50 research outputs found
Electropneumatic linear gimbal actuation system, model nv-bi, 29 june 1963 - 29 june 1964
Electropneumatic linear actuator for thrust vector control on J- 2 rocket engin
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Development of a current to pressure (I/P) converter. System analysis of a current to pressure (I/P) converter through physical modelling and experimental investigation, leading to a design for improved linearity and temperature independence.
Current-to-pressure (I/P) converters are pneumatic devices which provide precise control of pressure in various industries – for example these devices are often used in valve positioner systems (typically found in the oil and gas industry) and tensioning systems (typically used in the packaging industry). With an increasing demand for such devices to operate in harsh environments all by delivering acceptable performance means that Current-to-pressure converters need to be carefully designed such that environmental factors have no or minimal effects on its performance. This work presents an investigation of the principles of operation of an existing I/P converter through mathematical modelling. A simulation model has been created and which allows prediction of performance of the I/P converter. This tool has been used to identify areas of poor performances through theoretical analysis and consequently led to optimisation of certain areas of the I/P converter through a design change to deliver improved performances, for instance the average percentage shift in gain at 1mA input signal (over the temperature range of -40°C to 85°C) on the new I/P converter is 2.13% compared to the average gain of 4.24% on the existing I/P converter, which represents an improvement of almost two fold. Experimental tests on prototypes have been carried out and tests results showed that improved linearity and temperature sensitivity can be expected from the new design
Jet Mixing Enhancement by High Amplitude Pulse Fluidic Actuation
Turbulent mixing enhancement has received a great deal of attention in the fluid mechanics community in the last few decades. Generally speaking, mixing enhancement involves the increased dispersion of the fluid that makes up a flow. The current work focuses on mixing enhancement of an axisymmetric jet via high amplitude fluidic pulses applied at the nozzle exit with high aspect ratio actuator nozzles. The work consists of small scale clean jet experiments, small scale micro-turbine engine experiments, and full scale laboratory simulated core exhaust experiments using actuators designed to fit within the engine nacelle of a full scale aircraft.
The small scale clean jet experiments show that mixing enhancement compared to the unforced case is likely due to a combination of mechanisms. The first mechanism is the growth of shear layer instabilities, similar to that which occurs with an acoustically excited jet except that, in this case, the forcing is highly nonlinear. The result of the instability is a frequency bucket with an optimal forcing frequency. The second mechanism is the generation of counter rotating vortex pairs similar to those generated by mechanical tabs. The penetration depth determines the extent to which this mechanism acts. The importance of this mechanism is therefore a function of the pulsing amplitude. The key mixing parameters were found to be the actuator to jet momentum ratio (amplitude) and the pulsing frequency, where the optimal frequency depends on the amplitude. The importance of phase, offset, duty cycle, and geometric configuration were also explored.
The experiments on the jet engine and full scale simulated core nozzle demonstrated that pulse fluidic mixing enhancement was effective on realistic flows. The same parameters that were important for the cleaner small scale experiments were found to be important for the more realistic cases as well. This suggests that the same mixing mechanisms are at work. Additional work was done to optimize, in real time, mixing on the small jet engine using an evolution strategy.Ph.D.Committee Chair: David Parekh; Committee Member: Ari Glezer; Committee Member: Jeff Jagoda; Committee Member: Richard Gaeta; Committee Member: Samuel Shelto
Aeronautical engineering: A continuing bibliography with indexes (supplement 296)
This bibliography lists 592 reports, articles, and other documents introduced into the NASA scientific and technical information system in Oct. 1993. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics
Modelling of servo-controlled pneumatic drives: a generalised approach to pneumatic modelling and applications in servo-drive design
The primary objective of this research is to develop a
general modelling facility for modular pneumatic servo-drives.
The component-oriented approach has been adopted as the modelling
technique to provide the flexibility of modelling a wide variety
of components and the segmentation of the non-linear system to
less complex uncoupled component modules.
A significant part of the research work has been devoted to
identify a series of component modules of the single axis linear
pneumatic servomechanism with standardised linking variables. The
mathematical models have been implemented in a simulation software
which produces time domain responses for design evaluation
purposes. Alternative components for different servomechanism
design were modelled as mutually exclusive modules which could be
selected for assembly as if they were real physical entities. The
philosophy of the approach was validated by tests on prototype
servo-drives with matching components. Design analysis could be
performed by simulating and comparing the performance of
alternative system structures. [Continues.
Application of jet-shear-layer mixing and effervescent atomization to the development of a low-NO(x) combustor
An investigation was conducted to develop appropriate technologies for a low-NO(x), liquid-fueled combustor. The combustor incorporates an effervescent atomizer used to inject fuel into a premixing duct. Only a fraction of the combustion air is used in the premixing process to avoid autoignition and flashback problems. This fuel-rich mixture is introduced into the remaining combustion air by a rapid jet-shear-layer-mixing process involving radial fuel-air jets impinging on axial air jets in the primary combustion zone. Computational analysis was used to provide a better understanding of the fluid dynamics that occur in jet-shear-layer mixing and to facilitate a parametric analysis appropriate to the design of an optimum low-NO(x) combustor. A number of combustor configurations were studied to assess the key combustor technologies and to validate the modeling code. The results from the experimental testing and computational analysis indicate a low-NO(x) potential for the jet-shear-layer combustor. Key parameters found to affect NO(x) emissions are the primary combustion zone fuel-air ratio, the number of axial and radial jets, the aspect ratio and radial location of the axial air jets, and the radial jet inlet hole diameter. Each of these key parameters exhibits a low-NO(x) point from which an optimized combustor was developed. Using the parametric analysis, NO(x) emissions were reduced by a factor of 3 as compared with the emissions from conventional, liquid-fueled combustors operating at cruise conditions. Further development promises even lower NO(x) with high combustion efficiency
Control of a hydraulically actuated mechanism using a proportional valve and a linearizing feedforward controller
A common problem encountered in mobile hydraulics is the desire to automate motion control functions in a restricted-cost and restricted-sensor environment. In this thesis a solution to this problem is presented. A velocity control scheme based on a novel single component pressure compensated ow controller was developed and evaluated. The development of the controller involved solving several distinct technical challenges. First, a model reference control scheme was developed to provide control of the valve spool displacement for a particular electrohydraulic proportional valve. The control scheme had the effect of desensitizing the transient behaviour of the valve dynamics to changes in operating condition. Next, the pressure/flow relationship of the same valve was examined. A general approach for the mathematical characterization of this relationship was developed. This method was based on a modification of the so-called turbulent orifice equation. The general approach included a self-tuning algorithm. Next, the modified turbulent orifice equation was applied in conjunction with the model reference valve controller to create a single component pressure compensated flow control device. This required an inverse solution to the modified orifice equation. Finally, the kinematics of a specific single link hydraulically actuated mechanism were solved. Integration of the kinematic solution with the flow control device allowed for predictive velocity control of the single link mechanism