bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Poly-Disperse Multiphase Systems via Computational Fluid Dynamics
Authors: Marchisio Daniele L. , Vanni Marco , Barresi Antonello A. , Baldi Giancarlo
Published: September 2008

Multiphase systems, such as sprays and aerosols, are characterized by the existence of a continuous primary phase and a disperse secondary phase. The interaction between the two phases and/or the chemical reactions can affect both composition and characteristic velocity of the primary and secondary phases, as well as the size distribution of the secondary phase. In order to describe these systems, the continuity, mass balance and momentum balance equations as well as additional equations for turbulence, must be solved. Nevertheless if there is the need to account for the evolution of the secondary phase because of continuous and discrete events the population balance equation must be solved. In this work two very efficient ways to cope with these issues will be presented. In particular the use of the quadrature method of moments coupled with the mixture multiphase model, and the multi-fluid model will be presented and discussed.
A Modal-Geometrical Selection Criterion in Dynamic Condensation Techniques
Authors: Delprete Cristiana , Bonisoli Elvio , Rosso Carlo
Published: September 2008

Dynamic condensation techniques, usually applied to simplify the dynamic models of mechanical systems, are based on the choice of master degrees of freedom and the selection criterion entails important characteristics on the equivalent reduced models. Starting from geometrical data of analytical models or experimental setup and corresponding modal data, the present paper presents a modal-geometrical selection criterion of master degrees of freedom that can minimize the ill-conditioning of mass and stiffness matrices. Some analytical models are tested, by computing with the System Equivalent Reduction Expansion Process (Serep) methodology the equivalent dynamic reduced systems. Both the modal properties and the ill-conditioning of mass and stiffness matrices of reduced models are compared. In particular, by increasing the order of the reduced model, the ratios between the maximum and minimum eigenvalue of the matrices models computed through the modal-geometrical selection criterion are matched up with the best and worst choice of master nodes between all possible solutions. Therefore, performance and restrictions of the proposed criterion is discussed for increasing weight of models and modal properties until to consider complex finite element (FE) models of automotive subsystems, such as tire, wheel clamp and exhaust pipeline.
Machinery Faults Detection and Forecasting Using Hidden Markov Models
Authors: Calefati Paolo , Amico Biagio , Lacasella Antonella , Muraca Emanuel , Zuo Ming J.
Published: September 2008

The present work describes an automatic procedure for diagnostics and prognostic issues, and its application to the evaluation of gearboxes residual lifetime. The Hidden Markov Models — HMM — technique has been used to create quasistationary and stationary models and to take advantages of the multiple sensor data acquisition architecture. At first, Markov models for diagnostics have been defined. The main advantage of the HMMs approach is that all vibration raw data measured by a multisensor architecture can be used without any preprocessing. An effort to adapt the HMMs technique to the prognostic issue has also been carried out. To create Markov Models suitable for prognostics, the Viterbi Algorithm has been used to define the best sequence of model states and to optimize residual useful lifetime computation. Finally, experimental results are discussed, which encourage further research efforts according to the proposed approach.
A Master-Slave Robotic System for Haptic Teleoperation
Authors: Caracciolo R. , Boschetti G. , De Rossi N. , Rosati G. , Trevisani A.
Published: September 2008

This paper proposes a telerobotic system made up of an haptic master and a slave anthropomorphic robot communicating through the Internet. In the proposed teleoperation system the operator drives the robot by manipulating a five-dof pen-shaped master haptic device, whose movements are repeated by the robot. Moreover, the operator is provided with force feedback in order not only to let him feel the physical environment the robot is interacting with, but also to guide him through the correct execution of the teleoperation task. To this purpose, the slave system end-effector (a drill) is mounted on a home-made single axis load cell used to measure drilling forces. This work, in particular, addresses the problem of implementing an on-line trajectory planner assuring a smooth motion of the slave robot in the presence of piecewise constant and unpredictable position references received by the haptic master, even in the presence of random communication time delay. Additionally, in order to improve the drilling task outcome and to prevent the execution of inappropriate and abrupt operators’ movements, an algorithm has been developed, which makes use of a local force feedback to appropriately delay the position references received by the master.
Analysis of Thermoelectric Generators Replacing Low Temperature Heat Exchangers in the Biomass CHP Plant Gu¨ssing
Authors: Bolha`r-Nordenkampf Johannes , Pro¨ll T. , Hofbauer Hermann , Aichernig Christian
Published: September 2008

