다공질형 섬유재료의 밀도 분포 변화에 따른 흡음특성에 관한 연구

나혜중,이경민,김경도,전두환,Na, Hae Joong,Lee, Kyoung Min,Kim, Kyoung Do,Chun, Du Hwan 한국섬유공학회 2018 한국섬유공학회지 Vol.55 No.5

To improve the acoustic performance of porous fibrous materials, the material thickness should be increased or nonwoven fabrics with a double layered-system should be used as described in the previous paper [2]. In this study, the sound absorption characteristics of nonwoven fabrics with double-layered and triple-layered systems and different density distributions were investigated using an impedance-tube method. In the case of a double-layered system, the results show that a higher face material density increased the sound absorption coefficient in the middle-frequency region. In case of a triple-layered system, when combined with three kinds of materials, under the same condition of face material, a greater density difference with nonwoven in the back resulted in an increased sound absorption coefficient in the middle-frequency region.

회전하는 타이어의 동특성을 고려한 진동에너지 하베스터 성능 예측

나혜중 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.10

In general, tires require various sensors and power supply devices, such as batteries, to obtain informationsuch as pressure, temperature, acceleration, and the friction coefficient between the tire and the road in real time. However, these sensors have a size limitation because they are mounted on a tire, and their batteries havelimited usability due to short replacement cycles, leading to additional replacement costs. Therefore, vibrationenergy harvesting technology, which converts the dynamic strain energy generated from the tire into electricalenergy and then stores the energy in a power supply, is advantageous. In this study, the output voltage andpower generated from piezoelectric elements are predicted through finite element analysis under static state andtransient state conditions, taking into account the dynamic characteristics of tires. First, the tire and piezoelectricelements are created as a finite element model and then the natural frequency and mode shapes are identifiedthrough modal analysis. Next, in the static state, with the piezoelectric element attached to the inside of the tire,the voltage distribution at the contact surface between the tire and the road is examined. Lastly, in the transientstate, with the tire rotating at the speeds of 30 km/h and 50 km/h, the output voltage and power characteristicsof the piezoelectric elements attached to four locations inside the tire are evaluated

소형화 및 슬림형에 적합한 평면 플라이백 변압기의최적 설계에 관한 연구

나혜중,김종해 한국전기전자학회 2020 전기전자학회논문지 Vol.24 No.3

This paper presents the optimal design of planar flyback transformer suitable for small-size and low-profile of AC toDC adapter for 10W tablet. This paper also proposes the injection winding transformer of Hybrid and Drum typescapable of the winding method of automatic type and the reduction of transformer size and leakage inductance(Lk)compared to the conventional mass-production flyback transformer with the winding method of manual type. Inparticular, the injection winding transformer of Drum type proposed in this paper is constructed in a horizontal laying ofits transformer to solve the connection problem of copper plate injection winding on the secondary side of the one ofHybrid type. The primary and secondary windings of the injection winding transformer of Hybrid and Drum types usedthe conventional winding and the copper plate injection winding, respectively. For the injection winding transformer ofHybrid and Drum types proposed in this paper, the optimal design of planar flyback transformer suitable for small-sizeand low-profile was carried out using Maxwell 2D and 3D tool. 본 논문에서는 10W급 Tablet용 AC to DC Adapter의 소형화 및 슬림형에 적합한 평면 Flyback 변압기 최적화 설계에 대해서 나타낸다. 또한 본 논문에서는 수동권선의 기존 양산 Flyback 변압기에 비해 자동권선, Trans 크기 저감 및 누설 인덕턴스(Lk) 저감이 가능한 Hybrid형 사출 권선 변압기와 Drum형 사출 권선 변압기를 제안한다. 특히 본 논문에서 제안한Drum형 사출 권선 변압기는 Hybrid형 사출 권선 변압기 2차측의 동판 사출 권선 접속 문제를 해결하기 위하여 변압기를 수평으로 눕힌 형태로 구성하였다. 본 논문에서 제안한 Hybrid형 사출 권선 변압기와 Drum형 사출 권선 변압기의 1차측과 2차측 권선은 각각 기존 권선과 동판 사출 권선을 사용하였다. 본 논문에서 제안한 Hybrid형 사출 권선 변압기와 Drum형 사출권선 변압기에 대해 Maxwell 2D 및 3D Tool을 이용하여 소형화 및 슬림형에 적합한 평면 Flyback 변압기 최적화 설계를수행하였다.

정상상태조건에서의 개구부로 연결된 커플룸의 음향 특성

나혜중(Hae Joong Na),임병덕(Byoung-Duk Lim) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.3

Room acoustic properties of coupled rooms connected by an aperture has been analyzed using statistical acoustic model based on the diffused sound field assumption, which has limitation in dealing with the parameters such an room geometries and non uniform absorptivity of the boundary surfaces. In order to overcome these difficulties the acoustic diffusion model has been introduced, by which distribution of the acoustic energy density can be analyzed for various shapes and wall absorptivity. In this study acoustic properties of coupled rooms connected by an aperture(e.g. door) is analyzed using acoustic diffusion equation, which is solved numerically. The mean energy densities of two rooms obtained by the diffusion model are compared with those from the statistical model. The results show good agreement for various coupling aperture sizes and absorption coefficients. For a limiting case when the partition wall is substituted by an aperture and the two rooms eventually forms a single room, results of coupled room analysis using diffusion model show good agreement with those of a single room.

