Theoretical Consideration on Errors of Gibson Method in Compound Conduits

At the present time the Gibson method is commonly used at hydraulic power plants for flow measuring, but the results obtaind by this method have not been compared with those of quantity or weight measurements because of the difficulties involved in the field test. Therefore, the accuracy of the Gibson method need to be further checked. In this paper, the theoretical errors of Gibson method for the following cases are considered from the elastic water column theory. Namely, (1) When the Gibson method is used at practical hydraulic power plants, and if reservoir head over the intake changes with the guide vanes closure, the results of Gibson method will be different from the case of constant reservoir head. In this article, the effects of variation of reservoir head on the errors of Gibson method are checked from the theoretical calculation. (2) Penstocks at practical hydraulic power stations have occasionally stepwise changes in diameter or thickness, when Gibson method is used in th