Scientia Iranica
Volume:19 Issue: 4, 2012

In this paper, the lower-bound techniques of limit analysis are applied to obtain lateral earth pressures of rigid retaining walls subjected to earthquake forces. The well-known Mononobe–Okabe analysis is a direct modification of the coulomb wedge analysis. In this analysis, the earthquake effects are replaced by a quasi-static inertia force whose magnitude is computed on the basis of the seismic coefficient concept. This paper is describing an analytical solution to investigate the lateral force affect on retaining walls, using mathematical relations based on a lower bound limit analysis method. The lower bound of the exact solution can be obtained by use of different admissible stress fields in different regions of the media divided by stress discontinuity surfaces. This process is included in calculation of the direction and magnitude of passive lateral earth pressure. Numerical results of the proposed algorithm are presented in some practical dimensionless graphs.

In most concrete bridge decks subject to deicing slats or constructed in chloride-laden environments, corrosion has caused serviceability damage in the form of severe cracking and/or spalling of the concrete cover. In this paper, whilst an analytical model is used for the simulation of corrosion induced crack width, random fields are utilized accounting for the spatial variability of the concrete material and environmental factors. Then, using the Monte Carlo simulation method, the extent of the damage is simulated as a dependent random variable during the service life of the bridge deck. Finally, for finding optimum reliability-based inspection plans, with minimum life cycle costs, an integrated Artificial Neural Network-Genetic Algorithm (ANN-GA) approach is proposed. The applicability of this method is investigated on a hypothetical bridge deck. It is concluded that the employed approach can well handle the high computational complexity of the problem in finding optimum inspection plans.

In this paper، joint identification for structural systems، characterized by severe nonlinearities (softening) in the constitutive model، is pursued via the Sigma-Point Kalman Filter (S-PKF) and the Particle Filter (PF). Since a formal proof of the effects of softening in a stochastic structural system on the accuracy and stability of the filters is still missing، we comparatively assess the performances of S-PKF and PF. We show that the PF displays a higher convergence rate towards steady-state model calibrations and the S-PKF is less sensitive to the measurement noise. Both S-PKF and PF are robust، even if they tend to get unstable when a structural failure is triggered.

The tensile and fracture behavior of as-cast and age-hardened aluminium (6063), silicon carbide particulate composites produced, using borax additive and a two step stir casting method, was investigated. Al (6063), SiCp composites having 3, 6, 9, and 12 volume percent of SiC were produced, and sample representatives of each composition were subjected to age-hardening treatment at 1800 °C for 3 hours. Tensile and Circumferential Notched Tensile (CNT) specimens were utilized for tension testing to evaluate, respectively, the tensile properties and fracture toughness of the composites. Experimental results show that the ageing treatment resulted in little improvement in the tensile strength of the composites. The tensile strength and yield strength increased to almost the same magnitude with an increase in SiC volume percent for both as-cast and age-hardened conditions. The increase was, however, more significant for the 9 and 12 volume percent SiC reinforcement. The strain to fracture was less sensitive to volume percent SiC reinforcement and ageing treatment, with values less than 12% strain to fracture observed in all cases. The fracture toughness, however, improved significantly with ageing treatment (as-cast; ageing treatment).

In the present paper, the seismic response of an arch dam subjected to spatial variation of ground motions along the interface with its foundations is investigated. Recorded ground accelerations at the dam foundation interface of an arch dam were used for the purpose of this investigation. Topographic amplification between various points of the interface was studied by obtaining ratios of the response spectral displacement and spectral pseudo acceleration. Time shift and amplification between stations show the nonuniform nature of ground motions for large structures like dams. Recorded ground accelerations were interpolated for different nodes of the finite element model. The seismic responses of the Karun III dam subjected to multiple support excitations are determined. The results show that nonuniform ground acceleration can have extensive effects on dam behavior and can increase the responses. Pseudo static displacement is the dominant part of total displacement for points near the dam foundation interface; however, dynamic displacement is more significant for the middle part of the dam.

In this analytical study, it has been desired to develop a practical and simple control mechanism to control, at a given point and its neighborhood, the sound arriving from a distant source, assuming that a primary pure-tone sound pressure is propagated from a relatively far distance. The control model consists of a microphone as a sensor for measuring the sound pressure and a loud speaker for applying the control force. Corresponding equations have been developed to determine an optimum control force, and afterwards a parametric study on the factors affecting the control results has been performed. The results show that the control system can significantly reduce low frequency sound pressure in the region near the target point. The results also demonstrate less effectiveness in controlling high frequency sound pressures. Moreover, the larger the distance of the loudspeaker to the given controlled point is, the wider the controlled area will be. Also, it was found that though the distance between the sensor and the actuator does not have any effect on the size of the area which can be controlled, such distance is of greatest importance in that the available time to control increases directly by increasing the distance.

