• Transactions of the Korean Society of Mechanical Engineers B
• /
• 제33권7호
• /
• pp.506-511
• /
• 2009

Insect flight is adapted to cope with each circumstance by controlling a variety of the parameters of wing motion in nature. Many researchers have struggled to solve the fundamental concept of insect flight, but it has not been solved yet clearly. In this study, to find the most effective flapping wing dynamics, we conducted to analyze CFD data on fixing some of the optimal parameters of wing motion such as stoke amplitude, flip duration and wing rotation type and then controlled the deviation angle by fabricating wing tip motion. Although all patterns have the similar value of lift coefficient and drag coefficient, pattern A(pear-shape type) indicates the highest lift coefficient and pattern H(pear-shape type) has the lowest lift coefficient among four wing tip motions and three deviation angles. This result suggest that the lift and drag coefficient depends on the angle of attack and the deviation angle combined, and it could be explained by delayed stall and wake capture effect.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• 제23권8호
• /
• pp.681-689
• /
• 2013

The commercial tools to simulate the non-linear dynamic characteristics of wind turbine system are various but, the tool take much time to simulate the control algorithm and require many input variables. In this paper, the procedures to derive the simplified 4-degree-of-freedom mathematical model of a 2-MW wind turbine which could be used at the initial design stage of the controller are proposed based on RISO's suggested method. In this model, the 1st tower fore-after bending motion and 1st blade flapping motion are also considered in addition to the rotor-generator rotation motion in the 2-DOF model. The effectiveness of the 4-DOF model is examined comparing with the 2-DOF model and verification of the simplified model is accomplished through modal analysis for whole wind turbine system.

• Fashion & Textile Research Journal
• /
• 제6권5호
• /
• pp.565-574
• /
• 2004

The purpose of this study is to investigate the historical background and basic composition of costume of the Baekje period. Main official hats of Baekje include the transformed hat, jougwan and daeryun-style ipsikgwan. Daeryun-style ipsikgwan employed chowha shape in most cases, symbolizing good auspice under the harmony of the male and female principles. Main types of costume of the Baekje period are po, yu, go and sang. The king, governmental officials and the common people all put on po of jikryeong gyoim style. Yu' is classified into two styles, chaksu with the narrow sleeve and daesu with the broad one. 'Go' has two styles, gunggo and gwango. The former is narrow in the breadth of the trouser and the latter, wide. 'Sang' is classified into various style according to whether it contains stripes of many colors, thin wrinkles or thick wrinkles. For the decoration of official hat used in the period of the Three Kingdoms, Baekje employed chowha in shape, Kokuryo, chowha and joik and Shilla, joik. In Baekje, rhythmic patterns of flame were applied to official hats, presenting brilliance. In Shilla, shaking geumyeongrak was used for official hats to show movement. In Kokuryo, such hats used flapping feathers, symbolizing dynamic power. Most necklaces and bracelets of the Baekje period were simple and plain.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• 제14권7호
• /
• pp.639-647
• /
• 2004

This paper concerns the analytical modeling and dynamic analysis of advanced rotating blade structure implemented by a dual approach based on structural tailoring and viscoelastic material technology. Whereas structural tailoring uses the directionality properties of advanced composite materials, the passive material technology exploits the damping capabilities of viscoelastic material (VEM) embedded into the host structure. The main structure is modeled as a composite thin-walled beam Incorporating a number of nonclassical features such as transverse shear. anisotropy of constituent materials, and rotary inertia etc. The VEM layer damping treatment is modeled by using the Golla-Hughes-McTavish (GHM) method, which is employed to account for the frequency-dependent characteristics of the VEM. The displayed numerical results provide a comprehensive picture of the synergistic implications of both techniques, namely, the tailoring and damping technology on dynamic response of a thin-walled beam structure exposed to external time-dependent excitation.

• Wind and Structures
• /
• 제32권2호
• /
• pp.105-114
• /
• 2021

This paper describes a wind tunnel test on a 1:25 scale model of TTU building with several adjustable openings in order to comprehensively study the characteristics of fluctuating internal pressures, especially the phenomenon of the increase in fluctuating internal pressures induced by tangential flow over building openings and the mechanism causing that. The effects of several factors, such as wind angle, turbulence intensity, opening location, opening size, opening shape and background porosity on the fluctuating internal pressures at oblique wind angles are also described. It has been found that there is a large increase in the fluctuating internal pressures at certain oblique wind angles (typically around 60° to 80°). These fluctuations are greater than those produced by the flow normal to the opening when the turbulence intensity is low. It is demonstrated that the internal pressure resonances induced by the external pressure fluctuations emanating from flapping shear layers on the sidewall downstream of the windward corner are responsible for the increase in the fluctuating internal pressures. Furthermore, the test results show that apart from the opening shape, all the other factors influence the fluctuating internal pressures and the internal pressure resonances at oblique wind angles to varying degrees.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• 제32권10호
• /
• pp.118-126
• /
• 2004

