京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21353号 / 工博第4512号 / 新制||工||1703(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 藤田 正治, 教授 中川 一, 准教授 竹林 洋史 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Braided rivers represent one of the most complex forms of natural streams. Characterized by intense bed-load transport and highly dynamic channels, they carry significant naturalistic value and support a multiplicity of ecosystem services. Anthropogenic stressors and environmental changes put under stress hydro-morphological dynamics, biological processes, and ecosystem functioning and services of these fragile environments, necessitating integrated management and conservation strategies to preserve their biodiversity and ecological integrity. From a regulatory perspective, the two European Directives 2007/60/EC (the Floods Directive) and 2000/60/EC (the Water Framework Directive) identify and promote win--win measures that both reduce hydraulic risk and enhance the quality of water bodies. Some examples of win--win measures are river naturalization projects that not only restore river ecosystems to their natural state, enhancing biodiversity and ecosystem services but also provide flood protection, improve water quality, and offer recreational opportunities for local communities. This thesis contributes to the development of scientific knowledge in the previously mentioned areas, facilitating the know-how transfer of expertise from academia to the public institution. Building on these premises, this thesis aims to provide additional insights into the morphodynamics of braided rivers, offering new perspectives on the evolution of morphological indices during flood events and contributing valuable knowledge on how these complex systems respond to external stressors. The PhD thesis has been structured along three parts. The primary goal was to develop an innovative unsupervised algorithm for extracting the spatial and temporal evolution of braided river morphology. This computational framework is tailored for Sentinel--1 Synthetic Aperture Radar (SAR) data, overcoming the limitations imposed by weather conditions and day--night cicles. Moreover, it can be effortlessly adapted to additional SAR imagery databases. In cases where the water class covers only a minimal area of the entire scene, the histogram primarily represents the dry soil class. The framework faces this challenge employing a Self-Adaptive Thresholding Approach (SATA) to achieve a distinct bimodal distribution, enabling the accurate computation of threshold values for the 'dry soil' and 'water' classes. The tool, developed within the Python--API of Google Earth Engine (GEE), allowed us to assess the intra--event inundation dynamics, the estimation of the relationship between hydrometric level and wet area extension, and the assessment of bank erosion phenomena. The second chapter focuses on analyzing how morphological indices, such as the Total Braiding Intensity (TBI) index defined as the number of active channels, the Maximum Channel distance (MCD) defined as the distance between the most external channels, and the Cross-Sectional Cumulative Wetted Area (WA) defined as the sum of the wet area of all chanels in a cross section, correlate with discharge variations during flood events. To achieve this objective, the framework designed for Sentinel--1 images was adapted for use with high--definition imagery from the Italian COSMO--SkyMed satellite constellation. Leveraging the superior ground resolution of 3x3 meters provided by the Italian COSMO--SkyMed satellite constellation, we successfully segmented narrow secondary branches that remained undetected with Sentinel--1's 5x20 meter resolution. Thus obtained, the temporal evolution of the braiding system, enables us to evaluate the temporal evolution and the relationship between the TBI, MCD, and WA indices with increasing discharge values. The last part of the PhD thesis, deals with the assessment of the river bed grain size. The initial concept behind this PhD work was to analyze the potential of Synthetic Aperture Radar (SAR) data in assessing not only river morphology but also the pattern of patches with different grain size. While the initial two parts of the work addressed this, the final section's analysis of SAR data, unfortunately, did not provide significant results. Nevertheless, the subjects of surface roughness and the creation of spatially distributed grain size maps continue to hold significant scientific value in the fields of hydraulic and eco--hydraulic modeling and a key information for river management and renaturation projects. The principal role of this factor led us to slightly shift the research focus towards a detailed investigation of these elements, utilizing orthophotos, digital imagery, and corresponding analytical methods to model patterns of river roughness and grain size. A map illustrating the spatial pattern of grain size at the river reach scale was produced through regression analysis. This analysis correlated the texture properties derived from orthophoto tiles with the d50, d84, d90, and d95 grain size characteristics obtained from digital images, thereby providing considerable support for the implementation of detailed hydraulic models.

