bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Probability and Possibility for Design Against Catastrophic Failure Under Uncertainty
Authors: Nikolaidis Efstratios , Chen Sophie , Cudney Harley , Haftka Raphael T. , Rosca Raluca
Published: July 2004

This paper compares probabilistic and possibility-based methods for design under uncertainty. It studies the effect of the amount of data about uncertainty on the effectiveness of each method. Only systems whose failure is catastrophic are considered, where catastrophic means that the boundary between success and failure is sharp. First, the paper examines the theoretical foundations of probability and possibility, focusing on the impact of the differences between the two theories on design. Then the paper compares the two theories on design problems. A major difference between probability and possibility is in the axioms about the union of events. Because of this difference, probability and possibility calculi are fundamentally different and one cannot simulate possibility calculus using probabilistic models. Possibility-based methods tend to underestimate the risk of failure of systems with many failure modes. For example, the possibility of failure of a series system of nominally identical components is equal to the possibility of failure of a single component. When designing for safety, the two methods try to maximize safety in radically different ways and consequently may produce significantly different designs. Probability minimizes the system failure probability whereas possibility maximizes the normalized deviation of the uncertain variables from their nominal values that the system can tolerate without failure. In contrast to probabilistic design, which accounts for the cost of reducing the probability of each failure mode in design, possibility tries to equalize the possibilities of failure of the failure modes, regardless of the attendant cost. In many safety assessment problems, one can easily determine the most conservative possibilistic model that is consistent with the available information, whereas this is not the case with probabilistic models. When we have sufficient data to build accurate probabilistic models of the uncertain variables, probabilistic design is better than possibility-based design. However, when designers need to make subjective decisions, both probabilistic and possibility-based designs can be useful. The reason is that large differences in these designs can alert designers to problems with the probabilistic design associated with insufficient data and tell them that they have more flexibility in the design than they may have known.
Design Optimization for Structural-Acoustic Problems Using FEA-BEA With Adjoint Variable Method
Authors: Dong Jun , Choi Kyung K. , Kim Nam H.
Published: July 2004

A noise-vibration-harshness (NVH) design optimization of a complex vehicle structure is presented using finite element and boundary element analyses. The steady-state dynamic behavior of the vehicle is calculated from the frequency response finite element analysis, while the sound pressure level within the acoustic cavity is calculated from the boundary element analysis. A reverse solution process is employed for the design sensitivity calculation using the adjoint variable method. The adjoint load is obtained from the acoustic boundary element re-analysis, while the adjoint solution is calculated from the structural dynamic re-analysis. The evaluation of pressure sensitivity only involves a numerical integration process over the structural part where the design variable is defined. A design optimization problem is formulated and solved, where the structural weight is reduced while the noise level in the passenger compartment is lowered.
An Investigation of Nonlinearity of Reliability-Based Design Optimization Approaches
Authors: Youn Byeng D. , Choi Kyung K.
Published: July 2004

Because deterministic optimum designs obtained without taking uncertainty into account could lead to unreliable designs, a reliability-based approach to design optimization is preferable using a Reliability-Based Design Optimization (RBDO) method. A typical RBDO process iteratively carries out a design optimization in an original random space (X-space) and a reliability analysis in an independent and standard normal random space (U-space). This process requires numerous nonlinear mappings between X- and U-spaces for various probability distributions. Therefore, the nonlinearity of the RBDO problem will depend on the type of distribution of random parameters, since a transformation between X- and U-spaces introduces additional nonlinearity into the reliability-based performance measures evaluated during the RBDO process. The evaluation of probabilistic constraints in RBDO can be carried out in two ways: using either the Reliability Index Approach (RIA), or the Performance Measure Approach (PMA). Different reliability analysis approaches employed in RIA and PMA result in different behaviors of nonlinearity for RIA and PMA in the RBDO process. In this paper, it is shown that RIA becomes much more difficult to solve for non-normally distributed random parameters because of the highly nonlinear transformations that are involved. However, PMA is rather independent of probability distributions because it only has a small involvement with a nonlinear transformation.
A New Mathematical Model for Geometric Tolerances as Applied to Polygonal Faces
Authors: Mujezinovic´ A. , Davidson J. K. , Shah J. J.
Published: July 2004

A new mathematical model for representing geometric tolerances is applied to polygonal faces and is extended to show its sensitivity to the precedence (ordering) of datum reference frames. The model is compatible with the ASME/ISO Standards for geometric tolerances. Central to the new model is a Tolerance-Map®2, a hypothetical volume of points that corresponds to all possible locations and variations of a segment of a plane which can arise from tolerances on size, position, form, and orientation. Every Tolerance-Map is a convex set. This model is one part of a bi-level model that we are developing for geometric tolerances. The new model makes stackup relations apparent in an assembly, and these can be used to allocate size and orientational tolerances; the same relations also can be used to identify sensitivities for these tolerances. All stackup relations can be met for 100% interchangeability or for a specified probability. Methods are introduced whereby designers can identify trade-offs and optimize the allocation of tolerances. Examples are presented that illustrate important features of the new model.
Quasi-Kinematic Couplings for Low-Cost Precision Alignment of High-Volume Assemblies
Authors: Culpepper Martin L. , Slocum Alexander H. , Shaikh F. Zafar , Vrsek Gary
Published: July 2004

