bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Evaluation of a Small Scale High Efficiency Cogeneration System
Authors: Reini Mauro
Published: September 2008

In recent years, a big effort has been made to improve microturbines thermal efficiency, in order to approach 40%. Two main options may be considered: i) a wide usage of advanced materials for hot ends components, like impeller and recuperator; ii) implementing more complicated thermodynamic cycle, like combined cycle. In the frame of the second option, the paper deals with the hypothesis of bottoming a low pressure ratio, recuperated gas cycle, typically realized in actual microturbines, with an Organic Rankine Cycle (ORC). The object is to evaluate the expected nominal performance parameters of the integrated-combined cycle cogeneration system, taking account of different options for working fluid, vapor pressure and component’s performance parameters. Both options of recuperated and not recuperated bottom cycles are discussed, in relation with ORC working fluid nature and possible stack temperature for microturbine exhaust gases. Finally, some preliminary consideration about the arrangement of the combined cycle unit, and the effects of possible future progress of gas cycle microturbines are presented.
A Study of Factors Affecting Disc Brake Instability
Authors: Fawzy A. , Youness Y. K. , El-Butch A. M. A. , Ibrahim I. M.
Published: September 2008

In this paper, the dynamic behavior of disc brake is presented considering five degrees of freedom system and a formula representing the variation of friction coefficient with applied load, temperature, velocity and design is considered. In addition, the surface distortion and roughness of the disc are assumed to vary harmonically. The influences of the Tribological properties of the pad’s friction material and the surface roughness and distortion of the disc on the system stability are studied. The effect of other parameters such as, static friction coefficient, contact stiffness and damping between pad and caliper, position of the load application by piston on the disc brake stability is also investigated and discussed. The study concluded that, disc brake vibrations can be controlled by optimizing the previously mentioned parameters. And disc surface irregularities and distortion contribute in increasing vibration levels in disc brake systems.
Modal Methodology for the Simulation and Optimisation of the Free-Layer Damping Treatment of a Car Body
Authors: Danti Marco , Vige` Davide , Nierop Guido Vincent
Published: September 2008

The cost and weight reduction requirements in automotive applications are very important targets in the design of a new car. For this reason all the components of the vehicle have to be optimised, and the design of the damping material layout has to be deeply analysed in order to have a good NVH performance with the minimum of weight and cost. A tool for the optimisation of the damping material layout has been implemented and tested; the need to explore the entire design space with a big number of variables suggested the use of a genetic multi-objective algorithm for the optimisation. These algorithms require a large number of calculations and the solution of the complete NVH model would be too expensive in terms of computation time. For this reason, a new software tool has been developed based on the simulation of the damping material treatments by means of an auxiliary mass and stiffness matrix to be added to the baseline modal base; using this procedure the required time for the simulation of each damping material layout configuration is reduced to a few minutes, allowing to exploit the genetic algorithm capability to efficiently explore the design space. As a result, some configurations with an important weight reduction or a much better acoustic performance have been found. This method has been verified on a simple Aluminium box in order to verify all the assumptions and to test the effectiveness in predicting the vibration levels of plates with free layer damping added to it.
Statistics-Based Noise Analysis for Vibration-Based Damage Identification
Authors: Yu L. , Yin T. , Zhu H. P.
Published: September 2008

As the vibration-based structural damage detection methods are easily affected by the environmental noise, a novel noise analysis method is proposed based on the statistics in this paper together with the Monte Carlo technique for assessing the influence of experimental noise of modal data on sensitivity-based damage detection methods. Different from the commonly used random perturbation technique, the proposed technique is deduced directly by the Moore–Penrose generalized inverse of sensitivity matrix under the differential quotient rule of composite function. It can not only make the analysis process more effective but also analyze the noise influence on both frequencies and mode shapes in a similar way. Furthermore, an improved modal sensitivity based damage detection method is also proposed and compared with other two commonly used sensitivity-based methods in this paper. A one-story portal frame is adopted to evaluate the efficiency of both the proposed noise analysis technique and the improved modal sensitivity based method. The assessment results show that the proposed statistics-based noise analysis technique is effective and more suitable for the vibration-based damage identification. The improved modal sensitivity based method is more robust to noise than the other commonly used sensitivity-based methods.
Particle Tracking in Horizontal Ball Milling
Authors: Boschetto A. , Ruggiero A. , Veniali F. , La Barbera A. , Colella C.
Published: September 2008