Equivalent, three-dimensional elastic moduli are determined from unit cell models of balanced plain weave, 2D braid, 2D triaxial braid and 4x4 twill textile composite materials consisting of interlaced or intertwined yarns. The yarn paths are modeled with undulation portions, in which one yarn passes over and under one or more yarns, and with straight portions. It is assumed that the centerline of a yarn in the undulation portions is described by the sine function, and that the cross-sectional area of a yarn and the thickness of a yarn, normal to the centerline, are uniform along the centerline. For the balanced plain weave architecture, equations for the fiber volume fraction and the cross-sectional shape of the yarn are derived for large crimp angles. It is shown that the maximum crimp angle is limited to forty-five degrees, and that limits on the ratio of the length of the undulation portion of the path to the width of the unit cell impose constraints on the fiber volume fraction and yarn packing density. For small crimp angles, approximations to the volume fraction and yarn shape equations are obtained. This assumption is used in the derivation of the geometry of the remaining architectures, and subsequent equations are obtained for the corresponding geometric parameters. For each architecture, the yarns are assumed to be transversely isotropic and a stress averaging technique based on an iso-strain assumption is used to determine the effective moduli of the unit cells. Comparisons of the effective moduli are made to other unit cell models in the literature. The micromechanical models are implemented in Fortran programs and user material subroutines for ABAQUS, called UMAT, are created out of these programs. For a balanced plain weave fabric under the small crimp angle approximation, a progressive failure model is developed to predict failure within each yarn and to degrade the material properties of the representative unit cell. Material failure is predicted by discretizing the yarns into slices and applying Tsai-Wu quadratic criterion to the on-axis strains in each slice. A stiffness and strength reduction scheme is then used to account for the change in yarn compliance. At the present time, the UMAT has only been tested as a stand-alone program with Visual Fortran 6.0, and would require further development to be used within ABAQUS on sample structural problems. / Master of Science

This thesis primarily focused on the development of novel composite tubes by braiding. The objective was to use hierarchical scale technique, i.e., micro, meso and macro scales, with the transfer of information from one scale to another to develop novel braided composite tubes. This research was conducted and reported in three journal papers. The aim of the first paper was to predict plane elastic properties for E-glass/epoxy braided composite structures at different braid orientations, by analytical and finite element techniques. The lenticular shape has been used to describe the geometry of the tow. Modified lenticular geometric model was developed to improve an existing geometric model, in terms of tow parameters, thereafter, plane elastic properties from Chamis micromechanical model for E-glass fibre and epoxy matrix without any knockdown effects were used as benchmark to develop predictive models, namely; Lekhnitskii's methodology and braided unit cell meso-scale finite element model to account for the effects of tow geometry, undulations/crimp, cross-over and braid orientations on the plane elastic properties of E-glass/epoxy composite. The results showed agreement in trend between the predictive models, Chamis micromechanical model, and a similar existing model. However, the plane elastic properties were knocked down in predictive models by 30% in the E11 direction and 32% in the E22 direction, when compared with Chamis micro-mechanical model for largest ±65° braid angle, among the braid angles, considered. The aim of the second paper was to manufacture E-glass/epoxy braided tubes at different braid orientations by vacuum bag infusion technique, conduct internal pressure tests, and determine the hoop and axial moduli of the infused tubes. Lekhnitskii's methodology was also used to develop plane elastic moduli by experiment using microscopy results, and by calculation. The experimental elastic moduli of the infused tubes and the experimental elastic moduli from Lekhnitskii's methodology were used to compare the predictive elastic moduli for E-glass/epoxy braided structures by Chamis micro-mechanical model, and the braided unit cell meso-scale finite element model. The two were from another paper. Results showed a perfect agreement in trend between the experimental results and the predictive results. However, the values of the experimental results were close but lower than the predicted results. Optical microscopy was performed on braided tube cross-section to evaluate the level of crimp or undulation. This was done by the determination of tow centreline crimp angle and aspect ratio. Results show that when compared with the predicted crimp, there was an agreement in trend, although the experimental results were lower than the predicted. Also, the knockdown factor was evaluated and used to quantify the reduction in experimental elastic moduli when compared with the predicted. Results showed that the absences of crimp in the Chamis model caused a tremendous difference between it, other predicted models and the experiment results. The elastic moduli of Chamis were by far higher than all others, including other predictive models. The purpose of the third paper was to manufacture E-glass/epoxy braided tube at ±31°, ±45°, ±55°, ±65° braid orientations using vacuum bagging and resin infusion technique, to design and