bluuebunny/crossref_metadata_2025 huggingface dataset:
On Novel Operation Cycle of Freeze Dryer in P-T Diagram
Authors: Shahdi K. , Ayatollahi M. R. , Ghafoori Ahangar R.
Published: January 2011

In this paper, a comparison between a common and a novel prototype of freeze dryer has been considered. A freeze dryer does the action of drying based on freezing the product fluid in low pressure along with a sudden phase change. Using correct assumptions, the freezing heat, freezing time, drying time, and vacuum creating time have been calculated. The freeze dryer was designed in CATIA software based on a new P-T diagram cycle. The novel design is able to work as hot-air dryer and also vacuum dryer, as well as freeze dryer in vacuum. No need to extra refrigerator and the use of separate cycle for drying are two advantages of the novel design. A comparison between the capabilities of the classical and the novel designs suggests that the use of novel design as a domestic device would satisfy the users.
Multicriterion Offline Path Planning of a Biomimetic Underwater Vehicle Using NSGA II
Authors: Ataei Mansour , Yousefi-Koma Aghil , Shariat Panahi Masoud
Published: January 2011

In this paper an optimal 3-D path is generated offline for a Biomimetic Underwater Vehicle (BUV). The BUV swims forward by oscillating its body, turns by curving its body and dives by bending its head. The BUV is intended to systematically plan its path having only the initial and final points and the positions and dimensions of the obstacles. The four widely-accepted criteria of the optimal path planning of the BUV are “overall path length”, “margin of safety”, “smoothness of planar motion” and “gradient of dive”. In this study the multi-objective GA algorithm NSGA-II is employed to find a set of Pareto-optimal solutions where each solution represents a path that cannot be outrun by any other path considering all four criteria. The solution set, also called the Pareto front, gives the designer the freedom of choice when it comes to prioritizing various criteria.
Influence of Swirl Number on NOX Formation in a Turbulent Non-Premixed Flame
Authors: Zeinivand H. , Bazdidi-Tehrani F.
Published: January 2011

A numerical simulation of swirling methane/air non-premixed flame (TECFLAME swirl burner) in a two-dimensional model combustion chamber is carried out to assess the influence of entrance flow swirl number on temperature distribution, flow behavior and NO pollutant formation. A Finite Volume staggered grid approach is employed to solve the governing equations. The second-order upwind scheme is applied for the space derivatives of the advection terms in all transport equations. The eddy dissipation-finite rate model is employed to predict the heat release and the Reynolds stress turbulence model is applied to simulate the flow behavior. NO formation is modeled as a post-processing solution. NO formation prediction has reasonable agreement with experiments for smaller swirl numbers but with the increase of swirl number, deviations between numerical results and the experimental data increase. It may be due to incorrect prediction of temperature distribution in higher swirl numbers. With the increase of swirl number, maximum temperature of chamber decreases from 1900 (K) to 1650 (K). With temperature decline, NO concentration in the exhaust decreases from 27 (ppm) at swirl number of 0.7, to 4 (ppm) at swirl number of 2. On the other hand, with increase of swirl number, ratio of prompt NO formation to thermal NO increase rapidly. In another word, with decrease of flame temperature, prompt NO roles increase noticeably.
An Optical Fuzzy Control Servo System for Biomedical Specimen Inspections
Authors: Lee Fu-Shin , Lin Chang-Li
Published: January 2011

The object of this research is to build an optical servo inspection system by integrating optical acquisition mechanisms and controlling algorithm to perform auto biomedical specimen inspections. The system applies a fuzzy control algorithm to exercise optical zooming, focusing, and sectioning functions on the inspected specimens. The paper also utilizes the MATLAB/SIMULINK platform to implement the fuzzy logic controller, and a NI multi-function data acquisition board to deliver control signals, which minutely displace the optical lenses system to execute prescribed functions. The optical system consists of an image focusing subsystem, which receives processed sharpness values of captured images, a con-focal pinhole aperture subsystem, which holds a pinhole to allow only light beams from in-focus plane specimen images to pass through, and a piezoactuator, which serves to minutely displace a plate with the pinhole to perform the optical biopsy function. As to accomplish the optical biopsy goal, the biomedical sample images on slightly differentiated focus depth planes are therefore acquired separately according to calculated image sharpness values.
Comparison of Implicit Time Integration Schemes for Nonlinear Dynamic Problems
Authors: Demiral Murat
Published: January 2011

Implicit time integration schemes are used to obtain stable and accurate transient solutions of nonlinear problems. Methods that are unconditionally stable in linear analysis are sometimes observed to have convergence problems as in the case of solutions obtained with a trapezoidal method. On the other hand, a composite time integration method employing a trapezoidal rule and a three-point backward rule sequentially in two half steps can be used to obtain accurate results and enhance the stability of the system by means of a numerical damping introduced in the formulation. To have a better understanding of the differences in the numerical implementation of the algorithms of these two methods, a mathematical analysis of dynamic equilibrium equations is performed. Several practical problems are studied to compare the implicit methods.
Finite Element Simulation of Non-Isothermal Fluid Flow Past a Staggered Tube Bank
Authors: Alavi S. Mahmood Aboulhasan
Published: January 2011

