• 한국전산유체공학회지
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• 제8권2호
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• pp.24-32
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• 2003

In this work, we propose a new idea of flapping airfoil design for optimal aerodynamic performance from detailed computational investigations of flow physics. Generally, flapping motion which is combined with pitching and plunging motion of airfoil, leads to complex flow features such as leading edge separation and vortex street. As it is well known, the mechanism of thrust generation of flapping airfoil is based on inverse Karman-vortex street. This vortex street induces jet-like flow field at the rear region of trailing edge and then generates thrust. The leading edge separation vortex can also play an important role with its aerodynamic performances. The flapping airfoil introduces an alternative propulsive way instead of the current inefficient propulsive system such as a propeller in the low Reynolds number flow. Thrust coefficient and propulsive efficiency are the two major parameters in the design of flapping airfoil as propulsive system. Through numerous computations, we found the specific physical flow phenomenon which governed the aerodynamic characteristics in flapping airfoil. Based on this physical insight, we could come up with a new kind of airfoil of tadpole-shaped and more enhanced aerodynamic performance.

• 한국추진공학회지
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• 제9권1호
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• pp.1-8
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• 2005

설계단계에서 수행되는 액체로켓엔진의 추력실 형상설계와 성능예측을 위하여 화학평형을 고려한 축대칭 압축성 해석코드를 개발하였다. 사용자의 편리함과 효율성에 중점을 두었으며, 형상파라미터의 입력값에 따라 자동으로 격자를 생성하고 연소실 조건은 추진제 조합, 연소압 그리고 혼합비를 지정함으로서 내부에서 계산하게 된다. 따라서 설계자는 추력실 형상 및 작동조건을 변화시켜 각각의 설계변수가 추력성능에 미치는 영향을 빠르고 손쉽게 파악할 수 있도록 하였다. CEA의 결과, JPL 노즐의 실험결과, 두 종류의 LRE 실제 엔진 자료, 그리고 KSR-III의 설계점 및 탈설계점 연소시험결과와 비교함으로서, 다양한 측면에서 해석코드의 정확도와 적용성을 평가하였다.

• Physical Therapy Rehabilitation Science
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• 제12권2호
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• pp.130-139
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• 2023

Objective: This study aimed to analyze the effects and characteristics of the height of the treatment table on the force and time of ground reaction (GR) and contact hand (CH) generated from the therapist's feet to generate thrust during spinal manipulation (SM). Design: A cross-sectional survey study Methods: Thirty-six healthy subjects were recruited. SM was performed on the ilium using a knee-high table, where the therapist felt it was easy to control the subject's posture and body shape and comfortable to generate force, as well as a relatively high thigh-high table. The force and time generated by the therapist's GR and CH were simultaneously measured through a force plate. Results: As a result, there was a significant difference in peak force and rundown force at the therapist's GR according to the table height (p < 0.05). In the therapist's CH, there was a significant difference between PreMin (preload minimum) force and peak force (p < 0.05), and there was a significant difference between the time from PreMin to peak and the time of the entire section (p < 0.05). Conclusions: As a result, the generation of increased CH force and faster thrust duration were confirmed by mobilizing the reduced GR force of the therapist to generate thrust than the relatively high table on the knee-high table.

• Journal of Mechanical Science and Technology
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• 제14권11호
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• pp.1244-1249
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• 2000

Burr and shape distortion are two main problems in micro-grooving. In this study, a simplified model is proposed based on large thrust force due to the tool edge radius. Experiments are conducted with a single crystal diamond tool on a 3-axis snaper-like machine varying the depth of cuts, and groove angles on brass, aluminum and OFHC. Experiments have shown that the thrust force becomes a dominant variable in burr generation compared to the principal force when the depth of cut is less than 2${\mu}m$. And fewer burrs develop on more brittle materials. Shape distortion is significant only when the groove angle is small and the depth of cut is larger than 30 ${\mu}m$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제21회 추계학술대회 논문집
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• pp.57-60
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• 2003

An axisymmetric compressible flow solver accounting for chemical equilibrium has been developed as an analysis tool exclusively suitable for performance prediction and optimum contour design of LRE thrust chamber. By virtue of several features focusing on user-friendliness and effectiveness including automatical grid generation and iterative calculations with changes in design parameters prescribed through only one keyword-type input file, a design engineer can evaluate very fast and easily the influences of various design inputs such as geometrical parameters and operating conditions on propulsive performance. Validations have been carried out for various aspects by detailed comparisons with the result of CEA code, experimental data of JPL nozzle, actual data for two historical engines, and ReTF data for KSR-III.

