bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigations on Temperature Distribution Along the Liner Wall and Centerline of Small Capacity Gas Turbine Combustion Chamber for Fuel Rich to Fuel Lean Air/Fuel Ratios at Equivalence Ratio of 1
Authors: Kulshreshtha Digvijay B. , Channiwala S. A.
Published: September 2008

The development of the combustion chamber for 20kW gas turbine unit using kerosene type fuel has been undertaken keeping in view the basic requirements of a good combustion chamber, namely, high combustion efficiency, low pressure loss, smooth ignition, wide stability limits, size and shape compatible with engine envelop, low emissions of smoke, unburned fuel and gaseous pollutant species, durability and ease of maintenance. A sophisticated experimental test rig has then been developed to investigate over a wide range of air/fuel ratios for the temperature profiles at the few axial and liner wall locations of this combustion chamber. The range of overall air/fuel ratios considered varies from 22.7396 to 152.4 i.e. Rich Air/Fuel Mixture to Lean Air/Fuel Mixture Range. The temperature profiles for centerline and liner wall for eight different air/fuel ratios are summarized here. The two air/fuel ratios selected are near the designed value of 118.34. It could be concluded from the results that the air/fuel ratio of 122.106 gives the best results for centerline temperature and the liner wall temperature as well as the exit temperature profile. This is very near to the designed air/fuel ratio of 118.34. The temperatures of near 1400 °C achieved at the centerline of the combustion chamber and the liner wall temperatures in the range of 500 °C for lower air/fuel ratio and 300 °C for higher air/fuel ratio certainly ensures safe and reliable operation of this combustion chamber.
Molecular Modelling of Small Molecule Diffusion in Biopolymer Blends Membranes for Biomedical Applications
Authors: Ionita Mariana , Silvestri Davide , Gautieri Alfonso , Votta Emiliano , Ciardelli Gianluca , Redaelli Alberto
Published: September 2008

In order to improve the biological performance of synthetic polymers and to enhance the mechanical characteristics by tailoring the permeability properties of biopolymers, a new class of specifically designed materials (bioartificial polymeric materials), consisting of blends of synthetic polymers and biopolymers, has been recently introduced. In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD) techniques, to investigate their permeability to small molecules. The permeability properties was assessed of poly(vinyl alcohol)-(PVA)- dextran-(Dex) and poly(acrylic acid)-(PAA)-Dex membranes with different blend composition. Amorphous bulk models of PVA–Dex and PAA–Dex mixtures with 80:20, 60:40, 40:60 (w/w) ratios were generated. Two steps have been performed iteratively, the former using a MM simulation for equilibration and the latter using MD simulations for model refinement. Virtual uniaxial traction tests were performed, adopting the Second Derivative (SD) procedure, in order to assess the mechanical behavior of the bulk models. The diffusion coefficients for H2O were determined via NVT molecular dynamics simulations. Using the data of the motion of water inside the bulk models, the diffusivity constant was calculated applying the Einstein equation. Correlation of diffusion coefficients with free volume, was found. The results of the simulations agree with theoretical considerations: as the content of dextran increases from 80:20 to 40:60 a 86 % decrease of the diffusion constant is obtained and the values (range 0.14–56.5 10−6 cm2s−1) have the order of magnitude expected, and similar on the diffusion of small molecules in amorphous polymeric membranes.
A MOM-Based Algorithm for Identification of Moving Vehicle Loads on Bridges
Authors: Yu L. , Chan T. H. T. , Zhu J. H. , Chen M. Z.
Published: September 2008

An improved time domain method (ITDM) is proposed for moving force identification using bridge responses, which aims at an acceptable solution to the ill-conditioning problem that often exists in the inverse problem of moving force identification. Based on the method of moments (MOM) and the theory of moving force identification, the moving forces were described as a combination of whole basis functions, such as orthogonal Legendre polynomials or Fourier series, and were then estimated by solving the new system equations developed based on the basis functions. Under a number of response combination cases, the moving vehicle loads are identified using the ITDM and compared with the existing time domain method (TDM). Further a laboratory study was conducted to evaluate the effect of various parameters on the ITDM. Those parameters include basis function number, mode number, number of measured stations, and CPU executive time of the ITDM. Simulation and experiment results show that the ITDM has higher identification accuracy and robust noise immunity as well as being able to generate an acceptable solution to the ill-conditioning problem to some extent when it is used to identify the moving forces from bridge responses. Meanwhile, the ITDM can lessen the executive CPU time as well as being more flexible when compared with the TDM. This is beneficial to real time analysis of moving force identification in field.
Mechanical Properties of Tubulin Molecules by Molecular Dynamics Simulations
Authors: Enemark So̸ren , Deriu Marco A. , Soncini Monica
Published: September 2008