Ball milling is a material processing method that allows near room temperature process of elements in powder and permits to synthesize materials with peculiar properties otherwise difficult or impossible to obtain. Due to the repeated fractures and cold welding of the reactants particles, solid solutions, amorphous alloys and equilibrium nanostructured materials can be obtained. Products coming from mechanosynthesis process can be advantageously applied as high performance structural and functional materials. Different milling devices can be utilized for the powder processing: planetary mill, attritor, horizontal ball mill, 1D and 3D vibrating machines. The wide differentiation in configuration of the mills obstacles the development of a unified model on powder transformation kinetics in the milling process and then most of processing procedures are still developed by using a trial and error method. The focus of this paper is on a horizontal fixed vial ball mill; in this configuration a high speed rotor launches several tumbling against the vial wall. During hits, a quantity of energy is released to the trapped powder and the solid state reactions are promoted. To characterize the powder transformation process, knowledge of the kinematics of the balls system must be inferred. For this purpose an experimental setup based on digital image acquisition was constructed and the movement of balls inside the vial was filmed. Particle trace analysis methodology permitted to obtain balls trajectories, velocity vector field and total hit frequency. The kinetic energy of the impacting balls inside the vial was quantified, so that the energy released to the powder in a milling experiment can be estimated.
Corner Shaping by Barrel Finishing
Authors: Boschetto A. , Ruggiero A. , Veniali F.
Published: September 2008

Corner shaping is a necessary operation in manufacturing of most mechanical components. Edge radiusing is the principal way to reduce stress concentration in components like gear, crank shaft, ball bearing, to permit assembly and disassembly of parts, to avoid local damage and to reduce the possibility of hurting the operators. Often precise values of corner radius are specified in component design. Deterministic operations such as chipping, plastic deformation and non traditional ones such as electro discharge machining, abrasive jet deburring are well established technology. Yet, sometimes, it results not economic or even impossible to perform these operations due to the complicated part geometry, difficulty in part clamping and tool path, large number of parts to be produced. Barrel finishing is technique able to improve the roughness of parts of complicated shape by means of a soft mechanical action over the surface performed by abrasive media. The main features of this technology is that the parts do not need to be fixed. Radiusing is, in turn, a potential application area for barrel finishing which has been investigated in this paper. Experimental tests were conducted on finished specimens with sharp corners in order to achieve information about corner radius evolution as a function of the time for different set parameters. The radius values have been assessed by analyzing the acquired profiles with a proprietary fitting procedure. It has been found a square root relation between radius and working time and, by assessing the influence of single parameter, a radiusing model has been proposed.
Active Suspension Systems With Optimal Jerk Control
Authors: Taghipour M. , Shahriari D. , Shahsavari A.
Published: September 2008

An active suspension system should be designed/optimized in conjunction with the tradeoff between ride and handling. In recent years, jerk as a measure of ride quality is considered in performance index. In this paper, effects of jerk in active suspension system for a 1/4 car model is investigated. In contrast to the previous papers, the body acceleration and jerk are derived directly from the system Hamiltonian instead of solving Ricatti Equation. The result shows that a reduction of jerk and acceleration is obtained against a higher rattle space and tire deflection. The compromise/tradeoff can be managed by setting appropriate weights in the cost function.
Vibration-Based Damage Detection in Structural Members Utilizing Finite Elements and Evolutionary Algorithms
Authors: Poursamad Amir
Published: September 2008

Presented within this paper is the application of finite elements method combined with an evolutionary algorithm to the problem of damage detection in structural members using vibration data. The objective is to identify the position of the damage in structure, and to estimate the extent of the damage. To describe the damage, finite element method (FEM) is used here and the damage is modeled as a reduction in the stiffness of the associated element. Using this model, the effect of damage on the vibration characteristics of the structure is studied. The problem of damage detection is then formulated as an optimization problem. The decision variables are the position of damaged element and the extent of damage. The objective function is considered as the difference between measured natural frequencies and those obtained from FE model of the structure. Only natural frequencies are adopted here, because the measurement of mode shapes is usually accompanied by larger amount of error. The proposed damage detection approach is verified and assessed using a simulated cantilever Euler-Bernoulli beam.
Vibration Control of FGM Plate With Piezoelectric Sensors and Actuators Using Higher Order Shear Deformation Theory
Authors: Yeilaghi-Tamijani A. , Mirzaeifar R. , Ohadi A. R. , Eslami M. R.
Published: September 2008

In this paper, finite element formulation for the active control of functionally graded material (FGM) plates containing piezoelectric sensor/actuator patches by using higher order shear deformation theory is carried out. The major difference to previous studies is the new feedback control algorithm for active control of FGM plate which is presented in this paper. The effects of the configuration of the S/A pairs and the velocity and displacement feedback control gains on the static and dynamic response of the structure are studied. Numerical results are presented for the static deflection, natural frequency and dynamic control of FGM plate in both tabular and graphical forms. The result obtained by using new feedback control algorithm show that peak responses can be controlled by the displacement control gain and active damping can be provided by adjusting the velocity control gain. The model without feedback control is validated by comparing with existing results in the literature.
Conjugated Heat Transfer in Skirt Hot Box in Pressure Vessels
Authors: Shokouhmand Hossein , Bozorgmehrian Manoochehr
Published: September 2008

