bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathophysiological basis of acute inflammatory hyperaemia in the rat knee: roles of cyclo‐oxygenase‐1 and −2
Authors: Egan Colin G. , Lockhart John C. , Ferrell William R. , Day Suzanne M. , McLean John S.
Published: July 2002

The role of different isoforms of cyclo‐oxygenase (COX) in mediating the acute (0‐6 h) and late (24 h) phases of inflammation was investigated in the rat knee joint following intra‐articular injection of carrageenan. The hyperaemic response was assessed transcutaneously using laser Doppler imaging (LDI). Samples were taken at corresponding time points for detection of synovial COX‐1, COX‐2 and inducible nitric oxide synthase (iNOS) mRNA, and measurement of urinary prostaglandin (PG) and nitric oxide metabolites (NOx). A non‐selective COX inhibitor (indomethacin, 15 mg kg−1i.p.), a selective COX‐2 inhibitor (SC‐236, 16.8 mg kg−1i.p.) or vehicle were administered 1 h prior to carrageenan in the acute phase study. LDI scans were taken hourly for 4 h post‐induction. Inflammatory hyperaemia in the vehicle group was attenuated in the indomethacin‐ (P < 0.001, two‐way ANOVA) and SC‐236‐treated groups (P < 0.0001), with no difference between these treatments. At 24 h, i.v. infusion of indomethacin (0.1 mg min−1), increased vascular resistance (24 ± 7.1 %; P < 0.05) compared to vehicle infusion, whereas SC‐236 (0.11 mg min−1) did not. Resistance changes to indomethacin also differed from SC‐236 (P < 0.05). Knee joint diameter progressively increased over 24 h (P < 0.0001, one‐way ANOVA). Urinary PG levels increased by 6 h (P < 0.05), but returned to baseline by 24 h. COX‐1 mRNA was detectable at all time points; COX‐2 mRNA only at 3 h. Urinary NOx levels increased progressively over 24 h (P < 0.05), paralleled by induction of iNOS in the 3 and 24 h samples. Prostaglandin production via COX‐2 appears to mediate the development of acute inflammatory hyperaemia, but nitrergic mechanisms may supervene subsequently. COX‐1 but not COX‐2 contributes to the maintenance of basal blood flow in the hyperaemic joint at 24 h.
Periodic Sampling Interval Repetitive Control and Its Application to Variable Spindle Speed Noncircular Turning Process
Authors: Hanson Reed D. , Tsao Tsu-Chin
Published: July 2002

This paper addresses discrete-time, repetitive control for linear, periodic, time-varying systems. A periodic, repetitive control design method based on gain scheduling is proposed and the necessary and sufficient condition for closed-loop stability is presented. Utilizing the special structure of the repetitive controller, an efficient method for evaluating the closed-loop stability is developed. The algorithm is applied to the control of a piezoelectric fast-tool stage for variable spindle speed noncircular turning process. The tool performs dynamic variable depth of cut machining to generate noncircular workpiece profiles while the spindle carrying the workpiece rotates at a variable speed to inhibit machining instability (chatter). Experimental machining results are presented that demostrate the tracking performance of the period, time-varying controller design proposed, as well as the ability to increase machining stability using this approach. [S0022-0434(00)02402-3]
Surface Integrity of Die Material in High Speed Hard Machining, Part 1: Micrographical Analysis
Authors: El-Wardany T. I. , Kishawy H. A. , Elbestawi M. A.
Published: July 2002

The effects of cutting conditions and tool wear on chip morphology and surface integrity during high speed machining of D2 tool steel (60–62 Hrc) are investigated experimentally and analytically in this paper. Polycrystalline Cubic Boron Nitride (PCBN) tools are used in this investigation. The chips and the subsurface of the workpiece are examined using optical and scanning electron microscopy. Microhardness measurements are performed on the surface and subsurface of the workpiece. The X-ray diffraction technique is used to measure the residual stresses induced in the machined surface. The paper is divided into two parts. Part 1 presents the results obtained from the micrographical analysis of the chips and the surfaces produced. Part 2 deals with microhardness and residual stresses of the machined surface. The micrographical analysis of the chips produced shows that different mechanisms of chip formation exist depending on the magnitude of the cutting pressure and tool wear. Saw toothed chips are produced during the machining of D2 tool steel if the cutting pressure exceeds approximately 4000 MPa. The metallographic analysis of the surface produced illustrates the damaged surface region that contains geometrical defects and changes in the subsurface metallurgical structure. The types of surface damage are dependent on the cutting conditions, tool geometry and the magnitude of the wear lands. [S1087-1357(00)00104-0]
Computational Simulation of Gas Turbines: Part 1—Foundations of Component-Based Models
Authors: Reed John A. , Afjeh Abdollah A.
Published: July 2002

