bluuebunny/crossref_metadata_2025 huggingface dataset:
Data-Driven Surge Map Modeling for Centrifugal Air Compressors
Authors: Sodemann A. , Li Y. , Lee J. , Lancaster R. , Rucker M. , Carnagie J. , Inman A.
Published: April 2008

Surge is a phenomenon of large oscillations of pressure and flow that occurs in dynamic compressors when the compressor is operated at too low a flow rate for a given discharge pressure. In order to prevent damage to the compressor, surge must be avoided. A typical surge prevention measure for compressor operation is so-called surge avoidance control, which normally relies on a map of the operating conditions for surge occurrence, i.e. surge map or surge line. The surge map currently used in industry practice is insufficient since surge occurrence is affected by many more process variables, especially ambient air conditions. If large uncertainty exists in surge conditions, the compressor has to be operated conservatively far away from the surge line, which limits the dynamic range and usually sacrifices the efficiency. In order to obtain more accurate surge map adaptively, a data-driven surge map modeling approach has been developed using support vector machine (SVM) approach based on surge test data. Surge map is obtained as the classification surface between surge and not-surge data. Principal components analysis (PCA) is used to identify the variables that contribute most to surge. The method of asymmetric support vector machines (ASVM) is developed to reduce the possibilities of missed surge prediction. The developed methodology was verified with the actual testing data on the centrifugal air compressor in Toyota Motors.
Implications of the Dilute Approximation for the Prediction of Heat and Mass Transfer Rates in Multi-Component Systems
Authors: Kumar Ankan , Mazumder Sandip
Published: April 2008

Use of the Fick's law of diffusion is inappropriate in multi-component systems comprised of more than two species since it results in local violation of overall mass conservation. One approach that is often used to circumvent this problem is the dilute approximation, in which the conservation of the diluent is not enforced. It is generally believed that if the mass fraction of the diluent is "large" and it is a non-reacting species, the dilute approximation yields accurate results. In this study, the accuracy of the dilute approximation is quantitatively assessed by comparing its predictions against a rigorous multi-component diffusion formulation, derived from the Stefan-Maxwell equation. Both mass and heat flux errors are computed for a one-dimensional pure diffusion problem. It is found that even for quite dilute mixtures with mass fraction of the diluent exceeding 70%, the errors are ~15% for mass fluxes and as high as 35% for heat fluxes. In addition, the errors are found to be strongly dependent on the type of species in the mixture, implying that the validity of the dilute approximation cannot be judged a priori. Additional results are presented to show that in systems with combined heat and mass diffusion, net heat transfer can occur against the imposed temperature gradient. A Second Law analysis is presented and performed to corroborate these non-intuitive results.
Resistance Curve Calculations for a Soloflex Machine
Authors: Hubbard Boyd , Janna William S.
Published: April 2008

A Soloflex machine was analyzed mathematically. Dimensions of the components of the machine were measured, and calculations were made to determine a resistance curve. The machine consists of a mainframe bent into an L-shape, having a vertical post height of 6 ft. A loading post with 27 drilled holes is attached along the back of the vertical post. The loading piece receives a bench pin and the barbell arm pin. To perform an exercise, the barbell arm is attached with the barbell arm pin to the loading piece. Weight straps of equal rating are placed on both sides of the load and barbell arm pins. Pushing upward on the barbell arm will stretch the weight straps which provides resistance to the motion of the barbell arm. The weight straps behave like springs. The straps were stretched with a Tinius-Olsen machine to determine the force vs deflection behavior for a standard set of weight straps, including one pair each of 2.5 lb, 5 lb, 10 lb, 25 lb, 50 lb and 100 lb weight straps. The objective of this study was to make measurements of force versus deflection for each matched pair of weight straps, and then to calculate the force required at the barbell arm to perform an exercise for a particular "weight." Although several different exercises can be performed, the focus here is on a simple bench press, for which the resistance curve was determined.
Improving the Capacity and Performance of Air-Conditioning Screw Compressors
Authors: Broglia Thomas , Iobbi Matteo , Stosic Nikola
Published: April 2008

Traditional compressor design methods make it very difficult to make significant improvements to screw compressors required for refrigeration and air conditioning applications. The principles which determine the optimum design of such machines are reviewed and, in some cases, redefined. These include rotor profiling, configuration and proportions, clearance distribution and bearing clearances and it is shown that there are conflicting requirements for them when attempting to obtain optimum performance. The best result can thus only be obtained by consideration of all the relevant parameters in an optimisation procedure, which leads to rotor designs that vary according to the specific duty of a machine, rather than follow a standard pattern An outline description is given of a process modelling procedure which has been developed to optimise the design of a compressor by the use of multi variable minimisation methods that take simultaneous account of all these parameters As a result of a collaborative project between industry and an academic institution, this procedure was applied to the design of a new refrigeration screw compressor, which was then built and tested. Its performance was then compared with that of the machine it was intended to replace. It is shown that the optimised design was up to 9% better than the original machine.
Applying the Mahalanobis-Taguchi System to Vehicle Ride
Authors: Cudney Elizabeth A. , Ragsdell Kenneth M. , Paryani Kioumars
Published: April 2008

