• International Journal of Aeronautical and Space Sciences
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• v.15 no.3
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• pp.232-240
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• 2014

Transonic flow past a NASA SC(2)-0710 airfoil with deployments of a spoiler up to $6^{\circ}$ was studied numerically. We consider angles of attack from $-0.6^{\circ}$ to $0.6^{\circ}$ and free-stream Mach numbers from 0.81 to 0.86. Solutions of the unsteady Reynolds-averaged Navier-Stokes equations were obtained with a finite-volume solver using several turbulence models. Both stationary and time-dependent deployments of the spoiler were examined. The study revealed the existence of narrow bands of the Mach number, angle of attack, and spoiler deflection angle, in which the flow was extremely sensitive to small perturbations. Simulations of 3D flow past a swept wing confirmed the flow sensitivity to small perturbations of boundary conditions.

• The Journal of Korea Robotics Society
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• v.17 no.3
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• pp.359-364
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• 2022

This study presents a nonlinear model predictive control (NMPC)-based obstacle avoidance and whole-body motion planning method for the mobile manipulators. For the whole-body motion control, the mobile manipulator with an omnidirectional mobile base was modeled as a nine degrees-of-freedom (DoFs) serial open chain with the PPR (base) plus 6R (arm) joints, and a swept sphere volume (SSV) was applied to define a convex hull for collision avoidance. The proposed receding horizon control scheme can generate a trajectory to track the end-effector pose while avoiding the self-collision and obstacle in the task space. The proposed method could be calculated using an interior-point (IP) method solver with 100[ms] sampling time and ten samples of horizon size, and the validation of the method was conducted in the environment of Pybullet simulation.

• Fisheries and Aquatic Sciences
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• v.16 no.3
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• pp.211-220
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• 2013

A shaking motion could be used to improve fish escapement from a cod-end net by creating a sieving effect over the swept volume or by disturbing the optomotor response of the fish. In this study, a perpendicular shaking motion was generated in a towed cod-end net by a circular canvas attached to the end of the codend, which formed a biased cap-like shape. This concept was tested by using a model in a flow tank and by towing a prototype cod-end during sea trials. For the model tests, the amplitude of the shaking motion was $0.6{\pm}0.1$ times the rear diameter of the cod-end, and the period of the shaking motion was $2.6{\pm}0.1$ s at a flow velocity of 0.6 or 0.8 m/s. In the sea trials, the amplitude was $0.5{\pm}0.2$ times the rear diameter of the cod-end, and the period of the shaking motion was $7{\pm}4$ s at towing speeds of 1.2 or 1.7 m/s. Thus, the shaking amplitude during the sea trials was equal to or less than that observed in the tank tests, and the shaking period was twice as long. The shaking motion described by the amplitude and period could be an effective means to stimulate fish escapement from cod-end during fishing operations considering the response of the fish.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1356-1364
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• 1990

This paper deals with the preliminary design conditions of Stirling Engines based on an adiabatic analysis with regenerator effectiveness. The investigation of thermal regeneration process results that the definition of effectiveness proposed by Urieli et al. is appropriate for the present model. Then, it is applied to the already existing approximate analytic solution for the adiabatic model in order to optimize thermal efficiency as well as work parameter. Results show that thermal efficiency is less sensitive to the variation in design parameters than work. Phase angle for the maximum work is also the most efficient at high values of the effectiveness. Swept volume ratio should be chosen with care. The optimum value of dead volume ratio is at least less than the maximum efficiency condition. The feasible design range in compression ratio lies between the maximum efficiency condition and the structural limit of Stilring Engines, where the higher its value, the better. Changes in the temperature ratio do not alter the design conditions. Working fluids with the specific heat ratio 1.67 are more efficient that those with 1.4.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1197-1205
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• 1988