Designing and developing new aerospace propulsion systems is time-consuming and expensive. Computational simulation is a promising means for alleviating this cost, but requires a flexible software simulation system capable of integrating advanced multidisciplinary and multifidelity analysis methods, dynamically constructing arbitrary simulation models, and distributing computationally complex tasks. To address these issues, we have developed Onyx, a Java-based object-oriented domain framework for aerospace propulsion system simulation. This paper presents the design of a common engineering model formalism for use in Onyx. This approach, which is based on hierarchical decomposition and standardized interfaces, provides a flexible component-based representation for gas turbine systems, subsystems and components. It allows new models to be composed programmatically or visually to form more complex models. Onyx’s common engineering model also supports integration of a hierarchy of models which represent the system at differing levels of abstraction. Selection of a particular model is based on a number of criteria, including the level of detail needed, the objective of the simulation, the available knowledge, and given resources. The common engineering model approach is demonstrated by developing gas turbine component models which will be used to compose a gas turbine engine model in Part 2 of this paper. [S0742-4795(00)02303-6]
A Study of the Effects of Tip Clearance in a Supersonic Turbine
Authors: Dorney Daniel J. , Griffin Lisa W. , Huber Frank W.
Published: July 2002

Flow unsteadiness is a major factor in turbine performance and durability. This is especially true if the turbine is a high work design, compact, transonic, supersonic, counterrotating, or uses a dense drive gas. The vast majority of modern rocket turbine designs fall into these categories. In this study a parallelized unsteady three-dimensional Navier–Stokes analysis has been used to study the effects of tip clearance on the transient and time-averaged flow fields in a supersonic turbine. The predicted results indicate improved performance in the simulation including tip clearance. The main sources of the performance gains were: (1) a weakened shock system in the case with tip clearance, and (2) the fact that the reductions in the shock losses were greater than the losses introduced by tip clearance. [S0889-504X(00)02404-1]
1999 Turbomachinery Committee Best Paper Award: Development of Advanced Compressor Airfoils for Heavy-Duty Gas Turbines— Part II: Experimental and Theoretical Analysis
Authors: Ku¨sters Bernhard , Schreiber Heinz-Adolf , Ko¨ller Ulf , Mo¨nig Reinhard
Published: July 2002

In Part I of this paper a family of numerically optimized subsonic compressor airfoils for heavy-duty gas turbines, covering a wide range of flow properties, is presented. The objective of the optimization was to create profiles with a wide low loss incidence range. Therefore, design point and off-design performance had to be considered in an objective function. The special flow conditions in large-scale gas turbines have been taken into account by performing the numerical optimization procedure at high Reynolds numbers and high turbulence levels. The objective of Part II is to examine some of the characteristics describing the new airfoils, as well as to prove the reliability of the design process and the flow solver applied. Therefore, some characteristic members of the new airfoil series have been extensively investigated in the cascade wind tunnel of DLR cologne. Experimental and numerical results show profile Mach number distributions, total pressure losses, flow turning, and static pressure rise for the entire incidence range. The design goal with low losses and especially a wide operating range could be confirmed, as well as a mild stall behavior. Boundary layer development, particularly near stall condition, is discussed using surface flow visualization and the results of boundary layer calculations. An additional experimental study, using liquid crystal coating, provides necessary information on suction surface boundary-layer transition at high Reynolds numbers. Finally, results of Navier–Stokes simulations are presented that enlighten the total pressure loss development and flow turning behavior, especially at high incidence in relation to the results of the design tool. [S0889-504X(00)02602-7]
Impact of Film-Cooling Jets on Turbine Aerodynamic Losses
Authors: Walters Dibbon K. , Leylek James H.
Published: July 2002

This paper documents a computational investigation of the aerodynamic impact of film cooling on a linear turbine airfoil cascade. The simulations were for single row injection on both the pressure and suction surfaces, downstream of the leading edge region. The cases match experimental efforts previously documented in the open literature. Results were obtained for density ratio equal to 1.0 and 2.0, and a blowing ratio range from 0.91 to 6.6. The domain included the passage flow as well as the film hole and blade interior. The simulation used a dense, high-quality, unstructured hybrid-topology grid, comprised of hexahedra, tetrahedra, prisms, and pyramids. The processing was performed with a pressure-correction solution procedure and a second-order discretization scheme. Turbulence closure was obtained using standard, RNG, and “realizable” k-ε models, as well as a Reynolds stress model. Results were compared to experimental data in terms of total pressure loss downstream of the blade row. Flow mechanisms responsible for the variation of aerodynamic losses due to suction and pressure surface coolant injection are documented. The results demonstrate that computational methods can be used to predict losses accurately on film-cooled airfoils. [S0889-504X(00)01503-8]
Impeller–Diffuser Interaction in a Centrifugal Compressor
Authors: Shum Y. K. P. , Tan C. S. , Cumpsty N. A.
Published: July 2002

