Interior feedback stabilization of wave equations with dynamic boundary delay

In this paper we consider an interior stabilization problem for the wave equation with dynamic boundary delay.We prove some stability results under the choice of damping operator. The proof of the main result is based on a frequency domain method and combines a contradiction argument with the multiplier technique to carry out a special analysis for the resolvent

Dynamic and fluid–structure interaction simulations of bioprosthetic heart valves using parametric design with T-splines and Fung-type material models

This paper builds on a recently developed immersogeometric fluid–structure interaction (FSI) methodology for bioprosthetic heart valve (BHV) modeling and simulation. It enhances the proposed framework in the areas of geometry design and constitutive modeling. With these enhancements, BHV FSI simulations may be performed with greater levels of automation, robustness and physical realism. In addition, the paper presents a comparison between FSI analysis and standalone structural dynamics simulation driven by prescribed transvalvular pressure, the latter being a more common modeling choice for this class of problems. The FSI computation achieved better physiological realism in predicting the valve leaflet deformation than its standalone structural dynamics counterpart

Design and analysis of an instrument system for rheological testing of whole blood samples

The dissertation covers the conceptual design of a rheometer for testing whole blood samples through to the clotting state. While the design aims at increased measurement accuracy, the design employs well known technologies and available components. The main reason for preoccupation with blood testing is that recent investigations have indicated that physiological disorders can be correlated with rheological properties of blood. The pursuit of an improved means of correlation is initiated with a survey of the rheological properties of blood. The relevance of these blood properties is then discussed. From this discussion a broader blood model is developed as a guide to design of a special blood rheometer. The contribution of this work is an engineering study of the exploitation of known technologies to produce a rheometer which permits more precise measurement of fluid properties by better quantization of instrument errors. The quantization of instrument errors inherently requires new and original analysis of sample holder geometry, mathematical treatment of sample holder geometry for Newtonian fluids, discussion of exact and end effect characteristics of solutions of sample holder geometry for Newtonian fluids. Further reduction in errors are achieved by the control of sample holder motions (through management of motions in discrete steps), a flexible digital control of required motions, and a method for obtaining transient responses and fast time constants for torque measurement using a conventional counter torque servo system

Spatially-Dependent Reactor Kinetics and Supporting Physics Validation Studies at the High Flux Isotope Reactor

The computational ability to accurately predict the dynamic behavior of a nuclear reactor core in response to reactivity-induced perturbations is an important subject in the field of reactor physics. Space-time and point kinetics methodologies were developed for the purpose of studying the transient-induced behavior of the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor’s (HFIR) compact core. The space-time simulations employed the three-group neutron diffusion equations, which were solved via the COMSOL partial differential equation coefficient application mode. The point kinetics equations were solved with the PARET code and the COMSOL ordinary differential equation application mode. The basic nuclear data were generated by the NEWT and MCNP5 codes and transients initiated by control cylinder and hydraulic tube rabbit ejections were studied. The space-time models developed in this research only consider the neutronics aspect of reactor kinetics, and therefore, do not include fluid flow, heat transfer, or reactivity feedback. The research presented in this dissertation is the first step towards creating a comprehensive multiphysics methodology for studying the dynamic behavior of the HFIR core during reactivity-induced perturbations. The results of this study show that point kinetics is adequate for small perturbations in which the power distribution is assumed to be time-independent, but space-time methods must be utilized to determine localized effects. En route to developing the kinetics methodologies, validation studies and methodology updates were performed to verify the exercise of major neutronic analysis tools at the HFIR. A complex MCNP5 model of HFIR was validated against critical experiment power distribution and effective multiplication factor data. The ALEPH and VESTA depletion tools were validated against post-irradiation uranium isotopic mass spectrographic data for three unique full power cycles. A TRITON model was developed and used to calculate the buildup and reactivity worth of helium-3 in the beryllium reflector, determine whether discharged beryllium reflectors are at transuranic waste limits for disposal purposes, determine whether discharged beryllium reflectors can be reclassified from hazard category 1 waste to category 2 or 3 for transportation and storage purposes, and to calculate the curium target rod nuclide inventory following irradiation in the flux trap

Statistical Vibro-Acoustic Modelling of Nonlinear Systems with Applications in Vehicles

