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 Volume 4, 2009
Print ISSN: 1991-8747
E-ISSN: 2224-3429








Issue 1, Volume 4, January 2009

Title of the Paper: Experimental Visualization of Gas-Assisted Injection Long Bubble in a Tube


Authors: Cheng-Hsing Hsu, Kuang-Yuan Kung, Po-Chuang Chen, Shu-Yu Hu

Abstract: A long bubble-driven fluid flow in a circular tube is visualized by an optical method. A pressurized airflow was injected into an 8 mm I.D. and 1,500 mm long horizontally placed glass tube filled with silicon oil to produce a long bubble in the tube. The images were analyzed by two-value calculation and a thinning process to extract the contour of the bubble front. Data points on the contour were then deduced to undergo a regression curve fitting. The results show a good verification of the theoretically derived non-dimensional contour equation. The deduced penetration speed indicates that the speed is increasing downstream due to the decreasing fluid slug in the tube. The experimental results shows the theoretical bubble profile can be introduced to the simulation study to reduce the calculating time, the ratio (λ) of the bubble width to the diameter of the circular tube. The theoretical bubble profile is more precise in a lower λ value than in a higher one.

Keywords: Long bubble, Contour equation, Two-phase flow, Correlated number, Optical method

Title of the Paper: The Gas-assisted Expelled Fluid Flow in the Front of a Long Bubble in a Channel


Authors: C. H. Hsu, P. C. Chen, K. Y. Kung, G. C. Kuo

Abstract: Investigated in this study is the steady-state flow field of a long bubble penetrating into a region filled with a viscous fluid confined by two closely located parallel plates. Instead of using the complicated procedure for iteratively computing the free surface and flow patterns, we simply use a theoretical profile of the bubble so that the influence of bubble shape on the flow field can be examined directly. Due to the simplification, flow fields with higher Reynolds number are easier to be included and different flow phenomenon is found. The numerical techniques employed are finite difference method (FDM) with successive over-relaxation (SOR). The simulation results show coincidently with others the two typical flow patterns (complete bypass flow and recirculation flow). The gradually moving of the stagnation point in the front of the bubble tip between two typical flow patterns is clearly presented and explainable. Both of the position of the stagnation point parallel and perpendicular to the flow, *spx and*spy, depends on Reynolds number, Re, andλ, the ratio of asymptotic bubble width to the distance between two parallel plates. As λ or Re increases, *spy increases too, but*spx decreases. A quasi-linear relationship between λ and *spx is found in a recirculation flow region. Be ware that the stagnation point is very sensitive with λ for Re>100. As Re increases, the maximum value of stream function increases, and the recirculation zone near the bubble tip becomes bigger too.

Keywords: Long bubble, expelled fluid flow, stagnation point, two-phase flow, inertia forces

Title of the Paper: Numerical Simulation of Forging Process Using the Hybrid PCM/FEM


Authors: Yong-Ming Guo

Abstract: In this paper, for analyses of metal forming problems, a point collocation method (PCM) with a boundary layer of finite element is developed. PCMs have some advantages such as no mesh, no integration. While, the robustness of the PCMs is an issue especially when scattered and random points are used. To improve the robustness, some studies suggest that the positivity conditions can be important when using the PCMs. For boundary points, however, the positivity conditions cannot be satisfied, so that it is possible to get large numerical errors from the boundary points when using the PCMs. Specifically, the errors could arise in point collocation analyses with complicated boundary conditions. In this paper, by introducing a boundary layer of finite element in boundary domain of workpiece, unsatisfactory issue of the positivity conditions of boundary points can be avoided, and the complicated boundary conditions can be easily imposed with the boundary layer of finite element. A forging process is analyzed by using the hybrid PCM/FEM.

Keywords: Meshless method, Point collocation method, Positivity conditions, FEM, Hybrid method, Forging

Title of the Paper: Comparison of the Grey Theory with Neural Network in the Rigidity Prediction of Linear Motion Guide


Authors: Y. F. Hsiao, Y. S. Tarng, K. Y. Kung

Abstract: The purpose of this paper is to compare the prediction models constructed through neural network and grey theory, and to apply the prediction model established to study of correlation between linear motion guide rigidity under the stress of tension and compression. Strain data of tension and compression are simultaneously obtained by the computer that is linked with the Universal testing machine and translated into rigidity values through the formula of δkF=. Through this study we can understand the differences in prediction of rigidity between neural network and grey theory. Experiment results will serve as reference for manufacturers and users, with the hope that based on fewer measurement data testing time can be reduced and the outcome can be more accurately predicted. Based on fewer measurement data, the outcome can be more accurately predicted, and that with a nondestructive test can accurately predict the rigidity of the linear motion guide. The outcome indicates that the prediction model established through neural network is superior to the prediction model established through the grey theory, and that the neural network model can accurately predict the result.