The basic unit in microtubules is αβ-tubulin, a hetero-dimer consisting of an α- and a β-tubulin monomer. The mechanical characteristics of the dimer as well as of the individual monomers may be used to obtain new insight into the microtubule tensile properties. In the present work we evaluate the elastic constants of each of the monomers and the interaction force between them by means of molecular dynamics simulations. Molecular models of α-, β-, and αβ-tubulin were developed starting from the 1TUB.pdb structure from the RSCB database. Simulations were carried out in a solvated environment using explicit water molecules. In order to measure the monomers’ elastic constants, simulations were performed by mimicking experiments carried out with atomic force microscopy. A different approach was used to determine the interaction force between the α- and β-monomers using 8 different monomer configurations based on different inter-monomer distances. The obtained results show an elastic constant value for α-tubulin of 3.4–3.9 N/m, while for the β-tubulin the elastic constant was measured to be 1.8–2.4 N/m. The maximum interaction force between the monomers was estimated to be 11.2 nN. In perspective, these outcomes will allow exchanging atomic level description with key mechanical features enabling microtubule characterisation by continuum mechanics approach.
Numerical Analyses of Microchannels Filling in a Lab-on-Chip Device
Authors: Rasponi Marco , Soncini Monica , Montevecchi Franco Maria , Redaelli Alberto
Published: September 2008

A prototype of a Lab-on-Chip (LoC) device manufactured by ST Microelectronics Inc., which is intended to be a diagnostic platform for DNA analysis, has been analyzed. In particular, the dynamics of the filling process was evaluated by means of a 3-D numerical model. Measurements of wettability were also conducted by evaluating the surface tension of the examined liquids and their contact angles on the solid substrates. Two different filling conditions were simulated: pure capillarity and a pressure of 1.5 kPa applied to the inlet. Results in terms of filling time, fluids velocities and percentage of air entrapped in the channels were analyzed. The numerical model revealed the presence of 3.4% of air in the channels (localized in the corner regions), when the pressure of 1.5 kPa was applied. In case of zero pressure, the top corners of the central channel got completely wetted, thus reducing the amount of air to 2.7%. The results showed that capillary forces are dominant during the filling of channels with dimensions smaller than 200 μm. General parameters used to have an insight into the kind of forces leading a fluid-dynamic process are the Reynolds (Re) and Capillary (Ca) numbers, ratios between inertial and viscous forces, and viscous and surface forces, respectively. The computed maximum values in our simulations were Re = 60 and Ca = 0.018, showing the predominance of surface forces on both viscous and, indirectly, inertial ones.
Unusual Optical Techniques in Diffusivity Measurements
Authors: Paoletti Domenica , Ambrosini Dario , Rashidnia Nasser , Balasubramaniam Ramaswamy
Published: September 2008

In studying hydrodynamic instabilities between two miscible fluid mixtures one often faces the problem of assigning a reliable value to diffusion coefficients. As for diffusion between two binary mixtures such as water and glycerin, water and salt, etc., no complete data are available in the literature. This shortage of data justifies the search for simple and accurate experimental techniques. Optical techniques are now recognized as powerful tools to investigate fluid flow phenomena in transparent media. In particular, in this paper we discuss three different, recently proposed, optical techniques for diffusivity measurements, namely speckle decorrelation, common path shearing interferometry and digital moire´. Although all these techniques depend on variation of the index of refraction in a transparent fluid, each method involves the use of specific instrumentation, with experimental uncertainties and ranges of applicability which differ from case to case. A comparison of the techniques is presented as well as a discussion of their possible integration.
Hot Water Hydrolysis: Controlled Precipitation and the Preparation of Nano Alumina, Spherical α Alumina Powder
Authors: Thiruchitrambalam M. , Palkar V. R.
Published: September 2008

Aluminium metal has been hydrolyzed in hot aqueous-glycerol media composed of various volume % of glycerol. After hydrolysis in the aqueous-glycerol media, the product i.e., precipitate was aged at room temperature and the ageing medium was diluted periodically. The precipitation and ageing media has influenced the phase composition and morphology of the hydroxides significantly. The morphology of the hydroxide and α alumina powders were examined using TEM and SEM respectively. It has been found that the crystallinity and morphology of hydroxide influenced the morphology of α alumina, importantly the hydroxide powder prepared using 25 % aqueous-glycerol medium, upon calcination yielded spherical α lumina powder.
Computational Aeroacoustic of Buffeting Phenomena Coming From an Open Sunroof
Authors: Ribaldone Enrico , Casella Mauro , Scantamburlo Giuseppe , Tregnago Roberto
Published: September 2008

