Stochastic utility maximising dynamic programming applied to medium-term reservoir management

Medium-term reservoir management is a classic planning problem to which stochastic dynamic programming has been applied. An aspect of reservoir management modelling often neglected is 'risk', although it has been identified as being of prime importance. A utility function can imply an attitude to risk, and in this thesis, a modified stochastic dynamic programming model (SUMDP) is presented which can maximise expected utility, where utility is defined over the range of terminal storage and 'wealth' outcomes and hence is dependent on all decisions made over the planning horizon. SUMDP is applied to reservoir management in regulated and deregulated representations of the New Zealand electricity system. Experimental results showed that increasing the relative risk aversion to low terminal wealth values reduced the mean and variability of wealth and was achieved by conserving water and hence increasing storage. This effect was amplified by the contract level of the hydro firm in a deregulated case where the reservoir firm was a price setter with financial contracts and the remaining players were price takers. SUMDP can be applied to other problem classes, one of which is stochastic route choice in acyclic networks. SUMDP is discussed in this context and applied to some example problems. Rather than a single (static) route choice decision being optimal at each node of the network, SUMDP produces optimal non-static decisions which are dependent on the accumulated time taken to reach the node and take into account the utility associated with the time taken to travel the route. There are few approaches discussed in the literature which produce non-static solutions, consider uncertainty, and consider risk, so SUMDP also contributes to this literature

Analysis and design of multirate-multivariable sampled data systems

Imperial Users onl

Catalytic and Sorption Measurements Using Flux Response Technology

Advancements in characterisation techniques in the field of heterogeneous catalysis have been explored, in particular the powerful in situ perturbation method, Flux Response Technology (FRT). The adaptation of FRT as a novel in situ perturbation technique in gas sorption measurements continues to yield consistent results with literature values. This is made possible because FRT measures miniscule changes in transient flows in the order of 10-2 μl/min for gaseous processes involving a change in volume (dV/dt). These changes are measured directly by a very sensitive differential pressure transducer (DPT) in a pneumatic system analogous to an electrical Wheatstone bridge assembly, whereby gas molecules replace electrons and capillaries function as resistors. By showing the successful incorporation of the measurements of adsorption capacities and diffusivity coefficients in the same experimental window, FRT’s use as a bolt-on technology for the rapid screening of catalyst material has been highlighted. The technique possesses a distinct advantage in requiring no prior calibrations to the system, enabling the analysis of a broad spectrum of materials and gases. The FRT technique also features a unique ability in being able to act as a dual flowrate and composition detector through the use of carefully calculated delay lines to separate changes in flowrate caused by perturbations of concentration and changes in composition. The FRT technique provides a quick, simple, accurate, and inexpensive method of characterising material properties in situ in heterogeneous catalysis. Several studies into the dynamics of gas sorption processes utilising FRT measurements on adsorbents were undertaken in the completion of this PhD. The diffusivity parameters of propane in varying alumina/CeZrOx washcoats of Cordierite monoliths were investigated under isothermal conditions. A novel method of analysing FRT derived response profiles with the Zero Length Column (ZLC) model was established and reported on. The diffusion coefficients obtained were consistent with previously reported macroscopic data and compared well when evaluating the structural differences of the washcoats of each sample (Granato et al., 2010). The dynamics of ammonia sorption on commercially available zeolites with varying SiO2/Al2O3 ratios was analysed to investigate the total acidity of these zeolites. The dynamics of carbon dioxide sorption were also investigated to analyse the total basicity of the same zeolite samples. Process optimisations were conducted to obtain an ultra fast isotherm measurement technique for the analysis of nitrogen sorption on aluminium oxides with varying surface areas at 77 K. Finally, insights into the development of a dynamic parallel performance testing (DPPT) FRT setup were undertaken to directly compare the activities of catalytic material operating side by side.Open Acces

Electromagnetic modelling of planar circuits in bounded layered media

Printed circuits in bounded media encompass a wide range of practical structures such as discontinuities in waveguides, planar circuits embedded in shielded multilayered media or even two-dimensional printed periodic structures. The Electromagnetic (EM) modeling of printed circuits in layered bounded media is performed via an Integral Equation (IE) technique. Green's functions (GFs) are specially defined to satisfy both the Boundary Conditions (BCs) imposed by the layered media and by the transverse boundary enclosing the entire structure. Finally, a system of IEs on the equivalent sources can be solved numerically by means of the Method of Moments (MoM). Each of the problems enumerated above has already been solved by other authors using IE-MoM techniques. Nevertheless, our formulation introduces a unified approach applicable to all the aforementioned problems. Due to the symmetry presented by a bounded layered media, the GF problem can be reduced into a two-dimensional transverse boundary problem and a one-dimensional transmission line problem in the normal direction. Both problems can be treated independently. This thesis proposes and fully develops an efficient technique that encompasses different laterally bounded multilayered problems with a seamless transition between them. The method is based on a modal representation of the transverse boundary problem and on the expansion of the equivalent surface currents by zero-curl & constant-charge Basis Functions (BFs). It offers a unified and versatile approach that, on one hand eliminates redundancy in the formulation and on the other hand simplifies each particular problem to the evaluation of constant coefficients or basic line integrals. Analytical solutions can be found for the combination of linear subsectional basis functions in rectangular and circular Perfect Electric Conductor (PEC) boundaries as well as for periodic lattices. This thesis then solves the problem of transmission line model in the longitudinal direction by proposing an efficient algorithm that guarantees numerical stability under a variety of known critical conditions where other already known formulations fail. In addition, it introduces alternate equivalent expressions of this formulation that allow new interpretations of the problem. Due to its practical interest, the method is applied for the EM modeling of multilayered boxed printed circuits. This motivated the implementation of a dedicated software tool for the efficient analysis of these topologies including losses. Extensive numerical experiments have been carried out to assess the validity of the aforementioned theory and some properties of test-structures (losses, mesh, etc)

General function evaluation in a STPC setting via piecewise linear approximation

While in theory any computable functions can be evaluated in a Secure Two Party Computation (STPC) framework, practical applications are often limited for complexity reasons and by the kind of operations that the available cryptographic tools permit. In this paper we propose an algorithm that, given a function f() and an interval belonging to its domain, produces a piecewise linear approximation f() that can be easily implemented in a STPC setting. Two different implementations are proposed: the first one relies completely on Garbled Circuit (GC) theory, while the second one exploits a hybrid construction where GC and Homomorphic Encryption (HE) are used together. We show that from a communication complexity perspective the full-GC implementation is preferable when the input and output variables are represented with a small number of bits, otherwise the hybrid solution is preferable

Risk Management

Every business and decision involves a certain amount of risk. Risk might cause a loss to a company. This does not mean, however, that businesses cannot take risks. As disengagement and risk aversion may result in missed business opportunities, which will lead to slower growth and reduced prosperity of a company. In today's increasingly complex and diverse environment, it is crucial to find the right balance between risk aversion and risk taking. To do this it is essential to understand the complex, out of the whole range of economic, technical, operational, environmental and social risks associated with the company's activities. However, risk management is about much more than merely avoiding or successfully deriving benefit from opportunities. Risk management is the identification, assessment, and prioritization of risks. Lastly, risk management helps a company to handle the risks associated with a rapidly changing business environment