• Wind and Structures
• /
• 제7권3호
• /
• pp.203-214
• /
• 2004

This paper describes a method for developing a multi-degree-of freedom aero-elasto-plastic model of a base-isolated mid-rise building. The horizontal stiffness of isolators is modeled by several tension springs and the vertical support is performed by air pressure from a compressor. A lead damper and a steel damper are modeled by a U-shaped lead line and an aluminum line. With this model, the frequency ratio of torsional vibration to sway vibration, and plastic displacements of isolation materials can be changed easily when needed. The results of isolation material tests and free vibration tests show that this model provides the object performance. The peak displacement factors are about 4.5 regardless of wind speed in wind tunnel tests, but their gust response factor decreases with increment of wind speed.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
• /
• pp.528-531
• /
• 1997

This paper deals with the kinematic and dynamic modeling of a 3 degree-of-freedom redundantly actuated mobile robot for the purpose of analysis and control. Each wheel is driven by two motors for steering and driving. Therefore, the system becomes force-redundant since the number of input variable is greater than the number of output variable. The kinematic and dynamic models in terms of three independent joint variables are derived. Also, a load distribution method to determine the input loads is introduced. Finally we demonstrate the feasibility of the proposed algorithms through simulation.

• 소음진동
• /
• 제9권3호
• /
• pp.587-592
• /
• 1999

Piston slap is one of the sources producing engine block surface vibration and mechanical noise. To analyze piston slap-induced vibration, a realistic but simple model is proposed and verified experimentally. A piston is modeled by 3 degree of freedom system and an impact point between piston skirt and cylinder wall by 2 degree of freedom system. Numerical simulation estimates impact forces of piston in cylinder, and the engine block surface vibration response is predicted by the convoluton of the impact forces with measured impulse responses. Experimental verification on the predicted response has been also performed by using a commercial 4-cylinder diesel engine. the predicted and experimental vibration responses confirm that the suggested model is practically useful.

• 한국인터넷방송통신학회논문지
• /
• 제16권5호
• /
• pp.83-89
• /
• 2016

본 논문에서는 오행(五行)[1]의 상보성원리를 위상 간섭제거에 응용했다. 상생과 상극개념을 송신과 수신의 직접신호와 간섭신호에 대응시켰다. 오행(五行)(5 prime substances : 5 user networks)과 같은 네트워크 토폴로지(topology)를 제안한다. 전송된 신호의 할당 가능성을 조절 및 간섭 할당 방법을 잘 선택해, 최적의 대칭 DoF(degree of freedom)가 다른 채널동기 시간의 5 user 네트워크 달성이 가능함을 설명한다. 이론적으로는 5 user 네트워크가 무선 이동 채널 환경에 잘 match 된다는 결과를 보이고, 제안한 네트워크가 무선 네트워크 응용에 적용될 수 있음을 보여주는 다른 채널 동기 시간에 대해 대칭 DoF를 달성함을 보인다. 5 user 네트워크 토폴로지에서 modulo 3 성능을 이용하면 송신기 협력이 간섭 할당 방법으로 2/3의 DoF를 보다 쉽게 달성할 수 있다.

• 한국콘텐츠학회논문지
• /
• 제18권3호
• /
• pp.148-159
• /
• 2018

본 연구는 자원의존이론에 근거해 방송사의 소유구조(공영/민영)와 재원구조(고광고 의존/저광고 의존)가 기자들이 느끼는 취재보도의 자유도와 언론자유를 제약하는 주된 요인, 직무의 자율성 만족도, 편집 편성 정책 만족도에 미치는 영향을 방송사 기자에 대한 인식조사를 통해 실증적으로 확인했다. 그 결과 방송사의 소유구조와 재원구조는 모두 기자들이 느끼는 취재 및 보도의 자유도 인식에 영향을 미치는 것으로 확인됐다. 반면 자율성에 대한 만족도는 재원구조만 영향을 미쳤고, 회사의 편집 편성 정책에 대한 만족도와 언론 자유를 제약하는 요인에 대한 인식은 소유구조가 영향을 미치는 것으로 확인됐다. 이같은 결과는 광고수익 의존도가 기자들의 취재보도에 영향을 미치며, 특히 공영방송은 정부나 정치권력과 광고수익 의존도가 동시에 영향을 미치고 있다는 사실이 확인됐다는 점에서 의의가 있다.

