Numerical Analysis Procedure Research Articles

New numerical procedures for fully-grouted bolt in the rock mass with slip and non-slip cases at the rock-bolt interface

This paper aims to propose new numerical procedures for elasto-plastic analysis of the interactions between fully-grouted bolt and rock with slip and non-slip cases at a potential-failure interface. In the proposed procedure with the slip case, the iteration process accounts for the elongation of the bolt, and the calculation process is greatly simplified by considering only the initial and final states (i.e., no intermediate finite states as is the case for existing procedures) without compromising the accuracy of the predictions. In the proposed procedure with the non-slip case, the elasto-plastic solution of the plastic rock strain is rigorously derived; the two scenarios in which the length of the rock bolt is contained within the plastic zone or within the elastic zone are comprehensively considered. The obtained solutions of tensile force in the bolt, shear stress at the potential-failure interface, rock displacement and stress components in the rock from the proposed procedures are validated by analyses with purely analytical methods and a commercial finite-difference program. With influences of rock quality and plastic softening behaviour of rock mass, the differences of the solutions in the slip and non-slip cases at potential-failure surface are compared; the dependency of the relative movement on the shearing stiffness at the potential failure interface is also investigated.

Probabilistic procedure for numerical assessment of corroded pipeline strength and operability

The numerical procedure for analysis of nonuniform stress-strain state of welded pipeline elements with detected local corrosion-erosion metal losses based on Weibull statistics has been proposed for the probabilistic assessment of static strength and operability of specific structures. The multiphysics simulation of joint evolution of state of stresses, strains and subcritical damage was used for typical pipelines elements in operation for minimal conservativeness of numerical analysis. It is based on the principles of thermomechanics of elastic-plastic continuum along with tracing of ductile fracture of material. Following the number of experimental investigations of limiting state of typical pipelines with semielliptical defects Weibull parameters as functions of material properties have been determined. Using the specific examples of steel and aluminum pipeline elements, the influence of individual corrosion-erosion defects on failure probability has been studied.

Comments to “A simple method to achieve a uniform flux distribution in a multi-faceted point focus concentrator”

Abstract We have found the flux homogenization technique described in the paper published in volume 93, pages 115–124 (august 2016), does not provide homogenized fluxes in all out-of-focus distances of the solar receiver, but only above a certain transition distance, and that some of the numerical analysis procedures used in that document should be revised or complemented to achieve better reproducibility of the results. In addition, we also note that some statements and conclusions in that document are mistaken or formulated incorrectly, so it is necessary their correction.

Space-time Gaussian models for evaluating corrosion-induced damages in reinforcing bars

Chloride-induced steel reinforcing bars corrosion is a problem of worldwide importance because, in addition to massive industrialization, a majority of human population inhabit marine atmosphere zones where salinity is the main source of built infrastructure deterioration. Reinforced concrete structures vulnerable to chloride-induced corrosion potentially experience two stages of damage, namely non-structural and structural. Till date, with regard to non-uniform corrosion, there is very limited information regarding the significant role played by the non-structural stage of damage in influencing the progression of structural damage. The present work examines the process of non-uniform chloride ingress into concrete due to the existence of the steel bars and its influence on the spatial and temporal variations in the depth of corrosion penetration. Mathematical models in the form of Gaussian functions are proposed to represent space-time variation in corrosion initiation, spatial spread of corrosion penetration depth and corroded bar morphologies, and are compared with literature data. A numerical inverse analysis procedure is introduced to predict space-time evolution of non-structural damage from experimentally observed spatial spread of structural damage. Further, applicability of superposition approach for the evaluation of corrosion-induced stresses around the steel–concrete interface of a corner reinforcing bar is explored and shown to introduce spatial and temporal errors while evaluating structural damages.

Numerical model and procedure for spectral analysis of light-emitting diode with patterned electrode

Two-step decomposition procedure was developed and implemented to analyze experimentally measured electroluminescence (EL) spectra of light-emitting diode with two sets of InGaN/GaN quantum wells (QWs) for blue and green emission and mesh-like top electrode. At a first step EL-spectra were decomposed into basic Gaussian functions (GFs) for blue and green emission lines. Then each of the basic GFs was decomposed into the set of secondary GFs which give reasonable ground to relate broadening of EL-spectrum to position-dependent compensation of quantum-confined Stark effect(QCSE) in the InGaN/GaN QWs. Using basic GFs it was demonstrated how injected current is splitted between green and blue QWs depending on its value.

