bluuebunny/crossref_metadata_2025 huggingface dataset:
The Computation of Optimum Pressure Recovery in Two-Dimensional Diffusers
Authors: Ghose S. , Kline S. J.
Published: October 2010

A method is presented for computation of optimum recovery at fixed length (Cp*) in two-dimensional diffusers with incompressible flow and turbulent inlet boundary layers. Since Cp* lies in the zone of transitory stall, the method involves computation of not only attached but also detaching and detached turbulent boundary layers. The results agree with available data to the level of the uncertainty in the data. The model is zonal in character. Results suggest that the most important feature in computing detaching flows is the treatment of the interaction between the outer (inviscid) flow and the boundary layer; the use of velocity-profile forms that represent average back-flows adequately is also important.
A Wind-Tunnel Study of the Effect of Turning Vanes on the Aerodynamic Drag of Tractor-Trailer Trucks
Authors: Marks C. H. , Buckley F. T.
Published: October 2010

A Wind-Tunnel Study was made of the reduction of the aerodynamic drag of tractor-trailer trucks due to turning vanes used to control flow separation. A variety of vane settings and positions were investigated on the tractor and on the trailer. It was found that substantial drag reductions were obtained by employing vanes on the lower part of the front vertical edges of the tractor. Vanes mounted elsewhere had a smaller effect on the aerodynamic drag. Vane setting, turning angle and edge radius were found to be highly important.
A Numerical Study of the Laminar Viscous Incompressible Flow Through a Pipe Orifice
Authors: Nigro F. E. B. , Strong A. B. , Alpay S. A.
Published: October 2010

The present paper discusses a numerical algorithm for the solution of the steady flow of a viscous fluid through a pipe orifice which allows for considerable flexibility in the choice of orifice plate geometry. The results are compared to the data for a wide range of Reynolds numbers in the laminar regime and orifice/pipe diameter ratios for a 45 deg sharp edged orifice plate, a square edged orifice plate and a thin orifice plate. Based on the initial results presented here the numerical algorithm is deemed to provide a fast, accurate and relatively easy way of examining the effects of a wide variety of orifice plate geometries and flow situations. The solution efficiency is made possible by solving the equations of motion in general orthogonal coordinates.
Spectral and Probability-Density Nature of Square-Prism Separation-Reattachment Wall Pressures
Authors: Wedding J. B. , Robertson J. M. , Peterka J. A. , Akins R. E.
Published: October 2010

The statistical nature of the fluctuating pressures associated with the separation-reattachment flow were studied for a two-dimensional square prism in uniform flow for low (0.33 percent) and high (10.4 percent) turbulence levels. Studies were also made with a splitter plate to inhibit the feedback effect arising from vortex shedding. The nature of the separation reattachment flow was charcterized by use of the measured value of the mean and fluctating pressure fields. Spectral distribution of the unsteady pressures reveals strong energy spikes at the Strenthal frequency which are eliminated by the pressure of the splitler plate. Probability density distributions indicate appreciably non-Gaussian nature only in the wake. Additional information is presented on the variation with angle of the Strouhal frequency for the wake flow.
Fillet Size in a Liquid Jet
Authors: Pimbley W. T. , Rickenbach D. H.
Published: October 2010

As a liquid jet is formed by a nozzle, a fillet, wetting the outside face of the nozzle, can exist at appropriate jet velocities. The lack of azimuthal symmetry in such a fillet adversely affects the directional stability of the jet. A matrix of experiments was performed in which the dependence of fillet size upon a number of parameters was studied. Analysis of the data shows that a linear relationship exists between the relative fillet size and a nondimensional number composed of a number of relevant parameters.
Cross-Ventilation of Underground Railway Tunnels
Authors: Vardy A. E.
Published: October 2010

The aerodynamic merits and demerits of cross-ventilating adjacent tunnels in underground rapid transit systems are discussed. Three types of cross-ventilation are considered, namely (a) numerous small holes in the dividing wall between the tracks in a cut-and-cover tunnel, (b) a curtailed dividing wall and (c) passages linking separately bored tunnels. It is shown that considerable reductions in the air velocities expected on station platforms will result if the end regions of the tunnels are well cross-ventilated. Additionally, useful reductions in the aerodynamic drag force on trains can be expected if cross-ventilation is provided along the whole length of the tunnel. However, this is recommended only for low speed systems because interaction between passing trains will cause large pressure fluctuations at high speeds.
Compressibility Effects in Cavity Flows
Authors: Popp Simona , Teposu Iosif
Published: October 2010

The aim of this paper is to present the compressibility effects in cavity flows in the case of Joukowsky-Roshko model in a channel for a wedge shaped obstacle. In virtue of some exact formulas expressing the drag coefficient and other elements of the motion, numerical calculations are carried out for wedges of all angles. Tables and diagrams are included. A comparison is made between the results of this study and the analogous results corresponding to the incompressible fluid.
The 1978 Freeman Scholar Lecture: Buoyancy Induced Fluid Motions Characteristic of Applications in Technology
Authors: Gebhart Benjamin
Published: October 2010

