Unsteady two dimensional airloads acting on oscillating thin airfoils in subsonic ventilated wind tunnels

The numerical calculation of unsteady two dimensional airloads which act upon thin airfoils in subsonic ventilated wind tunnels was studied. Neglecting certain quadrature errors, Bland's collocation method is rigorously proved to converge to the mathematically exact solution of Bland's integral equation, and a three way equivalence was established between collocation, Galerkin's method and least squares whenever the collocation points are chosen to be the nodes of the quadrature rule used for Galerkin's method. A computer program displayed convergence with respect to the number of pressure basis functions employed, and agreement with known special cases was demonstrated. Results are obtained for the combined effects of wind tunnel wall ventilation and wind tunnel depth to airfoil chord ratio, and for acoustic resonance between the airfoil and wind tunnel walls. A boundary condition is proposed for permeable walls through which mass flow rate is proportional to pressure jump

Investigation of solid polymeric hollow fiber heat exchange devices for use in thermally-driven desalination processes

The heat exchange between hot brine (4 wt% NaCl) and cold water as well as between condensing steam and cold water without direct fluid-fluid contact using modules made out of solid polymeric hollow fibers of polypropylene (PP) and polyetheretherketone (PEEK) has been studied. The solid hollow fiber dimensions were 425μm/575μm (ID/OD) for PP and 420μm/570μm (ID/OD) for PEEK. Extensive heat transfer measurements have been performed and the experimentally-determined overall heat transfer coefficients utilized to isolate the wall heat transfer coefficient, the inside heat transfer coefficient and the outside heat transfer coefficient. The heat exchange between hot brine and cold water was evaluated at hot brine temperatures between 82 °C and 99 °C and cold water temperatures between 5 °C and 41 °C. The tube-side Reynolds Number was varied in the range of 58-2464 and 3-160, respectively for the hot brine-cold water and condensing steam-cold water systems. The maximum U (overall heat transfer coefficient based on the inside area) values attained in the hot brine-cold water system for PEEK and PP-based modules were 1914 W/m2-K and 2076 W/m2-K respectively. The maximum U value attained in the two-phase heat exchange system was 1700 W/m2-K. Overall, the PP-based module HEPP2 showed the highest conductance per unit volume (CUV) value (2.92x106 W/m3-K). The highest CUV value achieved was approximately 19 times higher than what can be achieved in conventional metallic shell and tube heat exchangers. The results for hot brine-cold water heat exchange demonstrated thermal efficiencies very close to 97% and up to four transfer units for devices having height of transfer unit (HTU) values as low as 5 cm. Those results were attained under conditions of lower tube-side Reynolds numbers

Finite state modeling of aeroelastic systems

A general theory of finite state modeling of aerodynamic loads on thin airfoils and lifting surfaces performing completely arbitrary, small, time-dependent motions in an airstream is developed and presented. The nature of the behavior of the unsteady airloads in the frequency domain is explained, using as raw materials any of the unsteady linearized theories that have been mechanized for simple harmonic oscillations. Each desired aerodynamic transfer function is approximated by means of an appropriate Pade approximant, that is, a rational function of finite degree polynomials in the Laplace transform variable. The modeling technique is applied to several two dimensional and three dimensional airfoils. Circular, elliptic, rectangular and tapered planforms are considered as examples. Identical functions are also obtained for control surfaces for two and three dimensional airfoils

A Finite Element and Experimental Study of Reinforced Concrete in Torsion

This thesis describes a study into the torsional behaviour of reinforced concrete members, in particular solid Lsections under pure torsion. It consists of three distinct but linked phases: (1) development, assessment and application of a three dimensional nonlinear finite element model for short-term behaviour of reinforced concrete, (2) an experimental programme and (3) a numerical parametric study. Nonlinear behaviour takes into account concrete cracking, nonlinear triaxial stress-strain relations of concrete, concrete crushing and yielding of steel reinforcement. Cracking behaviour is modelled by a fixed orthotropic smeared crack approach, allowing up to three cracks to occur at any sampling point. Modelling of post-cracking behaviour allows for shear transfer and tension stiffening effects. Concrete behaviour under all multiaxial stress states is governed by a short-term constitutive law and a peak stress failure criterion. A bilinear uniaxial stress-strain law allowing for isotropic strain hardening is used for steel reinforcement. 20-noded isoparametric brick element is used to represent concrete, with single bars embedded within the concrete elements to simulate reinforcement. A modified Newton-Raphson approach was used for solving the nonlinear problem, based on the evaluation of a secantial elasticity matrix. The program was assessed by studying the behaviour of deep beams, shallow beams simulating beam-column behaviour, rectangular beams subject to pure and combined torsion and L-sections under pure torsion. Through systematic study, the influence of some of the major nonlinear material and solution parameters was established for these applications and limits on their values were set. The experimental programme involved testing a series of solid reinforced concrete models of L-shaped cross sections under pure torsion in a specially designed and built test-rig. The tests were devised to: (1) assess the current British Code design procedure for torsion of solid L-sections, (2) obtain an insight into the torsional behaviour of these types of sections and (3) provide detailed results to assess the reliability of the finite element model in the analysis of torsion of fully reinforced flanged sections. A dual approach of complementing the experimental results with a numerical parametric study, using the developed finite element model, is adopted where more variables not included in the experimental programme were investigated. The current British Code design procedure for torsion was found to be too conservative for solid flanged sections, and it is concluded that the code's rules can be less stringent. Some recommendations that might help bring the code's torsion design procedure in line with other major codes of practice are given

