• Coupled systems mechanics
• /
• 제7권4호
• /
• pp.395-406
• /
• 2018

This paper proposes a linear damping model of tire-soil system using semi-empirical method. A test rig was designed and developed to measure the vertical equivalent linear damping ratio of tire only and tire-soil system using Free-Vibration Logarithmic Decay Method. The test was performed with two kinds of tractor tires using a combination of five inflation pressure levels, two soil depths and four soil moisture contents in the paddy soil. The results revealed that the linear damping ratio of tires increased with decreasing tire inflation pressure; the linear damping ratio of tire-soil system also increased with decreasing tire inflation pressure and increased with the increasing soil depth (observed at 80 and 120 mm). It also increased with a relative increase of soil moisture contents (observed at 37.9%, 48.8%, 66.7% and 77.4%). The results also indicated that the damping ratio of tire-soil system was higher than that of tire only. A linear damping model of tire-soil system is proposed as a damping model in parallel which is established based on experimental results and vibration theory. This model will have a great significance in study of tractor vibration.

• ALGAE
• /
• 제21권2호
• /
• pp.245-251
• /
• 2006

Diurnal and age-related changes in air pressure were measured in air bladders of Ascophyllum nodosum from the Atlantic coast of Nova Scotia. Exterior and interior bladder volumes vary significantly with 4 and 6 y bladders being about 40% larger than 2 y bladders (p < 0.01). Freshly collected bladders yielded a mean pressure of 40.8 ± 6.5 cm H2O. Overnight (20 h) dark treatment at 15°C generated pressure reductions by 80% in 2 y bladders but only by about 30% in 4 and 6 y bladders. Furthermore, in 2 y bladders 8 out of 11 bladders were reduced to atmospheric pressure. Pressure losses were inversely related to pressure recovery after 2.5 h in natural daylight, but after 5 h in daylight there was no significant difference in pressure within the age groups. Even under 25% of full illumination, bladders inflated to full pressure after 5 h. The results show that differences in bladder age and bladder wall thickness have roles in diurnal patterns of bladder inflation and deflation. These results confirm that bladder inflation is based on photosynthetic O2 production and not on partial pressures of O2 in the surrounding medium as was suggested for Sargassum. Chemical analyses of fluid recovered after the interior of bladders were washed with saline showed no evidence for the occurrence of surfactant that might be responsible for maintaining the air-liquid interface.

• 한국농업기계학회:학술대회논문집
• /
• 한국농업기계학회 1997년도 하계 학술대회 논문집
• /
• pp.49-54
• /
• 1997

• 국제지역연구
• /
• 제16권1호
• /
• pp.147-171
• /
• 2012

2000년 이후 오늘날에도 중국, 인도 등을 비롯한 신흥시장국의 경제규모가 날로 확대되면서 국제적으로 석유에 대한 수요가 크게 증가해온 반면 그 공급은 주요 산유국인 중동국가의 정세불안 등으로 차질이 발생하는 상황이 빈발함에 따라 스태그플레이션 위험은 항상 개연성이 높은 경제현상으로 인식되고 있다. 그러나 일반 사람들이 고유가가 지속되는 시기에 흔히 높은 인플레이션과 경기침체가 공존하는 현상을 스태그플레이션으로 쉽게 거론하더라도 스태그플레이션에 관한 학술적인 정의는 분명하지 않으며 현실적인 경제통계의 흐름을 보고 그러한 상황을 식별하기도 쉽지 않다. 본고에서는 경기국면으로서 스태그플레이션의 상황을 보다 구체적으로 정의한 연구사례들을 면밀히 살펴보고 월별로 조기에 입수 가능한 경제통계들을 종합하여 스태그플레이션의 상황을 체계적으로 식별할 수 있는 방법론을 제시하였다. 경기상황, 인플레이션 상황을 나타내는 월별 통계지표를 이용하여 스태그플레이션 상황을 나타내는 정도를 평가한 후 이 결과를 종합하여 스태그플레이션 종합지수를 산출하였다. 그 결과 한국에서 스태그플레이션 여부에 대한 논란이 많았던 2008년 상반기가 엄밀한 의미에서 스태그플레이션 상황은 아니었음을 규명하였다.