Buoyancy induced flows abound in nature and in our enclosures and devices. They arise through the interaction of a body force, like gravity, with a density difference. The difference is often caused by the diffusion of thermal energy and/or chemical species. Here we are not principally concerned with environmental matters, but rather with the engineering of buoyancy-induced transport in technology, up to a size scale of a number of meters. Early pioneering insights concerning such transport began about a century ago. Increasingly intensive study in the last thirty years has further clarified our conceptual basis. A single generation of researchers has explained in detail many of the simplest flows and transport, those immersed in an extensive and quiescent ambient medium. Study is well along for transport within enclosed bodies of fluid, and, in addition, for the most subtle kinds of transport, those that combine the features of both the external and internal flows. This work considers only the first group, external flows. There is a large recent accumulation of information of great value to design, in a wide range of engineering application. However, the emphasis here is not on equations and correlations, but rather on concepts and on the basic nature of many of the processes which very commonly arise. This kind of information is the basis of understanding inter-relations, multiple flows and conceptual design. A discussion of the agency of buoyancy drive is followed by consideration of the mechanisms arising in different kinds of vertical and inclined laminar flows. Then the progression of laminar flows to turbulence is considered, with a quantitative parameter for transition. The effects of a temperature-caused density extremum on transport, as in cold water, is considered in terms of mechanisms and regimes. Commonly arising multi-buoyancy effect transport, as in the combined thermal transport and species diffusion which occurs around our bodies, is considered in a general way and also specifically for melting ice in saline water. A series of additional kinds of transport effects are next considered, first that of changing buoyancy forces due to ambient fluid density stratification. An example of the formation of one flow out of another is then given. A similar but different kind of multiple flow interaction is detailed in the mutual interaction mechanisms of multiple plumes and of plumes and surfaces. Then, the curious ways in which flows separate from the surfaces which generate them are clarified, along with the resulting transport behavior. The examples were chosen throughout to demonstrate most important aspects and mechanisms in common applications. Many of the basically different phenomena, among the well-understood ones, are included. Of course the choice of coverage is the writer’s and the following account does represent a single point of view.
The Effect of Gaseous Cavitation on Fluid Transients
Authors: Wiggert D. C. , Sundquist M. J.
Published: October 2010

Gaseous cavitation, alternately termed gas release, is investigated for turbulent pipe flows subjected to transient wave motion. Experimental data are presented that exhibit developing two-component flow (air or carbon dioxide and water mixtures) in a 295 m laboratory pipeline; the flow is characterized by wave dispersion due to the increase in void fraction. An analytical model based on the method of characteristics yields simultaneous solutions for pressure, velocity and void fraction. The greatest uncertainty in the formulation is the rate of gas release; here it is allowed to depend upon the difference between saturation and instantaneous line pressures.
Laminar Boundary Layer on a Finite Disk in a Rotating Compressible Isothermal Flow
Authors: Toren M. , Solan A.
Published: October 2010

An improved momentum integral method for the solution of shrouded rotating disk problems is presented. The method admits compressibility and accounts for the radial variation of the velocity profiles within the boundary layer, to reproduce the correct asymptotic behavior. For the incompressible case, the integral solution is in agreement with an exact numerical solution of the boundary layer equations. Compressibility effects, controlled by the azimuthal Mach number of the outer flow, are shown to increase the boundary layer thickness and the axial velocity at the edge of the boundary layer and to decrease its radial mass flux. The method of solution can be applied to the solution of the interaction between an outer rotating flow—not necessarily rigid body like—and the boundary layer on a finite rotating disk in closed configurations.
Flow and Pressure Characteristics Downstream of a Segmental Blockage in a Turbulent Pipe Flow
Authors: Sparrow E. M. , Ramsey J. W. , Lau S. C.
Published: October 2010

Two mutually complementary sets of experiments were performed to study the flow and pressure fields created by the presence of a segmental orifice plate in a circular tube. In one set of experiments, axial and circumferential pressure distributions were measured, whereas in the second set the reattachment of the flow downstream of the blockage was studied by means of a visualization technique. Three degrees of flow blockage were employed and the Reynolds number ranged from 10,000 to 60,000. The pressure loss induced by the blockage, when normalized by the velocity head, is insensitive to the Reynolds number but increases markedly with the extent of the blockage; the values of the loss coefficient are comparable to literature values for a gate valve. The axial pressure distributions display a precipitous drop and a subsequent rapid recovery due to the acceleration—deceleration sequence experienced by the flow deflected by the blockage. Downstream of the blockage, beyond the reattachment and redevelopment regions, a fully developed flow is re-established. Relatively large circumferential pressure variations occur near the blockage but die away with increasing downstream distance; the high and low pressure regions of the circumferential distributions shift with distance along the pipe. Owing to the fluctuating nature of the separated flow, the reattachment point meanders within a zone of finite extent. The reattachment zone tends to shift downstream and to elongate with increasing blockage.
Trajectories of Single and Double Jets Injected Into a Crossflow of Arbitrary Velocity Distribution
Authors: Makihata Toshiaki , Miyai Yoshihiro
Published: October 2010