Pressure vessels are common equipment in oil, gas and petrochemical industries. In a hot containing fluid vessel, excessive temperature gradient at junction of skirt to head (weld line), can cause unpredicted high thermal stresses; Thereby fracture of the vessel may occur as a result of cyclic operation. Providing a hot box (air pocket) in crotch space is a economical, applicable and easy mounted method in order to reduce the intensity of thermal stresses. Natural convection due to temperature difference between the wall of pocket, will absorb heat near the hot wall (head of the vessel) and release that near the cold wall (skirt of the vessel), then the skirt wall conducts heat to the earth as a fin. This conjugated heat transfer removes the temperature gradient boundary at welded junction. This phenomena will lead the temperature gradient on the weld line from a sudden to smooth behavior, thereby the skirt-head junction, that is a critical region, could be protected from excessive thermal stresses. In this paper the profit of hot box and conjugated heat transfer in cavity has been demonstrated experimentally. As a result it is shown that the conductive heat transfer through the skirt (which acts as a fin) ensures the continuation of natural convection in the box. Also the governing equations has been solved numerically and compared with experimental results.
Failure Mode Analysis of Mechanical Systems at Conceptual Design Stage
Authors: Wani M. F. , Jan Muzamil
Published: September 2008

This paper presents a methodology for determining criticality of failure modes in mechanical system at conceptual design stage on the basis of functional and structural knowledge of the system, using statistical method ‘K-Clustering’. First of all component failure matrix (CF) is derived then its transpose is obtained. Then similarity matrix (SM) is obtained by pre-multiplying component failure matrix (CF) by its transpose. By adding each row corresponding to the given function and arranging the sums in ascending or descending order and selecting a range to determine critical failure modes. Prediction of critical failure modes during conceptual design stage using the component failure matrix (CF) and function component matrix (EC) matrices, the function failure mode matrix can be computed as EF = EC × CF.
Synthesis and Characterization of Mesoporous and Microporous Carbons With Potential Applications as Hydrogen Storage Media
Authors: Armandi Marco , Bonelli Barbara , Garrone Edoardo
Published: September 2008

The preparation and physico-chemical characterization of mesoporous and microporous carbons, obtained via a casting procedure, from a SBA-15 silica and a commercial Na-Y zeolite, is reported. XRD spectra showed that ordered carbon replicas occur in all cases. Micro-Raman spectra showed that rather homogeneous powders are obtained, exhibiting the presence of a graphitized carbon phase of small imperfect graphene sheets, typical of sp2 C, along with an amorphous one, notwithstanding the relatively low temperature adopted during the carbonization processes (1173 K). N2 adsorption isotherms at 77 K allowed the determination of BET surface areas and pore volumes: on account of the high porosity and the low specific weight, with respect to zeolites, for example, these carbon materials could be promising media for hydrogen storage. They could be used as such, or after convenient functionalization or metal doping.
Ash Fouling Under Co-Firing in a Pulverized Fuel Combustion Rig
Authors: Di´ez Luis I. , Corte´s Cristo´bal , Berdusa´n Mariano , Ferrer Eduardo
Published: September 2008

Co-firing of coal and biomass in existing coal-fired power stations is a cost-effective method to reduce CO2 emissions in energy generation. Nevertheless, the introduction of biomass has to be carefully considered since it could significantly modify combustion and heat transfer phenomena and enhance fouling and corrosion inside the boiler. This paper investigates the effect of substituting a fraction of coal by biomass on the heat transfer and ash deposition rates, by performing pilot tests under different operating conditions in a pulverized fuel combustion rig. Fouling rates have been characterized by means of air-cooled deposition probes installed at one tube bank, reproducing the performance of a large-scale superheater. Heat transfer has been simulated coupling thermal radiation models with semi-empirical approaches for the tube bank behaviour. Ash samples compiled from the wind- and the lee-side of the probe has been collected and analysed by SEM (Scanning Electron Microscopy). Low-to-moderate fouling rates have been typically observed for the tested coal and coal + biomass blends, but with somewhat potassium enrichment at the lee-side deposits when biomass is introduced. As a matter of fact, sootblowing manoeuvres in utility boilers should not be affected when co-firing the tested fuels. Furthermore, chlorine-induced corrosion on heat transfer surfaces is not expected to be significant since the concentration of chlorine in the sampled deposits has been always found to be negligible.
Comparative Response in Repeated Impact Tests of Hand Lay-Up and Vacuum Infusion Glass Reinforced Composites
Authors: Belingardi Giovanni , Cavatorta Maria Pia , Paolino Davide Salvatore
Published: September 2008