A thermoelectric generator (TEG) produces electric power directly out of a heat flux across a certain temperature difference. This thermoelectric effect is based on interlinking effects of thermodynamic forces and fluxes (Seebeck and Peltier effect). Within the present work, a prototype unit using Bi2Te3 semiconductor elements is installed at the biomass combined heat and power (CHP) plant in Gu¨ssing, Austria. Different operation points are examined according to a specific test program in order to find operating figures and describe the technical and economical potential of the TEG. A model of the TEG is implemented in the simulation software IPSEpro and verified with results from the experiments. Based on the model, the test plant is extrapolated to the size of possible demonstration plants for which electric output and energetic efficiency are calculated. For the entire CHP plant, the costs for retrofitting standard heat exchangers to TEGs are calculated and compared to the expected revenues from feeding the additional electricity into the grid. It can be concluded that the TEG gives way for new concepts and ideas but the expenses, especially with respect to the high material costs of the semiconductor, do not support a technically efficient and economically lucrative application of the TEG combined with decentralized heat and power production at present time.
Job Dispatching and Monitoring in an Agile Production System
Authors: Chiodi Andrea , Ballarino Andrea , Airoldi Francesco
Published: September 2008

An Integrated Pilot Plant (IPP) for agile production of customized footwear is discussed. Such a system integrates all the functions of an advanced shoe manufacturing company, starting from ERP/PDM, CAD/CAM till job dispatching, factory automation, supply chain management. In particular the innovative job dispatching and monitoring functionalities and tools are here presented. Such an environment specializes on the production of extremely small production batches — usually in fact they are one-pair orders. Each order is directly received from the final consumer via an Internet based Point of Sales, launched into production as-soon-as-possible, and delivered directly to destination into a personalized box. Each order is potentially different from the preceding, so the fast and automatic set-up of each machine involved in the process is a mandatory requirement for an efficient and effective production. Such a workflow imposed innovative solutions for scheduling, job dispatching, and monitoring, based on a strong integration among the various layers of the architecture: ERP/PDM to organize production requests and technological data, CAD/CAM to guarantee the coherence of geometry among the various components of a shoe, SCM/MES to coordinate the dispatching of production and technological data, internal-logistics and line-control to coordinate job-advancement, SCADA and cell automation to actually apply the transported technological information.
Development of a High-Performance Heat Sink for the International Space Station: Hydraulic and Thermostructural Analysis
Authors: Grassi Walter , Testi Daniele
Published: September 2008

The possibility of exploiting an electrohydrodynamic (EHD) technique of heat transfer enhancement for obtaining a high-performance heat sink is investigated in this work. The proposed heat sink is an evolution of a water-cooled cold plate (CP), designed by Daimler-Benz Aerospace (DBA) for the International Space Station (ISS). The dielectric liquid considered for the design process is perfluorohexane, also known as FC-72, a widely-used refrigerant, space-qualified, and present on the Japanese Experiment Module (JEM) of the ISS. The mechanical interfaces for accommodation on the ISS have been taken into account, along with the dynamic loads typical of the critical launch phase, defined by a given power spectral density (PSD) curve. The thermostructural behavior of the CP has been evaluated by the finite element method (FEM). The numerical analysis has been validated on the reference DBA model, whose performance data are available. The hydraulic results are based on simple calculations of pressure drops in ducts, arranged in series or in parallel. The step-by-step conceptual evolution to the final design solution is described in detail. Also, it is explained how to employ the global thermal resistance reduction for decreasing the pumping power, increasing the heat load or reducing volume and weight of the CP.
SOFC-MGT Hybrid Power Plants Fuelled by Methane and Methanol
Authors: Cocco Daniele , Tola Vittorio
Published: September 2008

In this paper the use of methane and methanol in SOFC-MGT hybrid power plants has been compared. As a matter of fact, SOFC-MGT hybrid plants are a very attractive near term option, as they can allow to achieve efficiencies of over 60–65%, even for small power outputs (200–400 kW). The SOFC systems currently developed are fuelled with natural gas, which is reformed inside the same stack at about 800–900 °C. However, the use of alternative fuels with low reforming temperature (for example, methanol reforms at about 250–300 °C) can lead to enhanced hybrid plant performance. In particular, this paper reports a comparative performance analysis of internally reformed SOFC-MGT power plants fuelled by methane and methanol. Moreover, in the case of methanol use, both internal and external reforming have been compared. The performance analysis has been carried out by considering different values for the most important operating parameters of the fuel cell. The comparative analysis has demonstrated that simply replacing methane with methanol in SOFC-MGT power plants slightly reduces the efficiency. However, the use of methanol in SOFC-MGT power plants with external reforming enhances efficiency significantly (by about 4–5 percentage points). The study shows that the use of methanol with external fuel reforming raises stack efficiency thanks to the improved heat management and to the higher hydrogen partial pressure.
Effect of Microgrooved Surfaces on Fibroblast Cells Orientation
Authors: Altomare L. , Fare` S. , Draghi L. , Tanzi M. C.
Published: September 2008

