• 오토저널
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• 제14권5호
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• pp.95-106
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• 1992

Active control of acoustic noise is an application area of adaptive digital signal processing with increasingly interest along the last year. This work studies the implementation of the multichannel LMS filter and the application of this algorithm for the reduction of the noise inside a vechicle cabin using a number of 'secondary sources' drived by adaptive filtering of a reference noise source. Firstly, we propose the use of an adaptive method for the time-varient optimal convergence factor. Secondly, we propose the use of adaptive delayed inverse model to estimate the elastic-acoustic transfer function presented in vechicle cabin. The original, primary source is often periodic, with a known fundamental frequency. A suitably filtered reference signal can thus be used to drive the secondary sources. An algorithm is presented for adapting the coefficients of an FIR filter feeding such a secondary source in such a way as to minimize the output of a suitably placed microphone. In this algorithm, the coefficients of adaptive filter driving an array of secondary sources can be adapted to minimize the sum of the squares of the outputs of a number of error microphones. The multichannel LMS algorithm displays that such an algorithm is considered suitable to used for the global suppression of noise in vehicle cabin.

• Journal of Hydrospace Technology
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• 제2권1호
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• pp.41-54
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• 1996

Sculptured surface structures such as ship hulls are traditionally formed up to the required double curved shape by line heating method. The nature of the line heating process is a transient thermal process, followed by a thermo-elastic-plastic stress field. The permanant shape is dependent on many factors involved in the process, Among them are torch speed and path, supplied heat type and amount , and plate size. Thus, the work is essentially leaded by experts with lots of experiences. However, in order to effectively improve productivity through automation, each factor should be clearly examined how much it affects the final shape. This can not be done only by experiments, but can be achieved by a mechanics-based approach. In this paper, we propose a conceptual configuration for plate forming system, and then present simulations of the line heating process with numerical data in practices and suggest a computerized process of the line heating for practical applications. The modeling of heating torch, water cooling, and the plate to be formed is proposed for the finite element analysis after the mechanics of line heating is studied. Parametric studies are given and discussed for the effects of plate thickness, torch speed and initial curvature in forming a saddle typed surface.

• 대한기계학회논문집
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• 제13권5호
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• pp.875-885
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• 1989

본 연구에서는 이러한 경우를 대상으로 하여, 채터발생의 주원인이 공구가 되도록 돌출길이를 충분히 길게 한 상태에서 공구체결부에 점탄성재료를 삽입하고 채터진동 억제 효과를 검토하였다. 또한 점탄성 재료 삽입으로 인한 공구 고정부의 강성 및 감쇠의 변화를 공구고정부에 대한 유한요소해석(FEA) 및 충격실험 등을 수행 하여 알아보았으며, 정적 강성의 저하로 인해 안정절삭조건에서 발생할 수 있는 정밀 도저하를 검토하여 보았다.

• Advances in nano research
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• 제10권3호
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• pp.271-280
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• 2021

The present work deals with an investigation on longitudinal wave propagation in nanobeams made of graphene sheets, for the first time. The nanobeam is modelled via a higher-order shear deformation theory accounts for both higher-order and thickness stretching terms. The general nonlocal strain gradient theory including nonlocality and strain gradient characteristics of size-dependency in order is used to examine the small-scale effects. This model has three-small scale coefficients in which two of them are for nonlocality and one of them applied for gradient effects. Hamilton supposition is applied to obtain the governing motion equation which is solved using a harmonic solution procedure. It is indicated that the longitudinal wave characteristics of the nanobeams are significantly influenced by the nonlocal parameters and strain gradient parameter. It is shown that higher nonlocal parameter is more efficient than lower nonlocal parameter to change longitudinal phase velocities, while the strain gradient parameter is the determining factor for their efficiency on the results.

• Smart Structures and Systems
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• 제26권3호
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• pp.331-343
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• 2020

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe₂O₄ and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

• 전산구조공학
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• 제4권3호
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• pp.79-88
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• 1991

내진설계를 하고 있는 나라들이 채택하고 있는 내진해석방법중 가장 일반적인 응답스펙트럽법(Response Spectrum Method)은 지진하중을 정적 수평하중으로 치환하여 정적해석하는 것을 기본으로 하고 있다. 여기서 계산된 대치수평하중은 구조물의 소성화에 따른 비선형거동으로 부터 오는 에너지분산현상 및 감쇠(damping)현상 등을 고려하기 위하여 소위 반응수정계수(behavior factor)란 일정수로 나누어 준다. 응답스펙트럼법에 의한 내진설계의 정확도를 좌우하는 지금까지 사용되어지고 있는 반응수정계수는 정확한 계산값들이 아닌 경험적인 값들이다. 반응수정계수를 해석적으로 결정하기 위해서는 구조물의 극한상태에 대한 정의가 선결되어져야 한다. 본 논문에서는 지진하중하에서 강구조물의 한계상태를 기하학적측면과 사용성 측면 및 재료공학적 측면에서 검토하였고 3가지 형태의 구조물을 모델로 하여 반응수정계수를 계산하였다.

