FEM Program Research Articles

Моделирование сейсмического воздействия на земляное полотно с демпфирующим слоем. Динамический расчет по акселерограмме

The problem of modelling of a seismic impact on a railway roadbed is examined. The modelling was conducted with the use of a generated accelerogram. Calculations of the stress-strain state of the roadbed during an earthquake are made with the GEO5 FEM program complex. The stress and deformation values in the construction of the roadbed considering several geometric parameters of the calculation scheme, physical and dynamical properties of soil are presented. The nature of the impact of these factors on the stress-strain state during an earthquake is detected. The effectiveness of the use of the finite-element method for the dynamic calculations of a soil construction considering the seismic impact is reasoned. The soil constructions with a damping layer serving to reduce the seismic negative effect are calculated. The dependences of stresses and deformations in the roadbed on the damping parameters are detected. The possibility to reduce the deformations and stresses in the roadbed during a seismic impact with the use of the damping layer or the use into the qualities of the material for the soil mounds with definite dynamical and physical characteristics is established.

Oil tanker under ice loadings

As a result of global warming, the area of the polar pack ice is diminishing, making merchant travel more practical. Even if Arctic ice thickness reduced in the summer, fractured ice is still presenting operational risks to the future navigation. The intricate process of ship-ice interaction includes stochastic ice loading on the vessel hull. In order to properly construct a vessel, the severe bow forces that arise must be accurately anticipated using statistical extrapolation techniques. This study examines the severe bow forces that an oil tanker encounters when sailing in the Arctic Ocean. Two stages are taken in the analysis. Then, using the FEM program ANSYS/LS-DYNA, the oil tanker bow force distribution is estimated. Second, in order to estimate the bow force levels connected with extended return periods, the average conditional exceedance rate approach is used to anticipate severe bow forces. The vessel’s itinerary was planned to take advantage of the weaker ice. As a result, the Arctic Ocean passage took a meandering route rather than a linear one. As a result, the ship route data that was investigated was inaccurate with regard to the ice thickness data encountered by a vessel yet skewed with regard to the ice thickness distribution in the region. This research intends to demonstrate the effective application of an exact reliability approach to an oil tanker with severe bow forces on a particular route.

An Analytical Algorithm for Determining Optimal Thin-Walled Hollow Pier Configuration with Sunlight Temperature Differences

Formulas for computing the line shape of a thin-walled hollow pier body based on structural characteristics and measured sunlight temperature difference are derived using an analytical algorithm. In a case study of the No. 5 pier of a newly constructed continuous beam bridge on a mountainous expressway of Guizhou Province in China, the pier top’s displacement calculated by the analytical algorithm, currently accepted code, and a FEM program were each compared to its measured values. Furthermore, the effects of sunlight temperature difference, pier height, and wall thickness on the line shape of the pier body were explored, and the results show that the calculation values from these formulas were closer to the measured values than the currently accepted code, with a maximum error of 0.507 mm, demonstrating that the formulas have a more dependable result, higher precision, and more specific applicability. Thus, the algorithm provides a better method for the line shape calculation and construction control of thin-walled hollow piers because it can accurately account for sunlight temperature differences and pier height.

Experimental research and numerical simulations of the actual response flat slab in case of column loss

AbstractThis study reports the influence of tie reinforcement on the load‐bearing capacity of a flat plate slab in a failure situation due to the removal of an edge column. The results are based on numerical model analysis, experimental investigations, and analytical estimation. A numerical model was developed using the ATENA FEM program and validated based on the test results of the materials used. Experimental studies on the edge column removal were carried out for three models of 16 field flat plate slabs with varying degrees of tie reinforcement. Furthermore, the columns removed in Models M1 and M2 were near the corner edge columns, whereas in Model M3, they were the middle edge columns. The behavior of a reinforced concrete flat plate subjected to large deflections was estimated analytically based on the current literature and compared with the results obtained from numerical analyses and experimental investigations. During the experimental investigations, many traditional and modern techniques were used to measure the strains and displacements of reinforcing steel and concrete.

