bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of a Nonlinear Harmonic Method to the Simulation of Clocking Effects
Authors: Vilmin S. , Lorrain E. , Hirsch Ch.
Published: February 2010

Pursuing higher levels of efficiency in turbomachines requires the capability to reproduce a fuller extent of the blade row interactions. This is especially true for the clocking phenomena, whose influence on the efficiency can be important. For instance, the efficiency variation over a set of relative positions between two successive stators could reach 1 to 2% in high pressure turbines (Huber et al, 1996, Haldeman et al, 2004). The simulation of these complex effects still relies on time-dependent methods for the reproduction of the unsteadiness and its impact onto the time-mean flow. The nonlinear harmonic method and its extension to clocking effects, as introduced by He (1998), and He and Chen (2002), can simulate the whole unsteady flow at considerably reduced CPU costs. The treatment is very powerful since it can predict the performances of a multirow component for all the clocking positions. This is done by means of harmonics that describe a spatial phase shift of the flow in a rotor or stator, due respectively to a co-rotating rotor or stator. The present paper applies this approach for the simulation of the clocking effects. This is handled by a full connection treatment, which was shown (Vilmin et al, 2006) to give a significant improvement over the mixing-plane method in the time-averaged flow estimations of the full unsteady flow across the rotor/stator interface. In a first part of the paper, implementation issues of the treatment are presented. In particular, consideration is made of the importance of the clocking effects related to the ratios between the blade numbers. In a second part, a validation pseudo-2D multirow test case is presented that demonstrate the capabilities of the method. The third part deals with the simulation of the clocking effect on the performance of a 1.5 stage turbine. CPU and cost are presented, that show the considerable efficiency of the extended harmonic method.
A Hybrid Unstructured/Spectral Method for the Resolution of Navier-Stokes Equations
Authors: Corral Roque , Crespo Javier
Published: February 2010

A novel high-order finite volume method for the resolution of the Navier-Stokes equations is presented. The approach combines a third order finite volume method in an unstructured two-dimensional grid, with a spectral approximation in the third dimension. The method is suitable for the resolution of complex two-dimensional geometries that require the third dimension to capture three-dimensional non-linear unsteady effects, such as those for instance present in linear cascades with separated bubbles. Its main advantage is the reduction in the computational cost, for a given accuracy, with respect standard finite volume methods due to the inexpensive high-order discretization that may be obtained in the third direction using fast Fourier transforms. The method has been applied to the resolution of transitional bubbles in flat plates with adverse pressure gradients and realistic two-dimensional airfoils.
Study of a Conical Coupling for Torque Transmission
Authors: Nyatando Rose , Ding Jian , Williams Edward J.
Published: February 2010

A study has been conducted on the design of a conical coupling joint in which torque is transmitted by frictional contact across conical surfaces on the flanges. Three dimensional finite element analyses were undertaken on the coupling, employing a full 360-degree model along with more detailed analytical studies using a representative cyclic symmetry model. Parametric studies were done on a number of geometries where investigations were made with the aim of improving the pressure distributions and values in the contact region, while working towards maximizing the torque capacity on the joint. The results showed that the torque capacity is strongly dependent on the angle of the conical surface. A 0.5° angular variation between two contacting conical surfaces provided an increase in contact area and a significant reduction in the contact pressure peaks. As part of the study on the design improvement, the potential effects of manufacturing variations were investigated and results showed that variations of ±0.25° should not significantly affect the assembly accuracy. A parallel experimental study of a prototype joint was also undertaken. Measured torque capacity on the prototype was in good agreement with values predicted by the finite element models.
Unsteady and Three-Dimensional Flow Phenomena in a Transonic Centrifugal Compressor Impeller at Rotating Stall
Authors: Iwakiri Kenichiro , Furukawa Masato , Ibaraki Seiichi , Tomita Isao
Published: February 2010

This paper presents a combined experimental and numerical analysis of rotating stall in a transonic centrifugal compressor impeller for automotive turbochargers. Stall characteristics of the compressor were examined by two high-response pressure transducers mounted on the casing wall near the impeller inlet. The pressure traces were analyzed by wavelet transforms to estimate the disturbance waves quantitatively. Three-dimensional unsteady internal flow fields were simulated numerically by Detached Eddy Simulation (DES) coupled LES-RANS approach. The analysis results show good agreements on both compressor performance characteristics and the unsteady flow features at the rotating stall. At stall inception, spiral-type breakdown of the full-blade tip leakage vortex was found out at some passages and the brokendown regions propagated against the impeller rotation. This phenomenon changed with throttling, and tornado-type separation vortex caused by the full-blade leading edge separation dominated the flow field at developed stall condition. It is similar to the flow model of short-length scale rotating stall established in an axial compressor rotor.
Application of Simple Gradient-Based Method and Multi-Section Blade Parameterization Technique to Aerodynamic Design Optimization of a 3D Transonic Single Rotor Compressor
Authors: Chen N. X. , Zhang H. W. , Xu Q. , Huang W. G.
Published: February 2010

