International Journal of Engineering
Volume:28 Issue: 2, Febr 2015

A numerical dynamic-aerodynamic interface for simulating the separation dynamics of constrained strap-on boosters jettisoned in the atmosphere is presented. The aim of the presented interface is to facilitate the simultaneous simulation of complicated dynamic separation mechanisms and full numerical CFD aerodynamic solver. A 6-DOF multi body dynamic solver using Constraint Force Equation Methodology is coupled with a numerical time dependent Euler flow solver. An automatic dynamic mesh updating procedure is employed using smoothing and local remeshing technique. This interface can simulate multi body separation problem by modeling the full separation mechanisms like springs، thrusters، joints and so on، regarding the aerodynamic effects. The flow solver is validated by the Titan-IV launch vehicle experimental data. The proposed simulated separation integration is usedfor a typical launch vehicle with two strap-on boosters using spring ejector mechanism and spherical constraint joints acting in the dense atmosphere.

One of the most important problems in target tracking is Line of Sight (LOS) rate estimation for using from PN (proportional navigation) guidance law. This paper deals with estimation of position and LOS rates of target with respect to the pursuer from available noisy RF seeker and tracker measurements. Due to importance of exact estimation on tracking problems most target position and LOS rates have been estimated with least error rather than actual values. In this paper, extended Kalman filter (EKF) and unscented Kalman filter (UKF) algorithms are used for estimation of target position in threedimensional (3-D) and LOS rates in elevation and azimuth for seekers and trackers. For comparison of algorithms, model of the system was simulated using MATLAB and many tests were carried out. Simulation experiments showed that the efficiency of EKF due to least RMSE had better performance. However, the performance of EKF algorithm dramatically decreased when initializations (initial state assumption) were not near to real values, which in this condition UKF method provided a more accurate approximation. Numerical results from simulations show that the UKF is robust against uncertainties and has better state estimation accuracy. Therefore, UKF algorithm is appropriate, and it can run on target tracking systems.

In the current paper, the results of a numerical simulation that were verified by a well instrumented experimental procedure for studying the arching effect over a trapdoor in sand is presented. To simulate this phenomenon with continuum mechanics, the experimental procedure is modeled in ABAQUS code using stress dependent hardening in elastic state and plastic strain dependent frictional hardening-softening with Mohr Coulomb failure criterion applying user sub-routine. The apparatus comprises of concentric circular trapdoors with different diameters that can yield downward while stresses and deformations are recorded simultaneously. As the trapdoor starts to yield, the whole soil mass deforms elastically. However, after an immediate specified displacement, depending on the diameter of the trapdoor, the soil mass behaves plastically. This behavior of sand occurs due to the flow phenomenon and continues until the stress on trapdoor is minimized. Then the failure process develops in sand and the measured stress on the trapdoor shows an ascending trend. This indicates gradual separation of the yielding mass from the whole soil body. Finally, the flow process leads to establish a stable vault of sand called arching mechanism or progressive collapse of the soil body.

Incremental dynamic analysis (IDA) requires the analysis of non-linear response history of a structure for an ensemble of ground motions, each scaled to multiple levels of intensity and selected to cover the entire range of structural response. Recognizing that IDA of practical structures is computationally demanding, an approximate procedure based on the reduction of the number of ground motions is developed. A methodology based on data envelopment analysis (DEA), mathematical programming that can handle large numbers of variables and relations, is proposed to reduce the number of ground motions needed for the production of a reliable median IDA curve. The IDA curves computed by the exact and approximate procedures for two different sets of ground motions for the 9 storey SAC-Los Angeles building are presented. The results demonstrate that the approximate procedure, which uses a limited number of input ground motions, is accurate enough for practical application in building evaluation and design.

