Thesis (M.Eng.) - Asian Institute of Technology, 1993

A thesis submittedinpartial fulfillment oftherequirements forthe Degree ofMasterofEngineering.

A one dimensional numerical model is developed to simulate the propagation of a surge front in a rectangular open channel under a subcritical flow condition. The governing equations are one dimensional equations of continuity and momentum for rapidly varied free surface flow. Gharangik (1988) derived these equations based on the Boussinesq theory which takes into consideration the non-hydrostatic pressure distribution. These equations are solved by the third order accurate Warming-Kutler-Lomax (WKL) explicit scheme. The De Saint Venant equations for unsteady free surface flow are also solved by the Maccormack and WKL schemes. The De Saint Venant equations can be obtained from Boussinesq equations by eliminating the non-hydrostatic pressure distribution terms. Several laboratory tests were carried out under subcritical flow ranges for two different test conditions. The test condition I considered the propagation of a surge front in the same direction with the base flow whereas the testcondition II considered thepropagation ofsurge front against thedirection of the base flow. The laboratory data thus obtained were used to verify the numerical model. From the sensitivity analysis, it is found that the effect of Manning's 'n' on the computed results is significant but the dissipation constant 'K' has negligible effect on computed results. In general, computed and measured results are in good agreement. The higher order accurate model using the Boussinesq equations and the Warming-Kuder-Lomax scheme gives slightly better results than the second order accurate model using the De Saint Venant equations and the Maccormack scheme. However, the Boussinesq term is found to have negligible effect on the computed results. The improvement is mainly due to the use ofthe third order finite difference scheme. Therefore, the second order accurate model developed in this study can be recommended for simulating the propagation of a surge front in a rectangular open channel under subcritical flow conditions with reasonable degree of accuracy for all practical purposes.