An analytical method to predict qualitative performance characteristics of the Stirling Engines in the preliminary design stages is investigated. Both the expansion and the compression cylinder are treated as adiabatic and piston motions are approximated as saw-toothed waves. Basic equations which were originally proposed by Finkelstein consist of mass conservation and energy balances for each adiabatic cylinder. The approximation on piston motions and physical conditions make it possible to divide an engine cycle into four fundamental processes. In each process, first, pressure can be expressed as a function of the crank angle by solving a nonlinear first order ordinary differential equation and other thermodynamic variables are determined in turn. Application of the cyclic steady condition to the whole processes can complete a cycle. Also, further analysis results in analytic expressions for cyclic work and heat transfer in terms of the engine parameters and thermodynamic variables at boundary points. The results are expected useful as a quick reference for the engine performances. Finally, the present method can be applied to the other adiabatic analyses on the Stirling Engines with piece wise linear piston motions, if mass variations are predictable.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.111-117
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• 2003

In the design of the split type free displacer Stilting cryocooler the motion of the displacer is very important to decide the cooling capacity, which depends upon the working gas pressure, the swept volume in the compression space and the expansion space, operating frequency, the phase shift between piston and displacer, etc. In this study, Stirling cryocooler actuated by the electric farce of the dual linear motor is designed and manufactured. Cool down characteristics of the cold end with laser displacement sensor in the expander of the Stilting cryocooler is evaluated. The charging pressure was 15kg$_{f}$/$\textrm{cm}^2$ and operating frequency was 50Hz. Input power and the lowest temperature were about 32W and 67K, respectively. And, displacement of the piston is measured by LVDTs (Linear Variable Differential Transformers), displacement of thedisplacer is measured by laser optic method, and phase shift between piston and displacer is discussed. As the peak-to-peak pressure of the compressor was increased, peak-to-peak displacement of the displacer was increased. The peak-to-peak displacement of the displacer increases in the range of 0 - 64.5Hz(resonant frequency of the displacer), but decreases steeply when the operating frequency is bigger than the resonant frequency. Finally when the phase shift between displacements of the Piston and displacer is 45。, operating frequency is optimum and is decided by resonant frequency of the expander, mass and cross section area of the displacer and constant by friction and flow resistance.e.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1572-1583
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• 1993

This paper deals with the analysis method of regenerator characteristics for designing a vuilleumier heat pump. First, models for evaluating the reheat and the flow losses are established by the comparative study between already proposed ones. Calculations based on the second-order method are performed for the well-known schulz heat pump. Results show that operating conditions as well as design parameters significantly affect the regenerator performances. The effects of operating conditions on the reheat and the flow losses appear to be similar in trends in both the hot-warm and the cold-warm regenerators. However, the losses in the one regenerator vary oppositely to those in the other with specific design parameters such as the phase angle and the swept volume ratio being changed. Also, it is confirmed that there is an optimum aspect ratio(D/L) which minimizes total loss for each regenerator.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1547-1555
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• 1993

An experimental study on convection heat transfer characteristics from a heated tube to an oscillating flow has been carried out, . This problem is of particular interest in the design of heat exchangers in Stirling cycle machines. Experimental system has been developed to measure temporal variations of temperature inside a heater tube during oscillating modes in a Stirling cycle machine. The dependence of temperature distributions and heat transfer rates on the oscillating frequency as well as the swept volume ratio and the mean pressure of a Stirling cycle machine is investigated in detail. The experimental results indicate that the measured temporal variations of temperature become nearly sinusoidal. The amplitude of temperature variation in the core of the tube is much more substantial than that near the tube wall, whereas the reverse is true for pulsating flows. It is also found that the heat transfer rate is increased significantly as the oscillating frequency or oscillating amplitude or the mean pressure in a tube is increased.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.4
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• pp.247-256
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• 2012

The purpose of this study is to decide the permeability and the rate of flow in a way of both site investigation and backward analysis and the most reasonable numerical analysis by performing a seepage model test for measuring the deformation swept volume of the embankment body in order to review a stability of the sea dyke being composed of multi-layers depending on variation of infiltration. As a result of the review, it could be forecasted that sweeping loss would be taken place at the boundary between bed protection works and embankment materials of the sea dyke due to a permeability difference of the multi-layered bed foundation structures and the sea dyke deformation would be occurred as a result thereby. As result of a numerical analysis for the seepage model test, it could be observed that critical velocity method was found to be smaller than the numerical analysis value but its tendency was similar and therefore it was judged that this method could be applied for the actual cross section.