Stochastic Structural Stability Theory applied to roll/streak formation in boundary layer shear flow

Stochastic Structural Stability Theory (SSST) provides an autonomous, deterministic, nonlinear dynamical system for evolving the statistical mean state of a turbulent system. In this work SSST is applied to the problem of understanding the formation of the roll/streak structures that arise from free-stream turbulence (FST) and are associated with bypass transition in boundary layers. Roll structures in the cross-stream/spanwise plane and associated streamwise streaks are shown to arise as a linear instability of interaction between the FST and the mean flow. In this interaction incoherent Reynolds stresses arising from FST are organized by perturbation streamwise streaks to coherently force perturbation rolls giving rise to an amplification of the streamwise streak perturbation and through this feedback to an instability of the combined roll/streak/turbulence complex. The dominant turbulent perturbation structures involved in supporting the roll/streak/turbulence complex instability are non-normal optimal perturbations with the form of oblique waves. The cooperative linear instability giving rise to the roll/streak structure arises at a bifurcation in the parameter of STM excitation parameter. This structural instability eventually equilibrates nonlinearly at finite amplitude and although the resulting statistical equilibrium streamwise streaks are inflectional the associated flows are stable. Formation and equilibration of the roll/streak structure by this mechanism can be traced to the non-normality which underlies interaction between perturbations and mean flows in modally stable systems.Comment: 16 pages, 24 figures, has been submitted for publication to Physics of Fluid

Co-tuning virtual-acoustic performance ecosystems: observations on the development of skill and style in the study of musician-instrument relationships

In this paper we report preliminary observations from an ongoing study into how musicians explore and adapt to the parameter space of a virtual-acoustic string bridge plate instrument. These observations inform (and are informed by) a wider approach to understanding the development of skill and style in interactions between musicians and musical instruments. We discuss a performance-driven ecosystemic approach to studying musical relationships, drawing on arguments from the literature which emphasise the need to go beyond simplistic notions of control and usability when assessing exploratory and performatory musical interactions. Lastly, we focus on processes of perceptual learning and co-tuning between musician and instrument, and how these activities may contribute to the emergence of personal style as a hallmark of skilful music-making

Nonlinear modal aeroservoelastic analysis framework for flexible aircraft

A nonlinear formulation in modal coordinates of the equations of motion of a flexible aircraft is presented. It relies on the projection of the intrinsic equations of geometrically nonlinear composite beams on the linear normal modes at a reference condition, which are coupled with two-dimensional unsteady aerodynamics. The resulting description is suitable for nonlinear dynamic analysis and control design, whereas the description in modal coordinates links directly to linear aeroservoelastic analysis methods. Results are presented on and compared to cantilever wings and full aircraft configurations previously studied in the literature. Linear H∞H∞ control synthesis and closed-loop nonlinear simulations are finally explored on a highly flexible flying wing under large-amplitude discrete gusts. Results show the ability of the proposed framework to capture the nonlinear dynamics of the aeroelastic system, while providing a seamless integration with linear methods, as well as its strength in identification of the dominant contributors to the nonlinear response

Customizing Message Content to Facilitate Decisions about Participating in Genomics Research: A Reasoned Action Approach

According to the doctrine of informed consent, research participants have a right to voluntarily decide whether to enroll in a study and to do so with an adequate understanding of what participation entails (Beauchamp & Childress, 2009). Mirroring these rights, investigators have a moral obligation to give people the facts that are most critical to their choices (Fischhoff, 2011). Yet, theory-based analytical tools for determining which information is likely to have the largest impact on participation decisions are underdeveloped. Lacking a basis to prioritize elements of disclosure for distinct audiences, the length and complexity of consent documents has increased over time. Ironically, these improvements may have hindered comprehension and people\u27s access to the information they need to make informed choices. According to the reasoned action model (Fishbein & Ajzen, 2010), decisions to participate in genomics research--like any other behavior--are driven by a limited number of factors. In this dissertation, consequences of participating that readily came to mind for respondents were expected to have a larger impact on attitudes and intentions to participate in genomics research than were nonsalient consequences. Moreover, customized messages designed to target salient versus nonsalient beliefs were expected to have larger effects on attitude and intention. Based on media priming theory (e.g., Price & Tewksbury, 1997), plausible downstream effects on belief salience resulting from message exposure were also explored, as was the conditional effect of salience on belief change (Jaccard, 1981). An open-ended belief elicitation in Study 1 revealed audience segments with different motivations for participating in a genetic biobank. Contributing to the greater good was especially salient for some respondents, while receiving personal test results was salient for others. In Study 2, an experimental design was used to test the conditional effects of segment-targeted messages on belief strength, attitudes and intentions toward participating in a fictional genomic research project. Both studies suggested that salient behavior-related beliefs had a larger influence on people\u27s participation decisions. Results from Study 2 further indicated that salient beliefs might also be more difficult to change. Theoretical and practical implications for fostering informed consent in large-scale genomic research are discussed