This paper describes the results of our experiments on and theoretical predictions of the trajectories of multiple buoyant and nonbuoyant jets. Our theoretical calculations employed a finite difference method of analysis of both a momentum integral equation and the law of conservation of momentum. Results are presented for cases in which the ratio of the jet velocity to the crossflow of arbitrary velocity distribution ranges from 1.2 to 10.6. Our theoretical predictions are shown to be in close agreement with available experimental data.
Subsonic Turbulent Flow Past a Downstream Facing Annular Step
Authors: Kangovi S. , Page R. H.
Published: October 2010

The flow past a downstream facing annular step was experimentally investigated in the Mach range of 0.1 to 0.95. The approaching flow was steady and uniform. The boundary layer ahead of the step was turbulent. The upstream influence of the step and the variation of base pressure and recovery pressure with the reference Mach number are described. Results of hot-wire measurements in the shear layer and the locations of reattachment and secondary separation points are also reported.
Numerical Analysis of Turbulent Flow Along an Abruptly Rotated Cylinder
Authors: Aguilar F. , Pierce F. J.
Published: October 2010

A parabolic system of equations governing turbulent, incompressible fluid motion along a stationary cylinder fitted with a rotating aft-section is solved with an implicit finite-difference algorithm. The mean flow is steady, axisymmetric, and characterized by abrupt skewing of the boundary layer. The equations of mean motion are closed with an eddy viscosity model based on Cebeci’s axisymmetric formulation. The analysis is compared with the experimental results of Bissonnette and Mellor, who have obtained data for ratios of cylinder wall speed to free-stream speed equal to 0.936 and 1.800. Predicted components of wall shear stress agree with the experimental values within the uncertainty associated with the experiment, and early boundary-layer development is predicted reasonably well. However, the analysis fails to predict the experimentally observed acceleration of the mean, axial flow.
The Propagation of Boiling Boundary Phase-Change Fronts in Moving Fluids
Authors: Kroeger P. G.
Published: October 2010

The transient propagation of boiling boundary phase-change fronts during the depressurization of a subcooled liquid has been investigated for the case of thermal equilibrium without friction or heat addition, using wave diagram solutions. Various modes of phase-change front propagations have been identified and it is shown that certain ranges of propagation speeds are impossible, while others require the simultaneous formation of shocks. Qualitative and quantitative results are given for two specific cases of interest.
Laminar Flow of Suspensions in the Entrance Region of a Diffuser
Authors: Chen R. Y. , Eldighidy S. M. , Comparin R. A.
Published: October 2010

An analytical investigation of the mechanics of deposition of fine particles in a two-dimensional diffuser from the diffuser to inlet to the point of separation has been made. The deposition of suspensions in a diffuser was found to depend strongly on the electrostatic charge parameter and the diffuser angle. The analysis is restricted to laminar flow of dilute suspensions with diffusive, electrostatic, and surface adhesive effects. The implicit finite difference method was utilized to obtain a solution of the governing equations.
Predictions of Induced Air Flows in Hollow Cone Sprays
Authors: Boysan F. , Binark H.
Published: October 2010

The problem of hydrodynamic interaction between a hollow cone spray and the encompassing unbounded fluid has been formulated in terms of a set of partial and a set of ordinary differential equations for the fluid and the spray respectively. These equations have been solved by adapting an existing numerical solution procedure to predict the flow patterns and the trajectories of individual particles for the practical range of operating conditions. The predictions have been found to agree well with the experimental data available in the literature.
Computational Fluid Dynamics Applied to Three-Dimensional Nonreacting Inviscid Flows in an Internal Combustion Engine
Authors: Griffin M. D. , Anderson J. D. , Jones E.
Published: October 2010

The three-dimensional inviscid flowfield between the face of the piston and the top of the cylinder in a reciprocating internal combustion engine is calculated for a complete four-stroke cycle (intake, compression, power, exhaust). The fluid dynamic aspects are emphasized; combustion is simply modeled by constant-volume heat addition. The computational method is an explicit time-dependent finite-difference solution of the governing fluid dynamic equations. The results show that a well-defined three-dimensional swirling flow pattern is established during the intake stroke, and that this swirl persists throughout the complete four-stroke cycle. Such a flowfield will have direct influence on I.C. engine combustion phenomena. Moreover, the radial distributions of pressure and temperature show a nearly-axisymmetric behavior, while the three-dimensional results in the valve plane show a striking similarity to previous two-dimensional results. The present investigation is the first three-dimensional calculation of the flowfield for all four strokes, and has important implications for future work in the application of computational fluid dynamics to I. C. engine analysis.
Water Tunnel Visualizations of Dynamic Stall
Authors: McAlister K. W. , Carr L. W.
Published: October 2010

