Robert Edward Shadwick

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Mechanics and Energetics of Rorqual Lunge Feeding (2010)

No abstract available.

Master's Student Supervision (2010 - 2018)
A comparative morphometric analysis of the sensory hair cells of the cochleas of echolocating mammals (2018)

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

View record

Determining the effects of sediment deposition on the growth, survival, and foraging efficiency of the endangered Nooksack dace (Rhinichthys cataractae sp. cataractae), and on the abundance, distribution, and community structure of their invertebr... (2016)

Alterations to riverine habitats from the excessive deposition of sediments present a challenge for the effective management and conservation of aquatic resources and endangered species. The Nooksack dace (Rhinichthys cataractae sp. cataractae) is an endangered, benthic riffle-dwelling specialist, which is threatened by sediment-induced habitat changes. The purpose of my thesis was twofold. First, using semi-natural streamside channels I experimentally tested how different levels of embeddedness and percentages of fine sediments
View record

How to make a tuna burst : the role of angle of attack in the production of thrust (2016)

Tuna—along with whales and lamnid sharks—utilise thunniform locomotion, a mode of swimming that optimises efficiency at high speed and isolates thrust production to the caudal fin. Thunniform performance is controlled by adjustments in the way the caudal fin interacts with fluid flow which, in turn, determines thrust and efficiency. The effect of tail motion on performance provides insight into the link between locomotor muscle biomechanics and hydrodynamics; these insights can be used to mimic and optimise animal motion in a robotic context. This study focuses on how the maximum angle of attack (α_max), contributes to tuna cruising and bursting, and the corresponding effects on fluid flow. I hypothesise that cruising tuna do not adjust α_max to modulate thrust but instead vary amplitude via Strouhal number. I also hypothesise that α_max affects thrust by changes in vorticity shed by the tail. To study these phenomena, I constructed a tuna tail model 3-D printed from CT scan data of a tuna tail. I then oscillated this model in a water tunnel across a range of biologically relevant motions. I calculated thrust and efficiency from direct measurements of force and torque and then used ink-flow visualisation and particle image velocimetry to reveal the resulting flow structures. The results indicate that the efficiency optimum of α_max peaks around 15° with the thrust optimum beyond 30°. Mechanistically, an increase of α_max increases the magnitude of the resultant force but angles it to the side, increasing the amount of wasted lateral energy. Increasing α_max increases the size and strength of shed vortices eventually causing shedding of an additional leading edge vortex at midstroke. These results, paired with red muscle work loop data, suggest that during cruise the α_max undergoes minimal variation, and suggest that in order to take advantage of the additional thrust that high values of α_max provide, white burst muscles need to advance peak force timing. In addition to contributing to a better understanding of the hydrodynamics of swimming and the associated musculature, these results also offer insight into the field of biomimetics and the construction of fish-mimicking robots such as AUVs.

View record

Woodpeckers and the biomechanics of concussion (2014)

Woodpeckers are a remarkable clade of birds commonly known to use forceful blows of their beaks to drill holes in trees while foraging for boring insects or sap, and they also use their beaks to excavate nest cavities and loudly announce their territory by drumming. They regularly tolerate forces ten times greater than those that would give a human a concussion.Human concussions are the focus of a lot of attention and research efforts recently, especially in the world of sports and veteran's affairs where head injury's debilitating effects on immediate and long-term health are becoming more recognised. Woodpeckers are good organisms to study to gain insights into concussions.Many factors have been proposed to contribute to the woodpeckers’ ability to withstand the blows to its head. Some hypotheses are more likely than others, but the topic suffers from a lack of data. This thesis addresses the hypothesis that the brain is semi-isolated from the forces experienced by the rest of the head, and the hypothesis that woodpeckers have minimal space between their brains and skulls, and minimal cerebrospinal fluid.We used high-speed video analysis of wild captured Pileated Woodpeckers to evaluate whether there was any evidence that the brain case is semi-isolated from the rest of the woodpecker’s head. The acceleration profiles of points on the head and on the beak were not significantly different, and the distances between the head point and the beak point before and after a strike also were not significantly different. We used CT and MRI scans to visualize and measure the space between the brain and skull. The space was quantified and was not smaller than might be expected once scaling between a human’s head and a woodpecker’s head was taken into account. We conclude that woodpeckers’ resistance to head injury is not likely due to force deflection away from the brain, or especially tight packing of the brain, and hypothesize that it is due to scaling effects, a short impact duration, woodpeckers’ smooth brain, and possible neuroprotective mechanisms.

