• Coupled systems mechanics
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• 제9권5호
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• pp.455-471
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• 2020

This paper presents the results of the study of vertically natural frequency of tractor tires are effected by changing different ground contacts and inflation pressures using the Free Decay Method. The results show that the natural frequencies of the tire are not affected while the vertical acceleration increased strongly due to the increase of inflation pressure when the tire performs free decay vibration on rigid ground. In addition, the number of natural frequency peaks of the tire also increases with increasing tire inflation pressure. On the other hand, the natural frequencies of the tractor tire increases strongly while the vertical acceleration decreases slightly with the increase of tire inflation pressure as the tire performs free decay vibration on soft soil. Further, the natural frequencies of tire-soil system are always higher than that of tire only, and it changed with changing the soil depth. Results also show the natural frequency of tire and tire-soil system is in the range of 3.0 to 10.0 Hz that lie within the most critical natural frequency range of the human body. These findings have to be mentioned and used as design parameters of the tractor suspension system.

• Earthquakes and Structures
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• 제12권2호
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• pp.145-152
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• 2017

The analytical method is used to develop new models for an elevated tank to estimate its natural period. The equivalent mass- spring method is used to configure the developed analytical models. Also direct method is used for numerical verification. The current study shows that developed models can have a good estimation of natural period compared with concluded results of finite elements. Additional results show that, the dependency of impulsive period to soil stiffness condition is higher than convective period. Furthermore results show that considering the fluid- structure- soil interaction has remarkable effects on natural impulsive and convective periods in case of hard to very soft soil.

• 한국지진공학회논문집
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• 제17권6호
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• pp.245-255
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• 2013

According to natural frequency of soil, characteristics of earthquake responses of an isolated containment building in nuclear power plants are examined. For this, earthquake response analysis of seismically isolated containment buildings in nuclear power plants is carried out by strictly considering soil-structure interactions. The structure and near-field soil are modeled by the finite element method while far-field soil by consistent transmitting boundary. The equation of motion of a soil-structure interaction system under incident seismic wave is derived. The derived equations of motion are solved to carry out earthquake analysis of a seismically isolated soil-structure system. Generally, the results of this analysis show that seismic isolation significantly reduces the responses of the soil-structure system. However, if the natural frequency of the soil is similar to that of the soil-structure system, the responses of the containment buildings in nuclear power plants rather increases due to interactions in the system.

• 한국전산구조공학회논문집
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• 제33권4호
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• pp.245-253
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• 2020

본 논문은 모노파일 풍력 지지구조물에 대한 공진 안전성 평가에서 여러 말뚝-구조물 상호작용(PSI) 모델을 사용하여 고유진동수를 비교하였다. PSI 재현을 위한 유한요소모델은 기저 스프링 모델, 분산 스프링 모델, 3차원 고체-쉘 모델을 사용하였다. PSI 모델이 고유주파수에 미치는 영향을 분석하기 위해 기저 스프링과 분산 스프링 모델 적용을 위한 강성행렬 산정법과 Winkler 보 모델을 각각 논문에 나타내고 이들 모델로부터 도출된 서로 다른 기하 및 지반조건을 갖는 모노파일의 고유진동수를 조사하였다. 해석결과는 또한 3차원 고체-쉘 모델의 고유진동수와도 비교되었다. 해석결과는 소구경 모노파일이 견고한 지반 및 암반에 관입된 경우 각 해석모델로부터 얻어진 고유진동수의 차이가 거의 없음을 보여준다. 반면 연약 지반에 설치된 대구경 모노파일에 대해 분산스프링 모델은 고유진동수를 과대평가할 수 있다. 따라서 고유진동수 평가 시 구조물 규모와 지반 조건을 고려해 적합한 PSI모델이 적용되어야 한다.

• Journal of Ecology and Environment
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• 제42권3호
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• pp.128-138
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• 2018

Background: This study investigated the variation of soil organic carbon in four land cover types: natural and mixed forest, cultivated land, Eucalyptus plantation and open bush land. The study was conducted in the Birr watershed of the upper Blue Nile ('Abbay') river basin. Methods: The data was subjected to a two-way of ANOVA analysis using the general linear model (GLM) procedures of SAS. Pairwise comparison method was also used to assess the mean difference of the land uses and depth levels depending on soil properties. Total of 148 soil samples were collected from two depth layers: 0-10 and 10-20 cm. Results: The results showed that overall mean soil organic carbon stock was higher under natural and mixed forest land use compared with other land use types and at all depths ($29.62{\pm}1.95Mg\;C\;ha^{-1}$), which was 36.14, 28.36, and 27.63% more than in cultivated land, open bush land, and Eucalyptus plantation, respectively. This could be due to greater inputs of vegetation and reduced decomposition of organic matter. On the other hand, the lowest soil organic carbon stock under cultivated land could be due to reduced inputs of organic matter and frequent tillage which encouraged oxidation of organic matter. Conclusions: Hence, carbon concentrations and stocks under natural and mixed forest and Eucalyptus plantation were higher than other land use types suggesting that two management strategies for improving soil conditions in the watershed: to maintain and preserve the forest in order to maintain carbon storage in the future and to recover abandoned crop land and degraded lands by establishing tree plantations to avoid overharvesting in natural forests.

