bluuebunny/crossref_metadata_2025 huggingface dataset:
Multi-Objective Optimisation of Herringbone Grooved Gas Bearings Supporting a High Speed Rotor, Taking Into Account Rarefied Gas and Real Gas Effects
Authors: Schiffmann Juerg , Favrat Daniel
Published: September 2008

Currently the herringbone grooved journal bearing (HGJB) has applications in the domain of small, low power energy related applications, where high rotational speeds are required for reaching reasonable efficiency and where standard oil lubricated bearings are limited or even unable to operate over the life time required. Furthermore the presence of oil requires auxiliary control systems reducing the overall system efficiency and reliability. High-speed rotors running in hermetic units processing refrigerant vapor require the bearings to operate with this same gas at thermodynamic conditions that are potentially very close to the saturation curve. In this region the usually applied perfect gas theory does not yield valid results when applied to the Reynolds-lubrication equation. Furthermore, depending on the processed gas and its thermodynamic condition, the Knudsen number may reach values where it is advisable to take gas rarefaction effects into account. In applications where the rotor is heavily loaded in terms of mass and inertia, the bearing design highly affects the dynamic stability of the rotor. In order to reach good stability margins, the bearing geometry tends towards low clearances leading to higher power losses. It has to be noted that bearing losses not only deteriorate the overall efficiency, but also as the unit size are getting smaller and smaller, cooling becomes an issue. The narrow groove theory (NGT) is modified in order to take into account the rarefied gas as well as the real gas effects depending on the thermodynamic and physical properties of the processed gas and on its thermodynamic state. The bearing module implementing the modified narrow groove theory allows calculating the stiffness and the damping matrices for a given bearing geometry. It is then linked to a rotor dynamic model that enables to calculate the critical speeds and the corresponding dynamic stability for a given rotor supported on herringbone grooved dynamic gas bearings. The latter module is linked to a multi-objective optimizer based on evolutionary algorithms. In this paper the evolutionary optimizer is used for two objectives: maximizing the stability margin and minimizing the bearing power loss. The optimizer yields in a Pareto curve representing a family of optimum solutions. One has the choice between a solution with a high stability margin but with high bearing losses to get dissipated or vice versa. A low power rotor for a refrigerant gas process illustrates the optimizing procedure discussed in this paper.
Behavior Study of High Impact Resistant Reinforced Concrete Frames Using Crack Conduction Method
Authors: Heidarzadeh Navid , Razavi S. Mohammad , Shamsaei Nima
Published: September 2008

In this study, the influence of crack conduction method on behavior of reinforced concrete (RC) frame under iterative high impact loading were experimented. To investigate the structural behavior through large deformations and progressive damage and to identify the failure modes, the falling weight and falling height were set more than the structural strength in elastic state. A comprehensive scheme which indicated influence of location of initial cracks on behavior and failure mode of structure was developed. Falling weight impact test was conducted on twenty-one laboratory scaled RC frames which were categorized in four series regard to considered scheme. Concrete volume and compressive strength, number of longitudinal and transverse rebar were constant factors in all specimens. Deformed shape and crack patterns, developed on the side surface of the RC frames, were sketched and total deflections vs. cumulative input energy of the RC girder were plotted. The results revealed the influence of crack conduction on improving the structural behavior and extending the endurance of RC frames against iterative high impact loading.
Characterisation of a Simplified Aeroengine Casing Subjected to a Radial Loading Condition Using FE and Approximate Methods
Authors: Rajaratnam Sabesan , Hyde Tom H. , Leen Sean B.
Published: September 2008

In general, aeroegine casings may experience an axial force, a bending-moment and radial loading. Under these loads, the high stress regions of these complex aerongine casings will experience local stress and strain concentrations, with various load combinations. The stiffness will also depend on the loading mode. Hence, careful design is required to avoid the various types of failure such as buckling, crack initiation and propagation must be taken into account when designing an aeroengine casing structure. In addition, aerongine casings require extremely high reliability in service and adequate strength under extreme load conditions, i.e. Fan-Blade-Off (FBO) condition, must be demonstrated. Under radial loading of aeroengine casings, which have spoke to shell connections, these are the most likely sites for plastic deformation to occur and cracks to initiate. Also, the load path for each spoke to shell connection within the casing structure changes during loading. Based on these observations, this paper concentrates on the behavior which occurs in spoke to shell connections, referred to as local joints. The intention is first to characterize the local joint behavior and then to incorporate this into a global casing model. The work reported in this paper includes studies of mesh sensitivity, predictions of load path at each local joint under radial load, FE failure loci, upper bound techniques for predicting limit loads and stresses-strains predictions at local casing notches under elastic-plastic and creep situations using approximate notch methods. Hence, the global responses of a casing structure were predicted by utilizing a “repeated local joint” technique in conjunction with simplified global models.
Strengthening Thermo-Cycling Heat Treatment Process of High-Speed Steels
Authors: Shmatov Alexander A.
Published: September 2008

