bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Thermal Buckling Analysis of FGM Shallow Arches Under Linear Temperature Gradient
Authors: Asgari H. , Eslami M. R.
Published: October 2014

In this study non-linear thermal buckling of circular shallow arches made of functionally graded materials subjected to a linear temperature gradient is investigated. For this purpose, a functionally graded circular shallow arch is considered that its strain-displacement relation follows the Donnells nonlinear shallow shell theory. The material properties are varied smoothly through the arch thickness according to the power law distribution of the volume fraction of constituent materials. Also, material properties are considered temperature-dependent. The classical single layer theory assumptions that are reasonable for slender arches are implemented. To investigate the large deformations of such arch, the von-Karman type geometrical nonlinearity is utilized that is suitable for moderately large class of rotations. The virtual displacement principle and calculus of variation are employed to derive the governing equilibrium equations and complete set of boundary conditions of the FGM arch. The adjacent equilibrium criterion is employed for the stability analysis of the FGM arch. An analytical approach is accomplished and a closed-forms solution for thermal bifurcation points of the FGM shallow arches is presented. Also critical bifurcation loads corresponding to the critical temperatures with the presence of non-linear pre-buckling deformations is obtained. Illustrative results examine the effect of various involved parameters such as power law index, opening angle, geometric parameter (or otherwise length to thickness ratio). Obtained numerical results represent that, in most cases, thermal bifurcation for the FGM arches occurs in the high temperatures and the critical buckling temperatures are approximately high even for slender FGM arches. Also effective of ceramic or metal rich area at the bottom surface of the FGM arch is investigated and results are presented for both cases and are compared together. Varieties between this two cases due to contrast between material and structural stretching-bending coupling effect. Results presented illustrative the ceramic rich area at the bottom surface cause the higher critical buckling temperatures for the FGM arches.
Design and Development of Instrumentation and Data Acquisition for a Photovoltaic Driven Community Scale RO Desalination System and its Performance Studies
Authors: Ahmad Naseer , Sheikh Anwar Khalil , Elshafie Mostafa , Al-Qahtani Hussain
Published: October 2014

This work is related to the design and development of instrumentation, data acquisition and graphical user interface of Photovoltaic driven Reverse Osmosis system for monitoring and performance evaluation purposes. Installed PV system comprises of 12 PV panels, trackers, batteries and inverter whereas RO system is equipped with pre filters, pumps, energy recovery devices and filtration membranes. Proper instrumentation is carried out in PV system to measure the irradiation, temperatures, voltage and current at various points. Moreover various sensors are used to measure the pressures, flows, salinities at RO unit. Signal conditioning circuits are designed to adjust sensor output signals for computer interface. A simple moving average filter is used to suppress the measurement noise. The experimental investigation of PVRO system is carried out by using LabVIEW interface capabilities. The developed system reveals and stores the pronounced impact of measured variables on the PV output power and specific energy consumption of the RO filtration system. The online data display in multi-scale window frame is very informative for system operation and analysis. During the experimental run of PVRO system using the developed DAQ system, the PV system generated 7.5kWh of energy during the whole day operation. Feed water having 7100ppm salinity and its flow rate was set to 850 lit/hour by adjusting the RPM of the high pressure pump. Clean water flow rate is recorded to be at 465 lit/hour having salinity of 115 ppm during the RO operation. Specific energy consumption of RO system comes out to be 2.083kWh/m3 for 7100ppm salinity of feed water.
A Methodology for Workspace Identification of Parallel Robots Using Parametric Sweep Search Method
Authors: Abdullah CheZulkhairi , Saadat Mozafar , Rakhodaei Hamid
Published: October 2014

In this paper, a methodology for real time identification of various singularities for various workspace types of parallel robots is proposed. Python 3D simulation software has been developed to position the moving platform of the robot’s CAD model through pre-defined rules in order to solve specific problems including singularity identification, obstacle avoidance, and path planning. The system is designed to identify the moving platform’s best possible pose. Boolean logic is used to identify valid path trajectory through parametric sweep search method. Joint constraints are checked to validate the platforms’ positions using the actuators’ stroke length, their angles, and any possible collisions. Solutions for any desired pose, based on line collision and mesh model algorithms, are then found. The path, position and workspace data are verified against a kinematic model of the robot, developed in Solid works and Matlab software tools. The simulation system has been successfully tested using various n-dimensional interpolations based on the given case study.
Influence of Real Car Longitudinal Acceleration Regime on the Vertical Vibrations of a Dynamic Car Simulator
Authors: Dumitriu Dan N. , Brişan Cornel , Munteanu Ligia
Published: October 2014

For dynamic car simulators, it is obvious that the longitudinal motion cannot be fully reproduced, the possibility to simulate longitudinal motions being generally reduced to less than 1m. In our case, a four post shaker is intended to be built as dynamic car simulator. Each post shaker, one under each car wheel, is aimed to generate mainly vertical vibrations and lateral motion. Since the displacements/motion in the longitudinal direction can only be partially reproduced, our problem was how to compensate the impossibility of fully reproducing the longitudinal motion by at least taking into account the influence of the longitudinal motion on the vertical vibrations.

