Dissertations / Theses on the topic 'Tidal Strait'

In the quest to reduce the release of carbon dioxide to limit the effects of global climate change, tidal-in-stream energy is being investigated as one of many possible sustainable means of generating electricity. In this scheme, turbines are placed in a tidal flow and kinetic energy is extracted. With the goal of producing maximum power, there is an ideal amount of resistance these turbines should provide; too little resistance will not a develop a sufficient pressure differential, while too much resistance will choke the flow. Tidal flow in a strait is driven by the difference in sea-level along the channel and is impeded by friction; the interplay between the driving and resistive forces determines the flow rate and thus the extractible power. The use of kinetic energy flux, previously employed as a metric for extractible power, is found to be unreliable as it does not account for the increased resistance the turbines provide in retarding the flow. The limits on extraction from a channel are dependant on the relationship between head loss and velocity. If head loss increases with the square of the velocity, a maximum of 38% of the total fluid power may be extracted; this maximum decreases to 25\% if head loss increases linearly with velocity. Using these values, the estimated power potential of BC's Inside Passage is 477MW, 13% of previous assessments. If a flow has the ability to divert through a parallel channel around the installed turbines, there are further limits on production. The magnitude of this diversion is a function of the relative resistance of impeded and diversion channels. As power extraction increases, the flow will slow from its natural rate. This reduction in velocity precipitously decreases the power density the flow, requiring additional turbine area per unit of power. As such, the infrastructure costs per watt may rise five to eight times as additional turbines are installed. This places significant economic limitations on utility-scale tidal energy production.

This thesis examines functional relationships between the morphologic, hydrodynamic, ecological and sedimentological characteristics of the Warraber reef platform, an inter-tidal reef island system, Central Torres Strait, Australia (10[degrees] 12??? S, 142 [degrees] 49??? E). Hydrodynamic and sediment-transport experiments were conducted on the reef flat using current meters, water level recorders and directional sediment traps. Results showed dominantly SE flows during the dry season and more variable NW to SE flows during the wet season. Topography and reefal water levels modulated the direction and strength of currents and the generation of wind-waves on the reef flat as well as the passage of waves over the reef rim. These hydrodynamic conditions are sufficient to induce significant transport of moderately fast to slow settling sediment (&gt-5.25 symbol psi) on the reef flat, though the platform as a whole is a relatively closed transport system. Carbonate production was estimated based on the key ecological variables of live assemblage distribution and cover. Overall, only 24% of the reef flat was occupied by carbonate-producing organisms. The average estimated carbonate-production rate for the reef was 1.6 kgm -2y-1 (0.07-4.37 kgm-2y-1). Production is dominated by coral (73%), with subordinate proportions contributed by coralline algae (19%). And molluscs, foraminifera and Halimeda (&lt4%) though actual reef-flat sediments did not reflect this potential. Instead, they were dominated by molluscs (35-55%), coralline algae (16-26%), coral (8-13%), Halimeda (7-8%) and foraminifera (5-10%). Differential rates of carbonate to sediment conversion meant the reef-platform sediments were more closely related to the cover of live organisms than to the contribution of carbonate production by each parent organism. The settling properties of the least altered particles of the five commonest constituents were measured and these provided the basis for an eco-sedimentological model of the reef-platform system. Modelled textures were compared to the actual textures, indicating the degree of textural alteration resulting from a combination of biological and physical processes, including sediment production, hydraulic sorting and mechanical breakdown. This analysis, integrated with the hydrodynamic, exposure and other data, was used to determine reef-platform surface-sediment sources, sinks and transport pathways. In using both the textual and constituent compositional properties of sediments, as well as information on local biological and physical processes, the model approach developed offers progress towards an integrative, interdisciplinary analysis of carbonate environments.