The results of the examination of structure and properties of high-speed steels S 6-5-2, P6M5 (6% W, 5% Mo), P18 (18% W), P6M5K5 (6% W, 5% Mo, 5% Co) subjected to a specific strengthening thermo-cycling heat treatment are presented. The newly developed process results in a fine-grained heterogeneous microstructure (primary and secondary carbides, martensite and residual austenite) with spatially uniform distribution of the carbide grains. This brings about a 10–20% increase in the bending strength with the impact strength increased by the factor of 1.5–2.5, improves surface hardness by HRC 1–3 and the wear resistance of tools by the factor of above 2 as compared with standard heat treatments.
A Thermoeconomics-Based Approach to the Integrated Optimization of Design and Operation for Decentralised Energy Systems and Variable Load Conditions
Authors: Piacentino Antonio , Cardona Fabio
Published: September 2008

The many comprehensive approaches formulated for the optimization of large industrial energy systems have been rarely applied to small and medium scale units, because of the difficulties in handling a continuously variable energy demand and of the lower margins for energy and emissions saving. Today, the growing interest for decentralised energy systems in the civil sector stimulates major efforts for the optimization of such plants, with a particular focus on the control system and on a management strategy able to exploit the opportunities existing in the free energy market. In this paper a methodology is proposed for the optimization of design and operation of variable demand systems supplying different non-storable products. In such systems, efficiency penalty due to off-design operation is usually assumed as a key issue; the proposed method, however, introduces an original and meaningful interpretation of the capital depreciation cost and keeps into account the possibility for grid connected power systems to produce surplus electricity to be sold. The proposed optimization process, based on the Lagrange multipliers method, assumes either an economic indicator (the Net Present Value, NPV or the Net Cash Flow, NCF) or a function depending only on fuel consumption (as usually proposed in literature) as objective function. Main advantages of the proposed method are the high level of integration between the optimization of design and operation and the possibility to automate the algorithm in order to drive a real-time optimized control system aiming to achieve the maximum profitability or the maximum primary energy saving.
The Thermodynamic Performance of Ideal Single-Tube Air-Breathing Pulse Detonation Engine
Authors: Qiu Hua , Xiong Cha , Yan Chuan-Jun
Published: September 2008

A new single-tube air-breathing pulse detonation engine (APDE) with bypass air duct is introduced. It is composed of inlet, valve, detonation chamber, bypass air duct and nozzle. Based on the analysis of the operation cycle of the APDE, airstreams flowing into the engine can be separated into three parts: one is flowing out from the engine through the bypass; one is exhausted from the nozzle as purge gas; and the else is mixed with fuel and is combusted. And the concept of cycle factor α that represents the ratio of air quantity for detonation combustion to incoming air quantity is defined to analyze the influence of the mass distribution on the performance of APDE. Although α has no effect on the cycle thermal efficiency of APDE, it influences the engine propulsive performance. When the APDE is full fuel filled and with the equivalent incoming air-flow and fuel-flow rate, the APDE will be superior to ramjet for 0∼5 Mach if α is larger than 0.8. When the APDE and ramjet work with equal mass fuel-air ratio of combustion, the specific fuel consumption of APDE is lower than that of ramjet for 0∼5 Mach. Also, if a is higher than 0.9, the specific thrust of APDE is higher than ramjet for 0∼5 Mach. Further, the operation mode of partial fuel filling can be used to enhance the performance, but it simultaneously decreases the total thermal cycle efficiency.
Optimal Design of Suspension Parameters of Flexible Multibody Vehicle Model Based on ADAMS Software and Improved Genetic Algorithms
Authors: Zhang Jingjun , Sun Yang , Gao Ruizhen
Published: September 2008

In this paper a new method for the optimal design of suspension parameters of flexible mutibody vehicle model is presented. This method is developed based on the interface between the ADAMS software and the improved genetic algorithms in this paper. The 44 degrees of freedom flexible muitibody and the 33 degrees of freedom multi-rigid bodies vehicle model are chosen as examples for the optimal design of suspension parameters. The results show that the optimization method developed in this paper is better than the other methods.
6-DOF Single-Inertial Mass, Isotropic Accelerometer With Optical Displacement Sensors
Authors: Chapsky Vladimir , Portman Vladimir , Sandler Ben-Zion
Published: September 2008

