Transactions of the Canadian Society for Mechanical Engineering
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Volume 39 (2015), Issue 2
Modeling of surface stress effects on the dynamic behavior of actuated non-classical nano-bridges
Hamid M. Sedighi
The influence of surface stress and small scale on the dynamic pull-in behavior of nano-bridges is investigated in this paper. For this purpose, the governing equation of motion is derived based on the modified couple stress theory and Homotopy Perturbation Method with an auxiliary term is employed to produce the approximate solution of nano-beam vibrations. The effects of actuation voltage, initial conditions, surface energy and length scale parameter on the pull-in instability and fundamental frequency of the system are studied. The accuracy of proposed asymptotic approach is validated with numerical simulations. The obtained results from asymptotic analysis reveal that two terms in series expansions are sufficient to produce an acceptable approximation. The nano-actuator dynamics exhibit periodic and homoclinic orbits.
Controlling boundary layer transition over a separation bubble: A complex-lamellar approach
Maureen L. Kolla, Jeffrey W. Yokota
In this paper, we develop a complex-lamellar description of the incompressible flow that exists as a boundary layer transitions from a fully developed laminar to fully developed turbulent flow. This complex-lamellar description is coupled to the shape of the universal intermittency distribution and experimental correlations to obtain a boundary layer model of transition. This transition model is used to analyze the effects of several different freestream turbulence levels on the reattachment location and the length of the resulting separation bubbles. Furthermore, we show that at the separation bubble reattachment location, the resulting boundary layer flow is both turbulent and fully developed. Results obtained from this transition model are compared with, and verified by several different DNS simulations.
Optimal design for a composite wind turbine blade with fatigue and failure constraints
Adam Chehouri, Rafic Younes, Adrian Ilinca, Jean Perron, Hassan Lakiss
The search for more efficient and sustainable renewable energies is rapidly growing. Throughout the years, wind turbines matured towards a lowered cost-of-energy and have grown in rotor size therefore stretched the role of composite materials that offered the solution to more flexible, lighter and stronger blades. The objective of this paper is to present an improved version of the preliminary optimization tool called Co-Blade, which will offer designers and engineers an accelerated design phase by providing the capabilities to rapidly evaluate alternative composite layups and study their effects on static failure and fatigue of wind turbine blades. In this study, the optimization formulations include non-linear failure constraints. In addition a comparison between 3 formulations is made to show the importance of choosing the blade mass as the main objective function and the inclusion of failure constraints in the wind turbine blade design.
Investigating the effect of sloshing on the energy absorption of tank wagons crash
Reza Razaghi, Majid Sharavi, Mohammad Mahdi Feizi
One of the main fluid mechanics phenomena is fluid sloshing which is originated from the free surface of fluid and should be taken into account in design of fluid structures such as fuel tank wagons, ships and so on. The aim of this paper is to investigate the effect of tank fluid sloshing on energy absorption and reducing tank acceleration during the tank wagon impact. For this purpose, methods of software simulation and dynamics solution methods are accomplished. The assumed wagon includes a tank with the approximate volume of 95 m³ and capacity of 65 tons of fluid. Using finite element method, the tank impact is simulated based on the corresponding standards for different heights of fluid in the tank. Obtained results show fluid height increase has an inappropriate effect on energy absorption among impact however the more fluid in tank, the more time would be consumed for energy absorption in general. At the end, by using crash test results for a tank with aforementioned scale, validity of impact software simulation and dynamic solution method considering the tank fluid as mass-spring model are checked.
Adaptive neural network control of a human swing leg as a double-pendulum considering self-impact joint constraint
Yousef Bazargan-Lari, Mohammad Eghtesad, Ahmad R. Khoogar, Alireza Mohammad-Zadeh
For human walking, the swing leg is usually modeled as a double pendulum. Considering a joint self-impact constraint at the knee joint of the double pendulum model is the main difference in this study. The primary objective of this research is to propose a nonlinear Adaptive Neural Network (ANN) for this system. By using Gaussian RBF networks, asymptotically stable tracking is attained. We will use the available data of normal human walking for the desired trajectories of the hip and knee joints. By simulation of the system, we perceive that the swing leg tracks the normal human gait with a negligible and tolerable error.
