment. When using blanks with planar anisotropy, this technology allows not only to eliminate earing on the edge surface of the semi-finished product and get a smooth face end of the product, but also to form any other profile of the edge of the part. The formation of articles without earing eliminates the operation of trimming the end face of the semi-finished product, which significantly increases the utilization of the material and reduces the cost of finished articles. The method for calculation of geometrical parameters of stamping equipment to obtain defect-free articles is given. Theoretical studies of the combination of drawing operations with thinning and extrusion of the cylindrical workpiece were carried out by the finite element modeling method using the QFORM software package. The scheme of universal experimental stamping equipment is shown.

Quantitative assessment of resistant contributions of two-bay beams with unequal spans

Following the sudden removal of an internal column from a steel-frame composite-floor system, the two-bay beams connected to the failed column play a key role in the internal force redistribution and rebalancing of the remaining structure. Moreover, the span–depth ratios of the adjacent two-bay beams have a significant influence on the collapse-resistant performance of the structure. To date, studies on structural progressive collapse of beams with unequal spans have been limited. In this study, based on the results of static loading tests on composite beam–column assemblies with cover-plate joints under three different span ratios, the finite element modeling method was validated and numerical models of the beam–column assemblies with three unequal spans were established. The influence of the unequal span of two-bay beams on the internal force development and load-resisting mechanisms of the composite beam–column assemblies were analyzed in detail. To gain deeper insight into the load-resisting mechanisms, the contributions of the flexural and catenary mechanism resistances to the total resistance of two-bay beams were quantitatively separated using the energy equilibrium theory, and it was found that the resistant contributions of the catenary mechanism, in general, account for less than a half of the structure’s resistance capacity. Moreover, theoretical formulas for the different resistant contributions of two-bay beams were proposed as recommendations for structural progressive collapse design and practical engineering applications. The analysis of results demonstrated that the span–depth ratios of two-bay beams determined the resistant contribution coefficients for the flexural mechanism, whereas the span ratios of two-bay beams determined the resistant contribution coefficient for the catenary mechanism, whereas the beam depth had little influence thereon.

Effect of the spatial variability of soil parameters on the deformation behavior of excavated slopes

The prediction of slope stability is difficult due to the spatial variability of soil parameters and measurement errors from core samples. This study proposed a Bayesian updating framework that based on the random finite element model (RFEM) method. The proposed approach was applied in a field excavation slope project. The field data of a soil slope with anti-slide bored piles under four-stage excavations were compared to elucidate the spatial variability of the cohesion, friction angle and stiffness in different soil layers. Then, a Bayesian updating model with random finite element analysis was developed by considering the COV and SOF of the soil parameters. The proposed analysis approach utilized the prior information from the site investigation and field measurement results. The posterior statistical characteristic values of the soil parameters were obtained from equivalent samples calculated by Markov Chain Monte Carlo simulations. The results indicated that the proposed method can reduce the effect of uncertainty related to the soil properties. Finally, the effects of soil parameters and excavation conditions on the slope stability were established, enabling an evaluation of safety based on field measurement results.

Discrete element modeling of the compression molding of polymer–crystal composite particles

Cold compression molding of polymer–crystal composite particles is a widely applied technique in chemical engineering fields. In this study, a discrete element modeling (DEM) method was developed and used to investigate the densification process and micromechanics of polymer–crystal composite particles undergoing compression. This method considered the realistic particle shape and internal microstructure of component crystals and polymeric binder, based on information from X-ray micro-computed tomography (μCT) and scanning electron microscopy (SEM) analyses of polymer–crystal composite particles. A series of single-particle crushing tests and comparative DEM simulations were conducted to verify and calibrate the novel DEM modeling method and the DEM parameters used to represent polymer–crystal composite particles. Furthermore, an in situ μCT scanning compression test and corresponding DEM simulation were conducted to investigate the densification process and micromechanics of polymer–crystal composite particles subjected to compression molding. The experimental and DEM results proved the efficiency and accuracy of the novel DEM method in modeling the fracture behaviors of molded polymer–crystal particle specimens. Various micromechanical behaviors were observed within these specimens, related to such aspects as interparticle pore structures, crystal grading, fracture development, and contact forces. These findings provide deep insights into the densification process and microstructural changes that occur in polymer–crystal composite particles during the compression-molding process.