3D FEM Simulation of Titanium Alloy (Ti6Al4V) Machining with Harmonic Endmill Tools

AbstractUsually, end milling operations have been carried out using conventional uniform helix tools with fixed helix angles. Thus, many studies have been conducted to study the effects of these tools on the thermomechanical properties of a milling process. Recently, there have been works that point to the benefits of using harmonic endmills. Harmonic endmills consist of cutting edge profiles that have continuously harmonically varying helix angles. The variation is described using a harmonic function of axial position (elevation) of points on the cutting edge. In this work, a 3D finite element simulation using ABAQUS, is carried out for the complex milling process of Titanium alloy Ti6Al4V. The envelope of the harmonic tool is first generated using a set of MATLAB codes and stored in a Standard Triangle Language (.stl) format. The machine tool is introduced into an FEM program which has been designed to provide for dynamic effects, thermo‐mechanical coupling, material damage law and the criterion for contact associated with the milling process. A Johnson‐Cook material constitutive equation which combines the effects of strain hardening, strain softening, and temperature softening is used. To account for the chip separation criterion, the Johnson Cook damage evolution equation is used. The milling process simulation for Ti6Al4V is then carried out. In the end, the stress distribution and the cutting forces are obtained.

Numerical simulation of fully grouted rock bolts with or without faceplates based on the tri-linear bond-slip model

A difference scheme of the governing equation of the bolt-grout interface of the fully grouted rock bolt was derived based on the tri-linear bond-slip model, local equilibrium condition, and finite difference method. The corresponding solution formats of the fully grouted rock bolts with or without faceplates were proposed according to their different boundary conditions. Consequently, a numerical model of the fully grouted rock bolts with or without faceplates was established. This model is able to simulate the bonding, softening, and decoupling characteristics of the bolt-grout interface of the fully grouted rock bolts with or without faceplates subjected to the pullout load or rock deformation. The prediction results of this model agree well with the pullout test results, the calculation results of related scholars, and the analytical solutions, which proves its correctness. Then, the formulas of the support reaction force of the rock bolts with or without faceplates were derived according to their support mechanisms, and the support reaction force was applied during the iteration to simulate the bolt-rock interaction. This method is convenient for engineering applications owing to that it does not need to add additional degrees of freedom for rock bolts. The abovementioned model and method were incorporated into a self-developed FEM program and the effect of the initial deformation of the surrounding rock before bolt installation was considered, resulting in a numerical simulation program for fully grouted rock bolts with or without faceplates in underground caverns. Finally, this program was applied in a circular tunnel and the influences of the faceplate, bolt installation timing, bolt length, and bolt radius on the support performance of rock bolts were investigated. The following conclusions were obtained. 1) The faceplate can greatly improve the support effect. 2) The main failure mode of the rock bolts without faceplates is the shear damage at the bolt-grout interface, while the bolt pull-off is the dominant failure mode of the rock bolts with faceplates. 3) There is a critical value of bolt length. Increasing the bolt length within the critical value can significantly enhance the support effect, whereas increasing the bolt length beyond the critical value has little effect on the support effect. 4) Increasing the bolt radius can effectively enhance the support effect.

Axisymmetric buckling analysis of submerged hemi-elliptic toroidal shells

Toroidal shells have been widely used in various industrial applications for over a decade. Most studies on buckling behavior have focused on circular toroidal shells with uniform loads. In contrast, the existing literature on the shell buckling of a toroid with elliptical cross-sections has received limited attention. This study aims to present numerical solutions for axisymmetric buckling of hemi-elliptic toroidal shells under linearly hydrostatic pressure to append available data and results in this field. The thickness of the hemi-elliptic toroidal shells is assumed to be constant before and after the buckling state. Solution procedures for solving critical buckling loads dealt with eigenvalue problems and were formulated by an energy approach. All relevant parameters such as membrane and bending strain components and in-plane stress resultants were derived based on differential geometry. An in-house FEM program solved the weak formulation derived from a variational method. The buckling results for elliptic toroidal shells with various b/a ratios were established as the critical seawater depth and compared to the previously published results. Additionally, parametric studies on the effect of the variable b/a ratios and the major radius R of elliptic toroidal shells on the axisymmetric buckling loads and mode shapes were examined thoroughly and addressed in more detail herein.

