Heuristically enhanced feedback control of constrained discrete-time linear systems

The merits of organic fluid space power cycles are surveyed and compared with those of alternate options Selection of an optimum working fluid is recognized as an important tool to improve system performance The main characteristics of organic power cycles are shown to be predictable with a good level of accuracy through a general method, which requests the knowledge of a limited information about the fluid properties: specific heat in the ideal gas state, a portion of the saturation curve, and the critical parameters On the ground of such a theory the adoption of fluids with a relatively complex molecular structure and condensation at the lowest practically admissible reduced temperature allow a better efficiency than achievable with the use of toluene, which is taken as a reference fluid The influence of turbine efficiency actually achievable in real machines on cycle performance is then addressed; performance diagrams of optimized turbines in the power range of interest for space cycles are calculated and presented It is shown that only the combined optimization of thermal and fluid dynamic variables leads to the definition of an optimum working fluid and power cycle A class of fluids is examined, that of the methyl-substituted benzenes, offering a wide variation of thermal properties A thorough optimization that considers a wide range of power outputs, one-and two-stage turbines, saturated and superheated cycles is performed For a power output of about 30 kW trimethylbenzene is found to offer the best overall efficiency, a moderate maximum pressure, reasonable turbine dimensions, and rotating speed A thermodynamic conversion efficiency in excess of 30 percent seems achievable at a maximum temperature of 360°C for a condensation temperature of 60°C Such energy performance suggests that ORC systems could represent a viable multifuel prime mover option also for terrestrial power generation Thermal stability of the proposed fluid is experimentally investigated and found to be similar to that of toluene, but its definite evaluation is shown to require further testing

Organic Working Fluid Optimization for Space Power Cycles

ONTROL systems for early aircraft turbine engines performed a rather simple task: metering the fuel to the combustor at the proper fuel-to-air ratio for both transient and steady-state operating conditions. More recently, however, things have changed significantly. To achieve higher thrust-to-weight ratios and to improve specific fuel consumption, many additional manipulated engine inputs have been added. Figure 1 shows the trend in complexity in terms of the number of controlled engine variables. Noted are a number of operational engines that have been put into service. Typical of the added engine manipulated inputs are afterburner fuel flow, variable compressor-inlet guide vanes, variable compressor stators, and variable exhaust-nozzle area. The task of designing a control algorithm for an engine having a number of inputs and outputs now becomes a formidable problem. Traditional single-input/single-output techniques can be used, but are often inadequate and require many judgmental interactions to get even close to a suitable engine control law. The designer would really like a direct, straightforward method for handling the multivariable problem. This procedure should be able to eliminate unwanted interactions between the different variables, while bringing into play those interactions that are favorable. Faced with these needs, in the early 1970s the engine control community began to investigate what new design methodologies were available. As a result, a number of researchers began to apply to the engine control design problem tools from the evolving methodology generally termed " modern control theory" (MCT). This paper reviews what has been accomplished in applying MCT to the aircraft turbine engine control design problem over the last 10 or so years and what work yet remains to be done. This review is organized as follows: first is a brief discussion of the evolution of control design methodology, followed by a description of the problems that must be faced in applying MCT to the engine control design task. The past accomplishments in applying MCT to engine control is the subject of the third and most detailed section. The paper concludes with a discussion of the future requirements for advanced engine control design. Evolution of Control Design Methodology In the early 1960s, control theoreticians began to use linear state-space methods to design closed-loop controls for large complex physical systems. At the same time, computers that could easily solve the numerical problems associated with large linear system problems were rapidly evolving and becoming readily accessible. Thus began the era of "modern control theory." This terminology was used to differentiate the new methods from the traditional linear system, single

/pdf/the-role-of-modern-control-theory-in-the-design-of-controls-mecp9oin9e.pdf

The role of modern control theory in the design of controls for aircraft turbine engines

A new optimization control method, which is based on the optimization employing Bezier curves of control variables, is proposed to improve engine thrust response performance. The minimum of the tim...

A global optimization control for turbo-fan engine acceleration schedule design:

Overshoot-free acceleration of aero-engines: An energy-based switching control method

Payload optimization of multistage launch vehicle- generalized Bolza problem for maximal payload capability analysis

https://ntrs.nasa.gov/api/citations/19660005415/downloads/19660005415.pdf

Payload optimization of multistage launch vehicles

Minimum time accelerations of aircraft turbofan engines are presented. The calculation of these accelerations was made by using a piecewise linear engine model, and an algorithm based on nonlinear programming. Use of this model and algorithm allows such trajectories to be readily calculated on a digital computer with a minimal expenditure of computer time.

https://ntrs.nasa.gov/api/citations/19770026223/downloads/19770026223.pdf

Minimum time acceleration of aircraft turbofan engines by using an algorithm based on nonlinear programming

Minimum-time accelerations of the F100 turbofan engine are presented. A piecewise-linear engine model, having three state variables and four control variables, is used to obtain the minimum-time solutions. The linear model which applies at a given time in the trajectory is determined by calculating a normalized distance from the current state to the equilibrium state associated with each linear model. The linear model associated with the closest equilibrium point is then used. The control histories for the minimum-time solutions are used as input to a nonlinear simulation of the F100 engine to verify the accuracy of the piecewise linear solutions.

Minimum-time acceleration of aircraft turbofan engines

Optimum launch trajectories for ATS-E mission with noncircular parking orbits, considering apogee motor size, perigee radius and duration constraints

/pdf/optimum-launch-trajectories-for-the-ats-e-mission-1c2h4wi6v9.pdf

Optimum launch trajectories for the ATS-E mission

Computer program for trajectory optimization and payload maximization in multistage launch vehicles

Fred Teren

Papers

Payload optimization of multistage launch vehicles

Minimum time acceleration of aircraft turbofan engines by using an algorithm based on nonlinear programming

Minimum-time acceleration of aircraft turbofan engines

Optimum launch trajectories for the ATS-E mission

A trajectory code for maximizing the payload of multistage launch vehicles