Brain trauma characteristics for lightweight and heavyweight fighters in professional mixed martial arts

ABSTRACT Mixed martial arts (MMA) is a sport where the fighters are at high risk of brain trauma, with characteristics, such as the frequency, magnitude, and interval of head impacts influencing the risk of developing short- and long-term negative brain health outcomes. These characteristics may be influenced by weight class as they may have unique fighting styles. The purpose of this research was to compare frequency, magnitude, and interval of head impacts between lightweight and heavyweight fighters in professional MMA. Frequency, interval, event type, velocity, and location of head impacts were documented for 60 fighters from 15 Lightweight and 15 Heavyweight professional MMA fights. Head impact reconstructions of these events were performed using physical and finite element modelling methods to determine the strain in the brain tissues. The results found that LW and HW fighters sustained similar head impact frequencies and intervals. The LW fighters sustained a significantly higher frequency of very low and high magnitude impacts to the head from punches; HW a larger frequency of high category strains from elbow strikes. These brain trauma profiles reflect different fight strategies and may inform methods to manage and mitigate the long-term effects of repetitive impacts to the head.

Cyclic behavior and hysteresis model of beam-column joint under salt spray corrosion environment

This paper aims to investigate a method predicting the cyclic behaviors of welded beam-column joints exposed to the salt spray corrosion environment based on the analysis of the quasi-static tests and numerical simulation results. Experimental results indicated that the reduction of the section caused by corrosion damage was the main factor affecting the degradation degree of bearing capacity and stiffness of the beam-column joints. The rough surface profile and significant corrosion loss of different flanges and webs could be observed for beam-column joints with long-term exposure to the salt spray environment, which had a noticeable influence on the local buckling and fracture of welded zones connecting beam and column, accelerating the failure process. As a result, the number of cycles and the area of the hysteresis hoop gradually decreased as the corrosion degree increased, so that the cyclic deformation capacity and the energy dissipation capacity deteriorated rapidly. When the exposure time was 18 months (the corrosion depth and the maximum pitting depth were 2.13 mm and 1.48 mm), the yield moment and ultimate moment of the beam-column joint decreased by 28.2% and 32.1%, the total rotation and total energy dissipation decreased by 49.4% and 70.8%. A finite element modeling method depended on the shell element was selected to carry out a series of numerical analyses to investigate the impacts of different corrosion factors on the seismic performances of beam-column joints, which pointed out the corrosion damage in the beam and panel zone causing the nonlinear degradation of seismic performance indices, then the linear skeleton curve model of the corroded beam-column joints was proposed. Furthermore, this paper discussed the effects of the plastic post-buckling strength degradation caused by the corrosion damage on the strength and stiffness of hysteresis curves, thereby the cyclic damage accumulation model and hysteresis model which included the characteristic parameters of corrosion was established to predict the hysteresis behaviors of corroded beam-column joints.

Nonlinear interaction effect on main cable clamp bolts tightening in suspension bridge

Elastic interaction effect commonly exists in the assembly of multi-bolted joint. It is defined as the loss of tension forces in some bolts due to progressively tightening of neighboring bolts. Main cable clamp is a large size bolted joint used in suspension bridge. Investigation on the interaction effect of the clamp bolt tightening has seldom been reported. This article presents a field experiment to study the interaction effect on the clamp bolt tightening. In the experiment, three types of clamp and three tightening sequences were included. Then, finite element models considering the actual nonlinear transverse compressed behaviour of main cables were devised to simulate the bolt tightening procedures, thus providing an effective numerical tool to understand the nonlinear interaction effect on clamp bolts tightening. The experimental results provide validations for subsequent numerical studies, showing that the devised finite element modeling method can effectively predict nonlinear deformation of the main cable and the residual tension force of the clamp bolts. Moreover, the tightening efficiency of different tightening sequeces are discussed based on the experimental and the numerical results. Conclusions can be drawn that for the clamps with much longer length and much more rows of bolts, the degree of the nonlinear interaction effect tends to be higher. The side-to-centre bolt tightening sequence is more effective than the centre-to-side sequence.

Time–Frequency Random Approach for Prediction of Subway Train-Induced Tunnel and Ground Vibrations

A time–frequency random approach is proposed in this paper for the prediction of subway train-induced tunnel and ground vibrations. This is a development of the random approach previously proposed by the authors, which takes the discrete track support, singular track defects, etc., into consideration. The proposed approach is developed using a two-step method. First, the pseudo-excitation method (PEM) and the two-dimensional multibody system/finite element method model are effectively combined to derive the track–tunnel pseudo-interaction forces by employing the power spectral density of track irregularity. Second, the random vibrations of the tunnel–soil system are obtained via the PEM in the wavenumber–frequency domain. To improve the computational efficiency, a fast-computing strategy is proposed based on the multipoint synchronous algorithm. Using numerical examples, the proposed time–frequency hybrid modeling process is verified by comparing it with the fully coupled time-dependent three-dimensional approach. Furthermore, the influence of the discrete track support on the random vibrations of the tunnel and ground is discussed by comparing the results predicted by the proposed approach with those predicted by the previously developed approach.