The Mahalanobis Taguchi System is a diagnosis and forecasting method for multivariate data. Mahalanobis distance is a measure based on correlations between the variables and different patterns that can be identified and analyzed with respect to a base or reference group. The Mahalanobis-Taguchi System is of interest because of its reported accuracy in forecasting small, correlated data sets. This is the type of data that is encountered with consumer vehicle ratings. MTS enables a reduction in dimensionality and the ability to develop a scale based on MD values. MTS identifies a set of useful variables from the complete data set with equivalent correlation and considerably less time and data. This paper presents the application of the Mahalanobis-Taguchi System and its application to identify a reduced set of useful variables in multidimensional systems.
Structure of Propylene Turbulent Diffusion Flames in Cross-Flow Near Smoke Point
Authors: Goh S. F. , Periasamy C. , Gollahalli S. R.
Published: April 2008

An experimental study of a propylene diffusion flame at its smoke point in a cross-flow with velocities ranging from 2 to 4 m/s and a series of diluted conditions was conducted. A gas jet flame from a circular tube burner (ID = 3.2 mm) with a range of exit velocities (4.2 to 34 m/s) corresponding to a Reynolds number range of 520 to 6065 was studied. Nitrogen was added to the fuel stream to eliminate smoking when the fuel flow rate was lower than the flow rate of pure fuel at smoke point condition (which is defined as the Critical Fuel Mass Flow Rate, CFMFR). The curve of N2 flow rate with fuel flow rate at the smoke point showed a skewed bell shape with two distinct regions. In the first region, the diluent flow rate increased with the fuel flow rate, and in the subsequent region the trend was reversed. These two regions were separated by a transition region. Our previous studies on flames in quiescent conditions concluded that these two regions were controlled by jet momentum and chemical kinetics, respectively. This study presents flame structure details such as transverse temperature and concentration profiles in typical flames representing these two regimes. Most of the temperature profiles show a dual peak structure, where the peak nearer to the burner was higher than the other. Furthermore, the peaks in the transition region flame were more distinct than those in the momentum dominated flame. Most of the flames in the 2 m/s cross-flow had lower O2 concentrations than the flames in the 3 and 4 m/s cross-flow. The temperature profiles, and the concentration profiles of O2 and soot change significantly when cross-flow velocity was changed from 2 to 4 m/s. Findings from this study enable us to understand industrial flares that are commonly used in petroleum refineries and chemical plants.
Reliability Metrics of ReduNdant Systems With Log-Normal Repair Times
Authors: Xu Shuzhen , Susemihl Enrique
Published: April 2008

The data usually available related to equipment failure and repair are the MTTF (mean time to failure) and MTTR (mean time to repair), with the underlying distributions assumed exponential. The analysis of repairable redundant systems can then proceed by means of integration of Markhov transition equations. It has been found that although the exponential distribution may represent adequately the failure probability, in some cases the log-normal distribution better represents the repair probability, but this distribution leads to non-Markhovian systems. The reliability of redundant systems is affected by the distribution used to model the repair time. This paper presents a comparison of the reliability metrics for redundant systems with exponential failure distribution and two cases of repair time distributions, i.e., exponential and log-normal. The exponential failure distribution is analyzed by integration of the Markhov transition equations, and the log-normal distribution by Monte Carlo simulation. The results obtained show that the use of exponential repair distributions when the data follows the log-normal distribution overestimates the reliability of the system. Nevertheless for values of the MTTR relatively small compared to the MTTF, 10% or lower, the results obtained by using exponential failure distributions are acceptable for engineering applications.
Modeling and Input Optimization Under Uncertainty for a Collection of RF MEMS Devices
Authors: Allen M. S. , Massad J. E. , Field R. V.
Published: April 2008

The dynamic response of an RF MEMS device to a time-varying electrostatic force is optimized to enhance robustness to variations in material properties and geometry. The device functions as an electrical switch, where an applied voltage is used to close a circuit. The objective is to minimize the severity of the mechanical impact that occurs each time the switch closes, because severe impacts have been found to significantly decrease the design life of these switches. The switch is modeled as a classical vibro-impact system: a single degree-of-freedom oscillator subject to mechanical impact with a single rigid barrier. Certain model parameters are described as random variables to represent the significant unit-to-unit variability observed during fabrication and testing of the collection of nominally-identical switches; these models for unit-to-unit variability are calibrated to available experimental data. Our objective is to design the shape and duration of the voltage waveform so that impact velocity at switch closure for the collection of nominally-identical switches is minimized subject to design constraints. The methodology is also applied to search for design changes that reduce the impact velocity and to predict the effect of fabrication process improvements.
The Evolution of the Positive Locking Mechanism in End Release Buckles
Authors: Renfroe David A. , Good Craig , Clarke Richard , Roberts Alex
Published: April 2008