In the last years aeroacoustics has become one of the most active research fields in the transportation industry: the success of new models of airplanes, trains, trucks and cars relies more and more on the level of comfort for passengers, where acoustic comfort plays a major role. Moreover, the progress in numerical techniques and in available computing power, has provided industry with more efficient and robust simulation techniques in the field of aerodynamically generated sound. Great efforts were spent by CRF in the past years in the development of tools for the prediction of noise levels associated with aeroacoustic phenomena and simulation of turbulent unsteady phenomena became possible (or even practical) much earlier than it was expected, even if limited to simplified cases. Today with the use of the supercomputing environment it is becoming possible to face real problems in realistic configurations, like aerodynamic noise from a complete car or from fluid-acoustic resonance of cavities. One example of this last case is represented by the buffeting phenomenon. It takes place when opening the sunroof, external flow comes into contact with the passenger compartment cavity. When the fluid-dynamic fluctuations of the external flow match one of the acoustic modes of the internal cavity resonance takes place: acoustic oscillations feed energy to the fluid-dynamic oscillation of the external flow, which respond with the generation of coherent structures (vortices traveling through the sunroof opening) that in turn feed more energy back to the acoustic modes, until an equilibrium is reached and steady oscillations take place. This paper describes recent development of aeroacoustic simulation of this phenomena, giving an overview on data coming from computation on sunroof systems with and without deflector and comparing these results with experimental data measured into wind tunnel.
Handling Investigation of Double Deck Bus With Three Wheel Axles in Thailand
Authors: Koetniyom Saiprasit , Choowichien Direk
Published: September 2008

For many years, Ratchaburi province has been known for the place where quality passenger buses are built. Its design and manufacturing are based on technician experiences and trial-error experiments. In addition, double deck buses three wheel axles are commonly used in Thailand as the way of inter-city transportation. Therefore, most of these buses are designed in Ratchaburi without automotive engineering knowledge. Some original parts of bus structure in Japan are used such as engine, drive train and the serial number of original structure part. With transportation department regulations, these buses can be registered as modified double deck buses. This is because it simply controls bus dimension and weight of wheel axle. For these reasons, this research will investigate bus handling together with steering behavior as cornering in term of neutral steer, understeer and oversteer. Furthermore, the quality of three wheel axle buses in Thailand is evaluated.
Two Material S-Frames Representation for Improving Crashworthiness
Authors: Hosseini-Tehrani P. , Nikahd M.
Published: September 2008

Crashworthiness analysis for a passenger car consists of car-body structural analysis and occupant behavior analysis. With raising the energy absorption of each component an improved car-body structure against crashing may be achieved. In this paper various design of a simplified front side rail is studied. Various possible model of S-frame is presented and characteristics of each model are compared and discussed. It is shown that a hybrid S-frame made of steel and aluminum shows better characteristics from the point of view of passenger safety.
Axisymmetric Solutions of Functionally Graded Circular and Annular Plates Using Second-Order Shear Deformation Plate Theory
Authors: Saidi Ali Reza , Sahraee Shahab
Published: September 2008

In this paper, axisymmetric bending and stretching of functionally graded solid circular and annular plate is studied based on the second-order shear deformation plate theory (SST). The solutions for deflections, force and moment resultants of the second-order theory are presented in terms of the corresponding quantities of the isotropic plates based on the classical plate theory from which one can easily obtain the SST solutions for axisymmetric bending of functionally graded circular plates. It is assumed that the mechanical properties of the functionally graded plates vary continuously through the thickness of the plate and obey a power law distribution of the volume fraction of the constituents. Numerical results for maximum displacement are presented for various percentages of ceramic-metal volume-fractions and have been compared with those obtained from first-order shear deformation plate theory (FST).
Improve Hunting of a Railway Vehicle Using Semi-Active Primary Suspension
Authors: Fotoohi Abbas , Yousefi-Koma Aghil
Published: September 2008

Hunting is a very common instability phenomenon in rail vehicles operating at high speeds. The hunting phenomenon is a self excited lateral oscillation produced by the forward speed of the vehicle and the wheel-rail interactive forces caused by the conicity of the wheel-rail contours and the friction-creep characteristics of the wheel-rail contact geometry. Hunting can lead to severe ride discomfort and eventual physical damage to wheels and rails. This research is conducted to demonstrate advantages of semi-active primary suspension in railway vehicle for control of hunting phenomenon. Semi-active suspension consists of some actuators on each bogie located in primary suspension position in addition to vertical passive dampers. A simple on-off switching is used here and the actuator force is determined regarding to wheelset displacement. An integration of a control design tool, i.e. MATLAB, together with a tool for railway vehicle simulation, i.e. ADAMS/Rail is utilized for modeling and control design simultaneously. Analysis has been performed on a traditional bogie model with passive primary suspension and on a new bogie model with semi-active suspension. The effects of semi-active suspension system on lateral displacement and yaw motion of wheelset have also been investigated. Results show that the semi-active suspension improves the stability by controlling displacement magnitude.
Multi-Point Energy and Exergy Analysis of a 1.5 MWe Hybrid SOFC-GT Power Plant
Authors: Calise Francesco , Dentice d’Accadia Massimo , Vanoli Laura , von Spakovsky Michael R.
Published: September 2008