Interest in exploring renewable energy resources has increased globally, especially with recent worldwide intentions to maintain the global climate. Looking at the oceans as a vast sustainable clean energy resource to satisfy present high humankind energy demands has been strongly recommended. Several types of renewable energy resources exist in the oceans: waves, tides, thermal and salinity variations, currents, and offshore winds. Exploiting tidal currents is considered one of the most effective approaches to the generation of electricity. Tidal turbines are deployed beneath the sea surface to transfer the kinetic energy in tidal currents to mechanical energy suitable for ongoing conversion to electricity and subsequent transmission. However, choosing a suitable site to deploy these turbines is not a trivial process. Various constraints must be satisfied subject to basic criteria dependent upon local factors, technology limitation and economic consideration. In addition, an important issue to consider is taking care to harness energy from tidal currents with minimum possible impact on the surrounding environment. The present study justifies the nomination of the Strait of Messina as an exceptional tidal current energy resource within the Mediterranean Sea basin. The maximum tidal current velocity at spring peak tide through the Strait may exceed 3 m/s. This mainly results from the tidal phase-difference (180°) between the northern (Tyrrhenian Sea) and southern (Ionian Sea) tips of the Strait, associated with a difference of 0.27 m in tidal wave amplitudes. In addition, the complex coastline configuration of the Strait plays an important role in enhancing tidal current velocities. Therefore, the Strait of Messina fulfils the basic criterion (2 m/s tidal current velocity) to be considered as a valid tidal current energy resource. This massive tidal current energy resource is assessed in the present study. A detailed full desk-based Environmental Impact Assessment (EIA) study is performed using the interactive matrix approach in order to investigate the anticipated environmental impacts on the marine ecosystem of the Strait of Messina resulting from the harnessing of energy from its tidal currents. Through the EIA study the different environmental components, both biotic and abiotic, which may be affected by the energy extraction process, are explained. In addition, the proposed key project activities are listed; the likelihood of occurrence and the magnitude of impact interaction with the environmental components are evaluated. The final judgment matrix guides to make a right decision on the proposed project. From the resulted matrix, the major impacts do not exceed 10% of the total anticipated effects. The positive point is that all the expected impacts, including the majors, can be controlled and minimised to the lowest possible limits by applying a good monitoring programme. The University of Edinburgh “Tidal Flow Development (TFD)” numerical model is used to mimic the tidal environment of the Strait of Messina in different cases. The model successfully simulates the tidal flow regime within the Strait under some exceptional conditions. Modifications to the main numerical code and coefficients were necessary in the present research to adjust the model according to each case study. In the three different cases of simulation, using these exceptional coefficients, the model simulates the main tidal characteristics of the tidal flow within the Strait. According to the results of the numerical simulation process, tidal currents are more intensive close to the eastern coast of the Strait of Messina near to Punta Pezzo. This area is far from any ferry route between Italy and Sicily. The best location to deploy tidal turbines for the energy extraction process is therefore recommended to be within these surroundings. Finally, a physical (laboratory) model is used to simulate the flow regime within the Strait of Messina. The Particle Image Velocimetry (PIV) technique was applied in the flow-table tank at the University of Edinburgh. The physical model simulates the flow behaviour within the Strait of Messina to a satisfactory degree. The cyclonic and anti-cyclonic motions observed at the southern extremity of the Strait are also very well simulated. The results of the present study assure confidence in the use of tidal currents within the Strait of Messina as a renewable energy resource. The safety of the environment must be ensured by following environmental guidelines, respecting the energy extraction limits and by applying an effective monitoring programme. The later is strongly recommended to be an adaptive one in which higher environmental authorities are able to watch, revise and control the environmental team within the project. These authorities are also able to postpone the project in case of any severe environmental case. The simulation processes emphasize the effect of morphometry and topography in enhancing tidal currents in the Strait of Messina. Moreover, numerical simulation assures that the complex morphometry and bathymetry, in addition to the open boundaries of the Strait of Messina, are challenging issues for modellers in order to mimic the real tidal current resource in the case of the Strait of Messina. The study also strongly recommends applying a more effective numerical model than TFD to assess the tidal hydrodynamical environment before and after any proposed energy extraction process. This will certainly, with the EIA of the marine ecosystem, help to make a right decision about the proposed project in order to achieve the goal of using clean and clear renewable energy resources while maintaining both natural and hydrodynamical environments to the most possible safest degree.

National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore zones around the UK for potential tidal stream resource development. Although a number of prospective tidal energy sites have been identified, the local hydrodynamics of these sites are often poorly understood. Tidal-energy developers rely on detailed characterisation of tidal energy sites prior to device field trials and installation. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal-energy development. Ramsey Sound (Pembrokeshire, Wales, UK) will soon host Wales’ first TST demonstration project. However, the local hydrodynamics of the sound have been underexamined. Ramsey Sound experiences a marked tidal asymmetry, with local bathymetric features that affect flow fields which are spatially heterogeneous in three dimensions. Using Ramsey Sound as a case study, this thesis has three objectives: (1) to examine the wake created by submerged objects through field- and laboratory-based measurements, (2) to experimentally investigate the effect of submergence on wake development and decay downstream of a conical island, and (3) to develop a TST suitability tool, which examines the effects of velocity, water depth and bed slope on power availability within a macrotidal coastal area. Laboratory experiments have shown that submergence level is an important parameter controlling wake structure and extent, and that changes in submergence level affect both the 3-D flow structure in the near wake and the 2-D far wake of islands. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, vertical shear in the stream flow, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments.