Crash tests conducted by Ford, General Motors, and other automakers have shown that localized accelerations on various objects, including seatbelt buckles, can experience many multiples of the center of gravity acceleration (sometimes exceeding 500 g's) due to contact with other objects within the vehicle or from elastic and plastic deflections of the vehicle structure. In March of 1959, the Cummings [18] pivoting cover buckle patent recognized that the moving parts should be so balanced that "the buckle will not open under the influence of inertia." This paper follows the development of the modern lock for the latch buckle design concept through its evolution. After a discussion of the realization of the inertial potential for unlatching of the buckle from numerous patents and testing, seatbelt locking mechanisms will be discussed by category, followed by a short summary of the inertial blocking mechanisms. These designs will be described, patents for each listed, examples given of vehicles where they have been installed, and the inertial capability of each buckle type catalogued. From this discussion, the reader should have a clear understanding of the capabilities of the modern lock for the latch seatbelt buckle and the roots from whence it has been developed.
An Extension to “Allowable Design Factor” Method for Free Span Calculation of Sub Sea Pipelines
Authors: Mirzaei Farhad
Published: April 2008

Using the design factors is a traditional method in solid mechanics design. This method is still also the base of some design standards in the world [1,2].In this paper, a modification has been performed to traditional Von Misses stress check method for the calculation of sub sea pipeline free spanning. The DNV OS F101 which is a well known standard for sub sea pipelines has been used for calibration [3]. A spread sheet type program for free span calculation has been developed for "Force Model" which facilitates the evaluation of the free span length based on the latest DNV proposed method as well as traditional Von Misses stress check. The method statement is the calculation of maximum allowable sub sea pipeline free span, by DNV proposed method and consequently evaluation of allowable stress to result the same free span length in Von Misses traditional method. The design factors which are the Stress Factors (SF) will be calculated by the ratio of existing equivalent Von Misses stress to yield strength of the pipeline material (fy).
Numerical Simulation of Tubular Type Combustion Chamber: A CFD Approach
Authors: Kulshreshtha Digvijay B. , Channiwala S. A. , Dikshit Saurabh
Published: April 2008

The challenges in designing high performance combustion systems have not changed significantly over the years, but the approach has shifted towards a more sophisticated analysis process. A technical discussion on combustion technology status and needs will show that the classic impediments that have hampered progress towards near stoichiometric combustion still exist. Temperature rise, mixing, liner cooling, stability, fuel effects, temperature profile control and emissions continue to confront the aerodynamic and mechanical designers with a plethora of engineering dilemmas and trade-offs. The process of combustion chamber design has taken a new meaning over the past several years as three dimensional codes and other advanced design and validation tools have finally changed the approach from a "cut and burn" technique to a much more analytical process. All of these new aspects are now integral elements of the new equation for advanced combustor design that must be fully understood and utilized. Only then will the operable, high temperature capable or low emission combustor systems needed for future military and civil aircraft as well as for stationary gas turbines can be developed. The present paper is an attempt to analyze the flow patterns within the combustion chamber of a 20 kW gas turbine engine using a CFD code CFX. It summarize the CFD simulation of the complete combustion chamber including primary zone, intermediate zone and dilution zone and finally attempts to achieve temperature distribution in the entire combustion chamber. These CFD results are then compared with experimental readings which not only validates analytical results but leads towards improved design.
Binary Diffusion Coefficients at Varying Temperatures and Partial Pressures in a Fuel Cell
Authors: Avsec Jurij , Naterer Greg F. , Oblak Maks
Published: April 2008

This article develops new predictive models of diffusion coefficients and ordinary diffusion coefficients for solid oxide fuel cells and proton exchange membrane fuel cells. In particular, diffusion coefficients are predicted with methods of nonequilibrium statistical thermodynamics, up to the third order. This article outlines a new analytical method for predicting changes of these coefficients at varying pressures and temperatures. The effective Knudsen diffusion coefficient is derived from kinetic theory, by means of associating the gas molecule mean free path with the pore diameter and a ratio of the solid porosity to the tortuosity.
CFD Analysis of Multiphase Flow in a Slab Continuous Caster Mold
Authors: Barron Miguel A. , Gonzalez Jesus , Miranda Raul , Plascencia Gabriel , Hilerio Isai´as
Published: April 2008