This paper presents a multi-point energy and exergy analysis of a hybrid SOFC–GT power plant. The plant layout consists of the following principal components: an internal reforming SOFC, a steam-methane pre-reformer, a catalytic burner, a radial gas turbine, a centrifugal air compressor, a centrifugal fuel compressor, plate-fin heat exchangers, counter-flow shell and tube heat exchangers, and mixers. The partial load performance of the centrifugal compressors and radial turbine is determined using maps, properly scaled in order to match required mass flow rate and pressure ratio values. The plant is simulated on the basis of a zero-dimensional model discussed in previous papers. Two different partialization strategies are introduced in order to assess the partial load behavior of the plant. Results show that the plant achieves the best partial load performance for the case when both air and fuel mass flow rates are simultaneously reduced.
The Mechanical Behaviour of Aluminium Foam Structures in Different Loading Conditions
Authors: Peroni Lorenzo , Avalle Massimiliano , Peroni Marco
Published: September 2008

Foams are one of the best solutions for energy absorption enhancement. Many types of materials can be produced in the form of foams, including metal and polymers. Among metal foams, the most advanced are aluminum based. They couple lightweight with good properties, not only mechanical, but also, for example, good thermal stability. Among the various aspects still to be investigated regarding their mechanical behavior, there is the influence of a hydrostatic state of stress on yield. Unlike metals, the hydrostatic component affects yields. Therefore different loading conditions have to be considered to fully identify the material behavior. Another important issue in foam structure design is the analysis of composite structures. To this purpose an aluminum foam has been examined (FOAMINAL, provided by IFAM within the 6th Framework Programme European Project APROSYS). The material behavior has been investigated by subjecting the foam to different stress state conditions (uniaxial, hydrostatic, pure deviatoric, and various combinations). Results obtained in various kinds of test will be presented: uniaxial compression, in quasi-static and dynamic conditions loading the components into a SHPB device, tension, bending, and shear loading. Moreover, composite structures were made by assembling the foam into aluminum cold extruded closed section tubes (in 6060 aluminum). All the results show that the energy absorption capability of the composite structures is much greater than the sum of the energy absorbed by the two components, the foam and the tube.
Parking System Demands on the Steering Actuator
Authors: Ro¨sth Marcus , Degerman Pa¨r , Palmberg Jan-Ove
Published: September 2008

This paper describes how a hydraulic power steering system with increased flexibility, Active Pinion, can be applied as the actuator to an automatic parking system, Parking Pilot. The requirements on the actuator from the parking system and how the actuator’s performance translates into parking maneuver performance is studied. The system have been installed in a test rig and in a demonstrator car.
Enhanced Splash Models for High Pressure Diesel Sprays
Authors: Allocca L. , Andreassi L. , Ubertini S.
Published: September 2008

Mixture preparation is a crucial aspect for the correct operation of modern DI Diesel engines as it greatly influences and alters the combustion process and therefore, the exhaust emissions. The complete comprehension of the spray impingement phenomenon is a quite complete task and to completely exploit the phenomenon a mixed numerical-experimental approach has to be considered. On the modeling side, several studies can be found in the scientific literature but only in the last years complete multidimensional modeling has been developed and applied to engine simulations. Among the models available in literature, in this paper, the models by Bai and Gosman [1] and by Lee et al. [2, 3] have been selected and implemented in the KIVA-3V code. On the experimental side, the behavior of a Diesel impinging spray emerging from a common rail injection system (injection pressures of 80 MPa and 120 MPa) has been analysed. The impinging spray has been lightened by a pulsed laser sheet generated from the second harmonic of a Nd-YAG laser. The images have been acquired by a CCD camera at different times from the start of injection (SOI). Digital image processing software has enabled to extract the characteristic parameters of the impinging spray with respect to different operating conditions. The comparison of numerical and experimental data shows that both models should be modified in order to allow a proper simulation of the splash phenomena in modern Diesel engines. Then the numerical data in terms of radial growth, height and shape of the splash cloud, as predicted by modified versions of the models are compared to the experimental ones. Differences among the models are highlighted and discussed.
Experimental Study on Wear and Fracture in Aeronautical Gear Transmissions
Authors: Bassani Roberto , Ciulli Enrico , Manfredi Enrico , Manconi Salvatore , Polacco Alessandro , Pugliese Giovanni
Published: September 2008

This work presents some of the results obtained from an extensive experimental test campaign performed at the Department of Mechanical Nuclear and Production Engineering (DIMNP) of Pisa University with the partnership of Avio Propulsione Aerospaziale S.p.A. This test campaign, that is still being performed, is concerned with the characterization of teeth damage in high performance gear transmissions, such as aeronautical ones, characterized by high levels of velocity and load. Damage detection and monitoring have been pursued during all the tests in order to achieve a better understanding of causes and evolution of teeth damage. Moreover, to investigate the effects of different parameters on teeth damage, tests with different load, velocity, teeth geometry, materials and surface finishing, have been performed. The surface conditions of the gear teeth have been investigated using in particular two different instruments: a computer-controlled stylus profilometer able to perform 3D investigations and a scanning electron microscope (SEM) recently provided by a software for surface reconstruction. Qualitative and quantitative changes in surface roughness have been detected. Besides the experimental activity, numerical analyses have been also started for finding theoretical criteria for surface damage prediction; some few obtained results are presented. Due to the vastness of the work performed, only a survey of the main results obtained till now is presented in the paper.
Thermal-CVD System Designed for Growth of Carbon Nanotubes
Authors: Porro Samuele , Musso Simone , Rovere Massimo , Giorcelli Mauro , Chiodoni Angelica , Tagliaferro Alberto
Published: September 2008