Gamma titanium aluminide alloys are emerging as a lightweight replacement to nickel superalloys, with current application in turbine stages of aero-engines, as well as in high performance automobiles and potentially the nuclear industry. The lack of toughness of its two constitutive intermetallic phases, γ-TiAl and α2-Ti3Al, prevents a conventional damage tolerant approach to fatigue lifing. To gain confidence in the use of γ-TiAl alloys and extend the temperature-stress envelope of applicability, the present work aims to achieve an understanding of the development of plasticity and flaw formation during cyclic loading. The general plasticity of a γ-TiAl alloy, Ti-45Al-2Nb-2Mn(at.%)-0.8vol.%TiB2, in compression was investigated by mapping the development of localised strain at the specimen surface. Methods were developed to produce speckle patterns for high resolution digital image correlation that were stable at test temperatures of 700 °C in air, in order to study the extent of plasticity generated by differing deformation mechanisms at application-relevant temperatures, with nano-scale resolution. At the colony scale (i.e. single stacks of co-planar α2-Ti3Al and γ-TiAl lamellae, where each stack is formed from a single high temperature disordered α-TiAl grain), macroscopic deformation bands were observed to develop at only a few percent strain. Within such bands, which propagated across many colonies of differing lamellar orientations, considerable lattice curvature and localised slip and twin operation occurred. This correlated with colony boundary failure in such bands. Twinning of the γ-TiAl phase parallel to the lamellar interfaces, longitudinal twinning, has rarely been studied, despite generalised twinning in equiaxed γ-TiAl grains being known to cause boundary decohesion. Here, the occurrence of longitudinal twinning in both microcompression and polycrystalline testpieces was investigated up to 700 °C by electron backscatter diffraction. The strength of constraint by surrounding lamellar domains was found to be the determining factor in the increased prominence of twinning at 700 °C, and hence determined whether twinning shear-induced flaws formed at colony boundaries. Using the high temperature digital image correlation strain mapping and electron backscatter diffraction techniques developed, along with transmission electron microscopy, the onset of plasticity at temperatures up to 700 °C was studied in both micro-scale and macro-scale test specimens for different lamellar thicknesses. Testpieces were loaded below the macroscopic yield stress in both monotonic and high cycle fatigue regimes, to 107 cycles, at a tensile stress ratio of R = 0.1. Longitudinal plasticity occurred in most colonies with soft mode lamellar orientations, and was located just 30 - 50 nm from lamellar interfaces. Lamellar refinement caused an increased number of slip bands to develop. In most cases, plastic strains decreased to zero by the colony boundary and strain transfer across such boundaries in high cycle fatigue was rare. At room temperature, the maximum applied stress was found to influence the number of slip bands more than the number of loading cycles.

This study set out to investigate the shear stress behaviour at the bed under combined wave and current action. The intention of the study was to make experimental measurements to determine how wave and current shear stresses combine, so that theoretical models describing the combined flow condition could be proposed. Two types of experiment were conducted, and theoretical models for the combined flow were assessed. One set of experiments attempted to use a shear plate to make direct measurements of the combined flow shear stress, and of the shear stresses for the component waves and steady currents. This approach failed because the large correction terms introduced by the non-uniform wave pressure field could not be accurately estimated. The second set of experiments used a laser doppler anemometer to make detailed velocity profile measurements over flat sediment beds. The onset of sediment motion was used as a criterion to carefully control the experiments. It is assumed that the threshold of sediment motion represents a specific shear stress intensity at the bed for sediments of narrow size ranges. As the shear stresses can be determined from the velocity fields under waves and currents, their additive nature under combined flow conditions could be investigated. For each sediment size range, it is shown that the same maximum velocity very near the bed can be used to specify the threshold of sediment motion condition for all flow types, be they under waves, currents, or combined waves and currents. It is also shown that the near-bed velocity under a laboratory wave can be predicted accurately from second order wave theory and that the velocity under a current can be predicted from combining Manning's relation with the universal log velocity law. It is further shown that the near-bed velocity under a combined wave and current can be described by the vectorial addition of the maximum component wave velocity and the average component current velocity. The shear stress for the onset of motion is calculated for the steady current using Manning's relation, for the wave by combining the oscillatory shear stress formula with Kamphuis's rough turbulent friction factor relation, and for the combined wave and current by the simple vectorial addition of the component shear stresses, and is shown to be comparable with Shields's threshold criterion for nearly all conditions tested.<br>Applied Science, Faculty of<br>Civil Engineering, Department of<br>Graduate

