Lin J.-R.,Nanya Institute of Technology
Tribology International | Year: 2010
Based on the magneto-hydrodynamic (MHD) thin-film lubrication theory, steady load capacity and dynamic characteristics of wide tapered-land slider bearings lubricated with an electrically conducting fluid by the application of an external magnetic field are presented. Compared with the non-conducting lubricant (NLC) tapered-land bearing by Lin et al. (2006), the MHD bearing provides higher values of load capacity and dynamic coefficients. Compared with the MHD inclined-plane bearing by Lin et al. (2009), the MHD tapered-land bearing how an increase in load capacity and dynamic coefficients as well as a reduction in the steady friction parameter. © 2010 Elsevier Ltd.
Lin J.-R.,Nanya Institute of Technology |
Lu R.-F.,Nanya Institute of Technology
Journal of Marine Science and Technology | Year: 2010
On the basis of the magneto-hydrodynamic (MHD) thinfilm lubrication theory, the dynamic characteristics of wide exponential-shaped slider bearings with an electrically conducting fluid in the presence of a transverse magnetic field are theoretically investigated. Taking into account me transient squeezing motion, the MHD dynamic Reynolds-type equation is derived from the continuity equation and the MHD motion equations. A closed-form solution for the steady film pressure and load-carrying capacity and me dynamic stiffness and damping coefficients are obtained. From the results obtained, the presence of externally applied magnetic fields signifies an enhancement in me film pressure. On the whole, the applied magnetic-field effects characterized by the Hartmann number provide a significant increase in values of the load-carrying capacity, the stiffness coefficient and the damping coefficient as compared to the non-conducting-lubricant (NCL) case. These improvements of bearing dynamics are more pronounced with increasing Hartmann numbers and decreasing minimum film thicknesses. To illustrate the use of the present study, a design example is guided. For engineering application, numerical results are further provided in the Tables.
Chung Y.C.,Nanya Institute of Technology |
Ooi J.Y.,University of Edinburgh
Granular Matter | Year: 2011
Over the past 30 years, the Discrete Element Method (DEM) has rapidly gained popularity as a tool for modelling the behaviour of granular assemblies and is being used extensively in both scientific and industrial applications. However, it is far from clear from reviewing the literature whether the large number of DEM codes have been verified and checked against fundamental benchmark problems. DEM simulates the dynamics of each particle in an assembly by calculating the acceleration resulting from all the contact forces and body forces. It is clearly necessary that such a model be validated or verified by comparing with experimental results, analytical solutions or other numerical results (e.g. Finite Element Analysis (FEA) results) at particle impact level. There appears to be no standard benchmark tests against which DEM codes can be verified. It is thus essential and useful to establish a set of standard benchmark tests to confirm that these DEM codes are modelling the particle dynamics as intended. This paper proposes a set of benchmark tests to verify DEM codes at particle impact level for spherical particles. The analytical solutions derived from elasticity theory for elastic normal collision of two spheres or a sphere with a rigid plane are first reviewed. These analytical solutions apply only to the elastic regime for normal impact. Secondly, the analytical solutions of frictional oblique impact between two spheres or a sphere with a rigid plane are scrutinized and derived. These analytical solutions originate from the dynamics principles and should be satisfied for any DEM contact force model with prescribed friction and restitution coefficients. A set of eight benchmark tests are designed and performed using commercial DEM codes. Test 1 and Test 2 consider the elastic normal impact of two spheres or a sphere with a rigid plane, whereas the other tests (Test 3-Test 8) investigate the energy dissipation due to the collision. These benchmark tests also involve different types of material. The DEM results were compared with the analytical solutions, experimental or FEA results found in the literature. All benchmark tests showed good to excellent match, providing a quantitative verification for the codes used in this study. These benchmark tests not only verify DEM codes but also enhance the understanding of fundamental impact phenomena for modelling a large number of particles. © 2011 Springer-Verlag.
Shiue Y.-C.,National Central University |
Chiu C.-M.,National Sun Yat - sen University |
Chang C.-C.,Nanya Institute of Technology
Computers in Human Behavior | Year: 2010
The motivation to share members' knowledge is critical to an online community's survival and success. Previous research has established that knowledge sharing intentions are based on group cohesion. Several studies also suggested that social loafing behavior will seriously corrode group cohesion. Therefore, social loafing is a key obstacle to fostering online community development. Although substantial studies have been performed on the critical factors that affect social loafing in the learning group, those on online communities are still lacking. By integrating two perspectives, social capital and perceived risk, a richer understanding of social loafing behavior can be gained. In the research model, social ties and perceived risk have been driven by anonymity, offline activities, knowledge quality, and media richness. Social ties and perceived risk are hypothesized to affect social loafing in the online community, which, in turn, is hypothesized as negatively affecting group cohesion. Data collected from 323 online users in online communities provide support for the proposed model. The study shows that social loafing is a significant negative predictor of the users' group cohesion. The study also shows that social ties and perceived risk are important components of social loafing. Anonymity, offline activities, knowledge quality, and media richness all have strong effects on social ties and perceived risk in the online community. Implications for theory and practice and suggestions for future research are discussed. © 2009 Elsevier Ltd. All rights reserved.
Lin J.-R.,Nanya Institute of Technology
Tribology International | Year: 2012
Based upon the ferrohydrodynamic flow model, a lubrication equation in cylindrical coordinates for ferrofluid squeeze films including the effects of convective inertia forces and the presence of transverse magnetic fields has been derived for engineering application. As an application, the problem of parallel circular disks is illustrated. It is found that the ferrofluid circular squeeze film considering fluid inertia effects provides a higher load capacity and a longer elapsed time as compared to the non-inertia non-ferrofluid case. These improved characteristics are further emphasized for larger values of the density parameter, the Langevin parameter and the volume concentration of particles. © 2011 Elsevier Ltd. All rights reserved.