In this paper the two-dimensional, non-isothermal fluid flow past a staggered tube bank is analyzed numerically by the finite element method. The flow is assumed to be incompressible, laminar and unsteady. To stabilize the discretized equations of the continuity and momentum, the streamline upwind/Petrov-Galerkin scheme is employed and the energy equation is solved using the Taylor-Galerkin method too. The computational domain for ten tubes in the direction of flow is meshed by using the four noded-quadrilateral elements. Equilateral-triangle (ET) tube pattern is considered for staggered tube bank. Reynolds numbers of 100, 200 and 300, Prandtl number of 0.71, and pitch-to-diameter ratios (PDR) of 1.25, 1.5 and 2.0 are chosen for the investigation. Having obtained the flow and the temperature fields, the local skin friction coefficient and the local Nusselt number are calculated for the tubes in the bundle at different times. A comparison of the results of the present study with the results of experiments of other investigators, for the steady-state case, shows good agreement between them.
Construction of a Prediction Model for an Acceptable T-Shape Tube Product in Magnesium Alloy Hydro-Forming
Authors: Lin S. Y. , Chang C. M. , Shyu R. F.
Published: January 2011

The finite element method in conjunction with abductive neural network is applied to predict an acceptable T-shape product of which the minimum wall thickness and the protrusion height being fulfilled the industrial demand in the magnesium alloy hydro-forming. AZ31 magnesium alloy circular tube is used as the billet material for hydro-forming with hydraulic pressure as the main forming power combined with the mechanically auxiliary force from the punch to fabricate a qualified T-shape tubing product. Finite element software is adopted to investigate the forming characteristics of T-shape tube forming, by changing process parameters such as punch velocity, hydraulic pressure, fillet radius of the die and tool-workpiece interface friction etc. to investigate the material flow of tube forming, and the variations of wall thickness and protrusion height. And the neural network method in turn is applied to synthesize the data sets obtained from the numerical simulations and a prediction model for an acceptable T-shape tube product in magnesium alloy hydro-forming is thus constructed. From the prediction model, a suitable range of the process parameters variation for producing those qualified T-shape tubes that may be accepted in industrial applications can thus be identified.
Experimental and Numerical Analysis of Fatigue Properties Improvement in a Titanium Alloy by Shot Peening
Authors: Bagherifard Sara , Giglio Marco , Giudici Lorenzo , Guagliano Mario
Published: January 2011

Shot peening (SP) is a mechanical surface treatment commonly performed to improve the fatigue behavior through creation of compressive residual stresses close to surface and work hardening of the surface material. Notwithstanding wide application of shot peening in the industrial environment, the determination of optimal peening condition for Ti alloys is still more an art than a science, taking into account that there is not a well established method to choose the process parameters in order to enhance the fatigue behavior. In this paper a comprehensive numerical and experimental study is presented aimed at finding the optimized peening conditions based on characterization of surface layer of material after multiple impacts. The numerical simulations provide a quantitative description of shot peening effects in terms of residual stress field and thickness of work-hardened surface layer. Comparison with numerical results, obtained by means of X-ray diffraction (XRD), shows a very good correspondence. Finally the results of experimental bending fatigue tests, performed on shot peened specimens by means of Rumul Cracktronics machine, confirm that shot peening significantly increases the fatigue strength of the considered Titanium alloy.
Towards “Green Tribology”: Self-Organization at the Sliding Interface for Biomimetic Surfaces
Authors: Nosonovsky Michael
Published: January 2011

“Green tribology” is the concept that was introduced in 2009 by the founder of Tribology, Prof. P. Jost, who defined it as “the science and technology of the tribological aspects of ecological balance and of environmental and biological impacts.” This includes tribological technology that mimics living nature (biomimetic surfaces) and thus is expected to be environment-friendly, the control of friction and wear that is of importance for energy conservation and conversion, environmental aspects of lubrication and surface modification techniques, and tribological aspects of green applications such as the wind-power turbines, tidal turbines, or solar panels. It is clear that a number of tribological problems could be put under the umbrella of “green tribology” and is of mutual benefit to one another. Biomimetic applications are of particular interest for the Green Tribology, because of their environment-friendliness. Nosonovsky and Bhushan suggested the “12 principles of the Green Tribology.” The common feature in various biomimetic surfaces is their hierarchical structure and the ability for self-organization. I will discuss the principles of self-organization in hierarchical tribological systems on the basis of the concepts of the non-equilibrium thermodynamics (the Onsager formalism). In particular, I will show that the thermodynamic approach in tribology can yield new and practically important results.
Trajectory Planning for Tricycle Mobile Manipulator With Moving Boundary Conditions Using Optimal Control Approach
Authors: Korayem Moharam H. , Abolhasani Mojtaba , Azimirad Vahid , Ansari Hassan
Published: January 2011