It is well known that cells can interact with patterned surfaces; although the mechanisms are still not clear, substrata containing periodic patterns of parallel grooves can impose directional constraints on cells and affect the rate and direction of cell migration. The aim of our work is to evaluate the possibility of replicating microgrooved surfaces by soft lithography and to assess, in vitro, the influence of three different microgrooved surfaces on fibroblasts alignment. Microgrooved substrata were obtained by Replica Molding out of two different polymers: PLLATMC and ChronoFlex AL from three different masters. From each master, a silicon mold was prepared and the polymers were casted in the mold using chloroform as solvent. By SEM and laser profilometry analysis we observed a good reproducibility of the different surfaces. The obtained results indicate that Replica Molding technique is an accurate method to reproduce a wide number of micropatterned surfaces with different polymers. In vitro tests with L929 murine fibroblasts showed different degrees of cellular alignment and elongation depending on grooves width.
Optimal H-Infinity Control of Ship Heading
Authors: Mahjoob M. J. , Poursina M. , Kashani Nia A.
Published: September 2008

A mathematical model is presented to describe the horizontal behavior of a ship. In order to design a robust controller for maneuvering problem, a number of uncertainties are considered. The transfer function derived from the mathematical model contains coefficients related to body configuration and hydrodynamic behavior. The multiplicative uncertainty bound on the plant transfer function is calculated with variation of hydrodynamic and geometric coefficients. The limitation on the rudder saturation is also considered. The robust control problem is formulated as an optimal H∞ control problem. The robustness, nominal performance and tracking objectives are fully met in the range of the plant linearity, while the control effort is well below the requirement.
Evaluation of Human Body Dynamical Behaviour During Handling Maneuvers and Crash Test Simulations Using Multi-Body Codes
Authors: Braghin Francesco , Pennacchi Paolo , Sabbioni Edoardo
Published: September 2008

The dynamic behavior of the human body during race car maneuvers and frontal crash tests is analyzed in this paper. Both the vehicle and the human body have been modeled using the multi-body approach. Two commercial codes, BRG LifeMOD Biomechanics Modeler®, for the simulation of the human body dynamics, and MSC ADAMS/Car® for the modeling of the vehicle behavior, have been used for the purpose. Due to the impossibility of co-simulating, at first the accelerations on the driver’s chassis are determined using the vehicle’s multibody code and approximating the driver as a rigid body. Then, the calculated accelerations are applied to the vehicle chassis in the biomechanics code to assess the accelerations in various significant points on the driver.
Assessment of a Robust Algorithm for the Detection and Diagnosis of Additive Faults
Authors: Dertimanis Vasilis K. , Koulocheris Dimitris V. , Spentzas Constantinos N.
Published: September 2008

This paper addresses the problem of additive faults (such as input/output sensor and actuator) in a dynamic system, from the view of system identification techniques. The relation between the residuals of the model–based fault diagnosis and the innovations of the system identification procedure is implemented and corresponding algorithms are extracted for the tracking of additive faults, while robustness to noise and disturbances is issued. The study is initiated using single input-single output models and extended to multiple inputs-multiple outputs structures. Furthermore, the detection problem of additive faults for systems with unobservable excitation is examined.
Robotised Cell for the Incremental Forming of Metal Sheets
Authors: Callegari Massimo , Gabrielli Andrea , Palpacelli Matteo-Claudio , Principi Marco
Published: September 2008

The incremental forming of metal sheet parts can be an interesting alternative to the manual forging of the blanks or to the manufacturing of resin dies for the production of prototypes or small lots of parts. Indeed the characteristics of small-volume production would call for an increase in the level of automation, possibly leading to a robotised cell able to complete the part after forming: in this case, the robot performing the deformation could automatically change its tools, cut the part, bend or flange the borders, load/unload the part, etc. Unfortunately the conventional industrial robots do not have the required stiffness nor are able to apply the necessary forces to the blank, but the rather new family of parallel robots have characteristics similar to machining centres, while still keeping the versatility of a robot. The present paper describes the tests that have been performed at the Polytechnic University of Marche in Ancona to assess the feasibility of the automated processing by using a hybrid robot interlocked to the incremental forming cell. The complexity of the experimental setup required the use of several simulation tools, able to design off-line the experiments and even to check beforehand their real feasibility. In the end an effective development environment has been set up, able to interface the different software tools in order to support the process designer in making the correct choices.
On the Use of Commercial CFD Software in the Study of Unsteady Aerodynamic Flows Around Oscillating Airfoils
Authors: Sangolola Bamidele A. , Lakey Stephen P.
Published: September 2008

Numerical simulations have been conducted to simulate the flow over an oscillating NACA 0012 airfoil operating at various Mach numbers, oscillatory frequencies and mean angles of attack, for nominally attached flow conditions. The simulations have been carried out using the ANSYS-CFX5 flow solver, to assess the performance of this tool in conducting unsteady aerodynamic analysis of this nature. Numerical results are compared to the experimental work of Landon, and discussed in relation to previous numerical studies. Overall a good agreement is found for the majority of cases, however, a number of discrepancies have been noted and discussed, particularly regarding simulation of high mean incidence angles and subsonic Mach numbers.
Task Specified Control of a Compliant Parallel Arm Mechanism
Authors: Tekes¸ Ays¸e , So¨nmez U¨mit , Gu¨venc¸ Bilin Aksun
Published: September 2008

