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김석현,이중혁,변준호,Kim, Seockhyun,Lee, Joong Hyeok,Byeon, Jun Ho 한국음향학회 2017 韓國音響學會誌 Vol.36 No.3
신라대종은 성덕대왕신종을 계승하여 새 천년을 울리기 위해 제작되었다. 본 연구에서는 신라대종이 구조와 음향 측면에서 성덕대왕신종과 어떻게 유사한지를 조사하였다. 먼저 설계 및 제작 과정을 소개하고 두 종의 크기를 비교하여 유사성을 평가하였다. 한국 종소리의 세 가지 주요 특성은 웅장하고 조화로운 타격음, 역동적인 맥놀이와 길게 지속되는 여음이다. 이 세 가지 특성을 물리적 인자를 사용하여 객관적으로 평가한다. 이를 통하여 수려한 외관과 웅장하고 아름다운 소리를 내는 대형 한국 범종의 제작에 유용한 자료를 제공하는 것이 본 연구의 목적이다. Silla Great Bell was manufactured in order to ring for the new millennium in succession to King Seongdeok Divine Bell. This study investigates how Silla Great Bell is similar to King Seongdeok Divine Bell in respect of structure and sound. First, design and manufacturing processes are introduced and dimensions of the two bells are compared and the similarity is estimated. Three main characteristics of the sound of a Korean bell are magnificent and harmonic striking sound, dynamic beat, and long lasting hum tone. These three features are compared and objectively estimated using physical parameters. The purpose of the study is to provide useful information to manufacture Korean bell which has beautiful appearance and excellent sound.
김석현,이중혁,Kim, Seockhyun,Lee, Joong Hyeok 한국음향학회 2017 韓國音響學會誌 Vol.36 No.3
신라대종은 성덕대왕신종을 재현하려는 목적으로 제작 되었으며, 동일한 구조와 문양을 갖도록 복원되었다. 가장 어려운 문제는 성덕대왕신종의 소리에 걸 맞는 웅장하고 조화로운 타격음과 끊어질 듯 이어지는 여음의 맥놀이를 재현하는 것이었다. 특히 맥놀이는 주조과정에서 발생하는 제어 불가능한 미세 비대칭성에 기인하므로, 주조 전에는 그 특성을 예측하거나 제어할 수 없다. 본 연구에서는 주조 후 맥놀이의 조절 작업을 통하여 신라대종의 맥놀이가 강하고 적절한 주기를 갖도록 만드는 방법과 과정을 소개한다. 강한 맥놀이를 만드는 모드 쌍과 당좌의 배치 조건을 구하였고, 적절한 주기를 갖도록 종 내부의 두께를 국부적으로 감소시켰다. 이 작업은 등가 종을 이용한 시뮬레이션 결과에 따라 수행되었다. 그 결과 약하고 매우 길었던 초기의 맥놀이는 강하고 적절한 주기의 맥놀이로 만들어졌다. Silla Great Bell was made to reproduce King Seongdeok Divine Bell and it was restored to have the same structure and patterns. The most difficult problem was to reproduce the magnificent striking sound and dynamic hum tone with strong beat like in King Seongdeok Divine Bell. Especially, beating sound is attributed to the uncontrollable asymmetry occurring in the casting process, so it can not be predicted or controlled before casting. In this study, we introduce the method and process to make Silla Great Bell have a strong beat with a proper period. Position conditions of mode pairs and striking point for a strong beat were identified. Bell thickness was locally decreased to make proper period of beat. The process was performed according to the simulation result of an equivalent bell model. As a result, the original weak and long beat was made to a strong beat with a proper period.
김석현(Seockhyun Kim),이중혁(Joong Hyeok Lee) 한국소음진동공학회 2016 한국소음진동공학회 학술대회논문집 Vol.2016 No.4
Beating sound of an oriental bell means the periodic repetition of the strong and weak sound. Beat with a proper period makes the people feel as if the bell were alive and breathing. To control the beat characteristics, mode pair data of the bell structure are necessarily required. However, a huge oriental bell is usually struck by a swing of a heavy wooden hammer and therefore, only response signal such as acceleration or sound pressure can be measured. This study proposes a experimental method to extract the mode pair data from the power spectrum of the vibration response under the striking by a wooden hammer. Validity of the method is verified on a huge oriental bell.
김석현(Kim Seockhyun),이현우(Lee Hyunwoo),김정태(Kim Jungtae) 한국철도학회 2008 한국철도학회 학술발표대회논문집 Vol.- No.-
In a high speed train, multi-layered panels for floor, side wall and roof are important sound insulating part. As these multi-layered panels require high bending strength vs. weight, corrugated steels or aluminium honeycomb panel are generally used. However, with some inevitable factors, these panels show lower sound insulation performance than that of the plate with the same weight. Transmission loss(TL) often severely decreases in a particular frequency range because of the decrease of the critical frequency, occurrence of local resonance modes and cavity resonance modes, which are not shown in a plate. In this study, frequency range and cause of the TL drop are investigated on the corrugated and honeycomb panels.
김석현(Seockhyun Kim),서태건(Taegun Seo),김정태(Jeong-tae Kim),송달호(Dalho Song) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.5
알미늄 압출재는 고속열차의 경량화를 위하여 기존의 주름강판을 대체하여 널리 사용된다. 알미늄 압출재는 고속열차 적층재 가운데 가장 큰 차음 기여도를 보이나, 동일한 중량의 평판과 비교할 때, 국부공진 주파수 대역에서 투과손실이 크게 떨어진다. 이 연구에서는 차세대 400㎞/h급 고속철도 차량용 알미늄 압출재를 대상으로 차음 문제를 검토하고, 차음성능의 향상 방안을 제시한다. 코어 구조를 변경시켜 국부공진 대역을 높이고, 우레탄 폼을 코어에 충진시킬 때의 차음성능 향상효과를 실험적으로 확인한다. 최종적으로 제시된 방법이 바닥 적층재의 총 투과손실을 어느 정도 개선시키는가를 평가한다. Aluminum extruded panels are widely used instead of corrugated steel panels for weight reduction in high-speed trains. Of the layers in the train body, it makes the largest contribution to the sound insulation. However, compared with that of a flat panel with the same weight, the TL of the aluminum extruded panel is remarkably lower in the local resonance frequency band. We study aluminum extruded panels for next-generation 400-㎞/h trains. We investigate the problem of sound insulation and propose a practical method to improve the sound-insulation performance. The local resonance frequency region is increased by a modification of the core structure, and urethane foam is placed in the core. The effect on the sound insulation is verified by experiments. Finally, the improvement for the entire sound-transmission loss is estimated for the layered floor panels of express trains.
김석현(Seockhyun Kim),박무열(Muyeol Park),C.X.Cui 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Vibration characteristics of a small stand alone W/T(wind turbine) system are experimentally and theoretically investigated. Vibration is monitored on a wind turbine structure model and the data are analysed with the analytical results. Resonance problem is investigated under various operating speed. To predict the resonance speed of W/T, Rayleigh-Ritz method is applied to the tower-guy cable coupled system. The effect of the cable tension on the vibration characteristics is considered experimentally and analytically. Results of the study are utilized to design the stable structure of small size wind turbines which consist of the pivoted tower and the guy cable.