Vacuum infusion is now being considered as a viable alternative to more traditional hand lay-up. Main reason in favor of the more costly technique is the cleaner and friendlier work environment. However, vacuum infusion potentially offers another important benefit over hand lay-up in that prepreg levels of resin may be achieved, resulting in stronger and lighter laminates. The present paper compares the two manufacturing techniques on the basis of the response to repeated impact loading. The laminate is a non-symmetric glass fiber reinforced plastics intended for nautical application. Four impact velocities (1.5 m/s, 2.2 m/s, 3.1 m/s and 3.8 m/s) were considered, and a minimum of four specimens for any given velocity were subjected to forty repeated impacts or up to perforation. The impact response was evaluated in terms of damage progression by visual observation of the impacted specimens, evolution of the peak force and of the bending stiffness with the number of impacts and by calculating the damage degree (ratio between the absorbed energy and the impact energy). Results point out that for impact velocities for which no perforation occurs within test duration, the experimental data of the two series essentially overlap. On the contrary, for perforation tests, the number of impacts to perforation is smaller for vacuum infusion specimens.
Tribological Characteristics of Carbon/Epoxy Composites With Respect to Surface Groove Dimensions
Authors: Lee Hak Gu , Kim Seong Su , Lee Dai Gil
Published: September 2008

Grooves on the surface of carbon/epoxy composite bearings yield good tribological characteristics because wear debris generated on the sliding surface are removed efficiently through the grooves. However, the surface grooves increase normal and shear stresses in composite bearings, consequently, excessive area of the grooves increases wear of the carbon/epoxy composite bearings, which necessitates the optimum selection of groove dimensions on the surface of composite bearings. In this work, the friction and wear characteristics of carbon/epoxy composites with micro-grooves were investigated by dry sliding test with respect to groove width and ridge width. Through comparison between the flat surface and the grooved surface, proper widths of the groove and ridge of carbon/epoxy composite bearings were determined.
Dynamic Simulation of the Anodic Side of an Integrated Solid Oxide Fuel Cell System
Authors: Traverso A. , Trasino F. , Magistri L.
Published: September 2008

A new dynamic SOFC model was integrated with the simulation modules of other system components (i.e.: reformer, anodic off-gas burner, anodic ejector) to construct a system model that could simulate an integrated 250 kW SOFC hybrid system. This work describes the preliminary results obtained for the anodic loop, which was studied in order to obtain a complete time characterization of its time-dependent behavior. The new dynamic model was then compared with an existing model for an integrated planar pressurized Solid Oxide Fuel Cell at the steady state. The two models differed due to their levels of complexity and calculation times: the first one was meant for real-time applications, hence retaining the basic dynamic information but including relevant simplifications in the internal information on fuel cell behavior; the second one was used for more accurate predictions at the steady-state, but required longer simulation times. The unsteady-state tests with the new dynamic model showed that the characteristic voltage transient due to changes in SOFC hydrogen concentration had a time scale that was of the order of fractions of seconds while the characteristic temperature transient was of the order of hours. The frequency characterization of the anodic loop with phased oscillations in the fuel flow and stack current enabled us to correlate the inner SOFC anode features with the anodic loop response, thus providing useful indications for designing robust anodic loop controllers.
Energy Absorption of Sandwich Panels Subjected to In-Plane Loads
Authors: Lindstro¨m Anders , Hallstro¨m Stefan
Published: September 2008

The energy absorption mechanisms of sandwich panels subjected to in-plane compression are studied. Quasi-static experiments are performed and analysed in order to support the development of a modelling strategy for failure initiation and propagation in sandwich panels. The test specimens consist of balsa wood cores and glass-fibre reinforced polyester faces. During compression of a tested panel, the displacement field on one outer face is measured using a digital speckle photography (DSP) equipment. The absorbed energy is related to debonding, delamination and crushing of the face sheets and crushing of the core. At initial failure, the load drops dramatically and is then relatively constant during continued compression. The energy per unit length necessary for propagation of the damage is considerably lower than for damage initiation. Assuming that the damage propagation is uniform through the thickness of the panels a simple model of damage growth is developed. Calibration of the model is however dubious due to the large scatter in the experimental results. The studied material shows damage mechanisms favourable for efficient energy absorption but the behaviour is far from being optimal.
Impact and Blast Pulse: Improving Energy Absorption of Fibre-Reinforced Composites Through Optimized Tailoring
Authors: Icardi Ugo , Ferrero Laura
Published: September 2008

This paper tries to conjugate an improvement of stiffness and delamination damage resistance. A number of published results allow us to guess the existence of fibre orientations that are a good compromise for an optimal absorption of the incoming energy and for maintaining of a high stiffness. Optimal absorption is herein intended as a way not involving weak properties, such as interlaminar strength. We seek for an optimal orientation of reinforcement fibres through definition of stationary conditions for bending and shear energy contributions under in-plane variation of plate stiffness coefficients. Our goal is to tune the energy absorption as desired. Two kinds of optimized layers are studied, that are compatible with current production technologies: type 1 reduces bending without substantially increasing the transverse shear stresses, type 2 reduces transverse shear stresses without substantially increasing deflections. Incorporation into the laminates of couples of these layers with opposite features and the same mean properties of those they substitute allows an energy transfer from an unwanted to a wanted mode, as shown by the numerical applications. In this way, the deflections and the stresses inducing delamination damage of laminates subjected to impact and blast pulse loads were reduced, while damping should not substantially change since the variation of the orientation of fibres lies in a range where mild variations of it are induced.
Modeling of Composite Material Behavior for Blast and Ballistic Impact
Authors: Yen C. F.
Published: September 2008