manufacture a rig for tube internal pressures experiment, to determine the hoop and axial stress performances of the tubes by internal pressure experiment, to compare experimental results with laminate analysis predictions to evaluate the effect of crimp on the internal pressure performance of the braided tubes. To use E-glass braided tow meso-scale unit cell finite element model to predict the tow critical stresses, and the optimum braided tube architecture, using tube hoop and axial failure stresses or strains. The tubes were manufactured and subjected to internal pressure test (2:1), to failure. Failure mode was by weeping and bursting. Hoop stress was twice the axial stress. The highest value of hoop stress was at the ±65° braid angle, higher than the hoop stresses at the ±31°, ±45°, and ±55 ° braid angles by 50%, 39%, and 28% respectively. Hoop stress increased with increase in braid angle. The experimental results were validated by laminate analysis predictions by Chamis micro-mechanical model and Lekhnitskii's methodology, and the trend of the laminate analysis prediction matched that of the experimental results. However, the predicted values were higher than the experimental results by 21%, 14%, 11%, 10% for the ±31°, ±45°, ±55°, ±65° braid angles for the Chamis micro-mechanical model and 5%, 7%, 7%, 5% for the ±31°, ±45°, ±55°, ±65 braid angles respectively for the Lekhnitskii's model, showing the severe effect of crimp in the experimental tube, mostly when compared with Chamis micro-mechanical model. Braided tow unit cell finite element model prediction, showed that tow axial stresses increased with increase in braid angle, while the tow transverse stresses decreased with increase in braid angle. The predictions showed that the tow critical stresses and the tube optimum braided architecture lie between the ±65° and 90° braid angles. The tow critical stresses are the stresses at which the tow decreasing transverse stress and the tow increasing axial stress causes the tube to fail.

The braided rivers and floodplains in the Upper Waitaki Basin (UWB) of the South Island of New Zealand are critical habitats for endangered and threatened fauna such as the black stilt. However, this habitat has degraded due to introduced predators, hydropower operations, and invasive weeds including Russell lupins. While conservation efforts have been made to restore these habitats, flood events may provide a natural mechanism for removal of invasive vegetation and re-creation of natural floodplain habitats. However, little is understood about the hydraulic effects of floods on vegetation and potential mortality in these dynamic systems. Therefore, this thesis analyzed the flood-induced processes that cause lupin mortality in a reach of the Ahuriri River in the UWB, and simulated various sized flood events to assess how and where these processes occurred. To determine the processes that cause lupin mortality, post-flood observations were utilized to develop the hypothesis that flood-induced drag, erosion, sediment deposition, inundation, and trauma were responsible. Field and laboratory experiments were conducted to evaluate and quantify these individual processes, and results showed that drag, erosion, sediment deposition and inundation could cause lupin mortality. Utilizing these mortality processes, mortality thresholds of velocity, water depth, inundation duration, and morphologic changes were estimated through data analysis and evaluation of various empirical relationships. Delft3D was the numerical model used to simulate 2-dimensional flood hydraulics in the study-reach and was calibrated in three stages for hydraulics, vegetation, and morphology. Hydraulic calibration was achieved using the study-reach topography captured by Structure-from-Motion (SfM) and various hydraulic data (depth, velocity, and water extent from aerial photographs). Vegetation inclusion in Delft3D was possible utilizing a function called ‘trachytopes’, which represented vegetation roughness and flow resistance and was calibrated utilizing data from a lupin-altered flow conveyance experiment. Morphologic calibration was achieved by simulating an observed near-mean annual flood event (209 m3 s-1) and adjusting the model parameters until the simulated morphologic changes best represented the observed morphologic changes captured by pre- and post-flood SfM digital elevation models. Calibration results showed that hydraulics were well represented, vegetation inclusion often improved the simulated water inundation extent accuracy at high flows, but that local erosion and sediment deposition were difficult to replicate. Simulation of morphological change was expected to be limited due to simplistic bank erosion prediction methods. Nevertheless, the model was considered adequate since simulated total bank erosion was comparable to that observed and realistic river characteristics (riffles, pools, and channel width) were produced. Flood events ranging from the 2- to 500-year flood were simulated with the calibrated model, and lupin mortality was estimated using simulation results with the lupin mortality thresholds. Results showed that various degrees of lupin mortality occurred for the different flood events, but that the dominant mortality processes fluctuated between erosion, drag, and inundation. Sediment deposition-induced mortality was minimal, but was likely under-represented in the modeling due to poor model sediment deposition replication and possibly over-restrictive deposition mortality thresholds. The research presented in this thesis provided greater understanding of how natural flood events restore and preserve the floodplain habitats of the UWB and can be used to aid current and future braided river conservation and restoration efforts.