Modelling of reinforced concrete slabs in fire

A numerical procedure for the thermal analysis of RC slabs at elevated temperatures is the subject of this study, where the moisture increase due to the so-called moisture clog occurring in the cooler parts of reinforced concrete (RC) slabs is introduced as well. Starting from a systematic investigation on the existing concrete constitutive laws available in the literature and in the codes, improved concrete constitutive laws are proposed to describe concrete thermal and mechanical properties at elevated temperatures. The proposed laws – called also models - are validated against well-documented full- and small-scale tests on simply-supported RC slabs. Parametric analyses on the behaviour of RC slabs in fire are carried out as well, to clarify the role that the different constitutive laws may have in the numerical prediction of RC slabs behaviour under fire conditions.

Ballistic impact analysis of double-layered metal plates

In the present study, ballistic impact analysis of double layered circular metal plates with different arrangements were investigated numerically using the finite element method. Nine different double layered plates configuration consist of steel 4340 (st), Aluminium 2014-T3 (Al), or titanium Ti-6A1-4V (Ti) having the same thickness were considered in this study and the energy absorption capability of each configuration were determined and compared. In order to validate the results obtained via the numerical method, an experimental ballistic test utilising a single stage gas gun was performed on single layer Al plates using a blunt projectile. It was found that the results obtained from numerical analysis agree well with the experimental results, which confirmed the accuracy of the numerical analysis procedure. The non-linear explicit finite element analysis employing Johnson-Cook plasticity material model coupled with was carried out using ABAQUS commercial package. A parametric study was conducted to determine the best configuration in terms of the energy absorption capability under ballistic impact. It was observed from the analysis that the double layered plate with titanium (front plate facing the projectile) and steel 4340 (back plate) produced the highest energy absorption with 279.72 J. However, the highest specific energy absorption (SEA) was given by titanium (front) and Aluminium (back) plate with 2830.45 J/kg.

Design approach for flexural capacity of concrete T-beams with bonded prestressed and nonprestressed FRP reinforcements

Concrete beams with prestressed and nonprestressed fiber-reinforced polymer (FRP) reinforcements are commonly employed in field applications. However, available flexural strength design approaches mainly focus on rectangular concrete beams exclusively prestressed with FRP tendons. This paper, therefore, presents a simplified yet rational design approach for flexural capacity of concrete T-beams with bonded prestressed and nonprestressed FRP reinforcements. Firstly, a new transition region between tension- and compression- controlled sections was proposed in terms of ratio of provided-to-balanced reinforcement (ρe,b < ρe ≤ 1.5ρe,b) based on a statistical analysis of an experimental database of 83 beams. Afterwards, numerical sectional analysis procedure of tension-controlled sections was developed by using an accurate stress block to approximate the nonlinear compressive stress distribution in concrete. Based on a detailed parametric study of over 160,000 sections, simplifed design equations for flexural capacity of tension-controlled section is derived from multiple regression analyses. Then, design equations were presented for flexural capacity of compression-controlled sections. Finally, the performance of the proposed approach was evaluated by comparing their predictions with experimental results of the 83 beams.

A fast and accurate dynamic relaxation scheme

Dynamic relaxation method (DRM) is one of the suitable numerical procedures for nonlinear structural analysis. Adding the fictitious inertia and damping forces to the static equation, and turning it to the dynamic system, are the basis of this technique. Proper selection of the DRM artificial factors leads to the better convergence rate and efficient solutions. This study aims to increase the numerical stability, and to decrease the analysis time. To fulfil this objective, the reduction rate of analysis error for consecutive iterations is minimized. Based on this formulation, a new time step is found for the viscous dynamic relaxation. After combining this novel relationship with the other DRM factors, various geometrical nonlinear structures, such as trusses, frames, and shells, are analyzed. The obtained results verify the efficiency of authors’ scheme.

