Andreas Schlenkhoff

Drag coefficients of boulders on a block ramp due to interaction processes

Block ramps are a common natural solution for bypassing large steps in riverbeds. The energy dissipation on these ramps was dealt with to develop formulas describing the hydraulic processes. Currently there are no detailed investigations available analysing the resulting forces for boulders on the ramp, although knowledge of these forces is necessary to guarantee an accurate and appropriate design. An investigation programme using a physical model was therefore conducted to describe the effect of boulder interaction processes with respect to forces and drag coefficients. The variable drag coefficients received a special focus because these influence the determination of mean water levels, mean velocities and forces on a single boulder. The physical model allows variation of both discharges and boulder arrangements. As a measurement technique, ultrasonic sensors and load cells were used to determine water levels and drag forces directly. New formulas for Reynolds number-dependent drag coefficients are developed.

Data-driven stochastic modeling for multi-purpose reservoir simulation

This paper presents an integration of data-driven modeling and stochastic models for simulation of reservoir operation. The simulation model developed in this study was applied to the Ruhr river reservoirs system in Germany. An adaptive neuro-fuzzy inference system, Thomas–Fiering model and hidden Markov model were integrated in a simulation model. The set of model input included the time of the year, reservoir storage, inflow and Standardized Precipitation Index; and the target output was the reservoir release. Predicted and observed release values were evaluated using several common evaluation criteria. Results of model performance showed that the proposed model is capable of simulating reservoir operation and provides reliable reservoir release prediction. Results showed also that the proposed approach could be a good tool at the real-time operation stage to quickly check operational alternatives due to emergency events or planning and real-time incongruence.

Artificial stationary breaking surf waves in a physical and numerical model

Surfing is one of the most popular water sports. A number of regional coastal hotspots have naturally breaking surf waves, but wave heights and breaking processes depend on various boundary conditions like seabed geometry, beach formation and swell direction. Since the optimum combination of these conditions is rare in time and place, the formation of surfable waves cannot be guaranteed. In addition, the sports popularity is currently rising even in inland regions, and with it the interest in generating artificial surf waves in rivers or technical constructions to provide surfable waves at any time and place. This research focuses on small-scale surf waves in a physical and numerical model to identify easy-to-handle geometries and to validate numerical simulations as a low-cost solution for varying boundary conditions. Breaking heights and generated tube lengths are analysed for various geometrical and hydraulic conditions to find set-ups for the creation of stationary breaking waves.