Keywords: Grey prediction model, rigidity, linear motion guide, neural network, tension, compression

Title of the Paper: Study of the Lubrication Oil Consumption Prediction of Linear Motion Guide through the Grey Theory and the Neural Network


Authors: Y. F. Hsiao, Y. S. Tarng

Abstract: To determine the lubrication oil consumption change of linear motion guide under some mileage, this study designs a test machine to fasten the linear motion guide. The grey prediction model GM(1,1) and neural network are employed for comparison and exploration. Through this study we can understand the differences in prediction of lubrication oil consumption between neural network and grey theory. Experiment results will serve as reference for manufacturers and users for the purpose of quality improvement and selection of better linear motion guides. Based on fewer measurement data, the outcome can be more accurately predicted, and that with a nondestructive test can accurately predict the lubrication oil consumption of the linear motion guide. The outcome indicates that the prediction model of neural network is superior to the grey theory model GM(1,1). The average prediction error of neural network prediction is around 2% - showing a very high accuracy level.

Keywords: Neural network, grey theory, linear motion guide, lubrication oil, prediction, GM(1,1)

Issue 2, Volume 4, April 2009

Title of the Paper: Measuring Full Displacement Fields on Scattering Surfaces by a Portable Low-Cost Interferometer


Authors: M. Bova, L. Bruno, L. Pagnotta, A. Poggialini

Abstract: The paper presents a device for measuring full displacement fields working on the principle of speckle interferometry. The proposed interferometer was designed with the aim of obtaining a lightweight selfcontained device, easy to assemble with cheap and standard equipment. The investigated area is illuminated by three laser diodes emitting 50 mW at 660 nm, and observed by a B&W firewire CCD camera. The accuracy of the measurements is improved by means of a PZT actuator realized on purpose and driven by a control electronics able to provide a very accurate supply voltage. Furthermore by the control electronics it is possible to turn on and off the diodes and to control the single light intensity of each laser. The paper describes in details all the parts of the interferometer and the systems implemented for optimizing the working conditions of the device. Furthermore all the steps necessary for performing the measurements are reported, and typical sets of experimental data are shown.

Keywords: Speckle interferometry, laser diode, phase-shifting, low-cost, 3D deformation, portable equipment

Title of the Paper: Application of Finite Element Method to an Overhead Crane Bridge


Authors: Camelia Bretotean Pinca, Gelu Ovidiu Tirian, Ana Josan

Abstract: This paperwork analyses the tension and deformation state of the resistance structure of an overhead crane bridge which used for all the processes performed in the hall of a continuous casting department of an iron and steel plant in order to find out the best sizes. This analysis is made up with the help of the COSMOS software who enables us to make evolved finite items – shell-type with three or four nodes per element. The shell-type finite items belong to the C1–class items, and they have a field variable and the I-type derivates working continuously alongside the frontier, meanwhile the II-type continuous derivates per item are not continuous alongside the frontier. These finite items allow us to design some complex structures more accurately, such as the resistance structure of the crane bridge. This example is not intended to be the only solution when designing symilar structures, but the authors of this paperwork believe that it is providing enough information and useful solutions for the analysis of the tension and deformation state in case of finite items.

Keywords: Crane bridge, analysis, model, resistance, overhead, finite elements, shell

Title of the Paper: 3D Shape of Specular Surface Measurement Using Five Degrees of Freedom Camera System


Authors: Khairi Yusuf, Prasetyo Edi, Amir Radzi Abdul Ghani

Abstract: In this report, we describe a new method in obtaining a 3D shape of specular surface by using five degrees of freedom (5-DOF) camera. We use the principle that the normal vectors of the surface are extracted by aligning the camera axis and the surface normal vector. From the normal vector data, the shape of the surface is reconstructed. After the flat and the ball surface, the objects of the research are continued to convex and concave specular surface. The convex object is an automobile glass window, where in this object we show that the back reflection of a parallel surface of a thin glass can be eliminated. In the concave object we have a limitation that the radius of object is not smaller than twice of the nearest distance from the camera to the surface. The result shows that the methodology improves the 3-D shape of object measurement with good accuracy.

