The Biglobal Instability of the Bidirectional Vortex

State of the art research in hydrodynamic stability analysis has moved from classic one-dimensional methods such as the local nonparallel approach and the parabolized stability equations to two-dimensional, biglobal, methods. The paradigm shift toward two dimensional techniques with the ability to accommodate fully three-dimensional base flows is a necessary step toward modeling complex, multidimensional flowfields in modern propulsive applications. Here, we employ a two-dimensional spatial waveform with sinusoidal temporal dependence to reduce the three-dimensional linearized Navier-Stokes equations to their biglobal form. Addressing hydrodynamic stability in this way circumvents the restrictive parallel-flow assumption and admits boundary conditions in the streamwise direction. Furthermore, the following work employs a full momentum formulation, rather than the reduced streamfunction form, accounting for a nonzero tangential mean flow velocity. This approach adds significant complexity in both formulation and implementation but renders a more general methodology applicable to a broader spectrum of mean flows. Specifically, we consider the stability of three models for bidirectional vortex flow. While a complete parametric study ensues, the stabilizing effect of the swirl velocity is evident as the injection parameter, kappa, is closely examined

The response of box-type structures to vibration.

The work described in this thesis deals with the vibration study of an open ended folded plate box type structure leading up to the prediction of its response to random excitation. Theoretical and experimental results for the box are presented as one of the main aims of the work is to predict theoretically the response of the structure to random excitation and compare these results with experimentally obtained values using various methods available. The determination of the response of a structure to random excitation depends on the prediction of the response spectral density. To determine the response spectral density of any point on a structure a knowledge of its natural frequencies and mode shapes and modal damping factors is required. In this work the finite-element method of analysis is used to determine the natural frequencies of vibration and the corresponding mode shapes of the box structure and computer programs were developed to perform this analysis. During the project, beam and plate structures have also been investigated to assess the accuracy of the technique and some results for these are included in chapter 7. The natural frequencies and mode shapes obtained are compared with experimental results as well as with those obtained using other theoretical analyses. For the beam the exact method was used and for the plate, the energy method using Warburton's formulae. Computer programs were also developed to calculate the structural receptance from the natural frequencies and mode shapes calculated using the finite element technique and damping factors obtained experimentally. From this, the response spectral density of the structure to a known excitation spectrum was obtained. Experimental work include a) sinusoidal excitation tests to determine natural frequencies, mode shapes and damping factors and b) random excitation using pseudo-random binary sequence signals to determine response to random excitation using narrow band frequency analysis and correlation techniques. The experimental apparatus and techniques used, including the development of a non-contacting combined exciter pickup probe, are described and discussed. The response to random excitation is obtained experimentally using a pseudo-random binary sequence signal generator and a time domain analyser, giving the cross-correlation function from which the cross spectral density is calculated in a Fourier transform. A Fast Fourier Transform computer program was developed during the work to perform this. The response spectral density is then obtained from a knowledge of the excitation spectral density. Finally the values of the response spectral density obtained were compared v/ith those obtained using the results of the finite element analysis and using the results of the sine sweep test and narrow band frequency analysis. The technique used in this work has proved satisfactory and the experimental apparatus and computer programs developed, suitable for the investigation. The work described in this thesis provides the necessary basic requirements for future work in the establishment of suitable experimental apparatus setup and provision of essential computer software. Suggestions as to possible extension of this work are made in the concluding chapter

Dynamic Modeling, Sensor Placement Design, and Fault Diagnosis of Nuclear Desalination Systems

Fault diagnosis of sensors, devices, and equipment is an important topic in the nuclear industry for effective and continuous operation of nuclear power plants. All the fault diagnostic approaches depend critically on the sensors that measure important process variables. Whenever a process encounters a fault, the effect of the fault is propagated to some or all the process variables. The ability of the sensor network to detect and isolate failure modes and anomalous conditions is crucial for the effectiveness of a fault detection and isolation (FDI) system. However, the emphasis of most fault diagnostic approaches found in the literature is primarily on the procedures for performing FDI using a given set of sensors. Little attention has been given to actual sensor allocation for achieving the efficient FDI performance. This dissertation presents a graph-based approach that serves as a solution for the optimization of sensor placement to ensure the observability of faults, as well as the fault resolution to a maximum possible extent. This would potentially facilitate an automated sensor allocation procedure. Principal component analysis (PCA), a multivariate data-driven technique, is used to capture the relationships in the data, and to fit a hyper-plane to the data. The fault directions for different fault scenarios are obtained from the prediction errors, and fault isolation is then accomplished using new projections on these fault directions. The effectiveness of the use of an optimal sensor set versus a reduced set for fault detection and isolation is demonstrated using this technique. Among a variety of desalination technologies, the multi-stage flash (MSF) processes contribute substantially to the desalinating capacity in the world. In this dissertation, both steady-state and dynamic simulation models of a MSF desalination plant are developed. The dynamic MSF model is coupled with a previously developed International Reactor Innovative and Secure (IRIS) model in the SIMULINK environment. The developed sensor placement design and fault diagnostic methods are illustrated with application to the coupled nuclear desalination system. The results demonstrate the effectiveness of the newly developed integrated approach to performance monitoring and fault diagnosis with optimized sensor placement for large industrial systems

Numerical Boundary Condition Procedures

Topics include numerical procedures for treating inflow and outflow boundaries, steady and unsteady discontinuous surfaces, far field boundaries, and multiblock grids. In addition, the effects of numerical boundary approximations on stability, accuracy, and convergence rate of the numerical solution are discussed

MATLAB

This excellent book represents the final part of three-volumes regarding MATLAB-based applications in almost every branch of science. The book consists of 19 excellent, insightful articles and the readers will find the results very useful to their work. In particular, the book consists of three parts, the first one is devoted to mathematical methods in the applied sciences by using MATLAB, the second is devoted to MATLAB applications of general interest and the third one discusses MATLAB for educational purposes. This collection of high quality articles, refers to a large range of professional fields and can be used for science as well as for various educational purposes