bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling and Control of a Variable Length Flexible Cable Overhead Crane Using the Modified Galerkin Method
Authors: Moustafa Kamal A. F. , Trabia Mohamed B. , Ismail Mohamed I. S.
Published: May 2009

A mathematical model that accurately represents an overhead crane with flexible cable and load hoisting/lowering is developed. The analysis includes the transverse vibrations of the flexible cable and the trolley motion as well as the load hoisting/lowering motions. A set of highly non-linear partial differential equations and ordinary differential equations that govern the motion of the crane system within time-varying spatial domain is derived via calculus of variation and Hamilton’s principle. Variable-time modified Galerkin method has been used to discretize the non-linear system. State space transformation is then used to get a set of first order ordinary differential equation. A proportional derivative control scheme is applied to derive the underlying crane so that the cable and payload swing are damped out. Numerical simulations for the control performance of the considered system are presented for various operating conditions.
Current Status of the SAPHIRE Risk Analysis Software
Authors: Smith Curtis L. , Knudsen James K.
Published: May 2009

As a supporting organization for risk activities at a variety of government agencies including the U.S. Nuclear Regulatory Commission (NRC), National Aeronautics and Space Administration (NASA), and Department of Energy (DOE), the Idaho National Laboratory (INL) has been a principal developer of probabilistic risk and reliability analysis tools for over 35 years. The current state-of-the-practice has evolved to the use of the SAPHIRE software. This tool started in the mid-1980s as part of the NRC’s general risk activities. In 1986, work commenced on the precursor to the SAPHIRE software — this software package was named IRRAS. While limited to the analysis of only fault trees of medium size, version 1 of IRRAS was the initial step in the progress that today has led to the SAPHIRE software, software that is capable of running on multiple processors simultaneously and is able to handle extremely complex analyses. SAPHIRE has been designed to handle large fault trees, where a tree may have up to 64,000 basic events and gates. To handle the fault trees, two mechanisms for developing and modifying the fault tree are available — a graphical editor and a hierarchical logic editor. In risk applications, there are two predominant event tree analysis methods, the “large event tree” approach and the “fault tree linking” approach. A couple of key identifying attributes of the large event tree approach is that the number of accident sequences becomes very large (measured in the millions or more) and the event tree branches are represented by probability values. For the fault tree linking approach, the number of sequences is low and fault trees represent the event tree branch points. The INL has designed SAPHIRE to handle both event tree methods. SAPHIRE uses logic models to determine minimal cut sets. Once the dominant cut sets are determined, the group of cut sets must be quantified to determine the overall probability of frequency. After the cut sets are generated, they are used to obtain the importance measures for each basic event in the cut sets. The resultant cut sets are also used to propagate (using either Monte Carlo or Latin Hypercube sampling) the basic event’s epistemic uncertainty.
Numerical Study of the Tool Rake Angle Effect on the Material Flow in Friction Stir Welding Process
Authors: Atharifar Hosein , Kovacevic Radovan
Published: May 2009

Minimizing consumed energy in friction stir welding (FSW) is one of the prominent considerations in the process development. Modifications of the FSW tool geometry might be categorized as the initial attempt to achieve a minimum FSW effort. Advanced tool pin and shoulder features as well as a low-conductive backing plate, high-conductive FSW tools equipped with cooling fins, and single or multi-step welding processes are all carried out to achieve a flawless weld with reduced welding effort. The outcomes of these attempts are considerable, primarily when the tool pin traditional designs are replaced with threaded, Trifiute or Trivex geometries. Nevertheless, the problem remains as to how an inclined tool affects the material flow characteristics and the loads applied to the tool. It is experimentally proven that a positive rake angle facilitates the traverse motion of the FSW tool; however, few computational evidences were provided. In this study, numerical material flow and heat transfer analysis are carried out for the presumed tool rake angle ranging from −4° to 4°. Afterwards, the effects of the tool rake angle to the dynamic pressure distribution, strain-rates, and velocity profiles are numerically computed. Furthermore, coefficients of drag, lift, and side force and moment applied to the tool from the visco-plastic material region are computed for each of the tool rake angles. Eventually, this paper confirms that the rake angle dramatically affects the magnitude of the loads applied to the FSW tool, and the developed advanced numerical model might be used to find optimum tool rake angle for other aluminum alloys.
The Kinematics of Conical Involute Gear Hobbing
Authors: Innocenti Carlo
Published: May 2009

The paper is aimed at finding all relative rigid-body positions of two conical involute gears that mesh together with no backlash. The results are then specialized to determine two key setting parameters for a hobbing machine that has to cut a conical involute gear. A numerical example shows application of the presented results to a case study.
Non-Intrusive Unilateral Measurements of Void Incidence Within a Microchannel
Authors: Heymann Douglas , Young Jordan , Cardenas Ruander
Published: May 2009

