• Journal of the Korean Institute of Gas
• /
• v.17 no.6
• /
• pp.52-57
• /
• 2013

In this study, the strain energy density, stress and deformation behaviors have been analyzed as functions of a thickness and a force area of protective helmets with and without an extruder on the top of the shell structure using the finite element method. The strain energy density in which is related to the absorption capacity of an impact energy transfer is one of a key element of the helmet safety. The FEM analyzed results show that when the impulsive force of 4,540N is applied on the top surface of the helmets, the maximum stress is linearly reduced for an increased area of impact forces. But, the maximum strain energy density has been reduced for the increased force area. The reduced strain energy density may increase the impulsive forces transferred to the head and neck of helmet wearers, which may decrease the impact energy absorption safety of the helmets. In thus, it is safer design of the helmet in which has an extruded structure on the summit surface, but the modified helmet may decrease the impact energy absorption capacity.

• The Bulletin of The Korean Astronomical Society
• /
• v.35 no.1
• /
• pp.72.2-72.2
• /
• 2010

We use three-dimensional hydrodynamic simulations to investigate nonlinear gravitational responses of gas to, and the resulting drag force on, a massive perturber moving on a circular orbit through a uniform gaseous medium. We assume that the background medium is non-rotating and adiabatic with index 5/3, and represent the perturber using a Plummer potential with softening radius a. This work extends our previous study where we showed that the drag force on a straight-line trajectory is proportional to a0.45 if the perturber is massive enough. This indicates that the orbital decay of supermassive black holes (SMBHs) near galaxy centers may take much longer than the prediction of the linear force formula applicable for low-mass perturbers. For the circular orbits are considered, however, we find that the nonlinear drag force becomes independent of a, but dependent instead on the orbital radius R as $\varpropto$ R0.5. This suggests not only that the choices of large values of a, for resolution issues, in recent numerical experiments for mergers of SMBH, are marginally acceptable, but also that the gaseous drag indeed provides an efficient mean for the orbtial decay of SMBHs.

• Journal of Welding and Joining
• /
• v.26 no.4
• /
• pp.61-65
• /
• 2008

The static force balance model (SFBM) has been used to analyze drop transfer in gas metal arc welding. Although the SFBM is capable of predicting the detaching drop size in the globular mode with reasonable accuracy, discrepancy between the calculated and experimental results increases with current. In order to reduce discrepancy, the SFBM is modified by considering the momentum of the molten metal flow, which is generated by the pinch pressure. The momentum increases with smaller drop size and becomes compatible to the electromagnetic force. The modified force balance model (MFBM) predicts the experimental results more accurately, and extends its application to the projected mode.

• Journal of Drive and Control
• /
• v.19 no.3
• /
• pp.1-8
• /
• 2022

In this paper, the design of automatic impact force control mechanism of hydraulic breaker was studied. The control mechanism uses the change of piston upper chamber pressure, when the hydraulic breaker impacts various strength rock. The piston stroke is controlled by rock strength sensing valve, piston stroke switching valve, and piston control valve. It is imperative to denote the area of each valve section, the spring constant of the spring. It provides convenience to users by automatically adjusting the appropriate striking force, according to the strength of the rock. Additionally, by increasing work productivity, it can contribute to reducing greenhouse gas emissions due to fuel efficiency reduction.

• 한국전산유체공학회:학술대회논문집
• /
• 2006.10a
• /
• pp.9-10
• /
• 2006

A numerical method for simulating tree surface flows including the surface tension is presented. Numerical scheme is based an a fractional-step method with a finite volume formulation and the interface between liquid and gas is tracked by Volume of Fluid (VOF) method. Piecewise Linear Interface Calculation (PLIC) method is used to reconstruct the interface and the surface tension is considered using a Continuum Surface Force (CSF) model. Several free surface flow phenomena were simulated to show its effectiveness to find such phenomena.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2006.06a
• /
• pp.59-60
• /
• 2006

Some useful flow regime data are obtained from the experiments using the flight producing hyper-gravity(2g) conditions and on ground(1g) with the identical flow conditions. The flow regime data obtained at 1g and 2g conditions are compared with new dimensionless flow regime map using Fr, Bo and We number related with gravity, surface tension and inertia force.

• Journal of Power System Engineering
• /
• v.9 no.4
• /
• pp.209-213
• /
• 2005

The effects of density change of ambient gas on mixture formation process have been investigated in high temperature and pressure field. To analyze the mixture formation process of evaporating diesel spray is important for emissions reduction in actual engines. Ambient gas density was selected as experimental parameter. The ambient gas density was changed from $r_a=5.0kg/m^3\;to\;r_a=12.3kg/m^3$ with a high pressure injection system(ECD-U2). For visualization of the experiment phenomenon, a CVC(Constant Volume Chamber) was used in this study. The ambient temperature and injection pressure are kept as 700K and 72MPa, respectively. The images of liquid and vapor phase in the evaporating free spray were simultaneously taken by exciplex fluorescence method. As experimental results, with increasing ambient gas density, the tip penetration of the evaporating free spray decreases due to the increase in the drag force from ambient gas.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.5 s.176
• /
• pp.1305-1313
• /
• 2000

In a co-rotating scroll compressor, both scrolls rotate on their fixed axes contrary to the conventional orbiting type scroll machine. This implies fixed locations and directions of the gas pressure force and sealing force. Because the tilting moment is mainly caused by interplay between the resultant force of above forces and bearing reaction force, the variation during one cycle is relatively small. Under real operation, this moment is balanced by the restoring moment created by the reaction between the baseplate and thrust bearing or between the scroll tip and baseplate. If these reactions become too large, greater torque is required due to increased friction in addition to the wear of mating parts. Consequently, appropriate study and minimization of tilting moment is important in the design of scroll machines. In this study, taking into account of the small variation of tilting moment during one cycle, we minimize the moment and thrust bearing reaction force by a properly designed back pressure chamber. As a result, for both the driving and driven scrolls, the tilting moment and the reaction force of thrust bearing can be minimized. And the stability is improved for all cases.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.37 no.4
• /
• pp.212-217
• /
• 2014

Recently, Korea Air Force has been facing a lot of problems in its pilot training system such as training time shortage due to the expensive gas price, noise pollution and difficulties in finding airspace for training. To tackle these problems, a new training system (called L-V training system) using both aircraft and its simulator has been suggested. In the system, a data link is established between aircraft and simulator to exchange their flight information. Using the flight information of simulator, aircraft can perform various air missions with or against imaginary aircraft (i.e., simulator). For this system, it is crucially important that fair fighting condition has to be guaranteed between aircraft and simulator. In this paper, we suggested an approach to impose a maneuvering restriction to simulator in order to provide fair fighting condition between aircraft and simulator.

• Proceedings of the Membrane Society of Korea Conference
• /
• 2001.10a
• /
• pp.39-50
• /
• 2001

The performance of membranes is governed their pore struture. Pore structures of porous materials can be determined by a number of techniques. However, The novel technique, capillary folw porometry has a number of advantages. In this technique, the sample is brought in contact with a liquid that fills the pores in the membrane spontaneously. Gas under pressure is used to force the liquid from the pores and increase gas flow. Gas flow rate measured as a function of gas pressure in wet and dry samples yield data on the largest pore size, the mean flow pore size, flow distribution and permeability. Pore characteristics of a number of membranes were measured using this technique. This technique did not require the use of any toxic material and the pressure employed was low. Capillary flow porometry is a suitable technique for measurement of the pore structure of many membranes.