Scientia Iranica
Volume:26 Issue: 4, Jul-Agust 2019

The Shuffled Complex Evolution (SCE-UA) method developed at the University of Arizona is a global optimization algorithm, initially developed by [1] for the calibrationof conceptual rainfall-runoff (CRR) models. SCE-UA searches for the global optimumof a function by evolving clusters of samples drawn from the parameter space, via a systematiccompetitive evolutionary process. Being a general purpose global optimization algorithm, it has found widespread applications across a diverse range of science and engineering fields. Here, we recount the history of the development of the SCE-UA algorithm and its later advancements. We also present a survey of illustrative applications of the SCE-UA algorithm and discuss its extensions to multi-objective problems and touncertainty assessment. Finally, we suggest potential directions for future investigation.

For an efficient solution of the equations arising from finite element analysis, the stiffness matrix of the model should be structured. This can be done by reducing the profile or wavefront of the corresponding graph matrix of the structure depending on whether skyline or frontal method being used, respectively. One of the efficient methods to achieve this goal is the use of the method of King, extended by Sloan. In this paper the coefficients of the priority function utilized in the generalized Sloan’s method are optimized using the recently developed metaheuristic algorithm, so-called vibrating particles system. The results are compared to those of other metaheuristic algorithms consisting of the particle swarm optimization, colliding bodies optimization, enhanced colliding bodies optimization, and tug of war optimization. These metaheuristics, are used for optimum nodal numbering of the graph models of the finite element meshes to reduce the profile and wavefront of the corresponding sparse matrices. Comparison of the results achieved by these metaheuristic algorithms and those of the King and Sloan, demonstrates the efficiency of the new metaheuristic utilized for profile and wavefront optimization.

Human brain and brainstem tissues have viscoelastic characteristics and their behaviours are functions of strains, as well as strain rates. Determination of the equilibrium and instantaneous stresses happening at low and high strain rates provide insights into a better understanding of the behaviour of such tissues. In this manuscript we present the results of a series of stress relaxation tests, at six different values of strains conducted on porcine brainstem tissue samples to indirectly measure the equilibrium and instantaneous stresses. The equilibrium stresses at low strain rates are measured from long-term responses of the stress relaxation test. The instantaneous stresses at high strain rates are determined using Quasi-Linear Viscoelasticity (QLV) theory at six strains. The results show that the instantaneous stresses are much larger (almost 11 times) than the equilibrium stresses and across all the strains. It can be concluded that the instantaneous response can be reasonably estimated from the long-term response which can be easily measured experimentally. The experimental results also show that the reduced relaxation moduli, estimated from the QLV theory, vary for the six strains tested.

In the present investigation, static, free vibration and buckling response of laminated composite plates based on the coupling of truncated hierarchical B-splines (THB-splines) and reproducing kernel particle method (RKPM) within higher order shear deformation plate theory are presented. The coupled THB-RKPM method blends the advantages of the isogeometric analysis and meshfree methods. Since under certain conditions, the isogeometric B-spline and NURBS basis functions are exactly represented by reproducing kernel meshfree shape functions, recursive process of producing isogeometric bases can be omitted. More importantly, a seamless link between meshfree methods and isogeometric analysis can be easily defined which provide an authentic meshfree approach to refine the model locally in isogeometric analysis. This procedure can be accomplished using truncated hierarchical B-splines to construct new bases and adaptively refine them. It is shown that THB-RKPM method is ideally appropriate for local refinement of laminated composite plates in the framework of isogeometric analysis. The flexibility of the proposed method for refining basis functions leads to decrease the computational cost without losing the accuracy of the solution. Numerical examples considering different boundary conditions, various aspect ratios, stiffness ratios and fiber orientations demonstrate validity and versatility of the proposed method.

In present paper, the stability analysis of boron nitride and silicon carbide nanotubes/nanowires is investigated using different size effective theories, finite element method, and computer software. Size effective theories used in paper are modified couple stress theory (MCST), modified strain gradient theory (MSGT), nonlocal elasticity theory (NET), surface elasticity theory (SET), nonlocal surface elasticity theory (NSET). As computer software, ANSYS and COMSOL multiphysics are used. Comparative results between theories and software and literature are given in result section. Comparative results are in good harmony. As results, it is clearly seen that nonlocal elasticity theory gives lowest results for every modes and structures while modified strain gradient theory gives the highest.