View record

Performance of thunniform propulsion : a high bio-fidelity experimental study (2013)

Tunas, lamnid sharks and whales are some of the fastest sustained swimming animals. To propel themselves these animals use the thunniform propulsion mode, and are physically characterized by having streamlined bodies with narrow necking of the caudal peduncle and a high aspect ratio lunate tail generating lift-based thrust. For these reasons, thunniform propulsion has received considerable attention from biologists and bio-inspired engineers. Thunniform propulsion is assumed to have the highest propulsive performance of all swimming modes, meaning high propulsive efficiency at fast swimming speeds. However, there is no direct empirical evidence to support this common idea, due to the difficulty of obtaining force measurements for these animals. Therefore, indirect approaches are used, such as theoretical and experimental studies. But these experiments oversimplify the animal (motion, shape or material property) and/or the flow condition. Our goal was to assess the propulsive performance of the Atlantic bluefin tuna, Thunnus thynnus, which is our case study for thunniform propulsion, by an experimental approach of the highest bio-fidelity currently performed. A computed tomography scanner and a polyjetTM 3-Dimensional printer were used to make three tail models: two with materials of similar properties to the caudal fin, and one of uniform stiffness. Each model was actuated in a water tunnel by a computer controlled, motorized system to follow motion paths typical for a tuna. Propulsive efficiencies and thrust coefficients were calculated from force and torque measurements. Flow structures were visualized by means of particle image velocimetry (PIV). For the 30 motion regimes the mean thrust over a tail-beat was positive. About half of those generated sufficient thrust to counter the whole body drag estimates (CT ≥0.19). Propulsive performance trends and values were similar for all our tail models and to previous experiments investigating a similar parametric space, where the peak propulsive performance was observed for all tail models and hydrofoils at Sttip =0.35 and α_max =20º. The average peak propulsive performance for the tail models was ηp =0.43 and CT =0.3. As with recent studies, we conclude propulsive performance is more sensitive to kinematics rather than the shape and bending behavior of the caudal fin.

View record

Stiffness of mouse aortic elastin and its possible relation to aortic media structure (2013)

Aortic elastin allows arterial expansion on systole and subsequent elastic recoil during diastole, providing crucial capacitance and associated dampening of the cardiac pressure pulses. The structure and mechanical properties of the aortic wall are not uniform along its length due to the varying hemodynamic conditions to which it is exposed, but elastin’s contributions to this variation are not well studied. The artery wall is a composite of two main structural proteins: elastin and collagen. Autoclaving an intact aorta removes the collagen and produces a mechanically competent vessel consisting of purified elastin, which can be used to study elastin’s contribution to arterial mechanics. Although it is generally assumed that elastin’s material stiffness is constant, a recent study in pigs found that it increased 30% along the thoracic aorta. I hypothesized that this increase in elastin stiffness was caused by a difference in the amount of elastin, the amount or orientation of the interlamellar elastin fibres (IEL), the partitioning of elastin between its three forms, the thickness or orientation of the elastic lamellae, or the number of elastin struts. Uniaxial tensile testing of autoclaved mouse aortas showed that elastin’s stiffness is 43% lower in abdominal aortas compared with thoracic aortas, allowing the mouse aorta to be used as a model to investigate this surprising variation in elastin stiffness. Elastin structure within the thin mouse aortic walls was imaged with multiphoton laser scanning microscopy to identify any differences in the elastin structure that could cause the variation in stiffness. No difference was found between the elastin structure of the thoracic and abdominal aortas that could account for the difference in elastic modulus; however, I was not able to count the elastin struts or measure the elastin fibre packing density in the elastic lamellae and so could not reject these two hypotheses.