In the present paper optimal path of the tricycle nonholonomic robot with two-link manipulator, obeying a particular equation with moving boundary conditions is obtained. These boundary conditions are a set of points that are called the moving boundaries. One of the main applications of this method is handling and transporting parts from one place to another by employing the aid of robot with cable strip. For example, for putting the tools and industrial parts in proper places in the product line, the reductions of time, cost and energy are guaranteed by a precise schematization and defining the best path. The methodology uses optimal control for finding optimum path. To do this, the dynamics and kinematic equations of robot are derived. Then by applying the optimal control method and Pontryagin’s minimum principle lead to deriving optimal conditions as a set of differential equations. Finally, will be solvable a boundary value problem. The formulation of the moving boundary for the tricycle robot using the optimal control includes state and co-state equations that replace the boundary conditions of the problem in the constant boundary state. As a result, solving the optimal path with moving boundary for minimization leads to obtaining a cost function that includes velocities and torques. Lastly, the simulation results of tricycle robot with two-link spatial mobile manipulator and moving boundary condition are presented that shows the accuracy and capability of the method.
On Active Diagnostics Method for Assessment of Technical Condition of Nuclear Facility Components
Authors: Spirochkin Yury , Odintsev Igor , Atroshenkov Roman
Published: January 2011

An active diagnostics method intended for identification of technical condition of pipelines and other components of nuclear facilities is considered. This method is based on detection of structural anomalies in components by observing changes in static and dynamic behavior of component structure which are registered during special tests. Static behavior is analyzed as response to time-independent mechanical or temperature loading. Dynamic behavior can be analyzed through studying fields of vibration displacements, velocities and accelerations when sinusoidal mechanical oscillations are generated. Structural anomalies can be presented as deviations of stiffness, geometry and inertial parameters from their nominal (design) values. Impact of these deviations on structural response may be bigger in spatial scale than anomaly dimensions. Therefore there is a theoretical possibility to detect structural anomaly in the areas which are inaccessible for direct observing by registration of structure response parameters in observable areas. The paper describes the theoretically basis and results of the experimental and numerical studies on detection of a hidden crack-like anomaly in pipe components. Experimental study of dynamic and static response is carried out by coherent optical methods, and numerical analysis — by finite element method. Theoretical and experimental data have a good agreement and allow to reveal anomaly position and to estimate roughly its dimensions. Application of the method to welded joint in pipe specimen which corresponds to real nuclear facility pipeline is under investigation now.
Load Effects on the Dynamics of Spur Gear Transmissions
Authors: Fernandez del Rincon Alfonso , Viadero Rueda Fernando , Iglesias Santamaria Miguel , Garcia Fernandez Pablo , de-Juan de Luna Ana , Sancibrian Herrera Ramon
Published: January 2011

Gear transmissions in general and spur gears in particular exhibit a different dynamic behavior depending on the level of the transmitted load. This fact justifies the interest in the study of the role of the load in gear dynamics not only in the context of design, vibration and noise control but also for condition monitoring. This task requires the development of advanced models achieving a compromise between accuracy and computation time. In this work, gear and bearing non-linearities associated with the contact among teeth and roller elements have been included, taking into account the flexibility of gears, shafts and bearings. Besides, parametric excitations coming both from gear and bearing supports, as well as clearance, were also considered. Gear contact force calculations are carried out following a hybrid approach which combines both analytical and numerical tools. This lets to achieve accurate results with an acceptable computational effort and thus dynamic analysis becomes feasible. This approach was improved and the calculation speeded up from the point of view of computational time. This was performed by using a pre-calculated value for gear tooth stiffness as a function of load and the angular position when it operates under stationary conditions. On the other hand, bearings were formulated just as deflections of Hertzian type. This means that bending and shearing of races and rolling elements are neglected. However, the variation in the number of loaded rolling elements as a function of the load and the angular position was taken into account. Shaft flexibilities were added to gear and bearing models to define a simple transmission that was used to study the vibratory behavior under different levels of applied torque. In a preliminary study, this model was linearized for several loads, obtaining the corresponding frequencies and mode-shapes in order to assess their variation with this parameter. Finally, dynamic simulations were carried out, showing the modifications undergone by the orbits, meshing contact forces and transmitted bearing forces.
Multi-Objective Optimal Design of a Passenger Car’s Body
Authors: Adl Amir Hosein , Shariat Panahi Masoud
Published: January 2011