Void fraction measurements are used to characterize two-phase flow within a microchannel. Limitations of typical void fraction measurement systems include disruption of the flow (intrusive optical probe) and non-continuous data acquisition. Using the principles of total internal reflection, a Non-Intrusive Void Incidence Sensor (NIVIS) has been developed to determine the void incidence (frequency of a vapor bubble passing a known position in the channel). Continuous data can be recorded with a typical computer. A light beam is introduced through a fiber optic to the outside of a transparent channel wall at a critical angle. This critical angle is designed such that when a vapor bubble is present at the specified location, total internal reflection will occur. An output fiber is fixed in a determined position to receive light in the case of total internal reflection. Without the presence of a vapor bubble, the light beam will be reflected past the output fiber. A substantial increase in output signal is noticed when total internal reflection occurs. Characteristics of the NIVIS, proven during non-intrusive testing, include: continuous data acquisition of bubble incidences, measurements within a 100 micron wide channel, and bubble boundary differentiation.
Dynamic Analysis of Soft Tissue Viscoelasticity Under Ultrasonic Radiation Force Using FEM
Authors: Kogit Megan L. , Shan Baoxiang , Pelegri Assimina A.
Published: May 2009

We have developed a solid mechanics model of nearly incompressible, viscoelastic soft tissue for finite element analysis (FEA) in MATLAB 7.2. Newmark’s method was used to solve the finite element equations of motion for our model. The solution to our dynamic problem was validated with a transient dynamic analysis in ANSYS 10.0. We further demonstrated that our MATLAB FEA qualitatively agrees with those results observed with acoustic radiation force methods on soft tissues and tissue-mimicking materials. We showed that changes in Young’s modulus and the damping coefficient affect the displacement amplitude and phase shift of the response data in the same manner: An increase in Young’s modulus or damping coefficient decreases both the displacement amplitude and response lag. Future work on this project will involve frequency analysis on response data and studying the initial transient region to help uncouple the effects of Young’s modulus and damping coefficient on response characteristics. This will get us one step closer to being able to explicitly determine Young’s modulus and the damping coefficient from the temporal response data of acoustic radiation force methods, which is the ultimate goal of our project.
An Adaptive Finite Element Model for Simulating Natural Convective Effects of Multiple Obstructions
Authors: Wang Xiuling , Pepper Darrell W.
Published: May 2009

The investigation of laminar natural convection in vertical channels with multiple obstructions on opposite walls is conducted using an h-adaptive FEM algorithm. The adaptive model uses an L2 norm based a posteriori error estimator with a semi-implicit, time-stepping projection technique. The advection terms are treated using an explicit Adams Bashforth method while the diffusion terms are advanced by an implicit Euler scheme. By using the adaptive algorithm, mesh independent studies can be avoided. Results are obtained for thermal and flow patterns including average Nusselt numbers for different parameters (Rayleigh number, aspect ratio and locations of obstructions).
Sizing, Part-Load Operation, and System Performance of Combined Heat and Power
Authors: Beyene Asfaw , Erpelding Benjamin
Published: May 2009

Because of its superior efficiency and peak load mitigation capabilities, considerable attention has been given recently to combined Cooling, Heating and Power (CCHP). They technology enjoys tax benefits, incentives, accelerated permit processes, etc both at the local, state, and federal levels. One serious challenge to the implementation of CCHP systems is matching and sizing of the system to strongly and frequently varying load conditions. This paper presents matching and sizing related challenges of CCHP systems with emphasis on operation-related and weather-driven load factors. Regional data from the California Public Utilities Commission (CPUC) were used to evaluate the success of recent incentive-driven CHP implementations. It is concluded that while CCHPs have significant cost and performance advantages over traditional single-cycle systems, inadequate strategies — failure to address system flexibilities to accommodate load variations in particular, seem to have negatively impacted these promising technology.
A Multiscale Approach for the Determination of Nonsingular Elastic Fields of Dislocations in Bulk and Nano-Layered Materials
Authors: Banerjee Sauvik , Shehadeh Mutasem , Lu Gang , Kioussis Nicholas , Ghoniem Nasr
Published: May 2009

The traditional description of elastic field and energies of dislocations is based on continuum theory of linear elasticity that suffers from the long-standing problem of singularities at the dislocation core. Singular solutions are often circumvented by introducing an artificial core-cutoff radius. This limits the applicability of the theory to describe situations where it is important to know the strained state and nanoscopic details within a few atomic spacings surrounding the dislocation center, known as the dislocation core. In this paper, a computationally tractable multiscale approach is developed to calculate the nonsingular elastic fields of dislocations in both bulk and nano-layered materials. The approach is an extension of Peierls-Nabarro (PN) model, with the following features: (1) all three components of the displacement vector for atoms within the dislocation core are included; (2) the entire generalized stacking fault energy (GSFE or gamma-γ) surface obtained from ab initio calculations is utilized; and (3) the method can be generalized to treat curved dislocations. We combine the parametric dislocation dynamics (DD) approach for the interaction and motion of dislocations with the ab initio calculations of the lattice restoring forces, which are extracted from the γ surface. The method is used to study two important problems: (a) dislocation dissociation in bulk crystals (b) dislocation transmission across interfaces in elastic bimaterials. Dislocation core structures in bulk aluminum and silver are determined. The results from the model are shown to be in excellent agreement with experiments for both Al and Ag. For bi-materials system, the effects of the mismatch in the elastic properties, γ surface and lattice parameters on the spreading of the dislocation onto the interface(s) and the transmission across the interface(s) are studied in detail.
A Practical Approach for Problem-Based Learning in Engineering
Authors: Hunt Emily M. , Lockwood-Cooke Pamela , Fisher Paul
Published: May 2009