A robust computational constitutive model has been developed to characterize the progressive failure behavior of composite laminates under blast and ballistic impact conditions. In this study, the capacity of the progressive failure model integrated within LS-DYNA has been evaluated by performing simulations of blast and ballistic impact composite panels. Correlation results indicated that the current composite model can be used to quantify the composite ballistic impact and blast damage behavior with reasonable accuracy. The present composite material model can provide insight into the damage development and progression that occurs during the ballistic impact or blast loading of lightweight composite armor. The availability of this design tool will greatly facilitate the development of composite structures with enhanced ballistic survivability.
Low-Velocity Impact on a Functionally Graded Circular Thin Plate
Authors: Chelu Pantele , Librescu Liviu
Published: September 2008

In this paper, an alternative analysis strategy based on a Wavelet-Galerkin scheme specially tailored to solve impact problems of functionally graded orthotropic thin plates subjected to low-velocity impact is presented. The plate considered to be circular, is assumed to be clamped on its lateral edge and has internal supports of rigid, elastic and viscoelastic types. The material properties of the plate are represented in the form of exponential functions of the thickness coordinate. A rigid spherical indenter impacts the plate. The study is based on the classical lamination plate theory (CLT). An advanced contact law of the Hertzian type is adopted. A nonlinear Volterra integral equation system is obtained in the following unknown functions: the impact force and the dynamic reaction forces at the rigid, elastic and viscoelastic internal point supports. Numerical simulations displaying the contact force, the transversal displacement and the penetration depth are graphically presented, and pertinent conclusions regarding the implications of incorporation of graded material systems are outlined.
A Model for the Energy Absorption Capability of Composite Laminates
Authors: Mian Stefano , Quaresimin Marino
Published: September 2008

A new methodology for the analysis of impact data has been recently proposed [1], based on the definition of two normalised coefficients, the absorption coefficient (ratio of absorbed to penetration energy) and the intensity coefficient (ratio of impact to penetration energy). The new approach allowed the definition of an empirical master curve suitable to summarize the impact data irrespectively of material system, laminate thickness and lay-up. This work is oriented to quantitatively validate the master curve on the basis of experimental impact data previously obtained and other “external” data taken from the open literature, referred to laminates with significant variation of properties in terms of type and architecture of the reinforcing fibers, lay-up and thickness. In spite of the very large number of data collected for the validation, the master curve turned out suitable to describe all the normalized data with a reasonably reduced scatter.
A Novel Design and Modelling of a Micro Underwater Vehicle With Flapping Fins
Authors: Mayahy Abdorasool , Yousefi-Koma Aghil , Maleki Hesam , Mohammadshahi Donya , Salek Sina
Published: September 2008

Systems and mechanisms of motion and stability applied in underwater vehicles although various but almost all rely on a conventional structure and frame work. In this paper in pursue of development a new mechanism in term of motion and performance, mainly biomimeticly inspired from fish flapping and their movement principles particularly flatfish, a new Micro Underwater Vehicle (MUV) is designed and fabricated. In modelling phase using ADAMS we simulated the dynamic performance of the mechanism. On the other hand in order to take the flexibility of the fins into account, we used ANSYS as a meshing tool. Linking these two software packages the modelling stages were completed.
Generalized Slab Method Analysis of Radial Forging With a General Curved Shape Die
Authors: Afrasiab Hamed , Movahhedy M. R.
Published: September 2008

Radial forging is an open die forging process used for reducing the diameters of shafts, tubes, stepped shafts and axels, and for creating internal profiles in tubes. Among parameters affecting process variables, the die geometry is of fundamental importance and greatly influences variables such as forging load, stress distribution on the dies, metal flow during deformation, and surface finish of the forged product. In this paper a generalized slab method analysis of radial forging process is presented which can handle this process with curved shape dies. Results for dies with various curves are presented and it is shown that the analysis reduces to that of Lahoti and Altan [2] when the die has a linear profile.
Experimental Activity on the Tubular SOFC CHP100 kWe Field Unit in Italy: Factor Significance, Effects and Regression Model Analysis
Authors: Cali` M. , Orsello G. , Santarelli M. , Leone P.
Published: September 2008

