bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Wear in Railway Wheel Profiles
Authors: Abeidi Abdelrahim S. , Bosso Nicola , Gugliotta Antonio , Soma` Aurelio
Published: September 2008

The work describes a method to predict the evolution of the wheel profile of a railway vehicle, depending on the load history acting on the wheelset. The method is based on the determination of the wear on the contact area, which is divided into finite elements according to the strip theory. For each element, in presence of slip, the amount of material loss is evaluated depending on the local value of tangential force and creepage (the meaning of creepage is assumed according to the definition given in [14], [15], [16] as the ratio between the sliding velocity and the tangential rolling velocity). The empirical relation is evaluated according to results of experimental test obtained from literature. The wear is calculated for the entire contact area superimposing the contribution of each element. The motion of the wheelset in lateral direction causes a motion of the contact patch along the profile. Sequentially, the contact area will acquire a different contact shape and stress distribution. The shape of the worn profile depends on both the load condition and the motion of the wheelset with respect to the track. This profile can be obtained from the new one by subtracting at each time step the material removed from the contact area. This procedure is simple, but requires variable profiles for each time step, and is not efficient in computational terms. The strategy proposed here by the authors, is to consider finite periods obtained superimposing several revolution of the wheelset. The worn profile is evaluated in a single step from the cumulative of damage of an entire period. The limitation of this method consists in the different behavior of a wheelset with worn profile respect to a wheelset with new ones, and therefore produces different wear. It is necessary to determine an optimal value for the period to be used to re-evaluate the profile shape, in order to minimize the difference in the predicted shape itself. The method is applied to a suspended wheelset, running on a simulated test track, with S1002/UIC60 profiles. Different periods of re-evaluation of the profiles are considered in order to demonstrate the influence of this parameter.
Numerical and Analytical Analyses of a High Temperature Heat Exchanger
Authors: Aquaro Donato , Donatini Franco , Pieve Maurizio
Published: September 2008

In this paper some analytical and numeric analyses of a high temperature heat exchanger are performed. This heat exchanger should be employed in a test loop of a EFCC (Externally Fired Combined Cycle), placed in a experimental facility owned by the Italian electric utility, ENEL. The heat exchanger is the crucial element in this cycle, as it undergoes temperatures above 1000°C and pressures of about 7 bars. The enthalpy of the combustion products of low cost fuels, such as coal, bottom tar, residuals from refineries, is used to heat a clean working fluid, in this case pressurized air. There are some outstanding benefits for the turbine, in regard to the manufacturing and maintenance costs, and also for its life. The heat transfer components are some bayonet tubes, assembled in 4 modules. A half of them is made of ceramic materials, the others of an advanced metallic material (ODS), due to the burdensome operating conditions. First of all, the heat exchanges are evaluated by means of a simplified analytical model. The radiant contribution also has been taken into account, due to the presence of non-transparent gases. Subsequently, the in-tube fluid temperature increase is calculated for all the heat exchanger modules, through an enthalpy balance and with some simplifying assumptions. Moreover, a comparison is made between the analytical solution and the results of a numerical model implemented in a CFD code. A good agreement is found, which indicates that the analytical model is reasonably valid. In fact, the whole heat exchanger temperature change is determined by means of the two methods with a difference of about 7% for both the streams. Finally, these results are to be compared with the experimental data which should be available in the near future, when the facility will begin working. Also, by this way, the developed calculation model would get a validation.
Design of an Optimal Control Strategy for an Active Front Steering System
Authors: Goodarzi Avesta , Esmailzadeh Ebrahim , Nadarkhani Babak
Published: September 2008

The concept of active steering control (ASC) has been considered by several researchers as well as auto manufacturing companies during recent years. This innovative system permits any correction of the driver’s steering angle in order to achieve the desired vehicle dynamic behavior. An optimal control law to evaluate the steering angle’s correction of the front wheels, being part of an active front steering system (AFS), has been developed. For this purpose a specific lateral vehicle dynamics index is defined in which way that the minimization of the performance index lead to improved vehicle dynamics. The optimal values of the control law’s gains are determined analytically. The performance of the proposed control system has been verified using 8-DOF nonlinear vehicle dynamic model. The simulation results illustrate that considerable improvement in vehicle handling is achieved particularly for the cases of the low and mid-range lateral acceleration maneuvers.
Taking the Grunt Work Out of Tolerance Optimization
Authors: Jayakaran Christopher , Patel Ragini , Momaya Prashant , Roopesh K. , Ananthanarayana Umeshchandra , Sardar Gautam
Published: September 2008

