Wave dissipation was previously investigated intensively in the frequency domain, in which the dissipation of waves is described as attenuation of pressure pulse decay with respect to the frequency or harmonics. In this thesis, wave dissipation, including decay of pressure pulse, peak of wave intensity and wave energy, is investigated in the time domain using wave intensity analysis (WIA). Wave intensity analysis benefits to this research in several aspects including: 1) WIA allows for wave dissipation investigated in the time domain; 2) WIA does not make any assumptions about the tube's wall non-linearity and the analysis takes into account the effects of the vessel's wall viscoelastic properties, convective, frictional effects and fluid viscosity; 3) WIA offers a technique (separation) to study wave dissipation in one direction whilst taking into account the effect of reflections from the opposite direction; 4) The physical meaning of wave intensity provides a convenient method to study the dissipation of energy carried by the waves along flexible tubes. In this research, it is found that the degree of dissipation in flexible tube were not only affected by the mechanical properties of the wall property and viscosity of liquid but also by the other factors including initial pressure and pumping speed of piston as well as direction of wave in relation to direction of flow. Also an new technique to separate waves into forward and backward directions only using diameter and velocity might potentially be used to separate the waves in both directions non-invasively based on the non-invasive measurement of diameter (wall movement) available.

Beach grain size plays a major role in controlling beach slope and sediment transport rates and is a crucial criterion in selecting the appropriate fill material for beach nourishment. Yet, little is known about how and why beach grain size (and sorting) varies both spatially and temporally on high-energy sandy beaches. Therefore, in this PhD research project, the presence, magnitude and predictability of any spatio-temporal sediment variability was investigated on a number of contrasting high-energy (average significant wave height = 0.8 to 3.5 m), predominantly macrotidal (MSR = 3.1 – 6.2 m), sandy (0.26 – 0.64 mm) beach sites around the southwest peninsula of the United Kingdom (UK). The spatial extent of the data collected ranges from regional (one off snapshot of the sediment conditions on 53 beaches over 485 km of coastline) to local scales (repeated high-resolution samples from across the inter- and subtidal zone of a single high-energy sandy beach; Perranporth, UK). The temporal scales of the sampling ranges from tidal scale (~12 hours) up to monthly (long-term monitoring since 2008). A combination of traditional and modern field data collection methods has provided new insights into the sediment dynamics of sandy beaches. Surface and 0.25 m core sediment samples from the 53 beaches around the southwest UK and high-resolution digital measurements with longer 1 m sand cores from the intertidal zone, plus grab samples from the subtidal zone, at Perranporth, indicated the presence of three quasi-permanent spatial trends. On all sandy beaches, surface sediments became coarser (and better sorted) in the seaward direction across the intertidal zone. Peak sediment sizes were observed on the lower beach around mean low water springs, which were an average 19% coarser (and 8% better sorted) than sediments sampled on the upper intertidal beach. Sediment size (and sorting) also increased (improved) with distance down the sediment column over the top 0.25 m to 1 m. Peak sediment sizes at depth were an average 16% coarser (and 16% better sorted) than surface sediments. In the subtidal zone, surface sediments became finer and poorer sorted with increasing offshore distance. Minimum sediment size occurred on the subtidal bar crest and were an average 21% finer (and 51% poorer sorted) than the lower beach sediments and 5% finer (and 38% poorer sorted) than upper beach sediments. The coarsest sediments were usually the best sorted at all locations. The intertidal coarsening was deterministically linked to the location and amount of breaking wave-induced turbulence. The peak sediment sizes (and sorting) on the lower beach correlated with the location of peak wave dissipation (sediment size to amount of wave dissipation, r2 = 0.86) and the finer sediment sizes on the upper beach and bar were coincident with reduced amounts of wave dissipation in these regions. Long-term seasonal monitoring of the surface sediments at Perranporth indicated a background seasonality, where the winter months were an average 35% coarser and 22% better sorted than samples collected in summer. This seasonal pattern was punctuated by episodic storm events that promoted a significant coarsening (up to 112% in the extreme winter storms of 2014) of the surface sediments and significant beach erosion up to 175 m3/m. An empirical model forced by the degree of disequilibrium between an instantaneous and antecedent (weighted