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<p>In this work, we tested the ability of an experimental system, involving the use of micropipettes as force transducers, to measure the coefficients of friction of several systems. Using a magnetic pipette puller, the micropipettes were produced by first heating and stretching the glass. The pipettes are then manipulated into an L-shape. This geometry allows one arm to act as the normal force transducer, and the other to act as the lateral force transducer for the purposes of friction measurements. We then analyzed the variation of the friction force of 15 micrometre polystyrene beads in contact with silicon and polystyrene in a fluid environment at increasing velocities. We also measured the variation in friction coefficient of poly(dimethyl siloxane) coated polystyrene beads in contact with a silicon surface. Our results were then compared to known values where possible, and the variation of the friction coefficient with increasing velocity was fit to a known phenomenological model. From our experiments, we have shown that our experimental technique can provide reproducible friction coefficient measurements, and these coefficients vary with velocity in a known manner. These results confirm the ability of micropipettes to act as both normal and lateral force transducers in friction experiments, and that they have the potential to be used in measuring friction coefficients of more complex materials.</p> / Master of Science (MSc)

<p> The performance enhancement of stretch shortening cycle (SSe) contractions has been well documented in the literature. However, the majority of these studies have been performed either on gross human systems for multijointed movements, or in isolated animal muscle studies using in-vitro preparations. This study was designed to apply the principles used for these invitro animal studies to the human system, under conditions that would allow results to be directly associated with a specific muscle or muscle group. Previous investigations by Lynch (1992) and Benoit and Dowling (1995) have supported the use of muscle models to predict elbow flexor torque and sse performance enhancement. The purpose of this study was to use an EMG based muscle model to investigate the possible relationship between sse tasks at different frequencies of elbow flexion-extension and performance enhancement of the elbow flexor muscles. </p> <p> A Hill based muscle model was used to predict elbow flexor torque of seven healthy male subjects (23-40 years of age) under voluntary and stimulated contraction conditions. EMG of the elbow flexors and extensors was recorded from the biceps brachii and triceps respectively. Elbow flexor stimulation was done transcutaneously with a voltage equivalent to a 60% MVe torque; stimulation lasted four seconds at a frequency of 50 Hz. A simulated constant muscle activation torque was also derived from the muscle model for all trials. Externally measured torque was measured using a strain gauge located on a shaft situated along the axis of rotation of the elbow joint. A torque motor was used to drive the forearm (fastened to a manipulandum) at four frequencies of elbow flexion-extension (.58, 1.5, 2.4, and 3.3 Hz) over a range of 162 to 105 degrees of elbow extension. Non-SSe trials were performed at these same velocities and over the same range of motion. Torque was then integrated as a function of joint angle displacement to yield the work produced about the elbow. Passive work was subtracted from all trials. </p> <p> The results indicate that a significant increase in muscle work followed sse tasks as opposed to non-SSe tasks and this increased work was relatively highest at 2.4 Hz. Work about the elbow decreased with increasing frequency of movement for both sse and non-sse conditions. The simulated constant activation muscle model predicted work well for all trials and conditions, indicating muscle model accuracy. The EMG driven model predicted well for all non-SSe trials but significantly underestimated the work for sse tasks, suggesting a decrease in myoelectric activity. This decrease was evidenced by a decrease in average M-wave amplitude with increasing SSe velocity. This study indicates that the contractile component is directly involved in optimizing muscle work during sse tasks and that the performance enhancement of sse tasks may take place at the myofilament and cross-bridge level. </p> / Thesis / Master of Science (MSc)