A 3D blade optimization strategy for improving turbomachinery performance is proposed mainly based on simple gradient-based method and multi-section blade parameterization technique (MS-BPT) in the present paper. The blade rebuilding method (BRM), the 3D grid generation method (RAPID3DGRID) and the N. S. solver are also used. By using the blade rebuilding method the coordinates of arbitrary blade profile (2D) of each section can be transformed into a set of blade design parameters. For all sections (i.e. in the 3D case) the number of the total design parameters to be searched is increased. But, it can be reduced by designers’ experiences. Since these design parameters, which are obtained by the present blade parameterization method, are independent each from other, this feature allows us to use a simple gradient-based method (SGBM) to search the optimum of the cost function, i.e. with changing any one of the parameters and using grid generator and N. S. solver the optimal design parameters can be obtained in each single optimal parameter searching. And then, instead the old one the new obtained parameter joins the other parameter optimum-searching process in an iteration turn. By repeating the iteration process the convergence of whole optimization process can be reached. The NASA single rotor compressor served as a computation example. The adiabatic efficiency was increased nearly by three percentages. The converged results can be obtained only by a few iterations turns. It is shown that the present method is efficient and can be applied as one of the optimization tools to the design optimization of turbomachinery blades.
Experimental and Numerical Investigation on the Influence of Trailing Edge Bleeding on the Aerodynamics of a NGV Cascade
Authors: Montis Marco , Niehuis Reinhard , Guidi Mattia , Salvadori Simone , Martelli Francesco , Stephan Bruno
Published: February 2010

A series of tests on a specific designed linear nozzle guide vane (NGV) cascade with trailing edge coolant ejection was carried out to investigate the influence of the trailing edge bleeding (TEB) on the loss behaviour of the profile. Wake traverses with a five-hole probe and measurements of the pressure distribution on the profile were taken varying the ejection rate under reference main flow conditions, namely Re2th = 1.056·106 and Ma2th = 0.8 (Re2th based on the true chord). Wake total pressure losses and isentropic Mach number distributions on the profile were compared to measurements without coolant ejection, showing a significant influence of the TEB both on the wake development and on the flow in the vane passage. Numerical simulations of the experiments showed good agreement with the measured data and provided a deeper understanding of the flow phenomena, revealing the differences in the development of the wake with and without trailing edge coolant ejection and illustrating the blockage effect of the TEB on the flow in the vane passage.
The Development of a Deviation Model for Radial and Mixed-Flow Turbines for Use in Throughflow Calculations
Authors: Cox Graham , Roberts Alex , Casey Michael
Published: February 2010

Radial and mixed-flow turbine stages are an important component of turbochargers in automotive engines. The aerodynamic design of such turbines is generally compromised by the severe mechanical and manufacturing constraints to withstand the harsh motor environment with high stresses, high temperatures and unsteady operation. Conventionally, the designer deals with these constraints in the preliminary design stage by using a high degree of empiricism. This is then followed in the detailed design by extensive and time-consuming 3D CFD analysis and geometry optimisation. This paper describes a new approach to the preliminary design of radial turbine impellers using a quasi-3D throughflow method, which allows a more rapid consideration of the design issues before moving on to a full 3D CFD analysis. The paper describes the development of deviation models suitable for radial and mixed-flow turbines out of a range of CFD solutions in which a number of important features have been varied: aerodynamic loading, tip clearance and blade root thickness. The features of the deviation model are related to predicted features of the flow. The results of throughflow calculations including the deviation model are compared against the CFD predictions.
Dry-Friction Whirl and Whip Between a Rotor and a Stator: Effect of Rotor-Stator Coupling Due to Seals and Rotor Rigid-Body Dynamics
Authors: Bhattacharya Avijit , Childs Dara W.
Published: February 2010

Dry friction backward whirl phenomena have been studied for some time, the most notable work starting with Black in 1967 and 1968. Other notable contributions include those of Crandall (1990) and Lingener (1990), and Bartha (2000). The authors (2007) extended those earlier studies that used lumped-parameter models to a multiple-degree-of-freedom rotor model showing excellent agreement between predictions and available measurements for whip frequencies and the transition frequencies from whirl to whip. One obvious question remains unanswered, namely: Why are dry friction whirl and whip readily induced in test rigs but rarely observed in turbomachinery? This question is addressed here by studying the effect of cross-coupled stiffness and direct damping connections between the rotor and stator (as provided by annular seals), support damping at the stator, and polar and diametral moments of inertia on regions of dry-friction whirl and whip. “Positive” cross-coupled-stiffness coefficients arise in fluid film bearings and fluid seals due to shaft and fluid rotation and produce a reaction force between the rotor and stator. They act to destabilize forward (in the direction of shaft rotation) precessional modes while stabilizing reverse-precession modes. The present predictions show that increasing positive cross-coupled-stiffness-coefficient magnitudes increases the Coulomb friction coefficient that is required to support whirl thus acting to suppress dry-friction whirl. Direct damping that is related to the relative velocity between the rotor and stator acts in exactly the same fashion. Direct damping that connects the stator to ground also acts to suppress whirl and whip. For the models considered here, enough stator damping eliminated the whip region. Test results of axial-compressor stages have shown “negative” cross-coupled-stiffness coefficients. The present study shows that negative cross-coupled stiffness coefficients can make dry-friction whirl more likely by reducing the magnitude of Coulomb friction required to sustain it. The influence of polar and diametral moments of inertia were investigated using a Stodola model comprised of a disk supported at the end of a cantilevered beam. Gyroscopic moments arising from the polar moment of inertia plus running speed had a negligible impact on the whirl-whip regimes. The diametral moment of inertia added an additional degree of freedom, creating an additional whip regime. However, it had no fundamental impact on the whirl-whip regimes.
The Measurement of Dynamic Vibration Modes and Frequencies of a Large LP Bladed Disc
Authors: Prchlik Lubos , Misek Tomas , Kubin Zdenek , Duchek Karel
Published: February 2010