The CHP 100 kWe tubular SOFC plant built by Siemens is operating at the Gas Turbine Technologies (GTT) in Turin. The generator started up on the June 2005 and produces electric and thermal power used in the factory. A first period of the activity was needed to lead the operation of the SOFC plant at the nominal condition and to reach the complete conditioning of the SOFC tubular fuel cells. Then, in order to characterize the operation of the generator and of the cogenerative system a first experimental campaign was designed by using the factorial analysis. With these methods, the effect of some independent variables (factors) on the plant operation is analyzed in form of screening tests: the analysis allows one to estimate the significance of the main and combined effects of each considered factor through an analysis of variance (ANOVA) on the experimental data. Moreover, the test plan has been designed by using a simple 2k factorial and a 2k factorial with spherical central composite design (CCD); these approaches allow to obtain respectively first-order and second-order regression models for some chosen dependent variables (i.e. DC and AC electric power, generator voltage, recovered heat etc...). The test plan has been performed at the fixed generator current of 500 Amps with two repetitions for each designed treatment. The factorial analysis has been applied considering two factors (22 factorial analysis): setup temperature of the generator and fuel utilization factor. First, the significance of the main and combined effects of the two considered factor has been evaluated. Then, the obtained data have been analyzed by using the Response Surface Methodology analysis (RSM). Finally, the regression models have been obtained for every dependent variable analyzed, with an outline of the sensitivity coefficient linking the dependent and the independent variables.
Modelling a Variable Displacement Axial Piston Pump in a Multibody Simulation Environment
Authors: Roccatello Alessandro , Manco` Salvatore , Nervegna Nicola
Published: September 2008

Analysis of a variable displacement axial piston pump, as in other complex fluid power and mechanical systems, requires appropriate insight into three multidisciplinary domains, i.e. hydraulics, mechanics and tribology. In recent years, at FPRL, modelling of axial piston pumps has evolved in AMESim (one dimensional code) where a three dimensional mechanical approach has required generation of proprietary libraries leading to the evaluation of internal forces/reactions in all pump subsystems. Tribologic aspects in axial piston pumps modelling are also being investigated but AMESim, in this respect, does not appear as the appropriate computational environment. Consequently, a new approach has been initiated grounded on MSC.ADAMS. In this perspective, the paper details how the model has been developed through proprietary macros that automatically originate all pump subsystems parametrically and further apply required constraints and forces (springs, contacts and pressure forces). The ADAMS environment has also been selected due to co-simulation capabilities with AMESim. Accordingly, the paper elucidates how the entire modelling has been construed where hydraulics is managed in AMESim while ADAMS takes care of mechanics. As such this paper indicates an innovative methodology for the analysis of complex fluid power systems in the hope that, eventually, tribology will also fit into the scene.
Energy Management Techniques for Small and Medium-Sized Companies
Authors: Giacone Elena , Manco` Salvatore , Gabriele Pietro
Published: September 2008

Energy management in the industrial context is an important factor to attain energy savings as well as environmental efficiency. In fact, if every single factory could achieve some even relatively small improvements, considerable progress in a countrywide dimension would be made. The purpose of this paper is to show how energy management can be introduced in small and medium-sized enterprises (SMEs). Even if, in general, only data about the system as a whole are available, it is enough to begin an analysis leading to the knowledge of the laws relating energy consumption (electricity and fuels) and energy drivers (production, weather, etc.). Statistical process control techniques are the tools that have been applied.
The Muscle Myogram as a Control Signal for Use in Powered Limb Orthosis
Authors: Antonelli M. , Beomonte Zobel P. , Giacomin J.
Published: September 2008

The choice of the command technique to be used in orthotic and prosthetic devices is very critical for the acceptance and, finally, the success of the specific device. Many variables influence this choice: the general characteristics of the signal, the quality of the correlation between signal and specific actions of the user and the algorithm that is derived, the acceptance of the technique, as applied to the specific device, from the user, etc. Among the command techniques, MMG signal seems to be promising to command an assistive device. In this paper a test protocol for studying MMG signal, to investigate the prospective for its use as a command technique of a powered lower limb orthosis capable of raising elderly and disabled people from the sitting position, is proposed. The definition of the test protocol, including the description of the test bed and the sensors application, is presented. Finally, the experimental results are showed and discussed.
Efficient Stress Analysis of Adhesively Bonded Joints by Finite Element Techniques
Authors: Castagnetti Davide , Dragoni Eugenio
Published: September 2008

The paper documents ongoing research on the field of stress calculations in the adhesive layer of bonded joints and bonded structures. Aim of the research is to develop simple, general, portable, efficient and accurate finite element techniques for adhesive stress analysis and strength assessment of the joint. Among four methods envisioned, two methods are presented for 2D configurations and applied to a reference single-lap configuration. In both methods, the adherends are described by means of beam elements and the adhesive layer by a single string of plane-stress solid elements. The plane-stress elements have either the original thickness of the true adhesive layer or an expanded thickness up to the offset between adherends. Beams and plane-stress elements are connected by standard constraining techniques (tied mesh) offered by the package employed (ABAQUS). The stress results provided by the two methods are compared step by step with the predictions of analytical models retrieved from the literature and with the outcome of a full, computationally-intensive finite element model using solid plane-stress elements for both adhesive and adherends. The simplified method using a single layer of plane-stress elements with the same thickness and properties as the true adhesive layer provides very promising results in terms of stress accuracy and computational efficiency.
A Numerical Model for Solid Oxide Fuel Cells
Authors: Massarotti N. , Arpino F. , Carotenuto A. , Nithiarasu P.
Published: September 2008