A two-dimensional experiment was conducted in a water tunnel using hydrogen bubble flow visualizations for the purpose of exposing, independently, the behavior of the viscous and inviscid domains during unsteady airfoil stall. By imposing a large amplitude pitch oscillation about the static-stall angle of a modified NACA 0012 airfoil, an unsteady environment was created that not only altered considerably the progression of flow reversal along the airfoil surface from what was observed in steady flow, but also caused a unique succession of vortical developments to appear that is unparalleled in steady flow.
Two Dimensional Lateral Flow Past a Barrier
Authors: Ramamurthy A. S. , Carballada B. L.
Published: October 2010

The well-known Schwarz-Christoffel transformation and the free streamline theory are used to solve the problem of flow past a lateral outlet housed in a two-dimensional conduit. The solution presented can be applied to lateral outlets which are fitted with a barrier that can be set at arbitrary inclinations. For the more general case, where the barrier inclination is arbitrary, numerical techniques were used to obtain the solution. The contraction coefficient and the inclination of the flow issuing out of the outlet are obtained as functions of the velocity ratios.
A New Formulation for Computational Fluid Dynamics
Authors: Reed D. B. , Oberkampf W. L.
Published: October 2010

A new vector quantity in fluid dynamics is defined and a vector transport equation for the quantity is derived. The new vector quantity is defined as the curl of the vorticity and is referred to as the angular vorticity. The transport equation for the new quantity is derived by taking the curl of the vorticity transport equation. The new transport equation combined with Poisson type velocity equations comprises the new angular vorticity-velocity formulation. The major advantage of the new formulaton is that computational boundary conditions for through-flow problems may be significantly relaxed. Boundary conditions for the newly defined variable are derived. A simple test case of laminar incompressible planar flow between parallel plates was executed to determine if the new formulation would produce results comparable to previous solutions. Numerical experiments were conducted using channel length, mesh size, and Reynolds number as parameters. The results are compared to values obtained by other investigators. The results show that the angular vorticity formulation is a feasible method for solution of fluid flow problems where fully developed flow is not attained.
Inverse Design of Optimal Diffusers With Experimental Corroboration
Authors: Hokenson Gustave
Published: October 2010

The equations of motion for a turbulent boundary layer are formulated in an inverse manner and solved to provide the geometrical configuration of optimal two-dimensional diffusers with a distinct inviscid core. For each Reynolds number/diffusion length, optimality is inferred when the lowest exit freestream velocity is computed from the members of an assumed one-parameter family of skin friction decay functions. In addition to the unique inverse formulation and establishment of the appropriate skin friction distribution, an integral part of the analysis is the development of an invertable adverse pressure gradient skin friction law, which is used to solve for the channel-averaged streamwise pressure (inviscid core velocity) distribution. The diffuser configurations are presented graphically for various Reynolds numbers/lengths/blockages and exhibit a distinctive concave shape. The results are compared to three sets of experimental data which support the validity of the viscous flow analysis, the formulation of the governing equations, and the skin friction law which is proposed.
A Vortex Model of the Darrieus Turbine: An Analytical and Experimental Study
Authors: Strickland J. H. , Webster B. T. , Nguyen T.
Published: October 2010

An aerodynamic prediction model has been formulated for two- and three-dimensional Darrieus turbines using a vortex lattice method of analysis. Experiments were conducted on a series of two-dimensional rotor configurations in a water tow tank. The agreement between analysis and experiment was in general found to be good. This model should allow one to make accurate predictions of instantaneous aerodynamic blade forces and to characterize the near wake flow behind the rotor.
Estimation of Pressure Loss in Ring-Type Exit Chambers
Authors: Escudier Marcel
Published: October 2010

A simple Borda-Carnot type of analysis is presented which enables an estimate to be made of the pressure loss in the exit chamber of an axial-flow turbomachine. Based upon the recent experimental investigation of Escudier and Merkli [1], it is argued that the loss is primarily accounted for by dissipation of the vortex generated in ring-type exit chambers by the tangential inflow. For the most part this dissipation occurs in the outlet tube from the exit chamber. The analysis is particularly useful in providing a qualitative guide for the design engineer as to the influence on performance of changing the geometric proportions of an exit chamber.
Velocity Characteristics of a Confined Coaxial Jet
Authors: Habib M. A. , Whitelaw J. H.
Published: October 2010