• KDI Journal of Economic Policy
• /
• 제36권3호
• /
• pp.95-120
• /
• 2014

본 논문은 경제주체들이 미래에 대한 기대를 형성하는 데 있어서 기대기간이 주요한 역할을 한다는 점을 밝히는 시도이다. 정보효율성과 관련된 경제학적 가정이 확률과정에 어떠한 제약으로 작용하는지에 대한 분석으로부터 출발하여, 기대변수에 대한 조정과정이 오로지 새로이 발생한 정보만을 반영하는 경우를 미래기대의 임의보정(random revision of expectation)이라는 새로운 개념으로 제시하였다. 이러한 가정하에 물가동학 결정식을 도출할 경우, 산출갭으로 측정한 수요압력의 인플레이션에 대한 영향은 기대기간에 따라 달리 식별되었다. 이러한 모형을 우리나라 자료를 이용하여 실증한 결과, 기대기간을 단기로 설정할 경우 계수 추정치는 작아지고 통계적 유의성도 떨어지는 것으로 나타났다.

• 한국자동차공학회논문집
• /
• 제11권4호
• /
• pp.125-134
• /
• 2003

In this study, Mooney-Rivlin 1st model and Mooney-Rivlin 3rd model are adopted as strain energy density functions of the rubber compounds of a radial tire. It is shown that the FE analysis using Mooney-Rivlin models for rubber compounds may provide good approximations by employing the appropriate strain range of experimental stress-strain data in a way to describe the stress-strain relationship accurately. Especially, Mooney-Rivlin 3rd model gives an accurate stress-strain relationship regardless of the fitting strain range used within the strain of 100%. The static nonlinear FE analysis of a tire inflation is performed by employing an axisymmetric model, which shows that the outside shapes of the tire before and after inflating the tire agree well with those of the real tire. Additionally, the deformations at crown center and turning point on sidewall, distribution of belt cord force, interlaminar shear strain are predicted in terms of variation of belt cord angle which is known as the most influential factor in inflation behavior of a tire.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1993년도 추계학술대회 논문집
• /
• pp.601-606
• /
• 1993

The natural frequency measurement of passenger car tire under the load and rotation are studied. In order to obtain theoretical natural frequency and mode shape, the plane vibration of a tire is modeled to that of circular beam. By using the Tickling method based on Hamilton's principle, theoretical results are determined by considering tension force due to tire inflation pressure, rotational velocity and tangential, radial stiffness. Modal parameters varying the inflation pressure, load, rotational velocity are determined experimentally by using frequency response function method. The results show that experimental conditions are parameter for shifting of natural frequency.

• 대한기계학회논문집A
• /
• 제20권1호
• /
• pp.1-13
• /
• 1996

The measurement of radial directional natural frequency ina passenger car tire rotating under the load is studied. In order to obtain theoretical matural frequency and mode shape, the ploane vibration of a tire is modeled to that of circular beam. By esing the Tieking method based on Hamiltons's principle, theoretical results are determined by considering tension horce due to tire inflation pressure, retational velocity and tangential, radial stiffness. Radial directional modal parameters varying with the inflation pressure, load, rotational velocity are experimentally determined by using frequency response function method. The results show that experimental conditions canbe considered as the parameters which shift the natural frequency.

• 오토저널
• /
• 제15권2호
• /
• pp.76-83
• /
• 1993

The vibration characteristics of radial tire are studied. In order to obtain theoretical natural frequency and mode shape, the plane vibration of a tire is modeled to that of circular beam. By using the Tielking method based on Hamilton's principle, theoretical results are determined by considering tension force due to tire inflation pressure, rotational velocity and tangential, radial stiffness. Modal parameters varying the inflation pressure are determined experimentally by using the transfer function method. Results show that material property and wear are parameter for shifting of natural frequency and damping.

• 한국농업기계학회:학술대회논문집
• /
• 한국농업기계학회 2001년도 동계 학술대회 논문집
• /
• pp.40-46
• /
• 2001