마찰스프링의 주퇴복좌장치 적용성 연구

차기업(Ki Up Cha),김학인(Hak In Gimm),조창기(Chang Ki Cho) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.3

The conventional medium and large caliber gun, in general, utilize the hydro-pneumatic recoil mechanism to control the firing impulse and to return to the battery position. However, this kind of mechanism may cause the problems like the leakages and the property changes in oil and gas due to the temperature variations between low and high temperatures. Accordingly, the friction spring mechanism has recently been researched as an alternative system. The friction spring mechanism consists of a set of closed inner and outer rings with the concentric tapered contact surfaces assembled in the columnar form, and can only be used under the compression load. When the spring column is axially loaded, the tapered surfaces become overlapped, causing the outer rings to expand while the inner rings are being contracted in diameter allowing an axial displacement. Because of friction between tapered contact surfaces, much higher spring stiffness is obtained on the stroke at the increase in load than the stroke at the decrease. In this paper, the dynamic equations regarding the friction spring system and the design approach have been investigated. It is also tried for a dynamic model representing the recoil motion and the friction spring forces. And the model has been proved from firing test using a gun system with friction springs. All the results show that the recoil mechanism using friction springs can substitute for the classic hydro-pneumatic recoil system.

실험계획법 및 메타모델 기반의 순차적 근사 최적화 적용 사례 연구

차기업(Cha Ki Up),김학인(Gimm Hak In),강대오(Kang Dae Oh) 제어로봇시스템학회 2012 제어로봇시스템학회 합동학술대회 논문집 Vol.2012 No.7

탄두내장형 탄약(CTA, Cased Telescoped Ammunition)과 회전식약실(Rotating Chamber)을 적용한 탄두내장형 탄약 발사장치(CTA GUN)의 운영과 작동은 탄의 장전과 추출이 원활히 이루어져야만 달성될 수 있게 된다. 회전식약실의 경우 테이퍼가 있는 기존의 고정식약실과는 달리 직선형 내경을 갖고 있기 때문에 원활한 탄피 추출 기능을 확보할 수 있는 체계적 분석 방안과 설계절차의 정립을 필요로 하게 된다. 본 연구에서는 원활한 탄피 추출 기능이라는 정성적 기준을 체계적 분석에 적합하도록 수치적으로 평가하기 위해 탄피 추출력을 성능지수로 설정하여 탄피 추출력이 최소화되는 설계조합을 산출하는 것을 목표로 하였다. 설계변수의 경우 회전식약실과 탄두내장형 탄약의 여러 형상 치수와 물성치가 될 수 있으며, 설계변수와 성능지수간 명시적 관계가 수립되어 있지 않기 때문에 각 설계변수 조합하에서 성능지수를 확인할 수 있도록 유한요소 모델을 구성하였으며 실험계획법을 기반으로 다수의 설계변수가 성능지수에 미치는 효과 및 영향을 분석하였다. 이후 효과분석을 위해 추출된 실험점을 초기점으로 한 메타 모델을 구성한 후 최적화 알고리즘을 적용하는 순차적 근사 최적화(SAO, Sequential Approximate Optimization) 기법을 적용하여 탄피 추출력이 최소화 되는 설계안을 도출할 수 있었다.

보문 : 느타리 갓 표면의 소수성이 세균갈색무늬병 발병도에 미치는 여향

이기영 ( Ki Young Lee ),양승업 ( Seung Up Yang ),한종우 ( Jong Woo Han ),윤건식 ( Kun Sik Yoon ),장후봉 ( Hoo Bong Jang ),차재순 ( Jae Soon Cha ) 한국균학회 2010 韓國菌學會誌 Vol.38 No.1

다공성 물질의 환형수직원통내에서의 자연대류 열전달 수치해석

차기업,김종보,Cha, Ki Up,Kim, Chong Bo 대한설비공학회 1989 설비공학 논문집 Vol.1 No.2

Numerical solutions for two-dimensional, steady, free convection are presented for a cylinder filled with saturated porous media. An annulus is bounded by inner wall with constant heat flux and two adiabatic horizontal walls with outer wall isothermally cooled. Governing equations are numerically solved for the range of Aspect Ratio 1 to 20, Radius Ratio, 1 to 20, and Rayleigh number, 50 to $10^4$ by Finite Difference method utilizing upwind scheme. Results are presented in terms of stream lines and isotherms, temperature distributions and local Nusselt numbers at the heated wall. Average Nusselt numbers are also presented for the comparisons.

Prediction of time-varying heat flux along a hollow cylindrical tube wall using recursive input estimation algorithm and thermal resistance network method

Noh, Jung-Hun,Cha, Ki-Up,Ahn, Sang-Tae,Yook, Se-Jin Elsevier 2016 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.97 No.-