average) wave steepness time series was able to capture up to 86% of the sediment grain size and sorting variability, incorporating both the seasonal and storm driven change. The same model, applied to daily observations of sediment size and sorting changes was able to explain 72% of the variability. A conceptual model is proposed that extends the cross-shore sediment transport shape functions to include the various sediment (size and sorting) responses alongside the morphodynamic evolution during persistently high and low wave steepness conditions. Under high steepness waves, the finer material is preferentially removed from the lower intertidal beach, leaving behind coasrer sediments. This fine material is transported to the subtidal bar, which becomes finer (and more poorly sorted) inversely with the coarsening (and improved sorting) of the intertidal zone sediments. Under low steepness waves, this fine material is returned from the bar to the intertidal beach. This work provides a detailed, quantitative insight into the magnitude of sediment grain size and sorting changes exhibited by sandy beaches on a number of spatial and temporal scales. Several consistent trends were observed on a range of sandy beaches despite their different environmental conditions and geological histories. This improved understanding of sediment grain size and sorting changes on beaches will hopefully aid future research efforts and ensure that this fundamental aspect of coastal science is not overlooked or oversimplified.

The hydrodynamic effects of long-line mussel farms are studied through a two-pronged approach. Large-scale hydrodynamic effects are investigated through the use of field measurements, primarily at a large mussel farm in Golden Bay, New Zealand (230 long-lines, covering an area of 2.45 km by 0.65 km). The research focuses on three areas: the effect of the farm on currents, mixing and stratification, and the dissipation of wave energy. Measurements are also made of the forces on long-line anchor ropes, and a limited investigation is made of phytoplankton depletion. The second approach is the use of laboratory drag measurements and Particle Tracking Velocimetry (PTV) to study the effect of mussel dropper (vertical lengths of mussel-encrusted crop rope) roughness and spacing on flow at small scales. These experiments provide data on very rough cylinders, and on cylinder arrays. The field measurements show that the local effects of mussel farms on currents are significant, but that magnitudes of the effects depend on dropper density, mussel sizes, orientation of the long-lines to the flow, and other parameters that are necessary to characterise the complex interactions between a farm and the flow. The drag on the submerged structures reduces water velocities within the Golden Bay farm by between 47% and 67%. Mussel farms present a porous obstacle to the flow, and flow that does not pass through the farm must be directed around or beneath it. The field measurements indicate that at the study site, most of the flow is diverted around the farm despite its large horizontal dimensions. The droppers at the study site extend over most of the water column (average dropper length ~ 8 m, average water depth ~ 11 m), providing a restriction to the flow beneath the farm. The strength of the density stratification may also favour a horizontal diversion. The flow around the farm is essentially two-dimensional. This suggests that two-dimensional numerical models should be sufficient to obtain reasonable predictions of the velocity drop within, and the diversion around, mussel farms. A simple two-dimensional pipe-network model gives reasonable estimates of the velocity within the farm, demonstrating that the drag of the farm may be adequately parameterised through local increases of bed friction. A wake in the form of reduced velocities extends downstream of the farm, and a mixing layer analogy suggests that this wake spreads slowly. The downstream extent of the wake cannot be determined, although it is likely to be limited by the tidal excursion. The degree of vertical mixing caused by the flow through a mussel farm cannot be quantified, although there are clear interactions between the stratification and the farm. Two mixing mechanisms are considered. A shear layer is generated beneath the farm due to the difference in velocities between the retarded flow within the farm and the flow beneath. Shear layers beneath mussel farms are likely to be weak unless the ambient currents are strong. It will be necessary for stratification to be weak or non-existent for this mechanism to generate significant mixing. The second mechanism is smaller-scale turbulence generated by the mussel droppers. Although the efficiency of this form of mixing is likely to be low, the large number of mussel droppers suggests that there will be some enhancement of vertical mixing. Frequency-dependent wave attenuation is recorded, and is predicted with some success by an analytical model. Both the model and the field data show that wave dissipation increases