The dynamics of mine hoist catenaries.

A Thesis Submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, South Africa for the Degree of Doctor of Philosophy.The dynamic analysis of catenary vibration of mine hoist ropes on South African mines is examined. This research has been preceded by studies in the mining industry, which have laid the foundation fot the definition of design guidelines of hoist systems to avoid catenary vibrations or rope whip. These guidelines are based on a classical linear analysis of a taut string, and in essence rely on ensuring that the frequency of excitation at the winder drum due to the coilingmechanism, does not coincide with the linear transverse natural frequency of the taut catenary. Such an approach neglects the nonlinear coupling between the lateral catenary motion and the longitudinal systern response. Although previous research sug gested the possibility of autoparametric coupling between the catenary and vertical rope, this was not developed further on a theoretical level.. The possibility of such behaviour is defined by considering the equations of motion of the coupled system. A design methodology is developed for determining the parameters of a mine hoist systern so as to avoid rope whip. The methodology accounts for the nonlinear coupling between the catenary and longitudinal system. In order to implement the proposed methodology, two phases of the analysis are developed. In the first phase the stability of the linear steady state motion is examined in the context of the nonlinear equations of motion, by applying a harmonic balance method. The stability analysis defines regions of secondary resonance, where it is shown that such regions may arise at sum and difference combinations of the linear lateral and longitudinal natural frequencies due to autoparametric excitation. Prior to this research, this phenomenon had not been appreciated in the context of the mine hoist system. A laboratory experiment was conducted to confirm the existence of these regions experimentally. In reality, the system is non-stationary since the dynamic characteristics of the system change during the winding cycle, and hence the steady state stability analysis can only describe potential regions of nonlinear interaction on a qualitative basis. The second phase of the analysis deals with a non-linear numerical simulation of the hoist system, which accounts for the non-stationary nature of the systems dynamic characteristics, and includes transient excitations induced during the wind. The methodology developed is assessed by considering the Kloof mine rope system, where rope whip was observed. This study demonstrates that although an appreciation of the steady state system characteristics is useful, the stability analysis alone is not sufficient. It is necessary to account for the non-stationary aspects of the winding cycle if a realistic interpretation of the observed behavlcur is to be achieved. To compliment this study, a motion analysis system was developed to record catenary response on an existing mine hoist installation. Such data has not been recorded before. This data provides direct evidence of the autoparametric nature of the coupled catenary/vertical rope system.AC201

The dynamics of mine hoist catenaries.