The purpose of this study was to determine the relationship between prekindergarten classroom quality indicators and student achievement at the prekindergarten level. Pre-existing data on prekindergarten classroom quality measures and student achievement was utilized. Quality indicators were assessed using the Classroom Assessment Scoring System (CLASS) (Pianta, La Paro, & Hamre, 2008) and student achievement was measured by the end of year results on the Phonological Awareness Literacy Screening (PALS) (Invernizzi, Meier, Swank, & Juel, 2004) and the Bracken School Readiness Assessment end of year results (Bracken, 2007). A quantitative ex post facto correlational research design was employed to identify relationships between program quality and student achievement among the prekindergarten classrooms. An ex post facto design was chosen because the circumstances of conducting the research did not allow for an experiment. The classrooms in this study site were rated overall as high in quality. The findings indicate that quality in classrooms established by high scores in the Emotional Support and Classroom Organizational domains, paired with scores in the middle to high range in the Instructional Support domain have no statistical correlation between high achievement related to PALS and Bracken scores, with the exception of one subgroup. For students that receive Public Assistance, there was a statistical significance in their end results for PALS and Bracken, indicating a positive relationship between classroom quality and student achievement. It is vitally important to develop prekindergarten programs that can be easily replicated. Replicating successful programs would save time, money, and effort. Practitioners can increase and standardize structural quality factors such as length of day, credentialing requirements of staff, and the maintenance of an organized system of in-service training and systematic curriculum oversight, while ensuring the presence of process quality, This focus will create prekindergarten programs that offer the most at risk students the highest quality possible.

The wandering river pattern represents one of the last remaining river patterns that are not well understood. Many aspects of these rivers are not well known, particularly the processes of their creation and maintenance. The term wandering describes gravel or cobble bedded rivers, transitional between braided and meandering, with multiple channel sections around semi-permanent islands connected by single channel sections. This dissertation investigates the controls on the characteristics of wandering rivers within the Miramichi region of New Brunswick through time and at three nested spatial scales. / At the scale of rivers, three factors appear to be needed for wandering to occur: (1) wide valleys, (2) channel energy between braiding and meandering, and (3) avulsion triggers, frequent overbank flows caused by icejams in the Miramichi. Principal component analysis showed that larger wandering rivers displayed greater anabranching intensity than smaller rivers, perhaps related to higher stage ice jams within larger rivers. / At the scale of channels, the wandering pattern of the Renous River was found to be in a state of dynamic equilibrium, with channel creation balanced by channel abandonment. The anabranch cycle model was developed to illustrate the temporal dynamics of anabranch creation, maintenance and abandonment within wandering rivers. / Also at the channel scale, principal component analysis of channel reaches within the Renous River displayed differences in grain size and hydraulic efficiency between side-channels and main-channels. Energy and sediment mobility within side-channels was related to their formation, maintenance and abandonment. Energy and sediment mobility within main-channels was related to mega bedforms called bedwaves. The apex of some bedwaves occurred at diffluences. / At the scale of channel elements, diffluences are stable where a large bar is formed and accretes upstream, creating a large reservoir of sediment upstream of anabranch channels to buffer their degradation. Where diffluences are unstable, a large bar forms within one anabranch channel to partially block flow and may cause its abandonment. The dissertation illustrates that within wandering rivers, processes occurring at multiple spatial and temporal scales interact to create and maintain the pattern.