Computational Methods in Engineering

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Artificial Neural Networks are information processing systems. Over the past several years, these algorithms have received much attention for their applications in pattern completing, pattern matching and classification and also for their use as a tool in various areas of problem solving. In this work, an Artificial Neural Network model is presented for predicting the tensile properties of cotton-covered nylon core yarns. Multilayer Feedforward network with Back Propagation learning algorithm was used to study the relationship and mapping among the process parameters, i.e. count of sheath part, count of core part, applying pretension to the core part, inserted twist to the core spun-yarn as well as tensile properties, i.e. breaking strength and breaking elongation. The results show that ANN is an effective method for the prediction of the tensile properties of these yarns. This is due to the fact that in each case, standard deviation of prediction error for test and train data was less than that obtained from the expreiments.

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A physical model of gabion overflow dams was studied to determine the velocity profile and Reynolds shear stress. Physical tests were done under two different conditions of dam crest, overflow dams with impermeable and with permeable crests. Instantaneous velocity components over dam crest were measured by an ADV (Acoustic Doppler Velocimeter) instrument. This instrument is capable of measuring instantaneous velocity components with frequencies up to 25 Hz. Average velocity components and bed shear stress were extracted from ADV measurements. The results of this research show the effect of crest permeability on velocity and Reynolds shear stress. The magnitude of Reynolds shear stresses, horizontal velocity components, and absolute value of vertical velocity components under the permeable scenario are bigger than those of the impermeable scenario. Velocity distribution over the dam crest is different from the universal logarithmic profile.

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A systolic serial multiplier for unsigned numbers is presented which operates without zero words inserted between successive data words, outputs the full product and has only one clock cycle latency. The multiplier is based on a modified serial/parallel scheme with two adjacent multiplier cells. Systolic concept is a well-known means of intensive computational task through replication of functional units and their repetitive use. Digital signal processing applications often involve high-speed sequential data. Bit-serial processing in particular can result in efficient communications, both within and between VLSI chips because of the reduced number of interconnections required. Serial input multipliers have received considerable attention, particularly for hardwired VLSI algorithms used in signal processing application, due to their minimal chip area required for interconnections. Bit-serial architectures are often used in parallel systems with high connectivity to reduce the wiring down to a reasonable level. The conventional add-shift technique for multiplication, which uses a minimum number of gates, is inexpensive to implement, but too slow to achieve the desired result. Iterative array multipliers are needed to satisfy the high speed requirement of systems. With the advantage of high scale integration, the hardware is not regarded as a major obstacle in implementation.

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In this paper, two suboptimum detectors are proposed for coherent radar signal detection in K-distributed clutter. Assuming certain values for several initial moments of clutter amplitude, the characteristic function of the clutter amplitude is approximated by a limited series. Using the Pade approximation, it is then converted to a rational fraction. Thus, the pdf of the clutter amplitude is obtained as a sum of simple exponential functions. Using such a pdf, we develop the suboptimum detectors PGLR and PAALR, which are simplified forms of the GLR and AALR. Computer simulations show that the suggested detectors have appropriate performance compared to OLD, GLR and AALR detectors.

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This paper presents a nonlinear mixed-integer programming model to minimize the stoppage cost of mixed-model assembly lines. Nowadays, most manufacturing firms employ this type of line due to the increasing varieties of products in their attempts to quickly respond to diversified customer demands. Advancement of new technologies, competitiveness, diversification of products, and large customer demand have encouraged practitioners to use different methods of improving production lines. Minimizing line stoppage is regarded as a main factor in determining the sequence of processing products. Line stoppage results in idleness of operators and machines, reduced throughput, increased overhead costs, and decreased overall productivity. Due to the complexity of the model proposed, which belongs to a class of NP-hard problems, a meta-heuristic method based on a genetic algorithm (GA) is proposed to obtain near-optimal solutions in reasonable time, especially for large-scale problems. To show the efficiency of the proposed GA, the computational results are compared with those obtained by the Lingo software.