A study has been conducted, using an unsteady three-dimensional Reynolds-averaged Navier–Stokes simulation, to define the effect of impeller–diffuser interaction on the performance of a centrifugal compressor stage. The principal finding from the study was that the most influential aspect of this unsteady interaction was the effect on impeller tip leakage flow. In particular, the unsteadiness due to the upstream potential effect of the diffuser vanes led to larger viscous losses associated with the impeller tip leakage flow. The consequent changes at the impeller exit with increasing interaction were identified as reduced slip, reduced blockage, and increased loss. The first two were beneficial to pressure rise, while the third was detrimental. The magnitudes of the effects were examined using different impeller–diffuser spacings and it was shown that there was an optimal radial gap size for maximum impeller pressure rise. The physical mechanism was also determined: When the diffuser was placed closer to the impeller than the optimum, increased loss overcame the benefits of reduced slip and blockage. The findings provide a rigorous explanation for experimental observations made on centrifugal compressors. The success of a simple flow model in capturing the pressure rise trend indicated that although the changes in loss, blockage, and slip were due largely to unsteadiness, the consequent impacts on performance were mainly one-dimensional. The influence of flow unsteadiness on diffuser performance was found to be less important than the upstream effect, by a factor of seven in terms of stage pressure rise in the present geometry. It is thus concluded that the beneficial effects of impeller–diffuser interaction on overall stage performance come mainly from the reduced blockage and reduced slip associated with the unsteady tip leakage flow in the impeller. [S0889-504X(00)01704-9]
Thermographic Inspection of Rail-Car Thermal Insulation
Authors: Birk A. M. , Cunningham Mark. H.
Published: July 2002

Over time, thermally protected and thermally insulated rail tank-cars may develop insulation deficiencies due to the continuous motion and vibrations. These deficiencies are generally not visible due to the protective outer steel jacket. A research program was undertaken to develop an inspection procedure to identify deficiencies in the thermal insulation. Thermography was selected as the most effective means of inspecting the thermal insulation because it is nondestructive, noncontact, and economical. Thermography takes advantage of the fact that when a temperature difference exits between the contents of the tank car and the ambient conditions, the presence of insulation deficiencies generates temperature gradients on the surface of the tank-car’s outer steel jacket that can then be identified using a thermal imager. A series of laboratory and field tests were conducted to determine under what ambient and tank conditions the inspection procedure is effective. Using a low-cost, uncooled, 8–12-μm waveband thermal imager, it was found that the imager could detect insulation deficiencies under temperature gradient conditions compatible with typical day-night cycle temperature variations. Field tests proved the technique to be practical and also showed that solar heating enhances the inspection procedure under certain conditions. This paper presents the results of the laboratory tests and shows some preliminary field test results. [S0094-9930(00)01104-5]
Experimental Investigation of the Blade-to-Blade Flow in a Compressor Rotor by Digital Particle Image Velocimetry
Authors: Balzani N. , Scarano F. , Riethmuller M. L. , Breugelmans F. A. E.
Published: July 2002

The purpose of this study is to investigate the blade-to-blade flow in an axial compressor, providing a detailed description of the entire flow-field on multiple layers through the use of Particle Image Velocimetry (PIV). Typical problems that relate to flow seeding, light-sheet generation, and camera-laser timing control are successfully dealt with, bringing additional knowledge in the domain. An extensive data set is analyzed to obtain statistical flow information (mean and fluctuating quantities). Spatial data reconstruction procedures allow the complete planar flow distributions to be determined. The multiplanar mean velocity field constitutes the final result of a three-dimensional reconstruction of the domain geometry and the proper introduction of the available planar measurements. [S0889-504X(00)00304-4]
Kinematics and Optimization of a Spatial 3-UPU Parallel Manipulator
Authors: Tsai Lung-Wen , Joshi Sameer
Published: July 2002

The structural characteristics associated with parallel manipulators are investigated. Using these characteristics a class of 3 degree-of-freedom parallel manipulators are enumerated. Several parallel manipulators with only translational degrees of freedom are identified and the 3-UPU parallel manipulator is chosen for design analysis and optimization. The kinematics of this 3-UPU parallel manipulator is studied. Two geometric conditions that lead to pure translational motion of the moving platform are described. Due to the simple kinematic structure, the inverse kinematics yields two equal and opposite limb lengths whereas the direct kinematics produces two possible manipulator postures with one being the mirror image of the other. The Jacobian matrix is derived and several singular conditions are discussed. Furthermore the conditions for existence of an isotropic point within the workspace are discussed and equations to compute the isotropic configurations of a 3-UPU manipulator are derived. Finally, we undertake architecture optimization and show that certain values of design variables maximize the global condition index of the 3-UPU manipulator. [S1050-0472(00)01404-5]
Product Design Selection Under Uncertainty and With Competitive Advantage
Authors: Li H. , Azarm S.
Published: July 2002

This paper presents an approach wherein product design is viewed as a selection process with two main stages: design alternative generation and design alternative evaluation. The focus of this paper is mainly on a design alternative evaluation model in that designer’s preferences, customers’ preferences, and market competition are accounted for in order to select the best possible design. In the model, uncertainties in the product design life, market size and its yearly change, cost and its yearly change, price, and discount rate are considered. Product design selection of a cordless screwdriver is used as a demonstration example. However, the emphasis in the example is on the approach, and not on the details per se. [S1050-0472(00)01504-X]
Dynamic Analysis of Piston Secondary Motion for Small Reciprocating Compressors
Authors: Prata A. T. , Fernandes J. R. S. , Fagotti F.
Published: July 2002