A Thesis Submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, South Africa for the Degree of Doctor of Philosophy.The dynamic analysis of catenary vibration of mine hoist ropes on South African mines is examined. This research has been preceded by studies in the mining industry, which have laid the foundation fot the definition of design guidelines of hoist systems to avoid catenary vibrations or rope whip. These guidelines are based on a classical linear analysis of a taut string, and in essence rely on ensuring that the frequency of excitation at the winder drum due to the coilingmechanism, does not coincide with the linear transverse natural frequency of the taut catenary. Such an approach neglects the nonlinear coupling between the lateral catenary motion and the longitudinal systern response. Although previous research sug gested the possibility of autoparametric coupling between the catenary and vertical rope, this was not developed further on a theoretical level.. The possibility of such behaviour is defined by considering the equations of motion of the coupled system. A design methodology is developed for determining the parameters of a mine hoist systern so as to avoid rope whip. The methodology accounts for the nonlinear coupling between the catenary and longitudinal system. In order to implement the proposed methodology, two phases of the analysis are developed. In the first phase the stability of the linear steady state motion is examined in the context of the nonlinear equations of motion, by applying a harmonic balance method. The stability analysis defines regions of secondary resonance, where it is shown that such regions may arise at sum and difference combinations of the linear lateral and longitudinal natural frequencies due to autoparametric excitation. Prior to this research, this phenomenon had not been appreciated in the context of the mine hoist system. A laboratory experiment was conducted to confirm the existence of these regions experimentally. In reality, the system is non-stationary since the dynamic characteristics of the system change during the winding cycle, and hence the steady state stability analysis can only describe potential regions of nonlinear interaction on a qualitative basis. The second phase of the analysis deals with a non-linear numerical simulation of the hoist system, which accounts for the non-stationary nature of the systems dynamic characteristics, and includes transient excitations induced during the wind. The methodology developed is assessed by considering the Kloof mine rope system, where rope whip was observed. This study demonstrates that although an appreciation of the steady state system characteristics is useful, the stability analysis alone is not sufficient. It is necessary to account for the non-stationary aspects of the winding cycle if a realistic interpretation of the observed behavlcur is to be achieved. To compliment this study, a motion analysis system was developed to record catenary response on an existing mine hoist installation. Such data has not been recorded before. This data provides direct evidence of the autoparametric nature of the coupled catenary/vertical rope system.AC201

Alienation and educational inclusion : a mixed methods study of teaching and learning with contemporary art in the Level 1 university curriculum

UNESCO (2006b) proclaims that' Arts Education is a universal human right'. However, art educators have observed that Western visual arts education is still dominated by a culturally exclusive canon of artworks which some students find alienating and irrelevant. Calls to abandon the canon in the name of inclusion have been made by school arts educators and research in secondary schools has shown that including contemporary art in the curriculum can empower and engage learners. However, inclusive visual arts curriculum development in higher education is infrequently explored.This thesis is intended to address such imbalance. It reports the findings of a mixed methods study exploring the impact of adults' affective and cognitive responses to art on their learning. A questionnaire and interviews were used to gather information about Open University undergraduates' responses to contemporary and non-contemporary artworks and their experiences of studying a visual arts module featuring meta-cognitive scaffolding and guided reflection. Quantitative and qualitative analysis of the data indicated that while the Western canon has the power to exclude, replacing canonical works with contemporary art is not a 'one size fits all' solution to achieving educational inclusion. Rather, it appears there is an age and experience-related divide in adults' affective and cognitive responses to art. Younger, and art-trained adults often relish studying provocative, emotionally potent and offensive contemporary artworks, especially works addressing topics they feel are personally relevant. In contrast, some older adults' cynical preconceptions about contemporary art's unworthiness for serious study, and preferences for visually pleasing, inoffensive artworks, can prevent productive engagement with contemporary art. However, the study findings suggest that meta-cognitive scaffolding can offer a structure within which students can reflect on and make sense of their responses to contemporary art, while also developing the skills to interpret works with unstable and controversial meanings

Four cornered code based Chinese character recognition system.

