• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.9 s.114
• /
• pp.919-925
• /
• 2006

An accurate mathematical model for complex stiffness of the pneumatic spring would be necessary for an efficient design of a pneumatic spring used in vibration isolation tables for precision instruments such as optical devices or nano-scale equipments. A diaphragm, often employed for prevention of air leakage, plays a significant role of complex stiffness element as well as the pressurized air itself Therefore, effects of the diaphragm need to be included in the dynamic model for a more faithful description of dynamic behavior of pneumatic spring. But the complex stiffness of diaphragm is difficult to predict In an analytical way, since it is a rubber membrane of complicated shape in itself. Moreover, the diaphragm should be expandable in response to pressurization inside a chamber, which makes direct measurement of complex stiffness of diaphragm extremely difficult. In our earlier research, the complex stiffness of diaphragm was indirectly measured, which was just to eliminate the theoretical stiffness of pressurized air from the measured complex stiffness of the pneumatic spring. In order to reflect complex stiffness of inflated diaphragm on the total stiffness at the initial design or design improvement stage, however. it is required to be able to predict beforehand. In this paper, how to predict the complex stiffness of inflated rubber diaphragm by commercial FE codes (e.g. ABAQUS) will be discussed and the results will be compared with the indirectly measured values.

• The Korean Journal of Applied Statistics
• /
• v.21 no.4
• /
• pp.603-613
• /
• 2008

We often encounter the situation that discrete count data have a large portion of zeros. In this case, it is not appropriate to analyze the data based on standard regression models such as the poisson or negative binomial regression models. In this article, we consider Bayesian analysis for two commonly used models. They are zero-inflated poisson and negative binomial regression models. We use the Bayes factor as a model selection tool and computation is proceeded via Markov chain Monte Carlo methods. Crash count data are analyzed to support theoretical results.

• Journal of Ocean Engineering and Technology
• /
• v.24 no.2
• /
• pp.47-52
• /
• 2010

The proper surface pressure on the pistons rings in the diesel engine of a ship is very important, because the pressure controls the oil that is needed to maintain friction at acceptable levels between the pistons and the cylinders. In this paper, basic and theoretical concepts to compute the ring pressure were formulated and applied to obtain the proper surface pressures on selected sample piston rings. During the calculation of the pressure on the piston rings, the computation of the accurate free shape of the piston ring was required. Earlier, Arnold and Prescott introduced theories to compute the free shapes of piston rings, and their approach used rectangular and polar coordinates. In this paper, the free shapes of piston rings using two different theories were computed and compared. The results were quite close, representing the free shape of the piston ring. Ring pressure was computed using the Arnold's free shape that was obtained. A simple GUI was made to compute the surface pressure on the piston rings.

• Journal of the military operations research society of Korea
• /
• v.3 no.1
• /
• pp.83-96
• /
• 1977

The combustion chamber and nozzle of an end burning, small spherical rocket is designed. A spherical external shape has a number of advantages such as fixed center-of-gravity and minimum aerodynamic precession torques during flight and a better mass distribution for gyro-stabilization as contrasted to a conventional ogive rocket shape. It is shown that the cross-sectional variation of the end burning solid propellant with length is an exponential geometry to provide a constant thrust-weight ratio of the rocket device during the propellant burning period, and that the factors which affect the attainment of the constant relationship of thrust to weight in the design are the initial propellant area, initial weight of the rocket and propellant density. The measurement of the transient thrust in the ground static test using black powder propellant supports the predicted results. A wind tunnel having a $30{\times}30{\times}75cm$ test section and Mach number 0.11 is constructed, and a simple balance-type device is designed for the measurement of the drag of a spinning sphere. The experimental results indicate that the. spinning has no effect on the magnitude of the drag up to the Reynolds number $3{\times}10^5$. Numerical computation of the flight trajectories for various launching angles is presented, and the gyro-stabilization of spinning sphere is discussed.

• Laser Solutions
• /
• v.12 no.1
• /
• pp.7-13
• /
• 2009

Engineering ceramics as sapphire are widely used in industry owing to their superior mechanical and corrosion properties. However, micromachining of sapphire is a considerable challenge due to its transparency. Recently, direct ablation of sapphire has been demonstrated with a visible laser pulse at sufficiently high laser intensity. In this work, the theoretical model for pulsed laser ablation of sapphire is suggested and numerical analysis is carried out using the model. Sapphire ablation begins with plasma generation by the laser interaction with surface defects, impurities and contaminations in the initial stage of machining. Subsequent absorption of the visible laser beam can be explained by three mechanisms: metalization of sapphire surface due to the EUV radiation from the hot plasma, increments of surface roughness and temperature-dependent absorption coefficient. Comparison of the computation results with experimental observation indicates that the proposed model of sapphire is reasonable.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.9C
• /
• pp.1323-1329
• /
• 2004

This paper presents an enhanced MSEA(multi-level successive elimination algorithm) which is a fast algorithm of the full-search motion estimation. We predict the SAD at the final level using the values of norms at the preceding levels in MSEA and then decide on whether the processing at the following levels should be proceeded or not. We skip the computation at the following levels where the processing is not meaningful anymore. Consequently, we take computational gain. For the purpose of predicting the values of SAD at each level, we first show the theoretical analysis of the value of norm at each level, which is verified by experiments. Based on the analysis a new motion estimation method is proposed and its performance is evaluated.