An efficient technique is proposed for calculation of coupled modes of fluid-structure interaction systems. The algorithm is presented with symmetric matrix operation mentality such that one feels that a symmetric eigen-problem is being solved. Furthermore, it is proved that each left eigen-vector is related to the corresponding right eigen-vector through a simple relation. Therefore, subsequent transient analysis can readily be performed. Overall, it is felt that the method is very efficient and it is ideal to be employed in general purpose finite element programs for solving above-mentioned eigen-problems

In this paper, an efficient reliability method is proposed. The Asymptotic Sampling (AS) and Weighted Simulation (WS) are two main basic tools of the presented method. In AS, the standard deviation of the distributions are amplified at several levels to find an adequate number of failed samples, then by using a simple regression technique, the reliability index is determined. The WS is another method which uses the uniform distribution for sampling, where the information about the distributions of the variables is taken into account through the weight indexes. The WS provides interesting flexibility where a sample generated for a specific standard deviation can be used as a sample for another standard deviation without having to reevaluate the limit state function. In AS the deviations of variables are scaled in each step, where one can use the flexibility of the WS to decrease the required calls of limit state function. Using this technique results in a new efficient method so-called Asymptotic Weighted Simulation (AWS). In addition, using the strengths of both AS and WS can be considered another superiority of the hybrid version. Performance of the presented method is investigated by solving several mathematical and engineering examples.

In this paper, a computational technique is presented based on a concrete plastic-damage model to investigate the effect of FRP strengthening of reinforced concrete arches. A plastic-damage model is utilized to capture the behavior of concrete. The interface between the FRP and concrete is modeled using a cohesive fracture model. In order to validate the accuracy of the damage-plastic model, a single element is employed under the monotonic tension, monotonic compression, and cyclic tension loads. An excellent agreement is observed between the predefined strain-stress curve and those obtained from the numerical model. Furthermore, the accuracy of the cohesive fracture model is investigated by comparing the numerical results with those of experimental data. Finally, in order to verify the accuracy of the proposed computational algorithm, the results are compared with the experimental data obtained from two tests conducted on reinforced concrete arches strengthened with FRP.

This paper is prepared to present the results of two major toxicity investigations of highway runoff in the state of California and verify or reject the hypothesis of whether highway runoff is toxic.  Two major toxicity studies were: (1) statewide highway runoff toxicity evaluation and (2) hydrographic (first flush) toxicity evaluation of runoff from highly urbanized highways.  Extensive grab and composite runoff samples were collected from numerous highway sites throughout the state of California for multiple storm events and multiple years. Wide ranges of toxicity testing, including the three U.S.EPA standard species, marine species, green algae growth and Microtox™ were performed on grab and composite samples.  The results obtained revealed that the highway runoff is generally toxic, and the toxicity is mostly associated with heavy metals and organic compounds such as herbicides, pesticides, and surfactants. While outside of the scope of this study, an independent performance evaluation of stormwater treatment showed that toxicity removal after best management treatments (BMPs) is possible even though some influent samples entering the BMP were toxic.

This paper presents a novel Gait Pattern Generator developed for the “Alice” social humanoid robot whichup to now lacked an appropriate walking pattern. Due to the limitations of this robot, the proposed gatepattern generator was formulated based on a nine-mass model to decrease the modeling errors; and theinverse kinematics of the whole lower-body was solved in such a way that the robot remains staticallystable during the movements. The main challenge of this work was to solve the inverse kinematics of a7-link chain with 12 degrees-of-freedom. For this purpose, a new graphical-numerical technique has beenprovided using the definition of the kinematic equations of the robot joints’ Cartesian coordinates. Thismethod resulted in a significant increase in the calculations’ solution rate. Finally, a novel algorithm wasdeveloped for step-by-step displacement of the robot towards a desired destination in a two-dimensionalspace. Performance of the proposed gate pattern generator was evaluated both with a model of the robot ina MATLAB Simulink environment and in real experiments with the Alice humanoid robot.