Small deflecting flexible parallel arm mechanisms are common in instrument design and often used for precision measurements. Large deflecting parallel arm mechanisms are found usage in MEMS as a suspension of comb drives. In this study control of a compliant parallel arm mechanism for specific tasks are investigated. Compliant parallel arm mechanism consists of two large deflecting initially straight cantilever beams and a rigid coupler and actuated by a magnetic force drive. The kinematic synthesis of mechanism has been studied using mathematically exact nonlinear Elastica theory. Mechanism dynamic response is obtained under time varying magnetic force input. Nonlinear equation of motion is solved numerically using Runge-Kutta methods. Simulation results have been obtained by including translational inertia of rigid coupler and damping forces. Load deflection characteristic of flexible beams are represented by polynomial curve fits obtained from nonlinear inextensible exact beam theory are used as the nonlinear lumped system stiffness. Compliant parallel arm mechanism might be used for different purposes either in macro scale or micro scale depending on specified task. It might be used as an indexing mechanism or a dwell mechanism if the rigid coupler could be positioned at specified points at specified times. Conventional controllers such as PID controllers are designed to achieve position control for specific trajectory. Trajectory simulation results for the compliant parallel arm mechanism are presented using linear and nonlinear spring stiffness.
Mixed Convection Heat Transfer in a Convergent Vertical Channel With a Moving Plate
Authors: Andreozzi Assunta , Bianco Nicola , Lacasa Giovanni , Naso Vincenzo
Published: September 2008

A numerical investigation of mixed convection in air in a convergent vertical channel, due to the interaction between a buoyancy flow and a moving plate induced flow, is presented. The plate moves at a constant velocity along the buoyancy force direction and the principal inclined walls of the channel are heated at uniform heat flux. The numerical analysis is carried out by means of the finite volume method, using the commercial code Fluent. The effects of the channel spacing, wall heat flux, moving plate velocity and converging angle are investigated. Heated wall temperature increases at increasing converging angle, except for natural convection in a 10 mm minimum channel gap. The effect of the converging angle on the wall temperatures is less marked at the larger channel spacing. Maximum temperature of the moving plate is attained in the parallel wall channel for a 30 W m−2 wall heat flux, both in the 10 mm and 40 mm channel, whereas for a 220 W m−2 wall heat flux in the 40 mm channel in mixed convection, maximum wall temperatures are exhibited for a 10° angle. Nusselt, Reynolds and Richardson numbers are correlated by a monomial equation for each converging angle and a unique monomial correlation for all investigated angles in the 2.1·10−2 – 5.1·105 Richardson number range is presented.
Forced Responce of Cylinder Manifold for Reciprocating Compressor Applications
Authors: Giacomelli Enzo , Passeri Marco , Romiti Matteo , Generosi Stefano
Published: September 2008

The system consisting of the reciprocating compressor and associated bottles, known as the “Cylinder manifold” may potentially be the source and location of high vibration problems. Consequently special attention must be paid to the complete simulation of the system to assure smooth and safe operation. Applicable standards specify the items to be included in the study (crosshead guides, distance pieces, cylinder flanges, joints, supports, etc.). However only a model built using manufacturing drawings and validated by site measurements can provide a sufficient accurate description of the characteristics of these critical components and therefore realistic results. Knowledge of the frequencies and amplitudes of pulsation induced shaking forces defined by acoustical simulation, internal gas forces in the cylinder, and unbalanced mechanical forces and moments allows a proper forced response analysis of the cylinder manifold system to be performed. These forces are applied to the finite element model to calculate the relevant vibrations and stress amplitudes by performing a harmonic analysis. When the dynamic stresses are out of the limits it is necessary to go back to the cylinder manifold system analysis or to the acoustical study to find a solution using different supports, with lower shaking forces, or by modifying the volume bottle design. This enables an iterative analysis of the system until all requirements have been satisfied. Additional results of a forced response analysis are the reaction forces on the cylinder and discharge volume bottle supports. When the application requires a large and heavy acoustic damping system with consequently a low mechanical natural frequency, or the compressor speed is significantly high, the possibility of mechanical resonance in the first design is very high. Therefore the execution of these studies at a very early stage of the project is fundamental. The proper solution can be found only by close cooperation between the compressor manufacturer, end user, engineering contractor and vibration specialist.
Analytical Solution and Experimental Verification of Shaped Charge Jet Penetration
Authors: Gozubuyuk Serkan , Yildirim R. Orhan
Published: September 2008