Keywords: Shape reconstruction, pattern recognition, computer vision, image processing, five degrees of freedom camera, specular surface, normal vector, robotics

Title of the Paper: The Design of Light Jet Aircraft


Authors: Prasetyo Edi, Khairi Yusuf, Amir Radzi Abdul Ghani, Hakim S. Sultan Aljibori

Abstract: This paper discusses the design of light jet aircraft (LJA) in the university level. The design process that covers by this paper is just from conceptual approach. Current technical information of the light jet aircraft in the market will be studied for competitor analysis purpose. After that, the calculation process will take part, like initial sizing, performance sizing, initial sizing of main component, weight breakdown, cg (centre of gravity) position and aircraft performance. It concludes with a discussion of the results and recommendations for future work. This paper will only concentrate on conceptual design, the next stage of design can be continuing in future with the data from this paper.

Keywords: Conceptual design, wing design, aircraft design, aerodynamic configuration, light jet

Issue 3, Volume 4, July 2009

Title of the Paper: Impact Energy Absorption of Concentric Circular Tubes


Authors: Lion Kok Hao, Amir Radzi Abdul Ghani, Prasetyo Edi, Khairi Yusuf

Abstract: Non-linear finite element code ABAQUS/Explicit was employed to evaluate the energy absorption characteristics of concentric circular tubes subjected to impact in the axial direction. Thin-walled circular tube plays a vital role as energy absorber due to its high energy absorption capacity. However, the main drawback of existing tube type energy absorber is the high initial peak load. This work evaluates the capability of concentric circular tubes in reducing the peak load that is exerted to the protected structures and occupants during impact. Clearance and thickness of the structure were varied and different materials such as aluminum alloy, high strength steel and stainless steel were used. The study found that aluminum alloy has great potential to be utilized as energy absorbing system due to its high specific energy absorption capacity and long stroke. For all materials, increasing the clearance between the inner and outer circular tubes resulted in a reduction of peak load and a significant increase of specific energy absorption (SEA). However, increasing the thickness adversely increased the initial peak load and reduced the SEA. It can be deduced that concentric circular tubes could be utilized as a safer design of energy absorber as it exhibited a lower initial peak load during impact which is a desirable feature when designing for occupant safety.

Keywords: Structural crashworthiness, impact energy absorption, non-linear explicit finite element

Title of the Paper: Sensitivity Analysis of Stability Problems of Steel Structures using Shell Finite Elements and Nonlinear Computation Methods


Authors: Zdenek Kala, Jiri Kala

Abstract: The paper analyzes the influence of initial imperfections on the ultimate limit state of a slender strut, applying the ANSYS programme. The geometrical and material nonlinear finite element method was applied for the theoretical analysis. Modelling of the steel structure was performed using SHELL elements. The effect of input imperfections on the load-carrying capacity is evaluated by sensitivity analysis. This paper is devoted to a class of sensitivity analysis techniques that are known as the variance-based methods. Input imperfections are of random origin. The Sobol’s sensitivity analysis was used to determine the sensitivity of load-carrying capacity of a strut with respect to the variance of initial imperfections. The sensitivity analysis results identify the imperfections the variability of which can influence the structure reliability. The Latin Hypercube Sampling method was applied for the evaluation of sensitivity indices. The computation model elaborated is unique with regard to its numerically demanding character.

Keywords: Reliability, steel, structures, imperfections, stability, sensitivity analysis, shell elements

Title of the Paper: Research on Increasing the Lastingness of a Rolling Bridge


Authors: Camelia Bretotean Pinca, Gelu Ovidiu Tirian

Abstract: The paper’s purpose is to analysis the stresses and strains state in the strength structure of a rolling bridge, presenting a fast and evaluated computer aided solving method for complex static indeterminate structures. The analysis of the stresses and strains state of the strength structure of a rolling bridge for increasing its solidity in exploitation is made using the calculation software with finite elements COSMOS/M. The research performed allows the evaluation of the stresses state, pointing out the critical areas and measures which are imposed in order to increase the solidity and bearing capacity of the strength structure for the rolling bridge. The results we have obtained allowed us to make up a study about the dimension optimization of the strength structure in order to design the rolling bridge. Thus, the material use could be reduced without exceeding the limits of the most appropriate resistance.

