28 research outputs found
Integrated flight dynamics and aeroelasticity of flexible aircraft with application to swept flying wings
No full text© 2015, American Institute of Aeronautics and Astronautics Inc. All Rights Reserved.The dynamics of flexible, swept flying wing (SFW) aircraft are described by a set of nonlinear, multi-disciplinary equations of motion. Aircraft structures are modeled using a geometrically-exact composite beam model which can, in general, capture large dynamic deformations and the interaction between rigid-body and elastic degrees-of-freedom. In addition, an implementation of the unsteady vortex-lattice method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-field around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be around a nonlinear equilibrium, is performed to yield linear time-invariant state-space models. Verification of aeroelastic stability analyses using these models is carried out. Subsequently, a set of SFW models are developed and the dynamic stability characteristics of these aircraft are investigated for a range of flight velocities and vehicle parameters
A study of rheological limitations in rotary jet spinning of polymer nanofibers through modeling and experimentation
No full textThe recently popularized method of rotary jet spinning (RJS) or centrifugal spinning is investigated to evaluate the rheological limitations of polymer solutions and melts to optimal spinnability. The influence of Newtonian or non-Newtonian behavior of the polymer on spinnability is discussed. We observe that highly viscous polymers tend to block the die channels within a rotary jet spinneret and therefore suggest the use of relatively low Newtonian viscosities of between 1 and 10 Pa s for optimal fiber production. Computational fluid dynamics simulations are used in conjunction with experimental data to establish important processing parameters, such as typical shear rates in the device and optimal polymer melt or solution viscosities. A theoretical model for RJS is compared to measured fiber diameters. The comparison shows that although fiber diameters can be estimated very roughly in the case of polymer solutions, the prediction of fiber diameter in the case of polymer melts require further modeling work
Induced Drag Calculations in the Unsteady Vortex Lattice Method
No full text21.05.13 KB. Ok to add the accepted version to Spiral. AIA
Identification, Geochemical Characterisation and Significance of Bitumen among the Grave Goods of the 7th Century Mound 1 Ship-Burial at Sutton Hoo (Suffolk, UK)
No full textAcknowledgments: We would like to thank Antony Simpson for formatting the figures for publication. We are indebted to Dr Sonja Marzinzik and Dr Sue Brunning, former and current curators of the Department of Britain, Europe and Prehistory at the British Museum, for facilitating access to the Sutton Hoo finds. Carbon and hydrogen isotopic measurements were carried out by Iso-Analytical Limited. We are grateful to colleagues and others who read and commented on the manuscript in draft. Funding: This research was supported by funding from the European Commission Research Executive Agency (REA) via the Marie Curie Actions – Intra-European Fellowships for Career Development funding scheme (FP7-MC-IEF), Grant Agreement No. 253942, awarded to PB and RJS for project AMPT (Ancient Maritime Pitch and Tar: a multi-disciplinary study of sources, technology and preservation). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe
Predictive Control for Alleviation of Gust Loads on Very Flexible Aircraft
No full text11/03/14 meb. Author retains copyright as beforeIn this work the dynamics of very flexible aircraft are described by a set of non-linear, multi-disciplinary equations of motion. Primary structural components are represented by a geometrically-exact composite beam model which captures the large dynamic deformations of the aircraft and the interaction between rigid-body and elastic degrees-of-freedom. In addition, an implementation of the unsteady vortex-lattice method capable of handling arbitrary kinematics is used to capture the unsteady, three-dimensional flow-eld around the aircraft as it deforms. Linearization of this coupled nonlinear description, which can in general be about a nonlinear reference state, is performed to yield relatively high-order linear time-invariant state-space models. Subsequent reduction of these models using standard balanced truncation results in low-order models suitable for the synthesis of online, optimization-based control schemes that incorporate actuator constraints. Predictive controllers are synthesized using these reduced-order models and applied to nonlinear simulations of the plant dynamics where they are shown to be superior to equivalent optimal linear controllers (LQR) for problems in which constraints are active
Optimal Manoeuvres with Very Flexible Wings
No full textThe single shooting method is used identify optimal manoeuvres in the lateral dynamics
of partially-supported wings of very low stiffness. The aim is to identify actuation
strategies in the design of aircraft manoeuvres in which large wing deflections can substantially
modify the vehicle structural and aerodynamic features. Preliminary studies are
presented for a representative high-altitude long-endurance aircraft wing in hinged confi-
guration. Nonlinear effects due to large deflections are captured coupling a geometrically
exact beam model with an unsteady vortex lattice method for the aerodynamics. The
optimal control problem is solved via a gradient-based algorithm. When lowering the wing
stiffness, the nonlinearities connected to the system — such as the fore-shortening effect
due to large bending deflections — increase the wing lateral stability but at the same time
they also reduce aileron authority. The single-shooting optimisation is shown to capture
these features and to provide satisfactory results, not only when refining a predetermined
actuation law but also when designing it from zero
Adaptive convex loss selection for m-estimation: adaptive rate and efficiency
No full textThis thesis delves into the classical linear regression problem, focusing on the estimation of the
unknown parameter β0 ∈ Rd given n random vectors (X1, Y1), . . . , (Xn, Yn) that follow the linear
model Yi = X⊤i β0 + ϵi. The covariates X1, . . . , Xn are independent and identically distributed
(i.i.d.) Rd-valued and independent of the i.i.d. real-valued errors ϵ1, . . . , ϵn with an unknown
distribution. We focus on the low-dimensional setting where the problem dimension d is fixed,
analysing the performance of estimators as n becomes large.
