Non-stationary flow around buildings during run-up of tsunami waves on a plain beach

This paper presents an experimental investigation that focuses on some predominant flow features that arise around surface mounted vertical obstacles which are exposed to a transient flow. The flow under investigation is caused by a tsunami-like long wave that climbs up a 1:40 sloping plain beach. In this study the wave height in offshore waters is varied. A single obstacle of 10 cm width as well as side-by-side arrangement of two identical square obstacles with different spacing are considered at an approximate length scale of 1 in 100. The analysis reveals important flow features around the various obstacle configurations. Particular emphasize is laid on the spatiotemporal evolution of the wake angle that linearly increases over time irrespective of the obstacle spacing. The growth rate of the wake angle reciprocally depends on the gap ratio over the investigated range of g† = 0.0 to g† = 3.0

Investigations on scour development at tripod foundations for offshore wind turbines: Modeling and application

Regarding offshore constructions, there is still a lack in knowledge of scour progression for complex structures like foundations for offshore wind energy converters at present, which is however necessary for its dimensioning. As an example of such complex structure types, Tripod foundations are constructed in German offshore wind farms at present. In order to describe physical processes and influencing factors on scour progression from a scientific point of view, comprehensive investigations on the scouring phenomena for Tripod foundations have been carried out and will be partly presented here. The overall investigation method consists of a combination of 1:40 small and 1:12 large scale physical model tests in wave flumes, numerical simulations using CFD methods and in-situ measured scour data. For the numerical modeling part, a sediment transport model formulation has been implemented into OpenFOAM software code. The results show a general variability of scour depending on the load boundary conditions and structural parameters. Scours occur both at the foundation piles and directly under the structure, which in this form could not be predicted using standard approaches, but which has to be taken into account when regarding the soil mechanical stability and the final dimensioning of the foundations.German Federal Environment Ministry (BMU)/GIGAWIN

Numerical and experimental study on tsunami run-up and inundation influenced by macro roughness elements

This research study considers long wave run-up experimentally and numerically. At first, an alternative methodology in long wave physical modeling is presented by means of a set of pipe pumps forcing the inflow of a controlled volume of water into a wave channel mimicking a tsunami-like wave shape that is consistently contained by a proportional plus integral plus derivative controller (PID) controller. Arbitrary wave lengths are persistently generated by means of the proposed methodology. First results are compared to tsunami data stemming from conventional experimental configurations with solitary waves as well as with recent numerical modeling results. Comparisons are thoroughly discussed and - in a second step - numerical simulations are accomplished taking the interaction of long wave run-up and macro-roughness elements into account. Four different experimental configurations of macro-roughness elements are carried out while spacing between elements and numbers of obstacle rows are alternated. A fundamental correlation analysis reveals that a correlation of the number of macro-roughness rows, effective area of flow cross section and a grouping factor of different element configurations exists in principle

The Java tsunami model: Using highly-resolved data to model the past event and to estimate the future hazard

This study is to validate the tsunami model with extensive field observation data gathered from the 2006 Java tsunami. In the relevant study area, where highly-resolved geometric data were recently made available and other related posttsunami field data have been collected, the tsunami maximum run-up onto land and its marigram have been simulated and evaluated. Several plausible tsunami sources are proposed to adequately mimic the 2006 Java tsunami by including the influence of low rigidity material in the accretionary prism as well as its single-multi fault source type's effect. Since it has a significant role on tsunami excitation, this parameter and other assumptions are then employed to study an estimated set of reasonable maximum magnitude earthquake-tsunami scenario and projected inundation areas for probable future tsunami on the South Java coastline. In a final step tentative technical mitigation measures are proposed and assessed to deal with adequate coastal protection issues by means of soft (greenbelt, etc.) and hard engineering (sand dunes, etc.) approaches. Their effectiveness in terms of reducing inundation area is assessed and general recommendations for coastal planning authorities are dealt with

Interaction of idealized urban infrastructure and long waves during run-up and on-land flow process in coastal regions