Piston dynamics plays a fundamental role in two critical processes related to fluid flow in reciprocating compressors. The first is the gas leakage through the radial clearance, which may cause considerable loss in the pumping efficiency of the compressor. The second process is the viscous friction associated with the lubricant film in the radial clearance. In the present contribution a numerical simulation is performed for a ringless piston inside the cylinder of a reciprocating compressor, including both the axial and the radial piston motion. The compressor considered here is a small hermetic compressor employed in domestic refrigerators, with the radial clearance between piston and cylinder filled with lubricant oil. In operation, the piston moves up and down along the axis of the cylinder, but the radial oscillatory motion in the cylinder bore, despite being usually small, plays a very important role on the compressor performance and reliability. The compromise between oil leakage through the piston-cylinder clearance and the friction losses requires a detailed analysis of the oscillatory motion for a good design. All corresponding forces and moments are included in the problem formulation of the piston dynamics in order to determine the piston trajectory, velocity and acceleration at each time step. The hydrodynamic force is obtained from the integration of the pressure distribution on the piston skirt, which, in turn, is determined from a finite volume solution of the time dependent equation that governs the oil flow. A Newton-Raphson procedure was employed in solving the equations of the piston dynamics. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction losses. Emphasis was placed on investigating the influence of the pin location, radial clearance and oil viscosity on the piston dynamics. [S0742-4787(11)00301-8]
Recommendations for Achieving Accurate Numerical Simulation of Tip Clearance Flows in Transonic Compressor Rotors
Authors: Van Zante Dale E. , Strazisar Anthony J. , Wood Jerry R. , Hathaway Michael D. , Okiishi Theodore H.
Published: July 2002

The tip clearance flows of transonic compressor rotors are important because they have a significant impact on rotor and stage performance. A wall-bounded shear layer formed by the relative motion between the overtip leakage flow and the shroud wall is found to have a major influence on the development of the tip clearance flow field. This shear layer, which has not been recognized by earlier investigators, impacts the stable operating range of the rotor. Simulation accuracy is dependent on the ability of the numerical code to resolve this layer. While numerical simulations of these flows are quite sophisticated, they are seldom verified through rigorous comparisons of numerical and measured data because these kinds of measurements are rare in the detail necessary to be useful in high-speed machines. In this paper we compare measured tip-clearance flow details (e.g., trajectory and radial extent) with corresponding data obtained from a numerical simulation. Laser-Doppler Velocimeter (LDV) measurements acquired in a transonic compressor rotor, NASA Rotor 35, are used. The tip clearance flow field of this transonic rotor is simulated using a Navier–Stokes turbomachinery solver that incorporates an advanced k–ε turbulence model derived for flows that are not in local equilibrium. A simple method is presented for determining when the wall-bounded shear layer is an important component of the tip clearance flow field. [S0889-504X(00)02504-6]
Dynamics of Spread Mooring Systems With Hybrid Mooring Lines
Authors: Garza-Rios Luis O. , Bernitsas Michael M. , Nishimoto Kazuo , Matsuura Joa˜o Paulo J.
Published: July 2002

The weight of a chain mooring line in deep water is the main source of mooring line tension. Chain weight also induces a vertical force on the moored vessel. To achieve the desired tension without excessive weight, hybrid mooring lines, such as lighter synthetic fiber ropes with chains, have been proposed. In this paper, the University of Michigan methodology for design of mooring systems is developed to study hybrid line mooring. The effects of hybrid lines on the slow-motion nonlinear dynamics of spread mooring systems (SMS) are revealed. Stability analysis and bifurcation theory are used to determine the changes in SMS dynamics in deep water based on pretension and angle of inclination of the mooring lines for different water depths and synthetic rope materials. Catastrophe sets in two-dimensional parametric design spaces are developed from bifurcation boundaries, which delineate regions of qualitatively different dynamics. Stability analysis defines the morphogeneses occurring as bifurcation boundaries are crossed. The mathematical model of the moored vessel consists of the horizontal plane—surge, sway, and yaw—fifth-order, large drift angle, low-speed maneuvering equations. Mooring lines are modeled quasistatically as nonlinear elastic strings for synthetic ropes and as catenaries for chains, and include nonlinear drag and touchdown. Excitation consists of steady current, wind, and mean wave drift. Numerical applications are limited to steady current, which is adequate for revealing the SMS design depending on the selected parameters. [S0892-7219(00)00804-9]
Combined DAE and Sliding Mode Control Methods for Simulation of Constrained Mechanical Systems
Authors: Compere M. D. , Longoria R. G.
Published: July 2002