In this study, the effect of freezing and thawing on the strength and permeability of two clayey soils (high and low plasticity), which had been stabilized with lime, were investigated. Before and after stabilization, the permeability and strength of the specimens were determined with various freeze-thaw cycles. Results of this study indicated that for both clays, 6% lime addition increased the hydraulic conductivity of the specimens 1000 times. However, the hydraulic conductivity of clay with 6% lime increased 10–20 times after only 3 freeze-thaw cycles. The results of strength tests exhibited different trends. The strength of stabilized high plasticity clay increased approximately 15 times at the end of 28 day curing, whereas the strength of stabilized low plasticity clay increased about 3 times only. The strength of both stabilized clays decreased 10–15% at the end of the freeze-thaw cycles.

The physico-mechanical properties of rocks and rockmass are decisive for the planning of mining and civil engineering projects. The Schmidt hammer Rebound Number (RN), Slake Durability Index (SDI), Uniaxial Compressive Strength (UCS), Impact Strength Index (ISI) and compressive wave velocity (-wave velocity) are important and pertinent properties to characterize rock mass, and are widely used in geological, geotechnical, geophysical and petroleum engineering. The Schmidt hammer rebound can be easily obtained on site and is a non-destructive test. The -wave velocity and isotropic properties of rocks characterize rock responses under varying stress conditions. Many statistics based empirical equations have been proposed for the correlation between RN, SDI, UCS, ISI and -wave velocity. The Artificial Neural Network (ANN), Fuzzy Inference System (FIS) and neuro-fuzzy system are emerging techniques that have been employed in recent years. So, in the present study, soft computing is applied to predict the -wave velocity. 85 data sets were used for training the network and 17 data sets for the testing and validation of network rules. The network performance indices correlation coefficient, Mean Absolute Percentage Error (MAPE), Root Mean Square Error (RMSE), and Variance Account For (VAF) are 0.9996, 0.744, 25.06 and 99.97, respectively, which demonstrates the high performance of the predictive capability of the neuro-fuzzy system.

This study presents conceptually effective layouts of materials, i.e. steel or fiber, optimally positioned into building frames. The design information of the material layout may be helpful in dealing with large-scale safety design issues in civil or architectural engineering fields, against natural phenomena, such as winds and earthquakes. The material topology optimization method evaluates an optimal layout reinforcing or arranging material of a specified volume in a given design space that maximizes stiffness for a given set of loads and boundary conditions. Generating the optimal distribution of material is similar to the so-called strut-and-tie method using truss members of straight lines, and it leads to the stiffest structures. Numerical applications verify that the present material topology optimization method is an applicable concept design tool to create effective layout designs of material in given structural frames in civil and building industries.

In this study, an effective and practical, -version, enrichment mesh generation, and finite element adaptive procedure for the non-linear solution of problems in continuous media is presented. Moreover, based on the gradient recovery rule, a general recovery technique is developed to measure error and refine mesh in general finite element solutions. The recovery technique is simple and cost effective to implement. The technique has been formulated for two dimensional problems by employing triangular elements. The formulation is consistent with non-linear formulations which iteratively equilibrate the continuous media problems.In the present study, in addition to correlating various norms (such as energy norm, norm for stress and norm for strain), a new norm, namely, deviating stresses norm (called norm in this study), is also correlated by the authors to estimate the error rate in the finite element method. Based on the results of this study, the norm can be used as a tool to estimate the error rate in the finite element method, and to determine the ultimate load and the possible failure path in continuous domains. For several numerical examples, the developed algorithms are demonstrated and the resulting meshes are presented.

In this study, interface direct shear tests were undertaken to investigate improvement in the mechanical behaviour of granular soils when reinforced with geotextile inclusions. Unlike past studies, various different parameters were investigated in the same study to uncover more assuring results. As expected, the interface friction angle of the reinforced sand was found to be lower than that of the unreinforced sand. No remarkable difference was seen in the shear strength of reinforced and unreinforced sands, but in reinforced sand, there was no post-peak loss of strength, as seen in unreinforced sand. Unexpectedly, geotextile inclusions did not restrict the soil from dilating. If the geotextile content was increased in the test specimen, only then did the dilation of the sand decrease. At the end of the results, it was concluded that the interface behaviour depends on the combined effects of the surface properties and deformability of the geotextiles, and also on the index properties of the soil.

Solving of MHD flow by the lattice Boltzmann method, utilizing classical equations has been investigated by presenting MHD mixed convection in a lid-driven cavity by a linearly heated wall. The Hartmann number varied from to 100; furthermore, the study has been conducted for Richardson numbers (Ri) from 0.01 to 100, while the directions of the magnetic field were investigated for and 90°. Results show that the augmentation of Richardson number causes heat transfer to increase, as the heat transfer decreases by the increment of Hartmann number for various Richardson numbers and the directions of the magnetic field. The highest decline of heat transfer on the linearly heated wall was found at for Richardson numbers of and. On the other hand, the least effect of the magnetic field is observed at from to 100 for both directions on the linearly heated wall. Moreover, the magnetic field influences heat transfer marginally at against, which changes dramatically. Heat transfer on the heated wall at the bottom of the cavity behaves like the linearly heated wall regarding the effect of the magnetic field.

