bluuebunny/crossref_metadata_2025 huggingface dataset:
Grasping Contact Analysis of Viscoelastic Materials With Applications in Minimally Invasive Surgery
Authors: Bonakdar Ali , Dargahi Javad , Bhat Rama
Published: April 2008

This paper presents a method to determine the contact force and pressure on the surface of viscoelastic objects grasped by an endoscopic grasper, used in Minimally Invasive Surgery (MIS). Normally, an endoscopic grasper is corrugated (teeth-like) in order to grasp slippery tissues. It is highly important to avoid damage to the tissues during grasping and manipulation in endoscopic surgery. Therefore, it is essential to determine the exact contact force on the surface of the tissue. To this end, initially a comprehensive closed form analysis of grasping contact force and pressure on elastic and particularly viscoelastic materials which have similar behavior as that of biological tissues is studied. The behavior of a rigid grasper with wedge-like teeth, when pressed into a delayed elasticity material is being examined. Initially, a single wedge penetrating into a solid is studied and then is extended to the grasper. The elastic wedge indentation is the basis of this study and the effects of time are included in the equations by considering the corresponding integral operator from viscoelastic stress-stain relations. Under the action of a constant normal load, the penetration of the indenter and the contact area will change. In this research, the variation of the contact area with time and the grasping contact force is studied. The results of this study which provides a closed form expression for grasping contact force and contact area are compared with those from elastic analysis.
Micromechanical Modeling of Composites: A Local Approach for Imposing Periodic Boundary Conditions
Authors: Tyrus J. M. , Gosz M. , DeSantiago E.
Published: April 2008

Recent advances in computational speed have resulted in the ability to model composite materials using larger representative volume elements (RVEs) with greater numbers of inclusions than have been previously studied. It is often necessary to assume periodicity for the effective evaluation of material properties, failure analysis, or constitutive law development for composite materials. Imposing periodic boundary conditions on very large RVEs can mean enforcing thousands of constraint equations. In addition, most commercial finite element codes incorporate these constraints on a global level, thereby drastically reducing computational speed. The present study investigates a method that uses a local implementation of the constraints that does not adversely affect the computational speed. As a step toward a three-dimensional formulation, the present study utilizes a two-dimensional triangular RVE of a periodically-spaced regular hexagonal array of composite material containing fibers of equal radii. In the present study, the finite element method is employed to obtain the response of the RVE. To impose the boundary conditions along the edges, this study utilizes a cubic interpolant to model the displacement field along the matrix edges and a linear interpolant to model the field along the fiber edges. The method eliminates the need for the conventional node-coupling scheme for imposing periodic boundary conditions, consequently reducing the number of unknowns to the interior degrees of freedom of the RVE along with a finite number of global parameters. The method results in a valuable computational savings that greatly simplifies the pre-processing stage of the analysis.
A By-Pass Sensor Package Design Enabling the Use of Microfluidics in High Flow Rate Applications
Authors: Sparks D. , Goetzinger D. , Riley D. , Najafi N.
Published: April 2008

The package design for microfluidic sensors is discussed. The MicroElectroMechanical Systems (MEMS) device covered in this paper requires a fluidic and electrical interface as well as vacuum packaging of the sensing element. By using a by-pass package design the limitations of low flow rate and high pressure drop often encountered with microfluidic products can be avoided. The MEMS device utilizes a resonating silicon microtube that is electrostatically driven and capacitively sensed. A platinum RTD is also integrated into the MEMS chip. To improve the Q of the resonator a thin-film getter has been integrated to lower the microcavity pressure. The microfluidic packaging technology lends itself to producing densitometers, chemical concentration meters and Coriolis mass flow sensors. The device has been applied to fuel cell concentration sensors for embedded Direct Methanol Fuel Cell (DMFC) systems. The DMFC systems require a methanol sensor to minimize crossover and hence optimize the water/methanol concentration over temperature and the life of the product. Other high flow rate applications include ethanol/gasoline concentration sensors for E85 vehicles and dialysis fluid monitoring. A microfluidic Coriolis mass flow sensor has been developed and applied to drug delivery to monitor the drug dose, total volume infused, drug type and concentration. Chemical and temperature compatibility of the MEMS chip and packaging materials must be considered when dealing with this wide range of applications and will be discussed in the paper.
Streamlined Modeling of Compressible Flows
Authors: Gaggioli Richard A.
Published: April 2008

The development of the compressible flow tables by Shapiro, Hawthorne and Edelman [1-3] was a boon to the one-dimensional modeling of compressible flows - isentropic flow, Fanno flow, Rayleigh flow, normal shock. Nevertheless, the use of the tables is cumbersome. Furthermore, becoming engrossed with the mechanics of applying the tables, students and practitioners often lose sight of the fundamentals that are being applied. The present paper will illustrate the direct application of the basic one-dimensional governing equations to the modeling of compressible flows. In a straightforward fashion mass, momentum, energy and entropy balances, along with transport and property relations, are applied directly (without the use of tables or graphs) to model and to find solutions. Moreover, unlike the tables, the modeling does not need to assume ideal gases, let alone a constant ratio of specific heats. The key to this improved and easy approach, unavailable at the time the tables were developed, is the accessibility of equation solving software that includes property relations for gases and liquids. In particular, in the present work, EES (from fchart software; see fchart.com) was employed.
An Alternative (Preferable) Friction Factor
Authors: Gaggioli Richard A.
Published: April 2008