In dynamic analysis of constrained multibody systems (MBS), the computer simulation problem essentially reduces to finding a numerical solution to higher-index differential-algebraic equations (DAE). This paper presents a hybrid method composed of multi-input multi-output (MIMO), nonlinear, variable-structure control (VSC) theory and post-stabilization from DAE solution theory for the computer solution of constrained MBS equations. The primary contributions of this paper are: (1) explicit transformation of constrained MBS DAE into a general nonlinear MIMO control problem in canonical form; (2) development of a hybrid numerical method that incorporates benefits of both Sliding Mode Control (SMC) and DAE stabilization methods for the solution of index-2 or index-3 MBS DAE; (3) development of an acceleration-level stabilization method that draws from SMC’s boundary layer dynamics and the DAE literature’s post-stabilization; and (4) presentation of the hybrid numerical method as one way to eliminate chattering commonly found in simulation of SMC systems. The hybrid method presented can be used to simulate constrained MBS systems with either holonomic, nonholonomic, or both types of constraints. In addition, the initial conditions (ICs) may either be consistent or inconsistent. In this paper, MIMO SMC is used to find the control law that will provide two guarantees. First, if the constraints are initially not satisfied (i.e., for inconsistent ICs) the constraints will be driven to satisfaction within finite time using SMC’s stabilization method, urobust,i=−ηisgnsi. Second, once the constraints have been satisfied, the control law, ueq and hybrid stabilization techniques guarantee surface attractiveness and satisfaction for all time. For inconsistent ICs, Hermite-Birkhoff interpolants accurately locate when each surface reaches zero, indicating the transition time from SMC’s stabilization method to those in the DAE literature. [S0022-0434(00)02404-7]
Thermodynamic Optimization of the HAT Cycle Plant Structure—Part II: Structure of the Heat Exchanger Network
Authors: Lazzaretto A. , Segato F.
Published: July 2002

In Part I of the paper a thermodynamic optimization methodology was presented for the “basic” configuration of a humid air turbine cycle plant in which the heat exchange section is viewed as a black-box separated from the rest of the plant (basic components), having a fixed structure. The results of the optimization apply to all the heat exchanger networks that fulfill the optimal boundary conditions between the black-box and the rest of the plant. The aim of this part is to define these heat exchanger networks using a combination of Pinch Technology and Second Law insights. The possibility of a further reduction in the number of heat exchangers is then investigated in order to achieve the best compromise between high performances and structural simplicity.
Modeling Electronic Cooling Axial Fan Flows
Authors: Grimes R. , Davies M. , Punch J. , Dalton T. , Cole R.
Published: July 2002

To address the requirement for prediction and understanding of airflow in forced convection cooled electronic systems, a detailed experimental investigation of the outlet flow of typical axial cooling fans has been performed. The flow is shown to be complex over much of the fans operational range, with significant radial and tangential velocities and regions with little or no flow. The effect of partially blocking a fan and running it at elevated temperatures are both shown to be significant. The effect of attaching a fan to an electronic system is then investigated. Flow drawn through a system is shown to be simple and well predicted by a standard CFD package. Flow blown into a system is far more complex, with large areas of recirculating flow, and less accuracy in the prediction. The paper gives valuable and novel design insight into forced cooling flows in electronic systems and shows that the industry is still some way from a reliable design method.
Advanced Coal-Fired Power Plants
Authors: Ruth Lawrence A.
Published: July 2002

The U.S. Department of Energy is partnering with industry to develop advanced coal-fired electric power plants that are substantially cleaner, more efficient, and less costly than current plants. Low-emission boiler systems (LEBS) and high-performance power systems (HIPPS) are based, respectively, on the direct firing of pulverized coal and the indirectly fired combined cycle. LEBS uses a low-NOx slagging combustion system that has been shown in pilot-scale tests to emit less than 86 g/GJ (0.2 lb/106 Btu) of NOx. Additional NOx removal is provided by a moving bed copper oxide flue gas cleanup system, which also removes 97–99 percent of sulfur oxides. Stack levels of NOx can be reduced to below 9 g/GJ (0.02 lb/106 Btu). Construction of an 80 MWe LEBS proof-of-concept plant is scheduled to begin in the spring of 1999. Engineering development of two different HIPPS configurations is continuing. Recent tests of a radiant air heater, a key component of HIPPS, have indicated the soundness of the design for air temperatures to 1150°C. LEBS and HIPPS applications include both new power plants and repowering/upgrading existing plants.
Shear Coefficients for Timoshenko Beam Theory
Authors: Hutchinson J. R.
Published: July 2002

The Timoshenko beam theory includes the effects of shear deformation and rotary inertia on the vibrations of slender beams. The theory contains a shear coefficient which has been the subject of much previous research. In this paper a new formula for the shear coefficient is derived. For a circular cross section, the resulting shear coefficient that is derived is in full agreement with the value most authors have considered “best.” Shear coefficients for a number of different cross sections are found.
Lubrication With Granular Flow: Continuum Theory, Particle Simulations, Comparison With Experiment
Authors: Sawyer W. Gregory , Tichy John A.
Published: July 2002