In this paper a simplified 4 DOF “bicycle” model is used for vertical dynamics, instead of a 7 DOF full car vertical dynamics model, which will be considered in a further study.

On the other hand, the vertical vibrations are different for the same car riding on the same road, but for different acceleration regimes: 1) null acceleration (e.g., 60km/h constant speed); 2) uniform acceleration from 10 to 110 km/h (during 8 seconds), followed by uniform deceleration from 110 to 10 km/h (during another 8 sec), then uniform acceleration from 10 to 60 km/h (during the last 4 sec of the simulation).

In order to reproduce in the dynamic car simulator the vertical vibrations of the above-mentioned longitudinal motion regimes (involving displacements of tens of meters), the following steps are proposed: a) direct dynamics CARSIM computer simulations of the car motion and its interaction with the road; b) inverse dynamics of car vertical model (4 degrees of freedom), using as input the following parameters computed in step a): the vertical displacements and velocities of the sprung mass and of the front and rear wheel centers as well as the pitch angle of the sprung mass and its rate. These inverse dynamics computer simulations are performed using an in-house Matlab software programming only the 4-DOF vertical car/road interaction (2D “bicycle” model in the pitch plane, no roll motion considered), without considering any longitudinal motion.

The output of these inverse dynamics computer simulations, using the in-house Matlab software, is the “modified/distorted road profile”. Thus, the modifications brought to the real road profile are aimed to compensate the lack of the longitudinal degree of freedom in the dynamic car simulator, in order to reproduce the vertical vibrations of the above-mentioned longitudinal motion regimes (so that to encounter the same car vertical displacements and accelerations for the in-house Matlab simulation, as for the CARSIM simulation).

Results are presented in order to show how the real road profile is modified/distorted in order to cope with this impossibility to simulate the road profile in dynamic car simulators, without huge costs.
Mechatronic Multicriteria Profile (MMP) for Conceptual Design of a Robotic Visual Servoing System
Authors: Mohebbi Abolfazl , Achiche Sofiane , Baron Luc
Published: October 2014

Mechatronic systems are a combination of cooperative mechanical, electronics and control components. The high number of their components, their multi-physical aspect, the couplings between the different domains involved and the interacting design objectives makes the design task very tedious ad complex. Due to this inherent complexity, a concurrent systematic and multi-objective design thinking methodology is crucial to replace the often used sequential design approach that tends to deal with the different domains separately. In this research we present a new multi-criteria profile for mechatronic system performance evaluation in conceptual design stage. The newly introduced Mechatronic Multi-criteria Profile (MMP) includes various quantitative members such as intelligence, reliability, complexity, flexibility and cost. A nonlinear fuzzy integral called 2-additive Choquet Integral will be used for the aggregation of criteria and fitting the intuitive requirements for decision-making in the presence of interacting criteria. Finally, the effectiveness of the proposed method will be validated via a case study of designing a robotic visual servoing system.
Numerical Algorithm for Non-Stationary Covariance Analysis of Nonlinear Mechanical System Using Equivalent Stochastic Linearization
Authors: Marano Giuseppe Carlo , Acciani Giuseppe , Abrescia Angelamaria
Published: October 2014

A quite important topic of structural dynamics is deterministic mechanical systems subjected to stochastic dynamic actions, such as for wind or earthquake. IN such cases structural response have to be properly evaluated by a stochastic approach. Unfortunately for nonlinear mechanical systems only in a very few cases exact solutions are available, and usually simply approximate solutions should be used. A well known one is stochastic equivalent linearization, easy and simple from the conceptual point of view. Moreover it needs of specific numerical techniques to be properly implemented, whose complexity increases in case of non stationary conditions.

In this paper a procedure to solve covariance analysis of stochastic linearized systems in case of non stationary excitation is proposed. The no stationary Lyapunov differential matrix covariance equation for the linearized system is solved by using a numerical algorithm that updates linearized system matrix coefficients step by step. This by a predictor-corrector procedure applied to a Euler-implicit integration scheme for the matrix covariance analysis.