We report a study on a thermal chemical vapor deposition (CVD) system optimized for the growth of well packed and vertically aligned carbon nanotubes (CNTs) on uncoated silicon substrates. The process of synthesis involves the co-evaporation of a carbon precursor and a metal catalyst in a nitrogen atmosphere inside a high temperature furnace. Beside the formation of CNTs, depending in particular on the deposition temperature, other carbon structures can be deposited, such as nanographite. We show the growth results analyzed by different characterization techniques (electron microscopy, porosity and thermal stability investigations, micro-Raman spectroscopy). In addition, we report an investigation on the development of secondary transversal vortex flows caused by the effects of distribution of temperatures inside the growth system, in order to correlate them with the growth results.
Diagnosability Modeling and Diagnosability Evaluation of Mechanical System at Conceptual Design Stage
Authors: Wani M. F. , Ummar Mohammad
Published: September 2008

Reliability, availability and maintainability (RAM) of mechanical system plays a significant role in decreasing the life cycle cost of product. It is well known fact that reliability and maintainability of mechanical systems depends to a large extent on diagnosability of mechanical system, i.e., systems with higher diagnosability, not only helps in reducing the failure of the system at operational stage, but will also help in identification and isolation of faulty components of the system in quick possible time. However, to reap maximum benefits of it is inevitable to consider the design for diagnosability of mechanical systems right from conceptual design stage. For the implementation of the same, designer should be provided with suitable and efficient tool for carrying out diagnosability design and evaluation at conceptual design stage. In this paper, a methodology is developed for carrying out diagnosability of mechanical systems at conceptual design stage. At conceptual design stage designer is well versed with the functional and structural hierarchies of the product. The relationship between the components and functions are used to determine the relationship between the components/assemblies and their performance monitoring parameters (PMP). These are modeled in terms of fuzzy diagnosability bipartite graph (FDBG). FDBG is transformed into fuzzy diagnosability matrix (FDM). The FDM represents the fuzzy relationship between the components and PMP. Diagnosability of the system design concept is evaluated in terms of diagnosability index (IDN) which is obtained from the normalized matrix by using −plog2p. First of all the system which has lowest diagnosability is evaluated from normalized FDM (derived by considering relationship value of 1 between components and PMP). Then reference diagnosability value is obtained from this matrix by using −plog2p and this is represented by DP, ref. FDM for design concept is obtained from the relationship between the components and the PMP. DPN of the design concept is also obtained. Diagnosability index (IDN) of the design concept is then obtained by the ratio of (DP, ref − DPN)/ DP, ref. The higher value of IDN means higher diagnosability and its lower value means lower diagnosability. Component which has lowest diagnosability is also identified, i.e., which has highest functional relationship. This provides guidelines to designer not only for the improvement of design from diagnosability point of view, but also helps in evaluation of dignosability at system conceptual design stage.
Failure Analysis of Mechanical Systems Based on Function-Cum-Structure Approach
Authors: Wani M. F.
Published: September 2008

This paper suggest failure analysis of mechanical systems using function cum structure approach. Operational parameters of system function are identified and their relationships are developed. The predicates, which comprise the components of the system and their properties as their attributes, i.e., type of connectivity (fixed or sliding contact) and functions (transmit torque, and transmit force etc.) represent the facts. The facts are modelled in terms of functional-cum-structure graph. By analysing interaction of a failure function i.e., function of a failed component in the graph with other functions, the failure cause-function is identified. The problem can either be solved by removing the cause-functions or by modifying the failure function. A critical function is also identified from function set on the basis of importance of a function. Appropriate parameters for in-situ design provision for condition monitoring of the system are also identified. The steps of the methodology are included and are illustrated by means of an example.
Trajectory Control of an Automated Guided Vehicle Using Feedback Linearization
Authors: Ansarey M. S. M. Mehdi , Mahjoob M. J.
Published: September 2008

In this paper, the dynamics and control of an automated guided vehicle (AGV) is described. The objective is to control the vehicle direction and location with respect to a prescribed trajectory. This is accomplished based on an optimum control strategy using vehicle state variables. A four-wheel vehicle with three degrees of freedom including longitudinal, lateral and yaw motion is considered. The nonlinearity of the tire and steering mechanism is also included. The control system design for circular, straight forward and composite path is presented based on feedback linearization. Some trajectory simulation for discrete curvatures is carried out. The controller was implemented within MATLAB environment. The design was also evaluated using ADAMS full vehicle assembly. The results demonstrated the accuracy of the model and the effectiveness of the developed control system.
Life Cycle Design and Evaluation at Conceptual Design Stage Using Digraph and Matrix Approach
Authors: Wani M. F.
Published: September 2008

