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Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam.
Thesis (MEng)--Stellenbosch University, 2024.
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Stellenbosch : Stellenbosch University
2024
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| _version_ | 1867613831002324992 |
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| access_status_str | Open Access |
| author | Yates, Ryan Arthur |
| author2 | Bosman, Adèle |
| author_browse | Bosman, Adèle Yates, Ryan Arthur |
| author_facet | Bosman, Adèle Yates, Ryan Arthur |
| author_sort | Yates, Ryan Arthur |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2024. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/130636 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA en_ZA |
| last_indexed | 2026-06-10T12:42:21.587Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2024 |
| publishDateRange | 2024 |
| publishDateSort | 2024 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/130636 Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. Yates, Ryan Arthur Bosman, Adèle Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. Hydraulic structures -- Design and construction Energy dissipation Log splitters (Machines) Dams -- Aeration Thesis (MEng)--Stellenbosch University, 2024. ENGLISH ABSTRACT: Since the 1940’s Roberts splitters have been utilised as an energy dissipation device on high head dams with the aim of limiting plunge pool scouring and therefore, preventing the dam foundations from becoming compromised. Unaerated splitters designed according to the original Roberts (1943) design procedure are limited to a prototype spillway head of 3.0 m, which equates to a unit discharge of approximately 12 m2/s, when assuming an optimised ogee crest design. Although there have been improvements to Roberts’ (1943) design procedure which have allowed for higher spillway heads to be accommodated, current research in this regard is still limited. To date, the inclusion of artificial aeration on Roberts splitters has primarily focused on alleviating cavitation damage to the structure, with limited research on its effect on plunge pool scouring. The current research aims to exploring the effects of introducing artificial aeration of Roberts splitters, using an aeration duct open to the atmosphere. The primary objective is to investigate how this aeration influences the dynamic pressure head at which the jet strikes the plunge pool bottom, and consequently, to understand its effects on the development of plunge pool scour. A 1:20 scale model of an ogee spillway fitted with Roberts splitters was designed and constructed. A total of four hydraulic models were tested, namely a standard ogee spillway without any splitters, an unaerated Roberts splitters model, followed by two aerated Roberts splitters models each having different diameter air vents (20 mm and 26 mm air vents). The standard ogee model was intended as a control model to allow impacting pressures generated by the three splitter models to be compared. The three splitter models allowed for comparison between impacting pressures as a result of varying degrees of jet aeration to a maximum tested prototype unit discharge of 45 m2/s. The inclusion of unaerated Roberts splitters was determined to significantly decrease the mean dynamic pressure head at which a plunging jet impacts the plunge pool bottom, a decrease of approximately 79% was observed between the standard ogee and the unaerated Roberts splitters at a prototype unit discharge of 45 m2/s, with the minimum and maximum dynamic pressure head decreasing by approximately 118% and 35% respectively. The inclusion of air vents on the Roberts splitters was found to further decrease the mean dynamic pressure head generated by the plunging jet by approximately 16.3% compared to the unaerated splitters. It was found that this decrease was more predominant at locations closer to the dam spillway while the increased degree of jet aeration was found to decrease further away from the spillway. After completion of the hydraulic model testing, it was found that in most cases the 26 mm aerated Roberts splitters resulted in the most favourable dynamic pressure heads in the area closest to the dam foundations with the unaerated Roberts splitters having decreased pressures further downstream. Even though this phenomenon cannot be conclusively explained, the addition of artificial aeration via Roberts splitters on high head dams was shown to effectively reduce dynamic pressure heads