Simulation of Continuous Stirred Tank Reactors (CSTR’s) Using Orthogonal Functions

Over the centuries, several numerical methods have been developed to approximate the solution of mathematical problems that are difficult to be solved by analytical methods. These numerical techniques succeeded in attaining a solution that is close enough to the exact solution with minimum errors and maximum stability. However, there may be the development of several other numerical methods which can be robust and efficient than the existing methods.My proposed research work is about the application of one such method-Orthogonal functions. Orthogonal functions can be broadly classified in to three families; namely, the piecewise constant, polynomial, and sine-cosine family. Walsh function and block pulse function belong to the piecewise constant family. So far orthogonal functions have been used in the optimal control, solving integro-differential equations, trajectory problems and so on. However, orthogonal functions have not been applied to chemical systems and processes. Hence my work is emphasised on simulating reactors using orthogonal functions; mainly block pulse functions and triangular functions. The continuous stirring tank reactors (CSTR’s) are widely used in the chemical industries. Hence the reactions in a CSTR are modelled by a set of differential equations which are discretised to a set of algebraic equations by orthogonal functions. Block-pulse functions have been used to obtain the dynamics of concentration and temperature of the continuous stirring tank reactors (CSTR’s). Further a recurrence relationship developed using block-pulse functions and triangular functions have been used in solving linear and non-linear system of differential equations. The major importance of orthogonal functions lies in its application to optimal control to systems. A recursive algorithm developed using block pulse functions has been applied to a linear control problem to determine the states and optimality criterio

Impact of a heterogeneous stator on the rotor-stator interaction-noise: an analytical, experimental and numerical investigation

La présente étude vise à quantifier par une modélisation analytique, des essais et des simulations numériques, l’impact d’un stator hétérogène sur le bruit d’interaction rotor-stator dans les turbomachines axiales. Le travail développé s’appuie sur des premières observations sur un ventilateur axial à basse vitesse à l’École Centrale de Lyon, l’étage LP3. Il a été observé que les deux premières fréquences de passage des pales (FPP) rayonnaient à des niveaux élevés alors qu’elles devaient être coupées par le conduit selon le critère de Tyler & Sofrin. Une campagne expérimentale est alors réalisée sur la configuration de ventilateur hétérogène qui permet la caractérisation des contenus spectral et modal. Afin de s’assurer qu’aucune distorsion d’entrée d’air n’est présente, un écran pour le contrôle de la turbulence est utilisé. Des techniques de décomposition modale sont utilisées sur des antennes pseudo-aléatoires afin d’obtenir les modes acoustiques prédominants. Les résultats montrent un fort rayonnement acoustique des deux premières fréquences de passage des pales et mettent en évidence des modes dominants. La même expérience est ensuite simulée numériquement en utilisant la méthode de Boltzmann sur réseau. Les simulations montrent un bon comportement de la turbomachine mais prédisent une augmentation de pression inférieure à celle de l’expérience. La comparaison entre un stator homogène et hétérogène permet de quantifier directement l’impact de l’hétérogénéité. L’hétérogénéité est alors responsable d’une augmentation du niveau tonal de plus de 10 dB aux deux premières FPP. Le contenu modal mesuré sur la configuration hétérogène est bien retrouvé par les simulations numériques. En outre, l’analyse de l’écoulement dans l’espacement inter-rotor-stator a permis de mettre en évidence l’impact de l’hétérogénéité sur le champ potentiel. Finalement, la modélisation analytique est axée sur deux sources dominantes : le bruit d’interaction de sillages et le bruit d’interaction potentielle. Les résultats montrent une contribution mineure de ce dernier. Les mêmes modes dominants sont retrouvés dans certaines directions de propagation en accord avec ce qui est observé expérimentalement. En dernier lieu, une étude d’optimisation de la position des bras support est présentée. Une des configurations optimales montrant une forte atténuation du niveau de bruit tonal est validée numériquement par des simulations numériques. Les résultats montrent que l’optimisation du positionnement angulaire des aubes structurelles permet d’obtenir une réduction significative des niveaux aux deux premières FPP. L’étude des différentes composantes (analytique, expérimentale et numérique) fournit ainsi une meilleure compréhension des mécanismes de bruit modifiés par l’hétérogénéité du stator.Abstract: The present study aims to quantify by means of analytical modelling, experiments and numerical simulations, the impact of a heterogeneous stator on the rotor-stator noise in axial turbomachines. This study starts with the first observations on an axial low-speed fan at École Centrale de Lyon, the LP3 stage. It has been observed that the first two blade passing frequencies (BPF) were radiating at high levels while they were expected to be cut-off by the duct according to Tyler & Sofrin’s criterion. An experiment is then carried out with the heterogeneous stator configuration which makes it possible to characterize the spectral and modal contents. To ensure that no inflow distortion is present at the inlet, a Turbulence Control Screen is used. Modal decomposition techniques are used with pseudo-random antennas to obtain the predominant acoustic modes. Results show a strong acoustic radiation of the first two BPFs and evidence some dominant modes. The same experiment is then simulated numerically using the lattice Boltzmann method. The simulations show a good physical behaviour of the turbomachine but predict a lower pressure-rise compared with the experiment. The comparison between homogeneous and heterogeneous stators allows quantifying directly the impact of the heterogeneity. The heterogeneity is responsible for a level increase of more than 10 dB at the first two BPFs. The modal content from the numerical simulations on the heterogeneous configuration is also in good agreement with the experiment. In addition, the analysis of the flow in the inter-stage made it possible to highlight the impact of the heterogeneity on the potential field. Finally, the analytical modelling is focused on two dominant sources: wake-interaction noise and potential-interaction noise. Results put in evidence a minor contribution of the latter despite the short rotor-stator spacing. The same dominant modes are found in certain propagation directions in accordance with what is measured in the experiment. Finally, an optimisation of the modified vanes angular position is carried out. One of the optimal configurations showing a great noise attenuation is numerically validated by the LBM. The numerical results show that the optimisation of the azimuthal positioning of the modified vanes makes it possible to obtain a significant reduction of the levels at the first two BPFs. Thereby, the comparison of the analytical, experimental and numerical investigations allows achieving a better understanding of the modification of noise mechanisms caused by the heterogeneity of the stator

