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Vid konstruktion av flygplan uppkommer svårigheter att efterlikna de tänktadriftsförhållandena vid vindtunnelprovning av mindre skalmodeller. Dessa svårigheter berorfrämst på att ekonomiska och skalbara begränsningar gör att tillräckligt stora vindtunnlar intekan byggas för att generera de strömningshastigheter som ger samma Reynoldstal som för detänkta driftsförhållandena. För att komma runt detta problem kan så kallade störelementanvändas vilka inducerar en övergång mellan laminär och turbulent strömning i skalmodellensgränsskikt och möjliggör vindtunnelprovning i lägre strömningshastigheter. Detta arbete ämnardärför att ta fram ett kostnadseffektivt och flexibelt designkoncept för störelement ämnade förvindtunnelprovning av en skalmodell. Under arbetets gång undersöktes olika typer avstörelement som sedan togs fram med hjälp av CAD och additiv tillverkning. Dessa testadessedan på en skalmodell i en vindtunnel i syfte att hitta anfallsvinkeln för vilken skalmodellenöverstegrade. Mätdata jämfördes sedan med tidigare simuleringar gjorda för skalmodellen ochslutsatsen som drogs var att de framtagna störelementen hade en otillräcklig förmåga i att fåskalmodellen att överstegra, men att ytterligare modifikation av störelementens höjd och breddskulle göra modellering i CAD och additiv tillverkning till ett attraktivt framtagningskonceptför störelement ämnade för vindtunnelprovning av en skalmodell.

Vid konstruktion av flygplan uppkommer svårigheter att efterlikna de tänktadriftsförhållandena vid vindtunnelprovning av mindre skalmodeller. Dessa svårigheter berorfrämst på att ekonomiska och skalbara begränsningar gör att tillräckligt stora vindtunnlar intekan byggas för att generera de strömningshastigheter som ger samma Reynoldstal som för detänkta driftsförhållandena. För att komma runt detta problem kan så kallade störelementanvändas vilka inducerar en övergång mellan laminär och turbulent strömning i skalmodellensgränsskikt och möjliggör vindtunnelprovning i lägre strömningshastigheter. Detta arbete ämnardärför att ta fram ett kostnadseffektivt och flexibelt designkoncept för störelement ämnade förvindtunnelprovning av en skalmodell. Under arbetets gång undersöktes olika typer avstörelement som sedan togs fram med hjälp av CAD och additiv tillverkning. Dessa testadessedan på en skalmodell i en vindtunnel i syfte att hitta anfallsvinkeln för vilken skalmodellenöverstegrade. Mätdata jämfördes sedan med tidigare simuleringar gjorda för skalmodellen ochslutsatsen som drogs var att de framtagna störelementen hade en otillräcklig förmåga i att fåskalmodellen att överstegra, men att ytterligare modifikation av störelementens höjd och breddskulle göra modellering i CAD och additiv tillverkning till ett attraktivt framtagningskonceptför störelement ämnade för vindtunnelprovning av en skalmodell.

Humans and other biological bipedal walkers are extraordinarily agile and robust. This is especially apparent when certain features of the environment are unknown such as unexpected downsteps (for example, suddenly walking off the side-walk or not expecting the last stair when descending). Humans can negotiate these downsteps ---both expected and unexpected--- with remarkable agility and ease. The contributions from active compensation, passive dynamics, and reflexes that humans employ to overcome these downsteps are however not inherently present in bipedal robots. This motivates us to assess whether externally observed behavior can be used to achieve the same capabilities in bipedal robots. One of the challenges with this proposal is the morphological differences between humans and robots. Taking the bipedal robot Cassie as an example, these differences predominantly constitute to overall- and segment mass, leg morphology, and a lack of an upper body. The observed behavior from the human should subsequently be scaled to represent an appropriate nominal and compensatory behavior of the robot. This thesis aims to systematically study the translation of this human behavior to bipedal walking robots, regardless of the morphology of the walkers. We start from human experimental data where nominal walking, expected downstep, and unexpected downstep trials were conducted. The human data is analyzed from the perspective of a reduced-order representation of the human. The reduced-order representation encodes the center of mass dynamics and contact forces. An equivalent reduced-order model is used to represent the bipedal robot, which allows for the translation of the nominal walking and downstep behaviors between human and robot. The morphological differences between the human and the robot are therefore resolved by realizing dynamically equivalent behavior which is embedded into the full-order dynamics of a bipedal robot via optimization-based controllers. The re, Mechanical Engineering