In this paper, we focus on the application of reinforcement learning to obstacle avoidance in dynamic environments in wireless sensor networks. A distributed algorithm based on reinforcement learning is developed for sensor networks to guide mobile robot through the dynamic obstacles. The sensor network models the danger of the area under coverage as obstacles, and has the property of adoption of itself against possible changes. The proposed protocol can integrate the reward computation of the sensors with information of the intended place of robot so that it guides the robot step by step through the sensor network by choosing the safest path in dangerous zones. Simulation results show that the mobile robot can get to the target point without colliding with any obstacle after a period of learning. Also, we discussed about time propagation between obstacle, goal, and mobile robot information. Experimental results show that our proposed method has the ability of fast adoption in real applications in wireless sensor networks.

Directional overcurrent relays (DOCRs) are widely used to protect power systems. For optimal coordination of DOCRs, several techniques have been proposed to solve this problem. A common way of optimal coordination of DOCRs is using evolutionary algorithms such as genetic algorithm (GA). In this paper, a novel strategy for DOCRs coordination is proposed. In the proposed strategy, a new objective function (OF) is introduced. The proposed objective function can removed mis coordination between paired relays and can result in better coordination. Proposed OF is applied to 6 bus and 30-bus sample networks.

The purpose of this paper is to extend a new balancing and ranking method to handle uncertainty for a multiple attribute analysis under a hesitant fuzzy environment. The presented hesitant fuzzy balancing and ranking (HF-BR) method does not require attributes’ weights through the process of multiple attribute decision making (MADM) under hesitant conditions. For the rating of possible alternatives, firstly, they are defined as hesitant fuzzy terms and then converted into hesitant fuzzy sets. Second, an outranking matrix indicates that a possible alternative overcomes the other alternatives regarding to each chosen attribute. Third, the outranking matrix is triangularized which means that we prepare provisional order of possible alternatives or implicit preordering under hesitant conditions. Eventually, the empirical order of alternatives goes through variant operations of balancing and screening that needs continuous application of a balancing axiom to the advantages–disadvantages table. It links incompatible attributes with pair-wise comparisons of the possible alternatives for the multiple attribute analysis. Finally, we present an application example for the supplier selection to show the applicability and feasibility of the proposed HF-BR method in the hesitant fuzzy setting.

Sometimes the quality of a process or product is described by a functional relationship between a response variable and one or more explanatory variables referred to as profile. In most researches in this area the response variable is assumed to be normally distributed. However, occasionally in certain applications, the normality assumption is violated. In these cases, the Generalized Linear Models (GLM) such as Gamma regression models are used to characterize the profile. Also, in statistical process control finding the real time of change in process, called as change point, is necessary because it leads to saving time and cost in finding assignable cause(s). Therefore, in this paper we considerGamma regression profile and use maximum likelihood to estimate the real time of a step change in Phase II. We evaluate accuracy and precision of the proposed change point estimator by simulation. The results show that the proposed change point estimator is effective in estimating the real time of step shifts in the process parameters of Gamma regression profiles. Also, a confidence set for the process change point based on the logarithm of the likelihood function is presented. Finally, the performance of the estimator is illustrated through a real case.

Two nondestructive electromagnetic techniques, hysteresis loop and eddy current methodologies, have been used to characterize the microstructural changes of D2 tool steel in the course of quench and tempering treatments. To measure the retained austenite fraction in the quenched microstructure, six specimens were austenitized in the range of 1000-1130 °C. Samples austenitized at 1080 °C were also tempered in the range of 200-650 °C for characterization by eddy current and magnetic hysteresis loop outputs.. Impedance point movement and maximum differential permeability were measured as a function of austenitizing/tempering temperature to characterize the microstructural features. The study showed that good correlations exist between microstructural variations detected by destructive methods (hardness, XRD and microscopic observation) and outputs of the nondestructive techniques.

Clearances in the joints are inevitable in practicedue to tolerances, and defects arising from design and manufacturing. In the presence of clearance at a joint, a mechanism gains some additional, uncontrollable degrees of freedom which are the source of error. Moreover, joints undergo wear and backlashes and so cannot be used in precision mechanisms. In this study, the dynamic behaviour of a planar mechanism with revolute joints, in the presence of clearances is investigated. A continuous contact force model, based on the elastic Hertz theory together with a dissipative term, is used to evaluate the contact forces. Moreover, using a new contact model,the dynamic characteristics of planar mechanical system with multiple revolute joints in the presence of clearance are analyzed. Numerical results for four-bar linkage with one, two and three revolute clearance joints are presented and compared.

