Engineering Commons^™

Nonlinear Vibrations Of Fractionally Damped Systems, Joe Padovan, Jerzy Sawicki

Jerzy T. Sawicki

This paper deals with the harmonic oscillations of periodically excited nonlinear systems where hysteresis is simulated via fractional operator representations. Employing a diophantine version of the fractional operational powers, the energy constrained Lindstedt–Poincaré perturbation procedure is utilized to establish the harmonic solution. The constrained perturbation procedure was employed since it allows for the handling of strong damping and exciting forces over the full span of the driving frequency range. Based on the approach taken, the long time behavior of the fractionally damped Duffing's equation is studied in detail. Of special interest is the determination of the influence of fractional order …

Indoor Localisation Using A Context-Aware Dynamic Position Tracking Model, Montserrat Ros, Joshua Boom, Gavin De Hosson, Matthew D'Souza

Dr Montserrat Ros

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Indoor wireless localisation is a widely sought feature for use in logistics, health, and social networking applications. Low-powered localisation will become important for the next generation of pervasive media applications that operate on mobile platforms. We present an inexpensive and robust context-aware tracking system that can track the position of users in an indoor environment, using a wireless smart meter network. Our context-aware tracking system combines wireless trilateration with a …

Influence Of Select Extracellular Matrix Proteins On Mesenchymal Stem Cell Osteogenic Commitment In Three-Dimensional Contexts, Silvia Becerra-Bayona, Viviana Guiza-Arguello, Xin Qu, Dany Munoz Pinto, Mariah Hahn

Dany J. Munoz Pinto

Growth factors have been shown to be powerful mediators of mesenchymal stem cell (MSC) osteogenic differentiation. However, their use in tissue engineered scaffolds not only can be costly but also can induce undesired responses in surrounding tissues. Thus, the ability to specifically promote MSC osteogenic differentiation in the absence of exogenous growth factors via the manipulation of scaffold material properties would be beneficial. The current work examines the influence of select extracellular matrix (ECM) proteins on MSC osteogenesis toward the goal of developing scaffolds with intrinsically osteoinductive properties. Fibrinogen (FG), fibronectin (FN) and laminin-1 (LN) were chosen for evaluation due …

Casting A Wider Net, Lynn Stein

Lynn Andrea Stein

This article is a book review of Mung Chiang's book Networked Life: 20 Questions and Answers. In this text intended for both classroom and online learning, Chiang uses questions about our online lives to explore the technology and computer science behind the Internet, wireless, and Web industries.

Simdrug: Tackling The Complexity Of Illicit Drug Markets In Australia, Pascal Perez, A Dray, Alison Ritter, Paul Dietze, T Moore, Lorraine Mazerolle

Professor Pascal Perez

Complexity of illicit drug markets mirrors the complexity of illicit drug use itself. The intricacy of multiple interactions between individuals, the various time lines linked to different aspects of harm reduction, and contrasted social rationalities observed among field practitioners (prevention, law enforcement, harm reduction) contribute to the creation of complex and unpredictable systems. In order to explore this complexity, an Agent-Based Model (ABM) called SimDrug was designed. The prototype model includes users, dealers, wholesalers, outreach workers and police forces. The model is focused upon local drug market and the hot spots in Melbourne. The time span for the model is …

Stochastic Optimal Control In Nonlinear Systems, Celestin Nkundineza

Celestin Nkundineza

Stochastic control is an important area of research in engineering systems that undergo disturbances. Controlling individual states in such systems is critical. The present investigation is concerned with the application of the stochastic optimal control strategy developed by To (2010) and its implementation as well as providing computed results of linear and nonlinear systems under stationary and nonstationary random excitations. In the strategy the feedback matrix is designed based on the achievement of the objectives for individual states in the system through the application of the Lyapunov equation for the system. Each diagonal element in the gain or associated gain …

Analysis Of Transient Response Of Cracked Flexible Rotor, Jerzy Sawicki, Andrew Gyekenyesi, George Baaklini

Jerzy T. Sawicki

No abstract provided.