Comparison of strengthening methods to improve punching behavior of two-way RC flat slabs

Within the scope of this study, three different strengthening methods have been proposed to increase the punching strength of reinforced concrete (RC) flat slabs. These methods are a shear stud, fiber-reinforced polymer (FRP), and textile-reinforced mortar (TRM). Ten large-scale RC flat slabs were produced to investigate the effectiveness of strengthening methods. One of these was chosen as a reference, one strengthened with shear stud, four strengthened with FRP and the rest with TRM. Reinforcement type (shear stud, FRP, and TRM), strip direction (straight and diagonal), and anchor usage were determined as experimental variables. The ultimate load capacity, initial stiffness, and energy dissipation capacity values were calculated and compared using the load-displacement graphs obtained as a result of the tests of specimens. According to the experimental results obtained, TRM, FRP, and shear stud methods increased the ultimate load capacity by an average of 58%, 52%, and 20%, respectively. These increased values for energy dissipation capacity are 118%, 63%, and 47%, respectively. In the numerical part of the study, the experimental study was simulated with the ABAQUS/Explicit FEM program, and the obtained results were compared with the experimental results. Moreover, the stresses and damage distributions in the specimens were evaluated. As a result of the study, it was seen that the method applied using textile reinforced strips gave the most successful results among three different strengthening techniques applied to improve the behavior of RC slabs under the effect of punching loading.

The Effect of Differences In Soil Nailing Length On The Value Of Safety Factor (Case Study: D.I. Batang Sinamar Project)


 
 
 
 Construction of irrigation canals in the Batang Sinamar area, Sumatra, is carried out in the highlands. The soil on the slope is known to have soft soil consistency. So, it is necessary to analyze the reinforcement design for slopes with soft soil conditions to avoid problems in the future. In this plan, design analysis is carried out using soil nailing, which is planned with different depths, namely 8 meters and 10 meters. Reinforcement analysis will be carried out with the FEM program. From the analysis results, a comparison of the effectiveness of the design will be carried out in terms of cost analysis and the method of implementation. From the analysis results, it was found that the length of soil nailing of 8 meters was more effective in terms of the safety factor value, cost analysis, and duration of the implementation method.
 
 
 

Tree-Like Structures in Architecture: Revisiting Frei Otto’s Branching Columns Through Parametric Tools

Tree-like architectures and branching structures are one of the analogical designs that are among the nature inspired structures arousing attention of the designers, inspiring them and that are frequently confronted throughout the history of architecture. Likewise, trees are structural models for designers beyond the plant and branching patterns that are used as architectural ornamentation. Trees have the characteristics of being mentors for architects and engineers concerning how the vertical and the horizontal loads are transmitted through the trunks, branches, and leaves and how the balance is provided. Within this context, it is possible to claim that a quite wide and intuitively developed structural knowledge is acquired with the tree analogies throughout the history of architecture. By the development of computational design technologies, there have been significant developments in the design and the building of tree-like structures. Especially the number of branching, angles of dendroids, lengths, and the other parameters can be defined by using algorithms and can be optimized also by the help of computational tools. In this paper, the historical development and classification of the tree-like structures have been carried out and Frei Otto who is the pioneer to pave the way for innovative structures related to this field has been selected to revisit the efficiency of lightweight columns inspired by nature. One of the experimental studies of Otto in which he called as “minimum path system” has been determined as the case study; the parametric design behind the structure has been analyzed and reproduced by using a parametric software. The structural effectiveness has been determined and discussed by testing the obtained models using a FEM program under horizontal and vertical loads. Consequently, the structural effectiveness of today’s computational technologies and the branching structures that Otto built intuitively and by natural analogies have been able to be tested and the possible potentials that can be leading for today’s architects have been demonstrated.