The body of a passenger car roughly constitutes 25–30% of its overall weight. Any reduction in the weight of the car’s body would not only mean less materials and fuel to be consumed, but also less exhaust emissions to be released and less non-biodegradable materials to be dumped or recycled. However, the automotive industry’s desire for an increasing weight reduction of passenger cars is inevitably limited by other design considerations such as mechanical strength, overall stiffness of the body, durability, safety and corrosion resistance. The problem of weight minimization can be expressed in the form of a constrained, multi-objective optimization problem in which the weight of the body and its fatigue life constitute the conflicting cost functions and values of such critical performance parameters as body’s natural frequency forms the constraint set. The above optimization problem poses a challenge to the designer, as the weight, fatigue life and natural frequency of the geometrically complex body cannot be readily evaluated and a comprehensive numerical model, such as a Finite-Elements (FE) one, has to be employed. This numerical model would nonetheless be highly time-consuming, especially considering the need for re-assessing the model dozens, and sometimes hundreds, of times per iteration of the optimization algorithm. To avoid this, we use a neural approximation of the FE model to reduce the time and computational cost. Results of a finite number of FE simulations are used to train the Multi-Layer Perceptron (MLP) neural network which will then be used as the evaluation engine of the optimization algorithm. An efficient computer code based on the improved Non-dominated Sorting Genetic Algorithms (NSGA II) is used to find the Pareto set of distinct solutions. The designer would then be able to choose from a set of non-dominated, feasible solutions based on economical and/or logistics requirements at an early stage of the design process.
Noise Immunity of Carbon Nanotube Based Switches
Authors: Rasekh M. , Khadem S. E. , Tatari M.
Published: January 2011

In this paper, two terminals, doubly clamped, nano-switch has been studied. Here the interest of this study is the situation in which the pull-in and pull-out voltages not be same as each other and the pull-in/pull-out trend follows a hysteresis loop. This property could be used to introduce a double threshold switch with greater stability or noise immunity. With only one input threshold, a noisy input voltage signal near that threshold could cause the output to switch rapidly back. The model comprises a clamped-clamped carbon nanotube (CNT) suspended over a graphite ground electrode plate from which a potential difference is imposed. The actuation is based on DC applied voltages and it is assumed that the neutral axis of bending is stretched when the beam is deflected, and also, due to closeness of the substrate and the CNT, the van der Waals interaction forces between CNT and ground plate is considered. The versatile Galerkin’s method is employed to reduce the nonlinear integral-partial-differential equation of motion to a nonlinear ordinary differential equation in time, and then, the reduced equation is solved by direct numerical integration. The pull-in/pull-out phenomena, hysteresis characteristic are studied. The obtained results are compared to Molecular Dynamic (MD) method. Eventually, a nano-switch immune to input noise is proposed which relies on the hysteresis characteristic of the system. The proposed CNT-based nano-switch can operate in nano-scale electronics similar to the well known Schmitt trigger circuit in classical electronics. When the input voltage is higher than a certain pull-in voltage threshold, the output of the switch is in “ON” state; when the input voltage is below the pull-out voltage threshold, the output is in “OFF” state; when the input voltage is between the two threshold values, the output retains in the previous state.
Analysis of Manufacture Errors for Space Truss With Bolted Spherical Joints Base on Monte Carlo Method
Authors: Guo Yongwei , Wang Qiming , Gu Xuedong
Published: January 2011

The active reflector of the five-hundred-meter aperture sphere radio telescope (FAST) is constituted by about 4600 triangular reflector elements, whose surface error will determine the telescope’s antenna efficiency. One solution is a grid structure backup with the bolted spherical joints, in which the surface accuracy is dominated mainly by the length accuracy of the rods in it. In this paper, an accuracy analysis based on Monte Carlo method is proceeded to predict the surface error. Random errors are input the rods, and the surface errors in root mean square (rms) are output. After the calculations, the final accuracy’s probability distribution charts are given for the different error inputs. And a relationship chart between rod length error and final accuracy is given to help determining the most reasonable rod length error. To solve the position of the grid structure, an iteration method is deduced. The relationship between joints and rods in the frame structure which is described as a graph, is presented by adjacency list. Forces on joints are balanced at the beginning, but when rod length errors are input, forces to pull or push the joints are yielded. The process of moving their positions to make the forces balance again is the process to solve the surface accuracy. An existing reflector element model was measured. The measurement verified the analysis. Finally, the proper accuracy of rods length error is given. It is useful for cost controlling and time keeping in FAST design, for the possibility to achieve a qualified surface by controlling the manufacture error of rods reveals that the reflector elements maybe avoid adjustment and can be mounted to the telescope directly. The method to predict accuracy can be generalized for the other grid structures.
Second Law Analysis of Nanofluid Flow Through Circular Pipe
Authors: Shokouhmand H. , Moghaddami M. , Siavashi M.
Published: January 2011