An alternative to the traditional friction factor for pipe flow is presented (φ = [R]f). For incompressible flows, the correlation of this new friction factor with Reynolds Number [R] and Relative Roughness [ε] is presented graphically, and appears much simpler and more intuitive than the Moody Diagram (or other equivalents). Moreover, relatively simple curve-fit formulas for representing φ explicitly as a function of R and ε are presented for various flow regimes, along with measures of error associated with these approximate formulas.
Performance of Two-Phase Microchannels at Sub-Atmospheric Pressure
Authors: Tong Tao , Devasenathipathy Shankar , Chang Je-Young , Dirner John , Prstic Suzana , Prasher Ravi S.
Published: April 2008

Two-phase microchannel system is a promising technology to achieve enhanced heat removal and more effective cooling of hotspots. The excellent thermodynamic properties of water make it a prime candidate as the working fluid in two-phase microchannel systems. While typical integrated circuit components require die temperature to remain below 95 °C, most of the earlier microchannel flow boiling studies were conducted at or above ambient pressure, where the saturation temperature of water is equal to or higher than 100 °C. In this paper, we tested flow boiling at sub-atmospheric pressure such that the saturation temperature of water can be significantly reduced below 95 °C. We study the pressure drop and heat transfer characteristics of our two-phase cold plate configuration, under uniform and hotspot (non-uniform) heating conditions at sub-atmospheric system pressures. A cold plate with 61 μm wide and 272 μm deep microchannels was tested at two systems pressures of 35 and 46 kPa and at two mass flow rates of 67 and 107 kg/m2-s. High-speed flow imaging was used for identifying flow patterns in the microchannels with the above test conditions. Pressure drop data were compared with the available semi-empirical correlations and the annular flow model. An explanation was proposed for the mismatch between the models under current microchannel configuration.
Thermal Radiation Through a Nano Aperture
Authors: Prasher Ravi
Published: April 2008

Far-field thermal radiation through a nano aperture is calculated in this paper. Results show that for aperture size ≪ dominant wavelength of thermally excited photons, heat flux deviates significantly from the well known Planck blackbody expression of σT4, where σ is the Stefan-Boltzmann constant and T is the temperature. The heat flux through a nano-hole is proportional to T8 and a4, where a is the radius of the hole. Heat flux is proportional to T8 and a4 due to diffraction effects. Potential applications of radiation heat transfer through nano apertures are also discussed in the paper.
Experimental Determination of Constraint Dependent J-R Curves for X80 Pipeline Steel Using Normalization Method
Authors: Zhu Xi. K. , Leis B. N. , Shen G. , Tyson W. R.
Published: April 2008

The normalization method is adopted for standard specimens and extended for nonstandard specimens in this paper to develop J-R curves for X80 pipeline steel directly from load versus load-line displacement records without the need of crack length measurement. Standard deep cracked specimens usually contain high crack-tip constraint, while nonstandard shallow cracked specimens involve low crack-tip constraint. To examine constraint effect on fracture toughness, six single-edge notched bend (SENB) specimens with different crack lengths for an X80 pipeline steel are tested according to ASTM standard E1820-05. The normalization method is then used to determine the constraint dependent J-R curves for these SENB specimens. To validate the experimental results obtained from the normalization method, the conventional elastic unloading compliance method is also used to measure crack extension, and determine the J-R curves for the X80 steel. The results show that the J-R curves determined using the normalization method agree well with those based on the elastic unloading compliance method for all SENB specimens, except for those experiencing severe splitting. Therefore, the normalization method can be used to determine J-R curves for the X80 pipeline steel for standard as well as nonstandard specimens. In determining the J-integral values, the resistance curve procedure, the basic procedure and the modified basic procedure specified in ASTM E1820-05 are evaluated. Comparisons of the resulting J-R curves indicate that the modified basic procedure can be equivalent to the resistance curve procedure.
Vascularized Materials: Grids of Channels and Trees Matched Canopy to Canopy
Authors: Kim Sunwoo , Wang Kuan-Min , Lorente Sylvie , Bejan Adrian
Published: April 2008