Quasi-kinematic couplings (QKCs) are alignment devices that incorporate elastic-plastic deformations to combine principles of elastic averaging and exact constraint to achieve precision alignment. This paper shows QKCs can be used for low-cost alignment in high-volume assembly applications. This is demonstrated via a case study of the process used to align main journal bearings in an automobile engine. Results of experiments show best case QKC performance of 0.35 microns compared to 4.85 microns for the widely-used dowel pin-hole design. Statistical analyses predict the QKC will meet five micron alignment requirements in 99.999 percent of all assembly cycles. Compared to the dowel pin-hole design, the QKC uses 60 percent fewer piece parts and costs 36 percent less.
A Document Analysis Method for Characterizing Design Team Performance
Authors: Dong Andy , Hill Andrew W. , Agogino Alice M.
Published: July 2004

The premise of this research is that the engineering design process is partially driven by achieving consensus and reconciling points of view among team members. Characterizing the quality of the design performance by measuring the coherence of the description of related design concepts and events in design documentation is examined. Latent Semantic Analysis (LSA) was used to analyze design documentation written by self-managing, cross-functional engineering design teams. Computational measurements of document variance and textual coherence were applied to the teams’ design documents, presentation materials and e-mail communication. The levels of semantic coherence were correlated to assessments by faculty and product designers and engineers from industry of the design teams’ process and outcome quality. The results indicated a statistically significant positive correlation between design document coherence and design performance, especially for poorly performing teams. The impact of this research is to provide team managers (people who create teams and manage teams) or self-organizing teams (teams that focus on self-reflection and peer evaluation) computational tools that could be integrated with design information management technologies to assist them in the management of engineering design teams.
Nonlinear Dynamic Modeling of Gear-Shaft-Disk-Bearing Systems Using Finite Elements and Describing Functions
Authors: Maliha Rafiq , Dogˇruer Can U. , O¨zgu¨ven H. Nevzat
Published: July 2004

This study presents a new nonlinear dynamic model for a gear-shaft-disk-bearing system. A nonlinear dynamic model of a spur gear pair is coupled with linear finite element models of shafts carrying them, and with discrete models of bearings and disks. The nonlinear elasticity term resulting from backlash is expressed by a describing function, and a method developed in previous studies to determine multi harmonic responses of nonlinear multi-degree-of-freedom systems is employed for the solution. The excitations considered in the model are external static torque and internal excitation caused by mesh stiffness variation, gear errors and gear tooth profile modifications. The model suggested and the solution method presented combine the versatility of modeling a shaft-bearing-disk system that can have any configuration without a limitation to the total degree of freedom, with the accuracy of a nonlinear gear mesh interface model that allows to predict jumps and double solutions in frequency response. Thus any single stage gear mesh configuration can be modeled easily and accurately. With the model developed it is possible to calculate dynamic gear loads, dynamic bearing forces, dynamic transmission error and bearing displacements. Theoretical results obtained by using the method suggested are compared with the experimental data available in literature, as well as with the theoretical values calculated by employing a previously developed nonlinear single degree of freedom model.
The Closure Modes of Bennett’s Twelve-Bar Planar Linkage
Authors: Baker J. Eddie
Published: July 2004

In building upon the unique properties of his famous four-bar loop and its planar and spherical counterparts, Bennett proposed a planar kinematic network of twelve bars, eight hinges and six loops with two degrees of mobility. It has since been studied in respect of its surprising variety of closure modes. This paper is concerned with a systematic investigation of the range of closures and their transitional states while retaining the form which exhibits only anti-parallelogrammatic loops. The opportunity is taken to introduce a 24-bar network based upon the scheme of concentric circles adopted by Bennett.
Conceptual Design and Dimensional Synthesis of a Novel 2-DOF Translational Parallel Robot for Pick-and-Place Operations
Authors: Huang Tian , Li Zhanxian , Li Meng , Chetwynd Derek G. , Gosselin Clement M.
Published: July 2004

This paper deals with the conceptual design and optimal dimensional synthesis of a novel 2-DOF translational parallel robot for pick-and-place operations. In a conceptual design phase, the conditions for generating such kinds of parallel robots are investigated, leading to the invention of a 2-D version of the Delta robot. Combining this robot with a 1-DOF feed mechanism, a hybrid robot can be created which is particularly suitable for transporting objects at very high speed in a plane plus a relatively slow or step-by-step, yet long distance motion, normal to the plane. The kinematic optimality of the 2-DOF translational parallel robot is achieved by minimizing a global and comprehensive conditioning index subject to a set of appropriate constraints. The application of this robot to the development of a device for quality inspection of rechargeable batteries is used to demonstrate its applicability.
Mesh Theory for Toroidal Drive
Authors: Xu Lizhong , Huang Zhen , Yang Yulin
Published: July 2004