Hsu T.-C.,Yuan Ze University |
Chen J.-H.,Yuan Ze University |
Chiang H.-L.,Nanya Institute of Technology |
Chou T.-L.,Nanya Institute of Technology
Tribology International | Year: 2013
The primary objective of this study was to investigate the performance of ferrofluids under the combined influence of surface roughness and a magnetic field generated by a concentric finite wire. The distribution of pressure was obtained and used to calculate the characteristics of the bearing. The results of this study indicate that the combined influence affect the distribution of film pressure, which enhances loading capacity and reduces the modified friction coefficient. The effect of longitudinal roughness was particularly significant and we expect these findings could further enhance the design of short journal bearing within a magnetic field. © 2013 Elsevier Ltd.
Chen Y.-L.,National Central University |
Wu Y.-Y.,Nanya Institute of Technology |
Chang R.-I.,National Taiwan University
Decision Support Systems | Year: 2012
The attribute-oriented induction (AOI) is a useful data mining method that extracts generalized knowledge from relational data and user's background knowledge. The method uses two thresholds, the relation threshold and attribute threshold, to guide the generalization process, and output generalized knowledge, a set of generalized tuples which describes the major characteristics of the target relation. Although AOI has been widely used in various applications, a potential weakness of this method is that it only provides a snapshot of the generalized knowledge, not a global picture. When thresholds are different, we would obtain different sets of generalized tuples, which also describe the major characteristics of the target relation. If a user wants to ascertain a global picture of induction, he or she must try different thresholds repeatedly. That is time-consuming and tedious. In this study, we propose a global AOI (GAOI) method, which employs the multiple-level mining technique with multiple minimum supports to generate all interesting generalized knowledge at one time. Experiment results on real-life dataset show that the proposed method is effective in finding global generalized knowledge. © 2011 Elsevier B.V. All rights reserved.
Yang C.-B.,Nanya Institute of Technology
Journal of Computational and Theoretical Nanoscience | Year: 2011
Currently, line segment fabrication using near field photolithographic microscopes can only generate nano-scale line segments of equal depth; fabrication of 3D shapes is impossible. The innovative line segment fabrication model of near field photolithography is a method used to analyze the exposure energy density of innovative line segment fabrication of near field photolithography by controlling exposure energy density through manipulation of the near field distance between the optical fiber probe and the photoresist, performing fabrication of profiles in the process. This study proposes that the difference between the target value of the profile where fabrication takes place and the simulation value is used as the target function. The Levenberg-Marquardt method and a reasonable convergence criterion are used to determine a suitable optical fiber movement speed of Vz. This value is then substituted into the innovative line segment fabrication model of near field photolithography where simulation is performed. Simulation results fall in the area of profile errors; therefore, the model proposed in this paper affirms the ability to perform near field line segment 3D shape fabrication. The innovative line segment fabrication model of near field photolithography proposed here is not suitable for cases where the distance between the photoresist and the optical fiber probe exceeds 35.6 nm. Otherwise, the fabrication would lose its near field photolithographic properties, and its base would become emerged. Copyright © 2011 American Scientific Publishers.
Tasgetiren M.F.,Yaşar University |
Pan Q.-K.,Liaocheng University |
Suganthan P.N.,Nanyang Technological University |
Chen A.H.-L.,Nanya Institute of Technology
Information Sciences | Year: 2011
Obtaining an optimal solution for a permutation flowshop scheduling problem with the total flowtime criterion in a reasonable computational timeframe using traditional approaches and optimization tools has been a challenge. This paper presents a discrete artificial bee colony algorithm hybridized with a variant of iterated greedy algorithms to find the permutation that gives the smallest total flowtime. Iterated greedy algorithms are comprised of local search procedures based on insertion and swap neighborhood structures. In the same context, we also consider a discrete differential evolution algorithm from our previous work. The performance of the proposed algorithms is tested on the well-known benchmark suite of Taillard. The highly effective performance of the discrete artificial bee colony and hybrid differential evolution algorithms is compared against the best performing algorithms from the existing literature in terms of both solution quality and CPU times. Ultimately, 44 out of the 90 best known solutions provided very recently by the best performing estimation of distribution and genetic local search algorithms are further improved by the proposed algorithms with short-term searches. The solutions known to be the best to date are reported for the benchmark suite of Taillard with long-term searches, as well. © 2011 Elsevier Inc. All rights reserved.
Yang C.-B.,Nanya Institute of Technology |
Deng C.-S.,National United University |
Chiang H.-L.,Nanya Institute of Technology
International Journal of Advanced Manufacturing Technology | Year: 2012
When using the Taguchi method, an L18 or L27 orthogonal array is usually adopted. However, this requires many experiments (18 or 27 runs, respectively), consuming time, and resources. This study proposes a progressive Taguchi neural network model, which combines the Taguchi method with the artificial neural network to construct a prediction model for a CO 2 laser cutting experiment. During CO 2 laser cutting, energy from the moving laser is accumulative. The paper develops an integral equation of energy density during laser beam movement and lets it determine the sliding level of control factor. Meanwhile, the paper proposes that in Stage 1, only less number of experiments is required to be conducted by L9 orthogonal array. After the crucial supplementary experimental training samples proposed in Stage 2 are also included, high-accuracy prediction of artificial neural network can be completed. Based on analysis from the progressive Taguchi neural network, the Stage 1 preliminary network-with only a few available experimental examples-has achieved good predictive ability from regions near the Taguchi control points. For regions further out, the predictions have been increasingly unreliable. Nevertheless, the high precision of Stage 2 Taguchi network has good predictive results for all regions. © Springer-Verlag London Limited 2011.