A novel design of high isotropy single mass six-degree-of-freedom (6-DOF) accelerometer has been developed and investigated. In the accelerometer, six spatial coordinates (three linear and three angular) of the inertial mass and their derivatives are observed by simple measurement of linear displacements of six optimally chosen points of the inertial mass. Calculation of the six acceleration components is then possible according to a specially developed mathematical algorithm. To provide the isotropy of the device’s sensitivity and to achieve the accuracy in the measurement of the linear and angular accelerations, three subsystems of the device — inertial, suspension, and measurement subsystems — have a spatially symmetrical structure. To provide the symmetrical structure of the inertial subsystem, the proof mass is manufactured from uniform material and has a cubic shape. All structural cavities in this cube (light guides and a light source cavity) are symmetrical relative to three coordinate axes. To provide the symmetry of suspension subsystem 24 elastic supports (springs) are mounted by three in all vertexes of the cube in the directions of X-, Y- and Z-axes. The springs have the same dimensions and stiffness. The damping elements (the rubber insets) are inserted into the springs. They are made of the same material and have the identical dimension. The measurement subsystem consists of six differential optical displacement sensors and the light source which is mounted in the center of the cube. Each optical sensor is based on three-component position-sensitive detectors (PSD) of a segmented type. This design ensures output signals that are independent of fluctuations in light source brightness and of optical and electromagnetic interferences. Optical sensors are mounted on the frame of the accelerometer and situated symmetrically opposite to the centers of the square faces of the cube. Six orts of measurement directions form three orthogonal pairs. The experimental model of isotropic 6-DOF accelerometer with differential optical measurement subsystem is manufactured, adjusted and tested. For this purpose the experimental apparatus consisting of the stand with standard accelerometers and computer-controlled data gathering and analysis system (multi-channel amplifier, analog-digital converter and LabView software system) is developed. The preliminary experiment results show that proposed device has high level of signal isotropy and it is hoped to have a good perspective for industrial application were it can replace the complex gyroscopic and combined multi-axis devices.
Finite Element Analysis of Residual Stresses on Butt Welded Joints
Authors: Armentani Enrico , Esposito Renato , Sepe Raffaele
Published: September 2008

Localized heating during welding, followed by rapid cooling, usually generates residual stresses in the weld and in the base metal. Residual stresses in welding processes give significant problems in the accurate manufacture of structures because those stresses heavily induce the formation of cracks in the fusion zone in high strength steels. Therefore, estimating the magnitude and distribution of welding residual stresses and characterizing the effects of certain welding conditions on the residual stresses are deemed necessary. In this work, residual stresses and distortions on butt welded joints are numerically evaluated by means of finite element method. The FE analysis allows to highlight and evaluate the stress field and his gradient around the fusion zone of welded joints, higher than any other located in the surrounding area. Temperature-dependent material properties, welding velocity, external mechanism constraints, technique of ‘element birth and death’ and latent heat of fusion are also taken into account. Some numerical results are compared with experimental data showing a very good correlation.
Sound Absorption Prediction Using Finite Element Model Based on Modified Biot Poroelastic Model
Authors: Ohadi A. R. , Moghaddami M.
Published: September 2008

Simulation of the porous materials based on modified Biot poroelastic model is done in this paper, and the obtained results are compared with the equivalent fluid model available from the literature. The effect of physical parameters of the solid phase and also boundary conditions are studied. For this purpose, the modified Biot equations are obtained in terms of a reduced number of variables. In order to investigate the acoustical behavior of porous materials, the governing equations are simulated using the weighted residual finite element code, developed by the authors. The absorption coefficient diagrams of a selected material are obtained and compared for modified Biot poroelastic model and equivalent fluid model. In addition, the effects of the physical parameters of the solid phase and boundary conditions on the acoustical treatment of the material are studied.
Study of a New Transmission System for Electric Scooters
Authors: Chang Shinn-Liang , Hsieh Long-Chung , Liu Jen-Yu , Chen Yu-Ren , Tsai Jia-Ling
Published: September 2008

Electric scooters are the most popular form of transport for old and disabled people in Taiwan and its popularity is fast increasing as people are living longer and longer. The main components of an electric scooter includes battery, motor, motor driver, and a transmission system, whose characteristics determine the overall energy efficiency. The commonly used transmission system of an electric scooter consists of a compound gear train (or a simple gear train) and a bevel gear differential, the quality of the former of which significantly influences the efficiency and noise level. In this paper, a new transmission system for use in an electric scooter is proposed. The finite element method was applied to evaluate the stress level experienced by the gears in the compound gear train. A test rig was also set up to compare the performance of the proposed transmission system with an existing commercial product. The new design was shown to produce better performance characteristics in terms of efficiency and noise level than the commercial product and has since been successfully manufactured and is currently being sold worldwide.
Effects of Mandrel Shape and Dimension on Deformation Behavior for Hot Mandrel Bending
Authors: Jang Soon-Tae , Naoi Hisashi , Kurita Takashi
Published: September 2008

