Ulrich Zanke

Characteristics of developing scour-holes at a sand-embedded cylinder

Abstract Characteristics of developing scour-holes at a sand-embedded 0.2 m diameter circular cylinder are presented. Non-intrusive, high-resolution topographic measurements of developing scour-holes were made with an experimental installation using a laser distance sensor (LDS) and precision step-motors. A clear-water experiment was conducted with bed shear stress equal to 95% of the critical bed shear stress for the initiation of sediment motion at the undisturbed plane sand bed with a d 50 of 0.26 mm. During the running experiment of 21 hours duration, measurements were taken by the LDS in different azimuthal half-planes with ϑ = 0, 15, 30, 45, 60, 75, 90, 105, 120, 135, 150, 165 and 180° in order to study the spatio-temporal variation of geometric properties in developing scour-holes. After 21 hours, the equilibrium condition was approached, with a scour rate less than d 50 per hour. Measurement of maximum scour depth in different azimuthal half-planes at different points in time during the experiment show that scour started at the cylinder side and surrounded the cylinder after about 20% of experiment time. Slopes of developing scour-holes presented three regions with different inclinations, which were attributed to vortex action. Both maximum scour depth and maximum scour radius at different azimuthal half-planes are well correlated with the maximum scour depth at plane with ϑ = 0°. When providing maximum scour depth at the cylinder front, the presented correlations are useful for simple calculation of scour-hole topography. This work provides an experimental database for advanced numerical simulation for loose sediment hydraulics.

Morphodynamic Simulation at the South Branch of Yangtze Estuary

In this paper a numerical morphodynamic model TIMOR3 has been introduced and applied to simulate the morphological response to the water and sediment changes in the Yangtze River Estuary. TIMOR3, coupled with Hydrodynamic Model and Wave Model, is used to simulate a long-term and huge area of the morphological changes in the Yangtze River Estuary. A detailed investigation was made to the south branch where the Deepwater Channel Navigation Project is under construction. The effect of the project in different phases with different water depth has been simulated and analyzed.Copyright

APPLICATION OF DATA ASSIMILATION FOR A SPECTRAL WAVE MODEL ON UNSTRUCTURED MESHES

The effect of the data assimilation of buoy data in the wind wave model (WWM) for wind wave simulations in both deep and shallow water regions developed by Hsu et al. [2005] is investigated. Following Lionello et al. [1992], the sequential method is implemented, where analyzed wave spectra and significant wave fields were assimilated by optimal interpolation (OI), then the analyzed values were used to reconstruct the wave spectrum. This paper examines the results of the assimilation of wave spectrum, significant wave height and significant wave period in a nearshore WWM model. The WWM model underestimates the wave period because it incorrectly applies past wave field data. The analysis has provided useful indications of the shortcomings of the WWM model. In summary, the OI approach is shown to be a reliable assimilation scheme in the WWM model.

Überfall und Ausfluß

Als normal angestromt sei ein gerader Uberfall bezeichnet, der im Grundris rechtwinklig zur Stromungsrichtung angeordnet ist. Meist handelt es sich dabei um Wehre oder ahnliche Hochwasserentlastungsanlagen, die mehrere Wehroffnungen haben konnen, Abb. 5.1.1.1. Die hydraulische Berechnungsaufgabe betrifft den Zusammenhang von Q = f(h,w,b,Form,....). Sind Bauwerkshohe w und Wehroffnungsbreite b fest gewahlt, so reduziert sich die gestellte Frage im wesentlichen auf die Abhangigkeit h = f(Q) bzw. Q = f(h). Der Durchflus Q gibt die Leistungsfahigkeit des Uberfalls bei einer Uberfallhohe h an. Als Uberfallhohe wird nicht die Hohe w des Uberfallbauwerks definiert, sondern die Hohe h des Oberwassers uber dem Scheitel des Bauwerks.

Verification of a 3rd Generation FEM Spectral Wave Model for Shallow and Deep Water Applications

This paper shows some results of the work currently carried out to improve the wave forecasting and hindcasting in oceanic and coastal regions. A new spectral wave model with a flexible numerical scheme using triangular elements to describe the model domain was developed by Hsu et al. (2002). This new spectral wave model called WWM (Wind Wave Model) is feasible for the spectral wave modeling of irregular coastlines and complicated bathymetries because of its numerical scheme. The Wave Action Equation is solved with the aid of the Fractional Step Method (Yanenko, 1971). The Integration in the spatial space is carried out with the Taylor-Galerkin Method and the terms describing depth and current induced refraction are integrated with the aid of Leonard’s (1979) TVD Ultimate Quickest scheme, which was already introduced in the WWIII (H. Tolman, 1991) for the same purpose. In three applications the wave model was verified against in-situ spectral measurements of directional and non-directional wave buoys. The results show that the new spectral wave model is capable of hindcasting the wave climate with a comparable accuracy like the SWAN model (Ris et al., 1998), though with a better efficiency since fewer nodes are necessary to resolve the model domain and the boundary conditions adequately.Copyright

A MORPHODYNAMIC MODEL FOR RIVER AND ESTUARY MANAGEMENT

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.