In this study, a simpler mesh equation for the toroidal drive is developed. Based on the equation, equations of the contact line, the limit curves, the induced normal curvature between the mating surfaces and the angle of the relative velocity vector to the contact line are introduced. On the basis of the presented equations, the instantaneous contact lines of the planet and the stator or the worm are calculated, the shape of the contact lines and the range of the meshing zone are analyzed, the undercutting of the stator surface and the worm surface is discussed, the induced normal curvature between the planet and the stator or the worm are investigated, and the angles of the relative velocity vector to the contact line are calculated. The solid model of the toroidal drive is presented.
Design of Input Coupled Split Power Transmissions, Arrangements, and Their Characteristics
Authors: Fussner Douglas R. , Singh Yesh P.
Published: July 2004

This paper presents input coupled split power transmissions, arrangements and comparisons between the single and dual stage designs. Selection of the shift point between stages is discussed. Mathematical models for the transmission are constructed. An algorithm is developed for an efficiency optimization routine. The effects of the gear material strength, gear module, gear tooth width, and shaft offset on the efficiency are determined. Power loss contributions are presented in conjunction with their effect on the overall transmission efficiency.
Path Curvature of the Single Flier Eight-Bar Linkage
Authors: Pennock Gordon R. , Kinzel Edward C.
Published: July 2004

This paper presents a graphical technique to locate the center of curvature of the path traced by an arbitrary coupler point of the single flier eight-bar linkage. The first step is to locate the pole for the instantaneous motion of the coupler link; i.e., the point in the fixed plane coincident with the absolute instant center of the coupler link. Since the single flier is an indeterminate linkage, comprised of one four-bar and two five-bar chains, then the Aronhold-Kennedy theorem cannot locate this instant center. The paper presents a novel graphical technique which can locate this instant center in a direct manner. Then the paper focuses on a graphical method to locate the center of curvature of the path traced by the coupler point. The method locates six equivalent four-bar linkages for the two five-bar chains, investigates six kinematic inversions and obtains a four-bar linkage from each inversion. This systematic procedure produces a four-bar linkage with a coupler link whose motion is equivalent up to, and including, the second-order properties of motion of the single flier coupler link. The radius of curvature and the center of curvature of the path traced by the coupler point can then be obtained in a straightforward manner from the Euler-Savary equation.
Elimination of Redundant Cut Joint Constraints for Multibody System Models
Authors: Mu¨ller A.
Published: July 2004

The problem of dependent cut joint constraints for kinematic loops in rigid multibody systems is addressed. The constraints are reduced taking into account the subalgebra generated by the screw system of the kinematic loop. The elimination of dependent constraint equations is based on constructing a basis matrix of the screw algebra generated by loop’s screw system. This matrix is configuration independent and thus always valid. The determination of the sufficient constraints is achieved with a SVD or QR decomposition of this matrix. Unlike all other proposed approaches the presented method is singularity consistent because it is not the Jacobian which is decomposed, but instead a basis matrix for the loop algebra. Since this basis is obtained after a finite number of cross products the computational effort is negligible. Furthermore, because the elimination process is only necessary once in advance of the integration/simulation process, it proved valuable even if it does not remove all dependent constraints, as for paradoxical mechanisms.
Automatic Undercut Feature Recognition for Side Core Design of Injection Molds
Authors: Ye X. G. , Fuh J. Y. H. , Lee K. S.
Published: July 2004

For any undercut region of a plastic molded part, a side core has to be designed to form the complex geometry while avoiding the interference between the injection mold and the plastic molded part (molding). Viewing undercuts as features in the context of injection mold design, this paper presents a new method to recognize both isolated and interacting undercut features extracted from a mold cavity or core. With the introduction of the face property and the EAFEG representation scheme, an undercut feature can be precisely defined by an undercut subgraph. Unlike conventional graph-based methods, which recognize features by graph matching, the proposed algorithm recognizes undercut features by searching the cut-sets of subgraphs. After recognizing undercut features, a Boolean operation is used to generate a side core for each undercut. Rules to eliminate the side core intersection are also presented for implementation.
Smoothing of Noisy Laser Scanner Generated Meshes Using Polynomial Fitting and Neighborhood Erosion
Authors: Vieira Miguel , Shimada Kenji , Furuhata Tomotake
Published: July 2004

This paper presents a method for removing geometric noise from triangulated meshes while preserving edges and other intended geometric features. The method iteratively updates the position of each mesh vertex with a position lying on a locally fitted bivariate polynomial. The user selects the width of the vertex neighborhood, the order of the fitted polynomial, and a threshold angle to control the effects of the smoothing operation. To avoid smoothing over discontinuities, the neighborhood can be eroded by removing vertices with normals that deviate beyond a threshold from the estimated median normal of the neighborhood. The method is particularly suitable for use on laser scanner generated meshes of automobile outer body panels. Smoothing methods used on these meshes must allow C2 continuous equilibrium surfaces and must minimize shrinkage. Despite the abundance of existing smoothing schemes, none addresses both of these specific problems. This paper demonstrates the effectiveness of our method with both synthetic and real world examples.
Dynamics of a Class of Parallel Wrists
Authors: Di Gregorio Raffaele , Parenti-Castelli Vincenzo
Published: July 2004