<p> It is known that high-resistance training induces morphological changes in skeletal muscle. Following a resistance training program, increases in maximum torque generating capacity are observed due to both neural adaptations and hypertrophic gains within the trained muscle. Although it has been established that a muscle hypertrophies due to the addition of myofibrillar proteins through increased protein synthesis, the exact mechanism which stimulates the hypertrophic response is unknown.</p> <p> Previous reports have shown that training in the absence of eccentric contractions generally produces less muscle growth and strength gains, as well as inflicting less damage to the muscle ultrastructure. Likewise, fast eccentric contractions have been shown to increase muscular strength to a greater extent than slow contractions. It has been hypothesized that fast eccentric contractions may maximize muscular damage, thus invoking a greater response of repair mechanisms, including satellite cell recruitment, which would allow an increased addition of contractile proteins to be added to the injured muscle, increasing muscle size and strength to a greater degree.</p> <p> The effect of fast and slow eccentric training was investigated using a bilateral, within subject model. Twelve men trained one arm fast (3.66 rad/s) and one arm slow (0.52 rad/s) for 8 weeks on an isokinetic training apparatus. Type I muscle fibre size increased with training by an average of 9.3±12.0% (P<0.05, main effect for time). Type II muscle fibres increased more in the subjects' fast trained arm when compared to the slow trained arm according to ATPase histochemical analysis (P<0.05, time x condition interaction). Likewise, whole arm cross-sectional area showed that the fast trained arms had an average increase of 6.8±5.5 % whereas the slow arms only had an average increase CSA of 5.1±5.7% (P=0.065, time x condition interaction). Maximum torque generating capacity was also increased to a greater degree (P<0.05, time x condition interaction) in the fast trained arm with an average of 10.3±16.4 Nm, whereas the slow trained arm increased only 7.3±15.0 Nm, across testing speeds. A decrease in the percentage of type IIx fibres was seen in both arms after training according to both ATPase histochemical staining and MHC gel electrophoresis; however, the percentage of type IIa fibre area increased in the fast trained arms (8.4±8.6%) more significantly (P<0.05, time x condition interaction) than the slow trained arms (1.7±10.9%).</p> <p> Seven males were trained in a similar manner to determine the extent of muscle damage which was evaluated by both Z-band streaming and force production decrements. After a single exercise bout of fast eccentric training in one arm and slow eccentric training in the other, it was determined that a 1.97±0.74 areas of moderate Z-band streaming per mm^2 of muscle in the fast exercised arm compared to 0.89±0.79 areas of moderate Z-band streaming per mm^2 of muscle in the slow trained arm (P<0.05). In conclusion, training using fast (3.66 rad/s) eccentric contractions causes a greater degree of muscle damage, hypertrophy, and strength gains than does training with slow (0.52 rad/s) eccentric contractions.</p> / Thesis / Master of Science (MSc)

The literature on stream reaeration was reviewed. A recirculating loop open channel system was desiqned and experiments were performed to study the effects of average stream velocity and temperature on the mass transfercoefficient for oxyqen dissolution into "clean" water. The applicability of the apparatus to the study of the effects of surfactants was also investigated. The velocity ranged from 0.1 to 0.9 ft/sec and the temperature from 5,0 to 25.o0c. The results indicated that the mass transfer coefficient varies approximately linearly with average stream velocity and that the temperature coefficient is a variable which depends on mixinq condHions. Furthermore, it was found that the temperature dependency of the mass transfer coefficient could be expressed as either a linear or power function. Correlations expressing the mass transfer coefficient in terms of easily measurable stream parameters. were developed and compared to those found in the recent literature / Thesis / Master of Engineering (ME)

Yes / In this paper, an analytical model that represents the streamwise velocity distribution for open channel flow with submerged flexible vegetation is studied. In the present vegetated flow modelling, the whole flow field has been separated into two layers vertically: a vegetated layer and a non-vegetated free-water layer. Within the vegetated layer, an analysis of the mechanisms affecting water flow through flexible vegetation has been conducted. In the non-vegetated layer, a modified log-law equation that represents the velocity profile varying with vegetation height has been investigated. Based on the studied analytical model, a sensitivity analysis has been conducted to assess the influences of the drag and friction coefficients on the flow velocity. The investigated ranges of drag and friction coefficients have also been compared to published values. The findings suggest that the drag and friction coefficient values are non-constant at different depths and vegetation densities, unlike the constant values commonly suggested in literature. This phenomenon is particularly clear for flows with flexible vegetation, which is characterised by large deflection.