A new weld material model used in welding analysis of narrow gap thick-walled welded rotor

A new weld material model was developed to improve simulation convergence and accuracy in welding stress analysis of thick-walled welded structure, taking use of the none-stiffness and none-strength properties of the weld metal corresponding to the globular transferring by controlling residual deformation in every weld bead. Single-pass welding model was employed to compare the new weld material model with the traditional one. Besides, the evolution of welding stress with the new weld material model was analyzed. Based on the new weld material model, welding stress in the thick-walled welded rotor was predicted by means of thermal elastic-plastic finite element analysis. Comparisons between the traditional weld material model and the new one were conducted during welding stress simulation upon thick-walled welded rotors. The results indicated that the new weld material model can make convergence practicable and quickly when the cut-off temperature is high in order to guarantee the accuracy. Comparisons between simulations and experimental data were also carried out to verify the effectiveness of the developed numerical analysis procedure.

PRACTICAL METHOD FOR ANALYSIS AND DESIGN OF SLENDER REINFORCED CONCRETE COLUMNS SUBJECTED TO BIAXIAL BENDING AND AXIAL LOAD

Reinforced and concrete-encased composite columns of arbitrarily shaped cross sections subjected to bi axial bending and axial load are commonly used in many structures. For this purpose, an iterative numerical procedure for the strength analysis and design of short and slender reinforced concrete columns with a square cross section under biaxial bending and an axial load by using an EC2 stress-strain model is presented in this paper. The computational procedure takes into account the nonlinear behavior of the materials (i.e., concrete and reinforcing bars) and includes the second order effects due to the additional eccentricity of the applied axial load by the Moment Magnification Method. The ability of the proposed method and its formulation has been tested by comparing its results with the experimental ones reported by some authors. This comparison has shown that a good degree of agreement and accuracy between the experimental and theoretical results have been obtained. An average ratio (proposed to test) of 1.06 with a deviation of 9% is achieved.

Determination of Elastic Modulus in Mouse Bones Using a Nondestructive Micro-Indentation Technique Using Reference Point Indentation.

The determination of the elastic modulus of bone is important in studying the response of bone to loading and is determined using a destructive three-point bending method. Reference point indentation (RPI), with one cycle of indentation, offers a nondestructive alternative to determine the elastic modulus. While the elastic modulus could be determined using a nondestructive procedure for ex vivo experiments, for in vivo testing, the three-point bending technique may not be practical and hence RPI is viewed as a potential alternative and explored in this study. Using the RPI measurements, total indentation distance (TID), creep indentation distance, indentation force, and the unloading slope, we have developed a numerical analysis procedure using the Oliver-Pharr (O/P) method to estimate the indentation elastic modulus. Two methods were used to determine the area function: (1) Oliver-Pharr (O/P-based on a numerical procedure) and (2) geometric (based on the calculation of the projected area of indentation). The indentation moduli of polymethyl methacrylate (PMMA) calculated by the O/P (3.49-3.68 GPa) and geometric (3.33-3.49 GPa) methods were similar to values in literature (3.5-4 GPa). In a study using femurs from C57Bl/6 mice of different ages and genders, the three-point bending modulus was lower than the indentation modulus. In femurs from 4 to 5 months old TOPGAL mice, we found that the indentation modulus from the geometric (5.61 ± 1.25 GPa) and O/P (5.53 ± 1.27 GPa) methods was higher than the three-point bending modulus (5.28 ± 0.34 GPa). In females, the indentation modulus from the geometric (7.45 ± 0.86 GPa) and O/P (7.46 ± 0.92 GPa) methods was also higher than the three-point bending modulus (7.33 ± 1.13 GPa). We can conclude from this study that the RPI determined values are relatively close to three-point bending values.

Hybrid reliability analysis and optimization for spacecraft structural system with random and fuzzy parameters

In aerospace engineering, the incomplete environment conditions have been realized to be a significant factor affecting the system safety assessment. Considering the hybrid random and fuzzy uncertainties in system inputs, the paper proposes a novel numerical procedure for reliability analysis and reliability-based optimization. Random parameters are adopted to denote the aleatory uncertainties with sufficient sample information; whereas fuzzy parameters are used to quantify the epistemic uncertainties associated with expert opinions. Using the level-cut operation, fuzzy parameters are converted into interval variables, and a satisfaction degree-based interval ranking strategy is utilized to precisely quantify the interval safety possibility. Then the system safety possibility is calculated by the multiple integral, where cut levels of different fuzzy parameters are treated as independent variables. Subsequently based on the given safety index, a hybrid reliability optimization model is established. To avoid the huge computational burden caused by nested-loop optimization, a modified interval Monte Carlo method (MIMC) is proposed for limit state function evaluation. Eventually, a numerical example about the refractory ceramics tile of spacecraft verifies the feasibility of proposed method for hybrid reliability analysis and optimization design in practical aerospace engineering.