Problem-based Learning (PBL) is a motivating, problem-centered teaching method with exciting potential in engineering education. PBL can be used in engineering education to bridge the gap between theory and practice in a gradual way. The most common problem encountered when attempting to integrate PBL into the undergraduate engineering classroom is the time requirement to complete a significant, useful problem. Because PBL has such potential in engineering, mathematics, and science education, professors from engineering, mathematics, and physics have joined together to solve small pieces of a large engineering problem concurrently in an effort to reduce the time required to solve a complex problem in any one class. This is a pilot project for a National Science Foundation (NSF) supported Science Talent Expansion Program (STEP) grant entitled Increasing Numbers, Connections, and Retention in Science and Engineering (INCRSE) (NSF 0622442). The students involved are undergraduate mechanical engineering students that are co-enrolled in Engineering Statics, Calculus II, and Engineering Physics I. These classes are linked using PBL to increase both student engagement and success. The problem addresses concepts taught in class, reinforces connections among the courses, and provides real-world applications. Student, faculty, and industry assessment of the problem reveals a mutually beneficial experience that provides a link for students between in-class concepts and real-world application. This method of problem-based learning provides a practical application that can be used in engineering curricula.
Mode-I Interlaminar Fracture Toughness and Fatigue Crack Growth of Carbon Nanofibers Modified Polyester/Glass Fiber Laminates
Authors: Lu Khoa , Farah Basil , Hsiao Kuang-Ting , Parker Martin R.
Published: May 2009

A major weakness of laminated composite is the susceptibility to delamination. Having a good understanding of composite material resistance to interlaminar fracture and fatigue is important to establish design allowable and damage tolerance guidelines for structures. Previously reported static delamination test results have shown that there is about 100% improvement in the critical energy release rates GIC by adding 1wt% carbon nanofibers (CNFs) to glass fiber/polyester laminates. Hence, this paper presents the fatigue resistance characterization of glass fiber/polyester composite modified with CNFs. CNFs were surfactant treated and dispersed in the thermoset polyester. The matrix with suspended CNFs was infused into glass fiber preform through vacuum assisted resin transfer molding (VARTM). The crack development of the laminated specimens during fatigue delamination testing was recorded along with the displacement and cyclic load applied. The fatigue measurement results for the traditional composite laminate and the one modified with CNFs is compared to understand the role of CNFs in the fatigue delamination process. It was found that CNFs significantly improve the low cycle fatigue performance, but it provides minimal improvement to the high cycle fatigue performance.
A Micromechanical Approach for Analyzing Thermo-Mechanical Responses of Functionally Graded Materials
Authors: Muliana Anastasia , Khan Kamran
Published: May 2009

Functionally graded materials (FGMs) consist of continuously or discretely changing thermal and mechanical properties in the graded directions. The FGMs are often used for applications that involve high temperature gradients. Under this condition, the thermal and mechanical properties of materials can strongly depend upon the temperatures, which create a thermo-mechanical coupling. Available micromodels of FGMs have focused on obtaining the through-thickness mechanical properties [2,4,7]. This study develops an integrated micromechanical and structural framework for analyzing coupled heat conduction and deformations in the FGMs. A through-thickness material variation is represented with piecewise homogeneous media. Average thermomechanical properties in each homogeneous medium are obtained using a micromodel of particle reinforced composites, whose constituents’ properties can change with temperatures and/or stresses. Sequentially coupled heat transfer and displacement analyses are performed, which allows analyzing stress/strain with temperature dependent mechanical properties, but the temperature field is obtained without knowledge of stress/strain responses. Parametric studies are performed to determine the effects of through thickness material variation and constituent properties on the overall performance of the FGM. Available experimental data and analytical models are used for comparisons.
Project Management in an Interdisciplinary Senior Design Team
Authors: Mawasha P. Ruby , Yelamarthi Kumar
Published: May 2009

Innovation in the changing undergraduate engineering curriculum mandates efficient management of interdisciplinary capstone senior design projects. This effort requires collaboration and management by students and faculty from multiple disciplines, and provides students an opportunity to learn from other engineering systems. In addition, this approach will i) emphasize problem solving and creative thinking; ii) provide first-hand experience in generating a management plan; iii) expose students to multiple engineering and management disciplines, and to work in diverse, multi-cultural teams; and iv) prepare students with a keen understanding of the interdisciplinary environment necessary for success. The senior design project (SDP) presented is based on the interdisciplinary collaboration of electrical, computer, and mechanical engineering students and faculty to design an integrated high altitude balloon system that would reach an altitude of 100,000 feet and return safely to earth. This paper presents the modes by which all the above issues in SDP are addressed, results obtained and improvements planned for the next interdisciplinary projects.
Thermal Boundary Layer Response to Far-Field Flow Temperature Transitions
Authors: Li Hongwei , Nalim M. Razi
Published: May 2009