Keywords: Stress, rolling bridge, analysis, model, strength, finite elements, shell type

Title of the Paper: Optimal Trajectories Towards Near-Earth-Objects using Solar Electric Propulsion (SEP) and Gravity Assisted Maneuver


Authors: Denilson Paulo Souza dos Santos, Lorenzo Casalino, Guido Colasurdo, Antonio Fernando Bertachini de Almeida Prado

Abstract: The solar electric propulsion could be the best option for the transports of the future due to its high specific impulse when compared to the chemical propulsion. Electric propellants are being extensively used to assist the propulsion of terrestrial satellites for the maneuvers of orbit correction and as primary propulsion in missions toward other bodies of the solar system. In this work the optimization of interplanetary missions using solar electric propulsion (SEP) and Gravity Assisted Maneuver to reduce the costs of the mission, is considered. The high specific impulse of electric propulsion makes a Gravity Assisted Maneuver 1 year after departure convenient. Missions for several Near Earth Asteroids will be considered. The analysis suggests criteria for the definition of initial solutions demanded for the process of optimization of trajectories. Trajectories to the asteroid 2002TC70 are analyzed. Direct trajectories, trajectories with 1 gravity assisted at the Earth and with 2 gravity assisted with the Earth and either Mars are presented. Shall be analyzed missions with thrusters PPS1350 and the Phall 1 for performance comparison. An indirect optimization method will be used in the simulations.

Keywords: Astrodynamics, Celestial Mechanics, Space Trajectories

Issue 4, Volume 4, October 2009

Title of the Paper: Evaluation of the Limit Load Capacity of Masonry Arch Bridges


Authors: Amaryllis Audenaert, Genserik Reniers, Wout Dullaert, Herbert Peremans

Abstract: Using a 2D decision support system based on a recent analytical model, this paper is the first to demonstrate that bridge specific characteristics require a detailed analysis to determine the collapse load. A parameterized study of the limit load capacity is necessary to calculate the worst case positioning of any kind of load. Because of the complexity of finite element modeling and the computation time requirements of 3D finite elements models for a large number of load positions, it is regularly assumed that collapse positions are situated at the crown of the arc. Empirical testing in this paper clearly demonstrates that this is not the case. The here developed approach allows for a quick scan of any type of masonry arch bridge, thus providing the necessary information on the critical range of load positions to be analyzed in more detail by a 3D modeling approach.

Keywords: Arches, collapse load, equilibrium,safety

Title of the Paper: Dimensional Optimization for the Strength Structure of a Traveling Crane


Authors: Camelia Bretotean Pinca, Gelu Ovidiu Tirian, Ana Virginia Socalici, Erika Diana Ardelean

Abstract: Most of the time, the strength structures who have not been statically determined, cut to the right sized, and checked out by the classic methods of the material strength cause the over sizing, because specialists use approximate measurements in order to decrease the number of mathematical calculation. This paper work describes the optimization of the main beam of a strength structure of a traveling crane used in metallurgy – by using the OPTSTAR mode that the COSMOS/M calculation software encloses which uses finite elements. In order to accomplish the best suited size, we have to perform both an analytic and experimental study about the performance of the traveling crane. In order to do that, we analyze the state of the tensions and deformation of the strength structure by using this calculation software based on COSMOS finite elements. In order to validate the analytic study, we have performed some industrial experiments by using specific devices for measuring the resistance of the electrical tension. Both the analytic and experimental studies have pointed out that we are able to come up with the best sizes in order to reduce the material consumption we used during the production process of the main beam within the strength structure of the traveling crane we have analyzed.

Keywords: Tension, traveling crane, optimization, deformation, over-sized, finite, elements

Title of the Paper: Non-linear Analysis and Stability of the Automotive Suspensions with Neo–Hookean Elements


Authors: Nicolae–Ddoru Stanescu

Abstract: In this work we present two systems with non-linear neo–Hookean components. In such systems there always exists an element with a non-linear characteristic equation. This element can be considered to be a rubber or another equivalent structure. We shall prove that the utilization of a neo–Hookean element will not destroy the properties of the structure, but it riches these properties and it could be a good solution in many cases. The first model describes a quarter of an automobile and the second one is dedicated to a half-automobile model. We obtain the equilibrium positions, study their stability in the most general case and for the first model we also discuss the stability of the motion. In the paper there are also numerical applications.

