• Journal of the korean Society of Automotive Engineers
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• v.14 no.5
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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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• v.2 no.1
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.875-885
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• 1989

This work is concerned with the chatter suppression by inserting viscoelastic materials into tool clamping area. Chatter was observed with and without the viscoelastic materials during cutting tests, where the overhang of the tool was made long so that the tool may be a major cause for the chatter. Two viscoelastic materials were used and the effects of thickness and prestrain were investigated. impact tests were performed on the tool in cases where the tool post was set on the cross slide and was free from any boundary conditions. Material properties of the viscoelastic materials were also obtained from resonance test results. The effects on the chatter suppression by the type of the viscoelastic material and prestrain are discussed in relation with the measured material properties.

• Advances in nano research
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• v.10 no.3
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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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• v.26 no.3
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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.

• Computational Structural Engineering
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• v.4 no.3
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• pp.79-88
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• 1991

The procedure of the elastic response spectrum method which is used in the codes of many countries involves the computation of a static horizontal substitute loading resulting from the earthquake. The substitute loading is divided by a behavioral factor in order to take energy dissipation due to the real nonlinear structural behavior and damping effects ect. into account. The behavioral factors widely used in many countries are based not on the exact calculation but only on the empirical data. In order to determine the behavioral factors analytically, it is necessary to define the limit state of structures as a first step. In this work, the methods of the determination of limit state for the steel structures are discussed in the geometric, serviceabile and material apsects, and the behavioral factors for the three types of structures are calculated.

• Geomechanics and Engineering
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• v.27 no.6
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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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.1
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• pp.15-20
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• 2006

It is well-known that the corrosive behavior of PMC (polymer matrix composite) structure is much better than the metal structure in the marine environment. The understanding of fracture behavior of PMC in the deep-sea environment is essential to expand its use in the marine industry. For a present study, fracture tests have been performed under low different pressure levels such as 0.1 MPa, 100 MPa, 200 MPa, and 270 MPa using the seawater-absorbed carbon/epoxy composite samples. Fracture toughness was determined from the work factor approach as a function of hydrostatic pressure. It was found that fracture behavior was a linear elastic far all pressure levels. The fracture toughness increased with increasing pressure.

• Journal of the Korean Society of Clothing and Textiles
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• v.26 no.2
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.2
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• pp.121-127
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• 2014

An atomistic-based finite bond element model for predicting the tearing mode (mode III) fracture of a single-layer graphene sheet (SLGS) is developed. The model uses the modified Morse potential for predicting the maximum strain relationship of graphene sheets. The mode III fracture of graphene under out-of-plane shear loading is investigated with extensive molecular mechanics simulations. Molecular mechanics is used for describing the displacements of atoms in the area near a crack tip, and linear elastic fracture mechanics is used outside this area. This work shows that the molecular mechanics method can provide a reliable and yet simple method for determining not only the shear properties of SLGS but also its mode III fracture toughness in the armchair and the zigzag directions; the determined mode III fracture toughness values of SLGS are $0.86MPa{\sqrt{m}}$ and $0.93MPa{\sqrt{m}}$, respectively.