This paper presents a dynamic model of parallel wrists with all links constrained to have a spherical motion with the same center. The model can also be applied to serial wrists. The model, based on Lagrangian formulation of dynamics, exploits the feature that all the links have the same fixed point. Three parameters defining the platform orientation are used as generalized coordinates. This choice allows the use of the generalized inertia matrix (GIM) appearing in the model to calculate effective dynamic performance indices proposed in a previous paper. The model can solve both the direct and the inverse dynamic problems. It also contains the Jacobian matrix useful to characterize the kinematic behavior of parallel manipulators. By the model it is shown that the best performances are reached in the workspace regions where the manipulator has a good kinematic and dynamic isotropy, whereas the incidence of nonlinear forces on performances is relevant at high end-effector speed. A numerical example is provided.
Application of Plasticity Theory and Absolute Nodal Coordinate Formulation to Flexible Multibody System Dynamics
Authors: Sugiyama Hiroyuki , Shabana Ahmed A.
Published: July 2004

The objective of this investigation is to develop a nonlinear finite element formulation for the elastic-plastic analysis of flexible multibody systems. The Lagrangian plasticity theory based on J2 flow theory is used to account for the effect of plasticity in flexible multibody dynamics. It is demonstrated that the principle of objectivity that is an issue when existing finite element formulations using rate-type constitutive equations are used is automatically satisfied when the stress and strain rate are directly calculated in the Lagrangian descriptions using the absolute nodal coordinate formulation employed in this investigation. This is attributed to the fact that, in the finite element absolute nodal coordinate formulation, the position vector gradients can completely define the state of rotation and deformation within the element. As a consequence, the numerical algorithm used to determine the plastic deformations such as the radial return algorithm becomes much simpler when the absolute nodal coordinate formulation is used as compared to existing finite element formulations that employ incrementally objective algorithms. Several numerical examples are presented in order to demonstrate the use of the formulations presented in the paper.
Quantitative Evaluation of Blood Damage in a Centrifugal VAD by Computational Fluid Dynamics
Authors: Song Xinwei , Throckmorton Amy L. , Wood Houston G. , Antaki James F. , Olsen Don B.
Published: July 2004

This study explores a quantitative evaluation of blood damage that occurs in a continuous flow left ventricular assist device (LVAD) due to fluid stress. Computational fluid dynamics (CFD) analysis is used to track the shear stress history of 388 particle streaklines. The accumulation of shear and exposure time is integrated along the streaklines to evaluate the levels of blood trauma. This analysis, which includes viscous and turbulent stresses, provides a statistical estimate of possible damage to cells flowing through the pump. Since experimental data for hemolysis levels in our LVAD are not available, in vitro normalized index of hemolysis values for clinically available ventricular assist devices were compared to our damage indices. This approach allowed for an order of magnitude comparison between our estimations and experimentally measured hemolysis levels, which resulted in a reasonable correlation. This work ultimately demonstrates that CFD is a convenient and effective approach to analyze the Lagrangian behavior of blood in a heart assist device.
Measurements of Surface-Roughness Effects on the Development of a Vortex Produced by an Inclined Jet in Cross-Flow
Authors: Yaras M. I.
Published: July 2004

This study examines the effects of surface roughness on the streamwise development of a vortex created by an isolated circular jet injected at 45 deg pitch and 90 deg skew into a crossflow. The study is motivated by the typical surface conditions encountered on in-service turbine blades of gas-turbine engines. Detailed measurements of the velocity field have been performed with a miniature four-wire probe at the jet exit plane, in the oncoming cross-stream boundary layer, and in a series of planes that capture the streamwise development of the vortex in the crossflow boundary layer up to about 15 jet-discharge diameters downstream of the jet. The paper presents the effects of surface roughness on the structure of the dominant streamwise vortex created by the interaction of the inclined jet with the mainstream, and documents the changes in the location, streamwise rate of change of circulation, and streamwise rate of diffusion of this vortex. Through these results, the change in the effectiveness of the vortex in energizing the boundary layer in the presence of surface roughness can be quantified.
Condensation During Discharging of Pneumatic System
Authors: Ying-zi Jin , Zu-wen Wang , Gang Bao
Published: July 2004

In order to make sure what factors have an effect on condensation, a mathematical model has been established for the discharging process of a pneumatic system using the fluid grid theory, an analytic equation has been derived to determine the maximum humidity of air during discharging of pneumatic system, and an analytic equation has been established as the first necessary condition for the determination of internal condensation in a pneumatic system. Flowing air may produce water droplets in a pneumatic system when the system satisfies the first necessary condition. An analytic equation has been developed as the second necessary condition for determination of internal condensation in a pneumatic system by introducing stroke and establishing an analytic equation for the stroke. The water droplets produced by satisfaction of the first necessary condition form drops of water inside the system when the system satisfies the second necessary condition. Internal condensation does not occur when the system does not satisfy the first necessary condition, and internal condensation occurs only when the system satisfies both conditions at the same time. The experimental results indicate that the points of internal condensation, external condensation and no condensation exhibit a regular distribution on the plane formed by the dimensionless volume of the discharging pipe and the average velocity of air, and the plane can then be divided into regions, providing a graphic discrimination method for determination of condensation in a pneumatic system.
Separation Criterion for Turbulent Boundary Layers Via Similarity Analysis
Authors: Castillo Luciano , Wang Xia , George William K.
Published: July 2004