Elbows, which belong to butt-welded steel pipe joints, are used in piping of various plants. Elbows are mainly manufactured by hot mandrel bending. In hot mandrel bending, short straight pipes are inserted into an inner tool of mandrel and are bent at specified bending radius, while they are compressed by pusher from one end of pipes and their outer diameter are expanded. Elbows manufactured by this bending process have small deviation in wall thickness and also high accuracy in roundness, even when they are processed into short bending radius. Shape and dimension of mandrel are designed by trial and error through many experimental tests. However, there are a few research works on hot mandrel bending. We focus on expansion ratio and bending radius ratio of mandrel, which are main variables, and greatly affect deformation behavior of hot mandrel bending. And we conducted experiment and numerical analysis using mandrels which have several kinds of expansion ratio and bending radius ratio. Following items are clarified by this research work: At extrados, axial strain decreases slightly, when expansion ratio increases. As a results, neutral axis of bending moves from extrados toward intrados by increasing of expansion ratio. And at intrados, wall thickness strain at intrados decreases, when expansion ratio increases. Wall thickness strain at intrados decreases, when bending radius ratio increases. Forming load increases, when expansion ratio increases and with bending radius ratio decreases. When experimental conditions do not coincide with optimized expansion ratio and bending radius ratio, deviation of wall thickness occurs in elbow.
Traumatic Events in Human Head: Biomechanical Insight by Means of a Finite Element Model
Authors: Belingardi Giovanni , Chiandussi Giorgio , Gaviglio Ivan
Published: September 2008

Head injuries due to traumatic events in case of head impact are one of the main causes of death or permanent invalidity in vehicle crash. The main purpose of the present work is to evaluate pressure and stress distributions in bones and brain tissues of a human head due to an impact by means of numerical simulations. Pressures and stresses in the different zones of the head can be related to the main brain injuries as verified by head traumatology doctors. The availability of a numerical model of head allows to quantify the relationship between type and intensity of the impact and the possible head injury. This capability represents a relevant step torward an effective traumatic injury prevention. The proposed numerical model is quite complex although some simplifications have been introduced like modeling all the inner organs as a continuum without sliding interfaces or fluid elements. Geometrical characteristics for the finite element model have been extracted from CT (Computer Tomography) and MRI (Magnetic Resonance Image) scanner images, while material mechanical characteristics have been taken from literature. The model has been validated by comparing the numerical results and the experimental results from literature. The protecting action of the ventricles and of several membranes (dura mater, tentorium and falx) has been evaluated.
Analysis of Shock Absorber Characteristics for Drillstrings
Authors: Elsayed M. A. , Aissi Cherif
Published: September 2008

Drillstrings are used extensively to drill for oil, gas and geothermal energy. Due to their construction, they are subject to instability which causes excessive vibrations. These vibrations cause extensive damage to the bit and drillstring. In this paper, we analyze the design parameters of a shock absorber (typically referred to as a shock sub) to be placed above the bit for the purpose of minimizing vibrations. The analysis is based on a laboratory drilling system at Sandia National Laboratories (SNL) referred to as the Hard Rock Drilling Facility (HRDF). We show that the choice of spring stiffness and damping are very critical to minimizing vibrations. Too weak or too stiff a spring does not lead to reduction in vibrations. Similarly, too low or too high a damping constant is not effective at dissipating energy. Even though a test rig is used to represent the drillstring, the methodology is applicable to actual drillstrings utilized in the field. The results are validated experimentally at SNL.
Thermal Fatigue Prediction for Leadless Solder Joint of TFBGA
Authors: Chang Chia-Lung , Lin Tzu-Jen , Lai Chih-Hao
Published: September 2008

Nonlinear finite element analysis was performed to predict the thermal fatigue for leadless solder joint of TFBGA Package under accelerated TCT (Temperature Cycling Test). The solder joint was subjected to the inelastic strain that was generated during TCT due to the thermal expansion mismatch between the package and PCB. The solder was modeled with elastic-plastic-creep property to simulate the inelastic deformation under TCT. The creep strain rate of solder was described by double power law. The furthest solder away from the package center induced the highest strain during TCT was considered as the critical solder ball to be most likely damaged. The effects of solder meshing on the damage parameters of inelastic strain range, accumulated creep strain and creep strain energy density were compared to assure the accuracy of the simulation. The life prediction equation based on the accumulated creep strain and creep strain energy density proposed by Syed was used to predict the thermal fatigue life in this study. The agreement between the prediction life and experimental mean life is within 25 per cent. The effect of die thickness and material properties of substrate on the life of solder was also discussed.
New Methods of Increasing Efficiency of Steam Turbine Plants
Authors: Vasserman Aleksandr A. , Shutenko Maxim A.
Published: September 2008

This paper describes two methods of increasing steam turbine plants efficiency by raising average temperature of heat supply in thermodynamic cycle. In the first method it is proposed to raise maximum temperature of steam in the cycle by mixing steam, exiting from super-heater of boiler, with products of combustion of methane in oxygen. In the second method it is proposed to raise maximum temperature of working substance and to continue heat supply on major part of expansion process in the turbine in order to make it quasi isothermal. This is done by mixing steam, exiting from super-heater of boiler, with products of combustion of hydrogen in oxygen and excess of hydrogen. Combustion of hydrogen during expansion in the turbine due to gradual admixing of oxygen to the working substance will produce heat required for quasi isothermal expansion. Methods yields increase in effective efficiency 7.9 and 18.8% respectively. Repayment term of modified plants will be 3.8 years for first method and 2.8 years for the second. Implementation of either of these methods will result in output of considerable quantities of pure carbon dioxide, which can be utilized or buried thus reducing its release into atmosphere.
The Effects of Load and Velocity on Friction and Interface Temperature of CGRP Sliding Against Smooth Stainless Steel
Authors: Yousif B. F. , El-Tayeb N. S. , Yusaf T. F.
Published: September 2008

