Winyu Rattanapitikon

VERIFICATION AND MODIFICATION OF BREAKER HEIGHT FORMULAS

This study is undertaken to find out the most reliable breaker height formulas that predict well for a wide range of hydraulic conditions. The applicability of 24 existing formulas, for computing breaking wave heights, is examined by using wide range and large amount of published laboratory data (574 cases collected from 24 sources). It is found that most formulas predict well for the breaking waves on the gentle slope (0 < m ≤ 0.07), but the prediction is unsatisfactory for the breaking waves on the steep slope (0.1 < m ≤ 0.44). Three formulas are selected and are modified by including the new form of bottom slope effect into the formulas. The new breaker height formulas predict well for wide range of wave and bottom slope conditions.

Energy dissipation model for regular and irregular breaking waves

Based on a large amount of published laboratory results, reliable models are developed for computing the average rate of energy dissipation in regular and irregular breaking waves. The average energy dissipation rate is assumed to be proportional to the difference between the local mean energy density and stable energy density. Wave height transformation is computed from the energy flux conservation law based on the linear wave theory. The models are examined and verified extensively for a variety of wave and bottom conditions, including small and large scale laboratory and field experiments. Reasonable good agreements are obtained between the measured and computed wave heights and root mean square wave heights.

A PROPOSAL OF NEW BREAKER HEIGHT FORMULA

A new breaker height formula is developed based on a re-analysis of available laboratory data. The analysis shows that the breaking wave steepness is mainly governed by its deepwater wave steepness. The power form could be used to fit the relationship between breaking wave steepness and its deepwater wave steepness. This finding is new. Although the breaker height has been a subject of study for a century, no researcher has tried to relate the breaking wave steepness to the deepwater wave steepness. Bottom slope effect is included explicitly into the present formula. The present formula and existing formulas are examined and compared with a large number and wide range of published laboratory data (695 cases collected from 26 sources). Overall, the present formula gives very good predictions over a wide range of experimental conditions and is better than existing formulas.

Simple model for undertow profile

Based on a re-analysis of the existing undertow models and the experimental results, a proper explicit model is proposed for computing undertow profile inside the surf zone. The model has been derived by using the eddy viscosity approach. The model is examined using published laboratory data from six sources covering small-scale and large-scale experiments, i.e. the experiments of Nadaoka et al. (1982), Hansen and Svendsen (1984), Okayasu et al. (1988), Cox et al. (1994), CRIEPI (Kajima et al., 1983) and SUPERTANK (Kraus and Smith, 1994). The present undertow model is considerably simpler than most of existing models. Although the model is simple, it shows good agreement with the experimental results above the bottom boundary layer. The calculation is so simple that the undertow profile can be calculated by using a pocket calculator.

BREAKING WAVE FORMULAS FOR BREAKING DEPTH AND ORBITAL TO PHASE VELOCITY RATIO

This study was undertaken to find out the suitable breaking wave formulas for computing breaker depth, and corresponding orbital to phase velocity ratio and breaker height converted with linear wave theory. A large amount and wide range of published laboratory data (695 cases collected from 26 sources of published laboratory data) were used to examine and develop the breaker formulas. Examination of some existing formulas indicates that none of them can be used for a wide range of experimental conditions. New breaker formulas were developed based on the re-analysis of the existing formulas. Overall, the new formulas give good predictions over a wide range of experimental conditions.

Irregular wave height transformation using representative wave approach

Many researchers have pointed out that the use of representative wave approach can give erroneous results in the computation of irregular wave height transformation. However, the representative wave approach seems to be an efficient tool incorporated into beach deformation models because of its simplicity and computational efficiency. It will be useful for practical work, if this approach can be used to compute the irregular wave height transformation. Therefore, this study is carried out to investigate the possibility of simulating irregular wave height transformation by using representative wave approach. A large amount and wide range of experimental conditions, covering small-scale, large-scale, and field experimental conditions, are used to calibrate and examine the model. The rms wave height transformation is computed from the energy flux conservation law. Various energy dissipation models of regular wave breaking are directly applied to the irregular wave model and test their applicability. Surprisingly, it is found that by using an appropriate energy dissipation model with new coefficients, the representative wave approach can be used to compute the rms wave height transformation with very good accuracy.

ENERGY DISSIPATION MODEL FOR IRREGULAR BREAKING WAVES

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.

ESTIMATION OF SHALLOW WATER REPRESENTATIVE WAVE HEIGHTS

If the Rayleigh distribution of wave heights is valid, the representative wave heights can all be converted one to another through the known relationships. In shallow water, it has been pointed out by many researchers that the wave height distribution deviates from the Rayleigh distribution. However, it is not clear whether this deviation can lead to significant errors on the estimation of representative wave heights or not. Experimental data from small-scale, large-scale, and field experiments were used to examine the errors of the relationships derived from the Rayleigh distribution on estimating representative wave heights. The examination indicates that if Hrms is given, the relationships give overall very good estimations on H̄ and H 1/3, good estimation on H 1/10 but fair estimation on H max. The effect of wave breaking was empirically incorporated into the relationships. The new relationships give better estimation than the relationships derived from the Rayleigh distribution.

ENERGY DISSIPATION MODEL FOR COMPUTING TRANSFORMATION OF SPECTRAL SIGNIFICANT WAVE HEIGHT

The objective of this study is to propose the most suitable dissipation model for computing the transformation of spectral significant wave height (H m0). A wide range of experimental conditions, covering small-scale, large-scale, and field experiments, were used to examine the models. Fourteen existing dissipation models, for computing root-mean-square wave heights (Hrms ), were applied to compute H m0. The coefficients of the models were recalibrated and the accuracy of the models was compared. It appears that the model of Janssen and Battjes [2007] with new coefficients gives the best overall prediction. The simple model proposed in the present paper was modified by changing the formula of stable wave height in the dissipation model. Comparing with the existing models, the modified model is the simplest one but gives better accuracy than those of existing models.

Estimation of Maximum Possible Wave Heights in Surf Zone

The breaking-limited (or depth-limited) approach is a traditional method to determine the maximum possible wave height for the design of coastal structures in the surf zone. It is well recognized that the maximum wave height in the surf zone is limited by wave breaking. The maximum possible wave height is usually determined from a breaker height formula. The present study was undertaken to examine the applicability of 14 existing breaker height formulas for computing the maximum possible wave heights. The existing breaker height formulas were examined against measured regular and irregular wave heights. A total of 17 863 data points from 30 sources of published experimental data were used to examine the formulas. The experiments cover a wide range of wave and bottom topography conditions including small-scale, large-scale, and field experiments. It was found that the errors of existing formulas for regular and irregular waves have the same tendency. The existing formulas give considerable underestimation of the maximum possible wave heights in shallow water. The top three formulas were modified by including a new form of relative depth into each formula. Overall, the modified formulas give a considerable better estimation than those of existing formulas.