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In recent years, many different plans have been considered to use the nuclear energy gained from inertial confinement fusion (ICF) as attempts to obtain high energy efficiencies. In conventional ICF methods, a small amount (about mg) of the deuterium–tritium compound is confined in a small spherical chamber of a few millimeters in radius and compressed by laser or heavy ion beams with powers in the order of W. The consequent plasma froming at the center of the chamber is an essential issue for fusion. The hydrodynamical instabilities during the fuel compression process arising in the conventional ICF technique leads to a decline in energy efficiency. The new plans for reducing instabilities involve compression of the fuel chamber in two stages using laser or ion beams. In the first stage, fuel is preheated by laser or ion and in the second phase, relativistic electrons are constructed by -W laser phases in the fuel. This heating method has come to be known as a fast “ignition method”. More recently, cylindrical rather than spherical fuel chambers with magnetic control in the plasma domain have been also considered. In this work, fast ignition method in cylindrical fuel chambers will be investigated and transportation of the relativistic electrons will be calculated using MCNP code and the Fokker–Planck program. Furthermore, the transfer rate of relativistic electron energy to the fuel will be calculated. Our calculations show that the fast ignition method and cylindrical chambers guarantee a higher energy efficiency than the one-step ignition and that it can be considered an appropriate substitute for the current ICF techniques.

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In this paper,  a numerical model  was first verified against dynamic centrifuge tests results performed on an
underground subway tunnel and then, the effect of underground structure on peak ground acceleration (PGA) at the ground
surface investigated considering linear and nonlinear behavior for the soil. The results show that in the range of natural
frequency of the system, nonlinear model shows deamplification of PGA with respected to the freefield. Whereas, linear model
shows opposite trend. Out of the range of natural frequency of the system, linear and nonlinear models predict same results and for both model, underground tunnel resulted in amplification of  low frequencies and deamplification of high frequencies with
respected to the freefield.

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Utilizing one of the mesh free methods, the present paper concerns static analysis of thin plates with various geometric shapes based on the mindlin classical plate theories. In this numerical method, the domain of issue is solely expressed through a set of nods and no gridding or element is required. To express the domain of issues with various geometric shapes, first a set of nodes are defined in a standard rectangular domain , then via a three-order map with, these nodes are transferred to the main domain of the original issue; therefore plates of various geometric shapes can be analyzed. Among meshfree numerical methods, Element Free Galerkin method (EFG) is utilized here. The method is one of the weak form integral methods that uses MLS shape functions for approximation. Regarding the absence of Delta feature in MLS functions, boundary conditions cannot be imposed directly; hence the Lagrangian method is utilized to impose boundary conditions. At the end, our outputs are compared with those of analytic and finite element methods for plates, in order to validate the exactness of our solution method, and then after reliability is established, a few new examples will be solved.

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This study shows how to create different types of crack and discontinuities by using isogeometric analysis approach (IGA) and extended finite element method (XFEM). In this contribution, two unique features of isogeometric analysis approach are utilized to create discontinuous zones. Discontinuities consist of crack and cohesive zone. In isogeometric analysis method NURBS is used to approximate both geometry and primary variable. NURBS can create quadratic shapes exactly. Also, stress intensity factors are calculated in the vicinity of the crack tips for two dimensional problems and are compared with corresponding analytical and numerical counterparts. Extended finite element method is the other numerical method which is used in this work. The enrichment procedure is utilized in extended finite element method to create discontinuities. The well-known path independent J-integral approach is used in order to calculate the stress intensity factors. Also, in mixed mode situation, the interaction integral (M-integral) is considered to calculate the stress intensity factors. Results show that isogeometric analysis method has desirable accuracy as it uses lower degree of freedoms and consequently lower computational efforts than extended finite element method. In addition, creating the internal cohesive zone as one of the most important issues in computational fracture mechanics is feasible due to the special features of isogeometric analysis. The present study demonstrates the capability of isogeometric analysis parametric space to control the inter-element continuity and create the cohesive zone.

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In this paper, wave propagation method was applied to detect damage of structures. Spectral Finite Element Method
(SFEM) was used to analyze wave propagation in structures. Two types of structures i.e. rod and Euler-Bernoulli beam were
modelled using spectral elements. The advantage of spectral finite element over conventional Finite Element Method (FEM), in
wave propagation problems, is its accuracy and lower computational time. Two examples of rod and Euler-Bernoulli beam with
embeded concentrated mass were presented to illustrate the superiority of SFEM to FEM. Finally, a cracked beam was modeled
and analyzed using spectral finite elements and the location of the crack was determined using time history response of beam
structure.

