Frederick L.W. Tang

Bio: Frederick L.W. Tang is an academic researcher from National Cheng Kung University. The author has contributed to research in topics: Wave height & Wave shoaling. The author has an hindex of 3, co-authored 17 publications receiving 45 citations.

Numerical Calculation of Wind Waves in Shallow Water

Abstract: For the purpose of estimating the waves raised by typhoons approaching continental shelf and inland seas, one of the authors (I960) devised graphical method to the forecasting the waves in the fetches travelling over shallow water area in I960. The method has been widely adopted to evaluate the waves of the bays and inland seas in Japan and the western coast of Taiwan, since it was proved that calculated results considerably agreed with measured records. On the account of the spread of electronic computers, numerical analysis will be more expedient than graphical operations nowadays. Wilson s numerical integration method (I96I)(I962) has been extended to facilitate the calculation of the waves of shallow water area. The procedures of calculation are described and example of hindcasting of waves in typhoon by the machine run are also submitted in this paper.

Studies on fixed rectangular surface barrier against short waves

Abstract: In short waves, the particle motion in deeper region are to be negligible. For rigid vertical breakwaters built in considerable deep water, the lower part of vertical wall does not play the vital role of wave defending. It can be replaced by a frame to support the surface barrier which bears the wave force, and remain vacancy of the lower part of breakwater. Hence the theoretical and experimental characteristics of wave transmission and spectra alternation are investigated respectively here for this kind of the fixed, rigid, rectangular surface barrier in order to obtain an economic section and verify its capable relative depth as the design basis of deep port breakwater.

Coastal engineering researches on the western coast of taiwan

Abstract: Taiwan is an island located at the edge of the continental shelf of the East China Sea. Her eastern coast fronts precipitously on the Pacific Ocean, whereas the major part of the western coast is formed by very flat sandy beaches. Various engineering works such as the planning of newly building or extension of harbors, tidal land development, cooling water intake of steam power plants as well as shore protection works have been performed on this coast. However, owing to the geomorphological situation of this coast, monsoons of NNE or NE direction originated from high pressure atomosphere overlaying East Asia continent prevail from September to March, and in the summer months, the coast is assailed by typhoons. Waves caused by these meteorological phenomena are mainly being generated in shallow water region, besides, their fetch areas are limitted by the China mainland and Taiwan island. The forecast technics must be reconsidered in stead of utilizing traditional methods. Most coastal engineering structures are subjected to the waves after breaking since the beach slope is exceptionally flat. Many rivers of rapid stream bring tremendous amount of sediment from the high mountains down to the sea. In consequence, sand drift along this coast is so severe that small harbors will be silted up only a few months during monsoon season or after one strong typhoon assailing.

The relationship between wave length and weight of armour blocks

Abstract: Every coastal engineer realizes that the weight of armour blocks decided by Hudson's formula is safe enough for short steep waves, however, suffering damage from long period swells, even though the incidental wave height is the same. Several corrections have been made and submitted to ICCE as well as in other occasion. The authors try to explain analytically the influence of wave length on the design weight of armour blocks and justify by much of experiments in order to offer new formula and graphs for practical application.

Practical method for evaluation directional spectra after shoaling and refraction

Abstract: Different Methods have been developed to calculate the deformation of spectrum as waves advance to the shallow water. Wave ray method is a traditional way to compute the change of wave ray after refraction. It is restricted to the regular wave. After slicing the linear spectrum, a lot of components of spectrum can be gained, and each component can be considered as a monochromatic wave. And then after the deformed components are worked out at the same point in sea, a deformed spectrum in shallow water is gained by summing up them. Therefore the wave ray method could be extended to the irregular wave in ocean. In real bathymetry, the difficulty in applying such method is to solve the wave ray which must pass through the assigned point. In this paper, calculation approach as well as computer program are contrived to adopted in real bathymetry. The results of computation reveal some significant characteristics of directional spectra in shallow water. Furthermore, the statistical features of waves at the point of interest are to be evaluated.

An empirical model for sediment resuspension in shallow lakes

Abstract: Suspended solids concentrations were measured at routine 2–3 week intervals and on additional windy days for at least one year in each of seven shallow (mean depth < 2 m) south Island, New Zealand lakes. Surface wave characteristics were estimated from water depths and local meteorological data using a shallow-water wave forecasting model for fetch-limited waves. Bottom shear stresses were computed from surface wave characteristics for the sampling stations and for a hypothetical lake-average station. The calculated shear stresses were, on average, much better predictors of suspended solids concentrations than alternative models using two different functions of wind speed, wave height2/depth or wavelength/depth. A combination of the sample station and lake average shear stresses provided slightly better predictions than the sample station values alone, suggesting that currents also contribute significantly to the concentration at a given point. Regressions of suspended solids on the combined functions had r 2 values ranging from 0.74–0.73 in the seven lakes. The slopes of these regressions were negatively related to the settling velocity of the lowest quartile of the sediment, and to macrophyte biomass, in multiple regression (r 2 = 0.94, p < 0.01).

Two-dimensional beach transformation due to waves

Abstract: Important physical parameters controlling sandy beach transformation were clarified on the basis of the result obtained by a laboratory test. They were not only wave steepness but also beach gradient and a ratio of sand size to wave length. These parameters enabled the previously obtained laboratory beach profiles to be classified into newly proposed three beach types. These parameters were also found to be effective in grouping the data of shoreline changes both in laboratories and in fields.

Floating breakwaters under regular and irregular wave forcing: reflection and transmission characteristics Brise-lames flottants soumis à une houle régulière et irrégulière forcée: caractéristiques de réflexion et de transmission

Abstract: In the present study the hydrodynamic interaction of regular and irregular waves with floating breakwaters (FBs) in shallow and intermediate waters is examined experimentally in a large-scale facility. The experiments were conducted in the CIEM flume of the Catalonia University of Technology, Barcelona. The influence of incident wave characteristics and certain geometric characteristics, such as the width and the draught of the structure, on its efficiency is examined. Four different FBs configurations are examined: (a) single fixed FB, (b) heave motion FB, (c) single fixed FB with attached front plate (impermeable and permeable) and (d) double fixed FB. Results related to transmission, reflection, and energy dissipation of the incident (regular and irregular) waves on the structure are presented. For the single fixed FB, the efficiency of the structure is proportional to the width/wavelength and draught/water depth ratios. The single fixed FB operates in a highly reflective manner. On the other hand, the heave motion FB operates in a dissipative manner with much lower reflection. The attached plate in the front part of the FB significantly enhances the efficiency of the structure. No significant differences are observed between the impermeable and the permeable plate cases. Generally, the most efficient configuration has been the double fixed FB. However, with regard to cost-effectiveness, the configuration of the FB with the attached plate should be considered the most efficient for design purposes. RESUME Dans la presente etude l’interaction hydrodynamique des vagues regulieres et irregulieres avec des brise-lames flottants (FBs) en eaux peu profondes

Onshore-offshore transport and beach profile change

Abstract: In this paper a model is presented to describe onshore-offshore sand transport in the surf zone. The model is based on the physical consideration that when the net transport attains a state of equilibrium, the power expended through gravitational force in suspending sand grains is balanced by that due to the uplifting force arising from the turbulence generated by breaking waves. Two important parameters controlling sand transport are the dimensionless fall-time parameter and bottom slope.