• 대한금속재료학회지
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• 제47권7호
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• pp.391-396
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• 2009

Tensile, low cycle fatigue, and fatigue crack growth rate tests were conducted at RT and $300^{\circ}C$ for type 304 stainless steel. Tensile was tested under displacement control and low cycle fatigue was tested under strain control. Fatigue crack growth rate test was conducted under load control and crack was measured by DCPD method. Yield strength and elongation decreased at $300^{\circ}C$. Dynamic strain aging was not detected at $300^{\circ}C$. Low cycle fatigue life increased but fatigue strength decreased at $300^{\circ}C$. Fatigue crack growth rate increased at $300^{\circ}C$. Dislocation structures were mixed with cell and planar and did not change with temperature. Grain size did not change but plastic strain increased at $300^{\circ}C$. Strain induced martensite after low cycle fatigue test increased at RT but decreased at $300^{\circ}C$. It was concluded that the increase of low cycle fatigue life at $300^{\circ}C$ was due to the decrease of strain induced martensite at which crack was initiated.

• Smart Structures and Systems
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• 제18권3호
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• pp.585-599
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• 2016

Steel cables serve as the key structural components in long-span bridges, and the force state of the steel cable is deemed to be one of the most important determinant factors representing the safety condition of bridge structures. The disadvantages of traditional cable force measurement methods have been envisaged and development of an effective alternative is still desired. In the last decade, the vision-based sensing technology has been rapidly developed and broadly applied in the field of structural health monitoring (SHM). With the aid of vision-based multi-point structural displacement measurement method, monitoring of the tensile force of the steel cable can be realized. In this paper, a novel cable force monitoring system integrated with a multi-point pattern matching algorithm is developed. The feasibility and accuracy of the developed vision-based force monitoring system has been validated by conducting the uniaxial tensile tests of steel bars, steel wire ropes, and parallel strand cables on a universal testing machine (UTM) as well as a series of moving loading experiments on a scale arch bridge model. The comparative study of the experimental outcomes indicates that the results obtained by the vision-based system are consistent with those measured by the traditional method for cable force measurement.

• Smart Structures and Systems
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• 제18권3호
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• pp.375-387
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• 2016

The classical Kalman filter (KF) can provide effective state estimation for structural identification and vibration control, but it is applicable only when external inputs are measured. So far, some studies of Kalman filter with unknown inputs (KF-UI) have been proposed. However, previous KF-UI approaches based solely on acceleration measurements are inherently unstable which leads to poor tracking and fictitious drifts in the identified structural displacements and unknown inputs in the presence of measurement noises. Moreover, it is necessary to have the measurements of acceleration responses at the locations where unknown inputs applied, i.e., with collocated acceleration measurements in these approaches. In this paper, it aims to extend the classical KF approach to circumvent the above limitations for general real time estimation of structural state and unknown inputs without using collocated acceleration measurements. Based on the scheme of the classical KF, an improved Kalman filter with unknown excitations (KF-UI) and without collocated acceleration measurements is derived. Then, data fusion of acceleration and displacement or strain measurements is used to prevent the drifts in the identified structural state and unknown inputs in real time. Such algorithm is not available in the literature. Some numerical examples are used to demonstrate the effectiveness of the proposed approach.

• 항공우주시스템공학회지
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• 제12권1호
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• pp.42-46
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• 2018

본 연구는 소형 엔진 추력 시험 장비에 대한 구조의 안전성 해석에 관한 연구이다. 본 연구에서 소형 엔진 시험 장치를 위한 철강 및 알루미늄 합금 적용 구조의 설계 및 해석을 수행하였다. 1차적으로 엔진 시험 장치의 구조 설계 요구 조건이 분석되었다. 구조 설계 이후 유한 요소 해석 기법을 활용하여 엔진 시험 장치의 구조 해석이 수행되었다. 적용 하중 조건에서 응력 및 변위 해석이 수행되었다. 최종 구조 해석을 통해 설계된 엔진 시험 장치 구조는 안전한 것으로 확인되었다.

• Structural Engineering and Mechanics
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• 제69권3호
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• pp.347-359
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• 2019

This paper aims to evaluate the behavior of Dorim-Goh bridge in Seoul, Korea, under static and dynamic loads effects by ambient trucks. The prestressed concrete (PSC) girders and reinforcement concrete (RC) slab of the bridge are evaluated and assessed. A short period monitoring system is designed which comprises displacement, strain and accelerometer sensors to measure the bridge performance under static and dynamic trucks loads. The statistical analysis is used to assess the static behavior of the bridge and the wavelet analysis and probabilistic using Weibull distribution are used to evaluate the frequency and reliability of the dynamic behavior of the bridge. The results show that the bridge is safe under static and dynamic loading cases. In the static evaluation, the measured neutral axis position of the girders is deviated within 5% from its theoretical position. The dynamic amplification factor of the bridge girder and slab are lower than the design value of that factor. The Weibull shape parameters are decreased, it which means that the bridge performance decreases under dynamic loads effect. The bridge girder and slab's frequencies are higher than the design values and constant under different truck speeds.