Analytical Solutions Of Piston Ring Lubrication Using Mass Conserving Cavitation Algorithm, Jerzy Sawicki, Biao Yu

Jerzy T. Sawicki

A novel analytical approach for piston ring lubrication solution is presented by taking proper account of mass conservation in the cavitated region (JFO boundary conditions). A system of five nonlinear equations is employed to calculate such parameters as oil film thickness, frictional force, power loss, and oil flow rate. For an enclosed cavitation pattern in piston-ring assembly it was found, that JFO boundary conditions give much better accounting of the estimation of friction force, power loss and flow rate. To show the effectiveness of the undertaken approach, the widely accepted Jeng's approach (Jeng, 1992a) was selected, in which the pressure …

Structural Damage Assessment Of Propulsions System Components By Impedance Based Health Monitoring, Richard Martin, Andrew Gyekneyesi, Jerzy Sawicki, George Baaklini

Jerzy T. Sawicki

No abstract provided.

Finite Element Analysis Of Coupled Lateral And Torsional Vibrations Of A Rotor With Multiple Cracks, Xi Wu, Jerzy Sawicki, Michael Friswell, George Baaklini

Jerzy T. Sawicki

The coupling between lateral and torsional vibrations has been investigated fora rotor dynamic system with breathing crack model. The stiffness matrix has been developed for the shaft element which accounts for the effect of the crack and all six degrees of freedom per node. Since the off-diagonal terms of the stiffness matrix represent the coupling of the respective modes, the special attention has been paid on accurate determination of their values. Based on the concepts of fracture mechanics, the variation of the stiffness matrix over the full shaft revolution is represented by the truncated cosine series where the fitting coefficient …

The Dynamics Of Rotor With Rubbing, Jerzy Sawicki, Joe Padovan, Rabih Al-Khatib

Jerzy T. Sawicki

This paper presents the description of some phenomena associated with dynamic behavior of rotors interacting with stationary components. Numerical simulations show rotor vibration spectrum rich in subharmonic, quasi-periodic, and chaotic vibrations. The nonlinear calculation techniques are applied to demonstrate the changes of the vibration patterns for different operating conditions. Some conclusions are discussed with regard to unique characteristics of rub-induced rotor response, initial conditions, as well as appropriate ranges of system parameters. Of special interest are the changes in the apparent nonlinearity of the system dynamics as rubs are induced at different rotor speeds. In particular, starting with 2nd order …

Analysis Of Elastic Distortions Of A Piston Ring In The Reciprocating Air Brake Compressor Due To The Installation Stresses, V. Dunaevsky, Jerzy Sawicki, J. Frater, H. Chen

Jerzy T. Sawicki

The objective of this paper is to present the results of an investigation of elastic distortions of split piston rings that are used in lubricated and non-lubricated air brake compressors. Concepts of advanced stress analysis and Finite Element Analysis (FEA) have been employed in this study.

The analysis of elastic distortions (twist) of piston rings due to the installation stresses has been quite poorly documented in the technical literature. As a result, unjustifiable engineering assumptions are some time made which result in misleading design solutions.

This paper demonstrates analytically and with the support of FEA the mechanical/geometrical parameters of a …

Frequency Driven Phasic Shifting And Elastic-Hysteretic Partitioning Properties Of Fractional Mechanical System Representation Schemes, Jerzy Sawicki, Joe Padovan

Jerzy T. Sawicki

Based on the Louiville–Riemann fractional formulation of lumped hysteretic mechanical system simulations, asymptotic-type relationships are derived. These are employed to determine how such operators, which act as viscoelastic elements, partition system energy into conservative and nonconservative components. Special emphasis is given to: (a) determine how operator order serves to weigh such a splitting, (b) determine how partitioning affects system phasing and amplitude response, and (c) to establish how conservative and nonconservative effects modulate during a given system cycle. The generality of the undertaken approach is such that multi-element fractional Kelvin Voigt formulations subject to spectrally rich inputs can be handled, …

Recent Advances In Vibration Based Damage Detection Techniques For Cracked Rotors, Jerzy Sawicki, George Baaklini