Les alliages à base d'aluminures de titane (TiAl) sont des matériaux légers introduits dans la dernière génération de turboréacteurs pour l'aéronautique civil sous la forme d'aube de turbine basse pression. Ces alliages disposent notamment d'excellentes propriétés mécaniques à haute température et d'une résistance spécifique élevée. Leur utilisation reste cependant délicate du fait de leur faible ductilité et ténacité à température ambiante. Afin de trouver de nouvelles applications à ces matériaux, les deux principaux défis pour les futures générations d'alliage sont l'augmentation de la température d'utilisation et l'amélioration des propriétés en fatigue thermomécanique. Dans cette optique, le présent travail consiste à établir un lien entre la microstructure des alliages TiAl et leur tenue en fatigue. Pour cela, des travaux expérimentaux et numériques sont réalisés à différentes échelles d'intérêt sur les quatre microstructures dites génériques de ces matériaux. Dans un premier volet expérimental, un lien entre microstructure et comportement mécanique cyclique est établi via la réalisation d'essais mécaniques à l'échelle macroscopique (i.e. réponse contrainte-déformation), et d'essais micromécaniques qui permettent d'étudier la répartition de la déformation dans la microstructure. Dans un deuxième volet numérique, un modèle de plasticité cristalline permettant de tenir compte des spécificités des microstructures à structure lamellaire des alliages TiAl est défini. Les comportements mécaniques cycliques des quatre microstructures génériques sont ensuite modélisés via la réalisation de calculs éléments finis sur microstructures virtuelles et homogénéisation numérique. Enfin, cette modélisation est utilisée afin de réaliser une analyse aux Indicateurs de Tenue en Fatigue (ITF). Cette analyse permet de comparer les tenues en fatigue des différentes microstructures et d'identifier les éléments microstructuraux qui pilotent la durée de vie en fatigue pour différents régimes de sollicitation. Les résultats obtenus permettent alors d'effectuer un retour vers la métallurgie en indiquant les zones à renforcer pour améliorer les propriétés en fatigue de futurs alliages<br>Technological advances in aircraft engine design require the use of lightweight materials at increasingly high temperatures. Therefore, intermetallics titanium aluminide alloys based on $\gamma$-TiAl have been introduced in the most recent civil turbo-engines as low pressure turbine blades. To extend the use of this material to other application technologies, new alloys are being developed with enhanced mechanical properties. Particularly, material development teams focus on increasing the working temperature and the fatigue strength. The aim of this work is to study the link between TiAl alloys microstructures and their fatigue strengths. Both experimental and numerical aspects are studied at various scales of interest. To begin with, the cyclic deformation of TiAl generic microstructures is studied experimentally by performing standard testing (i.e. stress-strain response) and micro-scale testing. Then, a crystal plasticity model that can be used to take into account the specific behavior of lamellar colonies is defined. The mechanical behavior of TiAl alloys is thereafter modeled by means of finite element computation on statistically representative microstructures and computational homogenization. Lastly, a Fatigue Indicator Parameters (FIP) analysis is performed to identify the various fatigue hot spot within TiAl microstructures. The results are used to suggest microstructure designs that could improve the fatigue strength of TiAl alloys next generation

碩士<br>國立臺灣海洋大學<br>海洋環境資訊學系<br>100<br>The Taiwan Strait (TS) is a 180×600 km shelf channel located between Taiwan and China. We analyzed five ADCP acoustic Doppler current profilers (ADCPs), four were deployed along the central part of the TS distributed uniform from Taichung to Wuchung and one was deployed in the Peng-Hu Channel (PHC). The data period is 1999-2001. In the general phase, tidal motions are dominated by barotropic component in TS due to shallow bathymetry and weak stratification. In this study, using in-suit data accompanying with OTPS (OSU Tidal Prediction Software), we found that the barotropic diurnal/semidiurnal tidal motions almost flowed along the topography trend of the strait. The current magnitudes of barotropic diurnal tides were 0.1~ 0.13 m/s in the central part of the TS and PHC. The current magnitudes of barotropic semidiurnal tides eastward decrease in the central part of TS, and the maximum magnitude of semidiurnal barotropic tidal current were observed in the PHC(~ 0.9 m/s), much stronger than that in the central TS. Also, the magnitudes of barotropic tidal currents were enhanced by the rising and nearshore narrow channel in the TS. Meanwhile, the baroclinic diurnal/semidiurnal tidal motions were not significant in the general phase, in TS, and the magnitudes were 30~50% and 20~35% of the magnitudes of the barotropic diurnal/semidiurnal tidal motions, respectively. The baroclinic tides were dominated by first-mode baroclinic tidal motions. The depth-integrated kinetic energy (KE) of the baroclinic tides revealed nearly spring-neap circle. However, KE of baroclinic tides were not only effected by the circle, other external events such as typhoon and eddy in the South Chain Sea could also enhance the KE of the baroclinic tides in the central part in TS. Meanwhile, the time lag (> 50hours) of the KE between the barotropic and baroclinic tides implied that internal tides were remotely generated in the Luzon Strait and subsequently proceeded to TS via South China Sea. Compiling typhoon track、Sea Surface Temperature (SST) and Sea Level Anomaly (SLA), we conclude that the internal tides could be intensified in the presence of horizontal fronts in the northern South Chinese Sea (SCS). The fronts could be produced by the typhoon-induced cold wake or cold eddy. As our observation, the strong mode-1 semidiurnal baroclinic tides were intensified, with a maximum velocity of ~0.27 m/s. The maximum depth-integrated kinetic energy of semidiurnal internal tides after the time of the thermal fronts impact were 1.5~2 times of those in the time of spring tide. And the enhancement of internal tides were the most remarkable in the west of strait (Mainland China side).

