• 대한조선학회논문집
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• 제41권4호
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• pp.68-76
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• 2004

Inherent strain method for analyzing deformation of line-heating is substituting experiments of high cost, because of its high accuracy and quickness. Nowadays, the progressing forms of line-heating are not straight moving motions used to traditional studies, but weaving motions which can diversely input heat source. In shipyard, reasons of weaving motions are induction of a special characteristic by water cooling, maximum temperature limitation for keeping plates from melting, and rhythm for workman's maintaining velocity. On this study, a method which can obtain optimal weaving heating condition was presented, some examples were introduced, and the results corresponded to works of shipyard. Lastly, what the specifications of plates on efficiency are is presented, through the quality standard of shipyard and FEM heat transfer simulation. The ultimate purpose of line heating is the automation, so in case of plates which need weaving heating, the optimal heating condition suggested by this study can be used well in designing coil specifications of induction heaters which are heat input sources of new generation.

• 대한조선학회논문집
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• 제45권3호
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• pp.303-308
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• 2008

The induction heating is more efficient for a plate bending because of its easy operation and control of working parameters, compared with the heating by a gas torch. The existing axis symmetric analysis method could neither handle initial curved plates nor be used in the optimization of coil shapes because of its limit of an axis symmetric coil shape. But the proposed method using some discrete part models and analysis processes could overcome these difficulties and show more accurate results in temperatures and deflections of flat or curved plates with initial curvature than those in the existing axis symmetric analysis method. This method is composed of the multi-disciplinary analyses such as an electro magnetic analysis, a heat transfer analysis and a deformation analysis based on inherent strain approach per each step. Traditionally, the coil shape in the induction heating is circular shape and it needs the moving process along heating lines. To overcome this, the 'Long Type Coil' with some linear parallel coils was proposed. It did not need the moving process along heating lines and reduced the heating process time. The results of experiments were compared with those of the simulation.

• International Journal of Ocean System Engineering
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• 제1권1호
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• pp.46-51
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• 2011

In a line heating process for hull forming, the phase of the steel transforms from austenite to martensite, bainite, ferrite, or pearlite depending on the actual speed of cooling following line heating. In order to simulate the water cooling process widely used in shipyards, a heat transfer analysis on the effects of impinging water jet, film boiling, and radiation was performed. From the above simulation it was possible to obtain the actual speed of cooling and volume percentage of each phase in the inherent strain region of a line heated steel plate. Based on the material properties calculated from the volume percentage of each phase, it should be possible to predict the plate deformations due to line heating with better precision. Compared to the line heating experimental results, the simulated water cooling process method was verified to improve the predictability of the plate deformation due to line heating.

• 대한조선학회논문집
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• 제42권5호
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• pp.472-478
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• 2005

From a rapid cooling to a slow cooling in the actual cooling process in shipyards, the phase of steel becomes martensite, bainite, ferrite, and pearlite. In order to simulate the cooling process, heat transfer analysis was performed considering the effects of impinging water jet, film boiling, and radiation. From above simulation it is possible to find the cooling speed at the inherent strain region and volume percentage of all phases in that region. By the suggested method based on the precise material properties calculated from volume percentage of all phases, it will be possible to predict the plate deformations by line heating more precisely. It is verified by comparing with some experimental results that the present method is very effective and efficient.

• 전자공학회논문지T
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• 제36T권4호
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• pp.88-93
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• 1999

본 논문에서는 한방의료에서 인체 전신의 상태를 파악하는데 주요한 요소인 맥파를 과학적으로 관찰하고자 스트레인 게이지를 이용하여 맥파를 검출하는 새로운 시스템을 구성하였다. 스트레인 게이지는 센서의 변형에 대해 선형적으로 고유한 저항값이 변화되므로 손목에서 맥의 변화는 스트레인 게이지를 이용하여 맥파의 파형으로 검출할 수 있다. 맥파 검출 시스템의 구성에서 스트레인 게이지로부터 발생된 저항변화값을 검출하기 위해 정밀 브리지회로와 고감도 증폭회로를 설계, 제작하였으며 이 시스템으로 미세한 맥의 변화를 상응하는 전압파형으로 출력시킨다. 구성된 시스템을 이용하여 6인의 맥을 직접 검출하고 시간영역과 주파수 영역에서 맥의 특성을 관찰하므로써 본 연구에서 구성된 맥파 검출 시스템의 과학적인 효용성을 입증하였다.

