bluuebunny/crossref_metadata_2025 huggingface dataset:
In Vivo Modeling of Interstitial Pressure in the Brain Under Surgical Load Using Finite Elements
Authors: Miga Michael I. , Paulsen Keith D. , Hoopes P. Jack , Kennedy Francis E. , Hartov Alex , Roberts David W.
Published: July 2002

Current brain deformation models have predominantly reflected solid constitutive relationships generated from empirical ex vivo data and have largely overlooked interstitial hydrodynamic effects. In the context of a technique to update images intraoperatively for image-guided neuronavigation, we have developed and quantified the deformation characteristics of a three-dimensional porous media finite element model of brain deformation in vivo. Results have demonstrated at least 75–85 percent predictive capability, but have also indicated that interstitial hydrodynamics are important. In this paper we investigate interstitial pressure transient behavior in brain tissue when subjected to an acute surgical load consistent with neurosurgical events. Data are presented from three in vivo porcine experiments where subsurface tissue deformation and interhemispheric pressure gradients were measured under conditions of an applied mechanical deformation and then compared to calculations with our three-dimensional brain model. Results demonstrate that porous-media consolidation captures the hydraulic behavior of brain tissue subjected to comparable surgical loads and that the experimental protocol causes minimal trauma to porcine brain tissue. Working values for hydraulic conductivity of white and gray matter are also reported and an assessment of transient pressure gradient effects with respect to deformation is provided. [S0148-0731(00)00804-9]
Propagation and Localization of Longitudinal Thermoelastic Waves in Layered Structures
Authors: Cetinkaya Cetin , Li Chen
Published: July 2002

Based on the generalized dynamical theory of thermoelasticity, a transfer matrix formulation including the second sound effect is developed for longitudinal wave component propagation in a thermoelastic layer. The second sound effect is included to eliminate the thermal wave travelling with infinite velocity as predicted by the diffusion heat transfer model. Using this formulation and the periodic systems framework, the attenuation and propagation properties of one-dimensional thermoelastic waves in both continuum and layered structures are studied. Strong localization of thermal waves predicted by the analysis in the transformed domain is demonstrated in the time-spacial domain by an FFT-based transient analysis. Also, a perturbation analysis for identifying leading terms in thermal attenuation is performed, and the role of the thermal elastic coupling term in attenuation is determined. The attenuation factor, defined as the real part of the propagation constant, is obtained in thermoelastic solids. The reflection and transmission coefficients between half-spaces are also calculated to evaluate the potential practical use of the approach in thermal-based nondestructive testing. [S0739-3717(00)00403-7]
A Correlation for Tip Leakage Blockage in Compressor Blade Passages
Authors: Hoeger M. , Lahmer M. , Dupslaff M. , Fritsch G.
Published: July 2002

Three-dimensional multistage Navier–Stokes simulations for compressor components, rigs, and cascades have been analyzed to gain insight into the tip leakage blockage evolution. From pitch-averaged flow quantities the local displacement caused by tip leakage is determined by means of a novel technique. Close to the throat an additional displacement of about 1–4 percent axial chord is observed for unchoked flow conditions. With tip gap height, stagger, and inlet Mach number as governing variables, a correlation for the tip leakage blockage transition function in blade passages is established, which may be used to improve the predictive capability of S1/S2 compressor aerodesign systems. [S0889-504X(00)00903-X]
Influence of Compressor Deterioration on Engine Dynamic Behavior and Transient Stall-Margin
Authors: Spakovszky Z. S. , Gertz J. B. , Sharma O. P. , Paduano J. D. , Epstein A. H. , Greitzer E. M.
Published: July 2002

This paper presents an experimental and analytical investigation of compressor stability assessment during engine transient operation. A two-dimensional, linear, compressible, state-space analysis of stall-inception (Feulner et al., 1996, ASME J. Turbomach., 118, pp. 1–10) was modified to account for engine transients and deterioration, with the latter modeled as increased tip-clearance and flow blockage. Experiments were performed on large commercial aircraft engines in both undeteriorated and deteriorated states. Unsteady measurements of pressure in these test engines during rapid accelerations revealed the growth of pre-stall disturbances, which rotate at rotor speed and at approximately half rotor speed. These disturbances are stronger in deteriorated engines. The model showed that the signal at shaft speed was the first compressible system mode, whose frequency is near shaft speed, excited by geometric nonuniformities. The computed behavior of this mode during throttle transients closely matched engine data. The signal increased in strength as stall was approached and as the engine deteriorated. This work firmly establishes the connection between observed signals in the these engines and first principles stability models. [S0889-504X(00)01603-2]
Discussion: “Estimating the Probability Distribution of von Mises Stress for Structures Undergoing Random Excitation” [ASME J. Vibr. Acoust., 122, No. 1, pp. 42–48 (2000)]1
Authors: Preumont A. , Pitoiset X.
Published: July 2002