In this research, effects of excess air ratio and waste gate opening pressure threshold on NOx emission and performance in a turbocharged CNG SI engine are experimentally studied at 13-mode ECE-R49 test cycle. The engine power, boost ratio and charge air temperature are investigated experimentally at the cycle for different waste gate pressure thresholds. A code is developed in MATLAB environment for predicting engine performance and NOx and the results are validated with the research experiments. The effects of excess air ratio on the engine indicated power and specific fuel consumption as well as NOx emission are numerically investigated at WOT by the code. NOx emission of WOT is max at excess air ratio of 1.1. Simulation reveals that higher excess air ratio at a rate of 20% decreases maximum indicated power 9% and improves minimum ISFC 7%. Experiments indicate that brake power augments with increase of the pressure threshold especially at high loads and speeds due to higher boost ratio. It is also found that changing the threshold from 16 mmHg to 200 and 265mmHg decreases total bsNOx at rate of 6 and 12%, respectively. The threshold increase to 323mmHg augments total bsNOx. Therefore, the threshold of 265mmHg is optimum threshold among the four pressure thresholds experimented.

A micro combustor is one of important devices in heat generation to power miniaturized products such as microrobots, notebook computers, micro-aerial vehicles and other small scale devices. An integrated micro combustor with thermophotovoltaic (TPV) in a micro-size electric generator supplies electricity to these micro devices. There is a growing interest in developing micro combustors as a power source due to their inherent advantages of higher energy density, higher heat and mass transfer coefficients and shorter recharge times compared to electrochemical batteries. A new micro combustion concept is described in this work by introducing a new terminology in the micro combustion. The effects of Area to Volume Ratio (AVR) of the micro-combustors were studied to find the best performance of designed micro-combustors. In order to test the feasibility of the designed micro combustors before the actual experiment is conducted, simulation work was performed. There are three key parameters involved in the current study: Area to Volume Ratio (AVR), Flow Velocity of the mixture (u), and Fuel-Air Equivalent Ratio (Ø). Main results of this experiment are images of temperature contour, graphs of temperature distribution profile, and graphs of mean temperature profile. This study found there is a specific range of mixture flow velocity (0.50 – 0.56 m/s) which result a high and uniform temperature distribution as well as its best mean temperature of micro combustion process. The simulation work could also localized the specific range of AVR-value (1.40 – 2.01) which require further investigation in the future.

This paper investigates the fault detection of a micro parallel plate capacitor subjected tononlinear electrostatic force. For this purpose, Thau observer, which has demonstrated good performance in fault detection of nonlinear systems,as well asgoverning nonlinear dynamic equation of the capacitor,is presented. Upper and lower threshold for fault detection have been obtained. The robustness of the observer to noise, uncertainty as well as sensitivity to faults wasinvestigated. Finally, simulation results for fault detection of the capacitor are obtained and the ability of the observer in the vicinity of dynamic pull-in voltage has been checked.

Split-hom together structure is a new heavy load rack structure, and its reliability needs to be verified. Through analyzingmultimodal hom-connection principle from the perspective of bionics and contact mechanics, the article establishes the finite element and mathematical model of the rack. Modal analysis has been done for the finite element model in the prestress state, whose results indicate the reliability of the rack. While numerical simulation is applied to the mathematical model of the rack for the first time in the working state. The results show that the deformations in two ways are almost at the same and meet the demand. Meanwhile, through the minimum frequency of the modal analysis is different from the result of the numerical simulation, the frequency in two states is higher than the workingfrequency. So, the results validate the reliability of the design on split-hom together rack.