New Equivalent Model and Modal Analysis of Permanent Magnet Motor Stator System

<div class="section abstract"><div class="htmlview paragraph">This paper proposes a new type of permanent magnet motor stator system equivalent model considering insulation materials and modal analysis is performed. First, the analytic method is used to estimate the modal natural frequency of the stator core and the stator winding system respectively, and the influence of the winding on the system modal is analyzed. Then, a new type of winding equivalent model was established using the finite element method (FEM), two traditional models were established at the same time. Compared with the traditional model, the new winding equivalent model considers the influence of insulating materials, so the calculation results are more accurate. At the same time, due to the innovative modeling of the new winding equivalent model, the Young’s modulus of the winding equivalent material is increased, which effectively reduces the appearance of useless local modes and improves the calculation efficiency. Due to the reduction of useless local modes, the new winding equivalent model can quickly calculate and accurately identify the natural frequency of the 0-order mode of the stator system. Finally, modal tests are used to verify the correctness of the analytical method and the accuracy of the calculation results of the new equivalent model. This paper provides a new finite element modeling method for the modal analysis of the motor stator system, which improves the calculation accuracy and efficiency.</div></div>

Finite Element Modeling Method and Analysis of Self-Compacting Concrete Prestressed T-Beam

Self-compacting concrete could be poured under the action of gravity, without vibration, and has good working performance. It could reduce the noise during production, and reduce the labor of workers. In recent years, more and more scholars begin to study the concrete. In this paper, ABAQUS finite element software is used to simulate the self-compacted concrete prestressed T-beam under different parameters, using the self-compacting concrete constitutive model. The cooling method is used to simulate the prestress applying, and the performance of beam is analyzed. It is found that the bearing capacity of the member improves with the increasing of the reinforcement ratio, the prestress increases the stiffness of the member, and reduces the deflection of the member, but the ductility is reducing with the increasing of prestress.

Research on Simulation Method of Steel-Concrete Composite Beam with Finite Element

The performance of composite girder double element model and composite cross-section model in the finite element analysis of composite beam were introduced, and three simulation method of the interface in the composite beam was studied, and then the three finite element modeling method of were adopt to analysis a composite beam under different load, and two simulation models including shrinking and the creep effect were computed. It is concluded from the computational results, when the mesh of dual element model is refined, the difference between the calculation results of the dual element model and the transformed section model remains very small, which means that dual element model can meet the requirements of calculation accuracy in case of the fine mesh size.

Finite element modelling of concrete-filled spiral-welded mild-steel and stainless-steel tubes in flexure

This study investigated the capability of widely-used finite element modelling (FEM) methods, to predict the flexural capacity behaviour of concrete-filled spiral-welded mild-steel and stainless-steel tubes (CF-SWMSTs and CF-SWSSTs). For this purpose, twelve CF-SWMST and CF-SWSST flexural tests each were modelled using the ABAQUS software. The main parameters that had been varied in the respective tests were the outside diameter to thickness (D/t) ratio and infill concrete strength. The nominal D/t of the modelled specimens were in the range 51–114.5, while the infill concretes were of nominal grades 20 and 50 MPa. The moment capacities predicted by the FEM were observed to be, on average, conservative for the modelled CF-SWMSTs. The predicted flexural capacities were more closely in agreement with the corresponding experimental capacities for the CF-SWSSTs. The respective average actual to predicted moment capacity ratios were 1.07 and 1.00, respectively. The experimental and predicted deformation modes were also in qualitative agreement, with local buckling also being predicted by the finite element models. Though the experimentally obtained local buckling patterns were not exactly replicated, there was, nonetheless, good qualitative agreement. This study provided evidence of the capacity of commonly used FEM approaches, relating to CFSTs, to act as a predictive tool for CF-SWMSTs and CF-SWSSTs in flexure. Given the distinct difference in capacity prediction conservativeness, the study also indicated that separate material model formulations may be warranted for CF-SWSSTs compared to CF-SWMSTs. The predicted results were also found to be negligibly sensitive to explicitly modelling the spiral weld seam geometry, even though it was the default case adopted for the FEM in this study.

