| dc.description.abstract | This dissertation presents a study of the main challenges and consequences of
imposing rapid hydropeaking production patterns on unlined hydropower tunnels.
It contains a thesis part and four research papers. The main contributions
are two-fold: physical effects observed, and predictions or monitoring methods
developed.
Close collaboration with hydropower companies and inspection of over 100 km
of hydropower tunnels in use has revealed that mechanical wear caused by
sediment transportation in Norwegian hydropower plants has increased due to
hydropeaking. The operational costs related to such damages are considerable.
It was found that when compared to non-hydropeaked systems, hydropeaked
systems experience an increase in the frequency and volume of rock falls.
To facilitate analysis of the hydrodynamics arising in hydropower tunnel system
several useful prediction and monitoring methods have been tested. A novel
scanning technique that describes the complex surface geometry of drill and
blast tunnels is introduced. The technique provides unique opportunities to reduce
the uncertainty in hydraulic calculations, and an improved method to estimate
the roughness of rock blasted tunnels based on scan data is proposed.
The surface meshes generated by scanning of the prototype were used to perform
3D CFD simulations. The numerical investigations demonstrate that combining
these two technologies yields a better understanding of the fluid-structure
interaction, and provides the possibility for spatially-distributed estimates of the
velocities, pressure, level of turbulence, shear forces and the volume fraction of
water/air occurring in a critical component of a HPT system. 3D simulations not
only contribute to reducing the uncertainty of 1D simulation, they can also serve
to calibrate discharge measurements. | nb_NO |
