Sharif Digital Repository

In this paper, design, simulation and optimization of a novel electrothermally-activated polymeric microactuator capable of generating combination of bidirectional lateral and rotational motions are presented. The composite structure of this actuator is consisted of a symmetric meandered shape silicon skeleton, a SU8 thermal expandable polymer and a thin film chrome layer heater. This actuator is controlled by applying appropriate voltages on its four terminals. With the purpose of dimension optimization, a numerical parametric study is executed. The modeled actuator which is 1560 ?m long, 156 ?m wide and 30 ?m thick, demonstrates a remarkable lateral displacement of 23 ?m at power... 

Effects of fringing electrostatic fields on the behavior of a double clamped initially curved microbeam are investigated. Galerkin's decomposition method is applied on the governing Euler-Bernoulli equation with distributed electrostatic force to obtain the lumped-parameter model of the system. The resulting single degree of freedom model is obtained with the Palmer's formula as a model for the fringing field effects. To derive an applied form of the fringing field effect in lumped model, we have used Genetic Algorithms as an optimization method. Then using the lumped model, we have investigated the system nonlinear dynamics. Comparison of the obtained bifurcation diagrams with the... 

In this work, the process of starch removal from starchy wastewater using a hydrophilic polyethersulfone membrane was investigated. The pore size of the membrane was 0.65 μm and the pattern of stream in plate and frame handmade membrane module was cross-flow. To design the layout of the experiments, response surface methodology was applied. The performance of the filtration process was evaluated by calculating the (chemical oxygen demand) COD removal percentage (rejection factor) and permeate flux. In this study, five operative parameters were investigated, including trans-membrane pressure, flow rate and temperature of feed, pH, and the COD concentration of starch wastewater. Two models... 

This study proposes a computer modeling approach to find the optimal damping coefficients of the viscoelastic ankle-foot prostheses for each specific amputee. A two-dimensional locomotion model was developed for a transtibial amputee and personalized using his body measures and the reference gait pattern of an equivalent able-bodied subject. By employing the forward dynamic simulation, the amputee’s locomotion was synthesized for different prosthetic settings to find the optimal damping coefficients, based on a kinematics and a total work cost function. Results indicated a good agreement between the model predictions and the experimental observations. © 2018, © 2018 RESNA  

An inverse dynamics musculoskeletal model of the lower extremity was combined with an optimization technique to estimate individual muscular forces and powers during stair ascent and descent. Eighteen Hill-type musculotendon actuators per leg were combined into the eleven functional muscle groups based on anatomical classification to drive the model in the sagittal plane. Simulation results illustrate the major functional differences in plantar flexors of the ankle and extensors of the knee and hip joints during ascent and descent. The results of this study not only could be employed to evaluate the rehabilitation results in the elderly but also could be used to design more anthropometric... 

A single-objective well placement problem is one of the classical optimization problems in oilfield development and has been studied for many years, by researchers worldwide. However, the necessity to face practical applications and handle insufficient data in a single-objective optimization leads to the introduction of a multi-objective optimization framework, which consequently allows an engineer to manage more information. In this study, for the very first time, a multi-objective well placement optimization framework, based on a Non-dominated Sorting Genetic Algorithm-II (NSGA-II) is utilized with a similarity-based mating scheme. To represent the power of this mating procedure, it is... 

This study proposes a computer modeling approach to find the optimal damping coefficients of the viscoelastic ankle-foot prostheses for each specific amputee. A two-dimensional locomotion model was developed for a transtibial amputee and personalized using his body measures and the reference gait pattern of an equivalent able-bodied subject. By employing the forward dynamic simulation, the amputee’s locomotion was synthesized for different prosthetic settings to find the optimal damping coefficients, based on a kinematics and a total work cost function. Results indicated a good agreement between the model predictions and the experimental observations. © 2018, © 2018 RESNA  

An inverse dynamics musculoskeletal model of the lower extremity was combined with an optimization technique to estimate individual muscular forces and powers during stair ascent and descent. Eighteen Hill-type musculotendon actuators per leg were combined into the eleven functional muscle groups based on anatomical classification to drive the model in the sagittal plane. Simulation results illustrate the major functional differences in plantar flexors of the ankle and extensors of the knee and hip joints during ascent and descent. The results of this study not only could be employed to evaluate the rehabilitation results in the elderly but also could be used to design more anthropometric... 

Application of the network equivalent concept for external system representation for power system transient analysis is well known. However, the challenge to utilize an equivalent network, approximated by a rational function, is to guarantee the passivity of the corresponding model. In this regard, special techniques are required to enforce the passivity of the equivalent model through a post processing approach that minimizes its impact on the original model characteristics. In this paper, the passivity is enforced by expressing the problem in terms of a convex optimization problem that guarantees the global optimal solution. The convex optimization problem is efficiently solved by recently... 

The evermore widespread use of microscopic traffic simulation in the analysis of road systems has refocused attention on sub models, including car-following and lane-changing models. In this research a microscopic model is developed which combines car-following and lane-changing models and describes driver behaviour as a crash risk reduction process of drivers. This model has been simulated by a cellular automata simulator and compared with the real data. It has been shown that there is no reason to consider the model invalid for drivers' behaviour in the basic segments of freeways in Iran, during not-congested conditions. Considering that uncertainty of position of vehicles is caused by... 