A framework for implementation of RVE‐based multiscale models in computational homogenization using isogeometric analysis

SummaryThis study presents an isogeometric framework for incorporating representative volume element–based multiscale models into computational homogenization. First‐order finite deformation homogenization theory is derived within the framework of the method of multiscale virtual power, and Lagrange multipliers are used to illustrate the effects of considering different kinematical constraints. Using a Lagrange multiplier approach in the numerical implementation of the discrete system naturally leads to a consolidated treatment of the commonly employed representative volume element boundary conditions. Implementation of finite deformation computational strain‐driven, stress‐driven, and mixed homogenization is detailed in the context of isogeometric analysis (IGA), and performance is compared to standard finite element analysis. As finite deformations are considered, a numerical multiscale stability analysis procedure is also detailed for use with IGA. Unique implementation aspects that arise when computational homogenization is performed using IGA are discussed, and the developed framework is applied to a complex curved microstructure representing an architectured material.

Investigation on Flexural Behaviour of Cold Formed Steel Latticed Built-Up I Section with Drop Web

This paper deals with the study of flexural behaviour of cold formed latticed built-up I beam with drop web for various sections by varying depth, thickness and span length of the section. The numerical analysis was carried out by FEM software ABAQUS 6.13[11]. The experimental works carried out by Cheng Yu and Benjamin W. Schafer (2006) [1] were taken for validating the numerical analysis procedure. It provides a cost effective way to explore the performance of products in a virtual environment. The ultimate capacity is obtained by performing both linear and non-linear analysis. Theoretical investigation as per AISI specification was carried out for all the specimens to check the accuracy of the design proposal. Numerical finite element procedure is used to instruct the effect of various parameters on behavior of beams. The critical load and different modes of failure are studied by this numerical investigation. Comparison between deformed shape and load vs. displacement curves of I section with drop web were presented.

The effect to flow rate characteristic on biodegradation of bone scaffold

This paper proposes an improved modeling approach for bone scaffolds biodegradation. In this study, the numerical analysis procedure and computer-based simulation were performed for the bone scaffolds with varying porosities in determining the wall shear stresses and the permeabilities along with their influences on the scaffolds biodegradation process while the bio-fluids flow through within followed with the change in the flow rates. Based on the experimental study by immersion testing from 0 to 72 hours of the time period, the specimens with different morphologies of the commercial bone scaffolds were collected into three groups samples of 30%, 41%, and 55% porosities. As the representative of the cancellous bone morphology, the morphological degradation was observed by using 3-D CAD scaffold models based on microcomputed tomography images. By applying the boundary conditions to the computational fluid dynamics (CFD) and the fluid-structure interaction (FSI) models, the wall shear stresses within the scaffolds due to fluid flow rates variation had been simulated and determined before and after degradation. The increase of fluid flow rates tends to raise the pressure drop for scaffold models with porosities lower than 50% before degradation. As the porosities increases, the pressure drop decreases with an increase in permeability within the scaffold. The flow rates have significant effects on scaffolds with higher pressure drops by introducing the wall shear stresses with the highest values and lower permeability. These findings indicate the importance of using accurate computational models to estimate shear stress and determine experimental conditions in perfusion bioreactors for tissue engineering more accurate results will be achieved to indicate the natural distributions of fluid flow velocity, wall shear stress, and pressure.