In order to analyze the influence of a third phase in the behaviour of the free surface profile in the mould of a slab steel continuous caster, multiphase flow in a mould water model is physically and numerically investigated. A one third scale mould water model was constructed in accordance with the Froude similarity criterion. The free surface profile in the experimental air-water system was tracked using ultrasonic level sensors which were located at six different positions along a line between the submerged entry nozzle and the mould narrow wall. Volumetric flow rates of water from 3.5×10-4 to 5.83×10-4 m3/s were employed in the physical experiments. Three submergence depths of the nozzle, namely 0.05, 0.07 and 0.09 m, were considered. On the other hand, two and three phase transient and steady state numerical simulations were carried out by means of computational fluid dynamics software. Oil engine was employed as the third phase in the numerical simulations. A comparison between the experimental results and the numerical ones with three phases suggests significant changes in the steel-slag interface due to the presence of the third phase, particularly in the neighbourhood of the discharge of the submerged entry nozzle.
Fabrication of Integrated Pressure-Flow-Temperature Sensor for Hydraulic Systems
Authors: Groepper Charles W. , Cui Tianhong , Li Perry Y. , Stelson Kim A.
Published: April 2008

This work develops a low cost multi-functional micro-electro mechanical systems (MEMS) sensor for use in fluid power systems. The device is small to facilitate easy integration into fluid power components, and has the capability to sense system pressure, fluid temperature, and small pressure differences that can be correlated to flow rate. The design of each of the sensing aspects of the device is outlined, as well as their layout on the sensor die. Pressure sensing with the device is accomplished through the use of polysilicon piezoresistors, while temperature sensing is accomplished using polysilicon thermisters. The procedure necessary to fabricate prototype units is illustrated in detail, and special processes noted. Performance characteristics of prototype sensors compare well to design model predictions. The polysilicon thermister demonstrated a linearity of 2.32%, a repeatability of 0.6%, and an accuracy of 1.5°C. The differential pressure sensor demonstrated a linearity of 0.4%, a repeatability of 0.13%, and an accuracy of 3.6%. The system pressure sensor demonstrated a linearity of 0.7%, a repeatability of 0.3% and an accuracy of 4.2%. These performance characteristics prove the functionality of the device.
Experiences From Screencasting Engineering Mechanics Lectures
Authors: Manteufel Randall D.
Published: April 2008

Screencasting is the simultaneous recording of a computer screen, audio narration, and possibly a video image included in a small portion of the screen. Instructors are beginning to screencast their lectures as an additional learning resource for students. Once produced, the files can be uploaded to an internet accessible site and reviewed by students. The author uses the Camtasia software running on a TabletPC, using Microsoft Journal. The software runs in the background on the Tablet during the lecture. After the lecture, the software can be used to edit the files and produce the lecture in a variety of internet-ready formats. The files can be uploaded into a course management system and linked for student access. This paper discusses the mechanics of screencasting, feedback from students, and an assessment of the effect on student performance.
Towards Object-Oriented Modeling of Complex Mechatronic Systems for the Manufacturing Industry
Authors: Zanichelli Davide , Secchi Cristian , Rubini Riccardo , Fantuzzi Cesare , Bonfe` Marcello , Borghi Davide , Borsari Roberto , Sacchetti Elena
Published: April 2008

The advantages of object-oriented modeling, as modularity and reusability of components, are very important also for modeling manufacturing systems and not only for software development. In [1] a unified object-oriented approach for modeling both the logical and the physical part of a manufacturing machine has been proposed. In this paper we report an industrial application of this modeling strategy and the case study consists of the package forming unit of a filling machine for liquid food packaging, developed by Tetra Pak Carton Ambient S.p.a.
Design Optimization of Snap-Fit Integral Parts by FEA and Statistical Analysis
Authors: Goteti L. , Choi J. , Park J.
Published: April 2008

Snap-fit integral attachments are used widely for joining plastic parts. The proliferated use of integral attachment in the form of snap-fit features in designs is due to the ability to mould such parts of great complexity at little cost. The exceptional diversity of part geometry and integral snap-fit features has made it seem that design possibilities may be unlimited. Thus, attempts at optimization might be intractable. A design of experiments (DOE) approach coupled with three-dimensional, geometrical non-linear finite element analysis (FEA) was used to calculate the insertion and retention responses on such parts for various geometrical parameters like length, width and angles. A statistical technique was employed to formulate empirical relationships among the geometrical dimensions, to investigate the effect of these parameters on the design as well as to obtain optimal insertion and retention forces or strains. Design equations obtained from this methodology were verified within the DOE domain and it was observed that the predicted responses were ranged within 30% of the FEA results. During this investigation, it was observed that geometrical features of a block, which exert force on the snap-fit features, have a considerable effect on the results. Therefore, the effects of the block parameters on the various responses were also studied. An attempt was also made to understand the effect of the block parameters such as corner radius and thickness on the design formula, which depicts the geometrical parameters of the snap-fit part as a function of insertion and retention forces. It is expected that the results help to find optimal design parameters in order to enhance the performance of such snap-fit features.
Thermomechanical and Creep Behaviours of Au/Sn Solder Alloy
Authors: Tew J. W. R. , Wei J. , Sun Y. F. , Su F. , Liu Y. C.
Published: April 2008