• 한국환경과학회지
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• 제8권5호
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• pp.587-592
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• 1999

The purpose of this study was to identify the controlling factors to construct tidal flat ecosystems having similar characteristics as natural ones. We transplanted the soil in a constructed tidal flat to a natural one and vice versa. Parameters monitored after these transplantations were silt content, organic matter, bacterial population and oxidation-reduction potential. Moreover, the relationship among silt content, organic matter and bacterial population was investigated by laboratory column experiment. The silt content, organic matter, bacterial population and vertical profile of oxidation-reduction potential in the soil transplanted from the constructed tidal flat to the natural one changed to similar values to those in the natural one. On the contrary, all the parameters for the soil transplanted from the natural tidal flat to the constructed one changed to similar values as those in the constructed one. The silt contents in thses two transplanted solis were in proportion to the organic carbon contents and bacterial population. Similarly, the bacterial population in laboratory column experiment increased with the increase in silt and organic matter contents. It seemed to be important to select a place to enhance accumulative of silt and/or to maintain the silt content by hydrodynamic control of seawater in order to construct a tidal flat having similar characteristics as natural one.

• 한국미생물·생명공학회지
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• 제28권3호
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• pp.129-133
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• 2000

Different actinomycete strains were isolated from natural lime caves of Ondal Chemongok Hwanseon and Yongyeon which are located at Kangwon or chungcheongbook province in Korea and were identified to the genus level. Soil sam-ples were collected at 6 sites inside and 2 sites outside of each natural lime cave, As the result the strains belonging to genus Streptomyces and rare actinomycetes were isolated at the average of 2.1 and 3.4 strains per g soil on inside cave whereas which were isolated at the 6.0 and 1.8 strains per g soil on outside cave. How-ever the generic distribution of Streptomyces and rare actinomycetes isolated from outside cave was quite dif-ferent from that of inside cave. It was shown that rare actinomycetes at natural lime caves is generally highly abundant than Streptomyces.

• 한국유기농업학회지
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• 제20권2호
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• pp.231-241
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• 2012

천일염의 농업적 활용은 관행농업에서 뿐만 아니라 친환경농산물 생산을 위해 농업인들 사이에서 증가하는 추세이다. 그러나 다량의 천일염을 지속적으로 살포할 경우 토양에 염류가 집적될 소지가 크고, 이로 인해 작물의 생육장해가 초래될 수 있다. 따라서 본 연구는 천일염을 토양에 살포하였을 때의 토양 이화학성과 마늘의 무기성분 함량과 수량에 미치는 영향을 조사하고자 수행하였다. 천일염을 살포하는 양이 증가할수록 토양의 전기전도도, 치환성 나트륨, 염소이온, 황산이온은 표토에서 높아졌다. 그러나, 수확기에는 천일염의 성분이 강우에 의해 심토로 용탈되어 작물이 생육하는 근권에서는 전기전도도, 치환성 나트륨, 염소이온, 황산이온은 감소하였고, 염소이온은 다른 성분보다 더욱 빠르게 심토로 용탈되었다. 토양의 나트륨 흡착비, 치환성 나트륨 백분율, 토양 분산율은 천일염이 투입량이 증가할수록 높아지는 경향이었다. 천일염을 토양에 살포하였을 때 마늘의 무기성분 중에 질소, 칼슘, 마그네슘, 미량원소인 철, 망간, 아연 등의 함량은 줄어들었고, 바닷물에 많은 성분인 염소 성분의 흡수는 증가하였으나, 마늘의 수량에는 큰 영향을 미치지 못하였다.

• 한국환경복원기술학회지
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• 제6권3호
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• pp.35-45
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• 2003

This study was performed to suggest growth status data of the large old trees as the natural monuments of Korea. Field investigation of 70 large old trees as the natural monuments of Korea was carried out in Seoul, Inchon, Kyungki, Chungbuk, Chungnam, Chonbuk, Chonnam. The main field of this study is classified into the growth condition, soil state and management situation. The results of this study are below : The age distribution of the large old trees as the natural monuments of Korea is as follows : above l00years in 5.9%, above 200years in 8.9%, above 300 years in 11.8%, above 400 years in 16.2%, above 500 years in 16.2% and above 600years in 41.1%. Location types of the large old trees as the natural monuments of Korea are found in 11 types; the types are hill side(22.9%), historical monument area(15.7%), field(l4.3%) and building area(12.9%), etc. Also, growth type of the trees is individually placed. In the aspect of soil environment, the acidification of soils has been appearing in all surveyed areas, and the soil of Seoul area has much acidum phosphoricum because of excessive fertilizer. Finally, in management situation. major factors inhibiting growth of the large old trees as the natural monuments of Korea are soil covering of protruded root above ground, soil hardening by human, embankments, small area that has been surrounded fence. Continuous monitoring and accumulation of status data are necessary to preserve the large old trees as the natural monuments of Korea.

• 아시안잔디학회지
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• 제7권1호
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• pp.31-34
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• 1993

There is a growing concern in the United Stares over the environmental and human health implications associated with heavy use of water, pesticides, and inorganic ferilizers in maintaining picture perfect golf courses. There is also a growing awareness that a beautiful course is not necessarily a healthy course. The following discussion reviews the interrelationship of turfgrass and the soil that supports it and provides basic information on currently available alternatives to turf management practices that feature intensive application of inorganic fertilizers. water and pesticides. Soil is a dynamic natural environment in which microorganisms play an important role. Soil contains a large mass of microorganisms which produce thousands of enzymes that can catalyze the transformation and degradation of many organic molecules. (In top soil under optimum conditions may contain 10 billion cells per gram of soil.). Turfgrass and the soil which supports it are interdependent. The natural organic cycle as applied to turf and soil begins with healthy vigorous grass plants storing up the sun's energy in green plant tissues as chemical energy. Animals obtain energy by eating plants and when plants and animals die, their wastes are returned to the soil and provide "food" for soil microorganisms. In the next step of the organic cycle soil microorganisms break down complex plant tissues into more basic forms and make the nutrients available to grass roots. Finally, growing plants extract the available nutrients from the soil. By free operation of this organic cycle, natural grasslands have some of the most fertile soils on earths.