This is a fundamental study of how to discover the optimal flow architecture to vascularize a volume so that fluid flow and function (e.g. cooling, sensing, maintenance, repair, healing) reaches every point of the material. The presentation is made by discussing flow architectures that deliver healing fluid to all the crack sites that may occur randomly through the material. Two concepts are explored. In the first, a grid of interconnected channels is built into the material, and is filled with pressurized healing fluid. When a crack forms, the pressure drops at the crack site and fluid flows from the grid into the crack. The objective is to discover the network configuration that is capable of delivering fluid to all the cracks the fastest. It is shown that the optimization of the ratio of channel diameters cuts in half the time of fluid delivery to the crack. In the second concept, one stream flows steadily through the material and bathes it volumetrically. The stream enters through one port, and distributes itself as a river delta through the volume. Later the stream reconstitutes itself as a river basin before exiting the volume through one point. This second concept is equivalent to matching two trees canopy to canopy. It is shown that the choice of tree-tree configuration has a decisive role on the global performance of the vascularized composite.
Pressure-Scaling of Pressure-Swirl Atomizer Cone Angles
Authors: Guildenbecher D. R. , Rachedi R. R. , Sojka P. E.
Published: April 2008

An experimental investigation was conducted to study the effects of increased ambient pressure (up to 6.89 MPa) and increased nozzle pressure drop (up to 2.8 MPa) on the cone angles for sprays produced by pressure-swirl atomizers having varying amounts of initial swirl. This study extends the classical results of DeCorso and Kemeny [1]. Shadow photography was used to measure cone angles at x/D0=10, 20, 40, and 60. Our lower pressure results for atomizer swirl numbers of 0.50 and 0.25 are consistent with those of DeCorso and Kemeny [1], who observed a decrease in cone angle with an increase in a pressure drop-ambient density product until a minimum cone angle was reached at ΔPρair1.6~200. Results for atomizers having higher swirl numbers do not match the DeCorso and Kemeny [1] results as well, suggesting that their correlation be used with caution. Another key finding is that an increase in ΔPρair1.6 to a value of 1000 leads to continued decreases in cone angle, but that a subsequent increase to 4000 has little effect on cone angle. Finally, there was little influence of atomizer pressure drop on cone angle, in contrast to findings of previous workers. These effects are hypothesized to be due to gas entrainment.
Length Scale in Solder Joints Materials
Authors: Gomez Juan , Basaran Cemal
Published: April 2008

Strain gradient plasticity theories that have emerged during recent years to provide an explanation for size dependent behavior exhibited by some materials have also created a need for additional material parameters. In this study on Pb/Sn solder alloys the material length scale, which is needed for use in strain gradient plasticity type constitutive models, is determined. The value of length scale is in agreement with values available in the literature for different materials like copper, nickel and aluminum.
Crush Analyses of Multi-Level Equipment
Authors: Martinez Eloy , Zolock John , Tyrell David
Published: April 2008

Non-linear large deformation crush analyses were conducted on a multi-level cab car typical of those in operation by the Southern California Regional Rail Authority (SCRRA) in California. The motivation for these analyses was a collision, which occurred in Placentia, CA, on April 23, 2002. The final deformed state of the leading cab car was unusual. This behavior contrasted with previous testing and analysis experience of single level equipment in collisions. This investigation explores the structural response of multi-level car structures. The structure of the multi-level equipment differs from single level equipment in that a significant change occurs in the load path from where load enters through the coupler and is subsequently reacted aft of the body bolster of the car. This change in load path results from a change in geometry of the car to accommodate quarter point doors and the upper level of the car. Load enters at the typical coupler height but descends to the lower platform level of the car through a transition structure. To better understand the influence of the varied geometry, a series of calculations were performed to obtain the force-crush characteristics and modes of deformation for the cab car subjected to a series of different initial conditions. Crush models were developed of both the lead and trailing end of the car, as well as the center section of the car. In addition to these sub-models, a full car model was constructed. Results from the sub-model analyses indicate that the longitudinal strength of the trailing end is comparable to that of the lead end, and the center section of the car is significantly stronger than either end. This suggests that crush will most likely occur at the ends of the car when it is overloaded. Initial conditions similar to the Placentia, CA accident were also investigated to better understand the atypical mode of deformation that occurred. These results indicated that the multi-level equipment can resist high force levels for longer crush distances than single level platform vehicles but will eventually experience softening behavior, which will result in focused crush at one end of a car.
Optimum Conditions for Variable Pitch Milling
Authors: Fazelinia Hassan , Olgac Nejat
Published: April 2008

From the perspective of regenerative chatter, variable-pitch milling process offers a mathematically very challenging task. It can be reduced to the problem of stability assessment on a linear time-invariant dynamics (LTI) which has more than one independent delays. This mathematically notorious problem is uniquely solved by a recent paradigm. It is called Cluster Treatment of Characteristic Roots (CTCR). This paper presents a process optimization procedure using CTCR over a special milling operation with variable pitch cutters. The optimization is based on maximizing the metal removal rate while avoiding the onset of chatter, which, in turn, enables production of the parts with a desirable surface quality. The end result is a powerful tool to determine some important geometrical and operational features of the process: (i) the pitch angle selection on the tool (i.e., variable pitch cutter vs. uniform pitch cutter), (ii) the optimum cutting conditions (i.e., depth of cut and the spindle speeds).
A Proposed Method for Determining the Heat Transfer Properties of Foam-Fins
Authors: Moffat Robert J. , Eaton John K. , Onstad Andrew
Published: April 2008