By using the RANS boundary layer equations, it will be shown that the outer part of an adverse pressure gradient turbulent boundary layer tends to remain in equilibrium similarity, even near and past separation. Such boundary layers are characterized by a single and constant pressure gradient parameter, Λ, and its value appears to be the same for all adverse pressure gradient flows, including those with eventual separation. Also it appears from the experimental data that the pressure gradient parameter, Λθ, is also approximately constant and given by Λθ=0.21±0.01. Using this and the integral momentum boundary layer equation, it is possible to show that the shape factor at separation also has to within the experimental uncertainty a single value: Hsep≅2.76±0.23. Furthermore, the conditions for equilibrium similarity and the value of Hsep are shown to be in reasonable agreement with a variety of experimental estimates, as well as the predictions from some other investigators.
Simulation of Spray Transfer Processes in Electrostatic Rotary Bell Sprayer
Authors: Im Kyoung-Su , Lai Ming-Chia , Yu Sheng-Tao John , Matheson, Robert R.
Published: July 2004

A numerical study of the spray transfer processes in an electrostatic rotary bell applicator (ESRB) has been conducted utilizing code for a newly developed simulation code. This code consists of three modularized solvers: a fluid flow solver, a spray dynamics solver, and an electrostatic solver. The development of the code consisted of the following steps. First, the flow solver designed for an unsteady three-dimensional Navier-Stokes equation was developed to simulate the shaping airflow with the initial condition and the boundary condition supported by experimental data. Second, the particle trajectory solver, which interacts with the airflow by momentum coupling, was developed to apply the spray transport processes. Finally, the electrostatic solver was developed to calculate the electrostatic field within the two phase flow field. The integrated code created by combining those three solvers was then applied to simulate the paint spray transport processes according to the operating conditions of interest. The numerical results show that the spray shape is very sensitive to changes in the charge to mass ratio. The voltage setting is a dominant operating parameter affecting the numerical transfer efficiency. The voltage range studied was 0 kV to 90 kV. In addition, the transfer efficiency decreases as the shaping airflow rate increases. However, a high shaping airflow rate produces a more uniform distribution of spray mass on the target plane.
Experimental and Numerical Study of Shock Wave Interaction with Perforated Plates
Authors: Britan A. , Karpov A. V. , Vasilev E. I. , Igra O. , Ben-Dor G. , Shapiro E.
Published: July 2004

The flow developed behind shock wave transmitted through a screen or a perforated plat is initially highly unsteady and nonuniform. It contains multiple shock reflections and interactions with vortices shed from the open spaces of the barrier. The present paper studies experimentally and theoretically/numerically the flow and wave pattern resulted from the interaction of an incident shock wave with a few different types of barriers, all having the same porosity but different geometries. It is shown that in all investigated cases the flow downstream of the barrier can be divided into two different zones. Due immediately behind the barrier, where the flow is highly unsteady and nonuniform in the other, placed further downstream from the barrier, the flow approaches a steady and uniform state. It is also shown that most of the attenuation experienced by the transmitted shock wave occurs in the zone where the flow is highly unsteady. When solving the flow developed behind the shock wave transmitted through the barrier while ignoring energy losses (i.e., assuming the fluid to be a perfect fluid and therefore employing the Euler equation instead of the Navier-Stokes equation) leads to non-physical results in the unsteady flow zone.
An Air Curtain Along a Wall With High Inlet Turbulence
Authors: Field Brandon S. , Loth Eric
Published: July 2004

A downward blowing isothermal wall jet at moderate Reynolds numbers (1,500 to 8,500) with significant inflow turbulence (ca. 6%) was investigated. The flow configuration is an idealization of the air curtains of refrigerated display cases. Flow visualization using particle seeding was employed to identify the flow field eddy dynamics. Particle Image Velocimetry was used to examine the velocity fields in terms of mean and fluctuating values. These diagnostics showed that the air curtain entrainment was dominated by a large variety of eddies that engulfed ambient air into the air curtain. The velocity fields generally showed linear spreading, significant deceleration and high turbulence levels (ca. 25%). It was observed that the air curtain dynamics, velocity fields and growth were not significantly sensitive to Reynolds number variation between Re=3,800 and Re=8,500. However, at low air velocities (Re=1,500), the curtain was found to detach, leading to a large air curtain thickness and high curtain entrainment.
Analysis and Modeling of Pressure Recovery for Separated Reattaching Flows
Authors: Yeung W. W. H. , Parkinson G. V.
Published: July 2004