The activity of tolerance allocation and optimization is a critical step in the product design process. This inherent trade-off between design objectives and process capability poses challenges in achieving right tolerances, both technically and effort-wise. Traditional methods in tolerance allocation are mostly regressive and are constrained by selection of the manufacturing processes. A progressive approach to tolerance allocation that does not assume these processes helps in achieving optimality of the tolerances and selection of manufacturing processes to realize the design. The two-stage process suggested in this paper formulates an optimization problem that allocates the tolerances based on sensitivities of tolerance values at the first stage followed by manufacturing process selection and further optimization to adhere to the processes selected in the second stage. The approach aims at achieving optimal allocation of tolerances and assignment of the manufacturing processes, while keeping the optimization problem computationally simple, although iterative.
Application of Magneto-Elastic Sensors to the Measurement of Fluid Flow Rates in the Automotive Domain
Authors: Merlo Alberto M. , Malvicino Carloandrea , Carpegna Giorgio , Ferraris Walter , Parodi Maria L. , Seccardini Riccardo , Pfu¨tzner Helmut , Kosel Ju¨rgen , Meydan Turgut , Va´zquez Manuel , Rohn Michael , Marquardt Bernd
Published: September 2008

The monitoring of several vehicle and engine operation parameters has been a key factor for the successful introduction of electronic control of the most important car performances. Among the several measured quantities, the measurement of fluid mass flow still requires sophisticated and expensive transducers, no convenient and low cost technologies having been available so far. The recent invention of the concept of bi-layer ribbons, has allowed to adjust the sensitivity of magneto-elastic sensing elements to be employed in the construction of bending sensors, in order to match their metrological properties to the wanted application. Due to their low production cost, small size and good reliability, magneto-elastic bi-layer sensors proved to be a promising technology for the large scale production of fluid flowmeters, which can be used in the automotive industry and are operated in a very wide temperature range, with temperatures spanning from −25 to 115 °C. In the present research, two main application domains have been taken into consideration namely the flow metering of the air streaming into engine air intake manifolds and the measurement of the flow rates of refrigerant fluid in the cooling loop of car air conditioning systems (HVAC). The technical feasibility of agglutinated bi-layer flow sensors, has been investigated and evaluated, by means of experimental testing under real like operating conditions. The present paper briefly describes the manufacturing process and the experimental methodologies. Preliminary results are given and future developments are foreseen, while further research guidelines are established.
Parametric Analysis for Thermal and Fluid Dynamic Management of Natural Convection in a Channel-Chimney System
Authors: Andreozzi Assunta , Buonomo Bernardo , Manca Oronzio
Published: September 2008

In this paper a parametric analysis of natural convection in air in a channel-chimney system symmetrically heated at uniform heat flux, obtained by means of a numerical simulation, is carried out. The analysed regime is two-dimensional, laminar and steady-state. The numerical procedure employs the full Navier-Stokes and energy equations in terms of the stream function-vorticity approach. Results are presented in terms of wall temperature profiles in order to show the more thermally convenient configurations which correspond to the channel-chimney system with the lowest maximum wall temperature. The analysis is obtained for a Rayleigh number in the range between 102 and 105, for a channel aspect ratio equal to 5, 10 and 20 and the extension and expansion ratios between 1.0 and 4.0. Correlations for dimensionless mass flow rate, maximum wall temperature and average Nusselt number in terms of Rayleigh number, aspect ratio, extension and expansion ratios are presented. Geometric optimal configurations, for assigned Rayleigh number and aspect ratio, are estimated as a function of the extension ratio. For considered Rayleigh number the difference between the highest and the lowest maximum wall temperatures increases increasing the channel aspect ratio. This behaviour is as greater as the extension ratio is. These differences decrease significantly for the highest Rayleigh number value. The optimal expansion ratio values depend strongly on Rayleigh number and extension ratio values and slightly on the aspect ratio.
Identification of Spatially Extended Pollution Sources by Means of Blind Sources Separation Algorithms
Authors: Cedola Luca , Villarini Mauro , Fioriti Enzo , Carlini Maurizio
Published: September 2008

Blind Source Separation (BSS) is able to recover original source signals from their mixtures. Well-known sources are brain electric activity, acoustic phenomena, earthquakes. Here we apply BSS to air pollution analysis identificating gas emissions using only sensor measurements mutually and statistically independent. This application consents an independent, low cost and real time environmental monitoring system. Besides, a real-world pollution case from an industrial region of central Italy is presented and processed by BSS.
Selective Peptide Recognition With Molecularly Imprinted Polymers in Designing New Biomedical Devices
Authors: Vitale U. , Rechichi A. , D’Alonzo M. , Cristallini C. , Barbani N. , Ciardelli G. , Giusti P.
Published: September 2008