Gas flows of varying temperature occur in heat exchangers, nuclear reactors, non-steady flow devices, and combustion engines, among other applications with heat transfer processes that influence energy conversion efficiency. A general numerical method is developed for predicting the transient laminar thermal boundary layer response to arbitrarily prescribed changes in the bulk far-field fluid temperature. The method is tested for the step change of the far-field flow temperature of a two-dimensional semi-infinite flat plate with steady hydrodynamic boundary layer and constant wall temperature assumptions. Changes of the fluid-wall temperature difference in magnitude and sign are considered, including flow with no initial temperature difference and built-up thermal boundary layer. The governing differential equations for momentum and energy are solved based on the Keller-Box finite difference method. The accuracy of the solutions is verified through comparing with the steady state solution. Transient heat transfer coefficients are presented, which indicate that both magnitude and direction of heat transfer can be significantly different from quasi-steady models commonly used.
Experiences With Thermal Driven, Desiccant Assisted Air Conditioning Systems in Germany
Authors: Schmitz G. , Joos A. , Casas W.
Published: May 2009

During summer, the use of conventional electrically driven air conditioning systems often results in high electricity consumption. On the other hand, heat demand is very low, therefore heat from Combined Heat and Power plants (CHP) or from solar collectors can not be used. Thermal driven desiccant assisted air conditioning systems offer the possibility to shift energy requirements from electricity to heat. Furthermore, as sorptive pre-drying air doesn’t require cooling under dew point for dehumidifying nor any subsequent heating, cold sources at higher temperatures (e.g. 18°C) can be used for cooling. Within the scope of research projects, different demonstration plants for office buildings and a private bungalow were built, where the operations were evaluated by the Hamburg University of Technology. One plant combines a desiccant wheel with a small (5 kWel) gas driven co-generation plant. Instead of an electric chiller or a water evaporation system (desiccant evaporating cooling), borehole heat exchangers in combination with a radiant floor heating system were used for cooling in summer. In this paper, performance comparisons with conventional systems based on numerical simulations and measurement data are shown, including a cost analysis. It is found that the combination of desiccant wheels and earth energy systems offers considerable energy savings compared to conventional electric systems. The operation of such systems is also cost-effective. It can lead to a reduction of up to 28% of primary energy consumption in a whole year compared to a conventional A/C system.
Replication of Reliable Assembly Features for Polymer Modular Microfluidic Systems
Authors: Chen Pin-Chuan , You Byoung Hee , Park Daniel S. , Park Sunggook , Guy Jason , Nikitopoulos Dimitris E. , Soper Steven A. , Murphy Michael C.
Published: May 2009

BioMEMS are compact devices which use microfabrication to miniaturize conventional benchtop instruments. The benefits of using micro devices are the need for less chemical reagents, faster processing, and portability. Realizing a powerful sample-to-answer micro system requires more than just microfabrication technology; thermal management, microfluidic control, and interfacing technology must also be considered. You et al. [1] applied kinematic constraint analysis using screw theory to design the assembly features for passive alignment structures for polymer, modular microfluidic devices. Three pairs of v-groove and hemispherical pin joints were chosen as kinematic pairs for mating two modules. Dimensional variation of the assembly features was one of principal contributions to the mismatch of 28 μm-75 μm between stacked plates in assembly that was reported. This was primarily a result of incomplete mold filling and deformation of the passive alignment structures during the demolding process. Hemisphere-tipped recesses, with additional annular walls as dummy structures, were used to designed to achieve better replication by improving polymer filling and reducing the deformation during demolding. In prototype devices, the posts with the annular dummy structures had a mean height of 922.2 μm – 924.1 μm while the original posts without dummy structures had mean heights of 865.3 μm – 891.2 μm in 10 samples under the same embossing conditions for a design height of 925 μm. Alignment accuracy of better than 10 μm was achieved in the assembly of two plates.
Implementation of a Modified Skyhook Control on a Purely Pneumatic Semi-Active Suspension System
Authors: Porumamilla H. , Kelkar Atul G. , Vogel Jerald M.
Published: May 2009

The paper presents implementation of a modified skyhook control on a purely pneumatic suspension system comprising of an airspring, a pressure-differential causing geometry such as a sharp edged orifice and an accumulator, which utilizes the dynamics of compressible air flow through an orifice to inject damping into the suspension rather than heat dissipation as in suspensions with oil-base damper. A continuous-skyhook logic is implemented on the hardware built as a single degree of freedom system. For a head-to-head comparison, a contemporary semi-active suspension using an MR-damper is modeled. The airspring of this suspension is modeled from first principles of Thermodynamics and a new continuously differentiable function describing the force-velocity profiles of the MR-damper is developed. An evaluation of the sprung mass acceleration shows that the performance of the pneumatic suspension rivals that of the MR based unit for an arbitrarily chosen base excitation input. The modified Skyhook law proposed for producing pneumatic damping is shown to be able to inject sufficient damping (compared to MR-Damper), thereby off-setting the need for an additional oil damper.
Tolerance Analysis of Dynamic Equilibria in Multibody Systems Having Prescribed Rotational Motion
Authors: Choi Dong Hwan , Yoo Hong Hee , Wickert Jonathan A.
Published: May 2009