Studies of particle flows have followed three parallel paths: (1) experiment, (2) analysis based on the assumption of a continuum, and (3) direct particle simulation. In this paper, we perform continuum and particle analyses and compare them to each other, and to previously reported experiments. Both the particle simulations and the continuum model over-predict the experimental normal load and shear force, however, the trends and orders-of-magnitude are in agreement. The modeling approaches are based on first principles, and do not rely on curve fitting to obtain effective properties of the mixture such as viscosity or conductivity.
Modal Analysis of Ballooning Strings With Small Curvature
Authors: Fan R. , Singh S. K. , Rahn C. D.
Published: July 2002

During the manufacture and transport of textile products, yarns are rotated at high speed. The surface of revolution generated by the rotating yarn is called a balloon. The dynamic response of the balloon to varying rotation speed, boundary excitation, and aerodynamic disturbances affects the quality of the associated textile product. Resonance, in particular, can cause large tension variations that reduce product quality and may cause yarn breakage. In this paper, the natural frequencies and mode shapes of a single loop balloon are calculated to predict resonance. The three-dimensional nonlinear equations of motion are simplified under assumptions of small displacement and quasi-static axial motion. After linearization, Galerkin’s method is used to calculate the mode shapes and natural frequencies. Experimental measurements of the steady-state balloon shape and the first two natural frequencies and mode shapes are compared with theoretical predictions.
Micro-Structural Analysis of Chip Formation During Orthogonal Machining of Al/SiCp Composites
Authors: Joshi S. S. , Ramakrishnan N. , Ramakrishnan P.
Published: July 2002

Discontinuously Reinforced Aluminum (DRA) Composites form unique case from the research in metal cutting point of view. Reinforcement in these materials acts as “macroscopic” and “isolated” discontinuities in the path of the tool. The mechanism of chip formation for such materials is yet to be evolved completely. In this paper, the mechanism of chip formation during machining of Al/SiCp composites based on the micro-structural analysis of chips and chip roots is presented. It was evident that the mechanism involves initiation of a gross fracture on the chip free surface and its propagation toward the tool nose. The extent of propagation of gross fracture depends upon the cutting speed and volume of reinforcement in composites. A model of deformation of the material along the shear plane is presented in terms of a ratio of length of flow-type deformation on the shear plane to the total length of shear plane. Influence of volume of reinforcement in composites and cutting speed on the ratio was verified experimentally.
Complex Modal Analysis of Non-Self-Adjoint Hybrid Serpentine Belt Drive Systems
Authors: Zhang Lixin , Zu Jean W. , Hou Zhichao
Published: July 2002

A linear damped hybrid (continuous/discrete components) model is developed in this paper to characterize the dynamic behavior of serpentine belt drive systems. Both internal material damping and external tensioner arm damping are considered. The complex modal analysis method is developed to perform dynamic analysis of linear non-self-adjoint hybrid serpentine belt-drive systems. The adjoint eigenfunctions are acquired in terms of the mode shapes of an auxiliary hybrid system. The closed-form characteristic equation of eigenvalues and the exact closed-form solution for dynamic response of the non-self-adjoint hybrid model are obtained. Numerical simulations are performed to demonstrate the method of analysis. It is shown that there exists an optimum damping value for each vibration mode at which vibration decays the fastest.
Analytical Approach to Crack Arrest Tendency Under Cyclic Thermal Stress for an Inner-Surface Circumferential Crack in a Finite-Length Cylinder
Authors: Meshii Toshiyuki , Watanabe Katsuhiko
Published: July 2002

This paper presents a study of the crack arrest tendency under cyclic thermal stress for an inner-surface circumferential crack in a finite-length cylinder with its edges rotation-restrained, when the inside of the cylinder is cooled from uniform temperature distribution. The effects of structural parameters and heat transfer condition on the maximum transient SIF for the problem were investigated with the formerly developed systematical evaluation methods. Then, a tentative value of threshold stress intensity range ΔKth being assumed as well as Paris law, the evaluation of crack length for crack arrest under cyclic thermal stresses was carried out. Finally, a map to find the crack arrest point for a cylinder with mean radius to wall thickness ratio Rm/W=1 and a specific length H under various heat transfer conditions could be originated. From the map, it was predicted that when the heat transfer coefficient and/or initial wall-coolant temperature differences become large enough, the nondimensional crack arrest length saturates to a specific value and is no longer affected by those conditions.
Residual Stress Analyses of a Multi-Pass Girth Weld: 3-D Special Shell Versus Axisymmetric Models
Authors: Dong P.
Published: July 2002

In this paper, detailed weld residual stress analyses are presented for a typical multi-pass girth weld in Type 316L stainless steel pipe with r/t ratio of 25. Advanced finite element procedures were used to simulate the residual stress development under controlled welding conditions associated with weld mock-ups. Both axisymmetric and 3-D special shell element models were used to reveal local residual stress details and global residual stress characteristics in the girth weld. Residual stress measurements using hole-drilling method were conducted for model validation on the laboratory weld mock-up welds. A good agreement between finite element predictions and experimental measurements were obtained. The major findings include: (a) Axial residual stresses within and near the weld area exhibit a strong bending feature across the pipe wall thickness, while the hoop residual stresses showed a much less variation through the wall thickness. (b) Some periodic variation of the residual stresses is present along the pipe circumference near the weld, particularly for the axial residual stress component. Such a variation tends to become more pronounced in thick wall than in thin wall girth welds. A 3-D model is essential to adequately capture such 3-D features in residual stress distributions. (c) A rapid variation in weld residual stresses can be seen at start/stop positions, where a high magnitude of axial residual stresses is present in both tension and compression.
On the Robust Regulator for Linear Systems With Limited Parameter Uncertainty
Authors: Huang Jie
Published: July 2002