by Tham Yiu-Man.Thesis (M.Phil.)--Chinese University of Hong Kong, 1993.Includes bibliographical references.Abstract --- p.iAcknowledgements --- p.iiiTable of Contents --- p.ivChapter Chapter I --- IntroductionChapter 1.1 --- Introduction --- p.1-1Chapter 1.2 --- Survey on Chinese Character Recognition --- p.1-4Chapter 1.3 --- Methodology Adopts in Our System --- p.1-7Chapter 1.4 --- Contributions and Organization of the Thesis --- p.1-11Chapter Chapter II --- Pre-processing and Stroke ExtractionChapter 2.1 --- Introduction --- p.2-1Chapter 2.2 --- Thinning --- p.2-1Chapter 2.2.1 --- Introduction to Thinning --- p.2-1Chapter 2.2.2 --- Proposed Thinning Algorithm Cater for Stroke Extraction --- p.2-6Chapter 2.2.3 --- Thinning Results --- p.2-9Chapter 2.3 --- Stroke Extraction --- p.2-13Chapter 2.3.1 --- Introduction to Stroke Extraction --- p.2-13Chapter 2.3.2 --- Proposed Stroke Extraction Method --- p.2-14Chapter 2.3.2.1 --- Fork point detection --- p.2-16Chapter 2.3.2.2 --- 8-connected fork point merging --- p.2-18Chapter 2.3.2.3 --- Sub-stroke extraction --- p.2-18Chapter 2.3.2.4 --- Fork point merging --- p.2-19Chapter 2.3.2.5 --- Sub-stroke connection --- p.2-24Chapter 2.3.3 --- Stroke Extraction Accuracy --- p.2-27Chapter 2.3.4 --- Corner Detection --- p.2-29Chapter 2.3.4.1 --- Introduction to Corner Detection --- p.2-29Chapter 2.3.4.2 --- Proposed Corner Detection Formulation --- p.2-30Chapter 2.4 --- Concluding Remarks --- p.2-33Chapter Chapter III --- Four Corner CodeChapter 3.1 --- Introduction --- p.3-1Chapter 3.2 --- Deletion of Hook Strokes --- p.3-3Chapter 3.3 --- Stroke Types Selection --- p.3-5Chapter 3.4 --- Probability Formulations of Stroke Types --- p.3-7Chapter 3.4.1 --- Simple Strokes --- p.3-7Chapter 3.4.2 --- Square --- p.3-8Chapter 3.4.3 --- Cross --- p.3-10Chapter 3.4.4 --- Upper Right Corner --- p.3-12Chapter 3.4.5 --- Lower Left Corner --- p.3-12Chapter 3.5 --- Corner Segments Extraction Procedure --- p.3-14Chapter 3.5.1 --- Corner Segment Probability --- p.3-21Chapter 3.5.2 --- Corner Segment Extraction --- p.3-23Chapter 3.6 4 --- C Codes Generation --- p.3-26Chapter 3.7 --- Parameters Determination --- p.3-29Chapter 3.8 --- Sensitivity Test --- p.3-31Chapter 3.9 --- Classification Rate --- p.3-32Chapter 3.10 --- Feedback by Corner Segments --- p.3-34Chapter 3.11 --- Classification Rate with Feedback by Corner Segment --- p.3-37Chapter 3.12 --- Reasons for Mis-classification --- p.3-38Chapter 3.13 --- Suggested Solution to the Mis-interpretation of Stroke Type --- p.3-41Chapter 3.14 --- Reduce Size of Candidate Set by No.of Input Segments --- p.3-43Chapter 3.15 --- Extension to Higher Order Code --- p.3-45Chapter 3.16 --- Concluding Remarks --- p.3-46Chapter Chapter IV --- RelaxationChapter 4.1 --- Introduction --- p.4-1Chapter 4.1.1 --- Introduction to Relaxation --- p.4-1Chapter 4.1.2 --- Formulation of Relaxation --- p.4-2Chapter 4.1.3 --- Survey on Chinese Character Recognition by using Relaxation --- p.4-5Chapter 4.2 --- Relaxation Formulations --- p.4-9Chapter 4.2.1 --- Definition of Neighbour Segments --- p.4-9Chapter 4.2.2 --- Formulation of Initial Probability Assignment --- p.4-12Chapter 4.2.3 --- Formulation of Compatibility Function --- p.4-14Chapter 4.2.4 --- Formulation of Support from Neighbours --- p.4-16Chapter 4.2.5 --- Stopping Criteria --- p.4-17Chapter 4.2.6 --- Distance Measures --- p.4-17Chapter 4.2.7 --- Parameters Determination --- p.4-21Chapter 4.3 --- Recognition Rate --- p.4-23Chapter 4.4 --- Reasons for Mis-recognition in Relaxation --- p.4-27Chapter 4.5 --- Introduction of No-label Class --- p.4-31Chapter 4.5.1 --- No-label Initial Probability --- p.4-31Chapter 4.5.2 --- No-label Compatibility Function --- p.4-32Chapter 4.5.3 --- Improvement by No-label Class --- p.4-33Chapter 4.6 --- Rate of Convergence --- p.4-35Chapter 4.6.1 --- Updating Formulae in Exponential Form --- p.4-38Chapter 4.7 --- Comparison with Yamamoto et al's Relaxation Method --- p.4-40Chapter 4.7.1 --- Formulations in Yamamoto et al's Relaxation Method --- p.4-40Chapter 4.7.2 --- Modifications in [YAMAM82] --- p.4-42Chapter 4.7.3 --- Performance Comparison with [YAMAM82] --- p.4-43Chapter 4.8 --- System Overall Recognition Rate --- p.4-45Chapter 4.9 --- Concluding Remarks --- p.4-48Chapter Chapter V --- Concluding RemarksChapter 5.1 --- Recapitulation and Conclusions --- p.5-1Chapter 5.2 --- Limitations in the System --- p.5-4Chapter 5.3 --- Suggestions for Further Developments --- p.5-6References --- p.R-1Appendix User's GuideChapter A .l --- System Functions --- p.A-1Chapter A.2 --- Platform and Compiler --- p.A-1Chapter A.3 --- File List --- p.A-2Chapter A.4 --- Directory --- p.A-3Chapter A.5 --- Description of Sub-routines --- p.A-3Chapter A.6 --- Data Structures and Header Files --- p.A-12Chapter A.7 --- Character File charfile Structure --- p.A-15Chapter A.8 --- Suggested Program to Implement the System --- p.A-1