Upper-tropospheric (200 hPa) velocity potential is useful in identifying areas of rising or sinking atmospheric motions on varying temporal scales (e.g., weekly, seasonal, interannual) especially in the global tropics. These areas are associated with enhancement (rising motion) or suppression (sinking motion) of tropical convection and subsequent weather phenomena dependent on these processes (e.g., tropical cyclones). This study employed three commonly used global weather reanalysis datasets (NCEP/NCAR Reanalysis 1, JMA JRA-55, ECMWF ERA5) to calculate and compare upper-tropospheric velocity potential fields on varying temporal scales and quantify any differences that existed between them from 1958 to 2020 over four key regions of variability (Equatorial Africa, Amazon Basin, Equatorial Central Pacific, and Equatorial Indonesia). To supplement this analysis, the highly correlated variables to velocity potential of outgoing longwave radiation (OLR) and daily precipitation rate were used and directly compared with independent OLR and precipitation datasets to determine the reanalysis' level of agreement with the independent data. The ECMWF ERA5 held the highest agreement to these data over all regions examined and was reasoned to have the highest confidence in capturing the variability of upper-tropospheric velocity potential fields for the study period. Confidence was decreased in the usefulness of the NCEP/NCAR Reanalysis 1 as it consistently performed poorly over much of the study domain. The results of this study also emphasized the usefulness in ensemble-based approaches to assessing climate variability and understanding potential biases and uncertainties that are inherent in the data sources. / Master of Science / Historical weather data across the globe is analyzed using global weather reanalysis datasets which provide the most complete picture of how the atmosphere has evolved over the course of the last several decades. This data is a vital component in today's research investigating climate change and variability over time. This study examined how the history of upper-tropospheric velocity potential was captured in three commonly used global weather reanalysis datasets (NCEP/NCAR Reanalysis 1, JMA JRA-55, ECMWF ERA5) from 1958 to 2020 over four key regions of variability (Equatorial Africa, Amazon Basin, Equatorial Central Pacific, and Equatorial Indonesia). The variable of velocity potential is useful in identifying areas of rising or sinking atmospheric motions on varying time scales (e.g., weekly, seasonal, interannual) especially in the global tropics. These areas are associated with enhancement (rising motion) or suppression (sinking motion) of tropical convection (i.e., thunderstorms) and subsequent weather phenomena dependent on these processes (e.g., tropical cyclones). The analysis conducted found that the newest of the reanalysis datasets, the ECMWF ERA5, held the highest agreement to independent weather observations over all regions examined was reasoned to have the highest confidence in capturing the variability of upper-tropospheric velocity potential fields for the study period. Confidence was decreased in the usefulness of the NCEP/NCAR Reanalysis 1, the oldest of the reanalysis datasets, as it consistently performed poorly over much of the study domain. The results of this study also emphasized the usefulness in ensemble-based approaches to assessing climate variability and understanding potential biases and uncertainties that can be found in the data sources.

Turbulence research in the laboratory has confirmed the existence of quasi-coherent structures amidst the chaos of a turbulent boundary layer. It has been observed that a quasi-periodic phenomena called “bursting” accounts for a major contribution to the turbulent Reynolds stress and the production of turbulent kinetic energy. Bursting is the term used for a sequence of events, where a low-speed streak of fluid from the near wall region lifts away from the wall, slowly at first, and then rapidly moves away from the wall as it convects downstream where it becomes unstable and breaks up violently upon interaction with the outer flow. This ejection of low speed fluid into the mean flow is responsible for locally high values of turbulent kinetic energy. Although a great deal is known about these structures in laboratory flows, little has been done to investigate if such structures are universal in turbulent flows, i.e., their existence in large Reynolds number flows such as the turbulent air flow over the ocean. It would seem, intuitively, that such structures, if present in the marine atmospheric boundary layer, would play a major role in the transfer of momentum, mass and heat across the air-sea interface. It is speculated that these motions may also be associated with large scale organized motions in wall bounded turbulent shear flows. The effort aimed at elucidating the physics underlying such structures would be invaluable in contributing to our understanding of the air-sea flux mechanism. In this dissertation, standard ejection detection schemes like the quadrant, the VITA and the modified u-level techniques have been applied to turbulent wind data measured over the ocean to confirm the existence of burst like structures. The proportions of contributions to the Reynolds stress from the four quadrants of the u’w’ plane are in close agreement with the corresponding contributions for a laboratory flow. Ejection detection followed by the grouping of ejections into bursts yielded a mean burst period of 47 s, at a height of 8.2 m above the water surface, where the mean wind velocity was 6.74 m/s. This burst period corresponds well with the peaks obtained from the autocorrelation of the streamwise velocity signal and the first moment of the stress spectrum, confirming the quasi-periodic nature of this phenomena. Furthermore, phase averages of these events show a structure which is similar to the structure of events detected in laboratory flows. The ejection periods are seen to decrease with increasing wind speed. The burst periods decrease at first with increasing wind speed and then appear to attain a constant value after a wind speed of 6-7 m/s. This has been attributed to the breakdown of the grouping algorithm at higher wind speeds. Ejection and burst frequencies exhibit no discernible dependence on the surface wave field. Ejection and sweep motions have been studied at various length scales. The original velocity signal is bandpass filtered for various frequency bands. For each band, the percentage contributions to the Reynolds stress from the quadrants of the u'w’ plane are close to the corresponding quadrant contributions of the other bands. This indicates similar turbulence structure at different scales. The velocity signals for each band have been normalized by their root mean square (RMS) value. Visualizing the signals on nondimensional time shows the signals from each band to be very similar. These results can also be interpreted as evidence for the ejection and sweep motions existing simultaneously at different scales, indicating the fractal nature of these events. Large scale motions, which appear to be associated with ejection and sweep motions, have been identified in the marine atmospheric surface layer using velocity probe measurements at multiple heights. Visualizing these velocity signals suggests that the organized features extend across the depth of the surface layer. Converting the temporal signals to spatial fluctuations suggests that these structures are inclined at an angle while convecting downstream. The inclination angle near the surface (z < 18 m) is approximately 15° and it increases with increasing height to about 45° when z = 45 m. The spatial velocity fluctuations also indicate that these organized features may be large transverse vortical arches. / Ph. D.