The velocity characteristics of a turbulent, confined, coaxial-jet flow have been determined by measurement and by the solution of conservation equations in differential form. The ratios of maximum annulus to pipe velocity were 3 and 1 and, in both cases, the profiles were fully developed in the exit plane. The geometric arrangement corresponded to a model furnace and the investigation was undertaken to provide information, for isothermal flow, relevant to furnace flows. The measurements were obtained with a hot-wire anemometer and include distributions of the axial mean velocity and the components of the Reynolds-stress tensor. They show, for example, that the larger velocity ratio results in a larger region of recirculation, larger velocity gradients and larger turbulence intensities in the mixing region and downstream of the region of reverse flow. Numerical solutions of the time-averaged forms of the equations of conservation of mass and momentum, together with equations for turbulence energy and dissipation rate, provided results which are in close agreement with the measurements except in regions of more than one major component of the velocity-gradient tensor where they are substantially in error. The reasons for the discrepancies and the consequential value of the calculation method are discussed.
Economic Potential of Solar Thermal Power Plants With Direct Steam Generation Compared With HTF Plants
Authors: Feldhoff Jan Fabian , Benitez Daniel , Eck Markus , Riffelmann Klaus-Jürgen
Published: October 2010

The direct steam generation (DSG) in parabolic trough collectors is a promising option to improve the mature parabolic trough solar thermal power plant technology of the solar energy generating systems (SEGS) in California. According to previous studies [Langenkamp, 1998, “Revised LEC Projections and Discussion of Different DSG Benefits,” Technical Report No. DISS-SC-QA-02, Almeria, Spain; Price, et al., 2002, “Advances in Parabolic Trough Solar Power Technology,” ASME J. Sol. Energy Eng., 124(2), pp. 109–125; Zarza, E., 2002, “DISS Phase II Final Report,” Technical Report EU Contract No. JOR3-CT98-0277, Almeria, Spain], the cost reduction in the DSG process compared with the SEGS technology is expected to be 8–25%. All these studies were more or less preliminary since they lacked detailed information on the design of collector fields, absorber tubes required for steam temperatures higher than 400°C, and power blocks adapted to the specific needs of the direct steam generation. Power blocks and collector fields were designed for four different capacities (5 MWel, 10 MWel, 50 MWel, and 100 MWel) and different live steam parameters. The live steam temperature was varied between saturation temperature and 500°C and live steam pressures of 40 bars, 64 bars, and 100 bars were investigated. To assess the different cases, detailed yield analyses of the overall system were performed using hourly data for the direct normal irradiation and the ambient temperature for typical years. Based on these results, the levelized costs of electricity were determined for all cases and compared with a reference system using synthetic oil as heat transfer fluid. This paper focuses on two main project findings. First, the 50 MWel DSG system parameter comparisons are presented. Second, the detailed comparison between a DSG and a SEGS-like 100 MWel system is given. The main result of the investigation is that the benefit of the DSG process depends on the project site and can reach an 11% reduction in the levelized electricity cost.
Three-Dimensional Generalizations of Reuleaux’s and Instant Center Methods Based on Line Geometry
Authors: Baroon Jasem , Ravani Bahram
Published: October 2010

In kinematics, the problem of motion reconstruction involves generation of a motion from the specification of distinct positions of a rigid body. In its most basic form, this problem involves determination of a screw displacement that would move a rigid body from one position to the next. Much, if not all of the previous work in this area, has been based on point geometry. In this paper, we develop a method for motion reconstruction based on line geometry. A geometric method is developed based on line geometry that can be considered a generalization of the classical Reuleaux method used in two-dimensional kinematics. In two-dimensional kinematics, the well-known method of finding the instant center of rotation from the directions of the velocities of two points of the moving body can be considered an instantaneous case of Reuleaux’s method. This paper will also present a three-dimensional generalization for the instant center method or the instantaneous case of Reuleaux’s method using line geometry.
A New Approach to Dimension Synthesis of Spatial Four-Bar Linkage Through Numerical Atlas Method
Authors: Chu Jinkui , Sun Jianwei
Published: October 2010

This paper presents a new method for the synthesis of spatial mechanism. Using harmonic analysis, the coupler curve and output angle function of spatial mechanism can be described as a series of harmonic characteristic component. For the path generation problem of the spatial mechanism, a technique of normalization processing eliminates the effects of scale, translation, and rotation; in other words, the harmonic characteristic component of the coupler curve is just determined by the basic dimensional type of spatial mechanism but not by the real dimension and the installing position. The numerical atlas database of coupler curve or output angle function of spatial mechanism can be created by the harmonic characteristic components and associated basic dimensional type of spatial mechanism. The best suitable basic dimensional type of spatial mechanism for prescribed function can be decided by using fuzzy identification method and numerical atlas database. On the basis of the basic dimensional type and formulas, which compute the coupler point, true size, and installing dimensions of the spatial mechanism, the dimension synthesis of the spatial mechanism is made possible. This paper takes the RSSR mechanism and RRSS mechanism as an example to illustrate the analysis process and application of this method.
Direct Linearization via the Gibbs Function
Authors: Parish Julie J. , Hurtado John E.
Published: October 2010