This paper reports experimental results of long wave run-up climbing up a 1:40 sloping beach. The resulting maximum run-up is compared with analytical results and a good agreement is found for single sinusoidal waves with uniform wave period and varying amplitude. Subsequently, the interaction with macro-roughness elements on the beach is investigated for different long-shore obstruction ratios. The reduction in wave run-up is expressed by means of a nomogram relating the wave run-up without macro-roughness elements present to those cases where on-land flow is modified by macro-roughness. The presented results mainly focus on a non-staggered and non-rotated macro-roughness configuration. In addition to the run-up reduction, surface elevation profiles on the shore are presented, that address the shock wave generation when the wave tongue approaches the first row of macro-roughness elements.LUHDFGBMB

Breaking wave kinematics, local pressures, and forces on a tripod support structure

This paper presents breaking wave loads on a tripod structure from physical model tests and numerical simulations. The large scale model tests (1:12) are described as well as the validation of the three dimensional numerical model by comparison of CFD wave gauge data and pressures with measurements in the large wave flume inside and outside the impact area. Subsequently, the impact areas due to a broken wave, a curled wave front as well as for wave breaking directly at the structure with a partly vertical wave front are compared to each other. Line forces in terms of slamming coefficients with variation in time and space are derived from CFD results and the velocity distribution is presented at the onset of wave breaking. Finally, the results are briefly discussed in comparison to other slamming studies.German Federal Environment Ministry (BMU)/GIGAWIN

Physical modeling of scour around tripod foundation structures for offshore wind energy converters

As a step to further develop the share of renewable energies, the first German offshore test site alpha ventus has been installed in the North Sea in 2009 in water depths of 30 m, where experience shall be gained and made available for future offshore wind farms. Regarding converter foundations in deep water, it is well known that in most cases scour phenomena occur around the structures. Due to the complexity of the tripod foundations, significant knowledge gaps in scour progression in general and especially in detail as well as its probable effects on the stability and durability are given. Therefore, investigations on scouring phenomena around complex foundation structures like the tripod are carried out within the research project. The investigation method consists of a unique combination of local scour monitoring as well as physical and numerical modeling, whereas the physical modeling part was carried by means of 1:40 laboratory tests and 1:12 large-scale physical model tests in wave flumes. The results show that scours around the tripod foundation do not only occur directly around the foundation piles, but also in the near-field of the structure. Compared to first in-situ measured scours in the test site, at least a good qualitative agreement of the modeled scour depths and evolutions could be shown.German Federal Environment Ministry (BMU)/GIGAWIND alpha ventus - LU

Wave overtopping at dykes with topped vertical wall - Impacts of oblique wave attack

Hydraulic model tests at a scale of 1:10 are carried out in a 40 m x 25 m wave basin with a state-of-the-art 3D wave generator in order to collect wave overtopping data at vertical walls and dykes with topped vertical walls. Wave conditions in the near field of the structures, velocities under waves and the mean overtopping discharge are measured. The experiments have been commissioned by the Lower Saxony Water Management, Coastal Defense and Nature Conservation Agency (NLWKN) with the purpose to deliver essential overtopping data for validation of numerical models. Two main geometries are analyzed – each for two specific wave spectra. Overtopping rates are investigated with respect to the remaining freeboard height Rc and the influence of oblique wave attack β{0°, 10°, 30°, 40°, 50°, 60°}. Results are compared with existing analytical approaches. As expected for this special geometrical coastal protection structure, it is examined that overtopping discharges increase with decreasing remaining freeboard. Intensity of the reduction is more dependent on the wave spectra than on the dyke geometry. Mean wave overtopping rate increases with decreasing relative water depth Hm0/d directly in front of the vertical wall. Furthermore, the mean wave overtopping rates decrease with an increasing angle of wave attack β. The correlation between mean wave overtopping rate and freeboard height is given in four newly adapted design formulas, describing the overtopping performance of the two discussed dyke geometries with topped vertical walls

On the Recovery of the Free Surface from the Pressure within Periodic Traveling Water Waves

We present a consistent derivation of the pressure transfer function for small amplitude waves within the framework of linear wave theory and discuss some nonlinear aspects