Sharif Digital Repository

In this paper, we introduce a new method and new motion variables to study kinematics and dynamics of a 6 d.o.f cable-driven robot. Using these new variables and Lagrange equations, we achieve new equations of motion which are different in appearance and several aspects from conventional equations usually used to study 6 d.o.f cable robots. Then, we introduce a new Jacobian matrix which expresses kinematical relations of the robot via a new approach and is basically different from the conventional Jacobian matrix. One of the important characteristics of the new method is computational efficiency in comparison with the conventional method. It is demonstrated that using the new method instead... 

Segmentation of aerial images has been a challenging task in recent years. This paper introduces a simple and efficient method for segmentation and classification of aerial images based on a pixel-level classification. To this end, we use the Gabor texture features in HSV color space as our best experienced features for aerial images segmentation and classification. We test different classifiers including KNN, SVM and a classifier based on sparse representation. Comparison of our proposed method with a sample of segmentation pre-process based classification methods shows that our pixel-wise approach results in higher accuracy results with lower computation time  

This paper considers scheduling tasks while minimizing the power consumption of one or more processors, each of which can go to sleep at a fixed cost α. There are two natural versions of this problem, both considered extensively in recent work: minimize the total power consumption (including computation time), or minimize the number of "gaps" in execution. For both versions in a multiprocessor system, we develop a polynomial-time algorithm based on sophisticated dynamic programming. In a generalization of the power-saving problem, where each task can execute in any of a specified set of time intervals, we develop a (1+23α) -approximation, and show that dependence on α is necessary. In... 

In this paper, we present a new method to solve tracking problem. The proposed method combines sparse representation and motion estimation to track an object. Recently. sparse representation has gained much attention in signal processing and computer vision. Sparse representation can be used as a classifier but has high time complexity. Here, we utilize motion information in order to reduce this computation time by not calculating sparse codes for all the frames. Experimental results demonstrates that the achieved result are accurate enough and have much less computation time than using just a sparse classifier  

We investigate the efficiency of a parallel direct simulation Monte Carlo (PDSMC) algorithm in solving the rarefied subsonic flow through a nanochannel. We use MPI library to transfer data between the processors. It is observed that PDSMC solver shows ideal speed up if sufficient workload is provided for each of processors. Additionally, this study shows that the computational time and speed up of the extended PDSMC solver do not depend (or slightly depend) on the number of cells. In contrary, increasing the total number of particles would result in a better efficiency of the PDSMC  

In this paper, we propose a new method for mobile robot path planning in dynamic environment when the trajectories of obstacles are unknown. Our algorithm first utilizes a global approach called clearance based probabilistic roadmap method to find a suitable path and then locally apply evolutionary algorithm to keep the structure of the path when obstacles collide with the path. As a result, the path will act like an elastic band. To reach real time applicability, a light fitness function is proposed compare to other genetic algorithms to reduce the computation time needed for calculating and repairing path. Simulation results show that our method not only can keep the original structure of... 

In this study an analytical model based on solving Maxwell equations in the machine layers is presented for linear resolver (LR). Anisotropy, field harmonics, slot effects, number of slots per pole per phase and the effect of tooth skewing are considered in the model. The proposed method is a design oriented technique that can be used for performance prediction and design optimisation of the LR due to its acceptable accuracy and fast computation time. Two- and three-dimensional time stepping finite element method (FEM) is employed to validate the results of the proposed model. Good correlations between the results obtained by the proposed method and the FEM confirm the superiority of the... 

In this paper, employing recorded images of multiple cameras, we propose a novel fast approach for three-dimensional (3D) human pose reconstruction. Opening a new framework to the pose estimation application, the proposed method is inspired by optical 3D reconstruction algorithms conventionally used for integral imaging. Thanks to the fact that the pose estimation can be carried out by using only key features of the raw recorded images, the computation time and the complexity of our method are considerably reduced. Furthermore, utilizing the here proposed algorithm, rapid variations in actions can be easily tracked. The validity of the proposed method is demonstrated by several experimental... 

In this paper we propose a fast iterative reconstruction algorithm for microwave-induced thermoacoustic (TA) imaging. Instead of calculating the forward and back projections in real time, we construct a library of the impulse responses of individual pixels in advance. During reconstruction, only covariance calculations are performed to reconstruct the intensity of each pixel. In addition, we propose to use a Wiener filter based-deconvolution to accelerate convergence, enabling even single iteration construction in some scenarios. We validate the proposed method both with simulations as well as experiments. Compared to the time reversal method, the proposed fast iterative reconstruction... 

An efficient multi-static millimetre-wave (MMW) imaging system is proposed with the aim of obtaining the information of an axially tilted object. It is known that a multi-static structure performs better than a mono-static array in detecting the reflected signal from axially tilted surfaces due to the specular reflection. Still, no efficient multi-static structure for the purpose of imaging tilted objects in view of the computational time, cost and image quality is proposed till now. The authors propose an efficient multi-static MMW imaging system tackle this issue with the minimum number of antennae. Furthermore, the small number of antennae in the proposed design and the proposed fast... 