A general formulation for the tolerance analysis of dynamic equilibria in multibody systems having prescribed rotational motion is developed. In a state of dynamic equilibrium, a subset of generalized coordinates assume constant values, while the remaining coordinates vary and respond in time. Applications in which multibody systems exhibit dynamic equilibria include robots, spacecraft, propulsion and power generation systems, and some sensor devices. In the derived approach, manufacturing tolerances are mathematically modeled by probabilistic and statistical variables, through an analytical approach and through Monte Carlo simulation. An efficient computational method based upon direct differentiation is developed to calculate the first order sensitivity of the equilibria with respect to the design and manufacturing variables. To verify the accuracy and effectiveness of the present method, the present analytical method and the companion Monte Carlo approach are applied in examples to a rotating pendulum, a mechanical speed governor, and a model of a rate gyroscope sensor.
Energy Consumption of an LS Excavator Hydraulic System
Authors: Zimmerman Joshua D. , Pelosi Matteo , Williamson Christopher A. , Ivantysynova Monika
Published: May 2009

This paper presents the results of a simulation study regarding the energy consumption of a load-sensing excavator hydraulic system and discusses the possible energy savings by eliminating the directional control valves. The energy consumption of the excavator hydraulic system has been studied for typical working cycles. For this purpose a coupled multi-body dynamics and hydraulic system model was developed in the Matlab Simulink environment, including a precise measurement-based loss model of the variable displacement pump. Power transmission and dissipation was calculated for each component and subsystem, including pumps, motors, valves, cylinders, transmission lines, and others. The simulation results show the amount of dissipated energy, indicating the major loss sources during various operations. Furthermore, the potential recoverable energy in the cycle is calculated, highlighting the prospective advantages of equipping the existing machine with new pump-controlled actuator technology.
Qualitative Observations of Dense Particle Motion in a Vibration-Excited Granular Bed
Authors: Morgan Timothy B. , Heindel Theodore J.
Published: May 2009

The Brazil nut effect is a classic phenomenon in which larger objects typically migrate to the top of a bed of smaller granular media when exposed to vibration. An example of this phenomenon is finding Brazil nuts on the top of a can of mixed nuts. In this study, the Brazil nut problem is simulated by submerging a large particle in a bed of granular media and then subjecting the system to vibration. Stereoscopic X-ray imaging is used to visualize the large particle motion. These images are then compiled into movies where the particle motion may be tracked. Observations of the large particle motion are made under varying conditions of large particle material, vibration frequency, and bed height. Particle percolation, where smaller particles fill small voids beneath the large particles, is the dominate mechanism at higher vibration frequencies. However, as the frequency decreases, or as the disparity between the densities of the large and small particles decrease, the effects of convection become more pronounced.
Modeling of a Circular Magnetic-Fluid Deformable Mirror for Ophthalmic Applications
Authors: Iqbal Azhar , Dukhu Devina , Ben Amara Foued
Published: May 2009

Adaptive optics (AO) systems make use of active optical elements namely wavefront correctors to improve the quality of imaging through dynamically varying media. Vision science is an area of application of these systems where they have been used to enhance the resolution of imaging of internal parts of the human eye. However, their widespread use in clinical devices is limited due to the insufficient performance and high costs of the currently available wavefront correctors. Recently, magnetic fluid deformable mirrors (MFDM) have been proposed as a type of wavefront correctors that can sufficiently overcome the problems associated with the existing wavefront correctors. The practical implementation of this new type of deformable mirrors is contingent on the development of effective methods to model and control the shape of their deformable surface. To help meet this critical requirement, this paper presents an analytical model of a circular MFDM in cylindrical geometry. The resulting model can be used in the design of control systems for ophthalmic adaptive optics systems. Preliminary results of an experimental investigation aimed at validation of the analytical model are also presented.
Tensionability Conditions of a Multi-Body System Driven by Cables
Authors: Rezazadeh Siavash , Behzadipour Saeed
Published: May 2009