In this paper, a procedure based on digraph and matrix approach is presented for carrying out life cycle design and evaluation of mechanical systems, at system conceptual design stage. Features which characterize life cycle aspects of the system are identified and are called attributes of life cycle of a the system. Consideration of these attributes and their interrelations are rudiment in design and evaluation of life cycle of the system. This is modeled in terms of life cycle Design (LCD) attributes digraph for the system. Nodes in the digraph represent attributes and their relations are represented by their edges. The digraph is represented by one-to-one matrix for development of life cycle design (LCD) expression, which is characteristics of the system. A variable life cycle design attributes permanent matrix is defined to develop VPF-d which is also useful in comparing two design concepts of the system. Life cycle design Index (LCD-I) is obtained from permanent of the matrix or from the LCD expression by substituting numerical values of the attributes and their interrelations. A higher value of the index implies good LCD of the system. The ideal value of LCD index (III) is also obtained from the matrix expression, which is useful in assessing the relative LCD, of the system alternatives. The procedure is useful in design and development of LCD of the system. A step by step procedure for evaluation of LCD index is also suggested and is illustrated by means of an example.
An Efficient Modelling of Flexible Airships
Authors: Bennaceur Selima , Azouz Naoufel , Boukraa Djaber
Published: September 2008

This paper presents an efficient modelling of airships with small deformations moving in an ideal fluid. The formalism is based on the Updated Lagrangian Method (U.L.M.). This formalism proposes to take into account the coupling between the rigid body motion and the deformation as well as the interaction with the surrounding fluid. The resolution of the equations of motion is incremental. The behaviour of the airship is defined relatively to a virtual non-deformed reference configuration moving with the body. The flexibility is represented by a deformation modes issued from a Finite Elements Method analysis. The increment of rigid body motion is represented similarly by rigid modes. A modal synthesis is used to solve the general system equations of motion. Time constant matrices appears (i.e. mass and structural stiffness matrices), and we show a convenient technique to actualise the time dependant matrices.
Numerical Analysis of a Tree-Shaped Cooling Structure for a 2-D Slab: A Validation of a “Constructally Optimal” Configuration
Authors: Robbe M. , Sciubba E. , Lorente S. , Bejan A.
Published: September 2008

A 2-d rectangular slab, internally cooled by circular tubes of different diameters, is used as a benchmark to perform a numerical thermal optimization procedure on a heat transfer configuration obtained by “constructal” considerations. Three different geometric arrangements are investigated: in the first one, all cooling holes have the same diameter; in the second, there are two hierarchies of holes with two different diameters; in the third, yet another series of smaller holes is added. To assist the user in systematically assembling multiple configurations, a custom user interface utility for generating constructal geometries has been developed. Thermal boundary conditions are assigned as if the slab were the axial cross-section of an elongated prismatic body, and as if the ducts were internally cooled by forced convection. For each case (single diameter of the cooling holes, 2 and 3 different diameters) a series of numerical simulations has been run to assess and compare the performance of different values of the geometrical parameters (location of the holes, slab aspect ratio, etc.). The best performing configurations for each case have then been compared with those identified for the other cases, the objective function being the average temperature of the slab “volume”. All results consistently indicate that, under the specified design conditions, the configuration obtained by a simple constructal optimization is the best performing one at each configuration level (1, 2 or 3 series of cooling holes).
Buckling Topology Optimization of Laminated Multi-Material Composite Structures
Authors: Lund Erik
Published: September 2008

The design problem of maximizing the buckling load factor of laminated multi-material composite shell structures is investigated using the so-called Discrete Material Optimization (DMO) approach. The design optimization method is based on ideas from multi-phase topology optimization where the material stiffness is computed as a weighted sum of candidate materials, thus making it possible to solve discrete optimization problems using gradient based techniques and mathematical programming. The potential of the DMO method to solve the combinatorial problem of proper choice of material and fiber orientation simultaneously is illustrated for a multilayered plate example and a simplified shell model of a spar cap of a wind turbine blade.
Damage Evolution in Stitched and Unstitched Graphite/Epoxy Laminates Subject to Low-Velocity Impact
Authors: Aymerich Francesco , Priolo Pierluigi
Published: September 2008