In the scope of this study a one dimensional shape charge code was developed using analytical and semi-empirical approaches. The penetration part of the code is based on the hydrodynamic theory of penetration. The code is capable of modeling and visualizing of shaped charge liner collapse, jet formation and target penetration. Factors affecting the penetration were investigated by utilizing the developed code. Since the code is based on the solution of some analytical expressions rather than the solution of finite difference equations, the solution cost comes out to be enormously less than those of 2 or 3 dimensional hydrocodes. Some number of experiments was performed by using copper liners on steel target plates. The results were compared with the developed code and a good consistency was obtained.
Gas Driven Micro-Cogenerator Incorporating Heat Pump: Exergetic, Economic and Environmental Analysis
Authors: Possidente Raffaello , Roselli Carlo , Sasso Maurizio , Sibilio Sergio
Published: September 2008

A natural gas-fired micro-cogenerator (MCHP) based on a reciprocating internal combustion engine that drives an electric heat pump (EHP), MCHP/EHP, has been analyzed. It allows a high degree of flexibility in terms of operating conditions, due to the possibility to use the two devices separately supplying electric and thermal (heating and cooling) energy (CCHT, Combined Cooling Heating and Power). The MCHP/EHP is a gas cooling technology that can contribute to optimize the natural gas and electricity consumptions in those countries where the HVAC systems are widespread. In particular, our interest was focused on micro-cogenerators (electric power ≤ 15 kW) at the moment available on the market, based on reciprocating internal combustion engine, that could have a great diffusion in the near future for domestic and light commercial applications. Starting by the results of an intense experimental activity an exergetic, economic and environmental analysis has been carried out to compare the proposed MCHP/EHP system to the conventional one based on separate “production”.
Vibration Control and Identification Analysis of Generally Cracked and Spring Added “L” Shaped Beams
Authors: Karadag Vedat
Published: September 2008

In this study, the analytical and experimental free vibration analysis of rectangular cross-section uniform cracked thin L shaped beam on noise isolating elastic spring, has been made by the finite element method. In the present analysis; vibration characteristics of “L” shaped beams with cracks and springs attachments have been analyzed giving particular attention to vibration control and noise identification aspects. This analysis is made by using the finite element method considering three dimensional motion of cracked L shaped beams, namely, for inplane, and out of plane bending, coupled bending-longitudinal and bending-torsional frequencies as new research aspects in the literature which, the related works are usually in plane uncoupled beam analysis. The L shaped beams were analyzed on clamped-free and free-free supported conditions. The cracks were put only one side of the beam and several types of cracks were modeled by massless rotational and longitudinal springs. The analytical and experimental results were compared with each other and with the results available in the literature, satisfactorily. As a result of analysis, it has been found that; there is a certain decrease on the natural frequencies of the beam that has different cracks, and it is concluded that, it is possible to have an exact detection and control idea about the shape and the largeness of the crack with analyzing the natural frequencies and noise patterns of the parts. The crack model used in this study is mentioned as a linear spring model used in the literature. The analytical and experimental results and comparisons show the efficiency and effectiveness of the proposed method.
Parametric Identification of Vehicle’s Vertical Dynamics Using Vector Autoregressive Moving Average Models
Authors: Koulocheris Dimitris V. , Dertimanis Vasilis K.
Published: September 2008

The assessment of vertical dynamics in modern ground vehicles is a difficult task with crucial importance, as it appears to be possessed by a number of conflicting objectives, such as ride comfort and stability. Thus, the effective use of possible control units is depended by the successful description of the vertical performance. The aim of this study is to provide a closed description of vehicles’ vertical dynamics using VARMA models, which are estimated by means of a novel, hybrid optimization algorithm and a corresponding estimation procedure. The hybrid algorithm interconnects the diverse characteristics of its deterministic and stochastic counterparts, while the estimation procedure assures the stability and invertibility requirements in the resulted models. For the practical implementation of the above, a five dimensional VARMA model is used for the description of a passenger vehicle, through the acquisition of noise–corrupted vertical acceleration measurements.
Model Validation Methodology for Design of Micro Systems
Authors: Anac Ozan , Basdogan Ipek
Published: September 2008

Micro Electro Mechanical Systems (MEMS) are the new and emerging technology of the future and have many applications on different disciplines like biomedical, imaging technology, biology etc. Predicting the dynamic performance and reliability characteristics of such systems early in the design process can impact the quality of the design. This paper presents our modeling, testing, and validation methodologies to predict the dynamic performance of micro systems. A two-dimensional torsional micro scanner mirror is chosen as the case study to demonstrate the developed methodologies. Modeling methodology includes modal analysis of the micro scanner using finite element modeling techniques. The validation methodology uses an experimental modal analysis set-up for measuring the dynamic characteristics of the scanner mirror. The finite element analysis and experimental results are compared to identify the inaccuracies in the modeling assumptions. Additionally, modal damping coefficients are also determined since they are critical to predict the response of such systems to external forces.
Backlash Adjustment in Plane Spiroid Gears
Authors: Gessner Andrzej , Staniek Roman
Published: September 2008

