Finite element modelling of lamb wave propagation in prestress concrete and effect of the prestress force on the wave’s characteristic

In order to assess the structural reliability of bridges, an accurate and cost effective Non-Destructive Evaluation (NDE) technology is required to ensure their safe and reliable operation. Over 60% of the Australian National Highway System is prestressed concrete (PSC) bridges according to the Bureau of Transport and Communication Economics (1997). Most of the in-service bridges are more than 30 years old and may experience a heavier traffic load than their original intended level. Use of Ultrasonic waves is continuously increasing for (NDE) and Structural Health Monitoring (SHM) in civil, aerospace, electrical, mechanical applications. Ultrasonic Lamb waves are becoming more popular for NDE because it can propagate long distance and reach hidden regions with less energy loses. The purpose of this study is to numerically quantify prestress force (PSF) of (PSC) beam using the fundamental theory of acoustic-elasticity. A three-dimension finite element modelling approach is set up to perform parametric studies in order to better understand how the lamb wave propagation in PSC beam is affected by changing in the PSF level. Results from acoustic-elastic measurement on prestressed beam are presented, showing the feasibility of the lamb wave for PSF evaluation in PSC bridges.

Wave analysis of sound decay in rectangular rooms

The decay of sound in a rectangular room is analyzed for various boundary conditions on one of its walls. It is shown that the decay of the sound-intensity level is in general nonlinear. But for specific areas and impedances of the material it is possible to obtain a linear initial decay. It is also shown that the coefficients derived from the initial decay rates neither correspond to the predictions of Sabine's or Eyring's geometrical theories nor to the normal coefficients of Morse's wave theory. The dependence of the coefficients on the area of the material is discussed. The influence of the real and the imaginary parts of the specific acoustic impedance of the material on the coefficients is also discussed. Finally, the existence of a linear initial decay corresponding to the decay of a diffuse field in the case of a highly absorbing material partially covering a wall is explained on the basis of modal coupling.

Parametric Study of Flood Wave Propagation

A parametric study of the flood wave propagation problem is made, based on numerical solution of the nondimensionalized unsteady flow equations of open channels. The propagation of a sinusoidal flood wave in a prismatic channel is studied for uniform initial flow. The governing parameters (initial uniform flow Froude number, wave amplitude, wave duration, channel width parameter and side slope) are varied over a wide range. In all, 49 cases are studied. Effects of these governing parameters on the subsidence of stage and discharge and the speed of the wave peak are described in detail. The relative wave amplitude is found to vary linearly with F0, the initial uniform flow froude number, for lower F0 values. Wave duration has a very pronounced effect on subsidence with greater subsidence at lower wave duration values.

Single network adaptive critic design for power system stabilisers

The recently developed single network adaptive critic (SNAC) design has been used in this study to design a power system stabiliser (PSS) for enhancing the small-signal stability of power systems over a wide range of operating conditions. PSS design is formulated as a discrete non-linear quadratic regulator problem. SNAC is then used to solve the resulting discrete-time optimal control problem. SNAC uses only a single critic neural network instead of the action-critic dual network architecture of typical adaptive critic designs. SNAC eliminates the iterative training loops between the action and critic networks and greatly simplifies the training procedure. The performance of the proposed PSS has been tested on a single machine infinite bus test system for various system and loading conditions. The proposed stabiliser, which is relatively easier to synthesise, consistently outperformed stabilisers based on conventional lead-lag and linear quadratic regulator designs.

Rail power conditioner technology in Australian Heavy Haul Railway: A case study

Aurizon, Australia's largest freight railway operator, is investigating the use of Rail Power Conditioner (RPC) technology for load balancing, reactive power compensation and harmonic filtering. The new technology has the capability of replacing Static VAr Compensators (SVC) and Harmonic Filters, and is expected to have a significant impact on the overall costs of railway electrification. This paper presents the theoretical analysis of the real and reactive power flows in an RPC used to balance active powers in an existing V/V feeder station. This informed an RPC feasibility study undertaken at four existing Aurizon's feeder stations with V/V connected transformers.

Radiation induced depinning of a charge density wave system

The frequency-dependent response of a pinned charge density wave is considered in terms of forced vibration of an oscillator held in an anharmonic well. It is shown that the effective pinning-frequency can be reduced by applying a d.c. field. If a strong a.c. field, superposed on a d.c. field is applied on such a system “jumps” can be observed in the frequency dependent response of the system. The conditions at which these “jumps” occur are investigated with reference to NbSe3. The possibility of observing such phenomena in other systems like superionic conductors, non-linear dielectrics like ferroelectrics is pointed out. The characteristics are expressed in terms of some “scaled variables” — in terms of which the characteristics show a universal behaviour

Wave analysis of sound decay in rectangular rooms

The decay of sound in a rectangular room is analyzed for various boundary conditions on one of its walls. It is shown that the decay of the sound-intensity level is in general nonlinear. But for specific areas and impedances of the material it is possible to obtain a linear initial decay. It is also shown that the coefficients derived from the initial decay rates neither correspond to the predictions of Sabine's or Eyring's geometrical theories nor to the normal coefficients of Morse's wave theory. The dependence of the coefficients on the area of the material is discussed. The influence of the real and the imaginary parts of the specific acoustic impedance of the material on the coefficients is also discussed. Finally, the existence of a linear initial decay corresponding to the decay of a diffuse field in the case of a highly absorbing material partially covering a wall is explained on the basis of modal coupling.

