{"created":"2024-06-18T08:48:21.334996+00:00","id":2007758,"links":{},"metadata":{"_buckets":{"deposit":"872be5bb-e005-43cf-a891-2cc8f12cbac3"},"_deposit":{"created_by":10,"id":"2007758","owners":[10],"pid":{"revision_id":0,"type":"depid","value":"2007758"},"status":"published"},"_oai":{"id":"oai:fra.repo.nii.ac.jp:02007758","sets":["12:14:1716955731445"]},"author_link":["2019"],"control_number":"2007758","item_10002_biblio_info_7":{"attribute_name":"書誌情報","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"1985-03","bibliographicIssueDateType":"Issued"},"bibliographicNumberOfPages":"61","bibliographicPageEnd":"87","bibliographicPageStart":"27","bibliographicVolumeNumber":"6","bibliographic_titles":[{"bibliographic_title":"水産工学研究所研究報告","bibliographic_titleLang":"ja"},{"bibliographic_title":"Bulletin of National Research Institute of Fisheries Engineering","bibliographic_titleLang":"en"}]}]},"item_10002_description_5":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"1. In recent years, as the problems related to coastal development, environmental conservation of water area and water resources development have become more serious and more complicated, it has become more important to clarify the hydraulic characteristics of the various kinds of density currents. In relation to reproduction of coastal fishery resources, formation of regular course for fish and coastal fishing ground reclamation, it is one of the most important problems in aquaculture engineering to investigate the characteristics of the head of bottom-layer density currents. This paper deals with hydraulic characteristics of the head of bottom layer flow of Densimetric Exchange Flow as far as that diffusion or mixing would be neglected. 2. Summarizing the previous studies on the head of density currents, two problems are noted as follows: (1) There exist some experimental results about shapes and velocities of the head. But, there is a wide difference among the results and a clear explanation has not yet been made on this point. (2) Although there were a few experimental results of internal structure of the head, it is very difficult to express quantitatively. Numerical simulation technique in the past was valid as far as relative density difference is larger than 0.05, but not valid in coastal water area for our purpose where the relative density difference is less than 0.03, because numerical catastrophe occurs in the surface region. 3. Considering the above-mentioned points, this study had the following objectives: (1) As to the shape and the velocity of the head, we should investigate the difference among the results in previous experiments, considering the time variation within a experiment or conditions of experiment. (2) As to the quantitative study of internal structure of the head, we should develop a two-dimensional numerical method modifying or extending the Marker-and-Cell method. (3) As to the verification of the numerical method, we should sufficiently compare the results of experiment and those of numerical simulation. 4. About the numerical method, free surface condition was applied more strictly to stabilize the calculation or to avoid the numerical catastrophe. At that time, variable about water level was introduced to calculate surface inclination easily. The coefficient of viscosity was treated as a constant in whole calculational area in previous studies, but in this method the modelling of sub-grid scale eddy viscosity that is called Smagorinsky-Deardorff model has been introduced. 5. For experiment, the flume, 3 m in length, 20 cm in width and 50 cm in height was used. There was no groove for a gate and the gate was guided by four rubber sash rolers only. 8 mm cinecamera has been used to record flow configulations. Time variation of the shapes and the velocity of the head was analyzed on the film. 6. The results of this study by both experiment and numerical simulation are as follows: (1) The head is immediately created after the flow started and the two-dimensional shape of the head has soon become almost constant. The part behind the head is quasi-steady. (2) It was confirmed that time averaged shape of the head which was non-dimensionalized by the thickness of the head is similar. (3) The velocity of the head U₁ varies periodically to some extent and declines with time. The period of that variation is different with the length of the storage and the initial depth of the storage, but is not so different with the relative density difference. (4) As mentioned above, the velocity of the head varies with time, so the mean velocity in a experiment must be calculated carefully. This point was not marked in the past and the large variance of the results in previous experiments might have occurred for this reason. (5) In this study, the author got the data with small variance about the mean velocity of the head. In addition, the conditions of experiment were altered systematically, and therefore it was possible to make clear the mutual relations between the non-dimentional mean velocity K̅ and the densimetric Reynolds number Re. (6) The head advances with internal vortex which rolls up the particles near the extreme point of the head. This phenomenon was observed in both experiment and numerical simulation. It has suggested the phenomenon of sediment rolled up that was observed in the field. Intermittent releasing of vortex was observed in experiments