Plane spiroid gears currently applied in feed motion rotary drives are roughly described in this paper. The theoretical possible methods of backlash adjustment in this kind of gear are mentioned. Referring to industry experience the only applied method, which uses the eccentric, is described. Its advantages as well as disadvantages related to operation and wearing process are pointed. The disadvantages are mainly connected with changing the gear axis distance while rotating eccentric in order to adjust backlash. A graph depicting the movements of the worm in the direction of backlash reducing and in the perpendicular one, which changes the axis distance, is given. In order to provide some information about the influence of changing axis distance on the mating of face toothing with the worm, mathematical model was created. Some effects of numerical calculations based on that model and showing the bearing contact of the face gear drive supplied with eccentric backlash adjustment are depicted. It can be noticed, how changing the axis distance influences the bearing contact. It can be also estimate if within the chosen range of eccentric rotation the theoretical bearing contact is still acceptable to operate correct. A simplified model presenting the wearing process is also provided. It reveals that after some operating time an edge contact appears while reducing backlash. It significantly decreases the operating time till the next adjustment. There are two methods of backlash reducing described: the first is typical whilst the second is improved and proposed by the author. The advantage of the proposed method is lengthening the operating time between two backlash adjustments. In the end a new type of spiroid gear mating with double-lead worm and deprived of aforesaid disadvantages is mentioned.
Experimental Investigation on the Effect of Longitudinal Aspect Ratio on Natural Convection in Inclined Channels Heated Below
Authors: Andreozzi Assunta , Buonomo Bernardo , Manca Oronzio , Nardini Sergio
Published: September 2008

In this paper an experimental investigation on natural convection in air in inclined channels with rectangular transversal section and lower wall heated at uniform heat flux is carried out. Wall temperature measurements and flow visualization are presented. The results allow investigating on the effect of the distance between the two principal parallel walls and of the inclination angle. The experiments are accomplished for two channel gap values: 20 and 40 mm. The inclination angle is equal to 80° and 88°. The flow development and the shape of flow transitions along the channel are visualized. Flow visualization allows to describe the secondary motion inside an inclined channel. Flow separation region along the lower heated plate begins at lower axial coordinate as the wall heat flux, the inclination angle and the channel gap are greater. The flow separation depends also on transversal coordinate. The detected secondary structures pass from thermals to plumes and vortices. Along the plane parallel to the heated wall, the visualization shows that thermal plumes split in V-shaped structures. For the largest considered channel gap value the instability phenomena in the channel are stronger and chaotic motion in the channel outlet zone is observed. When the channel gap value increases wall temperatures become lower because the higher distance between the walls determines a greater mass flow rate and an increase in the heat transfer.
A Two-Model Approach for the Improvement of a Fixed Tank Vehicle’s Vertical and Lateral Dynamics
Authors: Koulocheris Dimitris V. , Dertimanis Vasilis K.
Published: September 2008

The subject of this paper is to optimize the dynamic performance of a fixed tank biaxial vehicle, with respect to its vertical and lateral performance. For the vertical description of the fixed-tank vehicle, a linear full-car model with ten degrees of freedom is utilized, while its lateral description is determined according to international regulations. All the involved design parameters, such as suspension characteristics and tank’s supports, are included in the optimization process, so that both the vertical and the lateral acceleration of vehicle’s centre of mass are optimized. For the simulation tasks two distinct cases of road profiles are considered, while the optimization procedure is carried out using Complex method.
Effect of Channel Spacing on Mixed Convection in Vertical Convergent Channels
Authors: Bianco Nicola , Lacasa Giovanni , Manca Oronzio
Published: September 2008

Mixed convection in air in a convergent channel with the two principal flat plates at uniform heat flux is analyzed numerically by Fluent code. In the considered system two parallel adiabatic extensions are placed downstream of the convergent channel. The forced flow is obtained by imposing a pressure drop between the inlet and the outlet of the channel. The flow in the channel is assumed to be two-dimensional, turbulent and incompressible. A k-ε turbulent model is employed. Results in terms of dimensionless wall temperature distribution as a function of the walls converging angle, the Grashof number, the pressure drop and the channel aspect ratio are presented in the ranges: 0° ≤ θ ≤ 10°; 4.10 102 ≤ Gr ≤ 32.1 105, 0 ≤ ΔP ≤ 8.82·107, 10.15 < Lw/bmin < 58.0. Results show that Reynolds number, and then the mass flow rate flowing in the channel, increases at decreasing aspect ratios, Lw/bmin. The converging angle that optimizes the fluid-dynamic within the channel is equal to 5°. Dimensionless maximum wall temperature values decreases at increasing Reynolds number and the larger the aspect ratio, the larger the decrease. The Reynolds number over which natural convection become negligible, with respect to forced convection, increases at increasing converging angle and at decreasing aspect ratio.
Test-Bed Infrastructure for Industrial Control Systems Validation
Authors: Carpanzano Emanuelle , Cataldo Andrea
Published: September 2008