Molecular imprinting is a technique for the synthesis of polymers capable to bind selectively specific molecules. The imprinting of large proteins, like cell adhesion proteins or cell receptors, can lead to important and innovative biomedical applications. However such molecules show such important conformational changes in the polymerisation environment that the recognition sites are poorly specific. The “epitope approach” can overcome this limit by adopting, as template, a stable short peptide sequence representative of an accessible fragment of a larger protein. The resulting imprinted polymer can recognize both the template and the whole molecule thanks to the specific cavities for the epitope. In this work two molecularly imprinted polymer formulations (macroporous monolith and nanospheres) were obtained with the protected peptides Z-Thr-Ala-Ala-OMe, as template, and Z-Thr-Ile-Leu-OMe, as analogue for the selectivity evaluation, the methacrylic acid, as functional monomer, the trimethylolpropane trimethacrylate and pentaerythritol triacrylate, as cross-linkers. Polymers were synthesized by precipitation polymerisation in acetonitrile at 60 °C, thermally initiated with azobisisobutyronitrile. All polymers were characterized by the standard techniques SEM, FT-IR, and TGA. The supernatants from the polymerisation and the rebinding solutions were analysed by HPLC. The higher cross-linked polymers retained about the 70% of the template, against about the 20% for the lower ones. The extracted template amount and the rebinding capacity decreased with the cross-linking degree, while the selectivity showed the opposite behaviour. The pentaerythritol triacrylate cross-linked polymers showed the best recognition (MIP 2−, α = 1.71) and selectivity (MIP 2+, α′ = 5.58) capabilities.
Climate Variables That Influence the Thermal Performance of Horizontal Collector Ground Source Heat Pumps
Authors: Lohan John , Burke Niall , Greene Michael
Published: September 2008

The performance characteristics of new heat pumps are usually evaluated under standard test conditions in certified test laboratories prior to their market release. While this data allows potential customers an opportunity to compare different heat pumps under the same conditions it is difficult to assess how variations in operating conditions, particularly around horizontally oriented ground collectors impact on heat pump Coefficient Of Performance (COP). Indeed, harsh winter conditions of continental climates dictate that horizontal collectors are buried sufficiently deep enough to operate in a thermally stable environment, independent of the weather, but this is not as critical in milder maritime climates and shallower collectors that may be influenced by climate are used. This review paper therefore seeks to identify the key climate variables that have been shown to influence the efficiency of horizontal collector heat pump systems. The literature highlights the significant impact of soil moisture content on COP, but the extended relationship between climate, moisture content and COP has not been established. Historical climate data from both a continental and maritime climate is presented and key aspects of their respective weather patterns are compared to assess their capacity to influence soil condition and COP. A series of empirical models linking changes in soil moisture content to fluctuations in soil thermal conductivity, diffusivity and resistance are also presented so that the impact of climate on soil thermal energy content and heat transfer characteristics might be assessed. However, since no one study has experimentally determined the complex relationship between climate, soil heat transfer characteristics and heat pump performance, this paper concludes with an overview of an experimental test facility that allows this relationship to be established for horizontal collector heat pumps in maritime climates.
A Semi-Physical Model of a Hydraulic Power Steering System for Vehicle Dynamics Simulations
Authors: Cheli Federico , Leo Elisabetta , Sabbioni Edoardo , Zuin Andrea
Published: September 2008

A semi-physical model of an hydraulic power steering system is presented in this paper. The proposed model allows to evaluate the wheels dynamic response to steering inputs and to calculate the corresponding reaction torque on the steering-wheel (steering torque). The analyzed steering system increases its stiffness (so that the steering assist level is decreases) with the rise of the vehicle speed. Thus, vehicle maneuverability is improved during parking maneuvers, while at high vehicle speeds, stability and driver perceived steering feel are ensured. A two d.o.f. (steering-wheel and rack-pinion rotations) model has been implemented during this study. The model parameters have been identified through the standard laboratory tests carried out to characterize a steering system, minimizing the difference between the experimental data and the model numerical results. During laboratory tests the hydraulic power system has been characterized first, measuring its stiffness variation as a function of the relative rotation between the steering-wheel and the rack-pinion, and the steering torque as a function of the difference between the delivery and the reversal pressure of the double-acting ram. The complete steering system has been then characterized, suspending the vehicle and placing the wheels on appropriate low-friction plates which permit them to turn; sine and frequency sweep steering input have been applied by a robot and the corresponding reaction torque on the steering-wheel has been measured. Simulations results are in good agreement with the experimental ones for all the performed tests. The steering system model has been integrated into a 14 d.o.f. vehicle model developed by the Mechanical Department of the Politecnico di Milano in order to access its reliability during handling maneuvers. Several simulations have been performed both in open (step-steer, steering pad, etc.) and in closed loop (lane change, double lane change, slalom, etc). Simulation results have shown a reduction of the toe angle due to the deformability of the steering system and a time delay of the wheel angle respect to the cinematic condition introduced by the steering system dynamics. The reaction torque on the steering-wheel has also been calculated during the simulations to access the driver perceived steering feel during the maneuvers.
Analysis of Singularities of a 3DOF Parallel Manipulator Based on a Novel Geometrical Method
Authors: Pendar Hodjat , Roozbehani Hajir , Sadeghian Hoda , Zohoor Hassan
Published: September 2008