• Smart Structures and Systems
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• 제15권3호
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• pp.645-663
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• 2015

Recently, an indirect displacement estimation method using data fusion of acceleration and strain (i.e., acceleration-strain-based method) has been developed. Though the method showed good performance on beam-like structures, it has inherent limitation in applying to more general types of bridges that may have complex shapes, because it uses assumed analytical (sinusoidal) mode shapes to map the measured strain into displacement. This paper proposes an improved displacement estimation method that can be applied to more general types of bridges by building the mapping using the finite element model of the structure rather than using the assumed sinusoidal mode shapes. The performance of the proposed method is evaluated by numerical simulations on a deck arch bridge model and a three-span truss bridge model whose mode shapes are difficult to express as analytical functions. The displacements are estimated by acceleration-based method, strain-based method, acceleration-strain-based method, and the improved method. Then the results are compared with the exact displacement. An experimental validation is also carried out on a prestressed concrete girder bridge. The proposed method is found to provide the best estimate for dynamic displacements in the comparison, showing good agreement with the measurements as well.

• Journal of Welding and Joining
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• 제31권6호
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• pp.37-43
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• 2013

This study targets to make clear the connection between MS (Martensite start) point and welding shrinkage. We approved that a Martensite-transformed weldment may not yield state under low MS point, but also admitted the limitation of numerical calculation by inherent strain approach or thermal strain approach. Therefore, new thermal strain formulae during cooling stages were made. As a thermal strain is obtained by integrating thermal extension coefficient, a constant of integration should be decided. In our suggested formulae, the origin was based on totally remained austenite, and added strain from volume changes in Martensite transformation was based on totally transformed ferrite. Through the suggested methodology, It is verified that an MS point under a critical temperature can let weld shrinkage relax and the critical value can be obtained. For supporting this process, 15 weld-consumables were made, were tested by fillet type and were measured. As a result, a positive correlation between MS point and level of weld-distortion was obtained, but it was rather weak.

• 한국정밀공학회지
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• 제25권8호
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• pp.57-64
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• 2008

Corrugated flexible joint with bellows shape is widely used in many industrial fields as it provides a relatively simple means of absorbing mechanical vibration and deformation due to its inherent flexibility. In this study, an effective equivalent beam modeling technique of corrugated flexible joint bend using a commercial CAE software is proposed to reduce the excessive efforts and costs required for three dimensional shell modelling in vibration analysis of bellows shape structure. When this simple and practical technique, based on the strain energy concept, is employed to modify the beam sectional properties of the flexible joint bend, quite satisfactory results can be obtained.

• 소성∙가공
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• 제27권2호
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• pp.115-122
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• 2018

Most domestic and international standards on the forming limit diagram (FLD) including ISO 12004-2, use a 'position-dependent method,' which determines the forming limit from a strain distribution measured on the specimen after necking or fracture. However, the position-dependent method has inherent problems such as the incidence of asymmetry of a strain distribution, the estimation of missing data near fracture, the termination time of test, and the deformation due to the new stress equilibrium after a fracture, which is blamed for causing sometimes a significant lab-to-lab variation. The 'time-dependent method,' which is anticipated to be a new international standard for evaluating the forming limit, is expected to greatly improve these intrinsic disadvantages of the position-dependent method. It is because the time-dependent method makes it possible to identify and accurately determine the forming limit, just before the necking point from the strain data as continuously measured in a short time interval. In this study, we propose a new time-dependent method based on a Gaussian fitting of strain acceleration with the introduction of 'normalized correlation coefficient.' It has been shown in this study that this method can determine the forming limit very stably and gives a higher value, which is in comparison with the results of the previously studied position-dependent and time-dependent methods.

• 소성∙가공
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• 제9권4호
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• pp.404-412
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• 2000

It is desirable to use the square grid analysis with the aid of the stereo vision and image processing techniques in order to automatically measure the surface-strain distribution over a stamped part. But this method has some inherent problems such as the difficulty in enhancement of bad images, the measurement error due to the digital image resolution and the limit of the area that can be measured at a time. Therefore, it is still hard to measure the strain distribution over the entire surface of a medium-or large-sized stamped part even by using an automated strain measurement system. In this study, several methods which enable to solve these problems considerably without losing accuracy and precision In measurement are suggested. The superposition of images that have different high-lightened or damaged part from each other gives much enhanced image. A new algorithm for constructing of the element connectivity from the line-thinned image helps recognize up to 1,000 elements. And the geometry assembling algorithm including the global error minimization makes it possible to measure a large specimen with reliability and efficiency.