Analyses have been carried out on the mean pressure data for separated reattaching flows downstream of a variety of 2-D bluff-bodies to reveal some similarity features. The step height has been identified as an important parameter in relationships such as the correlation between the reattachment length xr and the initial shear-layer angle. The separation velocity (deduced from separation pressure cps) in the direction perpendicular to the upstream flow increases linearly with the reattachment length at fixed step heights. The streamwise location of the vortex center xv (deduced from mean streamline plots) correlates with the location of minimum pressure xm and each varies linearly with the reattachment length. Pressure force, moment and center of pressure induced by the standing vortex also increase with the reattachment length. An inviscid flow model of a rectilinear stationary vortex above a flat wall leads to a general form of the pressure recovery cp−cp min/cp max−cp min)=8/9x^2x^2+1/x^2+1/32xm<,<xr where 0⩽x^1=Xm/Xr and cp max and cp min are respectively the maximum and minimum pressure coefficients. It is demonstrated that the present analyses allow the pressure distributions downstream of various fore-bodies to be realistically predicted.
Numerical and Experimental Investigation of an Annular Jet Flow With Large Blockage
Authors: Del Taglia Christian , Blum Lars , Gass Ju¨rg , Ventikos Yiannis , Poulikakos Dimos
Published: July 2004

Unsteady 3-D numerical simulations and 3-D LDA measurements of an annular jet with a blockage ratio of 0.89 and Reynolds number 4400 are presented. At these flow conditions, the flow inside of the recirculation zone is asymmetric, with a preferential direction. Very good predictions of the velocity fluctuation values are achieved with the unsteady simulation technique in the same region, as the fluctuations are mainly large scale, structure dominated. A frequency near to 10 Hz is identified in the simulations, which is attributed to the principal shedding behavior of the vortical structures.
Experimental Turbulent Field Modeling by Visualization and Neural Networks
Authors: Hocˇevar Marko , Sˇirok Brane , Grabec Igor
Published: July 2004

Turbulent flow field was modeled based on experimental flow visualization and radial-basis neural networks. Turbulent fluctuations were modeled based on the recorded concentration at various locations in the Karman vortex street, which were used as inputs and outputs of the neural network. From the measured and the modeled concentration the power spectra and spatial correlation functions were calculated. The measured and the modeled concentration power spectra correspond well to the −5/3 turbulence decay law, and exhibit the basic spectral peak of fluctuation power at the same frequency. The predicted and measured correlation functions of concentration exhibit similar behavior.
Assessment of Reynolds-Averaged Turbulence Models for Prediction of the Flow and Heat Transfer in an Inlet Vane-Endwall Passage
Authors: Pasinato Hugo D. , Squires Kyle D. , Roy Ramendra P.
Published: July 2004

Predictions of the flow and thermal fields in an inlet vane passage are obtained via solution of the incompressible Reynolds-averaged Navier-Stokes (RANS) equations. RANS predictions of the steady-state solutions are obtained using two scalar eddy viscosity models and full Reynolds stress transport to close the turbulent stress in the momentum equations. The turbulent heat flux is modeled using a constant turbulent Prandtl number. In the geometric configuration of the inlet vane passage, the hub endwall is flat. Calculations are performed for a baseline configuration and an additional configuration in which secondary air is injected through three small, angled slots positioned upstream of the vane leading edge. Solutions are obtained on unstructured grids with the densest mesh comprised of 1.9×106 elements. The simulations are assessed via an inter-comparison of predictions obtained using the different models, as well as through evaluation against experimental measurements of the Stanton number and cooling effectiveness on the hub endwall. The flow develops from a turbulent boundary layer at momentum thickness Reynolds number 955 prescribed at the inlet to the computational domain, 1.3 axial chord lengths upstream of the vane leading edge. The mean velocity at the inlet is prescribed to match an experimentally-measured profile with low freestream turbulence. For the case with secondary air injection, the blowing ratio was 1.3. Solid surfaces are isothermal at temperatures below that of the mainstream gas. Simulation results show that the vortical structures resolved by the models in the vicinity of the vane leading edge for the baseline case are relatively insensitive to the particular turbulence closure. The elevation in heat flux levels due to entrainment of higher temperature mainstream gas towards the endwall by the horseshoe vortex is captured, Stanton number distributions exhibit adequate agreement with measured values. While there are similarities in the coherent structures resolved by the models, details of their evolution through the passage lead to differences in heat transfer distribution along the endwall. Secondary air injection strongly distorts the flow structure in the vicinity of the leading edge, the vortical structures that develop in the calculations with air injection evolve primarily from the interaction of the fluid issuing from the slots and the mainstream flow. Elevated levels of cooling effectiveness predicted by the models correspond to larger areas of the endwall than measured, peak Stanton numbers are higher than the experimental values.
Control of Volumetric Flow-Rate of Ball Valve Using V-Port
Authors: Chern Ming-Jyh , Wang Chih-Cheng
Published: July 2004

