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Calibration of damage parameters of super high-rise frame-core structural subsystem under torsional ground motion
No full textTo clarify the dynamic characteristics of the structure under torsional seismic excitation, a macroscopic dynamic model of the structure and simplified hysteretic models of each sub-system were established through theoretical derivation, and the accuracy of the models was verified using finite element models. To determine the design parameters of the hysteretic models for each sub-system, a multi-objective seismic optimization approach considering both structural cost and overall torsional damage was proposed. Through multi-objective optimization based on torsional overturning analysis, the design parameters of each sub-system were successfully determined. The results indicate that the outrigger truss sub-system plays a significant role in controlling the overall torsional behavior of the structure
Numerical simulation of the swelling and deswelling process of gel
Get PDFIt is well known that the entropy elasticity of rubberlike materials and Brownian motion are described by formally analogous equations as both originated from thermal fluctuations. In rubberlike materials, the shear modulus is conventionally considered to be proportional to the absolute temperature and the proportionality factor is the number density of polymer chains for an affine polymer chains’ network model. On the other hand, the self-diffusion coefficient of Brownian motion is described as the product of the mobility and the absolute temperature. However, for the polymer chains’ network in a solvent, the interaction between the polymer chains and the solvent molecules occurs and the collective diffusion coefficient of the solvent molecules should be different to the self-diffusion coefficient of Brownian motion. Moreover, the shear modulus of the resultant polymer gel should be dependent on the swelling ratio due to the nonaffine movement of polymer chains. Therefore, to verify the analogy of the equations for the shear modulus of the nonaffine polymer chains’ network model and the collective diffusion coefficient of the solvent molecules, in this study, the swelling and deswelling process of the polymer gel is investigated by the numerical simulations
Modeling the enhanced geothermal systems using the extended–FEM and an equivalent continuum model
Get PDF. In this paper, a computational technique is presented for Thermo-Hydro-Mechanical (THM) simulation of Enhanced Geothermal Systems (EGS) based on the eXtended Finite Element Method (XFEM) and Equivalent Continuum Method (ECM) in the framework of Local Thermal Non-Equilibrium (LTNE). Heat extraction from Enhanced Geothermal Systems involves several multi-physics coupling processes, including the seepage through the fractured porous media, the thermal exchange between the working fluid and the matrix, and the deformation of fractured porous media that play essential roles in exploiting the geothermal energy contained in hot dry rocks. The ECM provides the equivalent tensors for the fluid permeability and solid compliance, which is an essential feature for the coupled Thermo-Hydro Mechanical simulation of fracture networks. In the model, the XFEM is employed for large scale fractures to capture the mass and heat transfer between the fracture and matrix more accurately, while the ECM is applied on the network of small-scale fractures. Hence, the proposed model benefits from the advantages of both methods, and it allows for managing between accuracy and cost. The set of THM equations is solved with both Local Thermal Equilibrium (LTE) and Local Thermal Non-Equilibrium (LTNE) assumptions to find out the impact of each method on the production temperature. The capability of the proposed computational model is demonstrated for the diagonal arrangement of the injection and production wells with different fracture orientations in-between. The simultaneous effects of fracture connectivity and inclination are investigated between the two injection and production wells. It is observed that the temperature difference between the two cases is higher in the middle of the domain by comparing the results of LTE and LTNE assumptions. Moreover, it is concluded that the LTE model overestimates the fluid temperature in comparison to the LTNE model in cold water injection problems. The results show the proposed computational model is a promising tool for estimation of the heat mining performance of EG
Stabilization of mixed displacement-pressure finite elements at finite strains using polyhedral formulations and Voronoi meshing
Get PDFThe hexahedral mixed displacement-pressure finite element of the lowest order (H1/P0) has shown to be simple and effective during both linear and nonlinear analysis of incompressible solids. While the discrete displacement field is generally considered to be sufficiently accurate, the discrete pressure field can sometimes be heavily polluted by spurious pressure modes. This results from the fact that the element does not fulfill the inf-sup condition. While postprocessing techniques, such as pressure filtering or smoothing, exist to remove the spurious pressure modes from the solution, this contribution aims on the exclusion of spurious pressure modes from the solution a priori due to the element geometry. By employing polyhedral finite element formulations on Voronoi tessellations in three dimensions, we show that the discrete kernel of the linearized mixed bilinear form only consists of the hydrostatic pressure mode. A spurious pressure mode is automatically suppressed due to the vertex-to-volume ratio in the finite element mesh. These considerations hold for any arbitrary physically admissible displacement state that can occur within a Newton-Raphson framework. A nonlinear numerical example shows that spurious pressure modes are indeed suppressed if the type of tessellation is changed from hexahedral to Voronoi
Assessment of flow-induced stresses in spiral weld pipes with bends
No full textThis study numerically investigates flow-induced stresses and displacements in bent pipes at varying angles (20◦ ≤ θb ≤ 80◦ ) using Solids4Foam at Reynolds number of 20,000. The results indicate that increasing θb enhances the formation of symmetric vortex structures, which coincide with enhanced non-uniformity in pressure distribution and wall shear stresses. Additionally, maximum equivalent stresses (σeq) for the solid shell occur near the inlet. The pipes with higher θb also depict a reduced displacement magnitude(D), which hints at the strong role of fixed displacement boundary condition assigned at the pipe inlet and outlet. These findings provide essential insights for performing numerical investigation of pipeline reliability and structural integrity in oil transportation