Linearized governing equations are often used in analysis, design, and control applications for dynamical systems. Linearized equations of motion can be formed in either an indirect or direct manner, that is, by first forming or bypassing the full nonlinear equations. Direct linearization is useful for easing the computation of linearized equations, particularly when the full nonlinear equations are not immediately desired. Currently, direct linearization methods derived from a Lagrangian perspective are available. In this paper, these methods are extended to reflect a Gibbs/Appell viewpoint. The resulting directly linearized equations take advantage of features of a Gibbs/Appellian formulation such as the ability to handle nonholonomic constraints and use of quasi-velocities. The Gibbs function and resulting equations are reviewed, the direct linearization method is explained, and a new method for directly linearizing equations via an augmented Gibbs function is presented with examples.
A Use of a Mathematical Model in Updating Concept Selection
Authors: Takai Shun
Published: October 2010

This paper presents the use of a mathematical model in updating a decision maker’s belief before selecting a product/system concept and demonstrates a procedure to calculate the maximum monetary value of such a model in terms of the expected value of information. Acquiring information about uncertainty and updating belief according to the new information is an important step in concept selection. However, obtaining additional information can be considered beneficial only if the acquisition cost is less than the benefit. In this paper, a mathematical model is used as an information source that predicts outcomes of an uncertainty. The prediction, however, is imperfect information because the model is constructed based on simplifying assumptions. Thus, the expected value of imperfect information needs to be calculated in order to evaluate the tradeoff between the accuracy and the cost of model prediction (information). The construction and analysis of a mathematical model, the calculation of the expected value of information (model prediction) and updating the belief based on the model prediction are illustrated using a concept selection for a public project.
Semicompliant Force Generator Mechanism Design for a Required Impact and Contact Forces
Authors: Demirel Burak , Emirler M. Tolga , Sönmez Ümit , Yörükoğlu Ahmet
Published: October 2010

A novel design of compliant slider-crank mechanism is introduced and utilized as an impact and contact-force generator. This class of compliant slider mechanisms incorporates an elastic coupler, which is an initially straight flexible beam and buckles when it hits the stopper. The elastic pin-pin coupler, a buckling beam, behaves as a rigid body prior to the impact pushing the rigid slider. At a certain crank angle, the slider hits a stopper generating an impact force. This force can be changed by regulating the angular velocity of the crank and by achieving a desired velocity of the slider. Moreover, after the impact when the slider establishes a permanent contact with the stopper, the maximum contact force can also be adjusted by calculating the coupler dimensions (the length, the width, the thickness, and the amount of compression). The contact duration, the crank angular rotation range, can also be changed and attuned in this mechanism by moving the location of the impacted object. Several mechanism designs with the same working principle are introduced. A prototype compliant slider-crank mechanism is constructed and proved the conceptual contributions of the mechanism.
A Formula That Produces a Unique Solution to the Forward Displacement Analysis of a Quadratic Spherical Parallel Manipulator: The Agile Eye
Authors: Kong Xianwen , Gosselin Clément M.
Published: October 2010

A quadratic parallel manipulator refers to a parallel manipulator with a quadratic characteristic polynomial. This paper revisits the forward displacement analysis (FDA) of a quadratic spherical parallel manipulator: the Agile Eye. An alternative formulation of the kinematic equations of the Agile Eye is proposed. The singularity analysis of the Agile Eye is then dealt with. After an alternative solution to the FDA has been presented, a formula is revealed that produces a unique current solution to the FDA for a given set of inputs. A regular cube in the input-space, which is singularity free, is also proposed for the Agile Eye. This work will facilitate the control of the Agile Eye.
Conceptual Design of a 2× Trough for Use Within Salt and Oil-Based Parabolic Trough Power Plants
Authors: Kolb Gregory J. , Diver Richard B.
Published: October 2010

Recent studies in the United States suggest that parabolic trough levelized energy costs (LECs) can be reduced 10–15% through integration of a large salt energy storage system coupled with the direct heating of molten salt in the solar field. While noteworthy, this relatively small predicted improvement may not justify the increased technical risks. Examples of potential issues include increased design complexity, higher maintenance costs, and salt freezing in the solar field. To make a compelling argument for development of this new system, we believe that additional technical advances beyond that previously reported will be required to achieve significant LEC reduction, greater than 25%. The new technical advances described include the development of a high-concentration trough that has double aperture and optical concentration of current technology. This trough is predicted to be more cost-effective than current technology because its cost ($/m2) and thermal losses (W/m2) are significantly lower. Recent trough optical performance improvements, such as more accurate facets and better alignment techniques, suggest a 2× trough is possible. Combining this new trough with a new low-melting point salt now under development suggests that a LEC cost reduction of ∼25% is possible for a 50 MW, 2× salt plant relative to a conventional (1×) 50 MW oil plant. However, the 2× trough will also benefit plants that use synthetic oil in the field. A LEC comparison of 2× plants at sizes ≥200 MW shows only a 6% advantage of salt over oil.
Analysis of a Chaotic Electrostatic Micro-Oscillator
Authors: Towfighian S. , Heppler G. R. , Abdel-Rahman E. M.
Published: October 2010