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This paper focuses on the processing of structural health monitoring (SHM) big data. Extracted features of a  structure are reduced using an optimization algorithm to find a minimal subset of salient features by removing noisy, irrelevant and redundant data. The PSO-Harmony algorithm is introduced for feature selection to enhance the capability of the proposed method for processing the  measured big data, which have been collected from sensors of the structure and uncertainties associated with this process. Structural response signals under ambient vibration are preprocessed according to wavelet packet decomposition (WPD) and statistical characteristics for feature extraction. It optimizes feature vectors to be used as inputs to surrogate models based on the wavelet weighted support vector machine (WWLS-SVM) and radial basis function neural network (RBFNN). Two illustrative test examples are considered, the benchmark dataset from IASC-ASCE SHM group and a 120-bar dome truss. The results indicate that the features acquired by WPT from vibrational signal have higher sensitivity to the damage of the structure. Furthermore, the proposed PSO-Harmony is compared with four well-known metaheuristic optimization algorithms. The obtaind results show that the proposed method has a better performance and convergence rate. Finally, the proposed feature subset selection method has the capability of 90% data reduction

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This paper presents a probabilistic assessment on the free vibration analysis of functionally graded material plates, including layers with magneto-electro-elastic properties, using the 3D solution and surrogate models. The plate is located on an elastic foundation and the intra-layer slipping effect is also considered in the analysis by employing the generalized intra-layer spring model. Due to the high computational cost of the 3D solution in calculating the free vibration frequency of the plate, surrogate models are used. The meta models including kriging method, radial fundamental function method and polynomial response surface method are used to construct the surrogate model. For surrogate models training, the results of the three-dimensional solving method are used. The elastic foundation hardness, the intra-layer slipping effect, the material properties index, and the layer densities are considered as the variables with uncertainty. The three-dimensional solution method is validated through a comparison with other available reference. The results obtained through the surrogate models have been compared to those of the 3D solution formulation, showing a good agreement. The effects of some parameters including the elastic foundation hardness, the intra-layer slipping effect, the density of each layer, and the material properties index on the fundamental frequency of functionally graded material plates are investigated. By using three-dimensional solution method and Kriging Surrogate Model, it is shown that the shear and transverse components of elastic foundation hardness and the density of each layer have the greatest effect on the fundamental frequency of the functionally graded material plates.

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Continuously varying cross-section members have found wide applications in engineering for cost and resistance optimization. Since steel structures generally have more slender members compared to concrete structures, buckling analysis of steel members is of more importance. Determining the critical load of functionally varying cross-section columns using the analytical solution is a time-consuming process. In this paper, buckling analysis of non-prismatic steel columns is conducted using the meshless local Petrov-Galerkin (MLPG) method. In meshless methods, the scattered nodes are used rather than the elements to model the problem domain and its boundaries. The change of the inertia moment within the length of a column is characterized by introducing a power function with variable taper ratio and exponent. The radial basis function is used to discretize the differential equation governing the buckling. The penalty method is used for the imposition of the boundary conditions. Numerical examples of the critical buckling load for prismatic and non-prismatic columns using the proposed method are compared with the analytical solution, and the effectiveness of the MLPG method for buckling analysis of non-prismatic columns is validated. Also, buckling analysis of muscle column members subjected to non-uniform axial load is carried out to show the efficiency of the proposed method. The effect of several parameters such as non-uniformity of the load and variation of the cross-section on the buckling load of the column is discussed in details.

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Accurate modeling of fluidization and heat transfer phenomena in gas-solid fluidized beds is not solely dependent  on the particular selected numerical model and involved algorithms. In fact, choosing the right model for each specific operating condition, the correct implementation of each model, and the right choice of parameters and boundary conditions, determine the accuracy of the results in the evaluation of the performance of fluidized beds. In this research, in order to accurately simulate heat transfer in fluidized beds, important and effective parameters on two-fluid Eulerian model that incorporate the kinetic theory of granular flow were investigated. For this purpose, effects of particle-particle and particle-wall restitution coefficient, specularity coefficient, granular temperature and effective thermal conductivity coefficients determination methods on the numerical solution were evaluated. These investigations were first carried out on heat transfer from hot air to solid particles in an adiabatic fluidized bed, and then on a fluidized bed with constant temperature walls for bubbling and turbulent regimes. Results showed that specularity coefficient and effective thermal conductivity are important parameters in heat transfer process from wall to bed. In this case, the zero value of the specularity coefficient causes the air temperature to increase by about 7 degrees in the bubbling regime and about 5 degrees in the turbulent regime, and its unit value gives the same results with the no-slip condition. In addition, considering the solid and gas material thermal conductivities causes the outlet air temperature to be about 26 degrees higher than the temperature that is obtained by considering the effective thermal conductivity coefficients with standard approach. The partial differential and algebraic form of the conservation equation for the particles kinetic energy show identical results in dense fluidized beds, although considering a constant granular temperature can cause computational errors.