• Title/Summary/Keyword: Seabed Material

Search Result 29, Processing Time 0.024 seconds

The distribution and composition of seabed litter in the exclusive economic zone of the West Sea of South Korea (우리나라 서해 근해 해저 쓰레기 분포 및 조성)

  • KIM, Jung Nyun;KANG, Myounghee;JO, Hyun-Su
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.53 no.4
    • /
    • pp.437-445
    • /
    • 2017
  • Distribution and composition of the seabed litters in the exclusive economic zone of the West Sea of South Korea including 18 sea-blocks were investigated using a bottom trawl gear of the R/V Tamgtu 20 (National Institute of Fisheries Science) from 24th April 2011 to 4th May 2012. Each trawl shot was conducted for an hour in each sea-block and the total trawl shots was 18. As a result, 325.6 kg of seabed litter in total has been collected. The quantity of the seabed litter was highest at No. 202 of the sea-block, close to the Heuksan-Do. The highest occupied sea material was plastic (83.1% of entire seabed litters), the second highest material was metal combined with plastic (10.6%), and glass (2.9%), metals (2.3%), vinyl (0.6%), cloth (0.4%) and wood (0.2%) in order. The origin of seabed litters was from fishing gear (89.0% of all seabed litters). Therefore, it could be assumed that most seabed litters were derived from the fishing activity for example fishing nets and ropes.

A preliminary study on seabed classification using a scientific echosounder

  • FAJARYANTI, Rina;KANG, Myounghee
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.55 no.1
    • /
    • pp.39-49
    • /
    • 2019
  • Acoustics are increasingly regarded as a remote-sensing tool that provides the basis for classifying and mapping ocean resources including seabed classification. It has long been understood that details about the character of the seabed (roughness, sediment type, grain-size distribution, porosity, and material density) are embedded in the acoustical echoes from the seabed. This study developed a sophisticated yet easy-to-use technique to discriminate seabed characteristics using a split beam echosounder. Acoustic survey was conducted in Tongyeong waters, South Korea in June 2018, and the verification of acoustic seabed classification was made by the Van Veen grab sampler. The acoustic scattering signals extracted the seabed hardness and roughness components as well as various seabed features. The seabed features were selected using the principal component analysis, and the seabed classification was performed by the K-means clustering. As a result, three seabed types such as sand, mud, and shell were discriminated. This preliminary study presented feasible application of a sounder to classify the seabed substrates. It can be further developed for characterizing marine habitats on a variety of spatial scales and studying the ecological characteristic of fishes near the habitats.

Method of Correcting Hyperspectral Image for Seabed Material Analysis of Coastal Area (연안 해저 재질 분석을 위한 초분광영상의 보정 방법)

  • SHIN, Myung-Sik;SHIN, Jung-Il;KIM, Ik-Jae;SUH, Yong-Cheol
    • Journal of the Korean Association of Geographic Information Studies
    • /
    • v.19 no.2
    • /
    • pp.107-116
    • /
    • 2016
  • Airborne or spaceborne remote sensing can increase the efficiency of seabed material surveys compared with field surveying using a vessel. For the same seabed material, the optical remote sensing image shows variation in the reflectance depending on the water depth, which is due to the absorption and scattering by the water column. This study suggests a correction procedure to use the hyperspectral image for seabed material analysis. The study is conducted in the coastal area from Sacheonjin Port to Gyungpo Beach in Gangwon-do. The hyperspectral image is acquired using the CASI-1500 sensor. The diffuse attenuation coefficient is estimated for each band through regression models between the water reflectance and depth. Then, the coefficient is applied to each band of the image. As a result, the completely corrected image can be interpreted for a deeper area, although the interpretable area is very shallow without water column correction. Additionally, the water column corrected image shows decreased variation of reflectance with various water depths.