In this work, we attempted to develop an Implicit Coupled Density-Based (ICDB) solver using LU-SGS algorithm based on the AUSM+ up scheme in OpenFOAM. Then sonicFoam solver was modified to include viscous dissipation in order to improve its capability to capture shock wave and aerothermal variables. The details of the ICDB solver as well as key implementation details of the viscous dissipation to energy equation were introduced. Finally, two benchmark tests of hypersonic airflow over a flat plate and a 2-D cylinder were simulated to show the accuracy of ICDB solver. To verify and validate the ICDB solver, the obtained results were compared with other published experimental data. It was... 

Cell formation and cellular layout design are the two main steps in designing a cellular manufacturing system (CMS). In this paper, we will present an integrated methodology based on a new concept of similarity coefficients and the use of simulated annealing (SA) as an optimization tool. In comparison with the previous works, the proposed methodology takes into account relevant production data, such as alternative process routings and the production volumes of parts. The SA-based optimization tool is parallel in nature and, hence, can reduce the computation time significantly, so it is capable of handling large-scale problems. Finally, the SA-based procedure is compared with a genetic... 

Vehicle routing problem is one of the complex and NP-hard problems, which plays a crucial role in this hectic world regarding people's lifestyle. Nowadays, many people provide their stuff online, so a logistic problem has been outstripped for companies to reduce their transportation costs. In this article, a novel approach has been introduced, which can solve the multi-depot vehicle routing problem in shorter time. By using clustering and decomposing the main problem into smaller ones, solution time has been dropped dramatically. In addition, this approach obtains a reasonable cost, which can be considered as fuel consumption, distance, or so forth. This method could reduce the solution time... 

Linear resolvers are position sensors that are being used in a wide range of applications for linear motion systems. The electromagnetic design of a linear resolver, similar to any other electromagnetic device, demands an accurate, functional, and fast tool. While the finite element method (FEM) is considered the most accurate tool for electromagnetic analysis, it is not a good candidate for an optimization-based design which is an iterative process. In this article, first off, an analytical tool based on the subdomain model is briefly presented. This model is very accurate and much faster than FEM. However, it has high computational time for iterative design and optimization processes.... 

The curve of exhaled inert gas concentration against exhaled volume is called gas washout curve. The slope at the end part of gas washout curve (Sn) is a measure of structural abnormalities. Sn depends on the spatial concentration distribution and dynamic of gas washout, which depends on several mechanisms including asymmetry of airways, nonhomogeneous ventilation, sequential emptying, and gas exchange with blood. Due to a large number of airways in human lungs, using simplified models is inevitable. On the other hand, these simplified models cannot capture some of the mentioned mechanisms and subsequently were not able to predict experimental trend of change in Sn with breath number in... 

The curve of exhaled inert gas concentration against exhaled volume is called gas washout curve. The slope at the end part of gas washout curve (Sn) is a measure of structural abnormalities. Sn depends on the spatial concentration distribution and dynamic of gas washout, which depends on several mechanisms including asymmetry of airways, nonhomogeneous ventilation, sequential emptying, and gas exchange with blood. Due to a large number of airways in human lungs, using simplified models is inevitable. On the other hand, these simplified models cannot capture some of the mentioned mechanisms and subsequently were not able to predict experimental trend of change in Sn with breath number in... 

Multiscale finite volume (MSFV) method have been developed and applied in various complicated physics. The most important advantage of MSFV method is its computational efficiency. In this paper we present a new set of boundary condition for calculation of basis and correction functions which leads to further reduction in computational time in problems with medium heterogeneity and therefore improves computational efficiency. In standard MSFV (sMSFV) method reduced boundary condition is used to determine the basis and correction functions which is based on local information, however in modified MSFV (mMSFV) method global information is used at initial time for constructing boundary condition... 

This paper introduces a novel methodology for design and assessment of offshore structures exposed to irregular sea waves. For this, Constrained NewWave (CNW) is integrated with the Endurance Time Analysis (ETA) methodology, which is basically developed for the performance based analysis of onshore structures to earthquake loads. In this approach, the offshore structure is simulated in time-domain under a set of calibrated intensifying wave functions. They are devised to represent a gradually increasing roughness of the sea state by time. A performance index such as base shear, drift or stress in a critical structural members are monitored until they reach to a predefined maximum value. A... 

The development of a synthetic model of a pregnant woman abdomen with amniotic fluid and a fetus is discussed comprehensively in this paper. The model is intended to be used for studying the light propagation through physical 3D model of pregnant woman in reflectance mode. To construct the model, reported dimension values of body curvature in 26 and 28 weeks of pregnant woman are being used as main references. Although slightly adjustments have been made to the body dimensions, the values are still within the range of reference values. Optical simulation has been performed in order to test the model capability. Given the reasonable computational time and encouraging preliminary results, the... 

Finite Element Method (FEM) has proved to be a powerful tool for the analysis of mechanical problems such as finding natural frequency and deformation of structures. Design and implementation of super elements with a purpose in reduction of computational time along with accuracy is one of the challenges facing engineers in the past decade. In this study a newly spherical super element is designed and implemented to some problems. This element is generated in such a way that the user can select as many numbers of nodes as desired. Proper formulation is presented to generate the shape function for each node in this element. Some examples of static and vibration analysis using this element are...