Metallic and graphitic open-cell foams are being used as extended surfaces in some designs of compact heat exchangers. The shape and orientation of the solid material in the foam is hard to describe in classical terms and harder still to model. There appears to be a clear need for a method of characterizing foams that allows flexible, optimized design of a foam-fin heat exchanger. To be most useful, the description should be expressed in terms that are consistent with current heat exchanger design methods. The heat transfer performance of a foam-fin can be calculated if three parameters are known: the product hmAc* (the convective conductance per unit volume) as a function of flow rate, the product ksAk* (the effective conductive conductance as a fin), and Rbond, the effective thermal resistance between the foam fin and the surface to which it is attached. An experimental method is presented by which these three properties can be determined using the results from two tests: a conventional heat exchanger core test (single-blow-transient or cyclic) to measure hmAc* and a new type of "one-heated-wall" test, described here, from which the temperature distribution in the foam can be inferred. Results from these two tests can be combined to evaluate the three necessary parameters: hmAc*, ksAk* and Rbond. In this paper we describe the theory behind this approach and present sample calculations showing the type of data that are expected and demonstrating that the necessary parameters can be measured with these tests. Experimental testing of the method is underway but has not yet been completed, hence no data are available at this time to confirm the validity or practicality of the method.
Analytical Solutions for Effective Axial Mechanical Properties of Active Fiber Composites
Authors: Askari Davood , Nejhad Mehrdad N. Ghasemi
Published: April 2008

This work presents analytical solutions for the effective axial mechanical properties of the active fiber composites with different geometries, e.g., circular and rectangular cross-sections, and while the properties of the constituent materials are considered to be generally orthotropic. Analytical exact solutions of the effective longitudinal Young's moduli and major Poisson's ratios are obtained for two different geometries of a 2-phase composite model composed of orthotropic materials. Finite element analyses (FEAs) are also performed to verify the obtained analytical exact solutions. Excellent agreements are achieved between the results obtained from both techniques. Finally, the effective mechanical properties calculated from analytical solutions for the modeled geometrical configurations are compared.
Tire/Pavement Force Tensor Differential Evaluation Between Dynamometric Wheel and Infrastructure-Based System
Authors: Coiret A. L.
Published: April 2008

Tire/pavement contact characterization is a key point for both vehicle and road optimization in the context of road safety. LCPC laboratory has recently developed and validated an infrastructure-based measurement system to acquire the complete 6-components tire/road force tensor. In this paper; this system will be further assessed facing a testing vehicle equipped with a dynamometric wheel, in emergency braking situations, for dry or wet pavement surfaces. Regarding road management, the validated embedded system will offer the advantage of concerning a large set of vehicles, without need of any instrumentation. Measurement differences between the two systems will be discuss in terms of (intermediate) tire characteristics.
Tensile Stress-Strain Curves of Gold Film
Authors: Sharpe W. N. , Pulskamp J. , Mendis B. G. , Eberl C. , Gianola D. S. , Polcawich R. , Hemker K. J.
Published: April 2008

Freestanding vapor-deposited gold films 0.15 μm, 0.5 μm, and 1.0 μm thick were tested in tension with strain measured directly in the gage section by digital imaging. The average grain size of all three films was ~ 60 nm with some large grains in the 0.15 μm material. Young's modulus decreased as the thickness decreased - from 73.1 ± 6.7 GPa to 64.7 ± 9.9 GPa to 51.4 ± 10.6 GPa respectively. The yield stress decreased from 365 ± 25 MPa to 328 ± 28 MPa, but was 371 ± 36 MPa for the 0.15 μm film, which was more brittle. Microstructural studies provide no clear explanation for this behavior.
Corrugated Wall Jet Impingement Geometry for Combustor Liner Backside Cooling
Authors: Esposito E. I. , Ekkad V. , Dutta Partha , Kim Yong , Greenwood Stuart
Published: April 2008

The present study investigates alternative jet impingement geometries aimed at the reduction of detrimental crossflow effects for use in combustor liner backside cooling. Through the use of a corrugated wall design, the spent air of upstream jets is routed past downstream jets with minimal interference. Three configurations of the design are studied. First, the jet spacing is held constant, and the design of the corrugations is changed for sparse arrays. The second part of the study studied the effects of the corrugated wall on dense arrays. The average jet Reynolds number, Red, is varied and tested for 20000, 40000, and 60000. Local Nusselt number distributions were evaluated using a transient liquid crystal technique. The results show that the corrugated wall design can significantly reduce the negative effects of crossflow especially at higher jet Reynolds numbers. Further, the design of the corrugations has a substantial impact on the performance of the geometry. The corrugated wall geometries with smaller bypass channels outperformed the geometries tested with larger channels. The use of corrugated jet impingement configurations would allow larger jet impingement arrays without sacrificing heat transfer effectiveness.
Fire and Explosion Investigations: Why Heavy Trucks May Burn
Authors: Ferrone Christopher , Sinkovits Charles
Published: April 2008