'THz Torch' wireless communications links

The low-cost 'THz Torch’ technology, which exploits the thermal infrared spectrum (ca. 10 to 100 THz), was recently introduced to provide secure low data rate communications links across short ranges. In this thesis, the channel model for 'THz Torch’ wireless communications links is redeveloped from a thermodynamics perspective. Novel optimization-based channel estimators are also proposed to calibrate parameters in the channel model. Based on these theoretical advances, a cognitive 'THz Torch’ receiver, which combines conventional digital communications with state-of-the-art deep learning techniques, is presented to achieve cognitive synchronization and demodulation. The newly reported 'THz Torch’ wireless link is capable of bypassing the thermal time constant constraints normally associated with both the thermal emitter and sensor, allowing truly asynchronous data transfer with direct electronic modulation. Experimental results obtained in both laboratory environments and field trials demonstrate step-change improvements in channel range, bit rate, bit error rate and demodulation speed. This work represents a paradigm shift in modulation-demodulation with a thermal-based physical layer and offers a practical solution for implementing future ubiquitous secure 'THz Torch’ wireless communications links. The cognitive receiver concept also has wide-ranging implications for future communications and sensor technologies, making them more resilient when operating in harsh environments.Open Acces

Floating-Gate Design and Linearization for Reconfigurable Analog Signal Processing

Analog and mixed-signal integrated circuits have found a place in modern electronics design as a viable alternative to digital pre-processing. With metrics that boast high accuracy and low power consumption, analog pre-processing has opened the door to low-power state-monitoring systems when it is utilized in place of a power-hungry digital signal-processing stage. However, the complicated design process required by analog and mixed-signal systems has been a barrier to broader applications. The implementation of floating-gate transistors has begun to pave the way for a more reasonable approach to analog design. Floating-gate technology has widespread use in the digital domain. Analog and mixed-signal use of floating-gate transistors has only become a rising field of study in recent years. Analog floating gates allow for low-power implementation of mixed-signal systems, such as the field-programmable analog array, while simultaneously opening the door to complex signal-processing techniques. The field-programmable analog array, which leverages floating-gate technologies, is demonstrated as a reliable replacement to signal-processing tasks previously only solved by custom design. Living in an analog world demands the constant use and refinement of analog signal processing for the purpose of interfacing with digital systems. This work offers a comprehensive look at utilizing floating-gate transistors as the core element for analog signal-processing tasks. This work demonstrates the floating gate\u27s merit in large reconfigurable array-driven systems and in smaller-scale implementations, such as linearization techniques for oscillators and analog-to-digital converters. A study on analog floating-gate reliability is complemented with a temperature compensation scheme for implementing these systems in ever-changing, realistic environments