A new 48″ steam turbine last stage blade (LSB) has been developed by the common effort of Skoda Power and Ansaldo Energia. The successful detuning of eigen-frequencies with respect to the basic rotational frequency has been achieved by using interconnecting elements near the mid-span and at the shroud of blades. Friction forces among the contact elements resulted from the constraint blade untwist generated by the centrifugal-force. FEM calculation of the Campbell and interference diagrams was followed by a detailed measurement in a specialized vacuum testing rig with strain gages located near the blade root. The excitation was performed by a high-power variable-frequency magnet. For the critical 0-node “umbrella” shape frequency both the axial magnetic excitation and the direct torsional excitation with AC driving motor were applied. Nearly forty different bladed-disc frequencies grouped into five families were identified by the FFT analysis. The corresponding modal shapes were indentified from the relationship between the excitation and resonance frequencies using the time offset of the signal from strain gages distributed along the disc perimeter. An excellent agreement between calculated and measured frequencies and nodal shapes was observed. A typical difference between the predicted and actually measured critical frequencies did not exceed 3% of the nominal value for the relevant frequencies. A complementary measurement using tip-timing technique is currently underway.
Investigation of Tip Clearance Modeling Techniques for a Transonic Compressor Rotor
Authors: Barrows Sean T. , Balasubramian Ravishankar , Chen Jen-Ping
Published: February 2010

Computational fluid dynamics (CFD) codes are becoming an integral part of the design and analysis process involved with creating and improving upon new engine designs. This necessitates the investigation and development of accurate modeling techniques for flow simulations with a quick turn around time of typically 48 hours. The present paper is focused on increasing the fidelity of compressor rotor simulations by examining three rotor tip clearance modeling techniques. The first approach models the tip clearance region as a loss-less, periodic, un-gridded region as first proposed by Kirtley et al. The second approach is a modification of this technique to study the vena-contracta effects. The tip clearance region remains un-gridded, but, the physical radial depth of tip clearance is gradually reduced to the smallest constriction typically seen in the tip clearance because of flow phenomena such as the shroud and blade-tip boundary layers. The final approach is a completely gridded tip clearance region of full depth to verify the vena-contracta approach as well as to determine if any increase in fidelity is achieved through this computationally costly procedure. These three tip clearance modeling approaches are applied to the NASA transonic compressor rotor, Rotor-35, in a rotor only configuration and the predicted operational ranges are compared to available LDV data. Span-wise performance characteristics such as total pressure ratio and total temperature ratio are compared at a near peak efficiency and at a near-stall operating point. Tip-vortex resolution and predictions are also examined. The merits and demerits of the three approaches are discussed and recommendations are made for a viable approach in terms of accuracy and computational resources.
Simplified Forced Response HCF Assessment of Turbomachinery Blades
Authors: Ma˚rtensson Hans , Forsman Johan , Eriksson Martin
Published: February 2010

A method is proposed for HCF-analysis that is suitable for use in early design stages of turbomachinery blades. Quantitative measures of the risk for later encountering HCF life limiting vibrations are the goal for the development. The novelty of the system is the unique and rational way all design data are processed resulting in a mode risk priority listing. The method makes extensive use of FE calculated modal analyses and simple assumptions on the modal force and damping. The modal force is taken proportional to the tangential force on the blade over the operating range. This choice is made because the tangential force is known early on from the compressor performance map, and gives a reasonable scaling with the operating point. Crossings occurring at low speed get a lower force than at high speed. The system damping used is a constant critical damping ratio. Using a modal force and damping along with the FE model forced response amplitude can be directly computed at resonance crossings inside operating envelope. The modal force calculated this way can be compared to the force amplitude needed to reach the fatigue limit in a Haigh diagram. Using the Haigh diagram this way allows modes with localized high stresses, so-called hot spots, to be highlighted. Taking the ratio of the forces gives a ranking value that can be used to compare risk. Details of the technique along with example applications to compressor blades are presented in the paper. It is found that many mode crossings can be excluded as low risk this way and that a rational way of prioritizing is achieved.
An Empirical Method for Dynamic Stress Prediction in Turbomachinery
Authors: Allison Timothy C. , Moore J. Jeffrey
Published: February 2010