In this article singular points of a parallel manipulator are obtained based on a novel geometrical method. Here we introduce the constrained plain method (CPM) and some of its application in parallel mechanism. Given the definition of constraint plane (CP) and infinite constraint plane (ICP) the dependency conditions of constraints is achieved with the use of a new theorem based on the Ceva geometrical theorem. The direction of angular velocity of a body is achieved by having three ICPs with the use of another theorem. Finally, with the use of the above two novel theorems singularities of the 3UPF_PU mechanism are obtained. It should be emphasized that this method is completely geometrical, involving no complex or massive calculations. In the previous methods based on the Grassmann Geometry, the mechanism needs to be statically analyzed at first, so that the Inverse Jacobian Matrix is achieved, and then the Plucker-Vector is derived. This task is somewhat inconvenient and in the end there are plenty of conditions remained to be pondered in order to obtain the singularity conditions, while the novel method introduced here, involves no tiring calculations neither the analysis of numerous conditions and yields the answer quickly.
A Cost and Time Effective Alternative for an Aerial Reconnaissance and Surveillance Platform
Authors: Wowczuk Zenovy S. , Auld Jeffery R. X. , Smith James E.
Published: September 2008

An expanded need for information obtainable from aerial sensor platforms is driving research and development towards both the use of Unmanned Aerial Vehicles (UAV’s) and the extensive physical redesign of existing airframes to accommodate alternative capabilities. This trend in aerial platform development requires significant time and funding and has yet to transpire into low single-system cost that can be rapidly set to use. An alternative concept of utilizing existing and unmodified airframes as sensor platforms, through the use of peripheral systems, presents an attractive solution to this problem. A particular sensor platform system (Oculus) has been designed for use upon a C-130 aircraft and, as a blueprint concept, shows considerable design flexibility for use upon additional existing military and commercial airframes. This roll-on roll-off sensor platform is a stand alone system that requires no modification to the C-130 airframe and has the capacity to incorporate multi-mission sensor capabilities which can be used for a wide variety of missions. These missions are (but not limited to) Environmental Impact Assessment, Counter Drug, Counter Terrorism, Homeland Security, Resource Surveys, Environmental Surveys, and Search and Rescue. This system (patent pending) has been developed to support a broad spectrum of the latest in remote sensor technology for missions requiring highly proficient reconnaissance capabilities. It was also designed under the criterion of mission flexibility, stability, field of view, storability, modular attachment space and provisions for expansion and upgrade. This sensor platform system provides a superior cost-effective upgrade capability to existing airframes.
High Lift Circulation Controlled Helicopter Blade
Authors: Angle Gerald M. , Huebsch Wade W. , Wowczuk Zenovy S. , Prucz Jacky C. , Smith James E.
Published: September 2008

Circulation control techniques have a long history of applications to fixed wing aircraft. General aviation has used circulation control to delay flow separation and increase the maximum lift coefficient achievable with a given airfoil. These techniques have been gradually expanded to other applications, such as ground vehicles, to reduce drag. Circulation control technology can, potentially, be applied also to each blade of the main rotor in a helicopter, in order to increase the lift capacity of the rotor. Applications of circulation control technologies to fixed wing aircraft have demonstrated the potential of a three-fold increase in the lift coefficient, as compared to a conventional airfoil. This finding would suggest that a rotorcraft equipped with circulation control of the main rotor blades could, conceivably, lift up a payload that is approximately three times heavier than the maximum lift capacity of the same helicopter without circulation control. Alternatively, circulation control could reduce the required rotor diameter by up to 48%, if the maximum lift capacity remains unaltered. A High Lift, Circulation Controlled Helicopter Blade will be undergoing initial testing in the subsonic wind tunnel facility at West Virginia University. Two-dimensional elliptic airfoil models with air blowing slots for circulation control will be used as specimens in these tests in order to determine the aerodynamic changes, especially in lift and drag forces, achievable with various blowing slot configurations. Based on the results of the wind tunnel testing, an improved, detailed design will be developed for the entire main rotor of a helicopter with circulation control.
Numerical and Experimental Characterization of a Plate Compact Multipass Counter Flow and Locally Cross-Flow Recuperator
Authors: Congedo Paolo M. , Starace Giuseppe
Published: September 2008