A new computational technique is presented to find the optimal base position of dual arm robots in order to carry maximum allowable load. The maximum allowable load on a desired trajectory is limited by the number of factors such as; actuators torque limits, kinematic constraints, and kinematic redundancy of cooperative manipulators. For a dual arm robot mounted on a rail or table, load workspace (LWS) is introduced as the unionof places where the base can locate and robots carry a load on a desired trajectory. It is possible to increase the maximum allowable load by replacing the base of the arms robots in the LWS. By dividing the LWS into grid points, the base position of the railmounted dual arm robot considered at each point. Using the Newton-Euler formulation and appropriate procedure, maximum allowable load of the robots in all points of the LWS are computed. Then, by iteration, a smaller subspace near to optimum base position is selected until maximum allowable load and corresponding base position is found with acceptable precision. Finally, the application of the proposed algorithm is presented and verifiedfor two different cases.

This research presents the study on Manganese oxide (MnO2), Zinc oxide (ZnO), Iron oxide (Fe2O3) and Magnesium chloride (MgCl2) used as activated fluxes to find out its effects on SS 304 in Tungsten Inert Gas (TIG) welding. The Ultimate tensile strength, percentage elongation, Penetration depth, width and depth to width ratio of SS 304 have been studied. The experiment indicates that the use of MnO2 and Fe2O3 as flux increases the weld penetration depth and decrease the weld width. The use of ZnO and MgCl2 as flux also shows a little increase in penetration depth and weld depth to width ratio as compared to conventional TIG process. The ultimate tensile strength and the percentage elongation have been increased in Activated Flux TIG welding.

In this paper, the transverse vibration of cracked nano-beam has been studied based on modified couple stress theory. Crack is modeled by a rotational spring that creates a discontinuity. First, transverse vibration equation of cracked nano-beam is derived along with its general response. Then, the frequency parameters are calculated for different crack positions, different lengths of the beam, different length scale parameter, different crack properties, and some typical boundary conditions. Results indicate that the effects of the crack parameter and crack location on transverse frequency of the cracked nano-beam are quite significant. In addition, scale effect parameter is one of the important parameters in nanoscale that must be taken into account. Finally, the results of special cases with simple support boundary condition for classic and nonlocal theories are compared with those available in the literature.

In this paper, the effects of rigid triangular passive vortex generators on a hydrofoilwere investigated numerically. In the first step, using the Finite Volume Method forbare hydrofoil was modeled. Also, the results of lift and drag coefficients were validated using experimental data. In the next step, the hydrofoil equipped with vortex generators was modeled. So, its effect on the hydrofoil performance was examined. In the next step,by introducing a source term into the momentum equation the effect of vortex generators was considered. Their geometry, however, was completely removed. The results showed that this can significantly decrease the computational memory and calculation time. Furthermore, the results revealed that the use of vortex generators can delay the stall conditions by increase the stall angle leading to a higher lift coefficient in new stall angleand decreasing the drag coefficient. In a case study on NACA 0012 section profile results showed that the use of vortex generators increases the stall angle by 4 degrees and the lift coefficient at this point by 37%.

In the design of high Quality factor (Q) micro or nano beam resonators, different dissipation mechanisms may have damaging effects on the quality factor. One of the major dissipation mechanisms is the thermoelastic damping (TED) that needs an accurate consideration for prediction. In this paper, TED of the longitudinal vibration of a homogeneous micro beam with both ends clamped have been investigated. A Galerkin method has been used to analyze TED for the first mode of vibration of the micro beam. Then the quality factor and longitudinal vibrations frequency are obtained. Changing of quality factor versus geometrical properties and ambient temperature for different materials are plotted.

A simple method is proposed to model the open cracked beam structures. In this method, crack is modeled as a beam element. Hence cracked beam can be assumed to be a beam with stepped cross sections, and problem of determining natural frequency and mode shape of cracked beam, can be solved as determining these characteristics for a beam with different lengths and cross sections. With this work, it is not necessary to model crack as lumped flexibility model in according to fracture mechanics and related sciences to obtain crack stiffness, and this spring model of crack can be used for further analysis.