The effectiveness of fatigue and life prediction methods depends heavily on accurate knowledge of the static and dynamic stresses acting on a structure. Although stress fields may be calculated from the finite element shape functions if a finite element model is constructed and analyzed, in many cases the cost of constructing and analyzing a finite element model is prohibitive. Modeling errors can severely affect the accuracy of stress simulations. This paper presents an empirical method for predicting a transient dynamic stress response of a structure based on measured load and strain data that can be collected during vibration tests. The method applies the proper orthogonal decomposition to a measured data set to filter noise and reduce the size of the identification problem and then employs a matrix deconvolution technique to decouple and identify the reduced coordinate impulse response functions for the structure. The method is applied to simulation data from an axial compressor blade model and produces accurate stress predictions compared to finite element results.
Feedback Control to Prevent Damage by Rotor Rubbing After an Impact Load
Authors: Ginzinger Lucas , Heckmann Benjamin , Ulbrich Heinz
Published: February 2010

A new approach to control a rubbing rotor by applying an active auxiliary bearing has been developed. The control force is applied indirectly using the auxiliary bearing, only in case of rotor rubbing. The auxiliary bearing is actuated using two unidirectional actuators. A three-phase control strategy has been developed which stabilizes the rotor system in case of an impact load and effectively avoids “backward whirling” which is very destructive. As soon as the load ceased the auxiliary bearing is separated from the rotor again and normal operation mode is continued. During the normal operation state, the feedback control does not interfere with the rotor system at all. A test rig has been developed to experimentally verify the control system. Various experiments show the success of the control strategy. In case of rubbing, the contact forces are reduced up to 95 percent. At the same time, the rotor deflection is decreased too. The activation and deactivation of the control system is operated fully automatically. A simulation framework for an elastic rotor including the non-smooth nonlinear dynamics of contacts is presented, which has been used to develop the feedback controller.
Highlights of Roy Smith’s Career at GE
Authors: Koch C. C.
Published: February 2010

Dr. Leroy H. (Roy) Smith, Jr. of General Electric is to be honored at a special session of the ASME Turbo Expo 2009 in recognition of his 55 years of contributions to the gas turbine industry. Although best known to his ASME and IGTI colleagues for his many publications on compressor aerodynamic design theory, analysis methods and research, he has made equally impressive contributions to GE’s jet engine product line. This paper gives a brief chronology of his career, then focuses on the many outstanding fan and compressor aero designs he has created for several major GE engine families.
Very Early Stage of Elastic-Plastic Spherical Contact Fretting
Authors: Ovcharenko Andrey , Etsion Izhak
Published: February 2010

The contact area, friction force and relative displacement evolution at the very early stage of fretting are investigated experimentally. Copper and steel spheres of various diameters are loaded against a hard sapphire flat by a range of normal loads deep into the elastic-plastic regime of deformation. A reciprocating tangential loading is then applied with a maximum loading below the static friction to avoid gross slip. Real-time and in situ direct measurements of the contact area, along with accurate measurements of the friction force and relative displacement, reveal substantial junction growth and energy dissipation mainly in the first loading cycle. The so called “slip amplitude” is found to be attributed to residual tangential plastic deformation rather than to interfacial slip. Elastic shake-down is observed for the 2.5% hardening steel spheres while plastic shake-down is observed in the case of the elastic perfectly plastic copper spheres.
Development of a High-Temperature Repetitive-Impact Apparatus for Exhaust Valve Material Testing
Authors: Blau Peter J. , Jolly Brian C.
Published: February 2010

Some types of mating parts, such as exhaust valves and seats in diesel engines, must perform at elevated temperatures and in oxidizing environments, while at the same time resisting the effects of repetitive impacts and interfacial slip. The wear that takes place under such situations is the net result of a complex process that involves plastic deformation, tangential shear, and oxidation. Tribolayers form, are removed, and reform. An apparatus was designed to simulate the key aspects of elevated temperature wear of exhaust valves. Three degrees of motion: impact, slip, and rotation were taken into account. Two different test geometries were developed: (a) inclined cylindrical pins striking rounded corners, and (b) actual exhaust valve sealing surfaces striking the edges of flat blocks. The features of the high-temperature repetitive impact device are described, and examples of the wear scars produced by the two test configurations are presented.
Shakedown Response to Periodic Loading With Coulomb Friction
Authors: Ahn Young Ju
Published: February 2010

Coupled systems with frictional interface subjected to periodic loading may lead to either shakedown or cyclic slip depending on the initial condition. In this paper, we explore the phenomena in the context of the simplest coupled system involving two contact nodes, and findings show the possibility that a reduced form of Melan’s theorem might apply to such systems under suitable restrictions on the loading factor.
Impact of a Compound Pendulum With a Surface Using a Nonlinear Contact Force
Authors: Banu Eliza A. , Marghitu Dan , Jackson Robert
Published: February 2010