Estimation of Early-Age Tensile Stresses in Mass Concrete Containing Ground Granulated Blast Furnace Slag

In this study, the early-age mechanical properties of a concrete mix containing ground granulated blast furnace slag (GGBFS) were investigated and incorporated in a finite-element model. The viscoelastic behavior caused by early-age tensile creep was considered using a viscoelastic analysis in which the creep strain increment was calculated using a strain superposition method. Subroutines for a FEM program (ABAQUS) were developed to predict the stress time-history considering early-age tensile and compressive creep during thermal loading and unloading. Three 1.2-m (4-ft) cubes were cast with a mix design containing 50% replacement by weight of the cement with GGBFS. The FEM predictions match well with the experimental strain measurements. The results indicate that using the proposed analysis and the measured mechanical properties obtains an accurate estimation of the maximum tensile stress for a concrete mix containing GGBFS. Engineers can use the estimated tensile stresses to take preventative measures to minimize the risk of thermal cracking on mass concrete structures.

Development and application of triangulation joint network based on an FEM program (RS2)

Abstract It is widely known that the triangle is the finest geometric unit, and therefore applying the triangulation joint to the rock mass simulation can not only accurately describe the fracture morphology of rock engineering, but also inversely deduce the mechanical parameters of blocks and joints. Based on the rock and soil two-dimensional analysis program (RS2), this paper compiles a program with MATLAB and realizes the parameterized setting of triangulation joint network (TJN) in RS2 for the first time, using it for the uniaxial compression model and roadway model accordingly. In the simulation of a RS2-TJN uniaxial compression model, its element parameters and joint parameters are calibrated according to the uniaxial compression strength and the elastic modulus obtained from the uniaxial compression test in a laboratory. Then its simulation results are compared with those of the particle flow code (PFC), which shows that the stress–strain curve obtained from the RS2-TJN uniaxial compression model matches the laboratory test one more closely. In the RS2-TJN roadway model, the simulation results obtained by adjusting the joint density are in good agreement with the roadway deformation in situ so as to study the failure characteristics of roadway surrounding rocks. Since the research on adding the triangulation joint network (cracks) to RS2 has not been found, its development and the realization of the parameterized control in this paper enrich the joint base of RS2 and provide a reference for the variety of joint numerical model.

Effects of dynamic axial stiffness of elastic moorings for a wave energy converter

This work studies the effects of the dynamic axial stiffness of elastic moorings on the dynamic behaviour of a point absorber wave energy converter. Following two mooring analysis procedures, coupled dynamic analysis of a taut-moored WEC with three legs is performed using the FEM program DeepC in three irregular wave conditions. Two synthetic fibre rope materials are investigated, i.e. a normally stiff polyester and a wire-lay 3-strand nylon rope. The results of WEC motions and mooring tensions obtained from a quasi-static stiffness model and the dynamic stiffness model are compared and discussed. The former analysis applies the non-linear stiffness working curves of the ropes in the simulations, while the latter utilizes the dynamic stiffness expression with an iterative process following a practical mooring analysis procedure. For the nylon rope, the influence of the load amplitude on the dynamic stiffness and the WEC response is presented and analysed. It was found that the quasi-static stiffness model tends to underestimate the maximum mooring tensions, leading to 30%–40% lower results compared to the one accounting for the dynamic stiffness effects. For the studied WEC system, the nylon rope shows advantages over polyester, because of the lower mooring tensions and higher WEC motions.

Combining H-Adaptivity with the Element Splitting Method for Crack Simulation in Large Structures.