Collapse capacity is one of the fundamental factors for evaluating of collapse risk in performance-based design engineering field. Calculation of this parameter has been time consuming during past decade. This issue has prevented engineers from determining this parameter in a prevalent and practical way. Furthermore, defining of this value has been found more challenging in a near-source region due to special characteristics of its pulse-like records which make the collapse capacity more dependent on period ratio, T/Tp. In this study, amethod is proposed to obtain collapse capacity of reinforced concrete (RC) structures considering two main variables effecting columns behavior: axial load ratio and confinement ratio. The mentioned methodeschews the intensive computational challenges of incremental dynamic analyses to find collapse probability. By the proposed approach, the pulse period impact is incorporated into collapse risk using probabilistic equations. After the role of axial load ratio was illustrated,the resulted collapse probability distributions and the corresponding risk values are obtained for a near-fault site. The resultsexplain that asthe confinement ratio descends, the collapse capacity with near-fault pulse effect is decreased and the risk values are raised consequently. In addition, the results are found in compliance with ASCE acceptable risk value.

A powerful and new theoretical approach is used to obtain an expression for the effect of creep on reinforced concrete shear deformable beams. First, a method for Euler-Bernulli beam is proposed to represent long-term behavior of concrete beams based on linear strain theory. Secondly, a formulation is developed for analyzing the strain distribution in shear deformable concrete beams. Finally, three numerical examples are included in order to compare well-known codes with the proposed method. Comparison between proposed method, FEM, codes and experimental works demonstrate that the proposed analytical procedure can effectively simulate creep behavior in reinforced concrete beams.

In conducting mechanical tests on the brain tissue, it is preferred to perform multiple tests on the same sample. In this study we investigated the behavior of the bovine brain tissue in repeated compression tests with six recovery periods (10, 60, 120, 180, 240 and 300 s). Compression tests were performed on cylindrical samples with an average diameter and height of 18.0 mm and 15.0 mm respectively. Two testing protocols were employed: first protocol comprised of experiments with 5, 25 and 125 mm/min loading speed up to 33% strain and the second protocol consisted of tests with 25 and 125 mm/min loading speed up to 17% strain. Each experiment was conducted in two cycles separated by a specific recovery period. Stress-strain data from the first and second cycles were compared using three criteria, namely Normalized root-mean-square error (NRMSE), coefficient of variation (R2) and effective height ratio (EHR). The analysis suggests that the optimum recovery period for the first and second protocols are 120 s and 180 s respectively. Moreover, differences between the first and second cycles of medium and high speed tests were found to be smaller compared to the low-speed experiments.

The objective of this study is to develop analytical fragility curves for an ensemble of 3- to 6-story existing residential steel buildings with concentrically braced frames in two directions, designed during 2010 and 2015, and located in Qazvin, Iran. The buildings are modeled three-dimensionally in the OpenSees, considering braces buckling behavior. Maximum interstory drift ratio ( ) and spectral acceleration at fundamental period of the structure with 5% viscous damping ( ) are considered as Damage index ( ) and Intensity measure ( ), respectively. Limit states are specified as discussed in FEMA 356. Ground motion record selection and uncertainties assessment is carried out based on FEMA P695 methodology. Analysis is performed using truncated incremental dynamic analysis ( ). Fragility function is defined as a log-normal cumulative distribution function ( ) and maximum likelihood method is used to estimate fragility parameters. According to the fragility curves obtained, seismic vulnerability of the structures is generally increased as the number of stories rises. Concentration of the inelasticity is also found to be mainly at the first story level. The results also confirm the fact that the record to record variability is the main source of uncertainty in structural probabilistic evaluation.

This work investigates the turbulent flow and particles deposition in wavy duct flows. The v2f turbulence model was used for simulating the turbulent flow through the wavy channel.   The instantaneous turbulence fluctuating velocities were simulated using the Kraichnan Gaussian random field model. For tracking particles in the fluid flow, the particle equation of motion was solved numerically. The drag, Saffman lift, Brownian, and gravity forces acting on a suspended particle were included in the particle equation of motion. The effects of duct wave amplitude and wave length on deposition of particles of different sizes were studied. A range of waves with different amplitudes and wave lengths were simulated. The particle tracking approach was validated for turbulent flow in a flat horizontal channel where good agreement with previous studies was found. The presented results showed that the duct wavy walls significantly increase the particle deposition rate.