The propulsive characteristics of oscillating flat plates are investigated using a discrete vortex method. The plates and their wakes are represented by discrete point vortices. To analyze the closely coupled aerodynamic interference between the plates, a vortex core model and a vortex core addition scheme are combined. A calculated wake shape for a flat plate in heaving oscillation is compared with flow visualization. The effect of wake shapes on the propulsive characteristics of the plates in pitching oscillation is investigated. The propulsive characteristics of oscillating plates with three cases (1. one is stationary and another is oscillating, 2. both oscillating in phase, 3. both oscillating out of phase) are calculated. The plates oscillating out of phase showed the largest thrust force among the three cases.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• 제38권7호
• /
• pp.647-654
• /
• 2010

In this study, an efficient ornithopter aerodynamic model, which is applicable to ornithopter wing design considering fluid-structure interaction or ornithopter flight dynamics and control simulation, was proposed and experimentally validated through the wind tunnel experiments. Due to the ornithopter aerodynamics governed by unsteady low Reynolds number flow, an experimental device was specially designed and developed. A part of the experimental device, 2-axis loadcell, was situated in the non-inertial frame; the dynamic calibration method was established to compensate the inertial load for pure aerodynamic load measurements. The characteristics of proposed aerodynamic model were compared with the experimental data in terms of mean and root-mean-square values of lift and drag coefficients with respect to the flow speed, flapping frequency, and fixed angle of attack.

• Proceedings of KOSOMES biannual meeting
• /
• 해양환경안전학회 2006년도 추계학술발표회
• /
• pp.53-58
• /
• 2006

Along with the development of costal engineering, various type of breakwaters have been built. The main purpose of breakwaters are to provide harbour protection against waves, to stabilize beaches against erosion due to large wave action, and to provide for temporary wave protection for installation on or under water surface. This paper an application example of PIV system for analyzing the flow of Floating Breakwater with double barriers. We introduce an analysis method to predict the characteristics of flow around the neighboring fields of Floating Breakwater with double barriers in order to develop a high performance model. Flow visualization has conducted in circulating water channel by a high speed camera and etc. Flowing phenomenon according to velocity distribution and flow separation around the breakwater with double barriers were obtained by 2-D PIV system.

• Korean Journal of Poultry Science
• /
• 제46권3호
• /
• pp.155-160
• /
• 2019

The Korean Hanhyup broiler has commercialized native meat-type chicken. This study aimed to determine the effects of two types of litter material-sawdust and rice husk, and gender on the Korean Hanhyup broiler. Chicks (n=416) were randomly assigned in a $2{\times}2$ factorial design by type of litter material and gender. The behavior of chicken's was monitored continuously for 12 hours during the $1^{st}$ through $8^{th}$ week of age. The time spent on standing, sitting, and walking and the frequency of drinking, feeding, preening, dust bathing, flapping, and aggressive pecking, and pecking of chicken's behavior were recorded. The behavior of chickens during the starter (1 to 4 weeks) and finisher period (5 to 8 weeks) was compared to observe the changes upon maturity. Our results indicate that litter material type and gender have no effect on the behavior of chickens. However, aggressive pecking and pecking caused increment in the rice husk as compared to sawdust (P<0.05). Sawdust as litter material for bedding was found to be better than rice husk with respect to Korean Hanhyup broiler behavior.

• Journal of Aerospace System Engineering
• /
• 제17권6호
• /
• pp.63-71
• /
• 2023

In the present study, the effect of pitch amplitude on the unsteady aerodynamics of a NACA 0012 airfoil is numerically investigated. When the frequency ratio is equal to 1.0, airfoil pitching with 20 and 30 degrees of pitch amplitude shows almost small lift generation, but the lift is significantly increased in case of 10-degree pitch amplitude. When the frequency is 0.5, the lift coefficients have large values, and the lift increases with a decrease in pitch amplitude. When the frequency ratio is 1.0, the airfoil generates large thrust. The thrust decreases as the pitch amplitude decreases. When the frequency ratio is 0.5, drag is generated for the 30-degree pitch amplitude, but the thrust is generated for 10-degree pitch amplitude. In future, the effect of heave amplitude on the unsteady aerodynamics of the airfoil will be studied.