• Geomechanics and Engineering
• /
• v.10 no.2
• /
• pp.225-245
• /
• 2016

Settlement of foundations in permafrost regions primarily results from three physical and mechanical processes such as thaw consolidation of permafrost layer, creep of warm frozen soils and the additional deformation of seasonal active layer induced by freeze-thaw cycling. This paper firstly establishes theoretical models for the three sources of settlement including a statistical damage model for soils which experience cyclic freeze-thaw, a large strain thaw consolidation theory incorporating a modified Richards' equation and a Drucker-Prager yield criterion, as well as a simple rheological element based creep model for frozen soils. A novel numerical method was proposed for live computation of thaw consolidation, creep and freeze-thaw cycling in corresponding domains which vary with heat budget in frozen ground. It was then numerically implemented in the FISH language on the FLAC platform and verified by freeze-thaw tests on sandy clay. Results indicate that the calculated results agree well with the measured data. Finally a model test carried out on a half embankment in laboratory was modeled.

• Smart Structures and Systems
• /
• v.5 no.3
• /
• pp.241-260
• /
• 2009

Shape control of flexible structures using piezoelectric materials has attracted much attention due to its wide applications in controllable systems such as space and aeronautical engineering. The major work in the field is to find a best control voltage or an optimal placement of the piezoelectric actuators in order to actuate the structure shape as close as possible to the desired one. The current research focus on the investigation of static shape control of intelligent shells using spatially distributed piezoelectric curve beam actuators. The finite element formulation of the piezoelectric model is briefly described. The piezoelectric curve beam element is then integrated into a collocated host shell element by using nodal displacement constraint equations. The linear least square method (LLSM) is employed to get the optimum voltage distributions in the control system so that the desired structure shape can be well matched. Furthermore, to find the optimal placement of the piezoelectric curve beam actuators, a genetic algorithm (GA) is introduced in the computation model as well as the consideration of the different objective functions. Numerical results are given to demonstrate the validity of the theoretical model and numerical algorithm developed.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.6 no.8
• /
• pp.63-71
• /
• 1983

Aggregate planning coordinate the control variable over long-term to apply a demand variable and forcasting. In order to necessary the goal that doesn't make an inter-contradiction and explicitly defined. We made a considerable point of system approach for scheduling establishment. It include the control variables of aggregate planning : 1) employment 2) over time working and idle time 3) inventory 4) delivery delay S) subcontract 61 long - term facility capacity. Each variables composed of pure strategy as like a decision of inventory level, a change of employment level, etc. md alternative costs make a computation on the economic foundation. But the optimum alternative costs represent the mixed pure strategy. The faults of this method doesn't optimum guarantee a special scheduling as well as increasing a number of alternative combination. Theoretical, Linear Decision Rule make an including all variables, but it is almost impossible for this model to develope actually And also make use of the aggregate planning problem for developing system approach : LDR, heuristic model, Search Decision Rule, all kind of computers, simulation. But these models are very complex, each variables get an extremely inter-dependence. So this study be remained by theory level, some approach methods has not been brought the optimum solution to apply in every cases.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.9
• /
• pp.2181-2193
• /
• 1995

The effective elasticity and conduction of composite materials containing arbitrarily oriented multiple phases has been analyzed using the concept of orientation-dependent average fields and concentration factors. The analysis provided closed form expressions for the effective stiffnesses and conductivities. Under the prescribed boundary conditions, the concentration factors were evaluated by the equivalent inclusion principle, through which the interaction between various phases is approximated by the Mori-Tanaka mean-field approximation. SiC particulate(SiC$_{p}$) reinforce aluminum(Al) matrix composites were fabricated and their elastic constants and electrical conductivities were measured together with a careful study of their microstructure. The measured properties showed a systematic anisotropy and this behavior could be attributed to the preferred orientation of SiC$_{p}$. The theoretical model developed was applied to the computation of the anisotropic properties of these composites. Both two-phase and three-phase composites were considered based on the microstructural information. The SiC$_{p}$ was modeled as an ellipsoid with planar random orientation distribution in the extruded Al/SiC$_{p}$ composites. The effect of extraneous phase such as intermetallic compounds was also investigated.tigated.