Re-Sonification of Objects, Events, and Environments

abstract: Digital sound synthesis allows the creation of a great variety of sounds. Focusing on interesting or ecologically valid sounds for music, simulation, aesthetics, or other purposes limits the otherwise vast digital audio palette. Tools for creating such sounds vary from arbitrary methods of altering recordings to precise simulations of vibrating objects. In this work, methods of sound synthesis by re-sonification are considered. Re-sonification, herein, refers to the general process of analyzing, possibly transforming, and resynthesizing or reusing recorded sounds in meaningful ways, to convey information. Applied to soundscapes, re-sonification is presented as a means of conveying activity within an environment. Applied to the sounds of objects, this work examines modeling the perception of objects as well as their physical properties and the ability to simulate interactive events with such objects. To create soundscapes to re-sonify geographic environments, a method of automated soundscape design is presented. Using recorded sounds that are classified based on acoustic, social, semantic, and geographic information, this method produces stochastically generated soundscapes to re-sonify selected geographic areas. Drawing on prior knowledge, local sounds and those deemed similar comprise a locale's soundscape. In the context of re-sonifying events, this work examines processes for modeling and estimating the excitations of sounding objects. These include plucking, striking, rubbing, and any interaction that imparts energy into a system, affecting the resultant sound. A method of estimating a linear system's input, constrained to a signal-subspace, is presented and applied toward improving the estimation of percussive excitations for re-sonification. To work toward robust recording-based modeling and re-sonification of objects, new implementations of banded waveguide (BWG) models are proposed for object modeling and sound synthesis. Previous implementations of BWGs use arbitrary model parameters and may produce a range of simulations that do not match digital waveguide or modal models of the same design. Subject to linear excitations, some models proposed here behave identically to other equivalently designed physical models. Under nonlinear interactions, such as bowing, many of the proposed implementations exhibit improvements in the attack characteristics of synthesized sounds.Dissertation/ThesisPh.D. Electrical Engineering 201

Advanced hardware and software approach to seismic site response investigations

Vibration measurement is an essential aspect of modern geotechnical engineering. It is particularly vital task for measuring the dynamic soil parameters, estimating seismic hazards and evaluating influence of industrial, traffic and construction vibrations on the surrounding buildings, structures and their elements. Meanwhile, commercial exploration seismic stations and data acquisition systems require significant professional knowledge and training in geophysics or vibration measurement, as well as practical skills and experience in adjusting data acquisition parameters. Furthermore, available seismological investigation and vibrometry sensors are not universally suitable for field applications in geophysical studies, soil-structure interaction investigations or structural vibrations. The frequency range suitable for seismic studies and industrial vibration measurement vary from 1 Hz to 300 Hz with sensitivity corresponding to the expected vibration level. To address these challenges, the first part of this thesis was focused on developing an innovative data acquisition system and sensors that are easy to use in a wide range of field applications. Geophysical techniques, including the Multichannel Analysis of Surface Waves (MASW) and Horizontal to Vertical Spectral Ratio (HVSR) methods, are gaining popularity in site investigations and seismic hazard characterization applications. The second part of this thesis involved conducting field studies using MASW and HVSR methods to evaluate the influence of challenging site conditions such as sloping surface topography, complicated soil stratigraphy and sloping bedrock boundaries on the results of the applied methods. The application of theoretical or numerical models of site amplification often poses a challenge under real field conditions. In the third part of the thesis, an analytical model was developed to allow for the removal of site effects from strong motion records and proposed a method for HVSR curve parameterization that resulted in an analytical expression for the amplification factor based on HVSR results