• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.11
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• pp.895-903
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• 2007

CMBT(Curved Moving Boundary Treatment) is a newly developed scheme for the treatment of a no slip condition on the curved solid wall of moving obstacle in a flow field. In our research CMBT was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of CMBT on the complex shape of the obstacle, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of Navier-Stokes equation with deforming mesh technique. The simulations were performed in a moderate range of reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical reynolds number for vortex shedding is ar Re=250 and the result is the same as the case of fixed cylinder. As the cylinder approaching to one wall, the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. As the velocity ratio increase the third vortex are generated by interacting with the 2nd vortexes developed on the upper and lower wall boundary layer. The resultant $C_d$ decrease as reynolds number increasing and the Cd approached to a value when Re>1000.

• Journal of Korean Ophthalmic Optics Society
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• v.12 no.3
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• pp.71-75
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• 2007

This research was conducted from 1 March 2005 to 28 February 2007. We collected data from optician stores around Kwang-Ju city, 208 people aged 40 to 80 years using the cross cylinder method to find out age and gender dependence of near addition. 1. Age dependence of Refractive error shows 5% of emmetropia 34% of myopia and 43% of hyperopia. These results reveal that rate of hyperopia is higher than emmetropia and myopia. Mixed Astigmatism rate was 18%. 2. Near addition required to correct Presbyopia is analyzed as functions of gender and ages. In case of man: 40-44 (+0.75D), 45-49(+1.25D), 50-54(+1.41D), 55-59(+1.92D), 60-64(+2.35D), 65-69(+1.97D), 70(+3.12D), In case of woman: 40-44 (+1.08D), 45-49 (+1.38D), 50-54 (+1.67D), 55-59(+2.05D), 60-64 (+2.50D), 65-69 (+2.57D), $70{\leq}(+3.18D)$. Result shows it's Adding power higher than man. 3. Age dependence of Axis of Astigmatism. In case of horizontal astigmatism 61.2%, vertical 2.8% and rest else for 36%. Setting point from Binocular vision tells that average adding power of 40-44 (+0.75D) or (+1.00D), 45-49 (+1.25D) or (+1.50D), 50-54 (+1.50D), 55-59 (+2.00D), 60-64 (+2.50D), 65-69 (+2.50D) or (+2.75D), over $70{\leq}(+3.00D)$ or (+3.25D) of average adding power.

• Wind and Structures
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• v.29 no.1
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• pp.43-53
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• 2019

Vortex-induced vibration of three circular cylinders (each of diameter D) in an equilateral triangular arrangement is investigated using the immersed boundary method. The cylinders, with one placed upstream and the other two side-by-side downstream, are free to vibrate in the cross-flow direction. The cylinder center-to-center spacing L is adopted as L/D = 2.0. Other parameters include the Reynolds number Re = 100, mass ratio $m^*=2.0$, reduced velocity $U_r=2{\sim}15$ and damping ratio ${\zeta}=0$. Cylinder vibration responses are dependent on $U_r$ and classified into five regimes, i.e. Regime I ($U_r{\leq}3.2$), Regime II ($3.2<U_r{\leq}5.0$), Regime III ($5.0<U_r{\leq}6.4$), Regime IV ($6.4<U_r{\leq}9.2$) and Regime V ($U_r>9.2$). Different facets of vibration amplitude, hydrodynamic forces, wake patterns and displacement spectra are extracted and presented in detail for each regime.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.153-159
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• 2007

The performance of a direct-injection type diesel engine often depends on the strength of air flow in the cylinder, shape of combustion chamber, the number of nozzle holes, etc. This is of course because the process of combustion in the cylinder was affected by the mixture formation process. In the present paper, high speed photography was employed to investigate the effectiveness of holes penetrated from the bottom of cavity wall to piston crown for some more useful utilization of air. The holes would function to improve mixing of fuel and air by the increase of air flow in the cylinder. The results obtained are summarized as follows, (1) Activated first of the combustion by shorten of ignition timing and rapid flame propagation (2) Raised the combustion peak pressure, more close to TDC the formation timing of peak pressure.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_2
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• pp.661-667
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• 2020

The optimal shape modeling of core parts through 3D modeling and structural analysis for the development of small and medium-sized ships. The goal is to improve the efficient structure of the hydraulic system for controlling the rudder among the core steering parts in small and medium-sized ships. Through 3D modeling and structural analysis, a new concept of tiller parts and a double-acting hydraulic cylinder control system were proposed and operational structural stability was evaluated. Structural analysis of the three different tiller designs that can be replaceable onto existing fishing vessels was conducted to derive the final shapes. The emphasis was placed on evaluating the structural stability of the key drive components, the tiller, pin, and cylinder rodin the maximum torque condition of the hydraulic cylinder.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.1
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• pp.38-50
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• 1994