2015-07-17 Tribological properties of a new kind of friction-promoting grease in sliding point contacts
Wan Ma, Zhen C. Zhu, Yu X. Peng, Guo A. Chen
In this paper, the tribological properties and the film-forming properties of the friction-promoting grease (FPG) A under point-contact conditions were investigated by conducting respectively four-ball experiments and FPG A-lubricated ball-and-disc contact experiments. The experimental results indicate that the coefficient of friction (COF) decreases with an increase in the rotating speed at a constant load; FPG A has a good film-forming ability and a good adhesion property; the application of FPG A under hoistís normal operation conditions could greatly protect the contact surfaces from wear and supply a sufficient COF.
Experimental verification of a practical digital driver with switched gain-tuning for five-phase stepping-motors
Keisuke Yagi, Noriyuki Hori, Meyer Nahon
A digital driver that has a switched self-tuning gain in its current regulator is designed for five-phase stepping motors so that their performance could be improved and adjusted more easily, than with an analog driver. The regulator has a fixed gain block in its feedback loop and an adjustable gain in the feedforward path, replacing the integrator and the high gain that were required in previous designs to achieve good steady-state performance and fast response. Extensive experiments have been conducted under typical and extreme actuation conditions, and revealed that the proposed driver performs better than the analog drivers or their discretized equivalents, especially in eliminating undershoots, which were problematic with previous drivers.
Analysis of joint failures on the lateral undulation gait of a robotic snake
Rishad A. Irani, Robert J. Bauer, Lydia North, Michael Nicholson, David Nolan, Brennan West
This paper describes the development of a biologically-inspired hyper-redundant wheeled snake robot and a corresponding computer simulator to study the effects that joint failures have on the resulting lateral undulation motion. Experiments and corresponding simulations were carried out to study the robotic snakeís lateral undulation gait as power to individual joints was turned off. The results showed that joint failures were most detrimental to the snakeís lateral undulation gait when they occurred in the front half of the snake, while joint failures occurring between the midpoint and tail of the robotic snake were found to be less critical and generally resulted in slight lateral drifts as the forward motion progressed. To help compensate for joint failures in the tail-half part of the robot, a bias term was added to the control algorithm. For the conditions tested in this research, the use of a bias term appeared to be effective at reducing the lateral drift.
Analyses of free convection flow of an inclined plate embedded in a double layer porous medium
Nabil Ibrahim Beithou
Porous media offer wide practical applications, such as the use of the porous medium in solar water desalination systems to enhance water evaporation or condensation. Water condensation represents half of the desalination process. This study presents a simulation for the condensation process with double porous layers. This problem is simulated as the natural convection from an inclined plate embedded in a double layer porous medium; the plate was subjected to a constant wall temperature with variable layers thickness, permeability ratio and different plate angles. The effects of these parameters on the temperature distribution and total heat transfer were investigated. It has been found that the heat transfer rate increases with increasing the permeability ratio. Also increasing the layers thickness ratio in low permeability ratios, or keeping the layers ratio as minimum in the high permeability ratios are favorite. The inclination angle affects negatively the rate of heat transfer due to the buoyancy effect.
Research on flexible drill string vibration induced by sonic harmonic excitation
Changgen Bu, Long Sun, Yuanbiao Hu, Bairu Xia
The undisturbed sampling of the overburden soil is attracting increased attention due to the rapid increases in the construction of large-scale domestic foundations and environmental protection engineering. To date, systematic theoretical research on sonic drilling technology has rarely been published. In the present paper, the vibration response induced by sonic harmonic excitation is studied by modeling the flexible drill string of a sonic drill; its dynamic theory and design methodology have been developed, which reveal effects of the excitation frequency, the structural parameters on vibration response of the drill string. The study of sonic drill string vibration is beneficial for improving the drilling efficiency and reducing the damage.