The linear servomechanism problem has been studied for two extreme cases. On one extreme, the problem has been studied without considering the plant parameter uncertainty. On the other extreme, the problem has been studied for the worst parameter uncertainty in the sense that all the plant parameters are allowed to vary arbitrarily in the neighborhoods of their nominal values. Between these two extreme cases is what will be called limited uncertainty case where the entries of the plant matrices vary functionally with respect to some variables. This case will be studied in this paper. The main result is that, in the limited uncertainty case, the order of the robust regulator can be strictly less than the minimal order of the robust regulator with respect to the worst parameter uncertainty.
The Basic Thermodynamics of Turbine Cooling
Authors: Horlock J. H.
Published: July 2002

Analyses of gas turbine plant performance, including the effects of turbine cooling, are presented. The thermal efficiencies are determined theoretically, assuming air standard (a/s) cycles, and the reductions in efficiency due to cooling are established; it is shown that these are small, unless large cooling flows are required. The theoretical estimates of efficiency reduction are compared with calculations, assuming that real gases form the working fluid in the gas turbine cycles. It is shown from a/s analysis that there are diminishing returns on efficiency as combustion temperature is increased; for real gases there appears to be a limit on this maximum temperature for maximum thermal efficiency.
Tip Clearance Actuation With Magnetic Bearings for High-Speed Compressor Stall Control
Authors: Spakovszky Z. S. , Paduano J. D. , Larsonneur R. , Traxler A. , Bright M. M.
Published: July 2002

Magnetic bearings are widely used as active suspension devices in rotating machinery, mainly for active vibration control purposes. The concept of active tip-clearance control suggests a new application of magnetic bearings as servo-actuators to stabilize rotating stall in axial compressors. This paper presents a first-of-a-kind feasibility study of an active stall control experiment with a magnetic bearing servo-actuator in the NASA Glenn high-speed single-stage compressor test facility. Together with CFD and experimental data a two-dimensional, incompressible compressor stability model was used in a stochastic estimation and control analysis to determine the required magnetic bearing performance for compressor stall control. The resulting requirements introduced new challenges to the magnetic bearing actuator design. A magnetic bearing servo-actuator was designed that fulfilled the performance specifications. Control laws were then developed to stabilize the compressor shaft. In a second control loop, a constant gain controller was implemented to stabilize rotating stall. A detailed closed loop simulation at 100 percent corrected design speed resulted in a 2.3 percent reduction of stalling mass flow, which is comparable to results obtained in the same compressor by Weigl et al. (1998. ASME J. Turbomach. 120, 625–636) using unsteady air injection. The design and simulation results presented here establish the viability of magnetic bearings for stall control in aero-engine high-speed compressors. Furthermore, the paper outlines a general design procedure to develop magnetic bearing servo-actuators for high-speed turbomachinery.
Dimethyl Ether in Diesel Engines: Progress and Perspectives
Authors: Sorenson S. C.
Published: July 2002

A review of recent developments related to the use of dimethyl ether (DME) in engines is presented. Research work discussed is in the areas of engine performance and emissions, fuel injection systems, spray and ignition delay, and detailed chemical kinetic modeling. DME’s properties and safety aspects are discussed. A simplified theoretical explanation of the emissions behavior of DME is presented. A discussion is presented proposing DME as a significant factor in the future international energy picture. Due to its beneficial combustion properties, possibility of production from a variety of sources, and usefulness as a chemical feed stock, DME can be used in a variety of applications in addition to transportation.
Rotary Shouldered Thread Connections: Working Limits Under Combined Static Loading
Authors: Baragetti S. , Baryshnikov A.
Published: July 2002

Rotary shouldered connections (RSC), used in the oil and gas industries, are probably the most stressed components of the drill string because they are subjected both to make-up torque and to axial and bending loads. Since loads can vary and can result in fatigue crack initiation and propagation, there is often severe damage to the first threads engaged. Such damage leads to shoulder load reduction and discontinuity in the drill string. Once we know the geometric dimensions and the materials of the pin and box elements composing the RSCs, API standards make it possible to evaluate the working limits of RSCs when they are subjected to make-up torque, torsion and tension. It is not, however, possible to establish the stress state of the connection for extreme working limits. The aim of this paper is to propose a numerical procedure, confirmed by full-scale experimental tests, which enables the evaluation both of the working limits, combined make-up and axial tensile loads, and of the stress state of RSCs for any load condition and, in particular, when RSCs are subjected to extreme combinations of make-up, torsion and axial tensile loads.
Limitations on Gas Turbine Performance Imposed by Large Turbine Cooling Flows
Authors: Horlock J. H. , Watson D. T. , Jones T. V.
Published: July 2002