碩士<br>臺灣大學<br>海洋研究所<br>98<br>The volume transport from Taiwan Strait to East China Sea is 50 times more than that from Yangtze River, and the sediments and nutrients from Taiwan Strait to East China Sea is one third of the total. It has a great influence on the water mass exchanging and ecology of Taiwan coast and East China Sea. The research focuses on the major constituents of tidal currents and the volume transport (VT) of the northern Taiwan Strait. Because the of data density previous studies is low in time and space in this region, lacking of long-term and a cross section of the strait actual measurement data, we installed a shipboard ADCP on the TaiMa Ferry that navigates between Keelung and Matsu to measure and to gather along track current velocity data. We obtain 160~280 data sets in different grids after screening sixteen months, and then use Harmonic Analysis to find out along-track tidal amplitude and phase of M2, S2, K1, O1 constituents. The result from Harmonic Analysis showed that M2 is the major constituent and its energy is more than S2, K1 and O1 in our study area. Owing to the low and discontinuous sampling frequency on the fixed station, we can’t distinguish constituents that have similar period and low energy. For example, the relation between Harmonic Analysis result and OSU tidal model (TPXO) result of M2 reach 0.9 shows that most tidal current can be filtered. On the other hand, S2 is affected by M2, K1 and O1 still can’t be filtered correctly due to longer period and lower energy. To have 20% or less error on tidal current constituents, it requires data length of 3, 5 and 3 years for M2, S2 and K1 tides. Use two different methods that TPXO and Harmonic Analysis to remove tidal contribution show 1~3 Sv VT through TWS and VT difference value of to- and return-cruises may be -1~1 Sv. The cause of the difference of VT between to- and return-cruises maybe the influence of wind, but it also implies the inaccuracy of remove tidal contribution. In addition, the northeast of the TS is located at the edge of the Keelung Valley and the east side of TS has a hollow and large variation on topography. This research also suggests the existence of baroclinic tide in these two regions, the associated tidal current amplitudes differ about 5~10 cm/s between upper and lower water level. It means that the result of Harmonic Analysis can never match the result of barotropic tidal model of TPXO.

博士<br>國立臺灣大學<br>海洋研究所<br>93<br>The current velocity profiles, bottom water temperature, and sea level were observed to study the spatial and temporal variations of the tidal and subtidal current in the Taiwan Strait from 1999 to 2000. Results indicate both diurnal and semidiurnal tidal currents were primarily barotropic. The barotropic diurnal tide might be explained by a single Kelvin wave propagating along the Mainland China coast from north to south. However, the barotropic semidiurnal tide manifested as a more complicated form in the Taiwan Strait. In the northeast monsoon, the subtidal current generally fluctuated with the northeast winds. When the northeast wind was weak, the along- and cross-strait subtidal current flowed primarily against the wind and toward Taiwan, respectively. As the northeast wind intensified, the along-strait current flowed downwind, brought the cold China coastal water southward, and formed a baroclinic velocity front in the western portion of the Taiwan Strait. The Ekman effect forced the cross-strait current toward Mainland China in the upper water column. Nevertheless, the current in the lower water column remained toward Taiwan. From September 28 to December 14 of 1999, the along-strait volume transport, estimated from interpolated current velocity, varied from -5 to 2 Sv with a mean value of 0.12 �b 0.33 Sv. Similar transport was also estimated from the sea level difference across the Taiwan Strait. However, the difference between two estimates is non-negligible In the southwest monsoon, the subtidal current was stable with the along- and cross-strait subtidal current were northward and toward Taiwan, respectively. The large northward subtidal current generally occurred at the central and western Taiwan Strait. Temperature front was found in the eastern Taiwan Strait. During the transition of monsoon, both the wind and current velocities had large fluctuations. Such fluctuations were gradually reduced when the monsoon gained its full strength. Although the local wind played a dominant role for the fluctuations of current velocity and transport in the Taiwan Strait, it was not the only factor. The remote impacts on the current velocity variation from the north and south could be also important in the Taiwan Strait.