It is described in details to be simpler implemented by other researchers, and then applied to a typical and important applicative case, that is seismic response of a Bouc Wen Single Degree of Freedom (SDoF) system. Seismic input processes is modeled as linear filtered white noise non stationary separable process. Accuracy and computational costs are analyzed showing the efficiency of the proposed integrating procedure.
Static Balancing of a Parallel Kinematics Machine With Linear-Delta Architecture
Authors: Martini Alberto , Troncossi Marco , Carricato Marco , Rivola Alessandro
Published: October 2014

The study deals with the compensation of gravity loads in closed-loop mechanisms as a possible strategy for enhancing their working performance. This work focuses on the Orthoglide 5-axis, a prototypal parallel robot for milling operation, characterized by linear-delta architecture with two further serial DOFs. Starting from a general theory formerly proposed by the authors, gravity compensation of the mechanism is analytically carried out. The statically balanced Orthoglide 5-axis can be obtained by installing on one leg a proper set of extension springs and a simple additional linkage. A feasible design solution for developing the device in practice is presented. The proposed balancing device can be implemented with minor modifications of the original robot design, thus appearing a profitable solution to be possibly extended to other machinery with similar architecture.
Experimental Analysis of the Transition Between Veering and Crossing on a Two-Beam System
Authors: Giannini Oliviero , Sestieri Aldo
Published: October 2014

When there is a parameter varying in a system, so that one natural frequency approaches another one, the phenomenon of veering is generally found and highly coupled modes are the emerging characteristic of this dynamic behavior. It is far more difficult to find systems that instead of a veering present crossing between modes, and the crossing phenomenon is almost unreported in the scientific literature, unless the case of uncoupled modes is considered.

In this paper, the two-modes interaction is presented. In particular, mode veering and mode crossing are introduced and investigated through a simple analytic 2-dof model that allows for closed-form solution. Then, an experimental setup, appropriately designed to study the two-modes veering and crossing is presented and experimental evidences of both phenomena are measured showing the main characteristics of such modal interaction..
Compensation System for Thermal Deformations of Ballscrews
Authors: Kowal Michał , Staniek Roman
Published: October 2014

Accurate ballscrews are vital components of precise machine tool drive systems. As determined by direct measurement systems, the ballscrew positioning error has no bearing on the final positioning accuracy of the axis. For economical reasons, however, most machine tools are equipped with indirect measurement systems, in which errors stemming from thermal expansion of the ballscrew constitute approximately 60% of the kinematic chain error sum. Moreover, the currently observed boost in productivity of modern CNC machine tools leads to significant amplification of energy dispersal values in the nut-screw systems, due to the increased positioning velocity of the controlled axes. This, in turn, contributes to a rise of positioning error values through thermal expansion of the aforementioned ballscrews. This article deals with technological and constructional problems of screw lengthening compensation. It enumerates methods of thermal expansion-based error compensation as attained through utilization of indirect measurement systems. Finally, it presents experimental data indicating the possibility of effective screw lengthening compensation, thus proposing an alternative to the currently applied compensation systems.
Applying Actual Development Progress Into Education
Authors: Albrecht Katharina , Anderl Reiner
Published: October 2014

Todays’ product development process is characterized by an increasing use of embedded software solutions integrated into mechatronic products. The development is more and more translocated into a virtual environment. New software methods and tools have to be developed.

Industry 4.0 is an approach to highlight the tendency of modern development. Communication between smart products, communication via internet technologies, cyber-physical systems and the Internet of Things are the basis of Industry 4.0. Owing this development, used project management methodologies have to be adjusted. In special the well-known V-Model is now extended to the W-Model to cope with the new requirements like communications between different disciplines. New approaches in virtual development have to be adapted to modern teaching techniques. Therefore a course for first semester mechanical engineering students is conducted by the department of Computer Integrated Design at the Technische Universität Darmstadt. Industry 4.0 fundamentals are taught as well as the development process underlying the so called W-Model. The students will apply this knowledge while they participate in exercises. A web-based tutorial is provided every week with different learning packages. With these learning packages, the students learn to use the project management techniques as well as software development techniques to solve different tasks. Later complex data structures and algorithms can be coded and are applied. The software development techniques, established in development of information technologies, gets more important in mechanical engineering. Therefore the students learn these aspects. Over three months length the students work in groups and use all their skills to realize a bigger software-project — a digital factory. They use a virtual testing environment (ViTMeS 3.0) to develop their solution. The presented ViTMeS 3.0 is a further development of a virtual testing environment used in last year’s team work. Later they can test their code with a real life example. This example, the digital factory, built with LEGO Mindstorms, is an important part of teaching students the foundations of communication and information techniques as well as software development and programming skills. The last step of the team work is the coding of a graphical user interface for appropriate visualization.
Analysis of the GDI Spray Dynamics Through Multidimensional Modeling and Flow Visualization in an Optically Accessible SI Engine
Authors: Costa Michela , Sorge Ugo , Sementa Paolo , Montanaro Alessandro
Published: October 2014

Present work is aimed at studying into detail mixture formation and combustion in a gasoline direct injection (GDI) engine working under stoichiometric mixture conditions. The study is performed both numerically and experimentally. From the experimental side, the engine, optically accessible, is characterized by collecting, for various injection strategies, in-cylinder pressure cycles and digital images. From the numerical side, a 3D engine model is developed, that includes proper sub-models for the spray dynamics and the spray-wall interaction. This last phenomenon is studied into detail by resorting to a preliminary 3D simulation of the spray impingement realized in a proper experiment, where the engine injector is mounted at a certain distance from a cold or hot wall.

