Further developments in simple total energy sensors

A simple total energy probe concept using principles of laminar flow around a cylinder and pressure distribution is reviewed and flow fields around cylinders normal to and inclined to the flow are described. A variety of bent-up probe configurations were tested to explore variations in geometry. Test results are presented on the effects of sensor length, hole location, and angle of sweep. Comparisons are made with other probe tests reported in the literature. Damping restrictors and their use in filtering gusts are summarized. Flow field effects, indicating the variables involved for different mounting locations on aircraft, are discussed

Novel methods of drag reduction for squareback road vehicles

Road vehicles are still largely a consumer product and as such the styling of a vehicle becomes a significant factor in how commercially successful a vehicle will become. The influence of styling combined with the numerous other factors to consider in a vehicle development programme means that the optimum aerodynamic package is not possible in real world applications. Aerodynamicists are continually looking for more discrete and innovative ways to reduce the drag of a vehicle. The current thesis adds to this work by investigating the influence of active flow control devices on the aerodynamic drag of square back style road vehicles. A number of different types of flow control are reviewed and the performance of synthetic jets and pulsed jets are investigated on a simple 2D cylinder flow case experimentally. A simplified ¼ scale vehicle model is equipped with active flow control actuators and their effects on the body drag investigated. The influence of the global wake size and the smaller scale in-wake structures on vehicle drag is investigated and discussed. Modification of a large vortex structure in the lower half of the wake is found to be a dominant mechanism by which model base pressure can be influenced. The total gains in power available are calculated and the potential for incorporating active flow control devices in current road vehicles is reviewed. Due to practicality limitations the active flow control devices are currently ruled out for implementation on a road vehicle. The knowledge gained about the vehicle model wake flow topology is later used to create drag reductions using a simple and discrete passive device. The passive modifications act to support claims made about the influence of in wake structures on the global base pressures and vehicle drag. The devices are also tested at full scale where modifications to the vehicle body forces were also observed

Design and Nonlinear Control of a Haptic Glove for Virtual Palpation

This dissertation presents the design, kinematic analysis, and nonlinear control of a Haptic Glove for medical elastographic imaging virtual palpation. Of the 13 degrees of freedom present in the index finger, middle finger, and thumb of the hand, the design fixes 4, constrains 2 and controls 6 with pneumatic air cylinder actuators, allowing uncontrolled, but measured motion in the remaining 1 degree of freedom. Nearly linear bijective transfer functions between the actuator positions and joint angles are found in closed form for all 6 actuated joints. A nonlinear, sliding-mode controller that allows each actuator to be controlled by a single 5/3 proportional valve is designed and implemented. Test results for typical palpation motions are presented and discussed

Influence of short rear end tapers on the unsteady base pressure of a simplified ground vehicle

Short tapered sections on the trailing edge of the roof, underside and sides of a vehicle are a common feature of the aerodynamic optimization process and are known to have a significant effect on the base pressure and thereby the vehicle drag. In this paper the effects of such high aspect ratio chamfers on the time-dependent base pressure are investigated. Short tapered surfaces, with a chord approximately equal to 4% of the overall model length, were applied to the trailing edges of a simplified passenger car model (the Windsor Body) and base pressure studied via an array of surface pressure tappings. Two sets of configurations were tested. In the first case, a chamfer was applied only to the top or bottom trailing edge. A combination of taper angles was also considered. In the second case, the chamfer was applied to the side edges of the model base, leaving the horizontal trailing edges squared. In all configurations both the base and the slanted surfaces were covered with pressure taps for the entire width to ensure that any asymmetry was captured and two different sampling time were considered (respectively equal to 31.5 s and 630.0 s). The results show the effects produced on the base pressure by the presence of a long period bi-stable behavior, whose characteristics were further investigated by conditional averaging the recorded data and considering the distribution of the rms pressure values recorded over the entire model base

Fuel from straw: an in-field briquetting process

Disposal of large quantities of surplus straw, which lie in the fields after harvest, is a major annual problem to cereal farmers. The current preferred solution of burning the straw where it lies is environmentally unsatisfactory and appears to be a huge waste of a potentially valuable, renewable energy source. None of the currently available straw packaging systems provides an economically viable alternative. A process is proposed for producing industrial quality fuel briquettes using a tractor towed implement. The economic feasibility of such a system is investigated and comparisons are made with existing straw disposal methods. The projected cost of fuel, produced in this way, is compared with prevailing fossil fuel prices. A multistage continuous process machine concept is described and the various stages are proven workable both experimentally, in the laboratory, and analytically. Laboratory experiments determine the forces required to produce acceptable quality briquettes and comparisons are made between the power available from the tractor, the economical throughput rate and the energy consumed in the compaction process. The mechanism of bonding within the straw packages, under compression, is examined so that the parameters necessary to give the optimum machine design may be understood. The effect, on briquette quality, of variations in die shape within the constraints imposed by the machine concept is fully investigated. Experiments extend to compression at speeds representative of 'live' field operation and a die shape is developed which produces packages of consistently good durability. Many of the design ideas put forward in this thesis have now been incorporated in an original prototype machine, built and successfully field-tested by the company who has supported this project and now holds the relevant patents