Cable-driven mechanisms have been reported in the literature for the manipulation of a single rigid body. A cable-driven mechanism configured as a Completely Restrained Positioning Mechanism (CRPM) [6], requires a minimum of n+1 cables to maintain the tensionability of the manipulator (i.e. all cables can be made taut), where n is the dimension of the motion space (typically 3 in the planar and 6 in spatial manipulators). In this paper, the idea of cable-driven manipulators is extended to the manipulation of a multi-body system by cables. The first and most fundamental issue to be addressed is the required number of cables and the cable distribution over the links. This problem is thoroughly investigated in this paper. The major issue that differentiates between single rigid body and multi-body cable-driven systems is that in the multi-body systems, each link is subjected to not only the unilateral force of the cables, but also to the bilateral constraint forces and moments of the joints. This requires a new approach for the analysis of the tensionability. The proposed approach in this paper is based on the fundamental equilibrium equations. This will be shown to result that every subsystems of the cable-driven multi-body should satisfy the tensionability condition which also provides all the necessary conditions on the number of the cables attached to that sub-system. These necessary conditions will be then complied to provide the total sufficient number of the cables and their required distribution on the links.
A Study of Effect of Wettability on Heterogeneous Condensation: Varied Substrates
Authors: Pulipaka Sriharsha , Son Sang Young
Published: May 2009

Contact angle as a surface property of the substrate plays a vital role in the process of heterogeneous condensation. This paper deals with the visualization experiments that have been carried out to study the dropwise condensation of the vapor of degassed distilled water on hydrophobic substrate and the filmwise condensation on hydrophilic substrate. A study on effect of substrate wettability on the growth of the condensate drop on various surfaces is presented and compared. Also trend of the variation of the surface temperature for various substrates during condensation is presented.
Microchannel Size Effects on Two-Phase Local Heat Transfer and Pressure Drop in Silicon Microchannel Heat Sinks With a Dielectric Fluid
Authors: Harirchian Tannaz , Garimella Suresh V.
Published: May 2009

Two-phase heat transfer in microchannels can support very high heat fluxes for use in high-performance electronics-cooling applications. However, the effects of microchannel cross-sectional dimensions on the heat transfer coefficient and pressure drop have not been investigated extensively. In the present work, experiments are conducted to investigate the local flow boiling heat transfer in microchannel heat sinks. The effect of channel size on the heat transfer coefficient and pressure drop is studied for mass fluxes ranging from 250 to 1600 kg/m2s. The test sections consist of parallel microchannels with nominal widths of 100, 250, 400, 700, and 1000 μm, all with a depth of 400 μm, cut into 12.7 mm × 12.7 mm silicon substrates. Twenty-five microheaters embedded in the substrate allow local control of the imposed heat flux, while twenty-five temperature microsensors integrated into the back of the substrates enable local measurements of temperature. The dielectric fluid Fluorinert FC-77 is used as the working fluid. The results of this study serve to quantify the effectiveness of microchannel heat transport while simultaneously assessing the pressure drop trade-offs.
Variable Antagonistic Stiffness Element Using Tensegrity Mechanism
Authors: Azadi M. , Behzadipour S.
Published: May 2009

Tensegrity mechanisms are self-stressing mechanisms and it is known that the prestress of the elements affect the stiffness of the tensegrity. In this paper stiffness of a spatial tensegrity is studied for the purpose of the noise and vibration control and it is shown that an efficient variable stiffness element can be designed by using tensegrities. The antagonistic force and antagonistic stiffness are explained briefly and the kinematics of the tensegrity is analyzed. Also, the possible motion, the elastic stiffness, load stiffness and antagonistic stiffness formulation for the tensegrity are found symbolically. Some techniques for increasing the magnitude of the antagonistic stiffness are mentioned. The effect of the geometry on the stiffness, stiffness controllability and linearity are shown by examples. Finally, the results of this approach are verified by mechanical simulation of the designed tensegrity.
Real-Time Implementation of an Observer for Measuring Multiple Turns of a Shaft With a One-Turn Potentiometer
Authors: Pappano Vincenzo , Friedland Bernard
Published: May 2009

Accurate measurement of multiple rotations of a shaft with a single-turn potentiometer is made possible by a nonlinear observer. A PC-in-the-loop real-time implementation illustrates the performance of the system.
Design and Optimization of a New Highly Linear Tunable MEMS Capacitor
Authors: Shavezipur Mohammad , Khajepour Amir , Hashemi Seyed Mohammad
Published: May 2009

In this paper, a novel linearly tunable MEMS capacitor with high tunability is introduced. The characteristic air gap-voltage curve for an ideally linear tunable capacitor is studied. This curve is considered as a target for new designs. A three-structural layer process is used to develop the capacitor. The actuation and sense gaps in the three-plate capacitor are selected in such a way that for a voltage interval (between zero and pull-in), the gap-voltage response for sense electrodes becomes similar to the ideal curve. The resulting capacitance-voltage response of the new design demonstrates a combination of high linearity and tunability up to 250%. For processes which have fixed layer thickness and the sense and actuation gaps cannot be optimized, the design is modified by adding nonlinear springs and asymmetric geometry. The results of numerical simulation for a capacitor designed for PolyMUMPs process verify the improvement of linearity and tunability.
Inherently Safe Design of Home Elevator System by Passive Dynamic Control
Authors: Minamiyama Y. , Kiyota T. , Sugimoto N.
Published: May 2009