Different optimization methods are available for optimum design of structures including; classical optimization techniques and meta-heuristic optimization algorithms. However, engineers do not generally use optimization techniques to design a structure. They attempt to decrease the structural weight and increase its performance and efficiency, empirically, by changing the variables and controlling the constraints. Based on this professional engineering design philosophy, in this paper, a simple algorithm, termed the Constraint Control Method (CCM), is developed and presented whereby optimum design is achieved gradually by controlling the problem constraints. Starting with oversized sections, the design is gradually improved by changing sections based on a ‘control function’ and controlling the constraints to be below the target values. As the constraints move towards their targets, the design moves towards an optimum. The general functionality of the proposed algorithm is first demonstrated by solving several linear and nonlinear mathematical problems which have exact answers. The performance of the algorithm is then evaluated through comparing design optimization results of three, 2D steel frame benchmark problems with those from other, metaheuristic optimization solutions. the proposed method leads to the minimum structural weight while performing much smaller number of structural analyses, compared to other optimization methods.

A new higher-order triangular plane element with drilling degrees of freedom is proposed by assumption of second-order strain field. In addition to inclusion of drilling degrees of freedom and utilization of higher-order assumes strains, satisfaction of equilibrium equations improves performance of the suggested element in comparison with many of the other available elements. After proposition of the new element, a series of benchmark problems are solved to evaluate performance of the suggested element. Accuracy and efficiency of the suggested element is compared with other strain-based plane elements. Detailed discussions are offered after each benchmark problem. Finally, based on the attained results, a final conclusion about characteristics of robust membrane elements is made.

In this paper the influence of excitation angle on the Endurance Time (ET) analysis of skewed slab-on-girder bridges is studied. The excitation of the structure due to critical angle leads to the maximum seismic responses that are sometimes significantly higher than the average. The modeled bridges are slab-on-girder type which are typically used as highway bridges. The bridge models have skew angles of 0, 15, 30, 45, and 60 degrees. The ET excitations exerted on the structures cover a broad range of hazard levels. The results provide some insight for choosing multiple excitation angles in such a way that balances computational costs and retains acceptable accuracy for practical design purposes. Sensitivity of life cycle cost (LCC) to skewness is also studied.

An improved flexibility-based method hasbeen proposed in this studyfor damage detection, in which multi-scale convolution is utilized to decrease the interference of the measurementnoise and theDempster-Shafer evidence theory has been adopted to combine all scale information together to amplifythe damage characteristics. Threemain features make theproposed method distinguish with previous study:1)The proposed method is a kind of no-baseline flexibility-based method. Namely, this method can locate the damage with the absence of intact structural flexibility serving as baseline; 2) The flexibilityis estimated without requiring known the structural mass, which is a necessary in traditional method for flexibility estimation; 3) By utilizing multi-scale space theory and data fusion approach, the proposed methodhas a superior noise tolerant ability. Both numerical and experimental examples have been studied to reveal the effectiveness and accuracy of the proposed methodindifferent noise level. The comparison between traditionalmethod and proposed method demonstrates that the latteris well suited to detect damage in beams structure in a noisy environment.

An experimental study on the flexural behavior of reinforced concrete (RC) arches strengthened with glass fiber-reinforced polymer (GFRP) layers is performed. Totally, 36 specimens including 3 un-strengthened (control) and 33 strengthened RC arches were tested under centrally concentrated point load. The variables of this study were the steel reinforcement ratios, number of GFRP layers, and location and arrangement of GFRP layers. The failure mode, load-displacement response of specimens, crack propagation patterns, and GFRP debonding were examined. The extrados strengthening method was more effective than intrados strengthening approach in improving the failure load and rigidity of the arches. However, applying excessive GFRP layers at extrados can change the failure mode of arches from flexural to shear failure. The dominant failure mode of specimens was flexural and ductile failure due to the formation of five-hinge mechanism. Generally, GFRP strengthening could augment the ultimate load carrying capacity, secant stiffness, and energy absorption capacity of arch specimens by up to about 154, 300, and 93 percent, respectively. Statistical analyses were performed to assess the level of influence of each considered parameters on the behavior of RC arches. Finally, Analytical approach predicts the experimental data on arches with five-hinge failure mechanism satisfactorily.