An interesting comparison between numerical and experimental images of the in-cylinder spray dynamics is presented, that also allows individuating the difference in the wallfilm deposition under various injection strategies. This opens the way to understand the difference in the combustion development arising as injection is anticipated or retarded in the engine working cycle.
Dynamics Synchronization of the Running of Planar Biped Robots With SLIP Model in Stance Phase
Authors: Dadashzadeh Behnam , Mahjoob Jahromi Mohammad
Published: October 2014

In this work a control law is derived to synchronize dynamics of multibody biped robots and the spring loaded inverted pendulum (SLIP) model in stance phase of running. The goal is to use the vast literature on the SLIP model dynamics for the control of real multibody robots. Three kneed biped robot models are considered in this work: with springs parallel to motors, with springs series to motors, and without springs. Dynamic equations of the multibody biped models are derived using Lagrange equation and then the applicability of the derived control law to these models are investigated using simulation. The initial state of the multibody robot is found such that its center of mass (CoM) has the same initial condition as SLIP model. Then the trajectory of its CoM is compared to SLIP model. Also motor torque profiles are compared for the models with and without springs and also for the motors with and without rotor inertias. The results show that the effect of rotor inertia is a big challenge in implementing fast biped running on real robots.
Optimal Operation of Small Geothermal Systems Through Entropy Generation Analysis
Authors: Cosentino Sara , Sciacovelli Adriano , Verda Vittorio
Published: October 2014

Geothermal systems often experience non homogeneous behavior between the various boreholes, due to possible issues in the installation or to differences in the stratigraphy. In the case of small systems, this may create important inefficiencies or operational problems. In this paper, the use of entropy generation analysis is proposed in order to optimize the global performances, taking fluid dynamic and thermal phenomena into account.

The possible anomalous scenarios that are considered include borehole ovalization and differences in the heat transfer between borehole and ground due to fouling, groundwater level, etc. The analysis is conducted considering a transient model of the entire system, composed by the ground, boreholes and heat pump. Various operating scenarios are also considered. Results show that non negligible improvements in the efficiency can be obtained by proper selection of the operating conditions.
Dynamics of Ice Milling and Breaking During Arctic Ship Steering Operations
Authors: Keskinen Erno , Montonen Jori , Sharma Nikhil , Cotsaftis Michel
Published: October 2014

Interest to sailing in arctic zone is increasing, as due to the climatic change, the seasons when northeast and northwest passages are open enough for see transportation, are getting every year longer and longer. Some other activities like oil and gas exploration and drilling at Barents Sea require also regular sea traffic connections to be opened. Sea operations at arctic zone are challenging, because thick ice generates a high magnitude dynamic load against the hull and the propulsion units. Turning and backward sailing in thick ice field are the most critical operations, in which the steerable propulsion units are in totally different service as in the regular open sea cruising. In such operations the ice field, when guided downwards along the slope of the hull, is broken to large plates, which then are fed against the propulsion unit. The steering propulsion unit itself is a vertically mounted inverse mast column, at the top of which the horizontally spinning propeller(s) can be vertically turned to follow the steering commands. Such cantilever structure is now under random collision process when the column is breaking the underwater ice plates to smaller blocks. For hydrodynamic reasons the column has a limited cross-sectional area as compared to the propeller area making it sensitive to bending vibrations. Another dynamic interaction with ice is coming from the periodical blade-ice contact when the ice blocks pushed down to the propulsion depth are completely milled by the units. These two parallel dynamic processes have been the reason for several serious damages and losses of propulsion units leading to expensive service operations by means of support vessels. The purpose of this study has been to model the underwater propulsion system with all essential structures, parts and interactions with the surrounding fluid field and floating ice blocks. This brings a complex analysis, in which random collisions and periodical machining forces are loading the elastic hull-mounted inverse mast column with high end mass. The response behavior led to predictions for the reasons of the observed damages especially in case of collapsed bolt connections in the units.
A Mobile Augmented Reality Framework for Inspection and Visualization During Fatigue Tests
Authors: Re Guido Maria , Kharshiduzzaman Md. , Bordegoni Monica , Bernasconi Andrea , Anodio Luca Francesco , Comolli Lorenzo , Braghin Francesco
Published: October 2014

In this paper, a framework based on Augmented Reality (AR) and a mobile device is proposed for monitoring mechanical components during fatigue tests. This solution enables the user to move around and to inspect the component through AR from different points of view. In addition, the framework proposes a solution to estimate in real time the crack growth and to visualize it directly onto the component. A user application is developed according to the proposed framework and it is used for case studies of fatigue test for adhesively bonded joints.
Effect of Turbocharger Cut Out on Two-Stroke Marine Diesel Engine Performance and NOx Emissions at Part Load Operation
Authors: Hountalas Dimitrios T. , Sakellaridis Nikolaos F. , Pariotis Efthimios , Antonopoulos Antonis K. , Zissimatos Leonidas , Papadakis Nikiforos
Published: October 2014

The diesel engine is widely used for marine vessel propulsion due to its relatively high efficiency compared to existing alternative propulsion systems. The majority of these engines are slow speed two stroke ones. Despite the improvement of their efficiency there now exists a demand for drastic reduction of daily fuel oil consumption as a result of the global financial situation and continuously increasing fuel prices.