Studies on micro explosive driven blast wave propagation in confined domains using NONEL tubes

Explosive driven micro blast waves are generated in the laboratory using NONEL tubes. The explosive mixture coated to the inner walls of the plastic Nonel tube comprises of HMX and Aluminum ( 18mg/m). The detonation is triggered electrically to generate micro blast waves from the open end of the tube. Flow visualization and over pressure measurements have been carried out to understand the propagation dynamics of these micro-blast waves in both confined and unconfined domains. The classical cubic root law used for large scale blast correlation appears to hold good even for these micro-blasts generated in the laboratory.

Power Aware Real Time Scheduling in Constrained Devices

Real-time scheduling algorithms, such as Rate Monotonic and Earliest Deadline First, guarantee that calculations are performed within a pre-defined time. As many real-time systems operate on limited battery power, these algorithms have been enhanced with power-aware properties. In this thesis, 13 power-aware real-time scheduling algorithms for processor, device and system-level use are explored.

Localised spin wave modes in a Heisenberg ferromagnet with biquadratic interaction

The presence of biquadratic exchange in a one-dimensional ferromagnetic Heisenberg chain with an impurity spin is shown to change the nature of the impurity modes and its eigenvalues considerably which can be observed experimentally.

The jump in vorticity across a shock wave in relativistic hydrodynamics

Using the singular surface theory, an expression for the jump in vorticity across a shock wave of arbitrary shape propagating in a uniform, perfect fluid occupying the space-time of special relativity, has been derived. It has been shown that the jump in vorticity across a shock of given strength and curvature depends only on the velocity of the medium ahead of the shock.

The White Possessive : Property, Power and Indigenous Sovereignty

The White Possessive explores the links between race, sovereignty, and possession through themes of property: owning property, being property, and becoming propertyless. Focusing on the Australian Aboriginal context, Aileen Moreton-Robinson questions current race theory in the first world and its preoccupation with foregrounding slavery and migration. The nation, she argues, is socially and culturally constructed as a white possession. Moreton-Robinson reveals how the core values of Australian national identity continue to have roots in Britishness and colonization, built on the disavowal of Indigenous sovereignty. Whiteness studies are central to Moreton-Robinson’s reasoning, and she shows how blackness works as a white epistemological tool that bolsters the social production of whiteness—displacing Indigenous sovereignties and rendering them invisible in a civil rights discourse, sidestepping issues of settler colonialism. Throughout this critical examination Moreton-Robinson proposes a bold new agenda for critical Indigenous studies, one that involves deeper analysis of the prerogatives of white possession within the role of disciplines.

Power and Authority. Birgitta of Sweden and her Revelations

In the High Middle Ages female saints were customarily noble virgins. Thus, as a wife and a mother of eight children, the Swedish noble lady Birgitta (1302/3 1373) was an atypical candidate for sanctity. However, in 1391 she was canonized only 18 years after her death and became a role model for many late medieval women, who were mothers and widows. The dissertation Power and Authority Birgitta of Sweden and Her Revelations investigates how Birgitta went about establishing her power and authority during the first ten years of her career as a living saint, in 1340 1349. It is written from the perspectives of gender, authority, and power. The sources consist of approximately seven hundred revelations, hagiographical texts and other medieval documents. This work concentrates on the interaction between Birgitta and her audience. During her lifetime Birgitta was already regarded as a holy woman, as a living saint. A living saint could be given no formal papal or other recognition, for one could never be certain about his or her future activities. Thus, the living saint needed an audience for whom to perform signs of sanctity. In this study particular attention is paid to situations within which the power relations between the living saint and her audience can be traced and are open to critical analysis. Situations of conflict that arose in Birgitta s life are especially fruitful for this purpose. During the Middle Ages, institutional power and authority were exclusively in the hands of secular male leaders and churchmen. In this work it is argued, however, that Birgitta used different kinds of power than men. It is evident that she exercized influence on lay people as well as on secular and clerical authorities. The second, third, and fourth chapter of this study examine the beginning of Birgitta s career as a visionary, what factors and influences lay behind it, and what kind of roles they played in establishing her religious authority. The fifth, sixth, and seventh chapter concentrate on Birgitta s exercising of power in specific situations during her time in Sweden until she left on a pilgrimage to Rome in 1349. The central question is how she exercised power with different people. As a result, this book will offer a narrative of Birgitta s social interactions in Sweden seen from the perspectives of power and authority. Along with the concept of power, authority is a key issue. By definition, one who has power also has authority but a person who does not have official power can, nevertheless, have authority. Authority in action is defined here as meaning that a person was listened to. Birgitta acted both in situations of open conflict and where no conflict was evident. Her strategies included, for example, inducement, encouragement and flattery. In order to make people do as she felt was right she also threatened them openly with divine wrath. Sometimes she even used both positive persuasion and threats. Birgitta s power seems very similar to that of priests and ascetics. Common to all of them was that their power demanded interaction with other people and audiences. Because Birgitta did not have power and authority ex officio she had to persuade people to believe in her powers. She did this because she was convinced of her mission and sought to make people change their lives. In so doing, she moved from the domestic field to the public fields of religion and politics.