A compact and efficient heat exchanger for exhaust gas recovery energy was needed to raise the total efficiency of a thermo-photovoltaic system TPV (Thermo-Photo-Voltaic) for automotive applications (see [1]). In order to respect the strict condition of a high heat transfer surface to volume ratio, a heat exchanger configuration with a plate compact multi-pass counter flow and locally cross-flow recuperator has been chosen. The goal of this work is the understanding of the behaviour of the heat exchanger with numerical and experimental analysis for different geometrical and operating conditions. A high number of dimensions and manufacturing constraints was evaluated before reaching a definite design of a compact and efficient heat exchanger to be tested in the lab for initial experiments. The experimental work was needed in order to validate the numerical model. As the material needed for the real application could not be easily manufactured and instrumented in a workshop, a simplified real model, made of brass, was built, in order to compare numerical results and experimental findings. It was supposed that results obtained in this way would be sufficient to be considered valid when extrapolated in the real heat exchanger high temperature operating conditions and manufacturing material. The experimental results have been successfully compared with numerical ones obtained with the Fluent CFD code (release 6.2.16) Curves of performance (ε-NTU diagram plotted as a function of the ratio between the minimum and the maximum thermal capacities of the flows and pressure drop -mass flowrate diagram as a function of the average temperature) have been obtained and were useful to choose the adequate configuration for different applications, depending on the requested heat transfer and maximum allowable pressure drop. The output of the investigation was: heat transfer, outlet temperatures for both air flows, heat exchanger efficiency, differential pressure drop for both hot and cold sides. After this validation final numerical simulations have been carried out in order to understand the dependence of the heat exchanger efficiency on other geometrical parameters and operating conditions such as plates dimensions, numbers and height of vanes, operating pressure and so on.
Analysis of the Stress Distribution in Thermal Barrier Coatings
Authors: Botto Daniele
Published: September 2008

This paper investigates the state of stress induced by oxidation of a typical plasma sprayed thermal barrier coating. At high temperature a thin layer of thermally grown oxide forms in the barrier, and growth with time. Observation of specimens after laboratory tests gave important information about the shape of the oxide layer and about the oxidation law. The oxide is the main responsible for the stress in the thermal barrier coating. A finite element model of a TBC has been developed with temperature-depending material properties, simulating the strain due to lateral growth of the oxide and considering the sintering of the ceramic materials. Time dependent behavior, such as oxide creep, has been taken into account with a simplified model. Simulation has been done for both isothermal ageing and thermal cycles. The location of the maximum stresses in the model are consistent with the location of crack propagation observed in the experimental tests.
Artificial Neural Networks Modeling of Surface Finish in Electro-Discharge Machining of Tool Steels
Authors: Markopoulos A. , Vaxevanidis N. M. , Petropoulos G. , Manolakos D. E.
Published: September 2008

Electro-Discharge machining (EDM) is a thermal process with a complex metal removal mechanism that involves the formation of a plasma channel between the tool and the workpiece electrodes and the melting and evaporation of material resulted thus in the generation of a rough surface consisting of a large number of randomly overlapping craters and no preferential direction. EDM is considered especially suitable for machining complex contours, with high accuracy and for materials that are not amenable to conventional removal methods. However, certain phenomena negatively affecting the surface integrity of EDMed workpieces, constrain the expanded application of the technology. Accordingly, it has been difficult to establish models that correlate accurately the operational variables and the performance towards the optimization of the process. In recent years, artificial neural networks (ANN) have emerged as a novel modeling technique that is able to provide reliable results and it can be integrated into a great number of technological areas including various aspects of manufacturing. In this paper ANN models for the prediction of the surface roughness of electro-discharge machined surfaces are presented. A feed-forward artificial ANN trained with the Levenberg-Marquardt algorithm was finally selected. The proposed neural network takes into consideration the pulse current and the pulse-on time as EDM process variables, for three different tool steels in order to determine the center-line average (Ra) and the maximum height of the profile (Rt) surface roughness parameters.
Optimal Design of Supercavitating Vehicles Based on Trimmed Flight Performance
Authors: Ahn Seong Sik , Ruzzene Massimo
Published: September 2008

Supercavitating vehicles exploit supercavitation as a means to reduce drag and increase their underwater speed. The dynamic behavior of this class of vehicles is very complex as a result of the coupling between vehicle and cavity dynamics and of their strong interactions. In addition, the hydrodynamic stability of supercavitating vehicles needs to be carefully addressed as the loads are completely different from those on conventional submerged bodies. As a supercavity completely envelops the vehicle, most of its surface is acted upon by almost negligible water-vapor forces, and only a small percentage of it is wetted. As a result, the center of pressure is always ahead of the center of mass, thus violating a fundamental principle of hydrodynamic stability. To this date, a number of basic issues need to be addressed regarding configurational design and operating conditions of supercavitating vehicles. This paper presents a preliminary investigation, where the vehicle configuration is evaluated for optimal performance during trim, level flight. The dynamic behavior of the vehicle is investigated through a 6 degrees of freedom rigid body model. In the considered formulation, the vehicle is acted upon by gravity and propulsion and by loads generated by the control surfaces of the vehicle and by the interactions with the cavity. The control surfaces include 4 fins and the cavitator disk at the nose, which produces the cavity. Trimmed conditions for assigned velocity and vehicle configurations are evaluated by solving a nonlinear system of equations resulting from the vehicle’s equation of motion. The vehicle performance is defined in terms of achievable range of operation, which is used as an objective function in an optimization problem, where basic configurational and operational parameters are considered as design variables. The presented results show that proper selection of the vehicle configuration can significantly improve the selected performance index. The simulation of the vehicle dynamic behavior in trim conditions and its response to small perturbations with respect to the trim values show the challenges associated to the limited stability of the vehicle and provide indications for future investigations.
Manufacturing of Parts in Ultra High Strength Steel Using Local Heat Treatment
Authors: Carlsson Bjo¨rn , Russo Domenico , Arin˜o Oliver Jesu´s
Published: September 2008