• 한국문헌정보학회지
• /
• 제53권3호
• /
• pp.291-315
• /
• 2019

본 연구의 목적은 국내외 허위정보에 관한 연구동향을 비교분석하는 것이다. 이를 위하여 전학문 분야의 학술지를 대상으로 연구기간의 제한이 없이 국내논문 104편과 국외논문 861편에 나타난 저자가 부여한 영문키워드를 수집하였다. 국내논문에서 수집된 283개 영문키워드와 국외논문에서 수집된 3,551개 영문키워드는 NetMiner V.4를 사용하여 키워드 네트워크의 연결중심성과 매개중심성을 분석하였으며, 분석결과는 다음과 같다. 첫째, 연구 주제의 양적 측면에서 국내의 경우는 'Freedom of Expression', 'Fact Check', 'Regulation', 'Media Literacy', 'Information Literacy'로 순으로, 국외의 경우는 'Social Media', 'Post Truth', 'Propaganda', 'Information Literacy', 'Journalism' 순으로 나타났다. 둘째, 연구 주제의 영향력 측면에서 국내의 경우는 'Fact Check', 'Freedom of Expression', 'Hoax' 순으로, 국외의 경우는 'Social Media', 'Detection' 순으로 확인되었다. 마지막으로 연구 주제의 확장성 측면에서 국내의 경우는 'Fact Check', 'Polarization', 'Freedom of Expression', 'Commercial' 순으로 나타났다. 한편, 전체키워드에서 낮은 빈도를 보였던 'Commercial'이 'Media Literacy', 'Freedom of Expression' 등을 매개하며 상대적으로 매개역할정도가 큰 것으로 확인되었다. 국외의 경우는 'Social Media', 'Detection', 'Machine Learning'이 주요 연결다리로 나타났다.

• Earthquakes and Structures
• /
• 제11권1호
• /
• pp.165-178
• /
• 2016

The goal of energy-based seismic design is to obtain a structural design with a higher energy dissipation capacity than the energy dissipation demands incurred under earthquake motions. Accurate estimation of the story hysteretic energy demand of a multi-story structure is the key to meeting this goal. Based on the assumption of a mode-equivalent single-degree-of-freedom system, the energy equilibrium relationship of a multi-story structure under seismic action is transformed into that of a multi-mode analysis of several single degree-of-freedom systems. A simplified equation for the estimation of the story seismic hysteretic energy demand was then derived according to the story shear force and deformation of multi-story buildings, and the deformation and energy relationships between the mode-equivalent single-degree-of-freedom system and the original structure. Sites were categorized into three types based on soil hardness, namely, hard soil, intermediate hard (soft) soil, and soft soil. For each site type, a 5-story and 10-story reinforced concrete frame structure were designed and employed as calculation examples. Fifty-six earthquake acceleration records were used as horizontal excitations to validate the accuracy of the proposed method. The results verify the following. (1) The distribution of seismic hysteretic energy along the stories demonstrate a degree of regularity. (2) For the low rise buildings, use of only the first mode shape provides reasonably accurate results, whereas, for the medium or high rise buildings, several mode shapes should be included and superposed to achieve high precision. (3) The estimated hysteretic energy distribution of bottom stories tends to be underestimated, which should be modified in actual applications.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1994년도 Proceedings of the Korea Automatic Control Conference, 9th (KACC) ; Taejeon, Korea; 17-20 Oct. 1994
• /
• pp.334-339
• /
• 1994

In this work, we propose a planar three degree-of-freedom parallel mechanism as another type of assembly device which utilized joint compliances. These joint compliances can be adjusted either by properly replacing the joint compliances or by actively controlling stiffness at joints, in order to generate the desired operational compliance characteristics at RCC point, The operational compliance matrix for this mechanism is explicitly obtained by symbolic manipulation and its operational compliance characteristics are examined, it is found that the RCC point exists at the center of the workspace when the mechanism maintains symmetric configurations. Compliance characteristic and its sensitivity of this mechanism is analyzed with respect to the magnitude of the diagonal compliance components and two different matrix norms measuring compliance sensitivity. It is expected that the analysis results provide the designer with a helpful information to determine a set of optimal parameters of this RCC mechanism.

• 한국정밀공학회지
• /
• 제15권11호
• /
• pp.199-207
• /
• 1998

This paper presents the design and the control of three degree-of-freedom(DOF) fine positioning device based on an electro-magnetic force. The device is designed by use of a magnetic circuit theory and it is capable of fine motion due to the electro-magnetic force. The device consists of permanent magnets, yokes and coils. The magnetic fluxes generated from the permanent magnets constitute magnetic paths through steel, whereas the coils are arranged into the gap between two surfaces of the yokes. Therefore, by supplying current to the coils, the coils are capable of some motions due to Lorentz forces. For the optimal design of the actuating system, the system parameters are defined and investigated under the given constraints. From the system modeling in small displacement, three decoupled equations of motion are obtained. To get better performance of the system, a PID controller is implemented. Experimental results are presented in terms of time response and accuracy.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
• /
• pp.1040-1043
• /
• 1996

The accuracy of the servo control in CNC system has a great influence on the duality of machine product. Tracking performance of the servo control is deteriorated mainly by the time delay of the servo system and the inertia of the work table or bed. Contouring errors occur in every interpolation steps by the effect of the tracking performance. In this paper, $H_{\infty}$ two-degree-of-freedom(TDF) controller is designed for improvement to improve the tracking performance. The designed controller is applied 3-axis machining center model and the cutting accuracy is simulated in case of corner cutting, circular and involute interpolation. Simulation results show that $H_{\infty}$ TDF controller designed in this paper has a good effect to improve tracking performance in CNC system.