The coefficient of restitution for the impact of a compound pendulum with a flat surface is an important quantitative measure in contact analysis. The impact is analyzed for different lengths of the pendulum, different angles of impact, and different initial angular velocities of the pendulum. The impact with friction is studied using an elasto plastic force developed by Jackson and Green for the three phases of impact: elastic compression, elasto-plastic compression, and elastic restitution phase.
Experimental Investigation of the Effect of Angular Misalignment on the Instability of Plain Journal Bearings
Authors: El-Shafei Aly , Tawfick Sameh H. , Mokhtar Mokhtar O. A.
Published: February 2010

The effect of angular misalignment of plain journal bearings on the oil whirl and oil whip phenomena was investigated using a test rig comprising a flexible one inch diameter shaft supported on two cylindrical fluid film bearings. A matrix of experiments was designed where a precisely controlled angular misalignment between the shaft and the drive end, the non-drive end, or both bearings was induced. In each case we measure the onset of oil whirl and/or the onset of oil whip and the maximum speed that the test rig can reach before reaching a maximum vibration displacement of 1 mm at the location of the displacement sensor. The results show clearly that the angular misalignment of the bearings with respect to the shaft help delay the onset of oil whip from 3200 rpm to 4500 rpm in some cases. An interesting and new observation was the effect of the configuration of the misalignment on the overall stability characteristics. In particular, when the two bearings were misaligned in the same direction such that the two misaligned bearing planes were parallel to each other the onset of instability was more delayed and the overall operation was smoother.
Solid Lubricant Nanoparticles as Wear-Reducing Additives in Sheet Metal Forming Fluids
Authors: Mosleh M. , Atnafu N. D. , Belk J. H.
Published: February 2010

Dispersed nanoparticles of solid lubricants in sheet metal forming fluids are studied for enhanced lubrication that can lead to improved product surface quality and reduced tool wear. Molybdenum disulfide (MoS2) and hexagonal boron nitride (hBN) nanoparticles of varying size and concentrations have shown marked reduction in wear of steel counterfaces representing the tool and in scoring of titanium sheet surfaces. The most effective particle concentration and size ranges were 0.25–4% and 70–100 nm. The counterface wear was reduced by 50–75% while the friction coefficient only marginally improved.
Tribological Performance of Additives for Water-Based Lubricants
Authors: Tomala A. , Karpinska A. , Werner W. S. M. , Olver A. V. , Sto¨ri H.
Published: February 2010

Fully formulated metalworking fluids have been thoroughly described in literature, but the influence of individual additives on tribological performance of such compositions is still not fully clear. In this study we want to establish the mechanism of how different additives affect tribological properties of the system, and to select the best compounds and concentrations for this purpose. The influence of various individual additives on friction behaviour, anti-wear and anti-corrosion properties of metal working fluids was examined. Additionally, chemical characterisation of the surfaces before and after tribological tests was done. The results show that additives can enhance one property while adversely affecting another. The best results were obtained for triethylamine and 1, 4-buthylene glycol, however mixing both additives gives opposite behaviour.
Surface Chemical Patterning for Controlled Cell Adhesion
Authors: Cheng Q. , Komvopoulos K.
Published: February 2010

Thin films exhibiting nonfouling behavior toward protein and cell attachment were grafted onto different substrates by plasma polymerization and deposition. By combining nonfouling film grafting and partial film etching by Ar ion sputtering through the windows of a shadow mask (Si or PDMS), chemical patterns of different shapes and sizes were produced on polymer substrates. Results from cell culture studies illustrate the effectiveness of the present fabrication process to produce surface micropatterns for controlling the cell shape and morphology, with direct implications in vascular pathology.
Circular Contact of Incompressible, Nonlinear-Elastic Bodies
Authors: Diaconescu Emanuel , Glovnea Marilena , Ciutac Filip
Published: February 2010

Contact modeling of rubber bodies is based either on viscoelasticity, nonlinear elasticity or adhesion. This paper advances a simple approach to the analysis of the contacts involving incompressible, nonlinear elastic bodies and reports experimental results on rubber to justify this approach. A good agreement is found between theory and experiments.
Finite Element Modeling of Discontinuous Chip Formation During Rock Cutting
Authors: Menezes Pradeep L. , Lovell Michael R. , Lin Jeen-Shang , Higgs C. Fred
Published: February 2010

In this paper, chip formation process during mechanical cutting of rock is simulated by using an explicit finite element code, LS-DYNA. In the simulation, the work-piece material properties have been modeled using the damage constitute material model. This model simulates the separation of the chip from the work-piece and the simultaneous breakage of the chip into multiple fragments. In the simulation, a rigid steel tool was moved at various sliding velocities, namely 1, 4, 10, 50 and 100 mm/s against a stationary rock material. For a given sliding velocity, the simulations were carried out for various cutting depths, namely 1, 2, 3 and 4 mm. The variation of stresses and the amount of chip formation at different depths of cut and velocities have been investigated. Overall, the results indicate that the explicit FEM is a powerful tool for simulating rock cutting and chip formation. More specifically, the separation of chip from the work-piece at different depths of cut was distinctly shown using this numerical model.
Improving Punctuality of Train Traffic on Western Main Line of Swedish Railway Network: Simulation Approach
Authors: Anand Nilesh , Anayi Michel
Published: February 2010