• 한국유체기계학회 논문집
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• 제8권6호
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• pp.47-54
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• 2005

An oscillating foil can produce a driving force through the generation of a reversed $K\'{a}rm\'{a}n$ vortex street, and it can be expected to be a new highly effective propulsion system. A simple pitching foil model was made and it was operated within a water channel. The wake formation behind a pitching foil was visualized and unsteady fluid forces were measured using a 6-axis force sensor based on force and moment detectors. We have been examined various conditions such as reduced frequency, amplitude and pivot point in NACA 0010. The results showed that thrust coefficients increased with a reduced frequency. We also presented the experimental results on the characteristics of a pitching foil at various parameters.

• 한국CDE학회논문집
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• 제4권4호
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• pp.295-311
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• 1999

An increasing attention is paid to STEP-NC, the next generation CNC controller interfacing STEP-compatible data. In this paper, we first propose an Architecture for the STEP-NC (called FBCC: Feature Baled CNC Controller) accepting feature code compatible with STEP-data, and executing NC motion feature by feature while monitoring the execution status. The main thrust of the paper has been to develop an automatic on-line tool path generation and modification scheme for milling operation. The tool path it generated iota each feature by decomposing into a finite number of primitive features. The key function in the new scheme is haw to accommodate unexpected execution results. In our scheme, the too1 path plinker is designed to have a tracing capability iota the tool path execution so that a new path can be generated from the point where the operation is stopped. An illustrative example is included to show the capability of the developed algorithm.

• 한국군사과학기술학회지
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• 제10권3호
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• pp.189-199
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• 2007

The present survey paper introduces the research history, characteristics of body and fin shapes, basic principles of various locomotions and propulsion-generation mechanism of aquatic animals in nature, which utilize unsteady flow through a noble mechanism that is different in paradigm from the propulsion generation mechanism of man-made marine vehicles, and so have excellent performance and efficiency. The authors hope that the present paper helps to activate the domestic research interest on the fields of swimming in nature, which is expected to provide great ideas for improvement and innovation of today's marine vehicles.

• 대한기계학회논문집A
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• 제34권11호
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• pp.1575-1580
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• 2010

최근 수중 생물체의 특성과 운동성을 가진 생체 모방형 수중로봇의 모방연구가 활발히 진행 되고 있다. 본 논문은 수중에서 기동성과 항해성이 우수한 가오리류 어류 움직임을 모방하여 날개 짓에 의한 속도 및 이동거리를 수치적으로 연구하고자 한다. 유체-구조 연성해석의 방법을 사용하여 3 차원 해석을 실시하였으며, 날개 짓에 의한 큰 변형을 보정하고자 격자 재생성 기능을 사용하였다. 실제 가오리는 날개 진동수에 의해 추진력에 가장 큰 영향을 받는다. 이를 바탕으로 실제 가오리의 움직임과 관련된 파라미터를 이용하여 진동수 및 진폭의 변화에 대하여 최대의 추진력을 갖는 날개의 움직임을 연구하고자 한다.

• Tribology and Lubricants
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• 제39권1호
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• pp.21-27
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• 2023

Surface texturing is widely applied to friction surfaces of various machine elements. Most of the theoretical studies have focused on isothermal (ISO) analyses which consider constant lubricant viscosity. However, there have been limited studies on the effect of oil temperature increase owing to viscous shear. Following the first part of the present study that investigated the effects of film-temperature boundary condition (FTBC) and groove number on the thermohydrodynamic (THD) lubrication characteristics of a surface-textured parallel thrust bearing with multiple rectangular grooves, this study focuses on the effect of groove depths. Current study numerically analyzes the continuity, Navier-Stokes, and energy equations with temperature-viscosity-density relations using a commercial computational fluid dynamics (CFD) software, FLUENT. The results of variation in temperature, velocity, and pressure distributions as well as load-carrying capacity (LCC) and friction force indicate that groove depth and FTBC significantly influence the temperature distribution and pressure generation. The LCC is maximum near the groove depth at which the vortex starts, smaller than the ISO result. For intense grooves, the LCC of THD may be larger than that from ISO. The frictional force decreases as the groove becomes deeper, and decreases more significantly in the case of THD. The study shows that groove depth significantly influences the THD lubrication characteristics of surface-textured parallel thrust bearings.