The response to low velocity impact loadings, which may occur during manufacturing, service and maintenance, is a key factor in the design of composite material structures. Many techniques, ranging from the adoption of tough matrices/high-strain fibers to the introduction of through-thickness reinforcement, have been proposed to improve the damage response of composite laminates subject to impact. The insertion of transverse reinforcing threads by stitching, in particular, appears very promising to restrict damage growth and to improve post-impact performance of laminates. In order to develop general models capable of addressing the issues of damage tolerance and resistance, detailed understanding of the nature and extent of damage, identification of the dominant fracture modes and assessment of the effect of stitches on the damage development are essential. In this study instrumented drop-weight tests were carried out to examine and compare the damage response of stitched and unstitched cross-ply graphite/epoxy laminates subject to low-velocity impact. The progression of damage and its relationship with impact and absorbed energy were investigated by means of an extensive series of damage observations, conducted with various techniques (X-radiography, ultrasonics, optical microscopy, deply).
HENEA-3: A Second Law Based Expert Assistant for the Synthesis of Heat Exchanger Networks
Authors: Mastromanno S. , Petrucci J. , Sciubba E.
Published: September 2008

The present paper describes the latest development of an Expert System for the design and optimization of Heat Exchange Networks (HEN). The code described herein, HENEA (acronym for Heat Exchanger Network Expert Assistant) is a Knowledge Based System capable of interacting with a Process Engineer to generate an optimal configuration for a HEN under several different objective functions. Contrary to most of the currently available methods, the code is able to produce such solutions by making explicit use of a set of Second Law Analysis criteria and of some of the basic principles of the “Pinch Method”. With respect to the previous version, HENEA now includes an additional application, “HEN-SPLIT” that accounts for the possibility of splitting one or more of the participating streams according with a general “minimal entropy generation” criterion. In its present version, HENEA can be used both for process design (new HEN) and for process structural optimization (retrofit problems). The optimization procedure is based on Sama’s “Second Law Insight Method” and is directly and explicitly finalized to the reduction of the global entropy generation. The code is also endowed with a cost calculations utility, and can be thus employed to search for the optimum using two alternative optimization criteria: it generates in fact both a Maximum Energy Recovery (MER) and Minimum Exchange Area configuration (MCC, Minimum Capital Cost). Since the code is though intended for practical industrial use, and it is well known that a thermodynamically optimal configuration is not always the “most convenient” one from an engineering point of view, HENEA presents to the user also a certain number of additional sub-optimal configurations. An interactive graphic user interface makes HENEA very user-friendly: furthermore, the user can (indirectly) interrogate HENEA about its choices and understand the underlying physic in an unambiguous and immediate way. Several tests conducted on some of the available benchmarks have proven that the solutions generated by HENEA are always comparable to those produced by other optimization criteria (Pinch Method or Second Law method): in fact, for large problems (many participating streams, several splittings) they are often better than those obtained with its competitors.
Multi-Level Modeling of Low Velocity, Low Energy Impact on Metal-Skinned Sandwich Structure
Authors: Castanie´ B. , Bouvet C. , Barrau J.-J. , Thevenet P.
Published: September 2008

The research objective is to model the low velocity/low energy impact on sandwich structures with metallic skins. A progressive approach is carried out by considering first the honeycomb core alone, then static indentation on sandwich structures and finally a dynamic analysis. During the first step, a phenomenological study of the behavior of honeycomb subjected to crushing is completed. It appears that local rotations and cell edges plays an important role in the crushing phenomenon. It is then possible to propose a simple analytical model able to represent the indentation of honeycomb alone for various indenter geometries by modelling only the cell edges behavior. The compression law of the cell edges is identified by a basic uniform compression test. This key-idea is then used to create a finite element model using a grid of nonlinear springs to represent the honeycomb structure. The contact law of static indentation tests of metal-skins Nomex™ honeycomb sandwich structures can thus be found numerically and agree well with the experiments. Finally, this contact law can be used to model dynamic impacts which demonstrates the static/dynamic equivalence for this range of impact and structures.
Design Optimization of Anisotropic Pressure Vessels With Manufacturing Uncertainties Accounted For
Authors: Walker Mark , Tabakov Pavel Y.
Published: September 2008

Accurate optimal design solutions for most engineering structures present considerable difficulties due to the complexity and multi-modality of the functional design space. The situation is made even more complex when potential manufacturing tolerances must be accounted for in the optimizing process. The present study provides an in-depth analysis of the problem and then a technique for determining the optimal design of engineering structures, with manufacturing tolerances accounted for, is proposed and demonstrated. The numerical examples used to demonstrate the technique involve the design optimisation of anisotropic fibre-reinforced laminated pressure vessels. It is assumed that the probability of any tolerance value occurring within the tolerance band, compared with any other, is equal, and thus it is a worst-case scenario approach. A genetic algorithm with fitness sharing, including a micro-genetic algorithm, has been found to be very suitable to use, and implemented in the technique.
Dynamic Response of Sandwich Panels With a Flexible Core Under Simultaneous Low-Velocity Impacts of Multiple Small Masses
Authors: Malekzadeh K. , Khalili M. R.
Published: September 2008