There is a basic misconception that diesel fuel does not explode and/or ignite upon a collision or impact. This particular chain of events, in fact, does occur. However, it is not always thoroughly investigated or understood. The purpose of this paper, through mechanical analysis and accident reconstruction, is to inform truck manufacturers and operators of this hazard. In addition, it will supply design alternatives that will aid in mitigating and/or preventing injuries altogether.
Dinette Chair Tip Over Danger Analysis
Authors: Brickman Dennis B.
Published: April 2008

A three year old boy died when a dining room chair he was sitting on fell backward, triggering bleeding along his spinal cord. Approaches utilized in the danger analysis include: accident reconstruction, safety literature review, safety standards research and testing, accident statistics survey, and evaluation of alternative dinette chair designs. The primary goal of this investigation is to make dinette chair designers, retailers, and users more aware of the tip over danger and to identify design alternatives to help reduce the number of these types of injuries.
Nonlinear Behavior of a Disc-Shaft Rotating System With a Transverse Crack
Authors: Dai Liming , Chen Changping
Published: April 2008

This research intends to investigate the nonlinear behavior of a rotating system with a cracked shaft mounted with a disc. Effects of the geometric nonlinearity, the masses of the shaft and disc and the viscoelastic supports of the rotating system on the motion of the system are studied. The characteristics of the system, such as bifurcations, periodic, quasiperiodic and chaotic behavior are evaluated. Effects of crack depth and rotating speed on the nonlinear behavior of the system are also investigated.
Wave Field of Porous Medium Saturated by Two Immiscible Fluids Under Excitation of Multiple Wave Sources
Authors: Dai Liming , Wang Guoqing
Published: April 2008

Wave propagation in porous medium saturated by immiscible fluids has received significant interests from the researchers in searching for comprehensively understanding the behavior of underground motion such as seismic wave propagation and artificial vibration in oil or gas reservoirs. In this research, the wave field of a porous medium saturated by two immiscible fluids is investigated. The elastic domain considered is excited by multiple cylindrical energy sources. The wave field of the whole domain with the excitation of several fast compressible waves in low frequency range is considered. Polar coordinates are utilized for the need of describing the multi-energy sources, so that the propagating waves can be expressed with the utilization of Hankel function. A moving-coordinate method is employed to study the coupling of multiple waves. The combined effects from several sources on the wave propagation are investigated and comparison with that of a single phase fluid is also addressed. With the employment of the methodology established, the wave field at any desired domain considered can be quantitatively determined in terms of wave propagation, frequencies and amplitudes of the source waves. To demonstrate the implementation of the model developed in this research, a numerical simulation is provided. The results of this research contribute to the comprehension of liquids and solid interaction under the excitation of waves, such as seismic, electromagnetic and other artificial vibrations.
Preliminary Study on Combustion of Biodiesel for Power Generation
Authors: Tan Ee Sann , Palanisamy Kumaran , Hussein Ibrahim , Ani Farid Nasir
Published: April 2008

In the recent wake of escalating crude oil prices due to depletion of fossil fuel, biodiesel has generated a significant interest as an alternative fuel for the future. The use of biodiesel to fuel microturbines or gas turbine application is envisaged to solve problems of diminishing supplies of fossil fuel reserves and environmental concerns. This paper examines the combustion of biodiesel derived from Malaysian Waste Cooking Oil (WCO) in a combustion test facility to study the feasibility of using the designated fuel at five various volumetric ratios for gas turbine application. Biodiesel was produced from waste cooking oil in Malaysia, mainly from palm oil sources and animal fats. The oil burner was able to fire the five blends of fuel without any modification or pretreatment. The combustion performance of Malaysian WCO biodiesel and distillate blends was examined with respect to the combustion efficiency. The results indicated biodiesel combustion required less air for stoichiometric combustion due to presence of oxygen in the fuel. Indeed biodiesel stand as a potential alternative fuel for power generation application with the best efficiency at blended ratio of 20% biodiesel and 80% distillate.
Comparing Water (R718) to Other Refrigerants
Authors: Kharazi Amir A. , Mu¨ller Norbert
Published: April 2008

Even though water (R718) is one of the oldest refrigerants, state of the art technology is required to use water as a refrigerant in compression refrigeration plants with turbo compressors. To compare water (R718) to other refrigerants, a code is developed in which all refrigerants can be compared in a single p-h, T-s, or p-T diagram. Using the code, the COP isolines of water (R718) and any refrigerant can be generated in a graph to determine which refrigerant has a better COP for a certain evaporation temperature and temperature lift. In regard to using water (R718) as a refrigerant, some specific features complicate its application in refrigeration plants with turbo compressors. Because the cycle works at very low pressure, the volumetric cooling capacity of water vapor is very low. Hence, huge volume flows have to be compressed with relatively high pressure ratios. Therefore, the use of water (R718) as a refrigerant, compared to classical refrigerants, such as R134a or R12, requires approximately 200 times the volume flow, and about twice the pressure ratio for the same applications. Because of the thermodynamic properties of water vapor, this high pressure ratio requires approximately a two to four times higher compressor tip speed, depending on the impeller design; while the speed of sound is approximately 2.5 times higher. Reynolds numbers are about 300 times lower and the specific work transmission per unit of mass has to be around 15 times higher. Two factors are introduced to compare the irreversibilities of R718 and other refrigerants and the main source of irrevercibility in R718 cycle is identified. Finally, the current state-of-the-art R718 is reviewed.
Anisothermic Oxidation of Carbon/Epoxy Laminates
Authors: Trabelsi W. , Bellenger V. , Ghorbel E.
Published: April 2008