except the case with small depth. This phenomenon might be caused by three-dimensional structure of the head and was not observed in two-dimensional numerical simulation. (7) In numerical simulation, the value of vertical velocity in the head near the extreme point accounted for 30 to 70 percent that of horizontal velocity. Maximum horizontal velocity occurs 0.2 times inner side of the thickness of the head. (8) With starting of the flow, minute variation of water level occurs at both fresh water side and salt water side. At fresh water side water level rises and at salt water side water level drops and these propagate to both end of the channel. In a short time reflection occurs and propagation and reflection alternately occur. Main cause of these variation of water level might be propagation and reflection of surface wave, but the effect of density difference should also be considered. This phenomenon was made clear in detail for the first time in this study. The relation between the variation of water level and the velocity of the head was not clear quantitatively, but the strong correlation was observed qualitatively. 7. As have already been seen, the study was carried out on the hydraulic characteristics of the head of bottom-layer density currents both in experiment and in numerical simulation. In this study, we obtained good results on the quantitative study of density currents. As the results of numerical simulation were in very good agreement with those of experiment, the validity of numerical technique modified and developed in this study was confirmed and the foundation was made for this technique to be applied to the coastal area. The elucidation of the characteristics of the head of density currents is very important for the elucidation of the environment of aquatic life. For example, the head of density currents is observed as a saline wedge against river, a fresh water or blackish water front for the sea and an ascending front of internal wave of cold mass to the continental shelf. And these fronts are concerned in transportation and sedimentation of plankton or suspended particles, transportation and accumulation of spawns, larvae and juveniles and formation of regular course for fishes. Therefore, it is useful in the reclamation of nursery grounds and fishing grounds to understand the characteristics of the head. As for the detail, one will have to wait for future studies, and the results of this study may provide some important basis for them.","subitem_description_language":"en","subitem_description_type":"Abstract"}]},"item_10002_publisher_8":{"attribute_name":"出版者","attribute_value_mlt":[{"subitem_publisher":"水産工学研究所","subitem_publisher_language":"ja"},{"subitem_publisher":"National Research Institute of Fisheries Engineering","subitem_publisher_language":"en"}]},"item_10002_relation_16":{"attribute_name":"情報源","attribute_value_mlt":[{"subitem_relation_type_id":{"subitem_relation_type_id_text":"nrife_k_6_27","subitem_relation_type_select":"Local"}}]},"item_10002_relation_17":{"attribute_name":"関連サイト","attribute_value_mlt":[{"subitem_relation_name":[{"subitem_relation_name_language":"ja","subitem_relation_name_text":"日本農学文献記事索引(agriknowledge)"}],"subitem_relation_type_id":{"subitem_relation_type_id_text":"https://agriknowledge.affrc.go.jp/RN/2010320598","subitem_relation_type_select":"URI"}}]},"item_10002_source_id_11":{"attribute_name":"書誌レコードID","attribute_value_mlt":[{"subitem_source_identifier":"AN00332937","subitem_source_identifier_type":"NCID"}]},"item_10002_source_id_9":{"attribute_name":"ISSN","attribute_value_mlt":[{"subitem_source_identifier":"0388-9718","subitem_source_identifier_type":"PISSN"}]},"item_access_right":{"attribute_name":"アクセス権","attribute_value_mlt":[{"subitem_access_right":"metadata only access","subitem_access_right_uri":"http://purl.org/coar/access_right/c_14cb"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Takeuchi, Tomoyuki","creatorNameLang":"en"},{"creatorName":"武内, 智行","creatorNameLang":"ja"},{"creatorName":"タケウチ, トモユキ","creatorNameLang":"ja-Kana"}],"familyNames":[{"familyName":"Takeuchi","familyNameLang":"en"},{"familyName":"武内","familyNameLang":"ja"},{"familyName":"タケウチ","familyNameLang":"ja-Kana"}],"givenNames":[{"givenName":"Tomoyuki","givenNameLang":"en"},{"givenName":"智行","givenNameLang":"ja"},{"givenName":"トモユキ","givenNameLang":"ja-Kana"}],"nameIdentifiers":[{"nameIdentifier":"2019","nameIdentifierScheme":"WEKO"},{"nameIdentifier":"80116946","nameIdentifierScheme":"e-Rad_Researcher","nameIdentifierURI":"https://kaken.nii.ac.jp/ja/search/?qm=80116946"}]}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"jpn"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"departmental bulletin paper","resourceuri":"http://purl.org/coar/resource_type/c_6501"}]},"item_title":"底層密度流先端部の水理特性に関する研究","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"底層密度流先端部の水理特性に関する研究","subitem_title_language":"ja"},{"subitem_title":"A Study on the Hydraulic Characteristics of the Head of Bottom-Layer Density Currents","subitem_title_language":"en"}]},"item_type_id":"10002","owner":"10","path":["1716955731445"],"pubdate":{"attribute_name":"PubDate","attribute_value":"2024-06-18"},"publish_date":"2024-06-18","publish_status":"0","recid":"2007758","relation_version_is_last":true,"title":["底層密度流先端部の水理特性に関する研究"],"weko_creator_id":"10","weko_shared_id":-1},"updated":"2026-03-06T07:50:49.753747+00:00"}