as the wave period decreases. Wave energy dissipation at the study site averages approximately 10%, although the measurements are made during a period of low wave heights (Hs < 0.25 m). Measurements of long-line anchor rope tension at two study sites indicate that the loadings are induced by the tide, currents, and waves. Dynamic wave loadings may be significant, and higher wave forces are measured at the offshore end of a long-line. The issue of seston or phytoplankton depletion is considered briefly through the examination of fluorescence, turbidity, and acoustic backscatter data. Although the results are consistent with a reduction of seston within the farm, differences between the inside and outside of the farm are not statistically significant. Mussel droppers resemble extremely rough circular cylinders, with the mussel shells forming the surface roughness elements. Drag measurements and PTV flow visualisation are used to investigate the importance of the large surface roughness, and the influence of dropper spacing and long-line orientation on flow. Drag measurements conducted with smooth and rough cylinders show that high surface roughness (ks/D ~ 0.092) has little effect on the drag coefficient of single cylinders in the range 4,000 < Re < 13,000, yet increases the drag coefficient of a row of cylinders normal to the flow. High surface roughness on single cylinders has the effect of shortening the near-wake region, increasing the peak turbulent kinetic energy (TKE) behind the cylinder, and decreasing the Strouhal number (St = 0.21, 0.19, 0.17 for ks/D = 0, 0.048, and 0.094 respectively). Arrays of rough cylinders (ks/D = 0.094) demonstrate similar flow characteristics to those of smooth cylinders. At cylinder spacings of S/D < 2.2, the surface roughness acts to favour the formation of a particular metastable wake pattern, whereas different metastable wake patterns are formed each run behind the smooth cylinders. The experiments show that the drag on single row arrays of cylinders are related to the cylinder spacing (increasing drag with decreasing spacing), and the drag also varies with the sine of the angle to the flow, except where the array is at low angles to the flow. The PTV measurements provide new data regarding the two-dimensional distributions of velocity, TKE, and turbulence statistics behind the cylinder arrays.

The present study comprised an intensive investigation of the two newly proposed parameterisation forms for the wind input source term S[subscript]in (Donelan et a1., 2006) and the wave dissipation source term S[subscript]ds (Young and Babanin, 2006) proposed on the basis of the recent experimental findings at Lake George, New South Wales, Australia in 1997-2000. The main objective of this study was to obtain advanced spectral forms for the wind input source function S[subscript]in and wave spectral dissipation source function S[subscript]ds, which satisfy important physical constraints. A new approach was developed to achieve the objectives of this study, within the strong physical framework. This approach resulted in a new balance scheme between the energy source terms in the wave model, mentioned before as the split balance scheme (Badulin, 2006). The wave-induced stress was defined as the main physical constraint for a new wave model including recently suggested source functions for the wind input and wave dissipation source terms. Within this approach, a new methodology was developed for correction of the wind input source function S[subscript]in. Another important physical constraint was the consistency between the wave dissipation and the wind energy input to the waves. The new parameter, the dissipation rate, R, was introduced in this study, as the ratio of the wave dissipation energy to the wind input energy. The parameterisation form of the dissipation rate is presented as a function of the inverse wave age U ₁₀ / c[subscript]p Some aspects of wave spectral modelling regarding the shape of the wave spectrum and spectral saturation were revised. The two-phase behaviour of the spectral dissipation function was investigated in terms of the functional dependency of the coefficients a for the inherent wave breaking term and b for the forced dissipation term. The present study found that the both coefficients have functional dependence on the inverse wave age U ₁₀ / c[subscript]p and the spectral frequency. Based on the experimental data by Young and Babanin (2006), a new directional spreading function of bimodal shape was developed for the wave dissipation source term. The performance of the new spectral functions of the wind input S[subscript]in(f) and the wave dissipation S[subscript]ds(f) source terms was assessed using a new third-generation two-dimensional research wave model WAVETIME-I. The model incorporating the corrected source functions was able to reproduce the existing experimental data. / Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009

