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This paper compares three different sets of translation equations of motion for a space launcher. Two of these schemes, the Cartesian and the polar approaches, are widely used and the third one, the full quaternion approach has just been recently introduced. This paper does not present the mathematical development leading to each of them, but it compares the three schemes in terms of accuracy, robustness and computation time. The three schemes produce the exact same trajectory, but the polar one is the best suited for an onboard guidance algorithm as it is quicker to solve.

A main problem in controlling bioprocesses is the lack of manipulated variables. Batch and fed-batch processes do not allow the bioreactor to be drained of the (often) toxic waste substances produced by the biomass. A chemostat (CSTR) only has the dilution rate as the manipulated variable, which allows a certain control over the biomass concentration with a risk, however, of instability if the dilution rate gets higher than the maximum growth rate. Perfusion processes with full biomass retention are somewhat similar to batches, as no steady-state is really obtained until biomass growth is stopped by nutrient limitations. Cell bleed is often used in perfusion processes to improve viability and prevent accumulation of dead cells. However, the idea of using the cell bleed stream as a manipulated variable for control has not previously been studied for perfusion systems. We propose here a control strategy with three degrees of freedom that can be used to control the reactor level, biomass concentration, and a metabolite concentration. In the end, we shall address that controlling these concentrations could be the key to metabolic flux-based optimizations in bioreactors., 4th International Conference on Engineering Applications and Computational Algorithms (DCDIS Conference 2005), July 27-29, 2005, Guelph, Ontario, Canada

Flotation is multivariable process exhibiting uncertain and nonlinear dynamics as well as being perturbed by unmeasured disturbances. Optimization of this process is therefore a complex undertaking. Although real-time optimization (RTO) techniques for maximizing an objective function are aailable, steady-state assumptions in processes being frequently acted upon by unmeasured distrubances, strongly limit the optimization frequency, hierachical control systems allow to efficiently dealing with process uncertainty and complexity. In flotation processes, this has suggested to look at secondary variables correlated to performance variables that can be measured and regulated to indirectly optimize process operation. This research project feals with two major topics. The first one is the development of novel estimation algorithms to infer key secondary variables in flotation columns whereas the second topic deals with designing advanced control strategies towards process optimizacion. In the first part, techniques to measure on line froth depth and bias rate based on conductivity measurements were developed. A nonlinear dynamic observer for frother concentration estimation was also designed generating estimates with 1 ppm error. A Gaussian mixture model was used to on-line estimate bubble size distribution from sequential data coming from an image processing system. In the second part, a predictive control strategy was conceived to indirectly optimize column floration performance by maximizing gas holdup while ensuring a positive bias rate. Bubble size was then countrolled by an internal model controller based on Wiener model and the so-called frit and sleeve sparger. Good tracking and regulation against frother concentration and gas velocity variations were obtained. Results showed that using the frit and sleeve sparger, bubble size can be controlled independently from gas velocity, a key step to control bubble surface area flux. Moreover, gas holdup and bubble surface area flux were found to be highly correlated, initially implying that both variables can be used for control purpose. Finally, control of bubble size distributions is explored. It is shown that by using a Gaussian mixture model with fixed components to reprsent bubble size distribution turns the infinite dimensional problem of shaping it to a finite dimensional problem that can be approached using classical methods. Doctor en Ingeniería Eléctrica TERMINADA PFCHA-Becas 412p. PFCHA-Becas