[S0739-3717(00)00504-3]
Analysis of a Self-Tracking Rolling Element Bearing
Authors: Truman Christopher E. , Blake Jonathan J. , Sackfield Anthony
Published: July 2002

A novel rolling bearing design, which is patented, is first described and second analyzed with a view to optimizing the bearing parameters. Usually the sides of grooves or ribs guide the rolling elements in ball and roller bearings. By using element-raceway profiles, which are essentially concave–convex, forces can be generated in the two contact regions which: (1) provide positive skew, (2) give stability to the roller motion in response to a disturbing force, and (3) balance lateral traction forces, thus alleviating the need for grooves or ribs. This allows for potential advantages of: (a) up to 50 percent savings in ring material, (b) no need for selective assembly, (c) insensitivity to misalignment, and (d) lighter rolling elements and less centripetal loading effects at high speed. The slip velocities and stress distributions as functions of roller skew are required in order to refine the bearing design parameters. To find the contact stress distributions in the inner and outer element-raceway contacts is not straightforward, as the profiles are non-Hertzian. In this paper an influence function approach is used where the two contact zones are meshed into appropriate grids and a piecewise-linear pressure is assumed to act over each grid element. By superposing the displacements produced by each grid element and equating this to the profiles of the roller and raceway the magnitudes of the pressure acting over each grid element may be found. The forces and moments developed in the contact zones may now be found and used to iteratively refine the initial bearing geometry for optimum performance. Finally, experimental tests are conducted on a prototype self-tracking bearing using a standard tapered bearing as a reference.
Numerical Study of Two-Phase Granular Flow for Process Equipment
Authors: Djebbar R. , Beale S. B. , Sayed M.
Published: July 2002

This paper reports on a research program of modeling multi-phase granular flow. Both single-phase granular flow and two-phase liquid/granular flow in a pressure vessel were considered. For the latter case, detailed results based on a viscous/Mohr-Coulomb closure were compared to existing formulations. Idealized test cases indicated that the numerical procedure is sound. Subsequent simulations of two-phase flow using realistic geometries and boundary conditions showed that the pressure distribution in the solid phase is fundamentally different for the Mohr-Coulomb system than for the conventional system. The effect of the angle of internal friction, geometry, and other parameters is discussed. [S0094-9930(00)01204-X]
Investigation of the Unsteady Rotor Aerodynamics in a Transonic Turbine Stage
Authors: De´nos R. , Arts T. , Paniagua G. , Michelassi V. , Martelli F.
Published: July 2002

The paper focuses on the unsteady pressure field measured around the rotor midspan profile of the VKI Brite transonic turbine stage. The understanding of the complex unsteady flow field is supported by a quasi-three-dimensional unsteady Navier–Stokes computation using a k-ω turbulence model and a modified version of the Abu-Ghannam and Shaw correlation for the onset of transition. The agreement between computational and experimental results is satisfactory. They both reveal the dominance of the vane shock in the interaction. For this reason, it is difficult to identify the influence of vane-wake ingestion in the rotor passage from the experimental data. However, the computations allow us to draw some useful conclusions in this respect. The effect of the variation of the rotational speed, the stator–rotor spacing, and the stator trailing edge coolant flow ejection is investigated and the unsteady blade force pattern is analyzed.
Stability Analysis of an Initially Inclined Ship in Following Sea
Authors: Lee S. K.
Published: July 2002

Generally speaking, the causes of ship capsizing in waves are due to the pure loss of stability, parametric oscillation, and broaching-to phenomenon. In this paper, an analytic expression for the GZ value of a ship, inclined initially by some reasons like damage in longitudinal waves, is derived. And, the roll motion is calculated through the computer simulation to give the necessary information for the safe regions of various parameters of a ship moving in a longitudinal wave. [S0021-8936(00)00704-2]
Discussion: “Analysis of the Working Process and Mechanical Losses in a Stirling Engine for a Solar Power Unit” (Makhkamov, Kh. Kh., and Ingham, D. B., 1999, ASME J. Solar Energ. Eng., 121, pp. 121–127)
Authors: Prieto, J. I.
Published: July 2002

[S0199-6231(00)00204-5]
On the Theory of Thermal Elastohydrodynamic Lubrication at High Slide-Roll Ratios—Line Contact Solution
Authors: Yang Peiran , Qu Shiyue , Chang Qiuying , Guo Feng
Published: July 2002