To properly deal with the increasing complexity of industrial distributed and agile manufacturing control systems, the use of methods and tools that support the designer in the definition, implementation and verification of intelligent logic control software is more and more necessary. Nowadays, many different software tools are available to face the rapid prototyping and closed loop simulation based verification of an automation system control software. The possibility to validate the control strategies of an automation system for industrial plant during its design phases is very advantageous. In fact the control system validation on plant site is very expensive, both for the high man power costs and for the long time required to implement and test the software code implemented in the control system devices. Scope of this paper is to present the hardware/software infrastructure designed to interface an industrial PLC to a laboratory process simulator and to a real small scale plant, in order to validate the industrial PLC software control code before the real plant commissioning phase. In particular the PLC, communicating with its remote input/output terminal boards via Profibus, is firstly connected to the process simulator for a roughly control algorithm validation, secondly it is interfaced to a small scale plant so to deeply test the PLC logic control solution.
Suppression of Brake Squeal Using Shunted Piezoceramics
Authors: Neubauer Marcus , Oleskiewicz Robert
Published: September 2008

Due to increased interest in comfort features, considerable effort is spent by brake manufacturers in order to suppress brake squeal. This process can be shortened by eliminating the remaining squealing with shunted piezoceramics that are embedded into the brake system. The piezoceramic offers the unique ability to convert mechanical energy into electrical energy and vice versa. The damping performance is determined by the connected shunt. This paper presents a multibody system of a brake, which is capable to reproduce the important features of brake squeal. It includes the dynamics of a piezoceramic that is shunted with a passive LR shunt or a negative capacitance LRC shunt. Analytical stability analysis are carried out to obtain optimal shunt parameters. The performance increase with a negative capacitance is studied in detail. The simulations are validated with measurements on an automotive disc brake.
Thermic Influence on the Dynamics of Pneumatic Servosystems
Authors: Sorli Massimo , Gastaldi Laura
Published: September 2008

The gains values that can be imposed in pneumatic systems controllers are bounded to the restricted actuator bandwidth. That limitation, with low damping and stiffness, due to the air compressibility, seriously affects accuracy and repeatability when varying payload or supply pressures. For modelling and control intent a correct characterisation of the pneumatic actuator natural frequency is indispensable. The aim of this paper is to evaluate how heat exchange process affects the proper characteristics of pneumatic drivers, and in particular their hydraulic stiffness. To this purpose dynamic stiffness had been studied both by imposing in the cylinder’s chambers a polytrophic transformation of the fluid with a prefixed index and by employing energy equations. Numerical results obtained by implementing the two formulations for different working conditions are reported and compared in order to point out the ranges in which they overlap, and hence both approaches produce accurate results, or the ones in which there is a difference, and then it is necessary to consider the temperature dynamics.
Estimation of the Damping in MEMS Inertial Sensors: Comparison Between Numerical and Experimental Results Both at High and Low Pressure Levels
Authors: Braghin Francesco , Leo Elisabetta , Resta Ferruccio
Published: September 2008

Except for MEMS working in ultra high vacuum, the main cause of damping is the air surrounding the system. When the working pressure is equal to the atmospheric one (from now on called “high pressure”, i.e. 105Pa), the mean free path of an air molecule is much smaller than typical MEMS dimensions. Thus, air can be considered as a viscous fluid and two phenomena occur: flow damping and squeeze film damping. These two terms can be evaluated through a simplified Navies-Stocks equation. In vacuum (from now on called “low pressure”, i.e. 26Pa), the air cannot be considered as a viscous fluid any more since the free path of an air molecule is of the same order of magnitude of typical MEMS dimensions. Thus, the molecular fluid theory must be used to estimate the damping. To predict the damping of a MEMS device both at high and low pressure levels, a multi-physics code was used and the achieved numerical results were compared to experimental data measured on the same device.
Forced Response of Interlocked Vane Segments: Numerical Predictions and Experimental Results
Authors: Zucca Stefano , Filippi Sergio , Droetti Fabio , Gola Muzio M.
Published: September 2008

Resonant vibrations affect fatigue life of vane segments. Friction damping is employed to reduce vibration amplitude. When vane segments are assembled, they are twisted so that lower platforms are in contact. The sum of displacements of the two ends of the lower platform after twisting is defined ‘interlocking’. Different ‘interlocking’ values correspond to different values of normal contact force. When interlocked vanes vibrate under external force excitation, energy is dissipated by friction forces at lower platform contacts providing damping to the system. The aim of this paper is the experimental validation of a numerical code for forced response calculation of interlocked vane segments. Since friction forces depend on relative displacements of bodies in contact, the system is nonlinear. System force response is computed by means of Harmonic Balance Method (HBM). Contact model implemented in the code is characterised by tangential and normal stiffness to take into account local compliance of the contact area. Gross slip occurs when the instantaneous ratio of tangential force to normal force is equal to the friction coefficient. Also effect of microslip is taken in account. The experimental set-up used to validate the code is made of a vane segment fixed at the outer radius to an aluminium frame and in contact with two supports at the inner radius. Comparison between the numerical predictions and experimental results is performed for different values of interlocking (i.e. force normal to the contact).
A Fast and Reliable Dynamic Tyre-Road Contact Model for ABS Braking Manoeuvre Simulations
Authors: Braghin Francesco , Cheli Federico , Giangiulio Emiliano , Mancosu Federico , Arosio Daniele
Published: September 2008