Au/Sn eutectic solder alloy is particularly attractive for high-power electronics and optoelectronics packaging as hermetic sealing and die attachment material. The robustness and reliability of solder joint are essential to meet the global demand for longer operating lifetime in their applications. The mechanical response of Au/Sn solder alloy is studied using nanoindentation (Nano-Test 600). Miniature creep samples were created using a specially designed fixture and static loading creep tests were carried out on these solder samples at temperatures of 25°C, 75°C and 125°C using tensile testing machine (Micro-Testing System). The Young's Modulus and hardness of 80Au/20Sn solder alloy increase with an increase in load rate or a decrease in temperature. The microstructure and creep rupture fractography of 80Au/20Sn solder alloy have been observed and analysed.
Mechanical Properties Predictions and Responses of Defected Carbon Nanotubes Subjected to Axial Loading
Authors: Askari Davood , Nejhad Mehrdad N. Ghasemi
Published: April 2008

The increasing demand for fabrication of smaller structural and electronic devices with higher performance such as NEMS/MEMS has created great interest and motivation for extensive research and investigations in nanotechnology and its applications. Unique mechanical, thermal, and electrical properties of the one dimensional carbon nanotubes (CNTs) structures project CNTs as an excellent candidate for the future NEMS/MEMS devices. However, carbon nanotubes do not always exist in their perfect hexagonal lattice structures. Defects may appear during the purification stages or chemical treatments as it might even be desirable for functionalization of carbon nanotubes. On the other hand, defects can greatly influence the mechanical performance of carbon nanotubes in structural applications where they are subjected to external mechanical loads. Therefore, a detailed investigation of the effects of defects on mechanical performance of carbon nanotubes is needed to explain the behavior of such structures. Here in this work, finite element method (FEM) is employed to numerically investigate the responses of defected carbon nanotubes to external loads. Single-walled carbon nanotubes (SWCNTs) with different structural configurations, i.e., zigzag, armchair, and chiral, with different types of vacancy defects are modeled and their effective mechanical properties are investigated. Finally, results are discussed and compared with those obtained for SWCNTs without defects.
Frictional Pressure Drops of Two-Phase R-134A Flow in Horizontal and Vertical U-Type Wavy and Straight Tubes
Authors: Chen Ing Youn , Wu Yu-Shi , Chang Yu-Juei , Wang Chi-Chuan
Published: April 2008

This study presents the measurements of R-134a two-phase frictional pressure gradient subject to vertical and horizontal arrangements of a U-type wavy tube with inner diameter of 5.07 mm and a curvature ratio of 5. The ratio between two-phase pressure gradients of U-bend and straight tube is about 2.5 - 3.5. For the straight tube, the frictional two-phase pressure gradient ratio between the vertical and horizontal arrangements is marginally higher (1.0 - 1.2) for annular flow pattern at x > 0.5, and is 1.0 - 1.4 for the U-bend in the wavy tube. The higher resistance in the vertical arrangement is due to the buoyancy force against the flow inertia. However, for x < 0.5, this ratio is gradually increased due to the difference of flow pattern. The ratio is increased to 1.8 in the straight tube. For the U-bend, the ratio is 2.1 for flow entering the upper tube and is 1.5 for flow entering the lower tube at x = 0.1 and G = 200 kg/m2·s. For the vertical wavy tube, additional effects like the flow pattern transition, liquid flow reversal, and freezing slug may cause additional pressure drops.
Hands on Efforts Designed to Increase Design and Manufacturing Preparedness of Undergraduate Students
Authors: Schonning Alexandra , Cox Daniel
Published: April 2008

In an effort to better prepare the future workforce for sought after engineering skills, the mechanical engineering program at the University of North Florida (UNF) has updated its undergraduate curriculum to reflect these needs and is also providing its students with opportunities outside of the academic curriculum. This paper addresses how objectives of increasing the design and manufacturing preparedness of undergraduate students, increasing students' skills in applying theory to practice, and at the same time improving the students' communication skills can be achieved. In meeting these objectives the program has developed a course, Integrated Design and Manufacturing, The course also helps to provide the students with research opportunities with the local industry, and organizes opportunities for the undergraduate students to attend conferences to present their research findings.
A Parametric Study on Particulate Al-SiC Composite Bolted Joints
Authors: Shoukry Samir N. , Prucz Jacky C. , William Gergis W.
Published: April 2008

The main objective of this study is to predict theoretically the stress distributions around the holes in a bolted joint made of particulate metal matrix composite and to investigate the associated load transfer efficiencies both for a single and double lap bolted joints. A three-dimensional finite element parametric model has been developed to examine the effects of various design parameters on the structural performance of such joints. The main feature of this model is explicit modeling of the sliding interfaces between the connected plates and the washers, and those between the hole and the bolt. The model response showed an excellent agreement with a closed form solution as well as experimental data. The results indicated that unsymmetric configuration of single lap joints causes bending as the load is applied, which is opposite of the double lap joints. This research quantifies the relationship between the stress developed around the hole and washer diameter, tightening pressure, and clearance between the bolt and hole. It was also observed that variations in Young's modulus have no significant effect on the stress concentration around the hole.
Effect of Carbon Nanofiber on Thermal and Tensile Properties of Polypropylene
Authors: Zhou Yuanxin , Hasan Mohammad Monirul , Jeelani Shaik
Published: April 2008