Jerzy T. Sawicki

In recent years, there has been a growing interest in the development of structural health monitoring for rotating structures, and especially shaft crack detection methodologies and on-line diagnostic techniques. Crack initiated problems present a significant safety and loss hazard in nearly every application of modern turbomachinery, including aircraft engines and power generation units. Different approaches are used to model, sense, and localize crack-induced damage in rotating structures. This presentation will provide an overview of the recent progress in the vibration based health monitoring and rotor crack detection techniques developed by author in recent years. A brief review of the unique …

Experimental And Theoretical Rotordynamic Characteristics Of A Hybrid Journal Bearing, Jerzy Sawicki, R. Capaldi, M. Adams

Jerzy T. Sawicki

This paper describes an experimental and theoretical investigation of a four-pocket,oil-fed, orifice-compensated hydrostatic bearing including the hybrid effects of journalrotation. The test apparatus incorporates a double-spool-shaft spindle which permitsindependent control over the journal spin speed and the frequencyof an adjustable-magnitude circular orbit, for both forward and backwardwhirling. This configuration yields data that enables determination of thefull linear anisotropic rotordynamic model. The dynamic force measurements weremade simultaneously with two independent systems, one with piezoelectric loadcells and the other with strain gage load cells. Theoreticalpredictions are made for the same configuration and operating conditionsas the test matrix using a finite-difference solver of …

Nonlinear Prediction Of Rotordynamic Coefficients For A Hydrodynamic Journal Bearing, Jerzy Sawicki, T.V.V.L. Rao

Jerzy T. Sawicki

In the analysis of hydrodynamic journal bearings, linearized stiffness and damping coefficients are widely used for the evaluation of stability and dynamic response characteristics. Under given operating conditions, these coefficients vary along the locus of the orbital response, and are not valid at large amplitudes (40% of the bearing clearance) of the journal motion. The time history of journal bearing motion for large vibrations is accurately predicted herein using nonlinear (time-transient) analysis. This paper discusses the adequacy of bearing analysis based on linearized coefficients and presents the significance of variation of the coefficients under the dynamic conditions. A method to …

Analytical Solution Of Piston Ring Pack Lubrication For Truck Air Brake Compressor, Biao Yu, Jerzy Sawicki, V. Dunaevsky

Jerzy T. Sawicki

This paper presents an analytical solution of piston ring pack lubrication for two-cylinder truck air brake compressor. A system of nonlinear equations with seven variables was developed to describe lubrication phenomena of the piston ring pack for both fully flooded and starvation conditions. The full mass conservation boundary conditions defined by JFO ([ 14 ],[ 15 ]) theory were employed for complete description of the cavitation algorithm with enclosed and open cavitation patterns. Impact of the piston ring design parameters such as offset, crown height, and tension on the oil transport, lubrication conditions and friction losses of the compressor were …

High Temperature Fusion Reactor Cooling Using Brayton Cycle Based Partial Energy Conversion, Albert Juhasz, Jerzy Sawicki

Jerzy T. Sawicki

For some future space power systems using high temperature nuclear heat sources most of the output energy will be used in other than electrical form, and only a fraction of the total thermal energy generated will need to be converted to electrical work. The paper describes the conceptual design of such a “partial energy conversion” system, consisting of a high temperature fusion reactor operating in series with a high temperature radiator and in parallel with dual closed cycle gas turbine (CCGT) power systems, also referred to as closed Brayton cycle (CBC) systems, which are supplied with a fraction of the …

Balanced Model Reduction And Control Of Rotor-Bearing Systems, Jerzy Sawicki, W. Gawronski

Jerzy T. Sawicki

Aneffective technique is applied to the suppression of vibrations inflexible rotor-bearing systems with small gyroscopic effects. A balanced linear-quadratic-Gaussian(LQG) controller design procedure is implemented. The size of thecontroller is reduced in two stages by using (i) abalanced model reduction, and (ii) an LQG balanced reduction. Thecondition for a gyroscopic matrix is developed that allows oneto ignore the rotor gyroscopic effects in the process ofthe controller design, although they are included in the rotordynamics. The approach is illustrated on a typical rotor-bearing system represented by a 48 degree-of-freedom finite element model.