This paper aims to numerically investigate the effects of adding nanoparticles on the entropy generation of water-Al2O3 nanofluid flows through a circular pipe under constant wall temperature also constant heat flux thermal boundary conditions in laminar regime. Approved formulations of mixtures are used for density and specific heat of the nanofluids. Nanofluid model proposed by Koo and Kleinstreuer [1] based on experimental data of Das et al. [2] is employed for conductivity of the nanofluids and an experimental correlation presented by Rea et al. [3] is used to model the viscosity of the nanofluid. The problem has been simulated numerically using a CFD finite-volume code and results are validated with the available experimental data. It is found that for the case of constant heat flux boundary condition, adding nanoparticles decreases the entropy generation and improves the thermal performance of water-Al2O3 flow. Moreover optimum Reynolds number to minimize the ratio of nanofluid entropy generation number to water is obtained for this case. For the case of wall constant temperature boundary condition, adding nanoparticles to water leads to heat flux increase, therefore the entropy generation number remains approximately constant.
New Approach to Linear and Nonlinear Stability Analysis of Drill String
Authors: Jafari Ali Asghar , Kazemi Reza , Faraji Mahyari Mohammad
Published: January 2011

In this research, a new approach for stability analysis of drill string is investigated. To this goal, the potential energy of drill string for axial and lateral vibrations is written in an integral equation. In this equation, the effect of geometrical shortening, which causes nonlinear coupling between axial and lateral vibration, is considered. The work done by WOB force and weight of drill string is calculated. The finite element method is employed to convert the integral potential energy of the continuous system to a discrete one. The effects of stabilizers are modeled by dropping the nodes coincided with them. Dropping and considering third and fourth order tensor of potential energy lead to linear and nonlinear stability analysis, respectively. Taking the first order derivative of discrete potential energy, the equilibrium position of drill string can be found. Taking second order derivative, the stability of the equilibrium position can be analyzed. Illustrated results demonstrate that as the length of hole is increased, the differences between linear and nonlinear cases become larger. This analysis shows the working condition of drill string is stable or not. These results can be used to obtain safe working conditions in drilling progress.
Design Strategy of a High Pressure Regulator
Authors: Shahani Amir R. , Aryaei Ashkan , Najar Mosayeb , Mohammadi Sirvan , Esmaili Hamid
Published: January 2011

The main purpose of this paper is to design a high pressure regulator which reduces an input pressure varying between 400 to 500 bars to 350 bars constant pressure. First of all, for mathematical simulation of regulator’s performance, the related equations were derived. Because of nonlinearity and coupling, these equations were solved by using numerical methods. Also, the effects of different parameters variation on regulator performance were investigated. One of the most important parameters in regulator performance is the preload of control spring. Deriving the maximum and minimum values of the spring force from the mathematical simulation, the proper spring was designed. In the next step, Finite element analysis, considering thermal effects, was performed using commercial software ABAQUS. To achieve sufficient safety factor, thicknesses were specified by trial and error. The results were in good agreement with the analytical solution.
Stress Analysis of an Isotropic Plate Containing Three Aligned Circular Holes Under In-Plane Symmetric Loading
Authors: Asmar Ghazi H. , Chakar Elie A.
Published: January 2011

This paper presents a method for the calculation of the stresses around three non-intersecting identical circular holes in a row, in a thin and infinite isotropic plate subjected to in-plane longitudinal, transverse or biaxial tension at infinity. The calculation of the stresses around any of the three holes is obtained in terms of the stresses that would exist around and at the center of the contour of a third would-be hole in the plate, initially, containing two holes. The results from the present method are compared to finite element as well as to published results in the literature. It is seen that the method yields satisfactory results at key points around the contour of the holes.
Muscle Synergies Based on a Biomechanical Biaxial Isometric Shoulder Model Minimizing Fatigue
Authors: Nassajian Moghadam Mohamadreza , Aminian Kamiar , Asghari Mohsen , Parnianpour Mohammad
Published: January 2011

In this study we utilize the concept of synergy formation as a simplifying control strategy to manage the high number of degrees of freedom presented in the maintenance of the posture of the shoulder joint. We address how to find the muscle synergy recruitment map to the biomechanical demands (biaxial external torque) during an isometric shoulder task. We use a numerical optimization based shoulder model to obtain muscle activation levels when a biaxial external isometric torque is exposed at the shoulder glenohumeral joint. In the numerical simulations, different shoulder torque vectors parallel to the horizontal plane are considered. For each selected direction for the torque, the resulting muscle activation data are calculated and then used for grouping muscles in some fixed element synergies by nonnegative matrix factorization method Next, the muscle synergies are converted from activation level to the torque space to see how muscle synergy recruitment addresses the torque production in a specific direction at the shoulder joint. The results confirmed our expectation that the few dominant synergies are sufficient to address the torque vectors in directions which coincide to the basic vectors of torque space, such that each muscle contributed to more than one synergy.
Convective Heat Transfer Enhancement With Nanofluids: The Effect of Temperature-Variable Thermal Conductivity
Authors: O¨zerinc¸ Sezer , Yazıcıog˘lu Almıla G. , Kakac¸ Sadık
Published: January 2011