Continuity and Change in Eugène Ysaÿe’s Six Sonatas, Op. 27, for Solo Violin

The Six Sonatas, Op. 27, for Solo Violin by the Belgian violinist and composer Eugène Ysaÿe (1858-1931), written in 1923/24, are increasingly adopted into the standard repertoire of violinists. Ysaÿe saw them as containing his legacy to future generations of violinists and composers and also as a statement of his aesthetic identity. However, not much research has been done on the aesthetics reflected in them. Yet, a greater awareness of Ysaÿe’s aesthetics will add to the understanding of this important historical figure who did so much to popularise French and Belgian music of the turn of the twentieth century and very much identified with the circle of composers around César Franck. This thesis focusses on Ysaÿe’s relationship with music history as represented in Op. 27. It explores his aesthetics, in particular his attitude to the past, present and future as well as his insistence on the continuity of history. Part I examines Ysaÿe’s historical and biographical context as well as his aesthetic predilections. It particularly focuses on composers to whom he was close, notably the Franckists, as well as on the violin tradition of which he was part, with an emphasis on Henri Vieuxtemps. As each Sonata is dedicated to a violinist of the generation after Ysaÿe, their personalities and playing styles are also discussed. Part II turns to the Sonatas themselves and explores ways in which Ysaÿe engages with past and contemporaneous composers, notably J. S. Bach, César Franck and Claude Debussy, as well as with the violin tradition and the possible influence of the dedicatees on their Sonata. It also demonstrates Ysaÿe’s contribution to music history, especially to the development of the technical and expressive possibilities of his instrument

Characterisation of Nonlinear Structural Dynamic Systems in Conceptual Design

The engine and driveline systems of passenger cars generates and distributes the necessary driving power and are major contributors to vehicle emissions, noise and vibrations, etc. More environmental friendly technologies under development are expected to intensify and add new comfort related problems, since most of them affect vibration sources or system damping. A successful balancing of fundamental system qualities requires a better use of simulation in early design phase. This work focus on virtual tools for analysis of low-frequency structural dynamic vibrations. In conceptual driveline design, many possible system solutions are studied in parallel and their often nonlinear behaviour requires robustness evaluation across full operating and design parameter ranges. This situation calls for virtual methods that are generally valid and meet the demand for rapid prototyping. Thus, models need to be as simple as possible and as accurate as required for capturing phenomena that occur in real drivelines. Further, analysis tools must efficiently process data sets from extensive parameter variations and extract fundamental system characteristics that can be used to reliably rate competing proposals. For this, a complementing design analysis methodology is proposed that improves current automotive development tools and workflow. A general and over-parameterised multi-body system model is constructed from detailed linear structural and schematic nonlinear parts. State-space reduction methods are then applied to modal components to balance prediction accuracy and evaluation speed of resulting conceptual design models. Parameter variations in fully known system models are simulated under ideal periodic loading and low noise conditions. A feature based frequency analysis approach is used to extract precise system characteristics and sort responses into qualitative classes. To efficiently process large amounts of generated data, statistical learning methods are used to automate the response classification

Aeroelastic Tailoring of Transport Aircraft Wings: State-of-the-Art and Potential Enabling Technologies

This paper provides a brief overview of the state-of-the-art for aeroelastic tailoring of subsonic transport aircraft and offers additional resources on related research efforts. Emphasis is placed on aircraft having straight or aft swept wings. The literature covers computational synthesis tools developed for aeroelastic tailoring and numerous design studies focused on discovering new methods for passive aeroelastic control. Several new structural and material technologies are presented as potential enablers of aeroelastic tailoring, including selectively reinforced materials, functionally graded materials, fiber tow steered composite laminates, and various nonconventional structural designs. In addition, smart materials and structures whose properties or configurations change in response to external stimuli are presented as potential active approaches to aeroelastic tailoring