Testing the State of Internal Load and Strength of the Facade Mesh Wire Subjected to the Corrugation Process

Abstract The article presents an example of a structural solution of a mesh facade installed on a public building. The types of loads that can affect the structure of such a mesh have been characterized. The course of the wire shaping process used to produce the described mesh was reported. A finite element method (FEM) model was developed to simulate mechanical phenomena occurring during the technological process of crimping stainless-steel wire. Material model parameters have been defined. The developed model was verified in production conditions. Relations between wire-forming loads and tensile limit loads, as well as the distribution of equivalent tensile stress forced by the crimping process and internal stresses after crimping, were determined. The description of the technological process was presented in a form of a graph. The work contains the results of strength tests of wire materials and shaping tools.

Numerical simulation and testing verification of the interaction between track and sandy ground based on discrete element method

Tractive effort of tracked vehicles plays an important role in military and agricultural fields. In order to solve the problem of low precision in numerical simulation of the interaction between track and sandy ground, a systematic and accurate discrete element modeling method for sandy road was proposed. The sandy ground was modeled according to the mechanical parameters measured by soil mechanics tests. The interaction coefficients of sandy soil were measured by the repose angle test and triaxial compression test combined with the corresponding simulation. On this basis, a discrete element interaction model of track-sandy ground was established, which can be used to test the tractive effort of track. Numerical simulation calculation of track model at different speeds was carried out, and the simulation results were compared with the results of indoor soil bin test for verification. The verification results show that the interaction between track and sandy ground based on DEM simulation is consistent with the actual soil bin test. The discrete element modeling method in this paper can be used to model the track and sandy ground accurately, and the simulation model can be used to test the tractive effort of tracked vehicle.

Seismic Performance Evaluation of a Roof Structure of a Historic Chinese Timber Frame Building

ABSTRACT This paper presents a finite element modeling method for a prediction of lateral resistance and seismic response of the roof structure of a historic Chinese timber frame building. Force-displacement relationships of straight tenon joints, Mantou tenon joints, and Dougong bracket sets are calibrated by experimental results. In-plane and out-of-plane resistance analyses have been carried out, and force-displacement relationships and stress contributions are obtained. Acceleration and displacement responses are attained and adopted for the seismic performance evaluation of the historic roof structure. Results show that the overall in-plane and out-of-plane hysteresis performances of the roof are poor and energy dissipation abilities are weak. The seismic responses of measuring nodes are close under the same seismic excitation. As the seismic excitation increases, peak responses of all measuring nodes increase. Dougong brackets and mortise-tenon connections dissipate large seismic energy under strong excitation, and seismic responses (acceleration and displacement responses) of the roof structure are significantly reduced. The maximum drift angles of the entire roof truss are found to approach 1/2500 rad, demonstrating that the roof structure has good integrity.

Finite Element Modeling (FEM) vs. Simplified Force-Based Methods for Rigid Retaining Walls Under Earthquake Excitation

The performance of conventional rigid retaining wall under harmonic and transient ground motions is evaluated using three-dimensional finite element (FE) simulations. Rotation of wall about the base is found to be the predominant failure mechanism of the gravity retaining wall under seismic excitation. Earth pressure distribution corresponding to the peak ground acceleration is found to be nonlinear and unique in shape. The earth pressure distribution is strongly related to the rotational movement of the wall. Existing force-based methods for rigid retaining walls overestimated the earth pressure under seismic conditions compared to these numerical simulations.

Influence of the Cutterhead Configuration and Operation Parameters on the Face Stability of EPB Shield Tunnels in Dry Granular Soils

This paper presents a study on the face stability of earth pressure balance (EPB) shield tunnels in dry granular soils using the discrete element model (DEM) method to replicate realistic excavation processes of the EPB machine. Analyses were conducted at different buried depths to determine the limit face pressures and the face failure model induced by the EPB shield machine with varying open ratios and rotation speeds of the cutterhead. The failure kinematics of the soil and the soil arching effect were also determined. The results showed that both the open ratio and the rotation speed of the cutterhead have significant effects on the stability of the face in terms of the failure kinematics, limit face pressures, and the soil arching effect. The failure zone was highly dependent on the open ratio, but it depended less on the rotation speed of the cutterhead. The stability of the face is overestimated when the excavation is conducted with a cutterhead that has a large open ratio, but it is underestimated when the excavation is conducted with a cutterhead that has a smaller open ratio. Ignoring the effect of the configuration of the cutterhead and the rotation speed results in unexpected and unrealistic results.