A nanofluid is defined as the suspension of nanoparticles in a base liquid. Studies in the last decade have shown that significant amount of thermal conductivity and heat transfer enhancement can be obtained by using nanofluids. In the first part of this study, classical forced convection heat transfer correlations developed for pure fluids are used to predict the experimental values of heat transfer enhancement of nanofluids. It is seen that the experimental values of heat transfer enhancement exceed the enhancement predictions of the classical correlations. On the other hand, a recent correlation based on the thermal dispersion phenomenon created by the random motion of nanoparticles predicts the experimental data well. In the second part of the study, in order to further examine the validity of the thermal dispersion approach, a numerical analysis of forced convection heat transfer of Al2O3/water nanofluid inside a circular tube in the laminar flow regime is performed by utilizing single phase assumption. A thermal dispersion model is applied to the problem and variation of thermal conductivity with temperature and variation of thermal dispersion with local axial velocity are taken into account. The agreement of the numerical results with experimental data might be considered as an indication of the validity of the approach.
Dynamics of Rupture at Frictional Rough Interfaces During Sliding Initiation
Authors: Di Bartolomeo Mariano , Massi Francesco , Meziane Anissa , Baillet Laurent , Culla Antonio
Published: January 2011

The aim of this work is to present the results from a non linear finite element analysis in large transformations of the contact interface between two deformable bodies when sliding initiates and the roughness is introduced at the contact surfaces. The two-dimensional in-plane dynamic model consists of two different isotropic elastic media separated by an interface governed by Coulomb friction law, and subject to remotely applied normal and shear tractions (pre-stress phase). Once the ratio between the local values of tangential and normal stresses reaches the limit value, the sliding initiates and local ruptures are activated (nucleation phase). The propagation of the ruptures over the interface and the wave propagation inside the solids are analyzed. The interactions between the waves propagating into the two solids (P waves, shear waves, surface waves) give raise to different types of ruptures. They can be classified depending on their velocity front (sub-Rayleigh, sub-shear, super-shear) or on their interface states (pulse-like, crack-like). A sinusoidal roughness is introduced at the contact surfaces and the analysis is performed for different values of the roughness parameters. Depending on the relative dimension between the roughness wavelength and the width of the wave fronts, two different behaviour can be observed: i) a coupling between the wave propagating into the two bodies; ii) a decoupling of the wave propagation inside the two materials, characterized by an independent wave propagation. First the wave propagation is analyzed when a single rupture is originated in pre-sliding conditions; successively, the wave generation during sliding initiation is addressed.
Monte Carlo Simulation of Spine Geometry From T12 to Sacrum in Males
Authors: Komeilizadeh Koushiar , Asghari Mohsen , Junno Juho-Antti , Parnianpour Mohamad
Published: January 2011

In biomechanical modeling of spine, the prediction of spinal loading during occupational activities is crucial in assessment of the risk of low back pain and injury of spine. Current biomechanical models are based on the average data. Hence, they are unable to predict the effects of the observed natural anatomical variations on muscles moment arms and lines of action, while these variations ultimately influence the required muscular forces for balancing the external moments of any given task. In this work, a methodology based on the Monte Carlo technique has been developed to simulate spine geometry from T12 to S1 vertebrae for males. The lordosis of the assembled spine ranged between 21° to 63° with an average equal to 42.2°, which is within the reported values in the literature. Obtained data could be used as an input to equilibrium/stability based biomechanical spine models to assess the contribution of different geometry. This model is intended to merge with our stochastic spine model of spine to test the effects of various sources of variability on spinal loadings and its risk of failure.
Synthesis of Nanostructure MoSi2 Powder by Mechanically Assisted Self-Propagating High-Temperature Synthesis
Authors: Meshkizadeh R. , Abdollahpour H. , Honarbakhsh-Raouf A.
Published: January 2011

Nanostructured MoSi2 powder has been successfully synthesized by Ball milling of Mo and Si powder mixtures and subsequent self-propagating high-temperature synthesis (SHS) process. It was observed that in comparison with the normally mixed powder, it could be easily ignited and higher combustion temperature was achieved. Based on XRD and SEM, it was confirmed that nanostructure MoSi2 powder could be prepared through self propagating combustion method from the mechanical activated powder mixture.
Performance Analysis of Planar Cable-Based Parallel Manipulators
Authors: Zanotto Damiano , Rosati Giulio , Rossi Aldo
Published: January 2011