Crystalization studies in hollow fiber devices

Crystallization was examined under a new perspective and in a flow environment much different from that available in currently used industrial devices. Three crystallization techniques were tested in the unique flow environment offered by hollow fiber devices. In addition, a new type of heat exchanger based on hollow fibers was tested as well as the potential use of porous hollow fiber devices as mixing devices. Hollow fiber devices are compact, extremely efficient on a volumetric basis, easy to scale up and control and their inherent characteristics promote the creation of homogeneous temperature and concentration conditions on a scale considerably smaller than existing industrial crystallizers without the necessity of a large energy input. Porous hollow fiber heat exchangers (PHFHEs) were proven superior to conventional metal heat transfer equipment. For the liquid-liquid systems studied, they can transfer up to ten times more heat on a volumetric basis, achieve the same efficiency and number of transfer units at considerably smaller lengths; also, the height of a transfer unit achieved by them is 10-20 times smaller. In addition, they can transfer up to 20 times more heat at the same pumping power expenditure and need to utilize as low as 1 kPa for the achievement of one transfer unit compared to 30 kPa for metal heat exchangers. Considering their lower fixed cost, they can be considered suitable alternatives for metal and plastic heat exchangers at lower temperatures and pressures. Solid hollow fiber cooling crystallization (SHFCC) was proved to be a promising technique for crystal size distribution control of both aqueous and organic systems. A combination of a solid hollow fiber crystallizer with a mixing device downstream was the most successful. For the aqueous potassium nitrate system, this combination provided crystal size distributions with 3-4 times smaller mean sizes compared to those mentioned in existing literature of Mixed Suspension Mixed Product Removal (MSMPR) crystallizers. In addition, 90% of the crystals produced were confined to sizes at least two times smaller, while the nucleation rates achieved were 2-3 orders of magnitude higher. Runs with aqueous paracetamol (4-acetamidophenol) solutions showed that an SHFCstatic mixer assembly can be operated successfully up to 30-40°C below the metastable zone limit, a capability not existent in industrial cooling crystallizers. This ability allows the achievement of very high nucleation rates and the decoupling of nucleation and growth, an opportunity offered currently only by impinging jet mixers for antisolvent crystallization. Porous hollow fiber devices proved efficient mixing devices, which unlike other tubular devices offer the opportunity for substantial radial mixing and hence the production of good micromixing. By proper rating they can potentially be utilized for reaction purposes, especially for liquid-liquid reactions on a 1:1 stoichiometric ratio, a task never performed before in membrane reactors. Porous hollow fiber emulsion crystallization (PHFEC) of a system with an immiscible solvent-antisolvent pair, salicylic acid in 1-octanol and water, encountered difficulties. While an emulsion of droplets smaller than 50 μm was obtained, crystallization at the droplet surface or interior was strongly hindered probably due to the presence of the emulsifier. The latter, although beneficial for droplet stabilization and size control, prevents contact of the solute and the antisolvent and consequently the generation of supersaturation conditions. Polymeric hollow fiber antisolvent crystallization (PHFAC) was found to be a promising crystallization technique for miscible solvent-antisolvent pairs. When crystallization was performed at the tube side of the device, the crystal size distributions obtained for the system aqueous L-asparagine monohydrate and 2-propanol as the antisolvent were confined below 200 μm. However, prolonged operation of the membrane hollow fiber crystallizer was problematic due to pore and/or fiber blockage. The same was not true when crystallization was performed at the shell side of the device. Crystallization runs with the same system showed that, apart from stable operation, mean sizes as low as 30-40 μm can be achieved. The crystal size distribution was confined between 70 and 150 μm, a size range suitable for most pharmaceutical crystalline products and about 2-4 times smaller compared to 200-300 μm achieved in stirred crystallizers for the same system. In addition, 1-5 orders of magnitude higher nucleation rates were obtained at the same levels of supersaturation