Influence evaluation of flow diverter stent parent vessel coverage on cerebral aneurysm through the CFD-DEM coupling simulation
Get PDFCerebral aneurysms are a type of cerebrovascular disorder where a balloon-like bulge forms in part of an artery in the brain. One of the developed treatments for large cerebral aneurysms is the Flow-diverter Stent (FDS) placement technique. Effective treatment outcomes in cerebral aneurysm treatment using FDS require proper placement of the device. Improper placement can lead to increased blood flow velocity and Wall Shear Stress (WSS) within the aneurysm, as well as increased pressure, which suggests a potential risk of rupture in large aneurysms. Considering these circumstances, this study evaluates the impact of FDS positioning on cerebral aneurysms by creating multiple FDS placement models with the device positioned proximally and distally to the aneurysm. Subsequently, we conducted fluid-structure interaction simulation analyses using the Particle Finite Element Method-Second Generation (PFEM-2) for the non-Newtonian fluid model of blood and the Discrete Element Method (DEM) for the FDS. This study reports the results of comparing blood behavior, WSS, and pressure inside the cerebral aneurysm based on the FDS placement position
Incompressible viscous fluid analysis around complex shapes using Isogeometric Analysis
Get PDFThis paper aims to apply the Isogeometric Analysis(IGA) to fluid-structure interaction problem in the civil engineering field. Recently, IGA has attracted much attention as an analysis method to structure with arbitrary surfaces. In this paper, IGA is applied to a twodimensional incompressible viscous flow problem as a basic study for the fluid-structure interaction analysis using IGA. The vortex induced vibration of a circular cylinder is investigated as a numerical example, and the effectiveness and validity of the coupled analysis using IGA are discussed
Development of traffic noise evaluation system using finite element method
Get PDFThis paper presents a traffic noise evaluation system based on acoustic theory. The finite element method is employed for unsteady wave equations, which is suitable for arbitrary shapes and has excellent applicability to non-uniform materials. The 3D wave equation is employed for the governing equation and the Perfectly Matched Layer (PML) method is utilized as a treatment method for boundary condition. In order to consider multiple moving sound sources such as a traffic noise, a time-variant convolution method is introduced. The auralization method based on VR technology is also introduced to understand the noise level intuitivel
A kinematically-exact reduced-order rod model for elastoplastic failure in thin-walled members
Get PDFThis work profits from a weakly coupled multiscale approach to derive a 7-DOF kinematically-exact reduced-order rod model for thin-walled members (starting from [1]) with a plastic hardening constitutive equation (based on [2]-[3]) that emulates the coupling between local buckling effects and hardening plasticity at material level. The model is implemented in an in-house finite element program for flexible thin structures and shall be validated against reference solutions. The novelty as compared to [2]-[3] is the extension to the fully 3D context, including torsion-warping degrees-of-freedom and arbitrary (plastic) failure mode capabilities, allowing for the modelling of complex structural problems involving thin-walled rod members. Although kinematically-exact rod models are able to detect critical loads and represent postcritical configurations in many common scenarios, issues are bound to emerge when local effects (such as buckling of web and/or flanges) are relevant, especially when they are coupled with plastic deformations. For rod models, the combination of those factors can be satisfactorily represented in a phenomenological way by embedding them on a stress-resultant/crosssectional strains hardening plastic model, instead of enriching the model´s kinematics and related material law. One can employ weakly coupled multiscale modelling to generate constitutive relationships among the different strain and stress in a pre-processing stage. Information about plasticity, loss of geometrical stiffness and local buckling are passed to the macro-scale rod model without increasing the amount of global degrees-of-freedom. Incremental steps of the numerical solution are solved with the split operator, whereby local variables are solved in an element-wise fashion and thus not introduced in the global system. Quadratic convergence of the overall solution procedure is achieved. The coupling among geometrical and hardening effects limits the load bearing capacity of the structural members and determinates the failure load
Numerical simulations of origami-based folded carbon-reinforced concrete shells
Get PDFThe advantages of carbon-reinforced concrete (CRC) over traditional concrete elements reinforced with steel, including high strength, low weight, and corrosion resistance, make it a promising material for thin, efficient, and more sustainable designs. As the demand for less CO2-intensive materials such as concrete grows, a shift from simple massive elements to thin-walled elements with complex geometries is becoming increasingly necessary. However, to seek optimal design variants, efficient nonlinear numerical calculations that provide reasonable predictions of the structural behavior, including the stress-redistribution process and the failure mechanisms are essential. This paper presents FEM simulations of origami-based folded CRC shells that were experimentally investigated in a previous study. Two FEM modeling approaches were used, employing a smeared and a discrete representation of the carbon reinforcement. For both approaches a damage plasticity model for the concrete has been used. The load-deflection response from the discrete approach closely matches the experimentally obtained curves. Despite an overestimation of the load capacity, the computationally less expensive smeared FEM model qualitatively reproduces the structural response and the correct failure mechanism. Therefore, the quality of the results obtained from the smeared model is sufficient to determine preferable design variants in a typical design scenario. This is necessary to provide a deeper understanding of the structural behavior of these folded elements and to facilitate the sustainable design and application of thin-walled CRC elements in the future