• Journal of the Society of Naval Architects of Korea
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• v.44 no.6
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• pp.598-604
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• 2007

The purpose of this study is to establish the predictive method of welding distortion and residual stress for the channel I butt SA (submerged arc) weldment using FEA. In order to do it, the heat input model for the weldment was defined as the combined heat source with the surface heat flux of gaussian distribution and volumetric heat source uniformly distributed within weld groove by comparing the shapes of molten pool and temperature distribution obtained by FEA with those of experiments. The arc efficiency of SA welding for two-dimensional FE analysis was evaluated as 0.85. The welding distortion and residual stress of the weldment obtained by FEA and heat input model proposed have a good agreement with those obtained by experiment. Based on the results, it was suggested that the proper heat input model should be required to evaluate the welding distortion for weldment.

• Journal of the Institute of Convergence Signal Processing
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• v.5 no.1
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• pp.18-24
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• 2004

SPECT technology is used for the reconstructed image in the field of industry noncontact measurement system. One of the distortion problems in reconstructed image quality is a collimator characterictic. The image distortion is caused by a geometrical structure of the collimator. This paper indicated a correction method to remove the image distortion by the structure of the collimator, and compared with the existing correction method. The correction. method removed the image distortion to use deconvolution of projection data with the shift-variant blurring function in the frequency domain. In this pater, I simulated with the collimator angle and distance between the detector and the center of object. and verified with expeimental data. The validity and limitation of correction method is studied for actual industrial applications.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.11a
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• pp.348-351
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• 2002

Recently, the medical imaging field has been digitalized by the development of computer science and digitization of the medical devices. There are needs of the medical imaging database service and long term storage today because of the installation of PACS system following DICOM standards, telemedicine and etc. and ,also, the illegal distortion of the medical information, data authentication and copyright are being happened. In this paper, we propose watermarking technique as a method which can protect private informations and medical imaging from geometric distortion. Because many watermarks for images are sensitive to geometric distortion, we present a algorithm that is insensitive to RST distortion in medical image. we observed the robustness against several of the signal processing and attacks in medical imaging field by embedding watermark after making a region which is insensitive to RST distortion by using FFT and LPM transformation.

• Structural Engineering and Mechanics
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• v.38 no.3
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• pp.261-281
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• 2011

A new method of formulation of a class of elements that are immune to mesh distortion effects is proposed here. The simple three-noded bar element with an offset of the internal node from the element center is employed here to demonstrate the method and the principles on which it is founded upon. Using the function space approach, the modified formulation is shown here to be superior to the conventional isoparametric version of the element since it satisfies the completeness requirement as the metric formulation, and yet it is in agreement with the best-fit paradigm in both the metric and the parametric domains. Furthermore, the element error is limited to only those that are permissible by the classical projection theorem of strains and stresses. Unlike its conventional counterpart, the modified element is thus not prone to any errors from mesh distortion. The element formulation is symmetric and thus satisfies the requirement of the conservative nature of problems associated with all self-adjoint differential operators. The present paper indicates that a proper mapping set for distortion immune elements constitutes geometric and displacement interpolations through parametric and metric shape functions respectively, with the metric components in the displacement/strain replaced by the equivalent geometric interpolation in parametric co-ordinates.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.5
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• pp.465-470
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• 2014

Thin and wide airfoils are difficult to be machined precisely because they are deformed during and after machining processes. This paper presents the results of the airfoil deformation measured by three-dimensional (3D) scanning equipment. It also discusses the influences of fixture and the machining process on the distortion of the thin airfoil. The simple fixture bended the thin airfoil to a U-shape at the first process, and the vacuum fixture decreased the distortion of the machined airfoil at the second process. The long and thin airfoil supported by two points was buckled during the machining at its two end-regions at the third process. Results from this study suggest that use of vacuum fixture decreases the machining distortion of thin and wide airfoils.

• ETRI Journal
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• v.29 no.5
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• pp.559-568
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• 2007

This paper presents a new distortion control scheme with a simple estimation model for the propagation errors incurred by dropping some parts of the bitstream in a frame dropping-coefficient dropping (FD-CD) transcoder. The primary goal of this paper is to facilitate bit-rate conversions and rate-distortion controls in the compressed domain without introducing a full decoding and reencoding system in the pixel domain. First, the error propagation behavior over several frame sequences due to coefficient dropping is investigated on the basis of statistical and empirical properties. Then, such properties are used to develop a simple estimation model for the CD distortion accounting for the characteristics of the underlying coded-frame. Finally, the proposed estimation model allows us to determine the amount of coefficient dropping and to effectively allocate rate-distortions into coded-frames. Experimental results show that the proposed estimation model accurately describes the characteristics of propagation errors adaptively in the compressed domain and can be easily applied to distortion control over different kinds of video sequences.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.11
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• pp.37-44
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• 2003

A distortion suppression technology for employing multiple inputs in 3n＋1 type current mode Max circuit is proposed using the adjustment of transconductance. If the number of input blocks of the current mode Max circuit increases, the high frequency distortion in the output signal grows. In this paper, it has been disclosed that the distortion in the multiple input Max circuit is proportional to such accumulated parasitic capacitance, to the derivative of the output signal and also to tile inverse of transconductance of the common diode-connected transistor. The proposed idea is by employing as larger transconductance of the common diode-connected transistor as possible. The effectiveness of the proposed idea has been proved through the HSPICE simulation for the current mode Max circuits with various numbers of input signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.55-64
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• 2010

In this paper, we propose a new compensation scheme for combined channel distortions and RF impairments based on the analysis of the impacts of IQ(In-phase/Quadrature) imbalance and phase noise on the OFDM(Orthogonal Frequency Division Multiplexing) system in the direct conversion transceiver and frequency selective fading channel distortion. The proposed scheme estimates the combined distortion by the use of training symbols and the residual distortion by pilot symbols and compensates the combined distortion, including IQ imbalance, phase noise and multipath fading at the same time. The simulation results show that the proposed scheme compensates the combined distortion of IQ imbalance, phase noise and multipath fading simultaneously.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.489-492
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• 2005

In this paper, we present a system for robust face detection based on wavelet transform using the standard models of image distortion. In the previous works, it was known to be difficult to treat a distorting of image information such as noises and light of the images obtained by a still camera and a movie camera. we analyze the high frequence information by using wavelet transform. This information is used for testing the image distortion and constructing the standard models of image distortion. The experimental results show that our extracting method based on standard models of image distortion is very effective.

• Journal of Power Electronics
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• v.15 no.1
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• pp.10-17
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• 2015

A quasi-constant on-time controlled buck front end in combined discontinuous conduction mode and boundary conduction mode is proposed to improve power factor (PF).When instantaneous AC input voltage is lower than the output bus voltage per period, the buck converter turns into buck-boost converter with the addition of a level comparator to compare input voltage and output voltage. The gate drive voltage is provided by an additional oscillator during distortion time to eliminate the cross-over distortion of the input current. This high PF comes from the avoidance of the input current distortion, thereby enabling energy to be delivered constantly. This paper presents a series analysis of controlling techniques and efficiency, PF, and total harmonic distortion. A comparison in terms of efficiency and PF between the proposed converter and a previous work is performed. The specifications of the converter include the following: input AC voltage is from 90V to 264V, output DC voltage is 80V, and output power is 94W.This converter can achieve PF of 98.74% and efficiency of 97.21% in 220V AC input voltage process.