Due to the dimensions of the tyre-road contact area, transients in a tyre last approximately 0.1s. Thus, in the case of abrupt maneuvers such as ABS braking, the use of a steady-state tyre model to predict the vehicle’s behavior would lead to significant errors. Available dynamic tyre models, such as Pacejka’s MF-Tyre model, are based on steady-state formulations and the transient behavior of the tyre is included by introducing a first order differential equation of relevant quantities such as the slip angle and the slippage. In these differential equations the most significant parameter used to describe the transient behavior is the so-called relaxation length, i.e. the distance traveled by the tyre to settle to a new steady–state condition once perturbated. Usually this parameter is assumed to be constant.
A Traction and Instability Control Logic for Formula Student Race Cars
Authors: Braghin Francesco , Marchetta Federico , Sabbioni Edoardo
Published: September 2008

Race cars are characterized by very high drive torques and handling performances. However, high torques are useless if they cannot be converted into vehicle acceleration due to macro-slippage of the driven tyres. On the other hand, extreme handling performances are obtained by designing a vehicle that is almost unstable. Thus, small driver errors can lead to a sudden and unexpected off-road. Traction and instability control is of fundamental importance to avoid macro-sliding of the tyres and to combine extremely high handling performances with a safety margin that allows the driver to stabilize the vehicle.
Freeform Deformation vs. B-Spline Representation in Inverse Airfoil Design
Authors: Amoiralis Eleftherios I. , Nikolos Ioannis K.
Published: September 2008

In this work FFD technique is compared to the classical parameterization technique using B-Spline curves by performing inverse airfoil design tests, with a Differential Evolution (DE) algorithm to serve as the optimizer. The criteria of the comparison between the two techniques are the achieved accuracy in the approximation of the reference pressure distribution and the convergence behavior of the optimization algorithm. Experiments are presented, comparing FFD to B-Spline techniques under the same flow conditions, for various numbers of design variables.
Shape Memory Polymer Porous Structures for Mini-Invasive Surgical Procedures
Authors: de Nardo Luigi , De Cicco Sabrina , Jovenitti Matteo , Tanzi Maria C. , Fare` Silvia
Published: September 2008

In the recent past, clinical procedures underwent huge modifications. Among them, mini-invasive surgery has modified the clinical practice and the quality of life of patients. All these evolutions are strictly correlated to the advancement in materials science. Shape Memory Polymers (SMPs), a novel class of stimuli-responsive materials, can be considered ideal candidates for the design of devices for mini-invasive surgery. Such devices can be inserted in a compact temporary shape and subsequently expanded at body temperature: a bone defect, e.g., could be filled by a filler made of SMPs. With the aim of promoting tissue integration and healing, these structures should present a suitable porosity. In this work two different processing techniques to obtain shape memory polymer scaffolds from Calo·MER™, a SMP, are presented. Porous structures were obtained by micro-extrusion, with different chemical expanding agents or by particulate leaching with salt. Morphology, thermo-mechanical and shape recovery properties of the SMP porous samples were investigated. The obtained foams show a well interconnected morphology, with a pore size in the range suitable for bone applications. Shape memory properties were not significantly affected by the transformation processes: a good ability of recovering the original shape was verified. Therefore, foams obtained from these materials could be used to fabricate devices for mini-invasive surgical procedures.
Active Suspension Control Synthesis Using Reduced Order Models That Account for the Time Delay Between Road Inputs
Authors: Van Auken R. Michael
Published: September 2008

The control of wheeled ground vehicle suspension systems is well suited for analysis and refinement using multi-input multi-output (MIMO) control law synthesis methods for linear systems. Usually it is necessary and desirable to develop the control algorithms using a reduced order model of the system. Since such vehicles are also characterized by correlated road inputs with time delay between the front and rear wheels, it is also desirable to consider this delay during the model reduction process. If this delay is taken into consideration, then it may be possible to develop low order control algorithms which compensate for the vehicle modes that are disturbed by the road inputs, resulting in improved overall performance. This paper describes the application of model reduction to a model of a ground vehicle for active suspension control law synthesis. The vehicle is described by a high order MIMO model of a “half-car” with four rigid-body degrees of freedom and flexible body modes to account for structural vibration, plus additional states to represent colored noise road disturbance inputs. Fourth order MIMO models suitable for control law synthesis are then determined using internal balancing, taking into consideration the time delay between the front and rear wheels, followed by subsystem elimination. The performance of the vehicle (high order model) with the resulting low order active suspension control laws is then assessed.