碩士<br>國立成功大學<br>水利及海洋工程學系碩博士班<br>92<br>Among all the phenomena in the ocean, tide is the one with regular eustatic movement, which is closely linked to human activities. When tidal waves propagate towards the nearshore shallow water areas, the waveform deforms because of nonlinear interactions. The shallow water tidal constitutes, including overtides and compound tides are thus necessarily introduced in order to describe the deformed tidal waveform. Considering the northwest European continental shelf, tidal elevations are significantly affected by shallow water effects. The maximum amplitudes of quarter-diurnal tides M4 and MS4 can reach up to 0.25m and 0.21m high, respectively. These quantities are larger than those of most diurnal tides there. It could be seen that the shallow water tidal constituents ought to be taken into consideration for tidal elevation prediction. In present study, Princeton Ocean Model (POM) is adopted to simulate higher harmonics and long period tides in shallow waters in the Taiwan Strait. Computed tidal elevation amplitudes are compared with the observed data of shore-based tidal gauges on the western coast of Taiwan. Furthermore, tidal constituents of higher harmonics and long period tides are used to illustrate the magnitude and spatial variability over the Taiwan Strait. The results of simulations show that the Taiwan Bank, which locates in the southwest shallow water region of Taiwan Strait, induces significantly the spatial variations of amplitudes of third-diurnal, quarter-diurnal and sixth-diurnal tides. The spatial distribution of amplitudes of quarter-diurnal and sixth-diurnal tides is similar to the resonance of standing waves. This phenomenon can be confirmed by both theoretical derivation and the analyses of observed data. The fifth-diurnal constituent features the smallest amplitude in present study. The maximum amplitude of fifth-diurnal constituent occurs from TamShui to Hsinchu, whereas the minimun amplitude occurs in south of Kaoshiung. The spatial distribution of amplitudes of fifth-diurnal constituent is consistent with field data observed from the tidal gauges on the western coastline of Taiwan. In addition, the result of simulations also demonstrate the facts that the amplitude variations of higher harmonics and long period tides become significant in cases if the water depth is less than 120m. It is the water depth when tidal waves propagate from deep Pacific Ocean towards the continental shelves of the eastern Taiwan.

碩士<br>國立中山大學<br>海洋物理研究所<br>96<br>The studies of tidal current and sea level variation in the Taiwan Strait are popular topics in recent years. The sea level data, to be applied to data analysis or model forcing and validation, are mostly observed in the near shore region. It is relative not easier to obtain real tidal data in the offshore area. This study intended to obtain sea level data within Taiwan Strait, using in-situ water depth measurements collected by EK500 of research vessels OR1, OR2 and OR3 during 1989-2003. The basic assumption of this work is that the changes of sea level and topographical depth equal to observed water depth. By using a large set of field measurements, it is possible to get bottom topography such that tidal data can be extracted by harmonic analysis of long-term discrete time series of water depth data. A total of 1513 cruises of water depth data were collected, which account for nearly 6 million samples. These data were screened through a series of criteria for quality control. Firstly, data were plotted cruise by cruise ( longitude vs latitude , longitude vs depth , time vs depth), then reasonable range of time, depth and region were choosed manually. Second, outliers, defined as values greater than 3 standard deviations on 5 point moving mean along the cruise track (or time), were replaced by linear interpolation values. Finally, a 2-minute moving average was applied to the along track time series water depth data. This step was trying to remove the effect of surface waves. The original huge records were reduced to about 550,000 valuable samples for the 1513 cruises data. According to the density distribution of water depth samples in Taiwan Strait, 32 sub-region were selected for topography and harmonic analyses. In each sub-region, the bottom topography was mapped by an optimal interpolation method through a Gaussian weighting function. The radius of Gaussian weighting function applied is 3 time of the distance of grid. Water depth samples subtracted topographical depth of nearby grid to form a set of sea level data ready for harmonic analysis. The phase and amplitude of semi-diurnal tides (M2) and diurnal tides (K1、O1) in each sub-region were computed for the 32 regions in Taiwan Strait. The water depth measurements derived sea level variations were compatible with that of a global tidal model (OSU) and a set of moored long-term pressure records in the middle of the strait. Especially, the tidal phase among these results were quite close. However, the tidal amplitudes of water depth data derived were smaller. Sensitivity analysis showed that the errors, differences between OSU model and depth derived sea levels, were small with regions of high density of water depth measurements. Both harmonic derived sea level variations and OSU model predictions indicated a southward propagating tidal wave, which matched with the scenario of Kevin wave propagation in Taiwan Strait. Our analysis also showed that the sea level variations in the northern part of the strait were dominated by M2 and K1 components while the southern part of the strait were dominated by M2 and O1 components.