Wall-interference correction for the surface-pressure hysteresis of an airfoil undergoing plunging motion
Mohammad Saeedi, Mahmoud Mani, Armin Hamta
In the current research, the results of a number of wind-tunnel experiments on a moving airfoil with plunging motion are presented. The experiments have been conducted in two different configurations which are tunnels with conventional and slotted test-section walls to provide resemblance to a far-field condition. The difference in results obtained from two test-section configurations can be considered as the wall effect and regulated as a function of non-dimensional parameters which can be further used for correcting experimental results obtained from conventional wind tunnels. When the derived correction factor is applied to a numerical simulation of a wind tunnel with a conventional test section (for points located in the front portion of the airfoil), the resulting pressure variations closely resembled that of a far-field numerical simulation. This methodology showed promising results for the specific configurations used in this research.
Multidimensional dissipation technique for an AUSM scheme on triangular grids
Numerical instability of the AUSM scheme on two-dimensional structured triangular grids is investigated. By examining several test cases, it is found that both numerical flux formulations of the AUSM scheme (so-called the AUSM-M1 and AUSM-M2 schemes) do not have sufficiently robustness to satisfy the shockinduced anomaly so called the carbuncle phenomenon. The modified multidimensional dissipation technique is then proposed in order to heal such shock instability. The dissipation mechanism against perturbations is investigated by applying a linearized discrete analysis to the odd-even decoupling problem. The recursive equations show that the dissipation factor (δ) plays an important role in all perturbations of the AUSM-M1 scheme. But it does not have any effect on the density perturbation of the AUSM-M2 scheme. Finally, the scheme is further extended to achieve the second-order solution accuracy and evaluated theirs robustness against shock instability by solving several test cases.
Surface roughness and cutting forces in turning of tool steel with mixed ceramic and cubic boron nitride cutting tools
Tool steel has been widely used, especially to manufacture forming dies and molds by machining processes. Generally, cubic boron nitride (CBN) and ceramic tools are recommended for finish machining a specific steel. This study contributes to filling the research gap for the selection of low- content CBN tools or mixed ceramic tools for turning of hard tool steel. The turning tests were conducted to determine the performance of CBN and the mixed ceramic tools in turning soft (HRC22) and hard (HRC52) H13 tool steel with different cutting speeds, feed rates and depths of cut. ANOVA was used to determine the interaction of the cutting parameters on the surface roughness and cutting forces obtained from turning tests. The results indicate that the surface roughness in hard turning was lower with the CBN tool than with the ceramic tool. On the other hand, the cutting forces in turning with the ceramic tool were lower. Acceptable regular chip formation increases with the cutting speed for each tool.
Hydrodynamic calculations of rotating Weis-Fogh type water turbine with the advanced vortex method
In this study, a rotating-type water turbine model applying the principle of the Weis-Fogh mechanism is proposed, and its hydrodynamic characteristics calculated by an advanced vortex method. The unsteady flow and pressure fields around the wing for two revolutions were calculated by changing the uniform flow and maximum opening angle of the wing. The maximum efficiency for one wing of the water turbine was 45.3% at the maximum opening angle of the wing 36° and velocity ratio 2.0. The flow field of the water turbine is very complex because the wing rotates and moves unsteadily in the channel. However, using the advanced vortex method, accurate calculations were possible.
Effects of slip on the Von Kármán swirling flow and heat transfer in porous medium
Bikash Sahoo, Sébastien Poncent, Fotini Labropulu
Numerical solutions are obtained for the fully coupled and highly nonlinear system of differential equations, arising due to the steady Kármán flow and heat transfer of a viscous fluid in a porous medium. The conventional no-slip boundary conditions are replaced by partial slip boundary conditions owing to the roughness of the disk surface. Combined effects of the slip λ and porosity γ parameters on the momentum and thermal boundary layers are studied in detail. Both parameters produce the same effects on the mean velocity profiles, such that all velocity components are reduced by increasing either λ or γ The temperature slip factor β has a dominating influence on the temperature profiles by decreasing the fluid temperature in the whole domain. The porosity parameter strongly decreases the heat transfer coefficient at the wall for low values of β and tends to an asymptotical limit around 0.1 for β ≅ 10. The porosity parameter γ increases the moment coefficient at the disk surface, which is found to monotonically decrease with λ.
Full journal title: Transactions of the Canadian Society for Mechanical Engineering
Abreviated journal title: Trans. Can. Soc. Mech. Eng.
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