H-adaptivity is an effective tool to introduce local mesh refinement in the FEM-based numerical simulation of crack propagation. The implementation of h-adaptivity could benefit the numerical simulation of fatigue or accidental load scenarios involving large structures, such as ship hulls. Meanwhile, in engineering applications, the element deletion method is frequently used to represent cracks. However, the element deletion method has some drawbacks, such as strong mesh dependency and loss of mass or energy. In order to mitigate this problem, the element splitting method could be applied. In this study, a numerical method called ‘h-adaptive element splitting’ (h-AES) is introduced. The h-AES method is applied in FEM programs by combining h-adaptivity with the element splitting method. Two examples using the h-AES method to simulate cracks in large structures under linear-elastic fracture mechanics scenario are presented. The numerical results are verified against analytical solutions. Based on the examples, the h-AES method is proven to be able to introduce mesh refinement in large-scale numerical models that mostly consist of structured coarse meshes, which is also beneficial to the reduction of computational resources. By employing the h-AES method, very small cracks are well represented in large structures without any deletions of elements.

Agglomerated impact of CNT vs. GNP nanofillers on hybridization of polymer matrix for vibration of coupled hemispherical-conical-conical shells

This paper is dedicated to study the vibrational behavior of Coupled Hemispherical-Conical-Conical Shells (CHCCS) structures made composite materials reinforced with nanofillers. One of the most important issue in nanocomposites is the agglomeration effect of nanofillers in hybridization procedure. In this study, two well-known nanofillers including Carbon Nano Tubes (CNTs) and Graphene Nano Platelets (GNPs) are used for reinforcement of polymer matrix. In addition, the distribution of agglomerated nanofillers throughout the thickness of the structures is assumed to be uniform and functional. Therefore, three patterns of distribution including X, O and V are employed. To study these topics, first, the authors obtain the displacement fields of CHCCS using Donnell's shell theory. In this formulation, the First Order Shear Deformation Theory (FOSDT) is utilized to consider the shear deformation effect. Second, the Hamilton's principle is used for achieving the governing equations of motion associated with the CHCCS structure. Afterwards, an efficient and robust approximation numerical solution method, namely Generalized Differential Quadrature (GDQ) method, is employed to discretize the governing system of differential equations, apply boundary and connective conditions related to the CHCCS. Since there is no applicable benchmark for this analysis, the authors prove their proposed formulation by comparing the obtained results with the outputs of FEM program for some specific problems. Furthermore, several new and complex problems are designed and solved to investigate the effect of various factors such as geometrical characteristics, weight proportions, and distribution patterns of CNTs and GNPs on the vibration parameter of CHCCS. It is worth mentioning that the effect of agglomeration parameters associated with these nanofillers on the vibrational behavior of CHCCS structures is also studied numerically.

Proposal Of Simplified Way of Applying Wind Load on Circular Cross-Section

Wind action on circular cross section was described in many publications. It finds an application for flue gas ducts, pipelines, silo or chimneys. This study concentrate on elements with diameter greater than 1m. There are well recognized analytical solutions of static calculation with uses Fourier-series for wind distribution. Although during last 10 years numerical methods of solving problems get more popular, especially among young engineers. For surface structures ability of analytical finding internal forces disappears, and Finish Element Method substitutes analytical calculation. Modelling of wind load in FEM programs cause several problems. Using wind load distribution proposed in Eurocode 1-4, or from laboratory test, it is usually necessary to divide circular cross-section into 32 up to 72 rectangular elements. Applying load in that way is the most accurate method to imitate wind load in FE model. From the other hand that take much time, and requires preparing data about distribution before modelling. Applying wind on complicated model, with many independent parts of piping, for at least 2 load cases cause faults and slows down work. This paper shows and compares a few proposal wind load models for numerical calculation. Those models were built to obtain accurate internal forces in compare to Eurocode procedure. Proposed models offers simplification of Geometry in numerical model, and saves of time. It also helps to make FE mesh become independent from structural nodes, lines or divisions. This paper concern on one case of one Reynolds number, with refers to 2m wide cylinder, wind velocity of 22m/s and surface roughness of steel plate – 0,05 mm. This paper compares different wind load distributions, in terms of required number of division of model, time consuming, precision of results. Author selected one proposal load distribution, with give equivalent internal forces as wind load distribution obtained from Wind Flow simulation (for example CFD method). Proposed model is useful for structural engineers and statics in offer stage of project. With some safety factor it can be also used as wind load as case for detailing cylindrical structures.

