Hans-Erwin Minor’s research while affiliated with Hochschule für Technik Zürich and other places

A new model is proposed to predict the bed topography in steep open channels once the bed stability is exceeded. Existing relationships describe bed stability by defining an entrainment state, usually expressed by a threshold shear stress or a discharge. The approach proposed herein focuses the self-stabilization potential of the channel bed at discharges larger than the entrainment value for which there is no sediment supply from upstream. Flume experiments carried out at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) of the Swiss Federal Institute of Technology (ETH) Zurich, indicated that the self-stabilization potential occurs in various geomorphologic scales. These scales are associated with typical features of the channel bed morphology. As the self-stabilization process is always combined with erosion, the novel approach interrelates the product of water discharge and channel gradient with the channel bed degradations associated with the different geomorphologic scales.

For large-particulated fluids encountered in natural debris flow, building materials, and sewage treatment, only a few rheometers exist that allow the determination of yield stress and viscosity. In the present investigation, we focus on the rheometrical analysis of the ball measuring system as a suitable tool to measure the rheology of particulated fluids up to grain sizes of 10mm. The ball measuring system consists of a sphere that is dragged through a sample volume of approximately 0.5l. Implemented in a standard rheometer, torques exerted on the sphere and the corresponding rotational speeds are recorded within a wide measuring range. In the second part of this investigation, six rheometric devices to determine flow curve and yield stress of fluids containing large particles with maximum grain sizes of 1 to 25mm are compared, considering both rheological data and application in practical use. The large-scale rheometer of Coussot and Piau, the building material learning viscometer of Wallevik and Gjorv, and the ball measuring system were used for the flow curve determination and a capillary rheometer, the inclined plane test, and the slump test were used for the yield stress determination. For different coarse and concentrated sediment–water mixtures, the flow curves and the yield stresses agree well, except for the capillary rheometer, which exhibits much larger yield stress values. Differences are also noted in the measuring range of the different devices, as well as for the required sample volume that is crucial for application.

We recommend to use "Evers et al. (2019), Landslide generated impulse waves in reservoirs - Basics and computation, 2nd edition" for impulse wave or landslide-tsunami hazard assessment. The new version is based on this 1st edition, resolves some weaknesses and takes new work from the last 10 years into account. The full text of this new version is available on ResearchGate as well.

Chutes with flow velocities in excess of some 20 m/s are typically prone to cavitation. In order to avoid damages, these flows are aerated using chute aerators. The current literature describes the efficiency of these aerators mainly in terms of the air entrainment coefficient as the ratio of the entrained air and water discharges. However, this is a global coefficient neither specifying the precise air distribution in the flow nor its detrainment rate. As cavitation damages occur along the chute boundaries, the associated air concentration is of prime interest. The present investigation focuses on the flow structure and the air transport downstream of chute aerators. Systematic hydraulic model tests were conducted including a data analysis of the spatial air concentration distribution in the near and the far fields downstream of chute aerators. Based on these and other measurements, general air transport zones were described. Three flow zones were introduced, namely the: (1) Jet zone; (2) Re-attachment and spray zone; and (3) Far-field zone. It was further found that aerators have primarily an effect on the average air concentration, whereas they increase the bottom air concentration only slightly. A large de-aeration gradient was found near the bottom downstream of the re-attachment point. It was concluded that the bottom air concentration downstream of chute aerators is smaller than generally assumed. Nevertheless, these air concentrations obviously suffice to inhibit cavitation damages on spillways equipped with aerators. Key wordsaerator-cavitation-chute-deflector-offset

Flume experiments have been carried out to study the formation processes and the bed morphology of step–pool channels. From the experiments different step types and step configurations could be distinguished depending on the stream power. These step types can be seen as an image of the generation mechanisms of step–pool systems. These results suggest that the bed roughness geometry develops towards a condition that provides the maximum possible bed stability for a given grain size distribution. In contrast to a variety of other studies, antidunes did not contribute to the generation of the step structures. However, the data of the presented study fits well into the region of antidune formation proposed by Kennedy for sand-bed rivers. This observation points out that step–pool field-data located in the Kennedy region do not inevitably prove that antidunes played a role in step development. It is rather proposed that in Kennedy's region of antidune formation there exist hydraulic conditions where the flow resistance is maximized. It is suggested that such maximum flow resistance is associated with an optimal distance between the bedforms and their height, independently of whether these are antidunes in sand- and gravel-bed rivers or step–pool units in boulder-bed streams. The considerations of the Kennedy region of antidune formation and the analysis of planform step types depending on stream power both suggest that steep channels have a potential for self-stabilization by modifying the step–pool structure towards a geometry that provides maximum flow resistance and maximum bed stability. Copyright © 2008 John Wiley & Sons, Ltd.

Ski jumps are a standard element of dam spillways for an efficient energy dissipation if takeoff velocities are large, and stilling basins cannot be applied. This laboratory study investigates the hydraulic performance of a triangular-shaped, rather than the conventional circular-shaped, bucket placed at the takeoff of ski jumps. The following items were addressed: 1 pressure head maximum and pressure distribution along the triangular-shaped bucket; 2 takeoff characteristics as a function of the bucket deflector angle and the relative bucket height including the lower and the upper jet trajectories; 3 jet impact characteristics in a prismatic tailwater channel including the shock wave formation and the height of recirculation depth below the jet cavity; 4 energy dissipation across the ski jump, from the approach flow channel to downstream of jet impact; and 5 choking flow conditions of the flip bucket. A significant effect of the approach flow Froude number, the relative bucket height, and the deflector angle is found. A comparison with previous results for the circular-shaped bucket geometry indicates a favorable behavior of the novel bucket design.

Hydraulic scale modelling involves scale effects. The limiting criteria for scale models of subaerial landslide generated impulse waves including solid, air, and water are discussed both based on a literature review and based on detailed two-dimensional experimentation. Seven scale series based on the Froude similitude were conducted involving the intermediate-water wave spectrum. Scale effects were primarily attributed to the impact crater formation, the air entrainment and detrainment, and the turbulent boundary layer as a function of surface tension and fluid viscosity. These effects reduce the relative wave amplitude and the wave attenuation as compared with reference experiments. Wave amplitude attenuation was found to be more than 70 times larger than predicted with the standard wave theory. Limitations for plane impulse wave generation on the basis of the present research are given by which scale effects can be avoided.