Designing quiet cars has become an important issue in the automotive industry, where passive and active noise control techniques can be employed to improve the acoustic comfort without compromising the vehicle performance. At the design stage of a noise control system, the estimation of the structure-borne sound pressure levels in the car cabin is a challenging problem, as uncertainties in a physical structural-acoustic system have an impact on the vehicle dynamics at high frequencies. Additionally, the response of the system can be affected by nonlinearities in the vibrations transmission path. Therefore, this research has been focused in developing computationally efficient vibro-acoustic models to predict the statistical structural-acoustic response of a system to random inputs, as well as analysing the degree of dependency of the response to nonlinear behaviour in the interface between the excitation and the structure. Key aspects of the impact that a nonlinear transmission path might have in the response of a statistical structural-acoustic system, were investigated from an equivalent damper model of the structural vibrating subsystem, under the assumption of weak acoustic coupling and the infinite plate theory. Numerical data in the time domain were generated from the simplified nonlinear system excited by random inputs with known power spectral density. The effects of nonlinearities were observed and quantified in the power spectral density of the response, as well as in the reduction of coherence between the input and output. Additionally, the Wiener theory in the frequency domain has been explored to estimate the degree of contribution of a nonlinearity of second order to the total response of the system. Finally, an extended hybrid Finite Element-Statistical Energy Analysis (FE-SEA) model was proposed to analyse the response of a deterministic-statistic structural-acoustic system, where the nonlinear transmission path is considered as a deterministic structure. The equations of an existing FE-SEA approach, based on the diffuse field reciprocity, have been generalised to include prescribed displacements as inputs, in addition to external forces. The nonlinear analysis with the FE-SEA approach has been carried out by adopting the concept of equivalent linearisation of the deterministic dynamic stiffness matrix, and the capability of the approach has been validated against experimental data from a physical nonlinear structural-acoustic setup

Adaptive prescribed performance control for wave equations with dynamic boundary and multiple parametric uncertainties

In modern engineering, the dynamics of many practical problems can be described by hyperbolic distributed parameter systems. This paper is devoted to the adaptive prescribed performance control for a class of typical uncertain hyperbolic distributed parameter systems, since uncertainties are inevitable in practice. The systems in question simultaneously have unknown in-domain spatially varying damping coefficient and unknown boundary constant damping coefficient. Moreover, dynamic boundary condition is considered in the present paper. These characteristics make the control problem in the paper essentially different from those in the related works. To solve the problem, using adaptive technique based projection operator, backstepping method developed for ODEs and Lyapunov stability theories, a powerful adaptive prescribed performance control scheme is proposed to successfully guarantee that all states of the resulting closed-loop system are bounded, furthermore, the original system state converges to an arbitrary prescribed small neighborhood of the origin. Compared with the existing results, the developed control schemes can not only effectively handle the serious uncertainties, but also overcome the technical difficulties in the infinite-dimensional backstepping control design method caused by the dynamic boundary condition and guarantee prescribed performance

The 58th Shock and Vibration Symposium, volume 1

The proceedings of the 58th Shock and Vibration Symposium, held in Huntsville, Alabama, October 13 to 15, 1987 are given. Mechanical shock, dynamic analysis, space shuttle main engine vibration, isolation and damping, and analytical methods are discussed

STUDY OF COMPOSITE STRUCTURES SUBJECTED TO UNDERWATER SHOCK LOADING

Underwater explosions (UNDEX) produce severe and complex loadings in naval applications. Increased use of composite materials in naval applications requires better understanding of how composite structures will respond and survive an UNDEX. A legacy underwater shock loading method, using liquid nitrogen, was implemented to study the dynamic structural response and failure of flat carbon composite plates. Pressure data was collected using different layouts to study directionality and to characterize the pressure profile of this loading method. A composite test rig was built and utilized to hold composite plates under different backing conditions, water-back (WB) and air-back (AB). Strain response data was collected and analyzed for each composite plate tested. A comparison of water-back and air-back backing conditions was made to better understand the effects of Fluid Structure Interaction in these contrasting backing conditions. Imagery of failure regions was collected, compared, and characterized. Further research is required to validate and more deeply explain the AB and WB comparison results obtained in this research. A compressed air shock pipe underwater release (CASPUR) system was designed and built. Successful initial operational testing of CASPUR was completed. Future pressure profile characterization of CASPUR is needed. Assessment of its efficacy in providing more consistent loading and structure response compared to that of the legacy loading system is required.Lieutenant, United States NavyApproved for public release. Distribution is unlimited