Historically, the use of estimators that minimise the sum of the squared error losses has been
widely adopted in solving regression problems. In the linear regression setting, the Gauss–Markov
theorem justifies the ordinary least squares (OLS) estimator only under limited conditions. We be-
lieve that it is the convexity of the L2 loss function, which makes the minimisation computationally
tractable, makes OLS attractive to the practitioners. This thesis thus focuses on the adaptive (data-
driven) selection of convex loss functions for better estimation in linear regression, in the hope of
challenging the default use of L2 and L1 loss functions in modern high-dimensional regression.
Chapter 1 explores the mean estimation of univariate distributions symmetric around their mean
under irregular error distributions, where rates faster than n−1/2 can be achieved. We construct an
estimator achieving optimal rates up to n−1/α for compactly supported error distributions, where
α ∈ (0, 2]. The method involves a convex M -estimator based on a convex loss function Lγ (x) =
ii |x|γ , where γ is selected in data-driven fashion. The proposed method is computationally efficient
can be extended to linear regression settings. This chapter is based on the join work with Min Xu
and Cun-Hui Zhang, Kao et al. (2022).
Chapter 2 addresses linear regression under smooth error densities with finite Fisher informa-
tion, where a faster than n−1/2 rate is unattainable. We focus on selecting convex loss functions
to minimise asymptotic covariance among convex M -estimators. We identify the optimal convex
loss function with the log-concave projection of the noise distribution with respect to the Fisher di-
vergence and construct an adaptive estimator achieving the minimal asymptotic covariance among
the convex M -estimators. The proposed procedure is computationally efficient. This work is based
on the joint work with Oliver Y. Feng, Min Xu, and Richard J. Samworth, Feng et al. (2024).
iiiPh.D.Includes bibliographical reference
The effects of superimposed tilt and lower body negative pressure on anterior and posterior cerebral circulations
No full textSteady-state tilt has no effect on cerebrovascular reactivity to increases in the partial pressure of end-tidal carbon dioxide (PETCO2). However, the anterior and posterior cerebral circulations may respond differently to a variety of stimuli that alter central blood volume, including lower body negative pressure (LBNP). Little is known about the superimposed effects of head-up tilt (HUT; decreased central blood volume and intracranial pressure) and headdown tilt (HDT; increased central blood volume and intracranial pressure), and LBNP on cerebral blood flow (CBF) responses. We hypothesized that (a) cerebral blood velocity (CBV; an index of CBF) responses during LBNP would not change with HUT and HDT, and (b) CBV in the anterior cerebral circulation would decrease to a greater extent compared to posterior CBV during LBNP when controlling PETCO2. In 13 male participants, we measured CBV in the anterior (middle cerebral artery, MCAv) and posterior (posterior cerebral artery, PCAv) cerebral circulations using transcranial Doppler ultrasound during LBNP stress (−50 mmHg) in three body positions (45°HUT, supine, 45°HDT). PETCO2 was measured continuously and maintained at constant levels during LBNP through coached breathing. Our main findings were that (a) steady-state tilt had no effect on CBV responses during LBNP in both the MCA (P = 0.077) and PCA (P = 0.583), and (b) despite controlling for PETCO2, both the MCAv and PCAv decreased by the same magnitude during LBNP in HUT (P = 0.348), supine (P = 0.694), and HDT (P = 0.407). Here, we demonstrate that there are no differences in anterior and posterior circulations in response to LBNP in different body positions.Library OA FundFinancial support for the initial building of the apparatus (supplies) was provided by Mount Royal University, Faculty of Science and Technology, Laboratory Support Centre, and most of the funding for data collection (student salaries) by a Government of Alberta STEP Grant (MMT and RJS), an NSERC USRA (MMT), and the MRU Petro-Canada Young Investigator award (TAD). Funds for covering the costs to publish in open access were provided by Mount Royal University Library
Listening to narrative speech after aphasic stroke: The role of the left anterior temporal lobe
No full textThe dorsal bank of the primate superior temporal sulcus (STS) is a polysensory area with rich connections to unimodal sensory association cortices. These include auditory projections that process complex acoustic information, including conspecific vocalizations. We investigated whether an extensive left posterior temporal (Wernicke\u27s area) lesion, which included destruction of early auditory cortex, may contribute to impaired spoken narrative comprehension as a consequence of reduced function in the anterior STS, a region not included within the boundary of infarction. Listening to narratives in normal subjects activated the posterior-anterior extent of the left STS, as far forward as the temporal pole. The presence of a Wernicke\u27s area lesion was associated with both impaired sentence comprehension and a reduced physiological response to heard narratives in the intact anterior left STS when compared to aphasic patients without temporal lobe damage and normal controls. Thus, in addition to the loss of language function in left posterior temporal cortex as the direct result of infarction, posterior ablation that includes primary and early association auditory cortex impairs language function in the intact anterior left temporal lobe. The implication is that clinical studies of language on stroke patients have underestimated the role of left anterior temporal cortex in comprehension of narrative speech. \ua9 The Author 2005. Published by Oxford University Press. All rights reserved