Complete numerical solutions are obtained for the steady-state line contact thermal elastohydrodynamic lubrication (TEHL) problems. The contact surfaces are arranged to run in opposite directions. The slide-roll ratios are allowed to be as high as infinity. The new theory reveals that the characteristics of the high slide-roll contacts are significantly different from those of the low slide-roll contacts. The unusual zero-entrainment films discovered by Dyson and Wilson and the abnormal surface-dimple phenomena observed by Kaneta et al. are explained.
An Advanced Model to Study the Possible Thermomechanical Damage of Lubricated Sliding-Rolling Line Contacts From Soft Particles
Authors: Nikas George K.
Published: July 2002

A model presented earlier by the author (Nikas et al., 1998, 1999) for the study of the possible risks associated with the entrapment of debris particles in lubricated contacts has been refined to account for additional influential factors that could affect the results obtained from the initial model. The new results showed that soft contaminants could indeed be very destructive and damage a concentrated sliding contact mainly due to the thermal stresses developed from the frictional heating of the contact during the plastic compression and shearing of a particle. This model yielded flash temperatures of the order of 100°C and up to 2000°C (or more, until local yield occurs). It also showed that it is often the thermal stresses which cause the problems, rather than the mechanical stresses from particles’ deformation.
Heat Transfer Enhancements in Rotating Two-Pass Coolant Channels With Profiled Ribs: Part 2—Detailed Measurements
Authors: Nikitopoulos D. E. , Eliades V. , Acharya S.
Published: July 2002

Detailed heat/mass transfer distributions are presented inside a two-pass rotating ribbed coolant channel for two profiled-rib configurations. Several profiled-rib configurations have been studied (Acharya et al., 2000), and it was found that the best performance was achieved by saw-tooth ribs, and a pyramid–valley rib combination. The profiled ribs were placed directly opposite to each other on the leading and trailing surfaces. Smooth side walls were used in all the experiments. Heat transfer measurements were compared with straight ribs of equal blockage ratio. The measurements were made in a two-pass rotating facility using the naphthalene sublimation mass transfer technique, which provides highly resolved surface distributions. The results presented are for a Reynolds number of 30,000, two rotation numbers (0 and 0.3), and include average heat/mass transfer over the entire inter-rib module as well as detailed heat/mass transfer contours for two profiled-rib cases. Significant enhancement of up to 25 percent in heat/mass transfer was obtained with the pyramid–valley and saw-tooth shaped ribs under rotating conditions.
A Comprehensive Robust Design Approach for Decision Trade-Offs in Complex Systems Design
Authors: Kalsi Monu , Hacker Kurt , Lewis Kemper
Published: July 2002

In this paper we introduce a technique to reduce the effects of uncertainty and incorporate flexibility in the design of complex engineering systems involving multiple decision-makers. We focus on the uncertainty that is created when a disciplinary designer or design team must try to predict or model the behavior of other disciplinary subsystems. The design of a complex system is performed by many different designers and design teams, each of which may only have control over a portion of the total set of system design variables. Modeling the interaction among these decision-makers and reducing the effect caused by lack of global control by any one designer is the focus of this paper. We use concepts from robust design to reduce the effects of decisions made during the design of one subsystem on the performance of the rest of the system. Thus, in a situation where the cost of uncertainty is high, these tools can be used to increase the robustness, or independence, of the subsystems, enabling designers to make more effective decisions. To demonstrate the usefulness of this approach, we consider a case study involving the design of a passenger aircraft.
Scroll Compressor Simulation Model
Authors: Schein C. , Radermacher R.
Published: July 2002

A computer model has been developed in Visual Basic which predicts the power, capacity, and efficiencies of a scroll compressor for given operating conditions and scroll designs. The operating conditions and data related to the compressor’s geometry are inputs for the model. The model includes the effects of internal leakage and over and under compression. The compression process is broken up into a series of six degree compression steps. The work and thermodynamic state of each pocket of refrigerant are calculated as it travels from the suction to the discharge reservoir. Once the compression cycle is completed, the compressor’s volumetric and isentropic efficiencies are calculated. Lastly, the work and capacity of the compressor are calculated through energy balances using the appropriate inlet and outlet refrigerant conditions.
The Generalized Torque Approach for Analyzing the Results of Pedaling Tests
Authors: Doria Alberto , Lot Roberto
Published: July 2002

This paper deals with the analysis of experimental data obtained using an ergometer apparatus. A straightforward analysis method based on the power equation and the concept of generalized torques is presented. This method makes it possible to study the influence of the net muscle joint torques and gravity and inertia forces on the crank torque. The assumptions and limitations of the proposed method are discussed and this method is compared with the methods of analysis proposed by other researchers. In order to assess the validity of the method, some experimental data are elaborated. Results show that the method can highlight the effect of training and the pedaling technique of an athlete.
Wear in Partial Slip Contact
Authors: Goryacheva I. G. , Rajeev P. T. , Farris T. N.
Published: July 2002