Western main line is one of the most important railway lines in Sweden. The line section from Stockholm to Katrineholm, which connects the largest cities of the Sweden i.e. Stockholm, Gothenburg and Malmo¨, is studied. This line has heterogeneous train traffic consisting high-speed, regional, freight and commuter trains. This paper attempts to study different factors affecting punctuality on this railway line concentrating on traffic problem around Gnesta station and commuter train turn-back scenario — a bottleneck — at the same station. Simulation of existing and modified timetable is done using train traffic simulation software “Railsys”. Experiments including examining effect of rescheduling train timings, capacity enhancement and infrastructure changes in rail network are conducted and investigated. Robustness analysis is performed from the results of simulation and investigation of the consequences of delays and comparison of how different features in the timetables affect the robustness is done.
Vibration Signatures of Temperature Trended Bearings in Field and Laboratory Testing
Authors: Tarawneh Constantine M. , Kypuros Javier A. , Fuentes Arturo A. , Wilson Brent M. , Gonzalez Bertha A. , Rodriguez Graciela , Maldonado Rafael K.
Published: February 2010

Over the past two years, a series of papers have been published concerning bearing temperature trending and a mechanism to explain this troubling phenomenon. In September of 2008, a collaborative field test between The Union Pacific Railroad (UP), Amsted Rail, Rail Sciences Inc. (RSI), and The University of Texas-Pan American (UTPA) was conducted to corroborate the findings of laboratory research and testing. Field and laboratory results confirm that temperature trended bearings exhibit vibration signals that can be distinguished from healthy bearings. Distinct primary frequencies and overtones associated with the axle, cone, cage, and rollers can be readily identified within a bearing vibration signal. In a previous paper, it was demonstrated that a trended bearing exhibits vibrations of higher magnitude. However, all characteristic frequencies appear in both healthy and trended bearings, but those that dominate, i.e., have higher magnitude, are distinct for trended bearings when compared to healthy bearings. The latter can be repeatedly demonstrated in both field and laboratory experiments. Moreover, the current work identifies and distinguishes between the primary bearing frequencies and those linked to roller misalignment, which is known to increase friction and wear, and consequently raise the bearing temperature.
The Application of Reconfigurable Logic to Active Magnetic Bearing Controller
Authors: Kulesza Zbigniew
Published: February 2010

The article presents the main problems of implementing the PID control law in the reconfigurable logic, namely FPGA integrated circuit. The consecutive steps of discretizing and choosing the fixed-point representation of the continuous, floating-point PID algorithm are described. The FPGA controller is going to be used in the active hetero-polar magnetic bearings system consisting of two radial and one axial bearings. The results of the experimental investigations of the controller are presented. The dynamic performance of the controller is better when compared with the dSPACE controller, that was used so far. The designed hardware and software, the developed implementation procedure and the experience acquired during this stage of the whole project are going to be used during the implementation of more sophisticated control laws (e.g. H∞ robust) in the FPGA for AMB controllers.
Multi-Pulse Chaotic Dynamics of Laminated Composite Piezoelectric Rectangular Plate
Authors: Zhang Wei , Yao Ming-Hui , Cao Dong-Xing
Published: February 2010

The multi-pulse orbits and chaotic dynamics of the simply supported laminated composite piezoelectric rectangular plates under combined parametric excitation and transverse loads are studied in detail. It is assumed that different layers are perfectly bonded to each other with piezoelectric actuator patches embedded. The nonlinear equations of motions for the laminated composite piezoelectric rectangular plates are derived from von Karman-type equation and third-order shear deformation laminate theory of Reddy. The four-dimensional averaged equation under the case of primary parametric resonance and 1:2 internal resonances is obtained by directly using the method of multiple scales and Galerkin approach to the partial differential governing equation of motion for the laminated composite piezoelectric rectangular plates. The system is transformed to the averaged equation. From the averaged equation, the theory of normal form is used to find the explicit formulas of normal form. Based on normal form obtained, the extended Melnikov method is utilized to analyze the multi-pulse global bifurcations and chaotic dynamics for the laminated composite piezoelectric rectangular plates. The analysis of global dynamics indicates that there exist the multi-pulse jumping orbits in the perturbed phase space of the averaged equation. From the averaged equations obtained, the chaotic motions and the Shilnikov type multi-pulse orbits of the laminated composite piezoelectric rectangular plates are found by using numerical simulation. The results obtained above mean the existence of the chaos for the Smale horseshoe sense for the simply supported laminated composite piezoelectric rectangular plates.
Wind-Tunnel Testing of Shape Memory Alloys Actuators as Morphing Wing Driving Systems
Authors: Georges Thomas , Brailovski Vladimir , Morellon Emeric , Coutu Daniel , Terriault Patrick
Published: February 2010