This paper presents an experimental investigation to study friction and interface temperature characteristics of chopped strand mat fiberglass (type-R) reinforced polyester (CGRP) sliding against smooth stainless steel. Pin-on-disk (POD) apparatus is used to perform the experimental tests under dry sliding condition at room temperature. Several parameters are considered, namely load (30, 60 & 90N), sliding velocity (2.8, 3.52 & 3.9m/s) and sliding distance (0–2.51km). Three different orientations of chopped strand mat with respect to sliding direction, Parallel (P), Anti-parallel (AP) and Normal orientations (N) are investigated. Continuous measurements of friction forces using strain gauges, and interface temperatures using infrared thermometer are performed. In addition, Scanning electron microscopy (SEM) is used to study the worn surface to verify the results. Experimental results show that specimen’s orientations and the tested parameters play a major role in controlling friction and interface temperature characteristics of the CGRP/stainless steel. Maximum friction coefficient was taken place in AP orientation at 3.5 m/s and 2.5km, which was about 0.6. Although, AP-orientation had higher friction interface temperature in comparing to P and N-orientations, which was about 48°C at 3.9m/s and 2.5km.
Adsorption-Induced Surface Stress Effect on the Resonance Behavior of a Quartz Crystal Microbalance
Authors: Zhuang H. , Lu P. , Lim S. P.
Published: September 2008

The effect of adsorption-induced surface stress on the response of a quartz crystal microbalance (QCM) with reduced size is investigated. The model proposed here incorporates the adsorption-induced surface stress into the basic equations, where surface stress is characterized by experimentally determined parameters. Some numerical examples show that as the dimensions of a QCM shrinks, surface stress trends to play an important role in sensing, and is more significant for smaller scales. Therefore, the measured resonance frequency shift of a QCM is induced by combination of mass loading and adsorption-induced surface stress. The model discussed here can be used to provide an insight into the fundamental understanding of the effect of adsorption-induced surface stress on micro- and nano-QCM response of deposited metal films, or bio-molecular adsorption.
A Design and Simulation of CALUMA (CAssino Low-Cost hUMAnoid Robot)
Authors: Nava Rodriguez Nestor Eduardo , Carbone Giuseppe , Ceccarelli Marco
Published: September 2008

At LARM in Cassino a research line has been focused on the design of robotic systems with low-cost easy-operation features as challenges for a user-oriented Robotics. In this frame a final project has been stated to design and built a low-cost easy-operation humanoid robot as a systems summarizing experiences and prototypes that have been carried out at LARM. A humanoid robot, named as CALUMA (CAssino Low-cost hUMAnoid robot) has been designed and described by using suitable models and 3D-CAD kinematic simulations in order to define feasible design and operation. A dynamic simulations have been carried out by using ADAMS software in order to study the dynamical aspects of basic operation with the aim to optimise the design and operation programming. Results of this design activity through dynamical simulation are reported in this paper.
The Subjective Aspects of Design Structure Matrices: Analysis of Comprehension and Application and Means to Overcome Differences
Authors: Maurer Maik , Pulm Udo , Ballestrem Felix , Clarkson John , Lindemann Udo
Published: September 2008

Design Structure Matrices (DSMs) are a widely spread and useful tool for structuring and analysing design processes and related aspects such as products themselves, organisations, etc. Though this tool is simple, yet quite powerful, problems might arise in using them due to the subjectivity of the set up model within the DSM, as it is with every model building exercise. This contribution looks at the individual differences in filling out a DSM, the reasons for those differences, as well as means to overcome them. This covers a clear procedure for using DSMs, extended tools using and supporting DSMs, and a better understanding of this matrix approach. The latter covers different issues and “linkage types” that can be addressed by a DSM and its use in a system theory context. It also emphasises that DSMs are just one method using a matrix approach, which is only one representation of a graph or a network, with other methods using similar approaches and covering other useful aspects. A simple, yet important contribution of our research is the appropriate direction of DSMs, i.e. the dependencies going from rows to columns or vice versa, since this is an often discussed subject concerning DSMs.
Phase Interaction in Hydroxylapatite/LaPO4 Composite
Authors: Ergun Celaletdin , Halloran John W. , Bae Chang-Jun , S¸ahin Filiz C¸ınar
Published: September 2008

Hydroxylapatite composites with lanthanum phosphate were prepared with pressureless air sintering for 2 hours at different temperatures between 500°C and 1300°C. The interaction between the phases was monitored with XRD analysis. At sintering temperatures higher than 700°C, hydroxylapatite and lanthanum phosphate phase reacted and formed Ca8 La2 (PO4)6O2 as byproduct. In the mean time, hydroxylapatite decomposed and formed tricalcium phosphate.
Chaos Synchronization in a Class of Chaotic Systems Using Kalman Filter and Feedback Linearization Methods
Authors: Salarieh Hassan , Alasty Aria
Published: September 2008