The closed-loop dynamics of a chaotic electrostatic microbeam actuator are presented. The actuator was found to be an asymmetric two-well potential system with two distinct chaotic attractors: one of which occurs predominantly in the lower well and a second that visits a lower-well orbit and a two-well orbit. Bifurcation diagrams obtained by sweeping the ac voltage amplitudes and frequency are presented. Period doubling, reverse period doubling, and the one-well chaos through period doubling are observed in amplitude sweep. In frequency sweep, period doubling, one-well, and two-well chaos, superharmonic resonances and on and off chaotic oscillations are found.
Control-Based Continuation of Unstable Periodic Orbits
Authors: Sieber Jan , Krauskopf Bernd , Wagg David , Neild Simon , Gonzalez-Buelga Alicia
Published: October 2010

We present an experimental procedure to track periodic orbits through a fold (saddle-node) bifurcation and demonstrate it with a parametrically excited pendulum experiment where the tracking parameter is the amplitude of the excitation. Specifically, we track the initially stable period-one rotation of the pendulum through its fold bifurcation and along the unstable branch. The fold bifurcation itself corresponds to the minimal amplitude that supports sustained rotation. Our scheme is based on a modification of time-delayed feedback in a continuation setting and we show for an idealized model that it converges with the same efficiency as classical proportional-plus-derivative control.
A Thermodynamic Similarity Framework for Assessment of Working Fluids for Solar Rankine Power Generation
Authors: Sunter Deborah A. , Carey Van P.
Published: October 2010

Numerous studies have compared the merits of different working fluids for use in Rankine power systems. Most often, however, these have considered a limited number of specific fluids for which the thermodynamic properties are known. In the investigation summarized here, the Redlich–Kwong fluid model was used to develop a thermodynamic similarity framework that can be used as a comparative model for evaluating the performance of Rankine cycle working fluids. This can be viewed as a reduced order model that, based on thermodynamic similarity, quantifies the characteristics of the working fluids in terms of a single dimensional coordinate space defined by the choice of critical temperature. The advantage of this framework is that it allows exploration of the performance advantages of working fluids for which full thermodynamic properties are not yet available. Predictions of the model for common fluids were examined and conclusions regarding optimal fluids for solar Rankine systems are discussed.
Electrostatics and Self-Contact in an Elastic Rod Approximation for DNA
Authors: Lillian Todd D. , Perkins N. C.
Published: October 2010

Deoxyribonucleic acid (DNA) is an essential molecule that enables the storage and retrieval of genetic information. In its role during cellular processes, this long flexible molecule is significantly bent and twisted. Previously, we developed an elastodynamic rod approximation to study DNA deformed into a loop by a gene regulatory protein (lac repressor) and predicted the energetics and topology of the loops. Although adequate for DNA looping, our model neglected electrostatic interactions, which are essential when considering processes that result in highly supercoiled DNA including plectonemes. Herein, we extend the rod approximation to account for electrostatic interactions and present strategies that improve computational efficiency. Our calculations for the stability for a circularly bent rod and for an initially straight rod compare favorably to existing equilibrium models. With this new capability, we are now well-positioned to study the dynamics of transcription and other dynamic processes that result in DNA supercoiling.
Kinematic Optimization of a Redundantly Actuated Parallel Mechanism for Maximizing Stiffness and Workspace Using Taguchi Method
Authors: Shin Hyunpyo , Lee Sungchul , In Woosung , Jeong Jay I. , Kim Jongwon
Published: October 2010

We present an optimization procedure that uses the Taguchi method to maximize the mean stiffness and workspace of a redundantly actuated parallel mechanism at the same time. The Taguchi method is used to separate the more influential and controllable variables from the less influential ones among kinematic parameters in workspace analysis and stiffness analysis. In the first stage of optimization, the number of experimental variables is reduced by the response analysis. Quasi-optimal kinematic parameter group is obtained in the second stage of optimization after the response analysis. As a validation of the suggested procedure, the kinematic parameters of a planar 2-DOF parallel manipulator are optimized, which optimization procedure is used to investigate the optimal kinematic parameter groups between the length of the link and the stiffness.
Hybrid Power/Energy Generation Through Multidisciplinary and Multilevel Design Optimization With Complementarity Constraints
Authors: Lu Shen , Schroeder Nathan B. , Kim Harrison M. , Shanbhag Uday V.
Published: October 2010