In the present study, effect of vapor grown carbon nanofiber on the mechanical and thermal properties of polypropylene was investigated. Firstly, nanofibers were dry-mixed with polypropylene powder and extruded into filaments by using a single screw extruder. Then the tensile tests were performed on the single filament at the strain rate range from 0.02/min to 2/min. Experiments results show that both neat and nano-phased polypropylene were strain rate strengthening material. The tensile modulus and yield strength both increased with increasing strain rate. Experimental results also show that infusing nanofiber into polypropylene can increase tensile modulus and yield strength, but decrease the failure strain. At the same time, thermal properties of neat and nano-phased polypropylene were characterized by TGA. TGA results have showed that the nanophased system is more thermally stable. At last, a nonlinear constitutive equation has been developed to describe strain rate sensitive behavior of neat and nano-phased polypropylene.
Enhanced Electrohydrodynamic Pumping at the Microscale
Authors: Cremaschi Lorenzo , Iverson Brian D. , Garimella Suresh V.
Published: April 2008

An enhanced electrohydrodynamic micropump for use in small-scale liquid pumping applications is developed. The micropump can be incorporated into an integrated circuit chip to provide active cooling. Liquid flow is achieved by combining two actuation mechanisms: electrohydrodynamics (EHD) and the action of a vibrating diaphragm. Heat generated by active devices creates a thermal gradient in the fluid allowing induction of ions to be driven by EHD. The vibrating diaphragm enhances the EHD efficiency allowing more pumping power to be transferred to the fluid. The design and operation of the micropump are discussed, and results are presented in terms of volume flow rate.
Adaptive Sliding Mode Controller With Proportional Plus Integral Sliding Surface
Authors: Fei J. , Batur Celel
Published: April 2008

This paper presents an adaptive tracking controller with a proportional and integral switching surface. A new adaptive sliding mode controller based on model reference adaptive state feedback control is proposed to deal with the tracking problem for a class of linear dynamic systems. First, a proportional and integral sliding surface instead of a conventional sliding surface is chosen and then an adaptive sliding mode controller is derived and its stability is proved. It is shown that the stability of the closed-loop system can be guaranteed with the proposed adaptive sliding mode control strategy. The adaptive design is extended to the multiple inputs system. The numerical simulation is investigated to show the effectiveness of the proposed adaptive sliding mode control scheme with proportional plus integral sliding mode action.
Proposing a Pretwisted Bending Actuator
Authors: Dienerowitz Frank , Gaus Nicole , Seemann Wolfgang
Published: April 2008

Piezoelectric bending actuators take advantage of both piezoelectricity and kinematics of beams, i.e. (1) direct transformation of electric energy into mechanical energy without causing significant magnetic fields and (2) to be capable of turning small strain modifications into large deflections, provided the cross-section is rather flat. Unfortunately the latter usually implies that bending actuators provide only one axis of large deflection. Herein a pretwisted bending actuator is investigated, similar to a helicoid. The active elements along the beam axis are subdivided and controlled separately, hence allowing independent control of the curvature of each section. Due to the pretwist, this bending actuator can provide not only one but two axes of deflection. For a slender pretwisted bending actuator the problems emerging are presented and discussed, covering the work space of the actuator, optimization of electrode connecting patterns and experimental results.
The Effects of Hydrodynamics Characteristics on Mass Transfer During Droplet Formation Using Computational Approach
Authors: Javadi A. , Taeibi-Rahni M. , Bastani D. , Javadi K.
Published: April 2008

For the reason that flow expansion model (developed in our previous work) for evaluating mass transfer during droplet formation involves with manifest hydrodynamic aspects, in this research computational simulation of this phenomenon was done for characterization of hydrodynamics effects on the mass transfer during droplet formation. For this purpose, an Eulerian volume tracking computational code based on volume of fluid (VOF) method was developed to solve the transient Navier-Stokes equations for the axisymmetric free-boundary problem of a Newtonian liquid that is dripping vertically and breaking as drops into another immiscible Newtonian fluid. The effects of hydrodynamics effects on the mass transfer during droplet formation have been discussed in the three features, including: 1- The intensity of the interaction between two phases 2-The strength and positions of the main vorticities on the nozzle tip 3-The effects of local interfacial vorticities (LIV). These features are considered to explain the complexities of drop formation mass transfer between Ethyl Acetoacetate (presaturated with water) as an organic dispersed phase and water as continuous phase for two big and small nozzle sizes (0.023 and 0.047 cm, ID) which have different level of mass transfer rate particularly in first stages of formation time.
Size and Velocity Characterization of Asymmetric Twin-Fluid Nebulizer Sprays
Authors: Lopez Celienid , Sojka Paul E.
Published: April 2008