An Experimental Study on Properties of Seabed Unconsolidated Sediment for Wind Power System Construction (해상풍력발전단지 건설 시 해양미고결지반 물성 파악을 위한 실험 연구)

  • Yoo, Hyun-Jong;Lim, Jong-Se;Shin, Sung-Ryul;Jang, Won-Yil;Yoon, Ji-Ho
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.32 no.2
    • /
    • pp.365-373
    • /
    • 2008
  • When the wind power system is planned to construct, it is important to understand the physical, chemical and mechanical properties of sediment. Especially, If it is the seabed unconsolidated sediment, we need to experiment on sediment through seabed unconsolidated sediment test and sediment survey. Because the sediment's properties are different as its formation, accumulation and load, unconsolidated sediment is difficult to be expected to its behavior. So we can estimate suitability for mechanical material and decrease the uncertainty through seabed unconsolidated sediment test. Seabed unconsolidated sediment test can be experimented in laboratory or in-situ as purpose, in-situ condition, economic problem. In this study, we sampled the seabed unconsolidated sediment at offshore around Korea Maritime University and measured properties of sediment through the laboratory test, showed the effect on physical properties of seabed unconsolidated sediment when the wind power system is planned to construction.

A Case Study of Sediment Transport on Trenched Backfill Granular and Cohesive Material due to Wave and Current

  • Choi, Byoung-Yeol;Lee, Sang-Gil;Kim, Jin-Kwang;Oh, Jin-Soo
    • Journal of Advanced Research in Ocean Engineering
    • /
    • v.2 no.2
    • /
    • pp.86-98
    • /
    • 2016
  • In this study, after the installation of a subsea pipeline, backfilling was performed in the trenched area. During these operations, a stability problem in the subsea pipeline occurred. The pipeline was directly impacted by environmental loading such as waves and currents that were caused by backfill material when scouring or sediment transport and siltation was carried out. Therefore, this study reviewed whether trenching was necessary, and conducted research into an indigenous seabed property that contains granular soil. A study of cohesive soil was also conducted in order to cross-correlate after calculating the values of the critical Shields parameter relevant to elements of the external environment such as waves and current, and the shear Shields parameter that depends on the actual shearing stress. In case of 1), sedimentation or erosion does not occur. In the case of 2), partial sedimentation or erosion occurs. If the case is 3), full sedimentation or erosion occurs. Therefore, in the cases of 1) or 2), problems in structural subsea pipeline stability will not occur even if partial sedimentation or erosion occurs. This should be reflected particularly in cases with granular and cohesive soil when a reduction in shear strength occurs by cyclic currents and waves. In addition, since backfilling material does not affect the original seabed shear strength, a set-up factor should be considered to use a reduced of the shear strength in the original seabed.

A Case Study of Sediment Transport on the Seabed due to Wave and Current Velocities

  • Choi, Byoung-Yeol;Lee, Sang-Gil;Kim, Jin-Kwang;Oh, Jin-Soo
    • Journal of Advanced Research in Ocean Engineering
    • /
    • v.2 no.3
    • /
    • pp.99-111
    • /
    • 2016
  • Seabed affected by scouring, sedimentation, and siltation occurrences often cause exposure, which induces risks to existing structures or crude oil or gas pipeline buried subsea. In order to prevent possible risks, more economical structure installation methodology is proposed in this study by predicting and managing the risk. Also, the seabed does not only consist of sandy material, but clayey soil is also widespread, and the effect of undrained shear strength should be considered, and by cyclic environmental load, pore water pressure will occur in the seabed, which reduces shear strength and allows particles to move easily. Based on previous research regarding sedimentation or erosion, the average value of external environmental loads should be applied; for scouring, a 100-year period of environmental conditions should be applied. Also, sedimentation and erosion are mainly categorized by the bed load and suspended load; also, they are calculated as the sum of bed load and suspended load, which can be obtained from the movement of particles caused by sedimentation or erosion.

Seismic Influence on Subsea Pipeline Stresses

  • Choi, Byoung-Yeol;Lee, Sang-Gil;Kim, Jin-Kwang;Oh, Jin-Soo
    • Journal of Advanced Research in Ocean Engineering
    • /
    • v.3 no.1
    • /
    • pp.1-14
    • /
    • 2017
  • The safety analysis of an earthquake is carried out during the operation of a subsea pipeline and an onshore pipeline. Several cases are proposed for consideration. In the case of a buried pipeline, permanent ground deformation by the earthquake and an increase of internal pressure by the acceleration of the earthquake should be considered. In the case of a subsea pipeline, a bending moment is caused by liquefaction of the backfill material on a trenched seabed, etc., which results in a high bending moment of the buried pipeline. The bending moment causes the collapse of the subsea pipeline or a leak of crude oil or gas, which results in economic loss due to enormous environmental contamination and social economic loss owing to operation functional failure. Thus, in order to prevent economic loss and operation loss, structurally sensitive design with regard to seismic characteristics must be performed in the buried pipeline in advance, and the negative impact on the buried pipeline must be minimized by conducting a thorough analysis on the seabed and backfilling material selection. Moreover, it is proposed to consider the selection of material properties for the buried pipeline. A more economical review is also required for detailed study.