Towards this effort, slow steaming is a promising solution for the drastic reduction of daily and specific fuel consumption when expressed in tn/mile. This requires engine operation in the low load (low speed) range where these engines are not designed to operate for long term. The main problem related to slow-steaming, is the lack of air which has a negative impact on the engine and its subsystems. A promising solution to the problem is turbocharger (T/C) cut-out at low load when more than one T/C exists.

In the present work a combined computational and experimental investigation is conducted to evaluate the operation potential of a large two stroke marine diesel engine equipped with two T/Cs using T/C cut-out, for which the specific technology presents various challenges. This is achieved using an in-house engine simulation model and measurements with and without T/C cut-out. From the results it is revealed that using this technique the scavenging air and peak firing pressure increase while the specific fuel consumption decreases. In this way, some major problems related with the long term operation of the engine under low load conditions, i.e. accumulation of carbon deposits on the exhaust gas side and continuous operation of the auxiliary air blowers, are surpassed. Moreover, a theoretical investigation is conducted considering fuel injection retard to minimize the peak firing pressure penalty while taking care to limit the corresponding negative impact on specific fuel consumption. For NOx emissions the effect of T/C cut-out is also considered using tail pipe emission data measured during the official shop tests.

From the analysis conducted it has been revealed that the technique of turbocharger cut–out (one of two) is technically feasible and could offer certain advantages when slow-steaming is implemented. Moreover, comparing the calculated with the measured results, it has been revealed that the simulation model successfully estimates engine operation with and without T/C cut-out, being a valuable tool for the engineers to investigate combustion and pollutant formation mechanisms under various engine configurations.
Global Sensitivity Analysis of Railway Vehicle Dynamics on Curved Tracks
Authors: Bigoni Daniele , Engisg-Karup Allan P. , True Hans
Published: October 2014

This work addresses the problem of the reliability of simulations for realistic nonlinear systems, by using efficient techniques for the analysis of the propagation of the uncertainties of the model parameters through the dynamics of the system. We present the sensitivity analysis of the critical speed of a railway vehicle with respect to its suspension design. The variance that stems from parameter tolerances of the suspension is taken into account and its propagation through the dynamics of a full car with a couple of two-axle Cooperrider bogies running on curved track is studied.

Modern Uncertainty Quantification methods, such as Stochastic Collocation and Latin Hypercube, are employed in order to assess the global uncertainty in the computation of the critical speed. The sensitivity analysis of the critical speed to each parameter and combination of parameters is then carried out in order to quantify the importance of different suspension components. This is achieved using combined approaches of sampling methods, ANOVA expansions, Total Sensitivity Indices and Low-dimensional Cubature Rules.
Local Thermal Non-Equilibrium in Mixed Convection in Channels Partially Heated at Uniform Heat Flux Filled With a Porous Medium
Authors: Buonomo Bernardo , Manca Oronzio , Mesolella Paolo , Nardini Sergio
Published: October 2014

A numerical analysis of mixed convection in a vertical channel filled with metal foam partially heated at uniform heat flux is studied numerically. Local thermal non-equilibrium and Brinkman-Forchheimer-extended Darcy model are assumed. Boussinesq approximation with constant thermophysical proprieties are considered. Results are carried out for an aluminium foam with 10 pore per inch (PPI) and ε=0.909, the fluid is air. Results, for different Reynolds numbers and geometrical aspect ratios, are given in terms of solid and fluid temperatures, at heated walls and inside the channel at several heights, velocity profile along the channel, local and average Nusselt numbers. Results show that diffusive effect resulted lower temperature values inside the solid and the fluid temperatures are higher in all considered cases. For heated channel with smaller aspect ratios, an average Nusselt number increase is found for solid and fluid phases.
Optimal Design and Management of a Hybrid Photovoltaic-Pump Hydro Energy Storage System
Authors: Stoppato Anna , Cavazzini Giovanna , Benato Alberto , Destro Nicola , Ardizzon Guido
Published: October 2014

The exploitation of renewable sources is an opportunity to increase the number of people who have access to electricity. To assure better living conditions, the free and simple access to water is another fundamental key point in many developing countries. Stand-alone photovoltaic pumping systems are often installed in remote areas where the grid is not available: they are used for irrigation and/or other local water needs and can supply also electricity to small consumers. In this paper a system aimed at supplying electricity and water to an isolated small village has been studied. Ground water is pumped into a storage reservoir and can be used both for irrigation and domestic use. The system is composed by a photovoltaic plant, a pump as turbine (PAT), a diesel internal combustion engine for integration purposes and a battery storage. By means of an optimization model based on the Particle Swarm Theory, the size of the system and its managing strategy have been optimized in order to fulfill the requirement of the users, to improve the system efficiency and minimize the overall costs. The most suitable hourly-based profile of the flow rates of a pump-as-turbine as well was found.
Microstructure and Hardness of Friction Stir Weld Bead on Steel Plate Using W-25%Re Pin Tool
Authors: Iqbal Z. , Shuaib A. N. , Al-Badour F. , Merah N. , Bazoune A.
Published: October 2014