碩士<br>國立中山大學<br>海洋環境及工程學系研究所<br>97<br>In recent year, tidal gauge has progressed in temporal resolution or measurement accuracy, so that the quality of observational data tends to stable and reliable. However, setting up tidal gauge in the offshore areas restricts may apply due to many factors such as seabed topography, weather, sea state and leveling survey from land to gauge. Good tidal correction is one of key factors to the accuracy of bathymetric survey and to the area where tidal range is large. This study tried to use tide prediction data derived from the Yu(1993)’s tide numerical model and verified with actual observed tide data, and further establishing a tidal zone of Taiwan Strait by tidal characteristic. Using Taichung and Mailiao tide stations as a reference tidal station, the direct tide station correction, tidal zone correction, nearest model grid correction, and virtual station correction methods were applied to evaluate the accuracy of tide calculating value by amplitude ratio and tidal phase difference. The tidal zone correction is not totally depending on the spatial distance from reference tidal station, and it is found that correction result of this approach is one of the best. However, further improvement in tide correction may need to explore due to different spatial resolution applied in different numerical models. In addition, the boundary condition of a harbor for tidal model is very complicated. This is why it is hard to make a numerical model for a harbor. In this study, two additional high accuracy radar tidal gauge were installed in Kaohsiung harbor and first-class leveling survey was performed in order to maintain tidal measurement accuracy, also to avoid the effect of errors propagation. According to the results from experiment, average tidal phase of second entrance of the Kaohsiung harbor is earlier than that of first entrance about 6 minutes, and average difference of tidal height is approximately 2-3cm. For this reason, we should pay attention to decide a proper reference tide station for tidal correction for dredging hydrographic surveying. And any possible tidal observation errors, such as meteorological tide. If two additional tidal gauges of this study are removed in the future, we still can predict tide height from fixed tidal gauge.

碩士<br>國立中山大學<br>海洋物理研究所<br>95<br>Internal waves are vertical displacements of stratified water which can propagate a long distance without much energy dissipation. It plays on important role in conveying nutrient from deep ocean to shallower layers, and promoting biological growth. It also affects acoustics, ocean engineering and submarine navigation. Therefore, in the last few years, many scholars have devoted the research of internal waves, especially their generation and transportation in South China Sea. This research discusses the internal wave source, through the Princeton Ocean Model (POM). There are two simulations, one has bigger grid size 3.6km for the whole Luzon Strait in the region, 118°E ~123°E 18°N ~22°N, the other has smaller grid of 1.6km, for 118.5°E ~123°E and 19.5°N ~21.5°N. The total simulation period is 25 days, The north and south bomdawes use radiation boundary condition, the east side is driven by tidal calculated from WXTide32 model, the west side also uses radiation boundary condition. Three dimensional flow field during May, 2005, is simulated temperature, baroclinic velocity distribution, baroclinic energy flux, Empirical Orthogonal Functio ns (EOF), Fast Fourior transform (FFT), buoyancy frequency and Froude number are all analyzed, The results show that, when tidal current near the Batan island has the stronger baroclinic flow downward to transmit, after through Heng-Chun ridge the baroclinic energy flux to concenter, extrapolated this time possibly produces for internal tide.

We examine the tides in the Kitikmeot Sea using year-long time-series from moored instrumentation in Dease Strait, and a 3D barotropic numerical tidal model of the region. The in-situ data show strong tidal damping during wintertime seasonal sea ice cover, with a 50-60% reduction in M2 and K1 tidal elevation and 65% reduction in M2 and K1 tidal velocities at the sea ice maximum. We hypothesize the damping largely occurs in Victoria Strait, the eastern gateway of the Kitikmeot Sea, where tidal-induced ridging causes thick, rough ice to accumulate over its shallow sill. Using the numerical model, FVCOM, we independently vary sea ice friction and sea ice thickness, and show that the observed wintertime tidal damping likely requires both very rough ice and a partial sea ice blockage in the sill region. Analysis of the model shows different dynamics and dissipation of the dominant M2 and K1 tides. Both M2 and K1 tides are dominated by the Atlantic tides entering through Victoria Strait. Arctic tides, entering from the west, have a minor, but significant, contribution to the M2 tide. Overall, the K1 tide, after 19% dissipation in Victoria Strait and 24% in adjoining bays, propagates far into the region and behaves as a Helmholtz resonator in Dease Strait and Coronation Gulf. In contrast, 92% of the M2 tidal energy does not reach Dease Strait because, in addition to dissipation in Victoria Strait (29%), it is significantly diverted into adjoining bays and around an amphidrome in eastern Queen Maud Gulf. The K1 tide, with double the wavelength of the M2 tide, is less diverted.<br>Graduate<br>2020-07-22

The upper Baronia Fm. of the Ager Basin, Spain, is composed of a hierarchy of prominently stacked sets of primarily unidirectional cross-strata in units up to 40m thick. These large sets of cross-strata are interpreted as deposits of migrating subaqueous tidal simple dunes, compound dunes, and compound dune complexes within an approximately 10km wide north-east to south-west oriented seaway with water depths of a calculated 60-90m. These interpretations are opposed to prior interpretations of the upper Baronia Fm. which suggests deposits were formed by tidal bars within a deltaic environment (Mutti et al., 1985). Dunes developed due to dominantly north-east directed tidal currents driven through the strait by tidal phase differences between the two bodies of water (Mediterranean and Atlantic basins) connected by the seaway. Evidence for syn-tectonic deposition further constrains timing of movement of the northern basin bounding Montsec thrust to the early Eocene. Indicators for movement on the Montsec thrust include the development of the Ager Basin elongate to the thrust front, and syn-tectonic signals in the fill of the basin such as local conglomerate wedges and emplacement of olistoliths. Individual cross-stratified successions are interpreted to have formed with variable flow velocity and orientation, resulting in a basin wide stacking of compound dune complexes. These compound dune complexes form cross stratified successions which are distributed throughout the basin according to the variable current speeds, dune size which impacts migration, and sediment availability during deposition. This results in the observed distributions of muddy and sandy sediments, where finer grained materials accumulate preferentially in the low energy troughs of the hierarchy of compound dunes.<br>text