Fuel cells have been very much studied in the last few years as promising future energy conversion systems. In fact, these systems have a number of advantages with respect to more traditional energy conversion systems, such as, for instance, higher potential efficiency, flexibility for distributed generation, and reduced emissions. Accurate and physically representative numerical models are essential for the future development of energy conversion systems based on fuel cell technology. In the present paper, a general and detailed numerical model is proposed, in which all the quantities of interest are calculated locally, on the basis of general governing equations for the phenomena involved. The model proposed in this work is based on the solution of the appropriate set of partial differential equations that describe the phenomena that occur in the different parts of the fuel cell: 1) anodic compartment, which includes fuel channel, electrode and catalyst layer; 2) electrolyte; and 3) cathode compartment. To solve the momentum, energy and species conservation equations in the anodic and cathodic compartments, a finite element procedure is employed, based on the Characteristic Based Split (CBS) algorithm. The CBS, thanks to its generality and modularity, is able to successfully predict fuel cell performances. The results obtained from the simulations show a good agreement with other data available in the literature.
Two Phase Pressure Drops for Refrigerants: A Statistical Comparison Among Experimental Data and Correlations
Authors: Greco Adriana , Mastrullo Rita , Mauro Alfonso W. , Vanoli Giuseppe P.
Published: September 2008

A 962 points database for refrigerants two-phase flows by Greco A. and Vanoli G.P. was statistically compared to four widely used prediction methods by Lockhart and Martinelli, Chawla, Theissing and Mu¨ller-Steinhagen and Heck in order to determine the best one. The experimental points are in a wide range of operating conditions for six pure or mixed refrigerants (R134a, R22, R407C, R507A, R410A and R404A) during evaporation in a smooth horizontal tube of 6 m length and 6 mm ID.
Coupled Modelling of a “Flow-Piping” System in Dynamic Analysis
Authors: Vasilyev Peter S.
Published: September 2008

The paper considers the problem of simultaneous modeling of structure and flow in a piping system. It takes a middle road between full coupled analysis on the one hand, and the simplified case of treating the liquid as a rigid mass. The suggested method allows the use of standard beam and rod elements for the analysis. Two approaches to the problem of dynamic interaction between pipe and medium are compared in the given paper: 1) The first one treats medium as mass rigidly connected to the pipe finite-element model’s nodes. 2) In the second one medium is modeled by the finite-element system of rod-elements. In this case the basic fluid-structure interaction (FSI) effects are taken into account. The main techniques for FE modeling of some pipeline elements are presented in the paper. The second approach can be implemented by the use of general purpose FE programs. A model of a feed water pipeline of VVER-440 type NPP has been developed to study how the FSI affects on pipeline response. The results of the analysis which allow estimation of inaccuracy arising from medium dynamics neglecting are as follows: • calculation of eigen frequency and mode shapes; • seismic analysis using the response-spectrum method; • accidental blast impact assessment with the use of time history analysis; • operating vibration assessment on the basis of harmonic analysis. It has become apparent that the way of medium modeling has an essential influence on the dynamic behavior of pipelines.
Measurement of g Using a Flashing LED
Authors: Terzella T. , Sundermier J. , Sinacore J. , Owen C. , Takai H.
Published: September 2008

In one of the classic free-fall experiments, a small mass is attached to a strip of paper tape and both are allowed to fall through a spark timer, where sparks are generated at regular time intervals. Students analyze marks (dots) left on the tape by the timer, thereby generating distance-versus-time data, which they analyze to extract the acceleration due to gravity g with good results. The apparatus, however, is cumbersome and often frustrating for students.1 High-tech versions of this experiment are done with an object dropped and followed by a motion sensor connected to a computer. The sensor relies on ultrasonic ranging to record distance and time data, which may then be displayed graphically. Students inspect the graphs to determine the value of g. Although the results are excellent, the emphasis on the computer's ability to collect and analyze data leaves little analysis for the students to perform.2 Furthermore, neither technique gives an intuitive display of what is happening. The motivation for our work was to overcome these issues by developing an innovative method for measuring g. In our version of the experiment, students drop a flashing LED at a known frequency and record its trajectory using long exposure photography with a digital camera. Proper choice of flashing LED timing parameters produces an image that allows for an accurate measurement of g and at the same time helps to explain what happens during free fall. The experiment remains high-tech in the sense that students learn to use updated equipment to record data and to carry out the analysis.
A Cool Sport Full of Physics
Authors: Haché Alain
Published: September 2008