One of the challenges that impede the use of the relatively new friction stir welding (FSW) process in joining steels and high temperature alloys, as well as dissimilar materials, is the development of the right pin tool material that can stand the severe welding conditions of these alloys. Recent developments in FSW tool materials include tungsten rhenium (W-Re) alloys. The ductile to brittle transition temperature of pure tungsten is reduced by the addition of rhenium (Re).. The addition of Re also improve fracture toughness of the alloy. The major focus of this paper is studying the process of making a friction stir welding bead on mild steel using a proprietary W-25%Re alloy pin tool and investigating the effects of process parameters (i.e. tool rotational and welding speeds) on microstructure, microhardness as well as tool reaction loads. Grain refining of the steel microstructure was observed in all beads. Certain process conditions produced a bead with needle like microstructure with the highest values of hardness. Reaction forces were found to increase with the increase in the tool welding speed and to decrease with the increase of the tool rotational speed. Although the spectroscopic analysis of the beads confirmed the diffusion wear of the tool, the overall tool has shown excellent resistance to mechanical wear.
Influence of Drying Conditions and Mathematical Models on the Thin-Layer Drying of Mushrooms
Authors: Stegou-Sagia A. , Fragkou D. V.
Published: October 2014

In the present research, experimental data from several studies about drying behavior of mushrooms have been selected and used to compare different drying methods and different mathematical thin layer drying models to simulate mushroom drying rates. The white button (Agaricus Bisporus), the oyster (Pleurotus Ostreatus) and the milky mushroom slices have been considered for drying in different dryers such as hot air cabinet dryer and fluidized bed dryer with different slice thicknesses, drying air temperatures (45 °C to 90 °C) and drying air velocities (0.2 m/s to 5 m/s). The entire drying process has taken place in the falling rate period, assuming that internal mass transfer occurred by diffusion in mushroom slices. The study shows that the drying air temperature and the drying air velocity have an effect on the moisture removal from mushrooms and also on the drying time. Mathematical models have been proved to be useful for design and analysis of heat and mass transfer during drying processes. All the drying models considered in this study could adequately represent the thin layer drying behavior of mushrooms. Furthermore, as it is obvious, any type of mushrooms has its own most suitable model.
Design of a Wireless Sensor Powered by a Piezoelectric Energy Harvester
Authors: Milani Damiano , Bassetti Marco , Braghin Francesco , Tomasini Gisella
Published: October 2014

Sensor nodes are innovative devices that can perform measurements on a large scale and communicate over a network. One of the most significant problems regarding the sensor nodes is how to supply power to a large number of devices. For this reason, they greatly benefit from energy harvesting techniques which can provide energy recovered directly from the environment. A study of the design and the modeling of an autonomous sensor node, powered by a vibrational piezoelectric harvester, is reported here. Subject of the first part of the analysis is a piezoelectric bimorph: an analytical model is proposed in order to estimate the performance, giving particular attention to the optimal mechanical and electrical parameters. The model is then validated through experimental tests, assuming different kinds of real scenarios. Then the results are used to design a device that can benefit from this harvester. In particular a wireless sensor node is developed, for which the energy scavenging ensures energy autonomy and long-term operability. Thanks to a particular harvesting circuit and opportune algorithms for energy management, this system is able to extract energy from vibrations and store it into capacitors. The embedded accelerometer and a wireless module make this device ideal for Structure Health Monitoring purposes.
Numerical Investigation of Steady Air Injection Flow to Control Rotating Stall in Centrifugal Compressors
Authors: Halawa Taher , Alqaradawi Mohamed , Badr Osama , Gadala Mohamed S.
Published: October 2014

This paper concerns the role of air injection method in stabilization and stall control in centrifugal compressors. The main aim is to find the best arrangement of air injection parameters such as injection angle and injection mass flow rate in order to optimize the injection performance for stabilizing the compressor and increasing the surge margin. Numerical model was built to simulate high speed transonic centrifugal compressor working at an operating point close to surge. Air was injected at 12 locations at the vaneless region between the impeller and the diffuser at shroud surface with 5 different injection angles and 3 different injection mass flow rates. Results showed that the best injection method is when using an injection angle of 30° with injection mass flow rate of 1.5% of the design mass flow rate and the worst injection method is the injection at angle of 180° (reverse tangent injection). Results also indicated that by using air injection, the number of stalled diffuser passages is decreased compared to the case of no injection. The most significant result of this paper is that using an angle of injection around twice the value of the diffuser vane angle gives the best results and makes the ideal correction of the fluid kinetic energy and fluid angle at the diffuser inlet. It was found that injecting air at an angle less than the diffuser vane angle weakens the effect of injection and doesn’t increase kinetic energy of the fluid at diffuser inlet. It was also found that injecting air at an angle larger than the diffuser vane angle corrects the fluid direction but, at the same time, decreases the fluid kinetic energy at diffuser inlet.
Resonant Ultrasound Spectroscopy Used for Diagnosis of Some Medical Prosthesis Components Made From Zirconium Oxides
Authors: Savin Adriana , Craus Mihai Liviu , Steigmann Rozina
Published: October 2014