This work describes a new mathematical model to predict the so-called aircraft handling qualities via proper positioning of aircraft mass in the early stages of the design process. The methodology aims to help make handling qualities and therefore pilot rating an integral part of the design process. The main idea is to And proper mass distributions for an aircraft in given flight conditions based on the well-known quantitative measures of flying qualities described in military standards. The proposed methodology allows aircraft designers to associate a density to different segments of an aircraft and have a prior insight about an optimum arrangement of internal parts such as fuel tanks,... 

General regression neural network (GRNN) is employed to reconstruct the compressor performance map. Two different models are adopted to examine the accuracy of the GRNN technique. The results indicate that the GRNN predictions for both models are very sensitive to the width of the probability a. Further, since the distribution of data is multimodal with large variance differences modes, two solutions are suggested: a locally optimized value for the probability, and the second one is rotated general regression neural network (RGRNN) providing a more accurate result compared to an overall value for the probability. The results show that as the number of samples is reduced to about 70% of the... 

This paper describes a procedure that uses particle swarm optimization (PSO) combined with the simulated annealing (SA) to analyze the bidding strategy of Generating Companies (Gencos) in an electricity market where they have incomplete information about their opponents. In the proposed methodology, Gencos prepare their strategic bids according to the Supply Function Equilibrium (SFE) model and they change their bidding strategies until Nash equilibrium points are obtained. Nash equilibrium points constitute a central solution concept in the game theory and are computed with solving a global optimization problem. In this paper a new computational intelligence technique is introduced that can... 

Under-voltage load shedding is one of the most important tools for avoiding voltage instability. In this paper, an optimal load-shedding algorithm is developed. This approach is based on the concept of the static voltage stability margin and its sensitivity at the maximum loading point or the collapse point. The traditional load-shedding objective is extended to incorporate both technical and economic effects of load shedding. The voltage stability criterion is modeled directly into the load-shedding scheme. The proposed methodology is implemented over the IEEE 14 and 118 bus test systems and solved using a mathematical (GAMS/CONOPT) and two heuristic (PSO and GA) methods. The heuristic... 

Radial forging is an open die forging process used for reducing the diameter of shafts, tubes and axels. In the present research, a new velocity field was developed to analyze the radial forging process by the upper bound method. The forging load was predicted by minimizing the deformation power with regards to the location of neutral plane. The accuracy of the model was verified by comparing the predicted forging loads with experimental results published by the previous researcher. A good agreement was found between the two sets of results. © 2007 Elsevier B.V. All rights reserved  

During the last decade, the importance of process development has persuaded researchers to propose a great number of optimization models on "production planning" and "production scheduling" for different productive processes. Although many scheduling and planning models are proposed in the past decade, there are few models that handle various applicable goals. In this paper the main objective is developing and extending the traditional scheduling formulations to accommodate optimization of utility (especially energy barriers) demands and supplies. In the context of optimization, the final formulation takes the form of a mixed-integer programming. For this purpose a mathematical model is... 

Analysis of multi dimensional interactions of flow of energy in passenger vehicle is a complex task that necessitates development and utilization of analytical tools. Development of analytical tools with high complexity is usually based on conclusions of many concepts and theories from different scientific disciplines. In this approach, Passenger vehicle is supposed to be organized in the form of a firm and appears in the market that oriented towards establishing an effective energy supply system which may be identified as delivering the product (person kilometer or tone kilometer) with minimum operation costs. To this end, an optimization model named power software founded on theory of firm... 

In overlay networks, the mechanism of a peer randomly joining and leaving a network, causes a topology mismatch between the overlay and the underlying physical topology. This causes a large volume of redundant traffic in the underlying physical network as well as an extra delay in message delivery in the overlay network. Topology mismatch occurs because overlay networks are not aware of their underlying physical networks. In this paper we present a mathematical model for topology awareness of overlay networks (degree of matching between an overlay and its underlying physical network) and the efficiency of message delivery on them. Then we experimentally show that the model is precise in the... 

Advanced gas turbine cycles use advanced blade cooling technologies to reach high turbine inlet temperature. Accurate modeling and optimization of these cycles depend on blade cooling model. In this study, different models have been used to simulate gas turbine performance. The first model is the continuous model and the second is stage-by-stage model with alternative methods for calculating coolant, stagnation pressure loss and SPR. Variation of specific heat and enthalpy with temperature are included in both models. The composition of gas stream in turbine is changed step by step due to air cooling. These models are validated by two case study gas turbine results, which show good agreement... 

In this paper, two methods to solve multi-response statistical problems are presented. In these methods, desirability function, genetic algorithm and simulation methodology are applied. The desirability function is responsible for modeling the multi-response statistical problem, the genetic algorithm tries to optimize the model and, finally, the simulation approach generates the required input data from a simulated system. The methods differ from each other in controlling the randomness of the problem. In the first method, replications control this randomness, while, in the second method, the randomness is controlled by a statistical test. Furthermore, these methods are compared by designed...