This study focuses on deposition processes from sediment laden buoyant river plumes in deltaic regions. The goal is to experimentally examine the effects of various physical phenomena influencing the rate at which sediment is removed from the plume. Previous laboratory and field measurements have suggested that, at times, sedimentation can take place at rates higher than that expected from individual particle settling (i.e., C{W}_{s}). Two potential drivers of enhanced sedimentation are flocculation and interfacial instabilities. We experimentally measured the sediment fluxes from each of these processes using two sets of laboratory experiments that investigate two different modes of instability, one driven by sediment settling and one driven by fluid shear. The settling-driven and shear-driven instability sets of experiments were carried out in a stagnant stratification tank and a stratification flume respectively. In both sets, continuous interface monitoring and concentration measurement were made to observe developments of instabilities and their effects on the removal of sediment. Floc size was measured during the experiments using a separate floc camera setup and image analysis routines. Results from the stratification tank experiments suggest that the settling-driven gravitational instabilities do occur in the presence of flocs, and that they can produce sedimentation rates higher than those predicted from floc settling. A simple cylinder based force balance approach adopting the concept of critical Grashof number was used to develop a model for the effective settling velocity under settling-driven instabilities that is a function of sediment concentration in the plume only. Results from the stratification flume experiments show that under shear instabilities, the effective settling velocity is greater than the floc settling velocity, and increases with plume velocity and interface mixing. The difference between effective and floc settling velocity was denoted as the shear-induced settling velocity. This settling rate was found to be a strong function of the Richardson number, and was attributed to mixing processes at the interface. Conceptual and empirical analysis shows that the shear-induced settling velocity is proportional to U{Ri}^{-2}. Following the experiments, analyses were made among contributions of different mechanisms on the total deposition rate, and the locations that the various mechanisms may be active in the length of a plume. This analysis leads to a conceptual discretization of a plume into three zones of sedimentation behavior and Richardson number. The first zone is the supercritical near-field plume with intense interface mixing. Zone two represents the subcritical region where interface mixing still occurs, and zone three is the high Richardson number zone where mixing at the interface is effectively nonexistent. In zones one and two, individual floc settling and shear-induced settling mechanisms play the major roles in removing sediment from the plume. While, shear-induced settling rate was found to be maximum near the river mouth, its share of the total settling rate increases in the crossshore direction, since sand and large particulates deposit near the inlet and only small particles (with relatively low settling velocity) remain as the plume propagates. The third zone, starts when the interfacial mixing diminishes and leaking commences. / Ph. D.

No / Vegetation remains to be an important factor that can hinder the river flow. It needs innovative management scheme, in order to adapt these changes and ensure sustainability of their multiple usages. Vegetation plays an important role in floods and droughts adaptation within river system to alleviate any flood that may propagates from river to its surrounding. Vegetation within river can also retard its flow to cause building-up of deposition, and further adding to uncertainty of water use under extreme droughts. Due to these, it is important to study and understand vegetation drag behaviour toward flow in order to prevent flood risk and water security with hydrological drought in the basin and any other negative impact caused by it. In this study, an analytical approach for river flooding has been studied by improved representation of drag coefficient CD in flow velocity distribution modelling. The analysis of flow parameters, i.e. Reynolds number, on the drag coefficient CD has been conducted. The presented model has been used and analysed in open channel flows with flexible vegetation. In modelling, the flexible vegetated channel layers were divided into vegetation, top of vegetation and water layer zones in the model. The balance of forces for each layer has been established by validation using different reported measured data. The modelling results showed reasonably corresponding prediction of velocity profile in flows with flexible vegetation.