This paper presents a possibility to use Resonant Ultrasound Spectroscopy as nondestructive evaluation method for ceramic elements of prosthesis such as ceramic femoral heads. With this method can be emphasized the incorrect sintering of these elements as well as eventually cracks. If the number of resonance peaks is big enough, the elements of elasticity matrix can be determined, demonstrated by effective measurements on zirconia with different stabilizers cylindrical samples taken into study.
A Ranking Method for the Selection of the Interior Modes of Reduced Order Resonant System Models
Authors: Palomba Ilaria , Richiedei Dario , Trevisani Alberto
Published: October 2014

Resonant system design and optimization is usually supported by finite element models. Large dimensional models are often needed to achieve the desired accuracy in the representation of the vibrational behaviour at the frequency of interest. Unfortunately, large dimensional models are frequently too cumbersome to be actually useful, mainly at the optimization stage. On the other hand, the choice of the most appropriate reduction strategy and dimension for a reduced-order model is generally left to designers’ experience. Having recognized the effectiveness and spreading of the Craig Bampton reduction technique, the aim of this paper is to propose a rigorous ranking method, called Interior Mode Ranking (IMR), for the selection of the interior normal modes of the full order model to be inherited by the reduced order one. The method is aimed at finding the set of interior modes of minimum dimensions which allows achieving a desired level of accuracy of the reduced order model at a frequency of interest. The method is here applied to a resonator widely employed in industry: an ultrasonic welding bar horn, which is usually designed to operate excited in resonance. The results achieved through the application of the IMR method are compared with those yielded by other ranking techniques available in literature in order to prove its effectiveness.
Detection of Cracks in Stationary Rotors via the Modal Frequency Changes Induced by a Roving Disc
Authors: Haji Z. N. , Oyadiji S. O.
Published: October 2014

In this study, a crack identification approach based on a finite element cracked model is presented to identify the location and depth ratios of a crack in rotor systems. A Bernoulli-Euler rotor carrying an auxiliary roving disc has been used to model the cracked rotor, in which the effect of a transverse open crack is modelled as a time-varying stiffness matrix. In order to predict the crack location in the rotor-disc-bearing system, the suggested approach utilises the variation of the normalized natural frequency curves versus the non-dimensional location of a roving disc which traverses along the rotor span. The merit of the suggested approach is to identify the location and sizes of a crack in a rotor by determining only the natural frequencies of the stationary rotor system. The first four natural frequencies are employed for the identification and localisation of a crack in the stationary rotor. Furthermore, this approach is not only efficient and practicable for high crack depth ratios but also for small crack depth ratios and for a crack close to or at the node of mode shapes, where natural frequencies are unaffected.
On Non-Boussinesq Gravity Currents in Non-Rectangular Cross-Section Channels
Authors: Zemach T.
Published: October 2014

We consider the propagation of a gravity current of density ρc from a lock length x0 and height h0 into an ambient fluid of density ρa in a horizontal channel of height H along the horizontal coordinate x. The bottom and top of the channel are at z = 0, H, and the cross-section is given by the quite general −f1(z) ≤ y ≤ f2(z) for 0 ≤ z ≤ H. When the Reynolds number is large, the resulting flow is governed by the parameters R = ρc/ρa, H* = H/h0 and f(z) = f1(z) + f2(z). We show that the shallow-water one-layer model, combined with a Benjamin-type front condition, provides a versatile formulation for the thickness h and speed u of the current. The results cover in a continuous manner the range of light ρc/ρa ≪ 1, Boussinesq ρc/ρa ≈ 1 and heavy ρc/ρa ≫ 1 currents in a fairly wide range of depth ratio in various cross-section geometries. We obtain analytical solutions for the initial dam-break stage of propagation with constant speed, which appears for any cross-section geometry, and derive explicitly the trend for small and large values of the governing parameters. For large time, t, a self-similar propagation is feasible for f(z) = bzα cross-sections only, with t(2+2α)/(3+2α). The present approach is a significant generalization of the classical non-Boussinesq gravity current problem. The classical formulation for a rectangular (or laterally unbounded) channel is now just a particular case, f(z) = const., in the wide domain of cross-sections covered by this new model.
Influence of Underbody Suspended Equipment on Rail Ride Comfort
Authors: Corradi Roberto , Mazzola Laura , Ripamonti Francesco , Rosa Lorenzo
Published: October 2014