Of all sports, ice hockey is possibly the one with the widest array of physics elements in it. The game provides many examples that can bring physics to life in the classroom. Ice hockey (or just “hockey” as many Canadians would say) sees athletes sliding on ice at high speeds and in various ways, shooting and slapping pucks, and colliding against each other. The interaction between the skate blade and the ice is a problem of great physical complexity. The question “Why is ice so slippery?” has puzzled generations of scientists and, surprisingly, clear answers have come relatively recently. There is even some optics involved in hockey: how many sports are watched behind tempered glass (or Plexiglas) windows? The optical and mechanical properties of these materials are worth a physics classroom discussion. In this paper, I will review a few topics discussed at length in my book The Physics of Hockey.1,2 Interested readers may also find additional articles on our website.3
The Surprising Effectiveness of College Scientific Literacy Courses
Authors: Hobson Art
Published: September 2008

Research by Jon Miller, professor of Interdisciplinary Studies and director of the International Center for Scientific Literacy at Michigan State University, shows that the U.S. scientific literacy course requirements for nonscience college students pull the United States into second place in international rankings of adult scientific literacy. This despite the poor science scores of U.S. primary and secondary school students as compared with other nations. The far lower adult scientific literacy rankings of most European nations and other industrialized nations appear to be due to the lack of any such college scientific literacy requirement in those nations. Instituting such a requirement in all nations, and improving the quality and quantity of such courses on U.S. campuses, would increase global scientific literacy significantly, arguably doubling Europe's scientific literacy rate. In view of this result and today's crying need for scientific literacy, physics educators should make physics for nonscientists their top priority.
How Does It Sound? Young Interferometry Using Sound Waves
Authors: Machorro Roberto , Samano E. C.
Published: September 2008

This paper describes an enjoyable, simple, and inexpensive way to perform Young's two-source experiment using sound waves. The wave source is a simple aluminum rod (a “singing rod”).1–3
Computer-Based Experiment for Determining Planck's Constant Using LEDs
Authors: Zhou Feng , Cloninger Todd
Published: September 2008

Visible light emitting diodes (LEDs) have been widely used as power indicators. However, after the power is switched off, it takes a while for the LED to go off. Many students were fascinated by this simple demonstration. In this paper, by making use of computer-based data acquisition and modeling, we show the voltage across the LED undergoing an exponential decay after the power is switched off. We also describe a new approach for determining Planck's constant using LEDs. The simple experiment can be used either in an interactive lecture demonstration or an entry-level physics lab.
Einstein's Mirror
Authors: Gjurchinovski Aleksandar , Skeparovski Aleksandar
Published: September 2008

Reflection of light from a plane mirror in uniform rectilinear motion is a century-old problem, intimately related to the foundations of special relativity.1–4 The problem was first investigated by Einstein in his famous 1905 paper by using the Lorentz transformations to switch from the mirror's rest frame to the frame where the mirror moves at a constant velocity.5 Einstein showed an intriguing fact that the usual law of reflection would not hold in the case of a uniformly moving mirror, that is, the angles of incidence and reflection of the light would not equal each other. Later on, it has been shown that the law of reflection at a moving mirror can be obtained in various alternative ways,6–10 but none of them seems suitable for bringing this interesting subject into the high school classroom.
Being Careful with PASCO's Kinetic Friction Experiment: Uncovering Pre-sliding Displacement?
Authors: Lawlor T. M.
Published: September 2008

The widely used PASCO laboratory equipment is an excellent way to introduce students to many topics in physics. In one case, PASCO's equipment may be too good! Various experiments exist for calculating the kinetic coefficient of friction by measuring the acceleration of a sliding object under some constant force. With ever more accurate equipment, such as electronic motion sensors, students are capable of measuring motion over quite small time intervals. In measuring motion including friction, PASCO equipment can record more complicated aspects of friction associated with the transition between static friction and kinetic friction. This serves as an excellent exercise to introduce some fine details of friction not typically discussed in an introductory physics course. In fact, if one does not consider these fine details (or at least does not omit them) the “canned” PASCO friction lab will yield wildly spurious results. The erroneous results obtained are due to a nonconstant “recoil” acceleration during the first ∼0.2 seconds of motion. The problem does not show up in the PASCO instructor's manual because the manual restricts the experiment to a small range of low applied forces for which the effect is minor. The recoil was actually observed previously1 but was written off as equipment noise. If one ignores this “noise,” a relatively constant coefficient of kinetic friction can be found in this lab experiment, as we will show. We describe here the original experiment, a second experiment to rule out that this is an experiment-specific phenomenon, and how the experiments can be used for two or three different topics. Finally, we tabulate results and discuss what may be causing this “recoil.”