In this paper the manufacturing of a side impact beam, with the aid of local heat treatment, is described. The beam has two areas where the risk of fracture is high. Two zones of the blank, corresponding to these areas, are therefore heat treated before stamping to reduce the risk of fracture. The material is a martensitic steel with a virgin tensile strength of 1200 MPa. The heat treatment is made by laser to an approximate temperature of 850° Celsius. This heat treatment reduces the strength of the material to a tensile strength of approximately 650 MPa after cooling. The formability is increased accordingly. The method of local heat treatment with the objective to increase formability in selected areas can be seen as an alternative to the use of conventional tailor welded blanks.
Influence of Fibre Heating in PMC Production Technology
Authors: Gisario A. , Quadrini F. , Tagliaferri V.
Published: September 2008

Fibre heating can be employed to optimise composite fabrication in hand lamination. In order to show the fibre heating effect on the properties of hand laminated composites, dynamical and mechanical tests were performed on simply cured glass fibre reinforced laminates and on treated ones. In this second case the fibre content was heated before composite lamination by means of a hot parallel plate press. All the specimens were room temperature cured. A significant increase in storage modulus was observed as an effect of fibre heating as well as a data dispersion reduction. Additionally a lower thickness was measured due to the higher resin fluidity.
Nonlinear Stochastic Controllers for Semiactive and Regenerative Structural Control Systems, With Guaranteed Quadratic Performance Margins
Authors: Scruggs Jeffrey T. , Taflanidis Alexandros A. , Iwan Wilfred D.
Published: September 2008

In many applications of vibration control, the circumstances of the application impose constraints on the energy available for the actuation of control forces. Semiactive dampers (i.e., viscous dampers with controllable coefficients) constitute the simplest example of such actuation in structural control applications. Regenerative Force Actuation (RFA) networks are an extension of semiactive devices, in which mechanical energy is first converted to electrical energy, which is then dissipated in a controllable resistive network. A fairly general class of semiactive and regenerative systems can be characterized by a differential equation which is bilinear (i.e., linear in state, linear in control input, but nonlinear in both). This paper presents a general approach to bilinear feedback control system design for semiactive and regenerative systems, which is analytically guaranteed to out-perform optimal linear viscous damping in stationary stochastic response, under the familiar Quadratic Gaussian performance measure. The design for full-state feedback and for the more practical case of noise-corrupted and incomplete measurements (i.e., output feedback) are separately discussed. Variants of the theory are shown to exist for other quadratic performance measures, including risk-sensitive and multi-objective frameworks. An illustrative application to civil engineering is presented.
Simulation of Fluid Flow Through a Granular Bed
Authors: Jafari Arezou , Mousavi S. Mohammad
Published: September 2008

Numerical study of flow through random packing of non-overlapping spheres in a cylindrical geometry is investigated. Dimensionless pressure drop has been studied for a fluid through the porous media at moderate Reynolds numbers (based on pore permeability and interstitial fluid velocity), and numerical solution of Navier-Stokes equations in three dimensional porous packed bed illustrated in excellent agreement with those reported by Macdonald [1979] in the range of Reynolds number studied. The results compare to the previous work (Soleymani et al., 2002) show more accurate conclusion because the problem of channeling in a duct geometry. By injection of solute into the system, the dispersivity over a wide range of flow rate has been investigated. It is shown that the lateral fluid dispersion coefficients can be calculated by comparing the concentration profiles of solute obtained by numerical simulations and those derived analytically by solving the macroscopic dispersion equation for the present geometry.
Numerical Simulation of Buoyancy Affected Turbulent Air Flow in a Room
Authors: Nouri-Borujerdi A. , Fathi-Gishnegani A.
Published: September 2008

In this paper a three-dimensional steady state incompressible turbulent air flow is considered in a large single room. The buoyancy affected turbulent air flow is simulated by solving governing equations numerically. The turbulence modeling includes both k–ε and zero-equation models and their results are compared to the experimental data. The paper reviews several aspects such as displacement of radiator system performance, temperature and flow field distribution and comfort. The results show that the best temperature distribution and comfort obtain when radiator is installed under the window and its height be equal to or greater than that of the window.
The Periodic and Chaotic Vibration of Dynamical System With Elastic Pendulum
Authors: Sado Danuta
Published: September 2008