This work deals with the ageing of a carbon epoxy composite material for aeronautic and supersonic applications. One of the main parameters which governs the durability of this kind of materials is the matrix oxidation, which is limited to surface layers. The long-term behaviour of organic matrix composites includes combined effects of ageing: matrix oxidation occurring at high temperature and matrix cracking due to thermo-mechanical ply stresses induced by differential expansion between matrix and fibers or between the various plies. For some years ENSAM has developed for isothermal conditions a kinetic model of radical chain oxidation coupled with the equation of oxygen diffusion. This model is based on a "close-loop" oxidation mechanistic scheme and gives access to the concentration profile of oxidation products in the sample thickness. In this work we expressed the temperature by a Fourier series and we simulate the oxidative behaviour of samples exposed to the following thermal cycles: -50°C/+180°C, -50°C/+150°C and +50°C/+180°C. The weight loss of the oxidised samples was chosen as indicator of oxidation. Numerical results are compared to experimental ones to check the validity of the model. Good agreement between experimental and numerical results is obtained.
Multidisciplinary Topics in Senior Capstone Design Courses: Radio Astronomy
Authors: Tatum Paul , Linford James , Grabowsky Jeremy , McKenzie Lonzell , Cline Paul Con , Craft William
Published: April 2008

The exciting contributions to science and education made by radio astronomy over the last three decades would not have been possible without the development of radio telescopes of increasing sensitivity and power. The Pisgah Astronomical Research Institute (PARI) is located near Brevard, North Carolina. It was built in 1962 and was a facility for tracking the spacecraft of the NASA Mercury and Gemini missions. In the late 1970's it was used by the National Security Agency for monitoring Soviet satellite activity and was decommissioned in 1992. It was later purchased by PARI and is now used for astronomical education and research as a not for profit organization. During the spring of 2005, Mr. Don Cline, President of PARI and William Craft, began discussing ways in which engineering students could both learn about radio astronomy and contribute to the development to the educational and research programs at PARI. Since North Carolina Agricultural and Technical (A&T) State University is one of the closest engineering colleges, they concluded that student design projects that focused on the enhancement of radio astronomy equipment would both help PARI and provide a challenging capstone design experience to engineering students. The A&T capstone program covers two semesters and six semester credits, and among an initial listing of potential design experiences, we selected four that would enhance the operation of the two 26-meter PARI radio-telescopes. These two twenty-six meter radio-telescopes are known as 26E (East) and 26W (West). Both radio telescopes have roughly the same size and construction. The photo schematic (Figure 1) is representative of each. Note the major (lower) axis is 13 meters from the ground, and the minor (upper) axis is 20 meters from the ground. Both are at right angles to each other and parallel to the ground plane when the dish is in the upright position. The top of the instrument cage is 37 meters high.
Nature's Carnot Engine: The Hurricane
Authors: Bluestein Maurice
Published: April 2008

The typical curriculum in a thermodynamics course includes the Carnot cycle, a series of processes that constitute the most efficient heat engine between two constant temperature reservoirs. The conventional view of this cycle is that it is an ideal that cannot be achieved in practice. The spate of hurricanes that battered the U.S. in 2005 has given rise to extensive thermodynamic analysis of these storms with the finding that they in fact replicate the Carnot cycle. Heat energy fuels the storm through evaporation of the warm ocean waters at constant temperature. Work is produced by adiabatic expansion upward of the saturated air, resulting in strong winds. Energy is then released by radiation to space at the approximately constant temperature of the upper atmosphere. Adiabatic compression follows as the air descends back to sea level. Unlike the textbook Carnot engine, the work output of the hurricane is returned to the cycle by frictional dissipation due to the wind at the sea surface boundary layer. This paper will describe the hurricane in thermodynamic terms so as to appreciate its great power and efficiency. It may be a worthwhile topic to include in a thermodynamics course.
Dynamic Response Predictions of Quarter-Vehicle Models Using FEA and Rigid Ring Truck Tire Models
Authors: Chae Seokyong , Allen James , O¨ijer Fredrik , El-Gindy Moustafa , Trivedi Mukesh , Johansson Inge
Published: April 2008