In this paper a combination of Kalman filter and feedback linearization methods is used to present a controller-identifier system for synchronizing two different chaotic systems. The drive system has some unknown parameters which are supposed to have linear form within its dynamic equation. An identifier based on Kalman filter approach is designed to estimate the unknown parameters of the drive system, and simultaneously a feedback linearizing controller is used to synchronize the chaotic behavior of the response system with the drive chaotic system. The method proposed in this paper is applied to the Lure’ and the Genesio dynamic systems as the drive and response chaotic systems. The results show the high performance of the method to identify and synchronize two different chaotic systems with unknown parameters and in presence of noise.
Downsizing of SI Engines by Turbo-Charging
Authors: Police Giuseppe , Diana Salvatore , Giglio Veniero , Iorio Biagio , Rispoli Natale
Published: September 2008

During most of the operating conditions occurring on a vehicle driving cycle, a reciprocating IC engine works at low load and low speed, with poor fuel efficiency. In this regard downsizing appears as a major way of improving fuel consumption of Spark Ignition Engines. In fact, downsized engines have smaller friction surfaces and can work on the same vehicle and on the same driving cycle with higher mean effective pressure and higher efficiency. In this paper the main technical trends and problems related to SI engine downsizing are reviewed and discussed. Assuming a stoichiometric boosting, a simulation code is used to outline a strategy to improve low end torque of a downsized DISI engine. In the numerical experiments volumetric efficiency is enhanced by an optimal configuration of the inlet system. For the same objective, assuming a Variable Valve Timing, a proper selection of maximum lift and opening duration of the inlet valve allows a reduction of the reverse flow of fresh mixture. The optimization of the exhaust system and of the lift diagram of the exhaust valve leads both to the enhancement of volumetric efficiency and to the reduction of residual exhaust gas, with beneficial effects on knock phenomenon. An evaluation of fuel consumption gains resulting from downsizing is made as well, with reference to a New European Driving Cycle.
Experimental Calibration Method to Validate Flame Front Propagation Data Produced by Virtual Engine Model (VEM) Computation
Authors: Pontoppidan M. , Bella G. , Fabrizi C. , Ubertini S.
Published: September 2008

The main objective of the present paper is to describe the research work accomplished to develop a combined experimental/numerical calibration method, which has the capability to validate combustion models embedded in an advanced 3-D numerical engine simulation tool. The first part of the paper describes the background for the necessity to use 3-D numerical simulation techniques as well as the basic setup requirements for both the virtual engine model and the real engine experimental support. The paper continues with a description of the method used to derive a 3-D flame front propagation function from direct true-color combustion visualizations. Finally a validation of the suggested method is presented by comparing the obtained results with those produced by an independent thermodynamic computation approach.
PhotoMEA: A New Step Towards Total Optical Analysis of In Vitro Neuronal Networks
Authors: Ghezzi Diego , Menegon Andrea , Pedrocchi Alessandra , Mantero Sara , Valtorta Flavia , Ferrigno Giancarlo
Published: September 2008

Light stimulation of neurons is a promising approach for investigating the molecular mechanisms at the basis of neuronal physiology and plasticity. In particular, flash photolysis of caged compounds offers the unique advantage of allowing to quickly change the concentration of either intracellular or extracellular bioactive molecules, such as neurotransmitters or second messengers, for the stimulation or modulation of neuronal activity. In this field of research, we describe a simple laser-based set-up for the local activation of caged compounds. The coupling of a UV laser diode to a small-core optical fibre allows to reduce the uncaging area and to quickly change the stimulation point. The actual localisation of the light stimulation is determined using a caged fluorescent compound (dextran, DMNB-caged fluorescein). The efficiency of our set up for neuronal stimulation is tested with a caged neurotransmitter (MNI-caged-L-glutamate). Activation of caged glutamate evokes neuronal responses that are recorded using a MicroElectrode Array system and/or following the variations in the concentrations of the Cai2+. This work shows that our laser-based set-up is a powerful tool for local activation of caged compound allowing a unique opportunity to follow the effects of local neuronal pathways on neuronal network activity, for instance during pharmacological and toxicological treatments.
A Hybrid Optimization Method Research for Aeroengine Performance Seeking Control
Authors: Zhu Yu-Bin , Fan Si-Qi , Zhang Xiu-Hua , Li Hua-Cong
Published: September 2008

According to the optimization control modes of performance seeking control (PSC) in aeroengine, the aeroengine performance optimization problems which were described as a linear programming problem are studied. In respect that the linear programming is only guaranteed to converge to a local minimized and nonlinear method is much more computation, a hybrid algorithm based on linear programming (LP) and Model-Assisted Pattern Search (MAPS) is provided in this paper. And the hybrid optimization method is used for aeroengine control. Digital simulations are conduced in maximum thrust mode and minimum fuel mode in this paper. Simulation results demonstrate that the engine performance can be improved further and calculation time can be reduced rapidly by using hybrid algorithm.
Dynamic Behavior Analysis of a Floating Artificial Base-Building Assumed as Hybrid Structure Due to Wave Forces
Authors: Saijo Osamu , Eto Hiroaki , Maruyoshi Koichi
Published: September 2008