In the last two decades, many research works have been published on cable-based systems, reflecting the considerable interest of the scientific community in this area. Cables are used both in serial structures, to remotely actuate rigid links, and in parallel structures, to directly control the motion of a mobile platform or end-effector. The latter subclass is particularly appealing, thanks to ease of design, high payload-to-weight ratio, potentially high dynamic performances and wide workspace. Such devices have also been effectively employed in haptics, since the use of light-weight elements allows to develop structures with low mechanical impedance. Unilateral actuation represents a major issue in the study of cable-based devices, often forcing to adopt specially formulated design tools. This paper presents a set of performance indices, some of which are introduced here for the first time, that can be used for the optimization of the design and for the analysis of cable-based devices. To prove the effectiveness of these tools, a comparison of the kinematic and dynamic performances of three different designs of planar cable-based parallel manipulators is presented.
Entropy Generation Minimization of Confined Nanofluids Laminar Flow Around a Block
Authors: Boghrati Mehdi , Ebrahimnia Bajestan Ehsan , Etminan Vahid
Published: January 2011

According to the importance of cooling and heating process of a solid object, entropy generation in confined flow around a block is studied. In the current study, numerical simulation of laminar flow and heat transfer of nanofluids with nanoparticles of different shapes is considered. The nanofluids are water mixture with either Al2O3 nanoshperes or carbon nanotubes (CNTs). The incompressible Navier-Stokes and energy equations are solved numerically in a body fitted coordinates system using a control volume technique. The flow patterns and temperature fields for different values of the particles concentrations are examined in detail. Furthermore, the effects of nanoparticles shape and concentration on the heat transfer are studied. Furthermore the influences of nanofluids on pressure drop and pump power is examined. On the other hand, the entropy generation minimization is considered as the optimization criterion. The results indicate that in most cases the nanofluids enhance the heat transfer as well as pressure drop. It is interesting to note that the shape of nanoparticles is critical in determining the key mechanism of heat transport in nanofluids. Nanofluids with cylindrical nanoparticles exhibit a greater increase in heat transfer compared with nanofluids having spherical shape nanoparticles.
Model-Based Piezoelectric Self-Sensing Technique
Authors: Neubauer Marcus , Renner Andreas , Wallaschek Jo˜rg
Published: January 2011

Piezoelectric self-sensing allows the measurement of frequency response functions of dynamical systems with one single piezoelectric element. This piezoceramics is used as actuator and sensor simultaneously. In this study, the frequency response functions are obtained by measuring the current flowing through the piezoelectric element, while it is driven by a harmonic voltage signal with constant amplitude. The current flow is composed of the part which is required to drive the piezoelectric element as an actuator and a second part which is the sensor signal that is proportional to the vibration amplitude of the attached mechanical system. Especially for low electromechanical coupling the first part is dominant and the influence of the mechanical system is only marginal. With an idealized mathematical model of the piezoelectric element, the admittance can be calculated and the actuator current can be eliminated from the measured signal. This software-based solution does not require any additional electrical circuits or precise tuning during the measurements. The influence of errors of the parameters for the piezoelectric model on the recalculated signals are shown, which helps to improve the estimations. Alternatively, they can be obtained by additional measurements. The proposed technique is demonstrated on a clamped beam with attached piezoelectric element.
Analysis of the Influence of Blade Pattern Characteristics on the Forced Response of Mistuned Blisks With a Cyclic CMS-Based Substructure Model
Authors: Hohl Andreas , Panning Lars , Wallaschek Jo¨rg
Published: January 2011

In turbomachinery applications bladed disks and blisks are subjected to high dynamic loads due to fluctuating gas forces. The dynamic excitation results in high vibration amplitudes which can lead to high cycle fatigue failures (HCF). Herein, the blades are almost identical but differ due to wear or small manufacturing tolerances. These small deviations of the blade properties can lead to a localization of the vibrational energy in single blades and even higher risk of HCF. Intentional mistuning, for example an alternating alignment of two different blades AB around the blisk, has been studied in literature to decrease the sensitivity against statistical mistuning. Using a Component Mode Synthesis (CMS) based mistuning model the influence of intentional mistuning on blisks is analyzed in this paper. Therein, the CMS of the disk is calculated with a fast and accurate cyclic symmetry approach. Therefore, the CMS of the disk can be calculated with one disk segment of the underlying Finite Element Model. The so called Wave Based Substructuring (WBS) is used to reduce the (numerous) coupling degrees of freedom between the disk and the blades with a truncated set of waves. The orthogonal waves are derived with a Singular Value Decomposition or a QR decomposition from the normal modes at the coupling degrees of freedom (DOF) calculated by a cyclic modal analysis of the full structure. In a case study the Reduced Order Model (ROM) of a spatial Finite Element Model is used to determine the influence of intentional mistuning with additional statistical mistuning on the forced response of blisks.
Some Properties of Stratified Composites
Authors: Circiumaru Adrian , Bria Vasile , Birsan Iulian-Gabriel , Andrei Gabriel , Dima Dumitru
Published: January 2011

