Design and feasibility study for the application of an inflatable rubber structure in a navigation lock

Design and feasibility study for the application of an inflatable rubber structure in a navigation lock

Woudstra, S.D.

Jonkman, S.N. (mentor)
Molenaar, W.F. (mentor)
Pasterkamp, S. (mentor)
Adriaansens, D.H.M. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2014-12-02

Introduction In navigation locks levelling is executed under free flow. The net flow from the upper section into the lower section of the waterway is considered as a water loss. An innovative water saving concept is an IRS Lock. IRS stands for inflatable rubber structure. The concept consists of an air filled IRS applied in a lock chamber. In this way part of the water loss is substituted by an ‘air loss’. It was not clear whether or not the IRS Lock concept is a feasible water saving solution. IRSs are formed by a rubber sheet connected to a foundation. The sheet is so flexible that it is considered to have no bending stiffness. The shape of the IRS results from the loads acting on the sheet. During the use of an IRS, four phases are distinguished; the inflation, the inflated, the deflation and the deflated phase. In each phase, the internal pressure is different and thus a different shape results. In case of the IRS Lock, the IRS is completely submerged and the hydrostatic load is the main load. Also loads occur by flows from lock operations and vessel movements. The different phases of use, shapes and the new application area make the design of the IRS Lock a complex process. Design A first design of the IRS Lock has been developed. The Eastern Lock, located in the Terneuzen Lock complex, was used as an environment for the design. In the design the sheet of the IRS is connected to the lock chamber walls. In navigation locks a minimum keel clearance is required between the vessel and the lock chamber bottom. The IRS is located above the bottom of the lock chamber. The water level in the lock chamber, and therefore also the available depth and keel clearance, varies by the tide. The first design of the IRS is optimized in such a way that the design results in a large water saving while maintaining the minimum required keel clearance. The designed IRS has a crest height of 2,5 meter and still allows the draught of the design vessel. In total three IRSs are applied in the length of the Eastern Lock. Additionally, several elements of the IRS Lock have been elaborated. Among others the strength of the rubber sheet has been verified. Functional performance The functional performance of the first design of the IRS Lock has been assessed. Per Lock cycle the designed IRSs will save 9056 m3 of water. Because of the tidal fluctuations in the water levels, and the limitations in available depth and keel clearance, the IRS can only be used for 6 of the 18 lock cycles per tidal period. The total amount of water that is saved per tidal period is on average 25% of the total water loss. As part of a RAMS-analysis, a Failure Mode Effect Analysis has been performed. Measures have been taken to keep the risk of failure at an acceptable level. From the functional performance it follows that the designed IRS Lock is technically feasible. An alternative for the IRS Lock is a pumping station that pumps the lost water back into the upper section of the waterway. It has been found that in all possible situations the IRS Lock will use more energy per unit of saved volume than a pumping station. Also the Life Cycle Costs are higher. This makes the IRS Lock economically less attractive.

inflatable structure
navigation lock
water saving
functional performance

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Student theses

master thesis

(c) 2014 Woudstra, S.D.