The nonlinear damping effect on response of coupled three degree-of-freedom autoparametric vibration system with elastic pendulum attached to the main mass is investigated numerically. It was assumed that the main body is suspended by an element characterized by non-linear elasticity and non-linear damping force and is excited harmonically in the vertical direction. The elastic pendulum characterized also by -linear elasticity and non-linear damping. Solutions for the system response are presented for specific values of the uncoupled normal frequency ratios and the energy transfer between modes of vibrations is observed. Curves of internal resonances for free vibrations and external resonances for exciting force are shown. In this type system one mode of vibration may excite or damp another one, and except different kinds of periodic vibration there may also appear chaotic vibration. Various techniques, including chaos techniques such as bifurcation diagrams and: time histories, phase plane portraits, power spectral densities, Poincare` maps and exponents of Lyapunov, are used in the identification of the responses. These bifurcation diagrams show many sudden qualitative changes, that is, many bifurcations in the chaotic attractor as well as in the periodic orbits. The results show that the system can exhibit various types of motion, from periodic to quasi-periodic to chaotic, and is sensitive to small changes of the system parameters.
Effect of Damping on the Periodic and Chaotic Vibration of System With Double Pendulum
Authors: Sado Danuta , Gajos Krzysztof
Published: September 2008

The nonlinear response of three degree of freedom vibratory system with double pendulum in the neighborhood internal and external responses have been researched. Numerical and analytical methods have been applied for these investigations. Analytical solutions have been obtained by using multiple scale method. This method is used to construct first-order non-linear ordinary differential equations governing the modulation of the amplitudes and phases. Steady state solutions and their stability are computed for selected values of the system parameters. Numerically it was shown, that near internal and external resonances except different kinds of periodic vibrations there may also appear chaotic vibration. For characterizing an irregular chaotic response bifurcation diagrams and time histories, Poincare` maps and maximal exponents of Lyapunov have been constructed.
Reduced Order Modeling of the Squeeze Film Damping in MEMS
Authors: Soma` Aurelio , Spinola Guido , Ballestra Alberto , Pennetta Alessandro
Published: September 2008

In this work the effect of the Squeeze Film Damping on MEMS structures is studied. When a device is being designed, it is very important to preview with good approximation its dynamic behavior. However, as the simulation of the micro-systems involves different physical domains, the analysis with numerical methods can turn out remarkably onerous. Moreover the Reduced Order Modeling is preferable when, due to technological reasons, the membrane is built with several holes and the geometrical FEM coupled model will be computational heavy. Therefore Reduced Order Models allow to integrate in a total mathematical model the main parameters, obtained by the numerical analysis, considering the behavior of the structure analyzed in different physical domains. In the present work the non-linear coefficients of equivalent damping and stiffness by finite element models are investigated to be exported in a reduced order model. By means of numerical finite element calculation is studied the sensitivity analysis related to design parameters such as dimension of the plate and the presence, or lack, of holes.
Prediction of the Dynamic Behaviour of Electromagnetic Relays Submitted to Mechanical Shocks
Authors: Wattiaux D. , Conti C. , Verlinden O.
Published: September 2008

During space flights, pyrotechnic devices are widely used to separate structural subsystems, to unfold solar panels or to activate propellant valves. The firing of these pyrotechnic devices generates severe shock waves (so-called pyroshocks) with high intensity and wide frequency range, which can damage the surrounding electronic equipment. Common observed damages more especially concern relay chatter and transfer, as well as failure of magnetic components. There is a lack of failure criteria for electronic equipment as well as computational techniques able to predict the dynamic behaviour of complex structures subjected to high frequency shock waves. The pyrotechnic shock behaviour is checked experimentally: test specifications imposed through embarked electronic devices are generally defined as a maximum limit imposed to the Shock Response Spectrum (SRS). This paper describes a methodology to check the electrical and mechanical behaviours of some electromagnetic relays submitted to severe mechanical shocks. Experimental results obtained when checking the perturbations induced by shocks on the electrical behaviour of some relays, such as the latching GP250 relay are also presented. Microswitches levels have been correlated with the magnitude and shape of different Shock Response Spectra. This paper presents also a simplified model of electromagnetic relays allowing to predict the electrical dysfunctions such as the micro-openings. The model has been updated using experimental frequency and modal analysis.
Numerical and Experimental Analysis on a Small GDI, Stratified Charge, Motorcycle Engine
Authors: Gentili R. , Zanforlin S. , Frigo S.
Published: September 2008