The passive dynamic control (“PDC”) is a new mechanical system control method requiring less energy but ensuring higher safety, which is based on inherently safe design using variable passive elements. The PDC divides its control process into four steps: hold step, take-over step, unbalance step and free step. In each of these steps, it is confirmed that the next step has satisfied the inherently safe design and then the execution of the next step is permitted. In this study, the authors have developed a PDC balancer equipped with a constant-load spring balancer to provide a constant tension regardless of the wire elongation, and conducted positioning experiments using this PDC balancer. This paper proposes a new home elevator system using the PDC balancer. When the balance of the elevator is maintained by using the PDC balancer, the elevator can be moved by a small force. Even if power failure occurs or severance is caused to the spring of the PDC balancer, as long as the cage of the elevator is so mechanically arranged as to ascend in such case, impact on the passengers will be mitigated to be smaller than impact when it descends. Furthermore, this elevator is so designed as to prevent the passengers from being confined in the cage. The inherently safe design can be realized by multiplying the spring structure and employing the PDC for this system. This system is featured by its excellence in safety, energy saving and cost performance. If this system is realized, the home elevator can be used even in remote areas, which is expected to facilitate the spread of the home elevator.
Analysis of a Vibrating-Beam-Based Micromixer
Authors: Sun Hongwei , Wang Pengtao
Published: May 2009

The mixing of two or more streams in microscale devices is a slowly molecular diffusion process due to the unique laminar flows, and some ‘turbulence’ based mixing technologies which are effective in macroscales become hard to implement in such small dimensions. The chaotic advection based mixing, depending on the stretching and folding of interface, has been proved to be effective for low Reynolds numbers (Re) and is a very promising technology for micro mixing. We propose a new mixing concept based on a vibrating micro-beam in microfluidic channels to generate chaotic advection to achieve an efficient mixing. The simplicity of the proposed mixer design makes microfabrication process easy for practical applications. The feasibility of the concept is evaluated computationally and moving mesh technique (ALE) is utilized to trace the beam movement. The simulation shows that the mixing quality is determined by parameters such as flow velocities, amplitudes and frequencies of vibrating beam. The Reynolds number (Re) is less than 2.0, Pelect number (Pe) ranges from 5 to 1000, and Strohal number (St) 0.3 to 3.0. It was found that vortex type of flows were generated in microchannel due to the interaction between beam and channel wall. The mixing efficiency with this design is well improved comparing with the flows without beam vibration.
The Measurement of Diffusion Coefficient Using Nanofluidic Channels
Authors: Rhieu Steve , Huber David , Markel Marci , Palmore G. Tayhas R. , Pennathur Sumita
Published: May 2009

The behavior of molecules confined within nanochannels may provide new insight into important chemical and biological mechanisms. As such, the ability to measure the diffusion coefficient of molecules accurately and rapidly is critical. Toward this end, we demonstrate a new method for measuring the diffusion coefficient of analytes in nanoscale environments. Based on nanoscale electrokinetic transport theory, a numerical simulation was developed to determine the spatial concentration of analyte within a nanofluidic T-shaped channel for a given Peclet number. The resulting concentration profiles were compared to experimental data to determine the Peclet number that gives the minimum least-square error. Using this approach, the diffusion coefficient of sodium fluorescein was measured and found to be within the error of previously published values. This method is envisioned to be a novel analytical tool to rapidly and accurately measure diffusion coefficients of small analytes, and to measure the effective diffusion coefficients of more complex species such as DNA and peptides when confined within a nanochannel.
A 5 kWel Solid Oxide Fuel Cell Stack Operating on Biomass Gasification Producer Gas: System Design and Results
Authors: Stanghelle Daniel , Norheim Arnstein , Skreiberg O̸yvind , Hustad Johan E. , So̸nju Otto K.
Published: May 2009

This paper describes the system setup and presents results from the ongoing BioSOFC project. The project aims at demonstrating integration of atmospheric biomass steam gasification, high temperature gas cleaning and Solid Oxide Fuel Cells (SOFCs). This is done by taking a slipstream from a steam gasification reactor (the Fast Internally Circulating Fluidised Bed (FICFB) gasifier at Biomasse Kraftwerk Gu¨ssing in Gu¨ssing, Austria) as fuel feed for a 5 kWel Solid Oxide Fuel Cell (SOFC) stack. The system also includes a novel high temperature particle filter (the Panel Bed Filter (PBF)) and a high temperature H2S removal unit. The biomass gasifier, using wood chips as fuel, has a dry producer gas consisting of H2 (up to 45 vol%), CO (up to 30 vol%), CO2 (up to 20 vol%), CH4 (8–12 vol%) and N2 (1–2 vol%). This gas composition makes the producer gas highly suitable as fuel for SOFCs. However, the gas has a relatively high particle loading (up to 60 g/Nm3) and a tar content of up to 2 g/Nm3. In addition, it has been reported that the dry producer gas contains 100–200 ppmv H2S and 500–1000 ppmv NH3. Due to otherwise expected fuel cell performance degradation, the particles have to be removed before entering the SOFC stack. In addition, the sulphur (mainly H2S) concentration must be reduced to minimize the performance degradation in the SOFC. The slipstream is taken from the top of the gasifier freeboard, and is then cooled from about 900°C to 550°C before entering the PBF where the particles are removed. The H2S concentration is reduced in a separate fixed-bed reactor with a Zink-oxide based sorbent. The pressure in the producer gas is increased from the somewhat below atmospheric pressure in the filter to the atmospheric pressure required by the SOFC stack. This pressure increase is achieved by means of two high temperature fans operated at about 525°C. The producer gas is then heated again to up to 900°C before entering the fuel cell stack. This paper presents results from component tests carried out at the Norwegian University of Science and Technology (NTNU) as well as results from the field tests of the system in Gu¨ssing. This ongoing project is scheduled to continue until December 2007. The BioSOFC project is carried out in cooperation with TU-Vienna and Austrian and Norwegian technology companies. The project is funded by the Research Council of Norway and six Norwegian companies.
Experimental and Numerical Study of Evaporating Flow Heat Transfer in Micro-Channel
Authors: Lee HoKi , Richards C. D. , Richards R. F.
Published: May 2009