Development of a manufacturing feature-based design system

Traditional CAD systems are based on the serial approach of the product development cycle: the design process is not integrated with other activities and thus it can not provide information for subsequent phases of product development. In order to eliminate this problem, many modern CAD systems allow the composition of designs from building blocks of higher level of abstraction called features. Although features used in current systems tend to be named after manufacturing processes, they do not, in reality, provide valuable manufacturing data. Apart from the obvious disadvantage that process engineers need to re-evaluate the design and capture the intent of the designer, this approach also prohibits early detection of possible manufacturing problems. This research attempts to bring the design and manufacturing phases together by implementing manufacturing features. A design is composed entirely in a bottom-up manner using manufacturable entities in the same way as they would be produced during the manufacturing phase. Each feature consists of parameterised geometry, manufacturing information (including machine tool, cutting tools, cutting conditions, fixtures, and relative cost information), design limitations, functionality rules, and design-for-manufacture rules. The designer selects features from a hierarchical feature library. Upon insertion of a feature, the system ensures that no functionality or manufacturing rules are violated. If a feature is modified, the system validates the feature by making sure that it remains consistent with its original functionality and design-for-manufacture rules are re-applied. The system also allows analysis of designs, from a manufacturing point of view, that were not composed using features. In order to reduce the complexity of the system, design functionality and design-for manufacture rules are organised into a hierarchical system and are pointed to the appropriate entries of the feature hierarchy. The system makes it possible to avoid costly designs by eliminating possible manufacturing problems early in the product development cycle. It also makes computer-aided process planning feasible. The system is developed as an extension of a commercially available CAD/CAM system (Pro/Engineer), and at its current stage only deals with machining features. However, using the same principles, it can be expanded to cover other kinds of manufacturing processes

A 5-kW xenon ion thruster lifetest

The results of the first life test of a high power ring-cusp ion thruster are presented. A 30-cm laboratory model thruster was operated steady-state at a nominal beam power of 5 kW on xenon propellant for approximately 900 hours. This test was conducted to identify life-timing erosion modifications, and to demonstrate operation using simplified power processing. The results from this test are described including the conclusions derived from extensive post-test analyses of the thruster. Modifications to the thruster and ground support equipment, which were incorporated to solve problems identified by the lifetest, are also described

Design of a high pressure fluid intensifier

In this thesis the design of the major components of a high pressure intensifier is presented. The machine is a high pressure fluid intensifier which can develop an intermittent water jet of .01112 inches in diameter at a pressure of 100,000 psi and a flow rate of .9508 gpm. This machine can be used to study the capabilities of high pressure water jets to cut high compressive strength rocks. The primary machine elements of the intensifier system are the source, charging system, valve system, nozzle, and the intensifier. The source will be a Kobe Triplex Pump having a variable output with a maximum of 10,000 psi water and soluble oil mixture at a flow rate of 11.5 gpm. The charging system will be a Burks Series CT Turbine Type Pump with an output of 5 gpm at a pressure of 150 psi. The valve system will consist of three 4 gpm capacity solenoid operated valves manifolded together operating on 115 vac voltage. The nozzle with a diameter of .01112 inches causes enough restriction to a flow rate of .9508 gpm to produce a pressure of 100,000 psi. The intensifier is a single reciprocating piston arrangement with a piston area amplification ratio of 12:1. With a variable intensifier source the output of the intensifier is also variable. Further pressure variation can be achieved by a change of nozzle diameter. The intensifier will be cycled by two externally mounted microswitches that actuate the valve system when tripped by a plate bolted to the reciprocating piston cylinder. The distance between the microswitches can be adjusted, changing the intensifier length of stroke and therefore the cycles per minute of the intensifier. With the microswitch roller contacts 0.5 inches apart the cycling rate is at a maximum of 74.0 cpm. The cycling rate is a minimum of 5.68 cpm with the microswitch roller contacts 6.5 inches apart. The intensifier has a total length of 74.0 inches from the nozzle gland valve to the end of the input tube at full return position. The intensifier will be mounted on a concrete pad and secured by plates bolted to ·the intensifier and bolted to threaded rods secured in the concrete pad --Abstract, pages ii-iii

Characterisation of the unsteady wake of a square-back road vehicle

Square-back shapes are popular in the automotive market for their high level of practicality. These geometries, however, are usually characterised by high aerodynamic drag and their wake flow dynamics present many aspects, such as the coexistence of long- and short-time unsteady modes, whose full comprehension is still far from being achieved. The present work aims to provide some contributions to this field. An extensive experimental campaign consisting of balance, pressure tapping, particle image velocimetry and single point velocity measurements has been carried out in order to characterise the dynamic behaviour of the wake developing downstream of a simplified square-back geometry. Tests have been performed considering the Windsor body, at a Reynolds number (based on the model height) of ReH = 7.7 × 10^5. New insights on how the long-time instability develops are provided. The instability is shown to stem from the mutual interactions between the four shear layers bounding the wake rather than being the result of the state of perturbation of a single shear layer. Changes in the level of interaction between two or more shear layers are also reported to affect the short-time unsteady modes. A drag reduction is reported every time the symmetry of the wake is restored, as a consequence of the increased amount of reverse flow impinging on the base of the model. This seems to be true regardless of the configuration considered (with or without wheels) and the type of optimisation strategy adopted, although it does not necessarily imply the complete suppression of the long-time instability. In fact, a certain level of mobility in the flow reversal seems to be inevitable every time the symmetry of the wake is restored. Several elements that can alter this behaviour are also identified. A change in the curvature of at least one of the four shear layers is shown to increase the frequency of the switches between bi-stable states, until eventually the long-time instability disappears replaced by low frequency flapping or swinging motions. Such changes can be triggered by applying perturbations on either a global scale or a more local scale. Overall, the results presented in this work help to bridge the gap between simplified geometries and more realistic automotive shapes, as far as the characterisation of the time averaged and main unsteady features of the wake is concerned, and provide insights that may allow in the future the design of more effective flow control systems for drag reduction