The control of volume flow rate in a ball valve is very important when a ball valve is utilized in a piping system. It is difficult to linearly control the flow rate in a ball valve without external devices. V-ports are employed to achieve this purpose. In order to investigate the effects of V-port on the volume flow rate and flow features, 3-D numerical simulations and experiments were conducted to observe the flow patterns and to measure performance coefficients when V-ports with various angles were used in a piping system. Three V-ports with angles 30 deg, 60 deg, and 90 deg were studied. It was found that V-ports with angles 30 deg and 60 deg make the flow rate proportional to the valve opening. However, V-ports increase the pressure loss between the inlet and the exit of a ball valve. In addition, V-ports with a small angle such as 30 deg increase the possibility of cavitation compared with flows without V-ports.
Instability of Inelastic Shear-Thinning Liquids in a Couette Flow Between Concentric Cylinders
Authors: Coronado-Matutti O. , Souza Mendes P. R. , Carvalho M. S.
Published: July 2004

Circular Couette flow of inelastic shear-thinning materials in annuli is examined. The curved streamlines of the circular Couette flow can cause a centrifugal instability leading to toroidal vortices, well known as Taylor vortices. The presence of these vortices changes the hydrodynamic and heat transfer characteristics of the processes at which this type of flow occurs. Therefore, it is quite important to be able to predict the onset of instability. Most of the available theoretical and experimental analyses are for Newtonian and viscoelastic (dilute polymeric solutions) liquids. In this work, the effect of the shear-thinning behavior of high concentration suspensions on the onset of the Taylor vortices is determined theoretically by solving the conservation equations, constructing the solution path as the inner cylinder speed rises and searching for the critical conditions. This procedure avoids the need for a stability analysis of the flow and the solution of an eigenproblem. The differential equations were solved by the Galerkin/finite-element method and the resulting set of nonlinear algebraic equations, by Newton’s method.
Phase-Average Mean Flow and Turbulence Structure in a Staggered Cylinder Array Subjected to Pulsating Cross-Flow
Authors: Konstantinidis E. , Balabani S. , Yianneskis M.
Published: July 2004

The unsteady turbulent flow field in a staggered array of cylinders with streamwise and transverse spacing to diameter ratios of 2.1 and 3.6, respectively, was studied experimentally by means of laser-Doppler anemometry for a Reynolds number of 2300. Flow pulsations in the streamwise direction were employed to control the frequency of vortex shedding in the array as has been previously demonstrated in Konstantinidis et al. [1]. Under these conditions, it was possible to obtain velocity measurements and for each velocity sample assign the phase-angle with respect to the pulsation cycle. This methodology allowed reconstruction of the unsteady (periodic) mean flow and random turbulence fields over an average vortex shedding cycle. The experimental data obtained are analyzed and the results offer a unique insight into the flow processes that take place inside the cylinder array.
Numerical Analysis of Cavitation Instabilities Arising in the Three-Blade Cascade
Authors: Iga Yuka , Nohml Motohiko , Goto Akira , Ikohagi Toshiaki
Published: July 2004

Three types of cavitation instabilities through flat plate cascades, which are similar to “forward rotating cavitation,” “rotating-stall cavitation” and “cavitation surge” occurring in high-speed rotating fluid machinery, are represented numerically under the three-blade cyclic condition. A numerical method employing a locally homogeneous model of compressible gas-liquid two-phase medium is applied to solve the above flow fields, because this permits the entire flow field inside and outside the cavity to be treated through only one system of governing equations. In addition, the numerical method suites to analyze unsteady cavitating flow with a long time evolution. From the calculated results of the present numerical simulation with wide range of cavitation number and flow rate, we obtain a cavitation performance curve of the present three-blade cyclic cascade, analyze the aspects of unsteady cavitation, and discuss the characteristics and mechanisms of cavitation.
Towards Practical Flow Sensing and Control via POD and LSE Based Low-Dimensional Tools
Authors: Taylor J. A. , Glauser M. N.
Published: July 2004

Low-dimensional methods including the Proper Orthogonal Decomposition (POD) and Linear Stochastic Estimation (LSE) have been applied to the flow between a backward facing ramp and an adjustable flap. A range of flap angles provide a flow which is incipiently separated and can be used to flesh out ideas for active feedback separation control strategies. The current study couples Particle Image Velocimetry (PIV) and multi-point wall pressure measurements using POD and LSE to estimate the full velocity field from the wall pressure alone. This technique yields a sufficiently accurate estimate of the velocity field that the incipient condition can be detected. The ability to estimate the state of the flow without inserting probes into the flow is important for the development of practical active feedback flow control strategies.
Flow Patterns of Ice/Water Slurry in Horizontal Pipes
Authors: Hirochi Takero , Maeda Yasuhiro , Yamada Shuichi , Shirakashi Masataka , Hattori Masaru , Saito Akihiro
Published: July 2004