Fatigue Life Prediction For Large-Diameter Elastically-Constrained Ball Bearings, Jerzy Sawicki, Samuel Johansson, John Rumbarger, Ronald Sharpless

Jerzy T. Sawicki

Theapplication of large-diameter bearing rings and the thereof inherited lowstiffness make them susceptible to local distortions caused by theirsurrounding structures, which are often under heavy loads. The standardaccepted design criteria for these bearings are based on theestimation of the internal load distribution of the bearing, underthe assumption of rigid circular and flat supporting structures, thatkeep the bearing inner and outer races in circular, flat,i.e., not deformed shapes. However, in the presence of structuraldistortions, the element load distribution can be severely altered andcannot be predicted viathe standard design criteria. Therefore, theapplication of large-diameter ball and roller bearing rings as thecritical components …

Thermodynamic Properties Of Fractional Differ-Integro Type Constitutive Relations, Joe Padovan, Jerzy Sawicki, Arkadi Leonov

Jerzy T. Sawicki

Using the asymptotic properties of Riemann-Liouville form, the intrinsic rate-based first and second laws of thermodynamics properties of fractional differintegro operator type constitutive representations are investigated by illustrating how the conservative and nonconservalive features of the response behavior interact under spectrally rich inputs. Due to the generality of the development, fractional operator representations of any order are considered. This includes the determination of the underlying features giving rise to frequency dependencies in the phasing and amplitude behavior and in this context the irreversible energy release rate process associated with fractional viscoelastic simulations.

Limiting Stiffness And Damping Coefficients Of Foil Bearing, Jerzy Sawicki, T. Rao

Jerzy T. Sawicki

The limiting values of load capacity, stiffness and damping coefficients for a foil bearing are presented. The necessary conditions for high bearing numbers (journal operating at high speed) are obtained by simplifying the compressible Reynolds equation. Linearized stiffness and damping coefficients are obtained using infinitesimal perturbation method. Results of load capacity, stiffness and damping coefficients, for foil bearing are compared with those obtained for a rigid gas journal bearing. The limiting values of dynamic characteristics for a foil bearing are constant for all eccentricity ratios. ©2005 ASME

Lunar Surface Gas Turbine Power Systems With Fission Reactor Heat Sources, Jerzy Sawicki, Albert Juhasz

Jerzy T. Sawicki

No abstract provided.

Modal Uncoupling Of Damped Gyroscopic Systems, Jerzy Sawicki, G. Genta

Jerzy T. Sawicki

A new approach for uncoupling the equations of motion typical for rotordynamical systems is presented. The method does not neglect the speed-dependent e!ects, such as gyroscopic e!ects, and can be particularly valuable in the controller design of actively controlled rotors. In the presence of hysteretic type of damping, the resulting uncoupled gyroscopic systems come with an equivalent viscous damping, equivalent in a sense of yielding the same natural frequency and decay rate. The approach is illustrated through three examples of technical interest: a Je!cott rotor with hysteretic damping, a Stodola}Green rotor, and a rotor of a small gas turbine. The …

Introduction To The Geant4 Simulation Toolkit, Susanna Guatelli, D Cutajar, Bradley Oborn, Anatoly Rosenfeld

Dean Cutajar

Geant4 is a Monte Carlo simulation Toolkit, describing the interactions of particles with matter. Geant4 is widely used in radiation physics research, from High Energy Physics, to medical physics and space science, thanks to its sophisticated physics component, coupled with advanced functionality in geometry description. Geant4 is widely used at the Centre for Medical Radiation Physics (CMRP), at the University of Wollongong, to characterise and optimise novel detector concepts, radiotherapy treatments, and imaging solutions. This lecture consists of an introduction to Monte Carlo method, and to Geant4. Particular attention will be devoted to the Geant4 physics component, and to the …

Megavoltage Cone Beam Ct Near Surface Dose Measurements: Potential Implications For Breast Radiotherapy, Alexandra Quinn, Lois Holloway, Dean Cutajar, Nicholas Hardcastle, Anatoly Rosenfeld, Peter Metcalfe