Dynamic response of sandwich panels with a flexible core under simultaneous low-velocity impacts of multiple small masses has investigated in this paper. The contact forces between the panel and the impactors are treated as the internal forces of the system. Shear deformation theory is used for the face sheets while three dimensional elasticity is used for the soft core. The fully dynamic effects of the core layer and the face-sheets are considered in this study. The results in multiple mass impacts over sandwich panels are presented based on proposed improved higher-order sandwich plate theory (IHSAPT). As no literature could be found on the impact of multiple impactors over sandwich panels, the present formulation is validated indirectly by comparing the response of two cases of double small masses and single small mass impacts based on Olsson’s wave control principle.
Static Strength of Structural Adhesive Joints: Statistical Analysis and Design Parameter Correlation Based on an Extensive Experimental Campaign
Authors: Adamowski Jaroslaw , Gambaro Carla , Lertora Enrico , Monti Margherita
Published: September 2008

The goal of the present research was to find reference surfaces that would interpolate the results of a vast test campaign, performed on several epoxy adhesives, varying numerous parameters, and estimate static failure load values of joints characterized by identical geometries, but different dimensions. Results obtained from static shear tests of single-lap and double-lap specimens were statistically processed using Student’s unilateral test with confidence level of 99%. A multivariate regression was then applied in order to obtain polynomial functions able to describe the interpolation surface. In order to test the validity of the model, failure loads were calculated for two geometrical configurations within the dimensional range used in the experimental test campaign. These values were compared with those obtained from additional experiments, relative to the same geometries. The comparison confirmed the reliability of the developed model. Tendencies that could be translated into geometries characterized by different dimensions of the tested joints were sought, thanks to the experimental data for as much as 4 adhesives and 2 adherends. Scale factors were calculated that allow, in initial design phases, to estimate realistic failure loads based on initial indications, limited to a single geometry used by producers of adhesives in mechanical characterization.
Vibration of Functionally Graded Plates
Authors: Abrate Serge
Published: September 2008

This article considers the free vibration of plates for which materials properties vary continuously though the thickness. First, an examination of results available in the literature led to the discovery that the natural frequencies of such functionally graded plates are proportional to those of isotropic plates. In the usual formulation of existing plate theories, the midplane is taken as the reference surface and the variation in material properties through the thickness leads to coupling between inplane and bending deformations. The second part of this paper shows that it is possible to select a different reference plane so that this coupling is eliminated and the motion of the graded plate is governed by the same equation as that of homogeneous isotropic plates. This explains the relationship between the natural frequencies that was observed in the results presented by previous investigators. The study of functionally graded plate is made much simpler and results available for isotropic plates can be used directly.
Multibody Performance Optimization of a Formula SAE Car
Authors: Capitani Renzo , Rosti Daniele G. , Tozzi Pierluigi
Published: September 2008

The dynamic behavior optimization of the Formula SAE car built at the Universita` degli Studi di Firenze is discussed. A virtual model was built using MSC Adams Motorsports, in order to simulate the kinematics and dynamics of the car. A data acquisition system was mounted on board to record all the data useful to setup the car and the virtual model too. The multibody approach was coupled with a multi objective optimizer to start a design of experiments that was able to find the robust design that maximizes the performance along the Formula SAE track.
Fuzzy Statistics Approach for Aviation GTE Condition Estimation Technique
Authors: Abdullayev P. S.
Published: September 2008

In this paper is shown that the probability-statistic methods application, especially at the early stage of the aviation gas turbine engine (GTE) technical condition diagnosing, when the flight information has property of the fuzzy, limitation and uncertainty is unfounded. Hence is considered the efficiency of application of new technology Soft Computing at these diagnosing stages with the using of the Fuzzy Logic and Neural Networks methods. Training with high accuracy of fuzzy multiple linear and non-linear models (fuzzy regression equations) which received on the statistical fuzzy data basis is made. Thus for GTE technical condition more adequate model making are analysed dynamics of skewness and kurtosis coefficients’ changes. Researches of skewness and kurtosis coefficients values’ changes show that, distributions of GTE work parameters have fuzzy character. Hence consideration of fuzzy skewness and kurtosis coefficients is expedient. Investigation of the basic characteristics changes’ dynamics of GTE work parameters allows to draw conclusion on necessity of the Fuzzy Statistical Analysis at preliminary identification of the engines’ technical condition. Researches of correlation coefficients values’ changes shows also on their fuzzy character. Therefore for models choice the application of the Fuzzy Correlation Analysis results is offered. For checking of models adequacy is considered the Fuzzy Multiple Correlation Coefficient of Fuzzy Multiple Regression. At the information sufficiency is offered to use recurrent algorithm of aviation GTE technical condition identification (Hard Computing technology is used) on measurements of input and output parameters of the multiple linear and nonlinear generalised models at presence of noise measured (the new recursive Least Squares Method (LSM)). The developed GTE condition monitoring system provides stage-by-stage estimation of engine technical conditions. As application of the given technique the estimation of the new operating aviation engine temperature condition was made.