• Journal of Mechanical Science and Technology
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• 제17권3호
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• pp.350-356
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• 2003

In this study, a numerical analysis for the piston secondary dynamics of small refrigeration reciprocating compressors is performed. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the variation in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the lubrication characteristics as functions of crank angle under compressor running conditions. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction tosses.

• Tribology and Lubricants
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• 제18권4호
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• pp.291-298
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• 2002

In this study, a numerical analysis f3r the piston secondary dynamics and lubrication characteristics of small refrigeration reciprocating compressors is presented. In general, the length of cylinder in this class of compressors is shortened to diminish the frictional losses of the piston-cylinder system. So, the contacting length between piston and cylinder wall is in variable with the rotating crank angle around the BDC of the reciprocating piston. In the problem formulation of the piston dynamics, the change in bearing length of the piston and all corresponding forces and moments are considered in order to determine the piston trajectory, velocity and acceleration at each step. A Newton-Raphson procedure was employed in solving the secondary dynamic equations of the piston. The developed computer program can be used to calculate the entire piston trajectory and the hydrodynamic forces and moments as functions of crank angle under compressor running conditions. The results explored the effects of the radial clearance, lubricant viscosity, and pin location on the stability of the piston, the oil leakage, and friction losses.

• Advances in aircraft and spacecraft science
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• 제3권4호
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• pp.399-425
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• 2016

The dynamical requirements are obtained for airplanes to travel on inclined circular trajectories. Formulas are provided for determining the load factor, the bank angle, the lift coefficient and the thrust or power required for the motion. The dynamical properties of the airplane are taken into account, for both, airplanes with internal combustion engines and propellers, and airplanes with jet engines. A procedure is presented for the construction of tables from which the flyability of trajectories at a given angle of inclination can be read, together with the corresponding minimum and maximum radii allowed. Sample calculations are shown for the Cessna 182, a Silver Fox like unmanned aerial vehicle, and a F-16 jet airplane.

• International Journal of Fluid Machinery and Systems
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• 제8권3호
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• pp.132-141
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• 2015

This paper presents a CFD-based methodology for the prediction of guide vane torque in hydraulic turbine distributor for aligned and misaligned configurations. A misaligned or desynchronized configuration occurs when the opening angle of one guide vane differs from the opening angle of all other guide vanes, which may lead to a torque increase on neighbouring guide vanes. A fully automated numerical procedure is presented, that automates computations for a complete range of operation of a 2D or 3D distributor. Results are validated against laboratory measurements.

• 한국전산유체공학회지
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• 제9권2호
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• pp.43-51
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• 2004

Interaction between fluid flow and thermal radiation has received considerable attention due to its numerous applications in engineering field. In this case the thermofluid properties of radiating fluid vary with the variation of temperature field caused by absorption and emission of radiant heat. To analyze the radiation heat transfer in radiating fluid, the simultaneous solution of the radiative transfer equation (RTE) and the fluid dynamics equations is required. This means that the numerical procedure used for the RTE must be computationally efficient to permit its inclusion in the other submodels, and must be compatible with the other transport equations. The finite volume method (FVM) and the discrete ordinates method (DOM) are usually employed to simulate radiation problems in generalized coordinates. These two representative methods are examined and compared, especially in view of the numerical integration of the radiation intensity over solid angle. The FVM shows better accuracy than the DOM owing to less constraints of the selection of control angle.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.559-564
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• 2001

The design of an automobile mirror actuator system needs a systematic optimization due to several variables, constraints, geometric limitations, moving angle, and so on. Therefore, this article provides the procedure of a genetic algorithm(GA) based optimization with finite element analysis for design of a mirror actuator considering design constraints, geometric limitations, moving angle. Local optimum problem in optimization design with sensitivity analysis is overcome by using zero-order overall searching method which is new optimization design method using a genetic algorithm.

• 한국항공운항학회지
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• 제14권1호
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• pp.43-48
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• 2006

The present study was carried out in order to develope a seven-hole pressure probe which is able to measure high flow angles. The seven-hole pressure probe is a non-nulling, directional velocity probe used for measuring three dimensional flow that having high flow angles. A 4 mm diameter seven-hole conical pressure probe was manufactured with a cone angle of 70$^{\circ}$. The probe was comprised of seven 1 mm diameter stainless steel tubes packed close together and fitted into an outer stainless steel sleeve. The calibration procedure is based on the use of the Callington's polynomial curve-fit method. The validity of the seven-hole conical pressure probe is demonstrated by comparisons with hot-wire data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.62-70
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• 2004

Interaction between fluid flow and thermal radiation has received considerable attention due to its numerous applications in engineering field. In this case the thermofluid properties of radiating fluid vary with the variation of temperature field caused by absorption and emission of radiant heat. To analyze the radiation heat transfer in radiating fluid, the simultaneous solution of the radiative transfer equation (RTE) and the fluid dynamics equations is required. This means that the numerical procedure used for the RTE must be computationally efficient to permit its inclusion in the other submodels, and must be compatible with the other transport equations. The finite volume method (FVM) and the discrete ordinates method (DOM) are usually employed to simulate radiation problems in generalized coordinates. These two representative methods are examined and compared, especially in view of the numerical integration of the radiation intensity over solid angle. The FVM shows better accuracy than the DOM owing to less constraints of the selection of control angle.

• 한국생산제조학회지
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• 제22권6호
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• pp.1003-1009
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• 2013

This paper presents a simple procedure to obtain the instantaneous cutting force constants needed to predict milling forces. Cutting force data measured in a series of slot milling tests were used to determine the cutting force constants at different feed rates. The values of the cutting force constants were determined directly at the tool rotation angle that maximized the uncut chip thickness. Then, the instantaneous cutting force constant was obtained as a function of the instantaneous uncut chip thickness. This approach can greatly enhance the accuracy of the mechanistic cutting force model for end milling. In addition, the influences of several cutting parameters on the cutting forces, such as the tool helix angle and axial depth of cut, were discussed.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.57.2-57.2
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• 2011

In this study, the effects of shear flows around a 2-dimensional airfoil, S809 on its aerodynamic characteristics were analyzed by CFD simulations. Various parameters including reference inflow velocity, shear rate, angle of attack, and cord length of the airfoil were examined. From the simulation results, several important characteristics were found. Shear rate in a flow makes some changes in the lift coefficient depending on its sign and magnitude but angle of attack does not have a distinguishable influence. Cord length and reference inflow also cause proportional and inversely proportional changes in lift coefficient, respectively. We adopted an analytic expression for the lift coefficient from the thin airfoil theory and proposed a modified form applicable to the traditional load analysis procedure based on the blade element momentum theory. Some preliminary results applied to an well known load simulation software, FAST, are presented.