Drop size and velocity measurements were obtained for two nebulizers unique in their asymmetric configuration—a "quarter-moon" liquid exit port, whose axis of symmetry is located nearly co-axially with a circular air exit port. The two devices, a Mira Mist and an LB-30, are commercially available units originally designed for mass-spectrometry applications, but also useful for medicinal/pharmaceutical spray purposes. Sprays were characterized in terms of droplet velocity and size at a number of axial and radial positions. Measurements were performed using a Dantec DualPDA. Air injection pressures of 270 to 410 kPa (25 to 45 psig) and liquid flow rates of 75 to 1200 ml/hr were the operating conditions considered in this study. Water and ethanol were used as test fluids since their physical properties span the range of typical products. The results are useful because they show, for the first time, how sprays formed from such asymmetric devices evolve as they move away from the atomizer.
Drop Formation in Non-Newtonian Jets at Low Reynolds Number
Authors: Dravid Vineet , Loke Ping Bu , Corvalan Carlos M. , Sojka Paul E.
Published: April 2008

The major objective of this work is to develop accurate computational models to predict evolution of shear thinning liquid jets. A secondary objective is to investigate the formation of satellite drops, and to determine the conditions under which their diameter can be controlled. The theoretical approach of Galerkin-finite element analysis is used solve the complete two-dimensional set of axisymmetric governing equations and the kinematic and dynamic boundary conditions at the free surface. The effect of shear thinning behavior on break-up is studied in detail, in the case of an infinitely long non-Newtonian jet. It is found that the shear thinning behavior may be useful in controlling satellite drop sizes. (We observe that increasing the shear thinning behavior at moderate Reynolds number (Re = 5) leads to an initial increase in the satellite drop size, followed by a subsequent decrease.) Experimental validation for the theory is then presented for the case of a shear thinning non-Newtonian jet. The experimental fluid is pumped through a capillary and drop shapes are obtained using a high speed camera. The experimentally obtained shapes are compared to those predicted by theory with results found to be in good agreement.
Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels
Authors: Xiong Renqiang , Chung J. N.
Published: April 2008

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re<100. Those vortices appear and continue to develop with the Re number when Re> 100-300, and the shape and size of the vortices almost remain constant when Re>1000. The bend loss coefficient Kb was observed to be related with the Re number when Re<100, with the Re number and channel size when Re>100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.
Characteristics and Applicability of a Newly Developed Numerical Scheme for Simulating Liquid Sloshing in a Moving Tank
Authors: Chandra Sharat , Dai Liming
Published: April 2008

A novel mathematical model for analyzing the dynamic property of the liquid motion is developed. The work in this paper assesses and further develops the mathematical model formulated especially for analyzing the liquid motion in horizontal cylindrical tanks. The present research talks about the liquid sloshing and the cyclic forces produced as a result of it. These forces which are cyclic in nature degrade the structure of a tank vehicle transporting liquid cargo. The validation of the proposed model is performed by an effective Eulerian fixed grid technique, which implements the Volume of Fluid (VOF) model. Finally this paper presents a comparison for various results obtained by implementing both the models. Such a comparison is very important, as it will validate the effectiveness of the proposed model to be considered for integrating it with structural and fatigue analysis.
Estimation of Rotor-Bearing Parameters by a Global Optimization Method
Authors: Khorshid E. A. , Falah A. H.
Published: April 2008

Modeling, experiments and system identification of the linear dynamics of a flexible multi-bearing rotor with two concentrated disks are presented in this paper. Both rotor unbalanced vibration responses through critical speeds were experimentally obtained through accurate control of journal bearing static load. Vibration simulations of this laboratory rotor-bearing system were performed as a linear system. The simulation and the experimental results have large differences for both rotors. These differences occur because of (1)The errors in estimating the journal bearing damping and stiffness coefficients, and, (2)The neglect of the effect of the small radial air gap (20 Mils) at the two disks' outer diameter which provides some additional bearing-like radial stiffness and damping effects. An estimate of these coefficients for both the journal bearing and the rotor-radial air gap is obtained using optimization methods. Good agreement was found between the experimental and the optimized model.
Improving Energy Absorption and Dissipation of Composites Through Optimized Tayloring
Authors: Ferrero Laura , Icardi Ugo
Published: April 2008