The authors have observed flow patterns of ice/water slurry flow through horizontal circular pipes, and measured pressure loss for small diameter pipes, using three classes of ice particles. The slurry flows are classified into three patterns, dispersed-particle flow, cluster flow, and column flow. They are presented on a plane of two dimensionless parameters, the ice fraction f and the ratio of mixing energy to cohesion energy, πmix. The pressure loss for small diameter pipes is estimated accurately by the formula proposed in previous studies by the present authors based on experimental data for larger pipes.
On Electrical Conductivity Measurements of Molten Metals by Inductive Technique
Authors: Bakhtiyarov Sayavur I. , Dupac Mihai , Overfelt Ruel A. , Teodorescu Sorin G.
Published: July 2004

In this paper, we propose a new relationship between the opposing mechanical torque and the electric conductivity of a rotating liquid specimen in a permanent external magnetic field of constant induction, which includes the effect of fluid flow. The proposed relationship was applied to describe the experimental data for a conductive specimens rotating in a permanent magnetic field.
Laminar Liquid Flow Through Silicon Microchannels
Authors: Morini Gian Luca
Published: July 2004

The present work deals with the analysis of the fully developed laminar flow through silicon microchannels. The main integral flow parameters, such as the Poiseuille number f Re, the momentum flux correction factor, the kinetic energy correction factor, the asymptotic incremental pressure drop number and the approximate value of the hydrodynamic entrance length are numerically evaluated for trapezoidal and double-trapezoidal cross sections of the silicon microchannels. The results are quoted in tabular and in graphic form as a function of the microchannel aspect ratio. Finally, very simple polynomial representations of the integral flow parameters are given. These numerical data are a useful tool for technicians and designers involved in micro-fluidic applications and it is demonstrated that these results can be used (instead of or before a CFD simulation approach) for a first evaluation of the pressure drop for liquid flows through smooth microchannels having a hydraulic diameter greater than 30 μm.
A Numerical Analysis of Vapor Flow in Concentric Annular Heat Pipes
Authors: Nouri-Borujerdi A. , Layeghi M.
Published: July 2004

A numerical method based on the SIMPLE algorithm has been developed for the analysis of vapor flow in a concentric annular heat pipe. The steady-state response of a concentric annular heat pipe to various heat fluxes in the evaporator and condenser sections are studied. The fluid flow and heat transfer in the annular vapor space are simulated using Navier-Stokes equations. The governing equations are solved numerically, using finite volume approach. The vapor pressure and temperature distributions along a concentric annular heat pipe are predicted for a number of symmetric test cases. The vapor flow reversal and transition to turbulence phenomena are also predicted. The results are compared with the available numerical data and have shown good agreement in all cases. Therefore, the vapor flow model developed in this paper has shown good accuracy and convergence behavior in the range of low to moderate radial Reynolds numbers.
CONTRIBUTION OF DIMENSION-SIX BOSONIC OPERATORS TO H→γγ AT ONE-LOOP LEVEL
Authors: HOŘEJŠÍ JIŘÍ , KAMPF KAROL
Published: July 2004

The decay process H→γγ is examined in a model-independent way within the effective Lagrangian approach. Contribution of a set of irreducible one-loop diagrams involving SU (2)× U (1) invariant dimension-six bosonic operators is evaluated explicitly. The calculation is intended to fill the gap that exists in the current literature on the subject.
STATIC POTENTIAL AND A NEW GENERALIZED CONNECTION IN THREE DIMENSIONS
Authors: GAETE PATRICIO
Published: July 2004

For a recently proposed pure gauge theory in three dimensions, without a Chern–Simons term, we calculate the static interaction potential within the structure of the gauge-invariant variables formalism. As a consequence, a confining potential is obtained. This result displays a marked qualitative departure from the usual Maxwell–Chern–Simons theory.
WHAT CDF SEES WITH THE SILICON VERTEX TRIGGER
Authors: BOUDREAU JOSEPH
Published: July 2004

We review the impact of CDF's Silicon Vertex Trigger (SVT) on the physics program of the CDF experiment, after three years of experience operating the device at the Tevatron. By providing impact parameter information to the trigger system, the SVT allows CDF to collect a large number of all-hadronic decays of charm and bottom hadrons previously unseen at the [Formula: see text] collider, including hadronic [Formula: see text] decays, two-body charmless B decays, and decays of heavy baryons. Semileptonic decays are now collected with greater efficiency than in previous running. Most of the work reviewed in this note is performed with less than about 200 pb-1of data, in some cases considerably less. Already the SVT has radically changed the nature of B physics at the collider. Empirical data on event rates and background levels now constrain future projections of CDF's sensitivity to important topics in B physics, such as [Formula: see text] particle–antiparticle oscillations, and the measurement of CP asymmetries in two-body charmless B decays.
LARGE-N AND BETHE ANSATZ
Authors: JURČO BRANISLAV
Published: July 2004

We describe an integrable model, related to the Gaudin magnet, and its relation to the matrix model of Brézin, Itzykson, Parisi and Zuber. Relation is based on Bethe ansatz for the integrable model and its interpretation using orthogonal polynomials and saddle point approximation. Large-N limit of the matrix model corresponds to the thermodynamic limit of the integrable system. In this limit (functional) Bethe ansatz is the same as the generating function for correlators of the matrix models.