In this paper two finite element analysis (FEA) quarter-vehicle models (QVMs) are constructed using developed nonlinear 3-and 4-groove tread FEA radial-ply truck tire models. In addition to the FEA models, a rigid ring QVM is developed to observe the dynamic response of the rigid ring tire model under the effect of the sprung mass vertical motions. The rigid ring tire model was created in the authors' previous studies. In the rigid ring QVM, the suspension characteristics are similar to that used in the FEA QVMs. Simulations are conducted using explicit FEA simulation software, PAM-SHOCK. The FEA tire model predictions of contact patch area, static vertical stiffness, first mode of free vertical vibration, and yaw oscillation frequency response are compared with measurements and found to be in good agreement. After the successful validation tasks, the FEA QVMs is subjected to a durability test on a 74 cm-long and 8.6 cm-deep water drainage ditch to observe the dynamic tire responses. Meanwhile, measurements are conducted using a tractor-semitrailer. The vertical acceleration of the front axle that moves vertically together with front tires is measured and compared with the results from the QVMs. The predicted vertical accelerations from the QVMs exhibit similar results in magnitude and trend to each other. However, the measured peak values are lower than those observed from the QVMs due to a dynamic coupling effect from roll and pitch motions. Reasonable agreement between predicted and measured vertical acceleration is observed at higher speeds because the dynamic coupling effect is less significant on the front axle of the tractor-semitrailer at higher speeds. In order to compare the dynamic tire responses of the QVMs with measured values, special test equipment similar to the QVM is required to obtain the actual dynamic tire responses in the same quarter-vehicle environment.
Fatigue Testing of Microalloyed AAR Class C Wheel Steel
Authors: Lonsdale Cameron , Dedmon Steven
Published: April 2008

Railroad wheels guide a freight car along the rails while supporting mechanical loads, and also serve as the brake drum in the air brake system of a freight car. Since a 36-inch diameter freight car wheel experiences approximately 560 revolutions per mile, and since many North American freight cars accrue 100,000 miles per year in service, fatigue properties of steel are very important. Further, elevated tread temperatures resulting from tread braking are known to significantly reduce the yield strength of the wheel steel at the tread surface. This paper describes fatigue testing of AAR rim quenched Class C wheel steel manufactured with microalloy additions. Small amounts of selected alloy elements were purposely added to develop a wheel steel with improved high temperature yield strength. Rotating bending fatigue tests, conducted at a well-known professional testing laboratory, were performed at ambient and elevated temperatures using complete stress reversal (R = -1) cycling. Stress-life (S-N) curves were constructed and the microalloy steel results were compared to existing fatigue data, and to results for typical Class C steel with no microalloy additions. Past research work is briefly reviewed. Test results are discussed with emphasis on the implications for service performance of wheel steel.
Heavy Truck and Equipment Back-Up Alarm System Design Using Smart Technology
Authors: Ferrone Christopher W. , Sinkovits Charles , Ulmenstine Matthew
Published: April 2008

Accidents occurring from trucks and equipment backing up and contacting workers, laborers and pedestrians remain a problem even with the use of back-up alarms which beep when trucks and heavy equipment are shifted into reverse. A new method combining a warning when a vehicle is shifted into reverse with a separate and distinct warning to indicate that the vehicle is actually moving in reverse has been developed.
Hybrid Optimization Algorithm Using Enhanced Continuous Tabu Search and Genetic Algorithm for Parameter Estimation
Authors: Ramkumar Barathram , Schoen Marco P. , Lin Feng , Williams Brian G.
Published: April 2008

A new algorithm using Enhanced Continuous Tabu Search (ECTS) and genetic algorithm (GA) is proposed for parameter estimation problems. The proposed algorithm combines the respective strengths of ECTS and GA. The ECTS is a modified Tabu Search (TS), which has good search capabilities for large search spaces. In this work, the ECTS is used to define smaller search spaces, which are used in a second stage by a GA to find the respective local minima. The ECTS covers the global search space by using a TS concept called diversification and then selects the most promising regions in the search space. Once the promising areas in the search space are identified, the proposed algorithm employs another TS concept called intensification in order to search the promising area thoroughly. The proposed algorithm is tested with benchmark multimodal functions for which the global minimum is known. In addition, the novel algorithm is used for parameter estimation problems, where standard estimation algorithms encounter problems estimating the parameters in an un-biased fashion. The simulation results indicate the effectiveness of the proposed hybrid algorithm.
Advances in Sandwich Structural Optimization for Noise Transmission Reduction
Authors: Denli H. , Sun Jian-Qiao
Published: April 2008

The sandwich structures in aerospace industry experience high noise transmissions since they are often stiff and light, and have low damping. Optimization studies of sandwich structures for noise transmission are relatively fewer. Most optimization studies in composite sandwich community seek for high stiffness with minimal weight. Advanced sandwiches must meet not only stiffness to weight ratio demands, but also have improved acoustic transmission performance. This paper presents recent advances in optimization of sandwich structures for minimum sound transmission. The finite element models of sandwich beams and plates are presented in this paper. The acoustic radiation of the structure is computed by using the Rayleigh integral. Sensitivity plays an important role in optimization studies. Analytical expressions of sensitivity can improve computational efficiency dramatically and accuracy at the same time. The explicit sensitivity functions of power and natural frequencies with respect to design parameters are derived in this work. In the optimization studies, we have considered structural parameters that can influence the transverse propagation of sound from the sandwich to the acoustic medium. These parameters include core topology and coupling stiffiness between in- and out-of-plane strains. We also study the optimization of the structure with respect to the structural boundary conditions to minimize the sound transmission. Numerical examples of single tone and broadband applications are presented in the paper. The results show that significant reduction of sound transmission across sandwich structures can be obtained. Finally, it should be noted that the novel optimized sandwich structures can meet not only stiffness to weight ratio demands, but also have significantly improved acoustic performance.
Assessment of Relevant Physical Phenomena Controlling Thermal Performance of Nanofluids
Authors: Bahrami M. , Yovanovich M. M. , Culham J. R.
Published: April 2008