Fibre-reinforced and sandwich composites with laminated faces are the best candidate materials in many engineering fields by the viewpoint of the impact resistance, containment of explosions, protection against projection of fragments, survivability and noise and vibration suppression. Besides, they offer the possibility to be tailored to meet design requirements. A great amount of the incoming energy is absorbed through local failures. The most important energy dissipation mechanisms are the hysteretic damping in the matrix and in the fibers and the frictional damping at the fiber-matrix interface. The dissipation of the incoming energy also partly takes place as a not well understood dissipation at the cracks and delamination sites. As self-evident, the local damage accumulation mechanism on the one hand is helpful from the standpoint of energy absorption, on the other hand it can have detrimental effects. To date sophisticated computational models are available, by which the potential advantages of composites can be fully exploited. A large amount of research work has been oriented to improve the impact resistance, the dissipation of vibrations and to oppose the propagation of delamination. These goals can be obtained with incorporation of viscoelastic layers. Unfortunately this makes quite compliant the laminates and reduce their strength. Studies have been recently published that seeks to comply stiffness and energy dissipation. The existence of fiber orientations that are a good compromise between optimal stiffness and optimal absorption of the incoming energy can be supposed by the results of a number of published studies. In this paper, a variable spatial distribution of plate stiffnesses, as it can be obtained varying the orientation of the reinforcement fibres along the plate and their constituent materials, is defined by an optimization process, so to obtain a wanted specific structural behaviour. The key feature is an optimized strain energy transfer from different deformation modes, such as bending, in-plane and out-of-plane shears. Suited plate stiffness distributions which identically fulfil the thermodynamic and material constraints are found that make stationary the energy contributions and transfer energy between the modes as desired. An application to low velocity impacts and to blast pulse loads is presented. The use of the optimized layers with the same mean properties of the layers they substitute were shown to reduce deflection and the stresses that induce delamination. A new discrete layer element is developed in this study, to accurately account for the local effects. Characteristic feature, it is based on a C° in-plane approximation and a general representation across the thickness which can either represent the kinematics of conventional plate models or the piecewise variation of layerwise models.
Absolute Band Gaps in Two-Dimensional Phononic Crystal Plates
Authors: Vasseur Je´roˆme , Deymier Pierre A. , Djafari-Rouhani Bahram , Pennec Yan
Published: April 2008

The elastic band structures of two-dimensional phononic crystal plates are computed with the help of a super-cell plane wave expansion (PWE) method. These band structures strongly differ from the infinite 2D phononic crystal dispersion curves. In particular, these band structures exhibit surface modes and guided modes. The influence of the constituent materials, of the plate thickness and of the geometry of the array on the band structure is investigated. We focus more specifically on determining the thicknesses of the plate for which absolute forbidden bands exist. Namely, we show that absolute forbidden bands occur in the band structure if the thickness of the plate is of the same order of magnitude as the periodicity of the array of inclusions.
Robust, Non-Overshooting Control of a Rigid Rotating Link Using Exponential Segmentation
Authors: Shelton Jeffrey N. , Chiu George T.-C.
Published: April 2008

Exponential pyramid architecture plays a key role in human visual processing, as well as in learned muscle movement. Attempting to mimic the human capacity for making rapid minimally-overshooting movements, a variant of exponential pyramid architecture, called exponential segmentation, is utilized to develop a methodology for controlling the response of rigid links to step inputs. The resulting method consists of issuing iterative open-loop commands, each of which are guaranteed not to overshoot the desired target. Each time the mechanism comes to a stop, a new open loop command is issued that again drives the mechanism toward the desired final position without overshoot. Since this method always undershoots the target, the process is repeated until the link is within a specified interval of the desired final position. Using this framework, a designer can easily make tradeoffs between response and robustness, as this method is robust with respect to input perturbations, pivot friction, link inertia and damping rates. Furthermore, this method can be implemented using positional measurement alone.
Hybrid Pressure-Swirl/Twin-Fluid Atomizer for Emission Controls
Authors: Lee Andrew C. S. , Sojka Paul E.
Published: April 2008

An experimental study was conducted to characterize the performance of a hybrid atomizer used in emission control devices. Characterization included drop size distribution, measured using a forward light-scattering instrument, the air flow field (axial and radial velocities), measured using 2-D PIV, and turbulence characteristics of the air flow field, measured using LDA. The air flow field showed characteristics common to turbulent free round jets beyond approximately 8 exit orifice diameters from the atomizer exit plane. The centerline velocity increased with an increase in mass flow rate, while radial velocities were two orders of magnitude smaller than centerline values. The jet spreading factor initially increased with an increase in axial distance from the exit; however, it stabilized at a value of 0.09 at z/Do=11.8. Turbulence intensity along the jet centerline stabilized at 25% at z/Do=7.9. Drop size data showed complex dependencies on liquid and air mass flow rates, and on internal geometry. The influence of liquid mass flow rate on drop size was significantly smaller for the hybrid atomizer than for the pressure swirl atomizer component housed inside the hybrid unit, thus indicating a higher turndown ratio for the hybrid device. Drop size distributions produced by the hybrid atomizer showed multiple peaks, indicating there is more than one important atomizing mechanism. Finally, reducing the gap between the pressure-swirl atomizer and the exit plane of the outer casing resulted in a reduction in drop size.