To improve the efficiency of internal combustion engines, it is necessary to understand mixed air-fuel in-cylinder flow processes accurately at intake and compression strokes. There is experimental and numerical methods to analyse in-cylinder flow process. In numerical method, standard $k-{\varepsilon}$ model with wall function was mostly adopted in in-cylinder flow process. But this type model was not efficiently predicted in the near wall region. Therefore in the present study, low Reynolds number $k-{\varepsilon}$ model was adopted near the cylinder wall and standard $k-{\varepsilon}$ model in other region. Also QUICK scheme was used for convective difference scheme. This study takes axisymmetric reciprocating model engine motored at 200rpm with a centrally located valve, incorporated 60 degree seat angie, and flat piston surface excluding inlet port. Because in-cylinder flow processes are undergoing unsteady and compressible, averaged cylinder pressure and inlet velocity at arbitrary crank angle are determined from thermodynamic analytic method and incylinder states at that crank angle are iteratively determined from the numerical analytic method.

• International Journal of Automotive Technology
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• v.3 no.2
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• pp.47-52
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• 2002

The integration of CAD/CAM/CAE in product development is the key to realize concurrent engineering. Generally, different systems are employed in product development departments. These different systems create a lot of trout)toes such as difficulty in communication, misunderstanding and so on. A new approach to integrate CAD/CAM/CAE in one system based on CATIA thor the end-to-end process in cylinder head development is presented. Hulti Model Technology (MMT) is used to create consistent and associated CAD models for the end-to-end process in cylinder head development. The concept and method to create and organize multi models are discussed. A typical four-layer structure of HHT for mechanical products is defined. The multi level structure of the cylinder head models based on MMT is provided. The CAD models of cylinder head created based on MMT can be used as the consistent model. All models in the downstream of cylinder head development such as structure analysis, CFD, sand core design , casting simulation and so oil are associated with the CAD models. Practice shows the approach in this paper enables the development process to be carried concurrently and can obviously shorten time to the market, reduce product cost and improve product quality.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.2
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• pp.167-170
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• 2011

Purpose: This study was tried whether expectation of astigmatism from spherical equivalent visual acuity was possible. Methods: For 54 men and women (108 eyes) corrected to emmetropia, average age of 23.3, changes of visual acuity (5m) were measured with an increasing the powers at every ${\pm}$0.25D when the (-) axis of cross cylinder is $180^{\circ}$, $90^{\circ}$, and $45^{\circ}$, respectively. Results: As the power of cross cylinder was increased, visual acuity was decreased. When the powers of cross cylinder were ${\pm}$2.50D ($180^{\circ}$ and $90^{\circ}$) and ${\pm}$2.25D ($45^{\circ}$), visual acuity was 0.05 which is the minimum measurement possible. Conclusions: The diagram on astigmatism dealing with each spherical equivalent visual acuity was able to tabulate.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.9
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• pp.806-813
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• 2013

For the past years, higher power rating 2 stroke super long stroke diesel engines having more than 8 cylinders and larger cylinder bore are installed mainly on very large containerships to save on fuel consumption. However, these engines are prone to X-mode vibration due to 2nd node torsional vibration or the X-type moment, particularly because of the increase in total length and height. Recently, cases of excessive X-mode vibration often occurred on engine's major components. This vibration is manifested also as secondary vibration causing failure in engine-mount large structures. This study investigated the excitations caused by the 2nd node propulsion shafting torsional vibration that influence X-mode vibration of the main engine and practical countermeasures are proposed. An 8RT-flex82T 8 cylinder engine and 11S90ME-C 11 cylinder engine for a container ship was used as research model.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.1
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• pp.82-93
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• 2008

The flowfield behind two cylinders and flow-induced noise generated from the cylinders in various arrangement are numerically investigated based on the finite difference lattice Boltzmann model with 21 velocity bits. which is introduced a flexible specific heat ${\gamma}$ to simulate diatomic gases like air. In an isolated cylinder with two type of mesh. some flow parameters such as Strouhal number $S_t$ and acoustic pressure ${\Delta}p$ simulated from the solution are given and quantitatively compared with those provided the previous works. The effects of the center-to-center pitch ratio $L_{cc}/d=2.0$ in staggered circular cylinders as shown in Fig. 1 and angles of incidence ${\alpha}=30^{\circ}(T_{cc}/d=0.5)$, $45^{\circ}(T_{cc}/d =0.707)$ and $60^{\circ}\;(T_{cc}/d=0.866)$, respectively, are studied. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in staggered arrangement. With the results of drag $C_d$ and lift $C_l$ coefficients and vorticity contours. the mechanisms of the interference phenomenon and its interaction with the two-dimensional vortical structures are present in the flowfields under $Re\;{\le}\;200$. The results show that we successively capture very small pressure fluctuations, with the same frequency of vortex shedding, much smaller than the whole pressure fluctuation around pairs of circular cylinders. The upstream cylinder behaves like an isolated single cylinder, while the downstream one experiences wake-induced flutter. It is expected that, therefore, the relative position of the downstream cylinder has significant effects on the flow-induce noise, hydrodynamic force and vortex shedding characteristics of the cylinders.