Calculations of the performance of modern gas turbines usually include allowance for cooling air flow rate; assumptions are made for the amount of the cooling air bled from the compressor, as a fraction of the mainstream flow, but this fractional figure is often set in relatively arbitrary fashion. There are two essential effects of turbine blade cooling: (i) the reduction of the gas stagnation temperature at exit from the combustion chamber (entry to the first nozzle row) to a lower stagnation temperature at entry to the first rotor and (ii) a pressure loss resulting from mixing the cooling air with the mainstream. Similar effects occur in the following cooled blade rows. The paper reviews established methods for determining the amount of cooling air required and semi-empirical relations, for film cooled blading with thermal barrier coatings, are derived. Similarly, the pressure losses related to elements of cooling air leaving at various points round the blade surface are integrated over the whole blade. This gives another semi-empirical expression, this time for the complete mixing pressure loss in the blade row, as a function of the total cooling air used. These two relationships are then used in comprehensive calculations of the performance of a simple open-cycle gas turbine. for varying combustion temperature and pressure ratio. These calculations suggest that for maximum plant efficiency there may be a limiting combustion temperature (below that which would be set by stoichiometric combustion). For a given combustion temperature, the optimum pressure ratio is reduced by the effect of cooling air.
The Flow Structure During Onset and Developed States of Rotating Stall Within a Vaned Diffuser of a Centrifugal Pump
Authors: Sinha Manish , Pinarbasi Ali , Katz Joseph
Published: July 2002

Particle Image Velocimetry (PIV) and pressure fluctuation measurements are used for investigating the onset and development of rotating stall within a centrifugal pump having a vaned diffuser. The experiments are performed in a facility that enables measurements between the diffuser vanes, within part of the impeller, in the gap between them and in the volute. The diffuser is also instrumented with pressure transducers that track the circumferential motion of rotating stall in the stator. The timing of low-pass-filtered pressure signals are also used for triggering the acquisition of PIV images. The data include detailed velocity distributions, instantaneous and phase-averaged, at different blade orientations and stall phases, as well as auto- and cross-spectra of pressure fluctuations measured simultaneously in neighboring vane passages. The cross-spectra show that the stall propagation rate is 0.93 Hz, 6.2 percent of the impeller speed, and that the stall travels from the passages located on the exit side of the volute toward the beginning side, crossing the tongue region in the same direction as the impeller, where it diminishes. Under stall conditions the flow in the diffuser passage alternates between outward jetting, when the low-pass-filtered pressure is high, to a reverse flow, when the filtered pressure is low. Being below design conditions, there is a consistent high-speed leakage flow in the gap between the impeller and the diffuser from the exit side to the beginning of the volute. Separation of this leakage flow from the diffuser vane causes the onset of the stall. The magnitude of the leakage and the velocity distribution in the gap depend on the orientation of the impeller blade. Conversely, the flow in a stalled diffuser passage and the occurrence of stall do not vary significantly with blade orientation. With decreasing flow-rate the magnitudes of leakage and reverse flow within a stalled diffuser passage increase, and the stall-cell size extends from one to two diffuser passages.
The Transient Motion of a Ramp-Core Supersonic Dislocation
Authors: Markenscoff X. , Ni L.
Published: July 2002

The transient motion of a ramp-core dislocation spreading from −∞<x<∞ and jumping from rest to a supersonic speed in the x direction, is investigated by analysis on the complex transform plane. The new result of this analysis is that, instead of the Mach cone of the Volterra dislocation, there are two lines of discontinuity (of the stress) propagating in the ±z directions, inside of which there are arctan delta sequence (ε≠0) radiated supersonic fields, as well as subsonic fields. The lines of discontinuity arise at the tangent point of the Mach wavefront (ε=0) to the cylinder with radius r=c2t.
Effect of Body Aspect Ratio and Tank Size on the Hydrodynamics of a Rotating Bluff Body During the Initial Spin-Up Period
Authors: Maynes D. , Butcher M.
Published: July 2002

Hydrodynamic torque measurements on rotating bluff bodies are presented for 32 different bodies and three different sized tanks for Reynolds numbers in the range 104-105. The present results focus on the initial period, build-up regime, where the torque remains constant before the tank walls have impacted the flow field in the vicinity of the body. The results show that during the build-up regime, the torque coefficient is a function only of the aspect ratio and increases to a maximum at an aspect ratio near unity, followed by a decrease for further increases in the aspect ratio. This behavior is similar to a uniform flow past rectangular cylinders of varied width and a physical description for the observed variation is proposed. A nondimensional time scale describing the time until the tank geometry impacts the flow field near the body is also presented. This time scaling is based on all of the measurements and appears to be quite general, predicting the spin-up time for bodies differing in volume by three orders of magnitude and tanks differing by two orders of magnitude.