Numerical analysis of axisymmetric flows and methods for fluid-structure interaction arising in blood flow simulation

In this thesis we propose and analyze the numerical methods for the approximation of axisymmetric flows as well as algorithms suitable for the solution of fluid-structure interaction problems. Our investigation is aimed at, but are not restricted to, the simulation of the blood flow dynamics. The first part of this work deals with an axisymmetric fluid model based on three-dimensional incompressible Stokes or Navier–Stokes equations which are solved on a two-dimensional half-section of the domain under consideration. In particular we show optimal a priori error estimates for P1isoP2/P1 axisymmetric finite elements for the steady Stokes equations under the assumption that the domain and the data are axisymmetric and that the data have no angular component. Our analysis is carried out in the framework of weighted Sobolev spaces and takes advantage of a suitably defined Cl´ement type projection operator. We then introduce an axisymmetric formulation of the Navier–Stokes equations in moving domains and, starting from existing results in three-dimensions, we set up an Arbitrary Lagrangian–Eulerian (ALE) formulation and prove some stability results. In the second part, we deal with algorithms for the solution of fluid-structure interaction problems. We introduce the problem in a generic form where the fluid is described by means of incompressible Navier–Stokes equations and the structure by a viscoelastic model. We account for large deformations of the structure and we show how existing algorithms may be improved to reduce the computational time. In particular we show how to use transpiration boundary conditions to approximate the fluid-structure problem in a fixed point strategy. Moreover, in a quasi-Newton strategy we reduce the cost by replacing the Jacobian with inexact Jacobians stemming from reduced physical models for the problem at hand. To speed up the convergence of the Newton algorithm, we also define a dynamic preconditioner and an acceleration scheme which have been successfully tested in haemodynamics simulations in two and three dimensions

Analogue filter networks: developments in theory, design and analyses

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On the Development of Novel Encryption Methods for Conventional and Biometric Images

Information security refers to the technique of protecting information from unauthorized access, use, disclosure, disruption and modification. Governments, military, corporations, financial institutions, hospitals, and private businesses amass a great deal of confidential information about their employees, customers, products, research, and financial status. Most of this information is now collected, processed and stored on electronic media and transmitted across networks to other computers. Encryption clearly addresses the need for confidentiality of information, in process of storage and transmission. Popular application of multimedia technology and increasingly transmission ability of network gradually leads us to acquire information directly and clearly through images and hence the security of image data has become inevitable. Moreover in the recent years, biometrics is gaining popularity for security purposes in many applications. However, during communication and transmission over insecure network channels it has some risks of being hacked, modified and reused. Hence, there is a strong need to protect biometric images during communication and transmission. In this thesis, attempts have been made to encrypt image efficiently and to enhance the security of biometrics images during transmission. In the first contribution, three different key matrix generation methods invertible, involuntary, and permutation key matrix generation have been proposed. Invertible and involuntary key matrix generation methods solves the key matrix inversion problem in Hill cipher. Permutation key matrix generation method increases the Hill system’s security. The conventional Hill cipher technique fails to encrypt images properly if the image consists of large area covered with same colour or gray level. Thus, it does not hide all features of the image which reveals patterns in the plaintext. Moreover, it can be easily broken with a known plaintext attack revealing weak security. To address these issues two different techniques are proposed, those are advanced Hill cipher algorithm and H-S-X cryptosystem to encrypt the images properly. Security analysis of both the techniques reveals superiority of encryption and decryption of images. On the other hand, H-S-X cryptosystem has been used to instil more diffusion and confusion on the cryptanalysis. FPGA implementation of both the proposed techniques has been modeled to show the effectiveness of both the techniques. An extended Hill cipher algorithm based on XOR and zigzag operation is designed to reduce both encryption and decryption time. This technique not only reduces the encryption and decryption time but also ensures no loss of data during encryption and decryption process as compared to other techniques and possesses more resistance to intruder attack. The hybrid cryptosystem which is the combination of extended Hill cipher technique and RSA algorithm has been implemented to solve the key distribution problem and to enhance the security with reduced encryption and decryption time. Two distinct approaches for image encryption are proposed using chaos based DNA coding along with shifting and scrambling or poker shuffle to create grand disorder between the pixels of the images. In the first approach, results obtained from chaos based DNA coding scheme is shifted and scrambled to provide encryption. On the other hand in the second approach the results obtained from chaos based DNA coding encryption is followed by poker shuffle operation to generate the final result. Simulated results suggest performance superiority for encryption and decryption of image and the results obtained have been compared and discussed. Later on FPGA implementation of proposed cryptosystem has been performed. In another contribution, a modified Hill cipher is proposed which is the combination of three techniques. This proposed modified Hill cipher takes advantage of all the three techniques. To acquire the demands of authenticity, integrity, and non-repudiation along with confidentiality, a novel hybrid method has been implemented. This method has employed proposed modified Hill cipher to provide confidentiality. Produced message digest encrypted by private key of RSA algorithm to achieve other features such as authenticity, integrity, and non-repudiation To enhance the security of images, a biometric cryptosystem approach that combines cryptography and biometrics has been proposed. Under this approach, the image is encrypted with the help of fingerprint and password. A key generated with the combination of fingerprint and password and is used for image encryption. This mechanism is seen to enhance the security of biometrics images during transmission. Each proposed algorithm is studied separately, and simulation experiments are conducted to evaluate their performance. The security analyses are performed and performance compared with other competent schemes

Proceedings of the Fifth NASA/NSF/DOD Workshop on Aerospace Computational Control

The Fifth Annual Workshop on Aerospace Computational Control was one in a series of workshops sponsored by NASA, NSF, and the DOD. The purpose of these workshops is to address computational issues in the analysis, design, and testing of flexible multibody control systems for aerospace applications. The intention in holding these workshops is to bring together users, researchers, and developers of computational tools in aerospace systems (spacecraft, space robotics, aerospace transportation vehicles, etc.) for the purpose of exchanging ideas on the state of the art in computational tools and techniques

The Telecommunications and Data Acquisition Report

This publication, one of a series formerly titled The Deep Space Network Progress Report, documents DSN progress in flight project support, tracking and data acquisition research and technology, network engineering, hardware and software implementation, and operations. In addition, developments in Earth-based radio technology as applied to geodynamics, astrophysics and the radio search for extraterrestrial intelligence are reported

Aeronautical engineering: A continuing bibliography with indexes (supplement 255)

This bibliography lists 529 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Systolic computation of characteristic polynomials of hessenberg matrices

This paper describes the use of Instruction Systolic Arrays to compute a scalar multiple of the characteristic polynomial of a Hessenberg matrix in time O(n), where n is the order of the matrix