Bending of a Viscoelastic Timoshenko Cracked Beam Based on Equivalent Viscoelastic Spring Models

Considering the transverse crack as a massless viscoelastic rotational spring, the equivalent stiffness of the viscoelastic cracked beam is derived by Laplace transform and the generalized Dirac delta function. Using the standard linear solid constitutive equation and the inverse Laplace transform, the analytical expressions of the deflection and rotation angle of the viscoelastic Timoshenko beam with an arbitrary number of open cracks are obtained in the time domain. By numerical examples, the bending results of the analytical expressions are verified with those of the FEM program. Additionally, the effects of the time, slenderness ratio, and crack depth on the bending deformations of the different cracked beam models are revealed.

Elastoplastic-damage-seepage coupling model and numerical algorithm for rock slope stability evaluation

The stability of slope under complex geological conditions is one of the essential issues in geotechnical engineering. The mechanical damage caused by external force load and the hydraulic property of rock have both significant influences on slope stability. However, the two factors and the coupling process between them are not considered in the traditional slope safety calculation method. Firstly, in this paper, an elastoplastic-damage-seepage coupling model is established based on the modified Mohr-Coulomb (M-C) criterion. This model takes into account the weakening effect of damage on the strength of rock mass. Further, according to the Biot's theory and the evolution equation of permeability coefficient, a complete hydraulic-mechanics (HM) coupling model is established. Secondly, the fully implicit backward Euler algorithm and "strict-cornered" algorithm are used to integrate the stress precisely. The complete coupling analysis of HM is implemented by the step-by-step iterative method. By combining the centrifugal loading method (CLM) with the FEM program, the factor of slope safety (FOS) under the coupling influence of damage-seepage can be solved. The calculation results showed that, compared with the traditional rounded M-C model, the results obtained by the "strict-cornered" algorithm method in this paper are closer to the theoretical solution. The solution process is robust with a global second-order convergence rate. After considering the effects of damage and seepage, the FOS is obviously reduced. Finally, the model is applied to the stability evaluation of an actual engineering. The variation rules of pore water pressure, displacement field, damage zone and FOS are calculated under different head heights. The model built in this paper considers the coupling characteristics of rock seepage-stress-damage well. The proposed numerical algorithm ensures the accuracy and rationality of the calculation results which provides a theoretical foundation for engineering application.

Thermal Analysis of Mass Concrete Containing Ground Granulated Blast Furnace Slag

In this study, the early age thermal properties of a concrete mix containing ground granulated blast furnace slag (GGBFS) were investigated and incorporated in a finite-element model. A two-term exponential degree of hydration function was proposed to better capture the early age behavior. An FEM program (ABAQUS) was used to predict the temperature time-history of three 1.2-m (4-ft) cubes cast with a mix design containing 50% replacement of the cement by weight with GGBFS. The FEM predictions match well with the experimental temperature measurements. Results show that using the measurements of the thermal properties, an accurate estimation of the temperature difference can be obtained for a concrete mix containing GGBFS, and engineers can use the estimated temperature difference to take preventative measures to minimize the risk of thermal cracking.

Transversal vibrations of a toothed belt in linear drives during operation

AbstractVibrations of the toothed belt of a linear drive can affect the dynamic positioning accuracy and smoothness which is important for practical applications. An analytical, one‐dimensional model of a belt section is derived, taking into account the preload and flexural rigidity, as well as the non‐linear cable effect and the acceleration forces due to the belt mass. In addition to the case of constant belt length, the temporal change of the length as a result of the axial motion is an essential part of the modeling. The solution of the equation of motion is limited to the dominant transverse deflection of the belt. For the longitudinal extension, the assumption of a quasi‐static solution is taken. A FEM program is implemented to calculate the solution for given operation conditions. The evaluations are made for selected motions according to a path planning with trapezoidal velocity profiles. A modification of individual parameters, based on a practical parameter set, enables the analysis of the respective effects.