فهرست مطالب

Scientia Iranica
Volume:18 Issue: 1, 2011

  • Transactions B: Mechanical Engineering
  • تاریخ انتشار: 1390/03/02
  • تعداد عناوین: 7
  • M.M. Ettefagh, M.H. Sadeghi Page 59
    In this paper, a new method of gear fault diagnosis is proposed based on a combination of the time synchronized averaging method (TSA), time-varying ARMA model and MARTIN distance. This method contains three major steps. In the first step, a TSA method is proposed for averaging the gearbox signal. The second step deals with selection of a proper ARMA model for a signal produced via a gearbox and using an adaptive filter (with a weighted least square algorithm) for identifying the time-varying parameters of the model. In the last step, a new time-varying distance is defined for gear fault diagnosis. The proposed distance is an extension of the MARTIN distance. Finally, as the case study, the method is used on a YAMAHA gearbox for identifying gear faults. The results of the diagnosis are satisfactory.
  • M. Fadaei, H. Vafadar, A. Noorpoor Page 66
    The results of a thermo-mechanical analysis of a natural gas, internal combustion engine cylinder head are presented in this paper. The results are pertinent to the evaluation of overheating damage in critical areas. The three-dimensional geometries of the cylinder head and the water jacket were modeled by means of a computer-aided engineering tool. Commercial finite element and computational fluid dynamics codes were used to compute details of mechanical stress in the head and flow details in the cylinder and cooling jacket, respectively. A six-cylinder, four-stroke diesel engine and a spark-ignition natural gas engine were modeled over a range of speeds at full load. Computed results, such as maximum allowable cylinder pressure, output power, BMEP and BSFC, were validated by experimented data in the diesel engine model. The results were in good agreement with experimental data. The results show high stresses at the valve bridge. Cylinder head temperatures and comparison of output power with high stress measurements, often exceeding the elastic limit, were found at the valve bridge.
  • H. Sayyaadi, M.R. Doostmohammadian Page 75
    There are many practical situations where it is desirable or even required to achieve stable convergence in the finite-time domain. In this paper, a simple distributed continuous-time protocol is introduced that guarantees finite-time consensus in networks of autonomous agents. Protocol convergence in weighted directed/undirected and fixed/switching networks is explored based on a Lyapunov analysis. The stability of the system and the solvability of the consensus algorithm are proved for network topologies that contain a spanning tree frequently enough over contiguous time intervals. The decision value for different topologies and for multi-rate integrator agents is investigated, and a novel approach is proposed to determine the leader subgroup of agents. Communication time-delay and chattering phenomenon in the system are assessed, and additionally some protocols with Lipschitz right-hand sides are introduced. Herein, all proposed consensus strategies use a limited-gain control input to account for the physical limitation of control actuation devices, which, in general, are subject to amplitude saturation.
  • M.R. Homaeinezhad, A. Ghaffari, H. Najjaran Toosi, R. Rahmani, M. Tahmasebi, M.M. Daevaeiha Page 86
    The aim of this study is to develop and describe a new ambulatory Holter electrocardiogram (ECG) events detection–delineation algorithm via segmentation of an information-optimized decision statistic. After implementation of appropriate pre-processing, a uniform length sliding window is applied to the pre-processed trend and in each slide, some geometrical features of the excerpted segment are calculated to construct a newly proposed Discriminant Analyzed Geometric Index (DAGI), by application of a nonlinear orthonormal projection. Then the α-level Neyman–Pearson classifier is implemented to detect and delineate QRS complexes. The presented method was applied to several databases and the average values of sensitivity and positive predictivity, Se=99.96% and P+=99.96%, were obtained for the detection of QRS complexes, with an average maximum delineation error of 5.7 ms, 3.8 ms and 6.1 ms for P-wave, QRS complex and T-wave, respectively. Also the method was applied to DAY general hospital high resolution holter data (more than 1500,000 beats, including Bundle Branch Blocks-BBB, Premature Ventricular Complex-PVC, and Premature Atrial Complex-PAC) and average values of Se=99.98% and P+=99.97% were obtained for QRS detection. High accuracy in a widespread SNR, high robustness and processing speed (146,000 samples/s) are important merits of the proposed algorithm.
  • A. Mirbagheri, F. Farahmand, A. Meghdari, F. Karimian Page 105
    A robotic system was designed and developed to perform the camera handling task during laparoscopic surgery. The system employs an effective low cost mechanism, with a minimum number of actuated DOFs, enabling spherical movement around a remote centre of motion positioned at the the insertion point of the laparoscopic stem. Kinematic analysis showed a high manipulability measure for the system, with the left/right movements directly governed by rotation of the first rotary actuator, and zoom and up/down movements by the simultaneous motions of the linear and second rotary actuators. A prototype of the robot was developed for practical use in an operating room environment. Hands-free operator interfaces were implemented for user control, including a voice command recognition system and a smart 6-button foot pedal. The technical and operational features of the system were evaluated using experimental examinations and then during clinical trials of laparoscopic cholecystectomy on human subjects. Results indicated a high trajectory following accuracy, low response time, sufficiently large workspace for surgeon and assistants, and a stable and properly oriented image. The system was found to be easy to set up and use, and contributed to a faster and more accurate surgical operation.
  • M.A. Hosseini, H.M. Daniali Page 115
    In the presence of positioning and orienting tasks, the singular values of Jacobian matrices have different units, thereby making it impossible to order them and calculate the associated condition numbers. Here, this dimensional in-homogeneity is resolved by introducing a weighting factor. In this method, both the Jacobian and twist vector are made homogeneous, simultaneously. Moreover, relations between the weighting factors used here to the homogeneous Jacobian matrices derived by others are given. This factor should be constant throughout the workspace, while it is pose dependent in the latter methods. As a case study, both methods are applied to a Tricept parallel manipulator with complex degrees of freedom. A local conditioning index, as a dexterity index, is plotted in the workspace. Although both methods lead to homogeneous Jacobian matrices, obvious differences between the plotted local conditioning indices are revealed here. Therefore, those homogeneous Jacobian matrices derived by others, and the associated dexterity indices are unreliable.
  • M.H. Korayem, A. Kavousi, N. Ebrahimi Page 121
    The Atomic Force Microscope (AFM) scans the topography of a sample surface using a micro-sized flexible cantilever. In tapping-mode AFM, the tip–surface interactions are strongly nonlinear, rapidly changing and hysteretic. This paper explores, numerically, a flexible beam model that includes attractive, adhesive and repulsive contributions, as well as the interaction of the capillary fluid layers that cover both the tip and the sample in ambient conditions common in experiments. Forward-time simulation has been applied with an event handling numerical technique for dynamic analysis, and the Amplitude–Phase–Distance (APD) curves have been extracted. The branches of periodic solutions are found to end precisely where the cantilever comes into grazing contact with event surfaces in state space, corresponding to the onset of capillary interactions and the onset of repulsive forces associated with surface contact. The dissipated power, in the presence of conservative tip–sample interaction forces where the source of hysteresis is the formation and rupture of a liquid bridge between the tip and the sample, has been measured too. This simulation provides a more accurate way to validate the design of a new AFM probe and AFM controller than simulations which use the lumped-mass model.