This paper illustrates a methodology that, by means of laboratory and on-track tests, allows for an appropriate design of the connection elements between the suspended equipment and the carbody in order to enhance the rail ride comfort. In particular at first the connection elements are tested in laboratory to assess their visco-elastic behaviour simulating the common operating conditions. Subsequently on-track tests and experimental modal analysis are carried out to identify the interaction between underframe equipment motions and carbody modes. In the experimental tests, starting from the laboratory test results, it is possible to define the connection elements in order to minimise the negative influence on vehicle ride comfort. Two different solutions are proposed: the “TMD solution” (the suspension is tuned on the natural frequency of the carbody mode most relevant from the comfort point of view) and the “suspended solution” (the suspension system aims to decouple the two subsystems).
Theoretical Analysis of Thrust-Induced Delamination in Hemispherical Drilling Composite Materials
Authors: Tsao Chungchen , Kuo Keilin
Published: October 2014

The theoretical analysis of thrust-induced delamination in hemispherical drilling composite materials was investigated in this study. The theoretical analysis indicated that the thrust force of hemispherical drill at drill and delamination ratio (s) about 0.8 has a significant effect on prevention of delamination damage in drilling composite materials. The maximum thrust force of hemispherical drill at α = 2, however, was about 36% of that of twist drill. In other words, hemispherical drill has a correspondence with lower bearing stresses on drilling-induced delamination, which is liable to cause separation of plies at the exit as the interlaminar bonding yields.
A Longitudinal Study on the Relationship Between Aerobic Endurance and Lower Body Strength in Italian Sedentary Older Adults
Authors: Magistro Daniele , Candela Filippo , Brustio Paolo Riccardo , Liubicich Monica Emma , Rabaglietti Emanuela
Published: October 2014

Functional aging processes are characterized by a loss of performance capabilities for most physiological systems, such as aerobic endurance and lower body strength, which are important for independent living and active aging. The present study examines the direction of influence between aerobic endurance and lower body strength over time in Italian sedentary older adults. A three-wave longitudinal model was tested using cross-lagged analysis for 202 individuals aged over 65 years (mean = 73.92, SD = 5.84; 140 females). Analysis revealed that aerobic endurance and lower body strength decline over time. In addition, greater aerobic endurance positively affected lower body strength over time; however, the converse was true only during the first period (first 6 months). These findings emphasize the importance of these relationships for the design and implementation of effective physical intervention for older adults.
Habitual and Maximal Dual-Task Gait Speeds Among Sedentary, Recreationally Active, and Masters Athlete Late Middle-Aged Adults
Authors: Glenn Jordan M. , Vincenzo Jennifer , Canella Collin K. , Binns Ashley , Gray Michelle
Published: October 2014

Gait speed predicts survival in older adults; however, gait has not been evaluated in late middle-aged (LMA) populations.

Purpose:

Evaluate single- and dual-task gait speeds among sedentary (SED), recreationally active (RA), and masters athlete (MA) LMA adults.

Methods:

Participants were SED (n = 20, age = 61.0 ± 5.8), RA (n = 57, age = 63.5 ± 8.4), and MA (n = 25, age = 57.5 ± 7.9). Two trials of each task (10 m) were completed: habitual speed (HS), maximal speed (MS), dual-task (counting backward from a number by 3) habitual speed (DT-HS), and dual-task maximal speed (DT-MS).

Results:

MA (2.08 ± 0.63 m/s) had significantly (p < .05) greater MS compared with SED (1.94 ± 0.30 m/s) and RA (1.99 ± 0.53 m/s). Similar differences existed for DT-MS (SED = 1.77 ± 0.32 m/s, RA = 1.80 ± 0.51 m/s, MA = 1.89 ± 0.63 m/s). MA had smaller MS and DT-MS changes (difference between MS and DT-MS speeds) compared with RA (12%) and SED (13%).

Conclusion:

Maintaining a competitively active lifestyle increases MS in LMA adults and may support healthy aging.
A Systematic Review of Physical Activity Programs for Older People Receiving Home Care Services
Authors: Burton Elissa , Lewin Gill , Boldy Duncan
Published: October 2014

The proportion of older people living in our communities is rising and, to live independently, some require assistance from home care services. Physical activity can improve and maintain function, strength, and balance, which are important for those receiving home care. This study reviewed the evidence on physical activity/exercise interventions trialed with older people receiving a home care service. A systematic review of studies published from January 1982 to September 2012, from five databases, was undertaken. Inclusion criteria were: aged 65+ years; community dwelling; no dementia diagnosis; receiving home care services; and a physical activity/exercise program. Eight articles were included and results show there were few consistencies between intervention types, groups, outcome measures, and follow-up. Study quality was mixed. Future studies should include pragmatic randomized controlled trials involving home care practitioners and their clients to gain “real-world” knowledge of what interventions are effective and can be delivered within this setting.