• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2015년도 추계학술대회
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• pp.757-758
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• 2015

디지털 워터마크는 디지털 매체의 저작권 인증 문제를 해결하기 위해 중요한 기법 중의 하나이다. 그리고 디지털 워터마크의 연구는 다양한 매체에서 연구가 급속히 진행되고 있다. 워터마크 시스템은 신호 공격, 기하학적인 공격 및 프로토콜 공격과 같이 일부의 공격에 저항할 수 있다. 그러나 아직까지 워터마크의 강인성은 여전히 개선될 필요가 있다. 본 논문은 블랙핀 프로세서 기반의 디지털 사운드에 대한 소유권 보호 및 인증을 위해 웨이블릿 기반의 주파수 대역의 계수에 워터마크를 내장 및 추출하는 워터마킹 기법을 제안한다. 제안된 사운드 워터마킹 알고리즘의 하드웨어 구현은 소유권 보호의 실용화와 고수준의 프로그램 개발에 따른 워터마크의 강인성을 확인할 수 있다.

• 한국기계가공학회지
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• 제18권8호
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• pp.51-59
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• 2019

Flow forming is an eco-friendly and high-efficiency plastic deformation process with fewer chips during a process which is specifically used to manufacture seamless tubular products like tire wheels, rocket motor cases etc. On the development of mortar barrel using Inconel718 tube, some flow formed products had dimensional errors on their thickness. In this study, our purpose is to optimize the process conditions with the smallest dimensional error. In order to find an optimum process condition, 2D axisymmetric FEM simulation analyses with Taguchi method were conducted. Geometric variables (attack angle, flatting angle, roller nose radius) and operating parameters (depth of forming, feed rate) are considered as control factors. Forward flow forming with single roller was first analyzed to determine the effective factors using AFDEX software and attack angle of the roller was identified as the most influential factor. Also, the nose radius of the rollers was confirmed as a significant factor in multi-rollers flow forming system. The effect of rollers offset values are also studied and finally, we proposed optimal conditions to improve the accuracy of flow forming process with Inconel718 tube for mortar barrel manufacturing.

• Wind and Structures
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• 제35권4호
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• pp.243-253
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• 2022

The conformal mapping method (CMM) has been broadly exploited in the study of fluid flows over airfoils and other research areas, yet it's hard to find relevant research in bridge engineering. This paper explores the feasibility of CMM in streamlined box girder bridges. Firstly, the mapping function transforming a unit circle to the streamlined box girder was solved by CMM. Subsequently, the potential flow solution of aerostatic pressure on the streamlined box girder was obtained and was compared with numerical simulation results. Finally, the aerostatic pressure attained by CMM was utilized to estimate the aerostatic coefficient and flutter performance of the streamlined box girder. The results indicate that the solution of the aerostatic pressure by CMM on the windward side is satisfactory within a small angle of attack. Considering the windward aerostatic pressure and coefficient of correction, CMM can be employed to estimate the rate of change of the lift and moment coefficients with angle of attack and the influence of the geometric shape of the streamlined box girder on flutter performance.

• 정보처리학회논문지B
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• 제12B권3호
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• pp.283-290
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• 2005

워터마킹에서 영상의 평행이동, 회전, 크기변환 왜곡에 기인한 워터마크 삽입 위치와 추출 위치의 불일치는 해결해야 하는 문제이다. 본 논문에서는 복구패턴 정합을 통한 영상동기화를 이용함으로써 기하학적 왜곡에 강인한 워터마킹 방법을 제안한다. 제안하는 방법은 복구패턴을 정의하여 워터마크가 삽입된 영상에 복구패턴을 삽입 배포한다. 그리고 배포된 영상으로부터 복구패턴을 추출하여 삽입한 복구패턴과 비교함으로써 기하학적 왜곡 여부를 확인한다 기하학적 왜곡이 발생하였다면 왜곡된 만큼 역변환을 함으로써 워터마크 삽입 위치와 추출 위치를 동기화 한다. 제안한 방법의 성능을 평가하기 위하여 이동, 회전, 스케일링 공격에 대한 실험결과를 보인다.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1330-1338
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• 2024

Information on isotopic composition and geometric structure is necessary for identifying a true warhead. Nevertheless, such classified information should be protected physically or electronically. With a novel Hash encryption algorithm, this paper presents a Monte Carlo-based design of a neutron activation analysis verification module. The verification module employs a thermal neutron source, a non-uniform mask (physically encrypting information about isotopic composition and geometric structure), a gamma detector array, and a Hash encryption algorithm (for electronic encryption). In the physical field, a non-uniform mask is designed to distort the characteristic gamma rays emitted by the inspected item. Furthermore, as part of the Hash algorithm, a key is introduced to encrypt the data and improve the system resolution through electronic design. In order to quantify the difference between items, Hamming distance is used, which allows data encryption and analysis simultaneously. Simulated inspections of simple objects are used to quantify system performance. It is demonstrated that the method retains superior resolution even with 1% noise level. And the performances of anti-statistical attack and anti-brute force cracking are evaluated and found to be very excellent. The verification method lays a solid foundation for nuclear disarmament verification in the upcoming era.