개구부로 연결된 3중 커플룸의 음향특성

나혜중(Hae Joong Na),임병덕(Byoung-Duk Lim) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.3

A coupled room system consists of adjacent rooms and apertures where the sound energy is exchanged between the two rooms. Acoustically, a coupled room system shows a non-exponential decay profile. Most of the related researches have been to analyze the acoustic properties of two-room coupled system so far whereas three-room coupled system were seldom studied. In this regard, this paper aims to analyse the distribution of sound pressure level, sound decay curve of three-room coupled system and sound energy flow between them by using the acoustic diffusion model and to further verify them through experiments. Firstly, the sound pressure level distribution and mean sound pressure level in the steady-state condition are analyzed at various frequencies and source locations. Good agreements are observed in both experiments and analysis results. Secondly, two double slope effect quantifiers of sound attenuation, LDT/EDT and LDT/T10 are compared at various frequencies and for different source locations. The result indicates that LDT/T10, less affected by the early reflection patterns than LDT/EDT, is more suitable to the analysis and experiments of a multi-slope sound decay curve. Lastly, the sound energy flow in each room is analyzed based on the acoustic diffusion model. After the early decay stage, the sound energy is observed to flow from the room with a long reverberation time to the room with a short one.

음향파워 측정 시 오차에 대한 고찰

나혜중(Na, Hae-Joong),임병덕(Lim, Byoung-Duk) 한국소음진동공학회 2012 한국소음진동공학회 논문집 Vol.22 No.10

Noise power of large machineries, such as textile looms, winders, and twisting machines, is often measured in a reverberant space because they cannot be installed and operated in an anechoic chamber due to their size, weight, and operating conditions. Factors affecting the measurement error of an in-situ noise power measurement include the nonuniform reverberation time and the direction of sound intensity vector which is usually regarded as normal to the measurement surface. In this study errors due to these factors are estimated with the aid of numerical simulation based on the ray-tracing technique. The averaging of reverberation times measured at several points on the measurement surface is suggested to reduce the errors from nonuniform absorption. Also the direction cosine of each surface element is taken into account, which as a whole is represented as a solid angle of the measurement surface.

소음원 분석에 의한 직기 구조물의 소음 특성

나혜중(Hae-Joong Na),전두환(Du-Hwan Chun) 한국소음진동공학회 2005 한국소음진동공학회 학술대회논문집 Vol.2005 No.5

에어제트직기의 진동특성 분석에 관한 실험적 연구

나혜중(Hae Joong Na),이수영(Soo Young Lee),임병덕(Byoung Duk Lim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11

Among various textile machines, a jet loom typically generates a higher vibration level than other textiles machineries such as pre-weaving m/c, dyeing m/c, and so on because of the driving mechanisms. The purpose of this paper is that investigates the vibration characteristics of Air Jet Loom and carries out the operational deflection shape(ODS) during operating jet loom. Natural frequency and mode shape of air jet loom are calculated with experimental modal program(MEscope) using the measured vibration acceleration that receives the signal with FFT analyzer from the accelerometer.

전자기유도 방식 에너지 하베스팅 메커니즘을 이용한 축산용 IoT 센서의 설계 및 구현에 관한 연구

나혜중(Hae-Joong Na) 한국조명·전기설비학회 2020 조명·전기설비학회논문지 Vol.34 No.10

To determine diseases and estrus periods, the biometric information of cows is important, which can directly affect the profits of livestock farmers. As such, real-time management incorporating IoT technology is desired. Since history information of individual objects is essential for determining diseases and estrus periods using IoT sensors, lifetime for more than 10 years and power supply of sensors are very important. Therefore, this study proposes a design technology that can extend the life of IoT sensors to more than 10 years by power supply based on the energy harvesting mechanism of the electromagnetic induction method and by low-power sensor circuit design. In this study, an electromagnetic induction method by cows kinetic energy is presented, and a prototype is constructed and tested to verify the applicability. Further, this study presents an algorithm for estimating the amount of internal power generation by using the acceleration data inside the sensor.

Development of CFRP Tubes for the Light-Weight Propeller Shaft of 4WD SUV Vehicles

Hae-Jung Na(나혜중),Jin-Sung Chun(천진성),Kyu-Sang Cho(조규상) 한국기계가공학회 2018 한국기계가공학회지 Vol.17 No.4

In this study, the one-piece propeller shaft composed of carbon/epoxy was designed and manufactured for 4 wheel drive automobiles that can bear the target torsional torque performance of 3.5kN.m. For the CFRP tube, braiding machine was used to weaving carbon fiber and it was formed the braided yarns with the braid angle ± 45° and axial yarns to improve strength of the lengthwise direction. The final CFRP tube of propeller shaft was evaluated through the torsional torque test. The CFRP propeller shaft satisfied requirement of the target torsional maximum torque of 3.5kN.m. Also, it was found that the one-piece composite propeller shaft with CFRP tube had 30% weight saving effect compared with a two-piece steel propeller shaft.