Transactions of the Canadian Society for Mechanical Engineering
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Volume 35 (2011), Issue 1
Structural optimization algorithm for vehicle suspensions
Marc J. Richard, Mohamed Bouazara, Laouhari Khadir, Guoqiang Q. Cai
Stringent tolerances on mechanical components have created increasingly severe demands on the quality of new mechanical designs. The mathematical models used to analyze the various types of mechanical systems these days need to incorporate an optimization algorithm capable of minimizing the levels of vibrations coming from varied sources. The suggested method is based on the parallel combination of three methods; the Rayleigh-Ritz approach (to determine the first eigenfrequencies) which is incorporated into an efficient multicriterion optimization process based on the ESO (Evolutionary Structural Optimization) method and the finite element software ABAQUS. The analytical resolution and the numerical calculations of the mechanical component are, finally, validated by an experimental set-up which exploits a frequency analyser, acceleration sensors and an excitation hammer. The effectiveness of this approach is also demonstrated in the analysis of an upper car suspension arm. By gradually removing material from the initial car suspension design, the frequency of the component can be controlled in order to optimize the structural constraints.
The design of eddy-current magnet brakes
Der-Ming Ma, Jaw-Kuen Shiau
The eddy-current is created by the relative motion between a magnet and a metal (or alloy) conductor. The current induces the reverse magnetic field and results in the deceleration of motion. The proposed mechanism implements this phenomenon in developing a braking system. The potential applications of the braking system can be a decelerating system to increase the safety of an elevator or any guided rail transportation system. To provide scientific investigation for industrial application of magnetic braking, this study presents four systematic engineering design scenarios to design a braking system. The constant magnetic field is the simplest and easiest design to implement. The optimal magnetic field distribution is obtained by minimizing the deceleration effort. The piecewise-constant magnetic field distribution offers a compromise between performance and magnetic field requirements. The advantages of the section-wise guide rail are tolerable deceleration; and simple design requirement and manufacturing processes. In the study, an experimental braking system using constant magnetic field is build to demonstrate the design procedure.
Simulation of vortex sound using the viscous/acoustic splitting approach
Ting H. Zheng, Shiu K. Tang, Wen Z. Shen
A numerical viscous/acoustic splitting approach for the calculation of an acoustic field is applied to study the sound generation by a pair of spinning vortices and by the unsteady interaction between an inviscid vortex and a finite length flexible boundary. Based on the unsteady hydrodynamic information from the known incompressible flow field, the perturbed compressible acoustic terms are calculated and compared with analytical solutions. Results suggest that the present numerical approach produces results which are in good agreement with the analytical solutions. The present investigation verifies the applicability of the viscous/acoustic approach to flow structure-acoustic interaction.
A new four-bar linkage completing delassus’ findings
Jacques M. Hervé
In 1922, E. Delassus found out four-bar linkages including parallel screw joints (or helical pairs), which are movable with one degree of freedom. The Delassus linkages can move only when geometric conditions based on the Euclidean metric are achieved; their mobility is said to be paradoxical. Delassus stated that there is no paradoxical four-bar linkage with three helical H pairs and one prismatic P pair. In fact, Delassus did one error of logical deduction. After the error detection, the paper introduces a new HHHP linkage with a paradoxical mobility. Its three H axes are parallel and intersect a plane that is orthogonal to the H axes in three points forming an isosceles triangle. The P pair is parallel to the triangle side, which has a variable length. The three pitches have to satisfy one scalar relation. Through the consideration of helical trajectories in relative motions, the new mechanism is related to a geometric property of the right helicoid. Helices with a pitch that is half the helicoid pitch can be drawn on the right helicoid.
Modeling and multi-objective optimization of forward-curved blade centrifugal fans using CFD and neural networks
Abolfazl Khalkhali, Mehdi Farajpoor, Hamed Safikhani
In the present study, multi-objective optimization of Forward-Curved (FC) blade centrifugal fans is performed in three steps. In the first step, Head rise (HR) and the Head loss (HL) in a set of FC centrifugal fan is numerically investigated using commercial software NUMECA. Two meta-models based on the evolved group method of data handling (GMDH) type neural networks are obtained, in the second step, for modeling of HR and HL with respect to geometrical design variables. Finally, using the obtained polynomial neural networks, multiobjective genetic algorithms are used for Pareto based optimization of FC centrifugal fans considering two conflicting objectives, HR and HL.
Vibrations of a rotor system with multiple coupler offsets
Chao-Yang Tsai, Shyh-Chin Huang
In this paper, a transfer matrix method (TMM) for rotors with multiple coupler offsets was derived. The studies showed the coupler’s stiffness altered the rotor’s critical speeds but offset caused additional external excitation. The cases of two offsets in- and anti-phase in a typical rotor were given as examples. In the in-phase case, significantly increased response amplitude occurred at lower rotational speed and the increase was linearly proportional to the offset value. As to the anti-phase case, the increased response was insignificant, implying an opposite offset would cancel out a major response of the previous offset. The whirling orbits before and after the offset couplers were also illustrated. The results, as expected, showed the in-phase offset displayed much larger radii than the anti-phase’s. The rotor’s orbits changed the whirling direction once the rotation fell within a certain range and this feature seemed to be unaffected by coupler offsets.
Performance evaluation and wake study of a micro wind turbine
Graeme I. Comyn, David S. Nobes, Brian A. Fleck
In preparation for a study on icing of wind turbine blades, we tested a horizontal axis micro wind turbine in a low speed wind tunnel. The ratio of wind turbine rotor area to wind tunnel cross-sectional area resulted in highly blocked experimental configuration. The turbine was instrumented to measure rotational speed of the rotor, axial thrust and power output. Performance characteristics were calculated and compared with the manufacturer’s published data. In addition, the near wake of the turbine was measured with a Kiel probe. One dimensional axial momentum theory, including a modification that includes channel walls, was applied to determine power extracted from the wind by the rotor. The results were compared to actual power output and show that though the assumptions of the model over-predict power by 50 % the basic trend is followed.
Hydraulic design and analysis of the saxo-type vertical axial turbine
Edvard Höfler, Janez Gale, Anton Bergant
The paper presents a procedure for hydraulic design and analysis of the blade geometry of a high specific speed runner of the Saxo-type double-regulated vertical axial turbine. The meridional through-flow in the passage from the conical guide vane apparatus to the draft-tube elbow is designed by a streamline curvature method (SCM). To validate the design method and predictions and to investigate the design duty point and a number of off-design operating regimes, an extensive CFD simulation inside the entire turbine water-passage is performed. The flow patterns downstream the guide vane apparatus and the runner exit flow are analyzed. The focus of the analysis is on distribution of the angular momentum alongside the turbine, as well as on its impact on the flow around the runner blades. The SCM design procedure presented in the paper proves to be a robust and accurate tool for the runner blade row design.
Full journal title: Transactions of the Canadian Society for Mechanical Engineering
Abreviated journal title: Trans. Can. Soc. Mech. Eng.
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