The present study comprised an intensive investigation of the two newly proposed parameterisation forms for the wind input source term S[subscript]in (Donelan et a1., 2006) and the wave dissipation source term S[subscript]ds (Young and Babanin, 2006) proposed on the basis of the recent experimental findings at Lake George, New South Wales, Australia in 1997-2000. The main objective of this study was to obtain advanced spectral forms for the wind input source function S[subscript]in and wave spectral dissipation source function S[subscript]ds, which satisfy important physical constraints. A new approach was developed to achieve the objectives of this study, within the strong physical framework. This approach resulted in a new balance scheme between the energy source terms in the wave model, mentioned before as the split balance scheme (Badulin, 2006). The wave-induced stress was defined as the main physical constraint for a new wave model including recently suggested source functions for the wind input and wave dissipation source terms. Within this approach, a new methodology was developed for correction of the wind input source function S[subscript]in. Another important physical constraint was the consistency between the wave dissipation and the wind energy input to the waves. The new parameter, the dissipation rate, R, was introduced in this study, as the ratio of the wave dissipation energy to the wind input energy. The parameterisation form of the dissipation rate is presented as a function of the inverse wave age U ₁₀ / c[subscript]p Some aspects of wave spectral modelling regarding the shape of the wave spectrum and spectral saturation were revised. The two-phase behaviour of the spectral dissipation function was investigated in terms of the functional dependency of the coefficients a for the inherent wave breaking term and b for the forced dissipation term. The present study found that the both coefficients have functional dependence on the inverse wave age U ₁₀ / c[subscript]p and the spectral frequency. Based on the experimental data by Young and Babanin (2006), a new directional spreading function of bimodal shape was developed for the wave dissipation source term. The performance of the new spectral functions of the wind input S[subscript]in(f) and the wave dissipation S[subscript]ds(f) source terms was assessed using a new third-generation two-dimensional research wave model WAVETIME-I. The model incorporating the corrected source functions was able to reproduce the existing experimental data. / Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009

The present study comprised an intensive investigation of the two newly proposed parameterisation forms for the wind input source term S[subscript]in (Donelan et a1., 2006) and the wave dissipation source term S[subscript]ds (Young and Babanin, 2006) proposed on the basis of the recent experimental findings at Lake George, New South Wales, Australia in 1997-2000. The main objective of this study was to obtain advanced spectral forms for the wind input source function S[subscript]in and wave spectral dissipation source function S[subscript]ds, which satisfy important physical constraints. A new approach was developed to achieve the objectives of this study, within the strong physical framework. This approach resulted in a new balance scheme between the energy source terms in the wave model, mentioned before as the split balance scheme (Badulin, 2006). The wave-induced stress was defined as the main physical constraint for a new wave model including recently suggested source functions for the wind input and wave dissipation source terms. Within this approach, a new methodology was developed for correction of the wind input source function S[subscript]in. Another important physical constraint was the consistency between the wave dissipation and the wind energy input to the waves. The new parameter, the dissipation rate, R, was introduced in this study, as the ratio of the wave dissipation energy to the wind input energy. The parameterisation form of the dissipation rate is presented as a function of the inverse wave age U ₁₀ / c[subscript]p Some aspects of wave spectral modelling regarding the shape of the wave spectrum and spectral saturation were revised. The two-phase behaviour of the spectral dissipation function was investigated in terms of the functional dependency of the coefficients a for the inherent wave breaking term and b for the forced dissipation term. The present study found that the both coefficients have functional dependence on the inverse wave age U ₁₀ / c[subscript]p and the spectral frequency. Based on the experimental data by Young and Babanin (2006), a new directional spreading function of bimodal shape was developed for the wave dissipation source term. The performance of the new spectral functions of the wind input S[subscript]in(f) and the wave dissipation S[subscript]ds(f) source terms was assessed using a new third-generation two-dimensional research wave model WAVETIME-I. The model incorporating the corrected source functions was able to reproduce the existing experimental data. / Thesis (Ph.D.) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2009