In this study, a numerical analysis of the melting process with natural convection in an inclined cavity has been performed using the enthalpy-based lattice Boltzmann method. The D2Q9 and D2Q5 models were applied to determine the density and velocity fields, and the temperature field, respectively. The study was carried out for Stefan number of 10, Rayleigh number ranging from to, and inclination angle ranging from to. The predicted results indicate that an increase in Rayleigh number leads to intensifying the melting rate at each inclination angle. In addition, when the cavity is inclined counterclockwise, the effect of natural convection becomes more dominant, while, if it is inclined clockwise, the conduction regime endures longer.

Laser forming is a non-traditional process, in which the laser beam is used as a forming tool. Two major defects occur during this process: longitudinal distortion along the laser path and bending angle variation along the free edge of the sheet. These two phenomena were studied by using numerical and experimental approaches. Laser scanning speed was applied along the straight-line in two ways: a fixed scan speed pattern and a variable scan speed pattern. In order to record the experimental data, an accurate non-contact optical measuring method was used. Experimental and finite element results have shown that, in the fixed scan speed patterns, by increasing the speed, the longitudinal distortion and bending angle were reduced. In the variable speed patterns, the fluctuation of scan speed has no effect on the reduction of longitudinal distortion and bending angle. The numerical and experimental results were compared and good correlation was found between them

In this paper, a new method is proposed for solving the obstacle avoidance problem of discretely actuated hyper-redundant manipulators. In each step of the solution, the closest collision to the base is removed and then the configuration of the next part of the manipulator is modified without considering the obstacles. This process is performed repeatedly until no collision is found. The Suthakorn method is applied to solve the inverse kinematics problem. Two new ideas are proposed to reduce the errors of this the two-by-two searching method, and iterations. To verify the proposed method, some problems are solved numerically for 2D and 3D manipulators, each in two different obstacle fields, and the results are compared with those obtained by the genetic algorithm method.

This paper focuses on the study of dynamic modeling of nonholonomic wheeled mobile robotic manipulators, which consist of a serial manipulator with elastic joints and an autonomous wheeled mobile platform. To avoid computing the Lagrange multipliers associated with the nonholonomic constraints, the approach of Gibbs-Appell (G-A) formulation in recursive form is adopted. For modeling the system completely and precisely, dynamic interactions between the manipulator and the mobile platform, as well as both nonholonomic constraints associated with the no-slipping and the no-skidding conditions, are included. Based on developed formulation, an algorithm is proposed that recursively and systematically derives the equation of motion. In this algorithm, in order to improve the computational complexity, all mathematical operations are done by only and matrices. Also, all dynamic expressions of a link are expressed in the same link local coordinate system. Finally, two computational simulations for mobile manipulators with rigid and elastic joints are presented to indicate the capability of this algorithm in generating the equation of motion of mobile robotic manipulators with high degree of freedom.

The equations of motion for a beam on a flying support for Euler–Bernoulli and Timoshenko Beam Theories is derived. In modeling and attempting to have an accurate model at high speeds, a stretch variable instead of conventional axial deformation is used. For a planar rotating beam and a spatial rotating beam, equations of motion are lineralized and verified. Finite element and Newmark direct integration methods are employed for numerical simulations.

In this study, the homotopy perturbation transform method (HPTM) is performed to give analytical solutions of the time fractional diffusion equation. The HPTM is a combined form of the Laplace transform and homotopy perturbation methods. The numerical solutions obtained by the proposed method indicate that the approach is easy to implement and accurate. These results reveal that the proposed method is very effective and simple in performing a solution to the fractional partial differential equation. A solution has been plotted for different values of. , and some numerical illustrations are given.

In this paper, an irreversible quantum Brayton heat engine cycle model composed of two isomagnetic processes and two irreversible adiabatic processes is established. The quantum heat engine works with non-interacting spin-1/2 systems and has multi-irreversibilities. By using detailed numerical examples, this paper gives the fundamental optimal relationship of the quantum Brayton heat engine, in a general case and at high temperature limits, and analyzes the effects of internal friction and bypass heat leakage on the fundamental optimal relationship. Comparisons of the power output versus efficiency characteristics among this spin quantum heat Brayton engine, a quantum spin Carnot heat engine and a Brayton heat engine working with a classical working medium, are made. Three special cases, such as the endoreversible case, the frictionless case and the case without bypass heat leakage, are discussed.

In this paper, we propose a new technique for solving the nonlinear Fokker–Planck equation. This algorithm is based on the Laplace transform and new homotopy perturbation methods. The new technique is applied to solving two mathematical models of this problem. We show that the present approach is relatively easy, efficient and highly accurate.

In this paper, a relatively recent method, namely the Differential Transform Method (DTM), is applied to devise a simple scheme for solving the Fokker–Planck equation and some similar equations. The method can easily be applied to many linear and non-linear problems and is capable of reducing the size of computational work. The approach also introduces the solution in the form of a rapidly convergent series. Illustrative examples are provided to demonstrate the applicability and efficiency of the technique.