Seabed Classification Using the K-L (Karhunen-Lo$\grave{e}$ve) Transform of Chirp Acoustic Profiling Data: An Effective Approach to Geoacoustic Modeling (광역주파수 음향반사자료의 K-L 변환을 이용한 해저면 분류: 지질음향 모델링을 위한 유용한 방법)

  • Chang, Jae-Kyeong;Kim, Han-Joon;Jou, Hyeong-Tae;Suk, Bong-Chool;Park, Gun-Tae;Yoo, Hai-Soo;Yang, Sung-Jin
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
    • /
    • v.3 no.3
    • /
    • pp.158-164
    • /
    • 1998
  • We introduce a statistical scheme to classify seabed from acoustic profiling data acquired using Chirp sonar system. The classification is based on grouping of signal traces by similarity index, which is computed using the K-L (Karhunen-Lo$\grave{e}$ve) transform of the Chirp profiling data. The similarity index represents the degree of coherence of bottom-reflected signals in consecutive traces, hence indicating the acoustic roughness of the seabed. The results of this study show that similarity index is a function of homogeneity, grain size of sediments and bottom hardness. The similarity index ranges from 0 to 1 for various types of seabed material. It increases in accordance with the homogeneity and softness of bottom sediments, whereas it is inversely proportional to the grain size of sediments. As a real data example, we classified the seabed off Cheju Island, Korea based on the similarity index and compared the result with side-scan sonar data and sediment samples. The comparison shows that the classification of seabed by the similarity index is in good agreement with the real sedimentary facies and can delineate acoustic response of the seabed in more detail. Therefore, this study presents an effective method for geoacoustic modeling to classify the seafloor directly from acoustic data.

  • PDF

Deep-sea floor exploration in the East Sea using ROV HEMIRE (무인잠수정 해미래 활용 동해 저서환경 심해탐사)

  • Min, Won-Gi;Kim, Jonguk;Kim, Woong-Seo;Kim, Dong-Sung;Lee, Pan-Mook;Kang, Jung-Hoon
    • Journal of the Korea Academia-Industrial cooperation Society
    • /
    • v.17 no.4
    • /
    • pp.222-230
    • /
    • 2016
  • HEMIRE is a 6,000-meter-class remotely operated vehicle (ROV) that has been developed for observation and sampling of objects of interest on the deep seabed. We first carried out deep-seabed exploration around the slopes of the Hupo Bank and the Ulleung Basin in the East Sea in June 2015. Over two weeks, a total of 10 dives were made from a support ship, the R/V Onnuri, at eight stations with water depth ranging between 194 and 2,080 m. The dive times ranged from 1 to 6 hours, depending on the operating conditions. We obtained the following results: 1) video images of the deep seafloor; 2) red snow crab density data (a major fishery resource) and inventories of deep-sea fauna, including an unrecorded organism; 3) specific topographies such as canyons slopes; 4) an undisturbed sediment core obtained using a push corer; and 5) observations of the seabed surface covered with discarded anthropogenic waste material.

Analysis of offshore pipeline laid on 3D seabed configuration by Abaqus

  • Moghaddam, Ali Shaghaghi;Mohammadnia, Saeid;Sagharichiha, Mohammad
    • Ocean Systems Engineering
    • /
    • v.5 no.1
    • /
    • pp.31-40
    • /
    • 2015
  • Three dimensional (3D) non-linear finite element analysis of offshore pipeline is investigated in this work with the help of general purpose software Abaqus. The general algorithm for the finite element approach is introduced. The 3D seabed mesh, limited to a corridor along the pipeline, is extracted from survey data via Fledermous software. Moreover soil bearing capacity and coefficient of frictions, obtained from the field survey report, and are introduced into the finite element model through the interaction module. For a case of study, a 32inch pipeline with API 5L X65 material grade subjected to high pressure and high temperature loading is investigated in more details.