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Energiförluster i vattenkraftstunnlar och älvsträckor: Hur påverkas Manningtalet när skrovlighetens geometri är stor i förhållande till tvärsektionens geometri?
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy system.
2018 (Swedish)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
Sustainable development
The essay/thesis is partially on sustainable development according to the University's criteria
Abstract [en]

When water travels along a channel is the bottom which the water is in direct contact with, defined by a coefficient named

Manning’s coefficient of friction. This coefficient explains the roughness of the channel bed. A rough surface equals a low Manning’s coefficient. The purpose of this thesis is to study how Manning’s coefficient differs when different waterflows and depths is obtained. The Manning equation is depend-ent on using a constant Manning’s coefficient based on experience and tables. The experience in the line of business knows that the coefficient holds a different value in channels with similar bathymetry and different flow conditions, and the thesis will cover these questions.

At Vattenfall Research & Development in Älvkarleby, a flume made for fluid me-chanic experiments has been built, which is perfectly suitable for the experiments for this thesis. The flume has a roughness that has been programmed mathematically with a purpose of looking like a real channel bed or a blasted rock-tunnel. This is where all the measurements were made.

The measurements were made in totally 14 cross-sections with a few different flows and depths. The depth was controlled by a hatchway downstream the flume and the flow were controlled by the pumps. Depending on which setting the hatchway ob-tained measurements between 1.6 l/s to 280 l/s were made. The different settings that were used for the hatch was 100 %, 85 %, 75 %, 60 % and 30 % open hatch. The most obvious results appeared when the hatch was 100 % open, since the differ-ence in depth between each cross-section was large and the faults in the equipment

weren’t that important. 30 % open hatch generated such calm flow and a deep depth, so the errors were too big to include in the report. These different flow conditions were used to gain a big variation and accuracy, with the purpose of getting as good result as possible.

The measurements show that for every hatch-setting, the Manning coefficient gets lower when a lower depth and flow are held. If the results are plotted from all the hatch-settings, especially 100 % open in a graph with the Manning coefficient as a function of the flow, the results follow an obvious shape with a trend where the Man-ning coefficient reduces with lower flows. The same thing with the depth. Shallower depth equals lower Manning coefficient. This is because of the roughness elements that has a bigger part of the entire cross-sectional area, so that a bigger part of the cross-sectional area is affected by phenomenon caused by the roughness elements.

Key words: Manning’s coefficient,

streaming losses, energy losses, Vattenfall

2018. , p. 27
Keywords [sv]
Manningtal, Strömningsförluster, Energiförluster, Vattenfall
National Category
Water Engineering
Identifiers
OAI: oai:DiVA.org:hig-27333DiVA, id: diva2:1223169
Vattenfall R&D
Energy systems
Educational program
Energy systems – bachelor’s programme (in eng)
Examiners
Available from: 2018-06-25 Created: 2018-06-25 Last updated: 2018-06-25Bibliographically approved

Open Access in DiVA

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Cite
Citation style
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