A morphing wing, composed of flexible extrados, rigid intrados and a Shape Memory Alloys (SMA) actuator group located inside the wing box, is used to adapt an airfoil profile to variable flight conditions. The SMA actuator group developed for the morphing wing prototype consists of three main subsystems: the SMA active element, the transmission system, and the passive bias element. The functional requirements for the actuator group were determined using a coupled fluid-structure model of the flexible extrados. An original design approach was applied to determine the geometry and assembly conditions of the SMA active elements. For validation purposes, the morphing wing powered by SMA actuators was tested in a wind tunnel under subsonic flight conditions (Mach = 0.2 to 0.3 and α = −1 to 2°). The ability of the actuator group to move the flexible extrados up to 8 mm of vertical displacement and to bring it back to the initial profile has been successfully proven for all of the wind tunnel testing conditions. During the repetitive actuation, the force, displacement and temperature of the SMA active elements were measured and the results obtained in the force-displacement-temperature space were used to validate the SMA performances predicted during the design phase.
Prediction of Actuation Displacement and Force of a Pre-Stressed Piezoelectric Unimorph, Pumps Considering Internal Stress Effects
Authors: Kang Lae-Hyong , Lee Jong-Won , Han Jae-Hung , Chung Sang-Joon , Ko Han-Young
Published: February 2010

Pre-stressed piezoelectric unimorphs are widely used in many engineering field due to their good actuation performances. They are manufactured by using stress mismatch of adjacent layers, which results in the domed shape and internal stress profile of the piezoelectric layer. The internal stress of the piezoelectric layer can affect the actuation performance of the pre-stressed piezoelectric unimorph significantly. This paper investigates the effect of mechanical pre-stress on the piezoelectric actuation characteristics, and evaluated the actuation performance of a new pre-stressed actuator developed by the present authors, PUMPS, considering the internal stress effects.
Distributed Parameter Modelling and Experimental Validation of a Piezoelectric Bimorph Cantilever Energy Harvester
Authors: Rafique Sajid , Bonello P.
Published: February 2010

Recent developments in low-power portable applications have accelerated research in the field of energy harvesting from ambient sources. Piezoelectric energy harvesters have remarkable potential to convert unused ambient vibrations into useful electrical energy that can subsequently provide power to low-power electronic systems for an infinite life span. This paper concerns the derivation of the mathematical model of a bimorph piezoelectric cantilever beam with distributed inertia, and its experimental validation. Previous research on such a component included a tip mass, which reduced the influence of the distributed inertia of the beam and restricted effective operation to low frequencies. The present research excludes the tip mass. The effects of backward electrical coupling on the mechanical properties of the harvester are investigated, particularly the dependence of the induced additional stiffness and damping on the electrical load and the piezoelectric properties. Both the model and the experimental results showed that the natural frequencies and the response amplitude of the harvester exhibited considerable shifts due to the electrical coupling, indicating change in stiffness and damping. The mechanical coupling effects on the electrical parameters (voltage, current and power output) are also analyzed.
A Bistable Shape Memory Microswitch
Authors: Barth Johannes , Krevet Berthold , Kohl Manfred
Published: February 2010

A novel concept of a bistable microswitch is presented, which combines an antagonistic shape memory alloy (SMA) actuation mechanism with two end positions and magnetic components to maintain these positions in power-off state. The layout of the antagonistic SMA actuation mechanism consists of two mechanically coupled freely suspended TiNi microbridges of 20 μm thickness, which are prestrained with respect to each other. The electro-thermo-mechanical response of the coupled microbridges is investigated for various degrees of prestrain to determine the maximum actuation stroke, minimum required magnetic retention force and maximum switching force. For magnetic retention, the ferromagnetic attraction of different hard and soft magnetic microstructures is studied. By varying the diameter of a hard magnetic cylinder for a given diameter of a soft-magnetic disc and fixed thicknesses, the ferromagnetic attraction force displays a pronounced optimum. First demonstrator microswitches with outer dimensions of about 7×7×4 mm3 are presented, which show large work outputs, featuring strokes and contact forces up to 84 μm and 60 mN, respectively.
Finite Element Modeling and Effect of Electrical/Mechanical Parameters on Electromechanical Impedance Damage Detection
Authors: Kitts Daniel J. , Zagrai Andrei N.
Published: February 2010