• Geomechanics and Engineering
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• 제27권6호
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• pp.551-560
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• 2021

Due to the low strength and high compressibility characteristics, the loess deposits tunnels are prone to large deformations and collapse. An accurate stability evaluation for loess deposits is of considerable significance in deformation control and safety work during tunnel construction. 37 groups of representative data based on real loess deposits cases were adopted to establish the stability evaluation model for the tunnel project in Yan'an, China. Physical and mechanical indices, including water content, cohesion, internal friction angle, elastic modulus, and poisson ratio are selected as index system on the stability level of loess. The data set is randomly divided into 80% as the training set and 20% as the test set. Firstly, principal component analysis (PCA) is used to convert the five index system to three linearly independent principal components X1, X2 and X3. Then, the principal components were used as input vectors for probabilistic neural network (PNN) to map the nonlinear relationship between the index system and stability level of loess. Furthermore, Leave-One-Out cross validation was applied for the training set to find the suitable smoothing factor. At last, the established model with the target smoothing factor 0.04 was applied for the test set, and a 100% prediction accuracy rate was obtained. This intelligent classification method for loess deposits can be easily conducted, which has wide potential applications in evaluating loess deposits.

• 한국해안해양공학회지
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• 제18권1호
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• pp.15-20
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• 2006

해저환경에서 PMC(고분자기지 복합재)는 금속재 구조물에 비해 부식성이 우수한 것으로 알려져 있다. 해저환경에서 고분자기지 복합재의 파괴특성에 대한 이해는 증가하는 해저구조물 제조에 반드시 필요하다. 본 연구에서, 파괴시험은 해수흡수 된 카본/에폭시 복합재에 대해 정수압을 네단계(0.1 MPa, 100 MPa, 200 MPa and 270 MPa)로 증가시켜 수행하였다. 파괴인성은 정수압에서의 일인자방법을 적용하였다. 파괴거동은 모든 정수압에서 선형적이었고 파괴인성은 정수압이 증가할수록 증가하였다.

• 한국의류학회지
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• 제26권2호
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• pp.337-348
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• 2002

Based upon literature survey and questionnaire survey, this research tries to develop four new Cleanroom Garment in semiconductor industrial environment. The designs emphasize to minimize workers disconmfort so that they can not only cover human body fully but also reduce dust as much as possible during work hour in clean room. The new designs characteristics and results from both function test and dust emission test are as follows: 1. In order to reduce dust-emission, we develop new designs with hood, kimono sleeve, and back zipper. The designs with hood face positive test results in term of motion suitability and dust-omission. The design with seam in front, in particular, is effective to control dust-emission. 2. For the purpose of reducing dust-emission, we also emphasize to minimize ease of dust-proof wear, with reference to previous research and clothing experiment. The experiment participants report that the new wears are not so comfortable as existing ones, but they accept the new wears positive as effective in reducing dust-emission owing to reduced ease of Cleanroom Garment and sleeves. 3. A1so to reduce dust-emission in inner wear, we put inner wear in both Cleanroom Garments and inner wear, resulting to remove discomfort of wearers when changing clothes and of tight waist due to inner-trousers. 4. We develop new designs with elastic bands in both waist through the side lines and with velcro only at the back side. To remove twist in front contributes to reduce emission arising out of friction, also to free the appearance minding woman workers from worrying about exposed stomach. The new designs need to be accepted as a valuable alternative of Cleanroom Garment, in that they are highly effective to reduce dust-emission, which is the most important factor in the wear, in spite of some drawbacks in terms of motion-suitability, ease and appearance as shown in wearing test.

• 대한기계학회논문집A
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• 제38권2호
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• pp.121-127
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• 2014

단층 그래핀 시트(Single layer graphene sheet, SLGS)의 찢어짐 모드(모드 III) 파괴 예측을 위한 원자 기반 미세결합요소모델이 개발되었다. 이 모델은 그래핀 시트의 최대 변형률 관계를 예측하기 위해 수정된 모스포텐셜을 사용한다. 면외 전단하중 조건에서 그래핀의 모드 III 파괴를 광범위한 분자역학(Molecular mechanics, MM) 시뮬레이션으로 조사하였다. 분자역학은 원자의 균열선단 근처 원자의 변위를 설명하기 위해 사용되었고, 선형탄성파괴역학은 이 영역 바깥의 영역을 설명하기 위해 사용되었다. 해석 결과 분자역학 방법이 SLGS의 전단 물성 계산뿐만 아니라 armchair 및 zigzag 방향 모드 III 파괴인성 연구에도 단순하면서도 신뢰할만하다는 것을 보여준다. SLGS 의 모드 III 파괴인성은 zigzag 방향에 대해 $0.86MPa{\sqrt{m}}$, armchair 방향에 대해 $0.93MPa{\sqrt{m}}$로 예측되었다.