Dynamic response analysis of a floating artificial base-building due to wave forces was studied, which structural system was named as a hybrid structural system. It was assumed to be constructed by the combination of elastic plate and framed structure. The hybrid structure system enabled the matrix size to reduce in FEM analysis, and the improvement of the calculation efficiency was succeeded. The developed calculation tool made it possible to examine the dynamic characteristic of the building on the floating base under the various wave conditions. The natural frequency analysis and the structural response analysis were capable, besides the evaluation of habitability in relation with oscillation caused by wave motion became possible using the diagram of our result of the research.
Study on the Mechanical Properties of AZ31 Magnesium Alloy Products Under Hot Extrusion Process
Authors: Hsiang Su-Hai , Lin Yi-Wei
Published: September 2008

Magnesium alloy parts have the merits of low specific gravity, high specific strength, electromagnetic wave-proof shelter, and recyclability; therefore, it has been extensively applied to 3C and car industries. However, the processing and forming of magnesium is quite difficult to control due to magnesium’s hexagonal close-packed (HCP) structure, making the slipping face of itself less than the FCC material. Currently, common processing methods of magnesium alloys are die casting, semi-solid forming, and plastic forming. In the employment of a fixed-speed method for extrusion, the extruded sheet had serious defects in the forms of cracks on the surface. Hence, in this research, AZ31 magnesium alloy sheet metals were processed by hot extrusion using a variable speed method. The formability of AZ31 sheets under converging dies was investigated. Three converging dies with semi die angle of 20°, 30°, and 40° were used. Experiments were conducted and analyzed utilizing the Taguchi method. L9 orthogonal array was used to design the experiments under extrusion ratio of 35.9. Four important process parameters considered in this research are the heating temperature of the billet (320°C, 340°C and 360°C), the temperature of the container (300°C, 350°C and 400°C), the initial speed of extrusion (2mm/sec, 3mm/sec and 4mm/sec), and the lubricants (boron nitride, molybdenum disulphide and graphite) applied in the extrusion. The influences of these parameters to the extrusion load and the resulting mechanical properties were investigated. Moreover, the microstructure of the extruded sheets was observed to provide better insight of the formability. As a result, the optimal combinations of the process parameters were determined for the maximum tensile strength.
Model-Based Identification of a Shaft Bow Caused by Rubs in the Generator of a Power Unit
Authors: Vania A.
Published: September 2008

The dynamic behavior of rotating machines due to faults can be simulated with model-based methods in which the faults are modelled with suitable sets of equivalent excitations. When rotor-to-stator rubs occur the friction forces can cause time-varying thermal bows of the shafts. The equivalent bending moments that cause the shaft bows can be estimated with model-based identification methods developed in the frequency domain: these techniques minimize the error between the machine experimental vibrations induced by the rubs and the system response provided by the simulating model. In this paper the results of the analysis of the experimental vibrations of a large turbine-generator unit that was subjected to partial-arc rubs are shown and discussed along with the diagnostic strategy used to identify the fault severity and the location of the shaft cross-sections where the heaviest rubs occurred. Comparisons between experimental data and simulated vibrations caused by the identified fault are shown.
Drilling Thrust and Torque Prediction of Viscoplastic Materials
Authors: Vaghefpour Hossein , Nayebi Ali
Published: September 2008

A model for drilling of viscoplastic materials is presented. An analytical model is developed for predicting thrust force and torque in the drilling with a twist drill. The thermomechanical properties are accounted for describing the material flow in the primary shear zone and at the element-chip interface. A temperature friction law is introduced. The approach is based on the representing the cutting forces along the cutting lips as a series of oblique elements. Similarly, cutting in the chisel region is treated as orthogonal cutting with different speeds depending on the radial location. The section forces obtained by the model are combined to determine the overall thrust force and drilling torque. The results of the proposed model are compared with experimental results and a good agreement is obtained.
Supersonic Flutter of Functionally Graded Plates in a Thermal Environment
Authors: Navazi H. M. , Haddadpour H.
Published: September 2008