<P><B>Abstract</B></P> <P>In this study, a model using the thermal resistance network method and the recursive input estimation algorithm was developed to analyze two-dimensional inverse heat conduction problems. The recursive input estimation algorithm consisted of the Kalman filter and the real-time least squares. A two-layered hollow cylindrical tube was assumed with the convection heat transfer boundary condition at the outer wall of the tube. Using the model developed in this study, an unknown time-varying heat flux at the inner wall of the tube was predicted from the known temperatures at some positions on the outer wall of the tube in the longitudinal direction. In the process of predicting the unknown heat flux, the temperature distribution in the two-layered hollow cylindrical tube wall was also obtained. The present model was able to accurately predict the unknown time-varying heat flux profiles of square waves or sinusoidal-like waves with and without spatial variations in the longitudinal direction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A model was developed to analyze two-dimensional inverse heat conduction problems. </LI> <LI> The model employed the thermal resistance network method to solve heat conduction. </LI> <LI> An unknown heat flux was estimated by the recursive input estimation algorithm. </LI> <LI> Transient heat flux profiles of square waves or sinusoidal-like waves were assumed. </LI> <LI> The model precisely predicted transient heat flux with or without spatial variations. </LI> </UL> </P>

Characterizations of gun barrel vibrations of during firing based on shock response analysis and short-time Fourier transform

Hak In Gimm,Ki Up Cha,Chang Ki Cho 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.5

"The behavior of shock vibration for a medium caliber gun barrel was experimentally investigated and then, numerical modal analysis,a signal processing technique as well shock response analysis were carried out en route to the detailed analyses. This approach was initiated by identifying mode frequencies from the numerical model and thus the frequencies were clarified using the periodogram together with the spectrogram based on the time frequency analysis. A shock response analysis was employed to draw more physical interpretations regarding the barrel behaviors due to firing shock. In this paper, therefore, the overall process of shock vibration analysis was demonstrated for analyzing the shock behavior of the gun barrel."

A Study of Dynamic Impact Models for Pile-Driver Breech Fatigue Testing System

조창기,차기업,Cho, Chang-Ki,Cha, Ki-Up The Korea Institute of Military Science and Techno 2010 한국군사과학기술학회지 Vol.13 No.4

This paper presents the modeling and validation of a pile-driver breech fatigue testing system model to replicate actual high pressure in a large caliber gun barrel. A hysteresis damping function was incorporated in the nonlinear impact force model. Test of real pile-driver breech fatigue testing system had been performed for model validation. Comparison of the experimental result and model simulation during impact were made. Numerical studies were performed to evaluate how the actual chamber pressure pattern in the live firing of gun barrel was affected by parameters' variation. Some of the parameters simulated included input velocity, damping coefficient and stiffness. As a result, a variety of actual chamber pressure pattern could be reproduced and controlled through current simulation model.

강선율 최적설계에 관한 연구

차기업,이영현,이성배,조창기,Cha, Ki-Up,Cha, Young-Hyun,Lee, Sung-Bae,Cho, Chang-Ki 한국군사과학기술학회 2010 한국군사과학기술학회지 Vol.13 No.6

Rifling force has a torsion impulse effect on the gun tube and thus generates undesirable vibration of the gun tube about its bore axis, putting additional stress on the projectile. High rifling force at the muzzle of the gun tube may adversely influence the trajectory of the projectile. And, the service life of rifled gun barrels is known to depend on the rifling force. Rifling force along the path of the projectile in the longitudinal direction of the gun tube can be described with projectile mass, projectile velocity, gas pressure curve and rifling angle. Under the same conditions, the character of the rifling of the gun barrel decisively influences the rifling force curve. To reduce the above mentioned harmful effect, locally distinct maximum of rifling force has to be avoided and maximum rifling force needs to be minimized. The best way to minimize the maximum rifling force is to design a rifling angle function so that the rifling force curve has a near trapezoidal shape. In this paper a new approach to make the optimal rifling force curve is described. The rifling angle determining the rifling force is developed by combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems.

Torsional Vibration Control of the Rotating Chamber Using a Reaction Wheel

Lim, Seung-Chul,Kim, Ki-Kap,Shim, Jeong-Soo,Cha, Ki-Up,Cho, Chang-Ki 한국정밀공학회 2012 International Journal of Precision Engineering and Vol.13 No.6

The rotating chamber is expected to significantly benefit mid-caliber automatic guns with the high firepower-to-armament space ratio. However, the parallel index, which is a core component of the chamber system, tends to be flexible in rapid operation. This may cause the chamber prone to torsional vibration so that serious misalignment problems arise during ammunition loading as well as firing processes. In this context, an active control algorithm is proposed incorporating a reaction wheel as the actuator, suppressing only the residual vibration and optionally self-adapting the shooting rate to the actuator condition. For assessment of the idea, the entire system is mathematically modeled and then simulated in several cases. The comparative simulation results support that by the proposed method the chamber vibration can be reduced even to 6.5 percent at the expense of relatively small amount of actuator energy.

A residual stress analysis program using a Matlab GUI on an autofrettaged compound cylinder

Qiu-Ming Yang,이영신,이은엽,김재훈,Ki-Up Cha,홍석균 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.11

A program for the residual stress analysis of an autofrettaged compound cylinder is designed using a Matlab graphical user interface (GUI) and program design technique. The high-pressure vessels are autofrettaged in order to increase their operating pressure and fatigue life. An autofrettage process causes plastic expansion of the inner section of the cylinder, adding residual compressive stress to the bore after relaxation. Such a compound cylinder is produced via a shrink-fit procedure that incorporates a monobloc tube that has previously undergone autofrettage. This paper presents a simple and visual tool to calculate the residual stress and describe the distribution of residual stress for both the elastic-perfectly plastic model and the strain-hardening model.