Dean Cutajar

Purpose: Cone beam computed tomography (CBCT) is fast becoming standard on modern linear accelerators. CBCT increases the dose to regions within and outside the treatment field, potentially increasing secondary cancer induction and toxicity. This study quantified megavoltage (MV) CBCT skin dose and compared it to skin dose delivered during standard tangential breast radiotherapy. Method: Dosimetry was performed both in- and out-of-field using thermoluminescent dosimeters (TLDs) and a metal-oxide-semiconductor-field-effect-transistor (MOSFET) detector specifically designed for skin dosimetry; these were placed superficially on a female anthropomorphic phantom. Results: The skin dose from a single treatment fraction ranged from 0.5 to 1.4 Gy on …

Monte Carlo Study Of The Energy Response And Depth Dose Water Equivalence Of The Moskin Radiation Dosimeter At Clinical Kilovoltage Photon Energies, C Lian, M Othman, D Cutajar, M Butson, Susanna Guatelli, Anatoly Rosenfeld

Dean Cutajar

Skin dose is often the quantity of interest for radiological protection, as the skin is the organ that receives maximum dose during kilovoltage X-ray irradiations. The purpose of this study was to simulate the energy response and the depth dose water equivalence of the MOSkin radiation detector (Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia), a MOSFET-based radiation sensor with a novel packaging design, at clinical kilovoltage photon energies typically used for superficial/orthovoltage therapy and X-ray CT imaging. Monte Carlo simulations by means of the Geant4 toolkit were employed to investigate the energy response of the CMRP MOSkin …

Electrochemical Deposition Of Porous Vox And Mno2 Nanowires On Stainless Steel Mesh For Flexible Supercapacitors, Shulei Chou, Jiazhao Wang, Hua Liu, S Dou

Shulei Chou

Porous vanadium oxide (VO_x) and MnO₂ nanowires were synthesized by an electrochemical deposition method using stainless steel mesh as substrate. The as-prepared porous VO_x and MnO₂ nanowire films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The cyclic voltammetry (CV) results show that the MnO₂ nanowire film shows specific capacitance of 195, 170, 158, and 91 F g^-1 at scan rates of 5, 10, 20, and 50 mV s^-1, respectively. The porous VO_x film displays specific capacitance of 152, 124, 99, and 76 F g …

Enhanced Reversible Lithium Storage In A Nanosize Silicon/Graphene Composite, Shulei Chou, Jiazhao Wang, Mohammad Choucair, Hua Liu, John Stride, S Dou

Shulei Chou

Si/graphene composite was prepared by simply mixing of commercially available nanosize Si and graphene. Electrochemical tests show that the Si/graphene composite maintains a capacity of 1168 mAh g-1 and an average coulombic efficiency of 93% up to 30 cycles. EIS indicates that the Si/graphene composite electrode has less than 50% of the charge-transfer resistance compared with nanosize Si electrode, evidencing the enhanced ionic conductivity of Si/graphene composite. The enhanced cycling stability is attributed to the fact that the Si/graphene composite can accommodate large volume charge of Si and maintain good electronic contact.

One-Step Spray Pyrolysis Synthesized Cuo-Carbon Composite Combined With Carboxymethyl Cellulose Binder As Anode For Lithium-Ion Batteries, Chao Zhong, Jia-Zhao Wang, Xuan-Wen Gao, Shulei Chou, Konstantin Konstantinov, Hua Liu

Shulei Chou

Copper oxide-carbon composite with hollow sphere structure has been synthesized by a one-step spray pyrolysis method and tested as anode material for lithium-ion batteries. Different analytical methods, including X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, thermogravimetric analysis, and systematic electrochemical tests were performed. The results demonstrate that the CuO-carbon composite in conjunction with carboxymethyl cellulose (CMC) binder has an excellent electrochemical performance, with a capacity of 577 mAh g-1 up to 100 cycles. The usage of the water soluble binder, CMC, not only obviously improves the electrochemical performance, but also makes the electrode fabrication process much easier and …