within the impact zone and therefore reduce plunge pool scour and thus reduce the risk of undermining the foundations of a concrete gravity or arch dam. Masters AFRIKAANSE OPSOMMING: Die Roberts-verdeler word reeds sedert die 1940’s as ʼn energiedissipasie-toestel op hoëvaldammeaangewend, met die doel om dompelpoelspoeling te beperk en dus te voorkom dat die damfondamente gekompromitteer word. Onbelugte verdelers wat volgens die oorspronklike ontwerpproses vanRoberts (1943) ontwerp word, word beperk tot ʼn prototipe-uitloophoogte van3.0m, wat gelykstaande is aan ʼn eenheidsontlading van ongeveer12m2/s. Hoewel daar verbeterings aanRoberts (1943) se ontwerpprosedure was wat hoër uitloophoogtes moontlik gemaak het, is die huidige navorsing in hierdie verband steeds beperk. Tot op hede het die insluiting van kunsmatige belugting by Roberts-verdelers hoofsaaklik op die verligting van kavitasieskade aan die struktuur gefokus, met beperkte navorsing oor die effek daarvan op dompelpoelspoeling. Die huidige navorsing verken die effek van die invoeging van kunsmatige belugting in Roberts-verdelers, deur die gebruik van ʼn belugtingskanaal wat oop is vir die atmosfeer. Die primêre doelwit is om te ondersoek hoe hierdie belugting die dinamiese drukhoogte waarteen die straal die bodem van die dompelpoel tref, beïnvloed en gevolglik om die effek daarvan op die ontwikkeling van dompelpoelspoeling te verstaan. ʼn 1:20 skaalmodel van ʼn oorloop-uitloop met Roberts-verdelers is ontwerp en gebou. In totaal is vier hidrouliese modelle getoets, naamlik ʼn standaard oorloop-uitloop sonder enige verdelers en ʼn onbelugte Roberts-verdelersmodel, gevolg deur twee belugte Roberts-verdelersmodelle, elk met ontlugters van verskillende diameters(20 mm en26 mm). Die standaard oorloopmodel is as die kontrolemodelgebruik, om die impakdruk wat deur die drie verdelermodelle opgewek word, te vergelyk. Die drie verdelermodelle het die vergelyking van impakdruk as gevolg van verskillende grade van straalbelugting tot en met ʼn maksimum getoetsde prototipe-eenheidsontlading van45m2/smoontlik gemaak. Die invoeging van onbelugte Roberts-verdelers het die gemiddelde dinamiese drukhoogte waarteen ʼn vallende straal die dompelpoelbodem impakteer beduidende verlaag –ʼn verlaging van ongeveer79% is waargeneem tussen die standaard oorloop en die onbelugte Roberts-verdelers teen ʼn prototipe-eenheidsontlading van45m2/s, met dieminimum en maksimum dinamiese drukhoogte wat met ongeveer118% en35%,onderskeidelik, verlaag is. Die invoeging van ontlugters in die Roberts-verdelers het die gemiddelde dinamiese drukhoogte wat deur die vallende straal opgewek word, met nog ongeveer16.3% verlaag vergeleke met die onbelugte verdelers. Daar is bevind dat hierdie verlaging selfs meer deurslaggewend was by liggings nader aan die dam se uitloop, terwyl die verhoogde graad van straalbelugting verder van die uitloop af afneem. Náafhandeling van die toetsing van die hidrouliese modelle, is bevind dat diebelugte Roberts-verdelers van 26 mm die gunstigste dinamiese drukhoogtes in die area die naaste aan die damfondament gelewer het, met die onbelugte Roberts-verdelers wat verder stroomaf verlaagde druk gelewer het. Verdere navorsing is nodig om enige gevolgtrekking uit die voorkoms van hierdie verskynsel te maak. 2024-02-05T20:22:16Z 2024-04-27T00:49:30Z 2024-02-05T20:22:16Z 2024-04-27T00:49:30Z 2024-02 Thesis https://scholar.sun.ac.za/handle/10019.1/130636 en_ZA en_ZA Stellenbosch University xxvii, 271 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Hydraulic structures -- Design and construction Energy dissipation Log splitters (Machines) Dams -- Aeration Yates, Ryan Arthur Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. |
| title | Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. |
| title_full | Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. |
| title_fullStr | Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. |
| title_full_unstemmed | Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. |
| title_short | Effect of aeration via Roberts splitters on plunge pool scour development downstream of a high head dam. |
| title_sort | effect of aeration via roberts splitters on plunge pool scour development downstream of a high head dam |
| topic | Hydraulic structures -- Design and construction Energy dissipation Log splitters (Machines) Dams -- Aeration |
| url | https://scholar.sun.ac.za/handle/10019.1/130636 |
| work_keys_str_mv | AT yatesryanarthur effectofaerationviarobertssplittersonplungepoolscourdevelopmentdownstreamofahighheaddam |