Electromechanical Impedance (EMI) is a popular SHM technique, which has found applications in many fields of engineering: mechanical, aerospace, civil and others. Active elements of the technique are piezoelectric wafer active sensors bonded or embedded into a structural element. EMI detection of structural damage is achieved by comparing high frequency structural dynamic signatures reflected in the electromechanical impedance measured at the sensor terminals. Over a past decade, substantial efforts have been devoted to analytical and numerical modeling of various aspects of EMI method. The majority of prior studies focused on fundamental understanding of the sensor transduction mechanism and sensor-structure interaction. Although basic principles of the EMI method are now well understood, modeling of practical structural diagnostic scenarios remains challenging. This contribution expands current modeling efforts in the EMI SHM by considering issues related to energy dissipation in piezoelectric sensor and host structure, as well as its effect on detectability of structural damage. Piezoelectric element and a host structure were modeled using Comsol® Multiphysics finite element package. The finite element implementation allowed for considering contributions of active material, adhesive bond and structural damage. These contributions were studied parametrically for various model settings including mechanical and electrical losses. The study shows that sensor position may directly control damage manifestation in EMI signature; effect of adhesive bond thickness is comparable in magnitude to the effect of bond stiffness; influence of piezoelectric mechanical losses on the impedance signature is different for damaged and undamaged cases.
Thermal, Electrical and Mechanical Properties of Blended and Solvent Cast PLA-MWNT Composites
Authors: Rizvi Reza R. , Kim Jae K. , Naguib Hani E.
Published: February 2010

This paper compares melt blending and solvent casting as processing routes for fabricating Polylactide (PLA)-Multiwall carbon nanotube (MWNT) composites. Composites with an MWNT content of 0, 0.5, 2 and 5 wt.% MWNT were fabricated using both processing techniques and their thermal, electrical and mechanical properties were evaluated. Two types of solvents, chloroform and 1,4-dioxane, were used to disperse MWNTs in PLA when preparing the solvent cast composites. Melt blended PLA-MWNT composites were prepared in a mini twin-screw compounder at a temperature of 165 °C. Samples from both processing techniques were characterized for thermal, electrical and mechanical attributes. Scanning electron microscope (SEM) results indicated that composites prepared using solvent casting had a better MWNT dispersion in PLA. In particular, 1,4-dioxane was considerably more effective in dispersing MWNT than chloroform. Composites prepared using melt blending contained large sized MWNT aggregates suggesting that greater shear mixing or more suitable MWNT surface functionalization is required.
Artificial Muscle Membranes Fabricated Using Ultra-Short Pulse Laser Ablation
Authors: Anderson Iain A. , O’Brien Benjamin , Brastivaceanu Tiberius , Spooner Gregory J. R.
Published: February 2010

An Ultra Short Pulse (USP) laser has been used for surface milling of dielectric elastomer actuator (DEA) polymer (3M VHB tape). DEA’s, artificial analogues to natural muscle, act as flexible capacitors and consist of a polymeric dielectric membrane material sandwiched between flexible electrodes. Actuation is in part determined by the voltage difference across the electrodes and the dielectric membrane thickness. Prior to the present report, pre-stretching the membrane provided the sole means for controlling membrane thickness. Good quality ablation, without grossly observable thermal damage, was achieved at removal rates of 0.0047 mm3/s using a 250 kHz repetition rate and an energy delivery of 2 μjoules/pulse. The surface milling operation was performed as a set of parallel passes produced a series of small shallow trenches, the result of overlap between subsequent passes of the laser. These features did not significantly compromise performance of the test actuators and the USP machined polymer could be pre-stretched at least five times the original size without rupture. When placed in a support frame and subjected to high electric field strength the stretched membrane also maintained its relatively high breakdown strength. A proof of concept two-thickness actuator, one half of it milled, was produced and successfully actuated. USP laser processing has provided a design freedom, beyond pre-stretching, and has opened the way to novel variable thickness micro-actuators.
An Experimental Power Generation Evaluation of Cantilever Type of Piezoelectric Vibration Energy Harvester
Authors: Adachi Kazuhiko , Tanaka Tohru
Published: February 2010

Rotating machinery is widely used in the industrial plant, for example, power plant, chemical plant, mass-production plant and so on. In order to ensure safety operation of the rotating machinery, vibration condition monitoring of the machinery can play a crucial role. Authors have proposed a cantilever type of vibration energy harvester for vibration condition monitoring applications of rotating machinery. Proposed energy harvester consisted of Macro-Fiber Composite (MFC) which is flexible and durable piezocomposite type actuator. The mechanical resonant frequency of the piezoelectric bimorph cantilever is tuned to the rotating speed of a typical 4-pole induction motor driven rotating machine. In this study, the power generation performance of proposed energy harvester is evaluated through numerical simulations as well as experiment when subjected to vibration source input magnitude of 0.71(mm/s rms) at the resonant frequency of the harvester by using the electrodynamic shaker.
Stiffness Control of a SMA Actuator
Authors: Bhadane Minal Y. , Elahinia Mohammad H.
Published: February 2010

This paper presents a control of stiffness for an actuator that utilizes the properties of shape memory alloy (SMA) wires. The control algorithm is developed based on angular position of the SMA actuated arm. The model for calculation of stiffness is prepared in MATLAB/Simulink environment. In this application, a PID controller is designed to regulate the applied voltage of the SMA wire. For all the experiments, dSPACE hardware-in-the-loop solution is used. Simulation and experimental results are collected to validate system model. Result show good performance and control of stiffness through PID control system.