The optimal design of hybrid power generation systems (HPGSs) can significantly improve the technical and economic performance of power supply. However, the discrete-time simulation with logical disjunctions involved in HPGS design usually leads to a nonsmooth optimization model, to which well-established techniques for smooth nonlinear optimization cannot be directly applied. This paper casts the HPGS design optimization problem as a multidisciplinary design optimization problem with complementarity constraints, a formulation that introduces a complementarity formulation of the nonsmooth logical disjunction, as well as a time horizon decomposition framework, to ensure a fast local solution. A numerical study of a stand-alone hybrid photovoltaic/wind power generation system is presented to demonstrate the effectiveness of the proposed approach.
Quadratic Constraints on Rigid-Body Displacements
Authors: Selig J. M.
Published: October 2010

In this work, the solution to certain geometric constraint problems are studied. The possible rigid displacements allowed by the constraints are shown to be intersections of the Study quadric of rigid-body displacements with quadratic hypersurfaces. The geometry of these constraint varieties is also studied and is found to be isomorphic to products of subgroups in many cases. This information is used to find extremely simple derivations for general solutions to some problems in kinematics. In particular, the number of assembly configurations for RRPS and RRRS mechanisms are found in this way. In order to treat planes and spheres on an equal footing, the Clifford algebra for the Möbius group is introduced.
A Comparison of Long-Term Wind Speed Forecasting Models
Authors: Kritharas Petros P. , Watson Simon J.
Published: October 2010

This paper presents a time series analysis of historical observations of wind speed in order to project future wind speed trends. For this study, 52 years of data have been used from seven suitable stations across the UK. Four parsimonious models have been employed, and the data were split into two different segments: the training and the validation data sets. During the fitting process, the optimum parameters for each model were determined in order to minimize the mean square error in the predictions. The results suggest that the seasonal pattern in wind speeds is the most important factor but that there is some monthly autocorrelation in the data, which can improve forecasts. This is confirmed by testing the four models with the model having considered both autocorrelation and seasonality achieving the smallest errors. The approach proposed for forecasting wind speeds a month ahead may be deemed useful to suppliers for purchasing base load in advance and to system operators for power system maintenance scheduling up to a month ahead.
Nonlinear Responses of Dual-Pendulum Dynamic Absorbers
Authors: Ikeda Takashi
Published: October 2010

The nonlinear responses of a single-degree-of-freedom system with two pendulum tuned mass dampers under horizontal sinusoidal excitation are investigated. In the theoretical analysis, van der Pol’s method is applied to determine the expressions for the frequency response curves. In the numerical results, the differences between the responses in single- and dual-pendulum systems are shown. A pitchfork bifurcation occurs followed by mode localization where both identical pendula vibrate at constant but different amplitudes. Hopf bifurcations occur, and then amplitude- and phase-modulated motions including chaotic vibrations appear in the identical dual-pendulum system. The Lyapunov exponents are calculated to prove the occurrence of chaotic vibrations. In a nonidentical dual-pendulum system, a perturbed pitchfork bifurcation occurs and saddle-node bifurcation points appear instead of pitchfork bifurcation points. Hopf bifurcations and amplitude- and phase-modulated motions also appear. The deviation of the tuning condition is also investigated by showing the frequency response curves and bifurcation sets. The numerical simulations are shown to be in good agreement with the theoretical results. In experiments, the imperfections of the two pendula were taken into consideration, and the validity of the theoretical analysis was confirmed.
Reactionless Two-Degree-of-Freedom Planar Parallel Mechanism With Variable Payload
Authors: Lecours Alexandre , Gosselin Clément
Published: October 2010

A reactionless mechanism is one that does not exert any reaction force or moment on its base at all times, for any arbitrary trajectory of the mechanism. This paper addresses the static and dynamic balancing of a two-degree-of-freedom parallel planar mechanism (five-bar mechanism). A simple and effective adaptive balancing method is presented that allows the mechanism to maintain the reactionless condition for a range of payloads. Important proofs concerning the balancing of five-bar mechanisms are also presented. The design of a real mechanism where parallelogram linkages are used to produce pure translations at the end-effector is also presented. Finally, using dynamic simulation software, it is shown that the mechanism is reactionless for arbitrarily chosen trajectories and for a variety of payloads.
A Second-Order Reliability Method With First-Order Efficiency
Authors: Zhang Junfu , Du Xiaoping
Published: October 2010

The first-order reliability method (FORM) is efficient but may not be accurate for nonlinear limit-state functions. The second-order reliability method (SORM) is more accurate but less efficient. To maintain both high accuracy and efficiency, we propose a new second-order reliability analysis method with first-order efficiency. The method first performs the FORM to identify the most probable point (MPP). Then, the associated limit-state function is decomposed into additive univariate functions at the MPP. Each univariate function is further approximated by a quadratic function. The cumulant generating function of the approximated limit-state function is then available so that saddlepoint approximation can be easily applied in computing the probability of failure. The accuracy of the new method is comparable to that of the SORM, and its efficiency is in the same order of magnitude as the FORM.