View record

Katsuwonus pelamis : a case study in thunniform propulsion (2011)

Thunniform propulsion is considered a case study in convergent evolution. Independently derived at least four times (whales, lamnid sharks, tunas and ichthyosaurs) it is characterized by uniquely high lift based thrust and efficient performance. As such it has been the focus of a great deal of study from not only biologists but engineers and physicists as well. Unfortunately direct physical measurement of this phenomenon is notoriously difficult to obtain. Therefore the majority of the research on the topic so far has consisted of either theoretical modeling or experimental testing with low bio-fidelity.The purpose of this study was to create a test apparatus that would more accurately mimic thunniform propulsion as seen in the study organism skipjack tuna (Katsuwonus pelamis). Such factors as motion parameters and swimming speeds as well as caudal fin size, shape and material properties were all taken into account and matched with in-vivo measurements. Instantaneous lateral and in-flow force measurements were taken throughout testing over a range of motion regimes.Overall, general motion parameter requirements for thrust generation were determined and quantified. Thrust production, of up to 0.42 N with a coefficient of thrust of approximately 0.2, was found to be in line with whole body drag estimates at tested conditions. Efficiency measurements however, were found to be extremely low (max of 35%) when compared to estimates in the literature of up to 90%. Quasi-static analysis was also conducted and shown to under-predict true thrust values by approximately 50%. A maximum coefficient of lift value was found to be approximately 0.55 at an angle of attack of 25° using this method.

View record

On the filtration mechanisms and oral anatomy of lunge-feeding baleen whales (2011)

Here we endeavoured to quantify the filtration mechanics of rorquals and the material properties of baleen “gums” (termed zwischensubstanz) by examining and testing the baleen of a fin whale (Balaenoptera physalus). It was hypothesized that fin whales use cross-flow filtration to filter krill from engulfed seawater such that krill and other debris do not become entangled in the baleen fringes. Cross-flow filtration was proposed as an alternate mechanism to dead-end sieving since it would create a highly concentrated suspension of krill inside the mouth (potentially at the oesophageal opening) and would also not require krill to contact the baleen, eliminating clogging and filtering efficiency losses.We tested filtration mechanisms by placing a sixty-two centimetre section of baleen from a fin whale in a circular water tank and imitating the whale’s environment through various flow scenarios and setups. It was not conclusively determined whether cross-flow filtration is the mechanism used by fin whales, but a new mechanism was proposed called centripetal filtration in which two slugs of water spiral anteriorly on the left and right side of the whale’s oral cavity. Further examination of this proposed mechanism is required.The material properties of the zwischensubstanz that holds baleen plates together and the development of baleen plates through this zwischensubstanz were also examined. Zwischensubstanz exhibits isotropic properties similar to soft rubber in compression with an average Young’s modulus of 2.56 ± 0.60 MPa and 44.4 ± 2.4% hysteresis when compressed at 0.5 Hz, as it appears to space the baleen plates and absorb stresses translated from the plates. Through this rubbery zwischensubstanz, the baleen plates develop from conical papillae to hard, keratinized plates. The zwischensubstanz forms a matrix around the papillae and is calcified and keratinized before exiting the zwischensubstanz as a fully developed plate.The discoveries made here with regard to centripetal filtration and the properties of zwischensubstanz are preliminary attempts at quantifying baleen whale filtration and its associated feeding structures. Such work has been rare in the literature and there are many questions left to be answered by eager scientists with regard to the greatest biomechanical event in the world.

View record

The mystery of the whelk egg capsule protein : electrospinning, mechanical testing, and being outsmarted by an invertebrate (2010)

Whelks are carnivorous marine snails known for their elaborate and durable egg capsules. The mechanically complex capsules have been previously studied, and shown to have mechanical behaviour similar to keratin. The mature protein has an initial stiff linear elastic region at low strain, followed by a rubbery yield region with a fully repeatable order of magnitude decrease in stiffness. The material properties of the protein mature in distinct stages, with long-range elasticity developing first, followed by the development of the stiff Hookean region. As the capsule matures, it is massaged by a gland in the foot of the snail, which probably enables cross-linking. This study sought to mimic the development process using electrospinning to create fibres with charge-based assembly, then adding a cross-linking step to encourage the stiff spring behaviour to form. An electrospinning protocol was developed and parameters were optimized. The technique was applied successfully, and the resulting protein nanofibres could be cross-linked. The electrospun protein fibres were shown to have composition and secondary structures similar to the native protein. However, the mechanical properties of the cross-linked nanofibres were more similar to a transitional stage in the egg capsule’s maturation sequence than they were to the mature capsule. The fibres did not exhibit the bimodal behaviour seen in the native polymer.

View record

 

Membership Status

Member of G+PS
View explanation of statuses

Program Affiliations

Department(s)

 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.