Keywords: Neo–Hookean, stability, modeling, non-linear

Title of the Paper: Some Correlated Factors Including Chip Surface of Bending Strength


Authors: Aurel Lunguleasa

Abstract: This scientific article presents some aspects referring to static bending strength and its influencing factors. It is an exhaustive study of all influencing factors but it only details the more important and known of these. Only three wooden species are used, namely beech (Fagus silvatica L), spruce-fir (Picea abies Karst) and poplar (Populus tremula L), for obtaining chipboard. Main factors which are considered that they influence the bending strength are: wooden specie, chip thickness, specific surface of chips, percentage of resin, specifical consumption of adhesive and board density. All of these are individually presented for finding the influence. Then, some of these are extracted and try to find all the influences between them. Finally, based on many rigorous experiments, a diagram for the grouped influence of some correlated factors, were realized. The main influence of bending strength that is found in this paper is chip thickness, but there are other hard points such as specifically surface of chips or degree of compressin-compactation

Keywords: Chipboard, bending strength, factors of influence, correlated factors, chip thickness, resin percentage, specifical surface

Title of the Paper: Determining the Optimal Build Directions in Layered Manufacturing


Authors: A. Sanati Nezhad, M. Vatani, F. Barazandeh, A. R. Rahimi

Abstract: Determining the optimal build directions is one of the most critical factors in RP processes because it affects on the build time, support structure, surface quality as well as the cost. The previous methods could handle simple parts or limited objective functions. Moreover the methods with multiple objective functions, had abstracted them into a single fitness function in which the characteristics of individual objectives could not be reflected properly. In the present work a new algorithm is presented to determine the optimal build-up directions of the part in Stereolithography systems. The algorithm can help RP users select among the optimal build-up directions.The optimization is done using Multi-Objective Genetic Algorithm (MOGA). The method proposed here handles build time, support volume and surface finish as objective functions individually. At each GA step, the surface finish is achieved applying adaptive layer thickness method and optimization algorithm finds the optimal build directions with minimum build time and volume support. The algorithm is developed by MATLAB. To evaluate the algorithm, several sample parts are checked.

Keywords: Stereolithography- Optimal Build Direction- Multi Objective Optimization - Genetic Algorithm

Title of the Paper: Chaos in Grinding Process


Authors: Nicolae–Doru Stanescu

Abstract: This paper presents a non-linear model for the external grinding of a cylindrical work-piece. A system of non-linear differential equations for the vibrations of the tool and the work-piece is obtained. Non-linearity comes from the cutting force dependence on the feeding velocity and depth of cut. We determine the number of the equilibrium positions, we proved that there exists only one equilibrium position and we study its stability. Results of simulation are discussed. A chaotic regime is found for realistic values of the grinding parameters.

Keywords: Grinding, equilibrium, stability, chaos

Title of the Paper: Sommerfeld and Mass Parameter Identification of Lubricated Journal Bearings


Authors: Domenico Guida, Carmine M. Pappalardo

Abstract: In this paper we propose a method for identification of two parameters that define the structure of lubricated journal bearings. In rotordynamics literature these parameters are named Sommerfeld number and Mass Number, respectively. The system analyzed belongs to the class of systems that are described by n nonlinear second order differential equations. We have obtained the analytical solutions of these equations using Lie series expansion. This method can be applied to a vast class of dynamical systems, provided that they are described by smooth equations. Lie series expansion is a mathematical tool that allows us to obtain the system response in recursive way using symbolic PC-codes. Besides, this procedure involves only a few experimental data and makes the identification process very quick. It is worth noting that the application that we propose does not take into account neither the issue connected to experimental data noise nor the unavoidable disturbances that occurs in measurement process. Actually, in applied system identification one must always pay attention to the signal noise and to the robustness of the solution with respect to disturbances, but these issues are over the goal of this paper.

Keywords: Nonlinear System Identification, Parameter Identification, Lubricated Journal Bearings

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