In this paper, an analytical investigation intended to determine the flutter margin of supersonic functionally graded panels is carried out. For this purpose, piston theory aerodynamics has been employed to model quasi-steady aerodynamic loading. The material properties of the plate are assumed to be graded continuously across the panel thickness. The variation of temperature-dependent thermoelastic properties follows a simple power-law distribution in terms of the volume fraction of the constituent materials. The effects of compressive in-plane loads and static pressure differential are studied. Both uniform and through the thickness nonlinear temperature distributions are also considered. Hamilton’s principle is used to determine the coupled partial differential equations of motion. Using Galerkin’s method, the derived equations are transformed into a set of coupled ordinary differential equations, and then solved by numerical time integration. Some examples comparing the flutter margin of FG panels with that of plates made of pure metals and pure ceramics are presented. The results of the present study are compared with those of the previous works, where finite element method was used. It is shown that the use of functionally graded materials can yield an increase or decrease of the aeroelastic stability in the supersonic flow for different regions.
Laminar Vapor-Gas-Drop Flow in Vertical Ribbed Tubes
Authors: Shokouhmand Hossein , Ahmadzadegan Amir
Published: September 2008

A 3-dimensional Eulerian finite volume approach is used to predict heat and mass transfer in a laminar two-phase gas-vapor-drop flow in a ribbed tube. It is well known that extending heat transfer area enhances heat transfer and this is the base of studying ribbed faces. It is shown that ribbed faces can be more effective in two phase mist flows since evaporation and deposition of droplets mostly take place near hot surface [1]. Parallel ribs are analyzed. Vapor mass concentration and droplets diameter are calculated by separate transport equations. Analysis is continued from thermally inlet to fully developed vapor gas flow. This model can be used in many applications to understand the effects of changing parameters of hydrodynamics and thermodynamics of the flow, when the flow regime is changed from turbulent to laminar. The results are compared to single phase gas flow.
A CAD/CAE System for Structures of Dockside Container Cranes
Authors: Wang Chonghua , Li Hua
Published: September 2008

Dockside container cranes have huge complex structures which have various kinds of types and lots of parameters for design. Moreover the finite element analysis must be carried out on the structures. An integrated CAD/CAM system for crane’s structures is introduced in this paper. A CAD platform of 3D parametric model family is built to allow generation of feasible configurations of crane products. Using Visual C++ and the second exploiting software kit, an integration method of CAD/CAE which includes regeneration of 3D parametric model, synchronous updating and analysis of FEA model is achieved.
Performance of Valveless Diffuser Micropumps Under Harmonic Piezoelectric Actuation
Authors: Ahmadian M. T. , Saidi M. H. , Mehrabian Amin , Bazargan M. , Kenarsari S. D.
Published: September 2008

Valveless piezoelectric micropumps are in wide practical use due to their ability to conduct particles with absence of interior moving mechanical parts. The objective of this paper is to obtain the fluid flow response to actuation frequency of a passive diffuser valve under harmonic pressures. In this regards a 2D model of a micropump valves and chambers is analyzed. The analysis is performed for 10Kpa back pressure on micropump chamber and actuation frequencies within the range of 1Hz to 10 KHz. Results show the highest velocity in the direction of diffuser axis occurs at the narrow diffuser neck while flow direction reverses every half period. For low frequencies, a parabolic velocity profile is observed at the valve midway while, instabilities with the tendency of transition to boundary layer dominant profile is observed for high actuation frequencies. Oscillating flow in diffuser indicates existence of high shear stress regions near the wall along with the flow reversal in the center at high frequencies. Both valve and pump net flow rate decrease drastically as the frequency approaches a certain value. From electrical analogy viewpoint, nozzle/diffuser passive valves can be modeled as Low Pass Filters (LPF). The results are in good agreement with the relevant analytical findings. Similar to analytical results, flow rate is approximately in phase with actuation at low frequencies but phase shift ascends as actuation frequency is increased. The main head loss of flow occurs at the diffuser valves while sudden contraction and expansion of streamlines at the diffuser entrance and exit involve only 22% of the total energy. The results are in agreement with the previous experiments of micropump flow at high frequencies.
Analysis of Plastic Helical Gear
Authors: Jabbour Toni , Asmar Ghazi , Ghaith Chadi
Published: September 2008

The objective of this work is to present a mathematical model which studies helical gears made of a material with a small modulus of elasticity, when one or more pairs of teeth mesh prematurely during engagement. This phenomenon may lead to the modification of the load distribution on the teeth which are initially in contact and to a kind of interference causing additional tooth wear of the gear. In this case, the calculation of the contact ratio must account for the real number of pairs of teeth in contact. This is especially important when large deformations occur as is confirmed in the results presented to confirm the validity of the proposed method.
The Influence of Injection Pockets on the Performance of Tilting-Pad Thrust Bearings: Part I — Theory
Authors: Heinrichson Niels , Santos Ilmar Ferreira , Fuerst Axel
Published: September 2008

This is Part I of a two-part series of papers describing the effects of high pressure injection pockets on the operating conditions of tilting-pad thrust bearings. A numerical model based on the Reynolds equation is developed extending the three dimensional thermo-elasto-hydrodynamic (TEHD) analysis of tilting-pad thrust bearings to include the effects of high pressure injection and recesses in the bearing pad. The model is applied to the analysis of an existing bearing of large dimensions and the influence of the pocket is analyzed. It is shown that a shallow pocket positively influences the performance of the bearing as it has characteristics similar to those of a parallel step bearing.