This paper provides an overview of the important physical phenomena necessary for the determination of effective thermal conductivity of nanofluids. Through an investigation, a large degree of randomness and scatter has been observed in the experimental data published in the open literature. Given the inconsistency in the data, it is impossible to develop a comprehensive physical-based model that can predict all the trends. This also points out the need for a systematic approach in both experimental and theoretical studies. Upper and lower bounds are developed for steady-state conduction in stationary nanofluids. Comparisons between these bounds and the experimental data indicate that all the data (except for carbon nanotube data) lie between the lower and upper bounds.
Collaborative Product Realization of an Innovative Structural Damper and Application
Authors: Sweeney Shannon K. , Michael Robert J.
Published: April 2008

This paper describes an ongoing applied research project directed at producing a marketable viscoelastic structural damper system designed to protect buildings from seismic and wind events. The project is a collaborative effort involving Penn State Erie, Lehigh University, and Corry Rubber Corporation. This paper provides details of the damper realization steps which include product conceptual design and evolution, prototype manufacture and test results, application testing and evaluation plans, and the results of initial product market and commercialization studies. The collaborative efforts of this project demonstrate how the applied research capabilities of a mechanical engineering technology program can complement the pure research capabilities of a leading institution in their field.
Strength Evaluation and Fatigue Prediction of a Spur Gear Pair by Computer Simulation
Authors: Hu Zhong , Delfanian Fereidoon
Published: April 2008

Fatigue prediction of a three-dimensional mechanical component under dynamic load is critical for mechanical design. In this paper, computer simulation of three-dimensional dynamic stress followed by fatigue calculation was performed on a spur-gear pair using finite element modeling. Starting from gear pair geometry and operating conditions, the time histories of the dynamic loads and multi-axial stresses for a complete working cycle of a gear tooth were computed, and then post processed to produce fatigue strength information. Along with certain material properties obtained from experiments, this computer simulated fatigue design provides a useful tool for predicting fatigue failure of mechanical components.
The Binary Spatial Partitioning Algorithm for Efficient Tracing of Rays in the Monte Carlo Method for Surface-to-Surface Radiation Transport
Authors: Mazumder Sandip
Published: April 2008

The Binary Spatial Partitioning (BSP) algorithm has found prolific usage within the computer graphics community for efficient tracing of rays. In this paper, the BSP algorithm is described and demonstrated in the context of the Monte Carlo method for surface-to-surface radiation transport. In the BSP algorithm the computational domain is recursively bisected into a set of hierarchically linked boxes that are then made use of to narrow down the number of ray-surface intersection calculations. The geometric information pertaining to these hierarchically linked boxes is stored in the form of a binary tree or table. The algorithm is tested for two classical problems, namely an open box, and a box in a box, in both two-dimensional (2D) and three-dimensional (3D) geometries with various mesh sizes, and is found to result in orders of magnitude gains in computational efficiency over direct calculations that do not employ any acceleration strategy. In theory, the BSP algorithm is expected to scale logarithmically, i.e., the CPU time is expected to increase logarithmically with increase in the number of discrete surface elements (or faces) that the boundaries of the computational domain are broken into. In practice, however, it was found that balancing of the binary tree is critical for logarithmic scaling of the algorithm. Without balancing of the binary tree, only super-linear scaling can be attained.
A Methodology for Identifying Inherent Deviations in Universal Spindle Head Type Multi-Axis Machines by Simultaneous Five-Axis Control Motions
Authors: Dassanayake K. M. Muditha , Yamamot Ken , Tsutsumi Masaomi
Published: April 2008

In this paper, two different simulataneous five-axis control motions were newly proposed to identify the ten inherent deviations in universal spindle head type multi-axis machines. The ball bar was used as a measuring device. Both of the two motions were carried out bu using a single setup which was a simple extension bar. This leads to reduce non-productive time of the operator within the machine work space. Three measurments were used to estimate the ten deviations in which two measurements were extracted by means of axial direction motion and the other by tangential direction motion. By using the axial direction motion, seven deviations were estiamted in which four deviations were estiamted by means of the observation equation and simple geometric relations were used for other three. Remaining three of the ten deviations was estimated by using tangential direction motion. The validity of the proposed methodology for identifying the ten deviations inherent to universal spindle head type five-axis machining centers is confirmed by simulations.