In the field of engines for light motorcycles, two-stroke cycle survival is submitted to the application of direct fuel injection and charge stratification, even in the case of low-cost small engines. However, charge stratification is a difficult target in two-stroke engines, chiefly because timings of late injection (necessary for charge stratification) and of early injection (necessary for homogeneous charge) are much closer than in four-stroke engines. The compatibility between stratified and homogeneous charge operations needs a thorough CFD study of injection and mixing processes, with the support of techniques of spray visualization. Results strongly depend on the possibility of optimising the interaction between in-cylinder gas-dynamic field and spray; experimental activity is necessary as data source and verification of computational prediction. This paper shows the latest CFD investigation, experimental tests and results concerning a 50 cm3 engine for light motorcycles. The injection is of the liquid type with wall-and-air guided spray produced by a swirl injector. The research has been focused on the attainment of charge stratification at every engine speed. Spray actual characteristics have been investigated, attesting suitable repeatability and proper variation versus backpressure. Engine satisfactory behaviour even at light loads in unthrottled condition is proved by good fuel economy and engine stability in dynamometric bench tests. Exhaust gas analysis and indicated pressure behaviour confirm stratification and combustion correctness.
A FEM Model Analysis of Human Lumbar Spine With Bi-Level Artificial Disc Replacement
Authors: Faizan A. , Kiapour A. , Goel V. K. , Ivanov A. , Biyani A. , Ebraheim N. , Serhan H.
Published: September 2008

A finite element model of human lumbar spine (L3-S1 segment) was used to analyze biomechanical effects of the bi-level CHARITE artificial disc replacement (2LCHD) at L4-L5 and L5-S1 levels. The mechanical behavior and range of motion in implanted and intact models were compared using the finite element analyses and a hybrid loading protocol. In 2LCHD model the changes at L3-L4 level decreased by 25% also the model showed smooth changes in motion at implanted levels. In flexion there was an increase in facet loads at lower levels of 2LCHD however the bending moment in this model was less than intact model because of hybrid loading; in contrast, the facet loads in implanted model decreased in extension. It was observed that the bi-level disc replacement won’t affect much the kinematics of the spine and can be proposed as a good alternative for treatment in cases that disc degeneration occurs at more than one level of spine.
Control Development Process of the Brake-by-Wire System
Authors: Canuto Francesco , Turco Patrizio , Colombo Davide
Published: September 2008

The main goal of brake by wire technology is the development of compact, cheap and flexible braking systems. Since neither brake fluid nor hydraulic lines are used, brake by wire electro-mechanical actuation is a favourable solution both for production process and environmental aspect, and offer a precise control of braking torque amplitude. One of the most critical aspect is the lack of traditional link between brake pedal and brakes (calliper); this mean a potential safety problem to be correctly managed through the system architecture, redundancies, diagnosis and recoveries. During CRF brake by wire system development several architectures were deeply analysed using PHA, FMEA, and FTA methodology to identify the best configuration for production intent. The selected one is a fault-tolerant architecture based on a time-triggered communication network connecting fail-silent nodes. From safety analysis were defined critical events and system diagnosis and recovery requirements specifications. This paper describes the steps followed in the brake by wire software development, and its validation with respect to safety needs. For this purpose a three levels design and validation process was exploited. First of all, it was defined the complete simulation template including calliper electro-mechanical actuators and theirs ECU, time-triggered communication network and vehicle control ECU. The brake by wire system was interfaced to a complete vehicle dynamics model specifically developed for control design and validation purpose. Within this environment the control software was developed and the strategies were verified applying Software In the Loop technique. Then the ECU software was automatically generated using a customised tool chain based on Real Time Workshop Embedded Coder. Than, Hardware In the Loop testing was adopted to deeply verified high level software (application), low level software (OS, API, drivers,...) and hardware. HIL bench include the complete brake by wire system and a real time platform running the same vehicle model used during previous phase. Finally, vehicle testing phases complete the evaluation in the real environment and allows the system control development and tuning toward performances and subjective aspects. In each phase the system is tested both in normal and faulty conditions; a fault injection campaign was carried on to verify system response to fault with respect to the expected one. The process is cyclical, and a new loop has to be activated for each changes in the system. At the same time, testing complexity increases in order to guarantee the system safety.
Compatible Numerical Schemes for Coupled Flow and Transport in Porous Media
Authors: Zade Azad Q. , Manzari Mehrdad T. , Hannani Siamak K.
Published: September 2008

In this paper, the compatibility of various combinations of numerical schemes for the solution of flow and transport equations in porous media is studied and the possible loss of accuracy and global mass conservation are investigated. Here, the flow equations are solved using three popular finite element methods including the Standard Galerkin (SG), Discontinuous Galerkin (DG) and Mixed Finite Element (MFE) methods among which only the DG method possesses the local conservation property. Besides, the transport of a scalar variable which is governed by a convection-diffusion equation is studied in conjunction with the flow equations. The transport equation is solved using both the Streamline Upwind Petrov-Galerkin (SUPG) and the DG methods. Two test cases are numerically solved using various combinations of methods in order to explore the compatibility of flow and transport solution algorithms. In each test case, the error in total mass conservation and the deviation from the exact solution are compared for various solver combinations.