The multi-component composites could represent the cheapest solution when controllable properties are required. In order to establish the right amount of filler it is necessary to analyze not only the electro-magnetic and mechanical properties but also, the thermal ones. The filler presence in the matrix produces discontinuities at the fibre-matrix interface with consequences regarding mechanical properties. Using a single filler it is possible to improve one or two properties electrical and thermal conductivity for instance and mean time to induce a decrease of other properties as bending strength, shock resistance etc. Using polymer layers with relatively high electrical conductivity as external layers of laminate and magnetic particles filled polymer as core layers. An electric circuit might be, at the same time, the reinforcement of a composite leading to lighter structures and, based on carbon fiber’s properties might transmit information about the material’s loading, temperature or integrity. Fabric reinforced or textile composites are used in aerospace, automotive, naval and other applications. They are convenient material forms providing adequate stiffness and strength in many structures. The microstructure of composite reinforced with woven, braided, or stitched networks is significantly different from that of tape based laminates. The properties of the composite depend not only on the properties of the components but on quality and nature of the interface between the components and its properties. Reinforced composites with filled epoxy matrix were formed using a hybrid technique consisting in layer-by-layer adding of reinforcement sheets into a glass mould. Various distributions of reinforcement sheets and filled polymer layers were realized in order to point out the ways in which the final properties might be controlled. Mechanical properties were analyzed.
The Effect of Drilling Mud Flow on the Lateral and Axial Vibrations of Drill String
Authors: Kazemi Reza , Jafari Ali Asghar , Faraji Mahyari Mohammad
Published: January 2011

In this research, the effects of drilling mud flow and WOB force on the lateral vibration of drill string are investigated. To this goal, the kinetic and potential energy of drill string for axial and lateral vibrations are written in an integral equation. In potential energy equation, the effect of geometrical shortening, which causes nonlinear coupling between axial and lateral vibration, is considered. Drilling mud forces are modeled by Paidoussis formulations. The works done by WOB force, weight of drill string and drilling mud forces are calculated. The mode summation method is employed to convert the continuous system to a discrete one. Dropping and considering third and fourth order tensor of potential energy lead to linear and nonlinear system, respectively. The effects of stabilizers are modeled by a linear stiff spring. The wall contact is modeled by Hertzian contact force. Lagrange equation is employed for finding the equations of motions. First and second natural frequencies of drill string are found for different WOB and drilling mud flow. Also the effects of drilling mud and nonlinear terms on lateral vibration of drill string are investigated. The effect of drilling mud on the post buckling vibration of drill string is also delivered. This formulation can be used for optimization of drilling mud flow, WOB and the number and positions of stabilizer so that the lateral vibration of drill string is minimized.
A Systems Engineering Tool for Satellite Simulator Design
Authors: Mirshams Mehran , Vahid D. M. Amin , Taei Hojjat
Published: January 2011

Simulation is one of the best methods for education and understanding events and used in many fields of science, for example: space researches. For this reason, creating of a frictionless environment that can simulate the operations of satellites will be very usable and appropriate. Spherical air bearings, that we call them TESTBEDs in this paper, are one of the most common devices used in satellite attitude dynamics simulation, because they provide three degrees of freedom rotational motion. They are employed to develop, improve and carry out operational tests of sensors, actuators and attitude control algorithms in experimental framework. An explanation about system engineering tool for testbed design that used by our team in Space Research Lab will be presented in this paper. This systems engineering tool utilizes a testbed-based approach to efficiently track information regarding the mass, cost, operation and volume of simulator subsystems. This subsystem information is derived through a variety of means, including analytical relationships, iterative solvers, and databases of components appropriate for satellite simulators. Finally, a description of 3-DoF satellite simulator and it’s subsystems (manufactured in Space Research Lab) by means of this system engineering tool will be demonstrated as a sample for validating results.
Influence of Testing Parameters on the Surface Quality of Steel Roller-Roller System Under Grease Lubrication
Authors: Diaconu Nicoale , Deleanu Lorena , Biˆrsan Iulian Gabriel
Published: January 2011

This paper presents the influence of commanding parameters as load and relative sliding speed, on the surface characteristics. Tests were done on a roller-roller tribotester. There were studied the influence of load, relative sliding speed and lubricant on the skewness and the kurtosis of the surface profile, but also on common parameters such as Ra and Rz. Such a study may be used for selecting a suitable lubricant (especially grease), after testing it under severe conditions, close to the actual ones. Profilograms indicate that treated steel has a better tribological behavior, under the above-mentioned testing conditions, for a roller-roller system. When running at low temperatures, there were noticed gripping traces, pointed out in shape and size by profilograms recorded on the roller generatrix. For all testing conditions, the more viscous grease (UM185Li2 EP – multifunctional grease) had a better behavior as concerning the profile parameters of the roller surfaces, and it provides a probably almost continuous film between rollers thus, a good protection of the metallic surfaces, process also underlined by low values for the recorded friction moment. A comparative study of the surface topography, obtained under the same testing conditions, may do at least a qualitative hierarchy of the grease grades, which could give recommendations for selecting lubricants and durability improvement of actual tribosystems.