Intra-archipelago waterways, including tidal strait networks, present a complex set of barriers to, and conduits for sediment transport between marine basins. Tidal straits may also be the least well understood tide-dominated sedimentary environment. To address these issues, currents, sediment transport pathways, and seabed sedimentology & geomorphology were studied in the central Salish Sea (Gulf and San Juan Islands region) of British Columbia, Canada and Washington State, USA. A variety of data types were integrated: 3D & 2D tidal models, multibeam bathymetry & backscatter, seabed video, grab samples, cores and seismic reflection. This dissertation included the first regional sediment transport modelling study of the central Salish Sea. Lagrangian particle dispersal simulations were driven by 2D tidal hydrodynamics (~59-days). It was found that flood-tide dominance through narrow intra-archipelago connecting straits resulted in the transfer of sediment into the inland Strait of Georgia, an apparent sediment sink. The formative/maintenance processes at a variety of seabed landforms, including a banner bank with giant dunes, were explained with modelled tides and sediment transport. Deglacial history and modern lateral sedimentological and morphological transitions were also considered. Based on this modern environment, adjustments to the tidal strait facies model were identified. In addition, erosion and deposition patterns across the banner bank (dune complex) were monitored with 8-repeat multibeam sonar surveys (~10 years). With these data, spatially variable bathymetric change detection techniques were explored: A) a cell-by-cell probabilistic depth uncertainty-based threshold (t-test); and B) coherent clusters of change pixels identified with the local Moran's Ii spatial autocorrelation statistic. Uncertainty about volumetric change is a considerable challenge in seabed change research, compared to terrestrial studies. Consideration of volumetric change confidence intervals tempers interpretations and communicates metadata. Techniques A & B may both be used to restrict volumetric change calculations in area, to exclude low relative bathymetric change signal areas.<br>Graduate<br>2018-12-07

博士<br>國立中山大學<br>材料科學研究所<br>92<br>Ti3Al based intermetallic alloys are attractive for aerospace and aircraft applications due to their superior high temperature properties. Excellent high temperature superplasticity in the Ti3Al-Nb based alloy has been widely published. However, the alloys become brittle and hard to deform at temperatures below 600oC so that low temperature superplasticity is difficult to develop. In the current super ��2 Ti3Al based alloy, the ordered BCC �� phase is the continuous matrix, with the DO19 hexagonal ��2 grains ~2.2 �慆 in grain size distributed uniformly in the �� matrix. The initial �� and ��2 volume fractions are around 60% and 40%, respectively, and strong textures are present in both phases. Although the alloy exhibits superior superplastic elongations over 1000% at 920-1000oC, the elongation drops appreciably to 600% at 900oC, 330% at 850oC and 140% at 750oC. Upon subsequent static annealing and superplastic loading at 700-960oC, the alloy tends to undergo �� to ��2’ phase evolution, approaching to the equilibrium phase partition at the respective temperature. The transformation seems to be enhanced during dynamic straining at temperatures lower than 900oC, suggesting the strain enhanced phase transformation. With the fine ��2’ laths inside the �� grains, the accommodation process across the BCC �� grains is impeded, leading to premature failure and lower tensile elongations at lower temperatures. Mechanical anisotropy is observed in this alloy and relatively higher tensile elongations are obtained in the 45o specimen as loaded at room temperature to 960oC. The texture characteristics appear to impose significant influence on the mechanical anisotropy at temperatures below 750oC (under the dislocation creep condition), as well as during the initial stage at a higher temperature of 920oC (under the superplastic flow condition). Systematic tracing of the texture evolution from the as-received to superplastically loaded specimens has been accomplished using electron backscattered diffraction. With the extensive dislocation motion plus a certain degree of grain boundary sliding and grain rotation during loading at 750oC, the ��2 grains gradually rotate to form the {0001} basal texture and some of the �� grains concentrate into the {111}< > orientation. At higher temperatures such as 920oC, extensive grain boundary sliding proceeds and results in grain orientation distributions for the ��2 and �� phases basically random in nature. Rationalizations for the mechanical anisotropy in terms of the Schimid factor calculations for the major and minor texture components in the ��2 and �� phases provide consistent explanations for the deformation behavior at lower temperatures as well as the initial straining stage at higher temperatures.

Thesis (M.S.)--University of Wisconsin--Madison, 1996.<br>Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 26-29).