Experimental and numerical results are presented for steady evaporating flow heat transfer from open top square micro-channels. Radial channels, 40 microns high, and 35, 50 and 70 microns wide with 5 micron wide SU-8 walls are considered. The channels are filled with Fluorinert FC77 working fluid pumped by capillary forces from a reservoir at the outer circumference of the radial channels. An energy balance on the radial channels including heat into the channels, conduction heat transfer radially along the channels and latent heat transfer via evaporation of the working fluid from the channels is experimentally determined. Microphotography is used to visualize the working fluid and the meniscus contact angles in the channels. A three-dimensional finite difference time-domain integration is used to predict sensible heat transfer rates and latent heat transfer/ evaporation rates. Experimental measurements are compared to the numerical results to extract estimates of the liquid thickness in the channels.
Open Accumulator Concept for Compact Fluid Power Energy Storage
Authors: Li Perry Y. , Van de Ven James D. , Sancken Caleb
Published: May 2009

Energy storage devices for fluid power applications that are significantly more compact than existing ones will enable energy regeneration for many applications, including fluid power hybrid vehicles and construction equipment. The current approach to hydraulic energy storage makes use of a compressed gas enclosed in a closed chamber. As the system must contain the expanded gas and the hydraulic oil displaced, the optimal energy density occurs at a modest expansion ratio resulting in a small energy density. By allowing intake and exhaust of compressed and expanded air from and to the atmosphere, a potential order of magnitude increase in energy density is available in the new open accumulator approach. Potential methods for realizing the new configuration are described. Analysis and simulation case studies illustrate both the advantages and challenges of the new approach.
Macro/Micro Mechanical Level Characterization of Spot Friction Welded Lap Joints in 6111 Aluminum Alloy Using Combined Experimental/Numerical Approaches
Authors: Thoppul Srinivasa D. , Gibson Ronald F.
Published: May 2009

Modal vibration testing and static flexure testing at the macromechanical level combined with numerical finite element (FE) models have been used to indirectly determine the elastic moduli of 6111 aluminum alloy base metal and spot friction welded (SFW) joints which have been formed at different processing times. It was observed that the frequency (and the corresponding apparent stiffness) of the joint oscillates at low amplitudes as processing time increases. For each vibration mode, the amplitude of the oscillation in the frequency vs. processing time is only a few percent of the mean frequency with 99% confidence level, while the corresponding lap shear strength increases monotonically by a factor of about 8 as the processing time increases. Due to the scatter in the damping data it is difficult to detect any significant trends. Comparison of predicted modal frequencies and static load-displacement response of SFW joints at the macromechanical level with the corresponding measured responses seems to indicate that the weld zone is not as stiff as the base metal, but more detailed micromechanical analysis is required before definite conclusions can be drawn. In addition, studies of microstructural characteristics and Vickers microhardness distributions across the weld zone for the SFW samples reveals the formation of a partial metallurgical bond in the direction of flow, which is governed by the tool used, whereas the hardness distribution in the weld zone depends on the processing time.
Bridging the Entropy Chasm!
Authors: Foley Andrew C.
Published: May 2009

Typically a Thermodynamics course spend at least half of its allotted teaching schedule introducing the first law in its various guises followed by the more mysterious property entropy and its convoluted ‘birth’ from Carnot engine analyses. The author describes a ‘catch all’ approach that first describes the ‘accounting’ techniques used not only for the first law (energy) and the second law (entropy) but also continuity, momentum etc. This is done with non thermofluid examples not typically associated with these courses but more aligned with a student’s own day to day experiences. Once this accounting framework is in place then the physical properties of energy and entropy are introduced and used within the previously described framework to allow students to confidently tackle a myriad of thermofluid problems. The author is particularly pleased with the explanation of entropy which he believes allows a truer appreciation of the property not normally presented in traditional texts. Overall the approach allows the theory of a thermofluids course to be undertaken much more rapidly than many conventional courses. The formulations are greatly reduced and their generality is increased significantly. Ultimately this allows more time in a course for the practice of application of these tools.