Humans and other biological bipedal walkers are extraordinarily agile and robust. This is especially apparent when certain features of the environment are unknown such as unexpected downsteps (for example, suddenly walking off the side-walk or not expecting the last stair when descending). Humans can negotiate these downsteps ---both expected and unexpected--- with remarkable agility and ease. The contributions from active compensation, passive dynamics, and reflexes that humans employ to overcome these downsteps are however not inherently present in bipedal robots. This motivates us to assess whether externally observed behavior can be used to achieve the same capabilities in bipedal robots. One of the challenges with this proposal is the morphological differences between humans and robots. Taking the bipedal robot Cassie as an example, these differences predominantly constitute to overall- and segment mass, leg morphology, and a lack of an upper body. The observed behavior from the human should subsequently be scaled to represent an appropriate nominal and compensatory behavior of the robot. This thesis aims to systematically study the translation of this human behavior to bipedal walking robots, regardless of the morphology of the walkers. We start from human experimental data where nominal walking, expected downstep, and unexpected downstep trials were conducted. The human data is analyzed from the perspective of a reduced-order representation of the human. The reduced-order representation encodes the center of mass dynamics and contact forces. An equivalent reduced-order model is used to represent the bipedal robot, which allows for the translation of the nominal walking and downstep behaviors between human and robot. The morphological differences between the human and the robot are therefore resolved by realizing dynamically equivalent behavior which is embedded into the full-order dynamics of a bipedal robot via optimization-based controllers. The re, Mechanical Engineering

For the purpose of fully and systematically observe, research and optimize the U-sharp ventilation system in Vilafruns mine, a simulation model based on the principles of geometric, kinematic and dynamic similarity is stablished in the simulation laboratory. By simulating a U-shape ventilation network, the air volume distribution and wind velocity in different sections of the model were measured and compared with practical data obtained in Vilafruns mine. Results show that the lowest wind velocity in the models is higher than 0,42 m/s, thus it is in a turbulent flow state, which satisfies the kinematical and dynamic similarity principles. The characteristic of air volume distribution and wind velocity in Vilafruns mine are basically simulated by the experimental model through the obtained data and figures, which reflects the establishment of the model is correct and successful, and the experimental data is accurate and reliable. Moreover, this model provides useful references for the selection of mine ventilation types and for the optimization of the existing ventilation network., Peer Reviewed, Postprint (published version)

With the United States? push towards using unmanned aerial vehicles (UAVs) for more military missions, wide area search theory is being researched to determine the viability of multiple vehicle autonomous searches over the battle area. Previous work includes theoretical development of detection and attack probabilities while taking into account known enemy presence within the search environment. Simulations have been able to transform these theories into code to predict the UAV performance against known numbers of true and false targets. The next step to transitioning these autonomous search algorithms to an operational environment is the experimental testing of these theories through the use of surrogate vehicles, to determine if the guidance and control laws developed can guide the vehicles when operating in search areas with true and false targets. In addition to the challenge of experimental implementation, dynamic scaling must also be considered so that these smaller surrogate vehicles will scale to full size UAVs performing searches in real world scenarios. This research demonstrates the ability of a given sensor to use a basic ATR algorithm to identify targets in a search area based on its size and color. With this ability, the system's target thresholds can also be altered to mimic real world UAV sensor performance., The original document contains color images.

In an open channel, the transition from super- to sub-critical flow is a flow singularity (the hydraulic jump) characterised by a sharp rise in free-surface elevation, strong turbulence and air entrainment in the roller. A key feature of the hydraulic jump flow is the strong free-surface aeration and air-water flow turbulence. In the present study, similar experiments were conducted with identical inflow Froude numbers Fr1 using a geometric scaling ratio of 2:1. The results of the Froude-similar experiments showed some drastic scale effects in the smaller hydraulic jumps in terms of void fraction, bubble count rate and bubble chord time distributions. Void fraction distributions implied comparatively greater detrainment at low Reynolds numbers yielding some lesser aeration of the jump roller. The dimensionless bubble count rates were significantly lower in the smaller channel, especially in the mixing layer. The bubble chord time distributions were quantitatively close in both channels, and they were not scaled according to a Froude similitude. Simply the hydraulic jump remains a fascinating two-phase flow motion that is still poorly understood.

This report presents an alternative method whereby the anti-plane strain equations of elastodynamics, for which the boundary conditions are of mixed type, may be integrated. The method exploits the similarity property of the solution through the use of integral transforms together with Riemann-Hilbert theory. As an application, the transient stress field around a semi-infinite crack is obtained for a homogeneous material and for a bimaterial; the dynamic stress concentration factor for each case is extracted. (Author)

The shape of the wind and temperature profiles in the surface boundary layer of the atmosphere for thermally stratified flow is presented as dimensionless parameters. The development of the hypothesis follows dynamic similarity as applied to the atmosphere near the earth's surface. The approach used for thermally stratified unstable flow assumes the scaling ratio, z/L, is numerically equivalent to the gradient Richardson number, Ri. In stable air, z/L is taken as a function of Ri. The Richardson number is considered to be the sole controlling parameter of similarity in the surface boundary layer over a large stability range from approximately Ri = -5.0 to Ri = 0.204. A Richardson number of 0.204 is taken to be the nominal critical value at which turbulence experiences a complete decay and denotes the onset of undulance. (Author)