Validation of a numerical model for curtain walls with MVHS during free burning

Glass breakage of curtain wall coverings during a fire can promote the spread of a fire in high-rise buildings. Prior to the development of sprinklers to prevent and delay glass breakage, it is necessary to identify the breakage mechanism of curtain wall glass panes and to establish a numerical model to simulate various fire situations using sprinklers to design effective sprinkler systems. The present study was conducted to establish a numerical model and analysis procedures to simulate fire situations. First, curtain wall was installed on one side of a testing chamber that was 3 m (L) × 3.2 m (W) × 2.4 m (H), and a free burning experiment was conducted using heptane. The same experimental conditions were simulated using a numerical model employing the modified volume heat source (MVHS) model. To analyze the validity of the numerical model, the air temperature inside the room and the surface temperatures of the curtain wall Al frame and glass panes calculated by numerical analysis were compared with experimental values, and the location and timing of the initial crack were compared. Thermocouples were installed on the Al frame and the glass surface to measure the surface temperature of the curtain wall during the fire for approximately 100 s after the onset of the fire. Additional thermocouples were installed to measure the air temperature inside the room to verify the results of the numerical analysis. A numerical model using the MVHS model was established to analyze the overall temperature distribution and the behavior of thermal stress on the curtain wall caused by the fire. MVHS calculations were based on measured fuel consumption, and the numerical analysis results were compared with the experimental values. We confirmed that the temperature calculated using computational fluid dynamics (CFD) was in good agreement with the temperature measured in the experiment. The temperature distribution and thermal stress of the curtain wall up to the point of glass breakage were reviewed using a thermal stress structural analysis that employed the results of the CFD analysis with MVHS. The time required to reach the temperature required for glass to break in the numerical analysis and the time required for the first crack to occur in the experiment were identical. The crack positions obtained from the numerical model and experiments were also the same. Overall, our results showed that the numerical model using the MVHS model is suitable for predicting curtain wall breakage and temperature distributions inside a space during the fire.

Numerical analysis of LEAP centrifuge tests using a practice-based approach

The Liquefaction Experiment and Analysis Project (LEAP) George Washington University (GWU) 2015 consisted of a group of centrifuge facilities' duplications of one liquefaction lateral spreading experiment that was also numerically analyzed by a series of predictors. The author was one of the LEAP predictors, and in this paper, the prediction exercises conducted by this author as part of LEAP GWU 2015 are summarized. For the initial prediction, the author analyzed the centrifuge tests using an approach similar to that used in dam engineering practice for embankment dams. For subsequent predictions, the author made improvements to the analysis by refining both the constitutive model calibration and the numerical analysis procedures. Following the completion of the LEAP GWU 2015 predictions, additional analyses were completed with further refinements after the author received useful feedback from a reviewer of this paper and held discussions with other experts in the field. The process and results from this new set of analyses were seen as an important complement to those completed during the LEAP GWU 2015 predictions and are also included in this paper.

Limit Analysis Method for Evaluating Soil Resistance to Lateral Motions of Pipelines Partially Embedded in a Seafloor

The lateral soil resistance available to pipelines partially embedded in a seafloor is of interest in evaluating pipeline lateral buckling capacity, stability under forces resulting from current loads, or route pullout loads. An upper-bound limit analysis method, including equilibrium requirements in a manner common to lower-bound theories, was used to evaluate lateral soil resistance to pipe displacements. The method is applicable to sand and clay foundations with homogeneous or layered conditions. Comparisons with results from physical tests and other limit analysis and finite-element investigations are presented. The numerical limit analysis procedure was implemented through numerical-computing software. An optimization procedure was used to identify the minimum resistance satisfying the governing objective equations. The seafloor surface geometry may include soil berms or other features. The soil strength may be described by a linear Mohr-Coulomb criterion or a curved criterion representing a varying material friction angle.

Numerical simulation of pre-stressed concrete slab subjected to moderate velocity impact loading

Abstract This paper presents an efficient numerical analysis procedure to simulate failure analysis of a pre-stressed concrete slab subjected to the hard impact using LS-DYNA commercial software. In this study, the moderate velocity (60 m/s–300m/s) used in the corresponding tests, is chosen in order to assess the punching resistant capacity of the slabs. Material nonlinearity is employed to consider failure and damage. The structural dynamic behavior of the materials is considered by taking into account the strain-rate effect, and damping effects are also investigated. An efficient method on the simplified modeling of pre-stressed concrete, namely the “Spotweld” method, is proposed, which allows introducing the pre-stressing force directly into the pre-stressing bars. To illustrate the accuracy of the proposed numerical analysis procedure, two different impact tests are used for the verification of the numerical modeling. The effects of modeling parameters are examined by several parametric analyses. It is shown that proposed modeling may be effectively used to investigate the structural behavior of pre-stressed concrete structures subjected to hard missile impact.