• 대한물리의학회지
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• 제14권1호
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• pp.15-23
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• 2019

PURPOSE: This study was conducted to investigate the effects of the myofascial meridians release technique on pain and postural control of college students with forward head posture and to compare the intervention effects of the Grastone massage and the Rollfing massage. METHODS: Thirty subjects with forward head posture were randomly and equally allocated to experimental group I (myofascial meridians release technique using Grastone massage, n=15) or experimental group II (myofascial meridians release using Rollfing massage, n=15). All subjects underwent 30 minutes of different myofascial meridians release techniques in addition to general physical therapy (hot pack: 15 min, interferential current therapy: 15 min, ultra sound: 5 min) three times a week for a total of 6 weeks. Outcome was measured before and after 4 weeks of intervention. RESULTS: In both groups, the numerical rating scale of pain was significantly decreased after intervention, with experimental group I showing a greater decrease than experimental group II. The neck disability index decreased significantly after intervention in both groups, with experimental group I showing a significantly greater decrease than the controls. The distance of the head forward displacement did not differ significantly between the two groups (p>.05). CONCLUSION: This study suggests that the Grastone method combined with the myofascial meridians release technique is a more effective intervention for improvement of pain and postural control in adults with moderate forward head posture.

• 한국전문물리치료학회지
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• 제26권3호
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• pp.76-83
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• 2019

Background: The hyoid bone is the only non-jointed structure among the skeletal tissues of the head and neck region, and its movement and posture depend on the attached muscle, ligament, and fascia. The location of the hyoid bone is important for airway maintenance, vocalization, chewing, swallowing, breathing, and head and scapular position. In general, the location of the hyoid bone is measured using radiographs and 3D computed tomography, and no studies have reported on clinical measurement methods. Objects: This study was performed to suggest clinical measurement methods for lateral deviation of the hyoid bone and to evaluate their reliability. Methods: In this study, 24 healthy volunteers (12 males, 12 females) in Cheongju-si participated. Two examiners performed the center point test and lateral motion test twice each to measure the lateral displacement of the hyoid bone. The reliability of the center point test was analyzed using intra-class correlation coefficients (ICC), and the reliability of the lateral motion test was analyzed using Cohen's kappa coefficient. Results: The intra-rater reliability of the center point test was good, and the inter-rater reliability was moderate. The intra- and inter-rater reliability of the lateral motion test showed substantial reliability. Conclusion: Based on these results, the center point test and the lateral motion test can be used as an alternative methods of the measurement of lateral deviation of the hyoid bone for people who have musculoskeletal disorders of the head, neck, and scapula.

• 로봇학회논문지
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• 제14권2호
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• pp.131-138
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• 2019

In this study, we developed an FSEA(Force-sensing Series Elastic Actuator) composed of a spring and an actuator has been developed to compensate for external disturbance forced. The FSEA has a simple structure in which the spring and the actuator are connected in series, and the external force can be easily measured through the displacement of the spring. And the characteristic of the spring absorbs the shock to the small disturbance and increases the sense of stability. It is designed and constructed to control the stiffness of such springs more flexibly according to the situation. The conventional FSEA uses a fixed stiffness spring and the actuator is not compensated properly when it receives large or small external force. Through this experiment, it is confirmed that FSEA compensates the external force through the proposed algorithm that the variable stiffness compensates well for large and small external forces.

• 농업과학연구
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• 제46권2호
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• pp.323-333
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• 2019

In Korea, origin labeling is one of the main issues in the food service sector. Many restaurants presented the incorrect or no origin of the food material, and Korean consumers have kept complaining about it. Even though the origin labeling program was welcomed by consumers, the food service sector has claimed that there is an increasing cost due to the origin labeling program. It is an important issue to determine whether the origin labeling program is good for the social welfare; however, the specific effects of the origin labeling program have rarely been measured. The purpose of this study was to measure the effect of origin labeling of beef in the Korean food service sector. Through survey and model analyses, a few findings are presented. First, Korean consumers showed a positive willingness-to-pay for the origin labeling of beef. Especially, consumers without information on the origin of the beef showed a larger willingness-to-pay for the origin labeling. Second, the origin labeling of beef changed the price and quantity of beef, and this change became larger when the consumers had no information on the origin of the beef. The change in the marketing margin due to the origin labeling program also affected the changes in the price and quantity of the beef. Third, the origin labeling of beef increased the social welfare, which is the sum of the consumer surplus and producer surplus. And this increase of the social welfare became larger when the consumers had no information about the origin.

• 한국항공우주학회지
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• 제47권5호
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• pp.319-325
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• 2019

본 논문의 목적은 항공기에 장착되는 복합재 라미네이트 및 샌드위치구조를 가지는 레이돔에 대한 조류충돌해석을 수행하고 해석결과와 시험결과를 비교 및 분석하기 위함이다. 먼저 SPH(Smoothed Particle Hydrodynamics)법을 통해 물의 특성을 가지는 조류를 모델링하였으며, 조류충돌시험을 통해 조류가 충돌할 때의 속도를 입력하여 조류충돌해석을 수행하였다. 해석결과를 통해 레이돔의 파손 여부를 조사하고 최대 변형량을 시험결과와 비교하였으며 충돌과정에서의 압력변화추이가 기 연구되었던 결과와 일치함을 확인하였고, 이를 통해 수치해석모델의 신뢰성을 확보하였다. 또한 조류모델을 이루는 입자의 밀도가 레이돔의 파손 형상에 영향을 미친다는 사실을 확인하였다.