• Wind and Structures
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• 제19권6호
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• pp.665-686
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• 2014

This study presents a comprehensive investigation of the aerostatic and buffeting response characteristics of a suspension bridge catwalk. The three-dimensional aerostatic response analysis was carried out taking into account the geometric nonlinearity and nonlinear dependence of wind loads on the angle of attack. The buffeting response analysis was performed in the time domain. The aerostatic and buffeting responses of the catwalk show strong coupling of vertical and lateral vibrations. The lateral displacement is the main component of the wind-induced static and buffeting response of the catwalk.

• 로봇학회논문지
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• 제4권4호
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• pp.265-272
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• 2009

IVarious driving mechanisms to adapt to uneven environment have been developed for many urban search and rescue (USAR) missions. A tracked mechanism has been widely used to maintain the stability of robot's pose and to produce large traction force on uneven terrain in this research area. However, it has a drawback of low energy efficiency due to friction force when rotating. Moreover, single tracked mechanism can be in trouble when the body gets caught with high projections, so the track doesn't contact on the ground. A transformable tracked mechanism is proposed to solve these problems. The mechanism is designed with several articulations surrounded by tracks, used to generate an attack angle when the robot comes near obstacles. The stair climbing ability of proposed robot was analyzed since stairs are one of the most difficult obstacles in USAR mission. Stair climbing process is divided into four separate static analysis phases. Design parameters are optimized according to geometric limitations from the static analysis. The proposed mechanism was produced from optimized design parameters, and demonstrated in artificially constructed uneven environment and the actual stairway.

• 수산해양기술연구
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• 제32권3호
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• pp.302-309
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• 1996

Cavitation erosion-corrosion implies damage to materials due to the shock pressure or shock wave that results when bubbles form and collapse at a metal surface within a liquid. If the liquids corrosive to the material, a condition typically encountered in industry, the component materials may suffer serious damage by a combination of mechanical and electrochemical attack. To suppress cavitation erosion as well as cavitation erosion-corrosion to hydraulic equipments, innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. This study was tested by using the piezoelectric vibrator with 20kHz, 24${\mu}$m for cavitation generation. And also, the vibratory cavitation erosion-corrosion tests on commercial mild steel SS41were carried out. We carefully observed the erosion pattern and surface photography. The geometrical mechanism of pit growth, which is to be likely these processing; shallow typelongrightarrowundercut typelongrightarrowwide shallow type.

• 전자공학회논문지CI
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• 제46권5호
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• pp.57-70
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• 2009

벡터 데이터 기반의 CAD 설계도면은 대부분 산업 분야에서 매우 주요한 저작물로, 저작권 보호 기술이 매우 필요한 콘텐츠로 인식되고 있다. 본 논문에서는 k-means++ 기반의 CAD 설계도면 워터마킹 기법을 제안한다. 하나의 CAD 설계도면은 여러 레이어들로 구성되며, 각 레이어는 폴리라인, 원, 호, 폴리곤 등의 다양한 기하학 객체들로 구성된다. 이들 기하학적 요소들 중 폴리라인 호 및 쿼드폴리곤 객체들은 CAD 설계도면의 기본적인 객체들로 객체 분포의 거의 대부분을 차지한다. 따라서 제안한 기법에서는 설계도면 내에 폴리라인, 쿼드폴리곤 및 호 객체들 중 가장 많은 수를 가지는 객체를 선택한 후, 이들 객체를 많이 분포하는 레이어들을 선택한다. 그리고 선택된 레이어 내에 객체들을 k-means++ 기반으로 그룹화한 다음, 각 그룹내에 기하학 특징 분포에 워터마크를 삽입한다. 이 때 기하학 특징 분포로는 폴리라인의 정규화된 길이 분포, 쿼드폴리곤의 정규화된 면적 분포 및 호의 각도 분포이다. 실험 결과로부터 제안한 기법이 CAD 도면툴 상에서 제공하는 다양한 기하학 편집과 파일포맷변환, 레이어 공격 등에 대하여 강인함을 확인하였다.

• Selected Papers of The Society of Naval Architects of Korea
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• 제1권1호
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• pp.76-90
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• 1993

A new propeller series is developed using the newly developed blade section (KH 18 section) which has better cavitation characteristics and higher lift-drag ratio at wade angle-of-attack range than a conventional section. The radial patch distribution of the new series propellers is variable stance they were designed adaptively to a typical wake distribution. Basic geometric particulars of the series propellers. such as chord length, thickness, skew and rake distributions, are determined on the basis of recent full scale propeller geometric data. The series is developed for propellers having 4 blades, and blade area ratios of 0.3, 0.45, 0.6 and 0.75. Mean pitch ratios are varied as 0.5, 0.6, 0.7, 0.95 and 1.1 for each blade area ratio. The new propeller series consists of 20 propellers and is named as the KD(KRISO-DAEWOO)-propeller series. Propeller open-water tests are performed at the towing tank, and cavitation observation tests and fluctuating pressure tests are carried out at the cavitation tunnel of KRISO. $B_{p}-\delta$ curves, which can be used to select the optimum propeller diameter at the preliminary design stage, are derived from a regression analysis of the propeller open-water test results. The KD-cavitation chart is derived from the cavitation observation test results by choosing the local maximum lift coefficient and the local cavitation number as parameters. The cavity extent predicted by the KD-cavitation chart would be more accurate compared to that by an existing cavitation charts, such as the Burrll's cavitation chart, since the former is derived from the cavitation observation test results in a typical ship's wake, while the lather is derived from the test results in a uniform flow.