An analytical method that evaluates the evolution of stress and surface profile in fretting under the partial slip conditions is presented. The repeated slip occurring near the edges of contact generates wear that changes the contact geometry and contact stresses. The method is based on two scales of time: time for one cycle of the oscillating tangential force and time corresponding to the number of cycles. Archard’s wear law is used to evaluate wear and gap variation within the slip zones during one cycle. The governing integral equations are reduced to calculate the contact pressure after each cycle. Evolution of the contact characteristics (contact pressure and shear stress, contact width, gap and slip functions) in fretting is calculated using a stepwise procedure. It is shown that the size of stick zone does not change in wear process of bodies with similar elastic properties under the constant amplitude load conditions, and that an asymptotic solution corresponding to the number of cycles approaching to infinity exists. Analytical expressions for the asymptotic contact pressure, shear and tensile stress, and the gap function are presented. It is proved that the asymptotic contact pressure and shear stress are singular at the ends of stick zone. Detailed results are given for two initial shapes of elastic indenter contacting with an elastic half-space: for the parabolic cylinder and for the indenter having a flat base with rounded edges.
Layered Manufacturing: Current Status and Future Trends
Authors: Dutta Debasish , Prinz Fritz B. , Rosen David , Weiss Lee
Published: July 2002

This paper reviews the emerging field of layered manufacturing. This field is little over 10 years old but a significant amount of research has been conducted and results to date are quite promising. We consider three broad topics namely, design systems for heterogeneous objects, layered manufacturing processes, and process planning techniques. Several applications/examples are included in the course of the survey and limitations of current technology identified. We conclude with some possibilities for the future.
Demonstration of Fluidic Throat Skewing for Thrust Vectoring in Structurally Fixed Nozzles
Authors: Yagle P. J. , Miller D. N. , Ginn K. B. , Hamstra J. W.
Published: July 2002

The experimental demonstration of a fluidic, multiaxis thrust vectoring (MATV) scheme is presented for a structurally fixed, afterburning nozzle referred to as the conformal fluidic nozzle (CFN). This concept for jet flow control features symmetric injection around the nozzle throat to provide throttling for jet area control, and asymmetric injection to subsonically skew the sonic plane for jet vectoring. The conceptual development of the CFN was presented in a companion paper (Miller et al. [1]). In that study, critical design variables were shown to be the flap length and expansion area ratio of the nozzle, and the location, angle, and distribution of injected flow. Measures of merit were vectoring capability, gross thrust coefficient, and discharge coefficient. A demonstration of MATV was conducted on a 20 percent scale CFN test article across a range of nozzle pressure ratios (NPR), injector flow rates, and flow distributions. Both yaw and pitch vector angles of greater than 8 deg were obtained at NPR of 5.5. Yaw vector angles greater than 10 deg were achieved at lower NPR. Values of thrust coefficient for the CFN generally exceeded published measurements of shock-based vectoring methods. In terms of vectoring effectiveness (ratio of vector angle to percent injected flow), fluidic throat skewing was found to be comparable to shock-based vectoring methods.
An Evaluation of Engine Faults Diagnostics Using Artificial Neural Networks
Authors: Lu P.-J. , Zhang M.-C. , Hsu T.-C. , Zhang J.
Published: July 2002

Application of artificial neural network (ANN)-based method to perform engine condition monitoring and fault diagnosis is evaluated. Back-propagation, feedforward neural nets are employed for constructing engine diagnostic networks. Noise-contained training and testing data are generated using an influence coefficient matrix and the data scatters. The results indicate that under high-level noise conditions ANN fault diagnosis can only achieve a 50–60 percent success rate. For situations where sensor scatters are comparable to those of the normal engine operation, the success rates for both four-input and eight-input ANN diagnoses achieve high scores which satisfy the minimum 90 percent requirement. It is surprising to find that the success rate of the four-input diagnosis is almost as good as that of the eight-input. Although the ANN-based method possesses certain capability in resisting the influence of input noise, it is found that a preprocessor that can perform sensor data validation is of paramount importance. Autoassociative neural network (AANN) is introduced to reduce the noise level contained. It is shown that the noise can be greatly filtered to result in a higher success rate of diagnosis. This AANN data validation preprocessor can also serve as an instant trend detector which greatly improves the current smoothing methods in trend detection. It is concluded that ANN-based fault diagnostic method is of great potential for future use. However, further investigations using actual engine data have to be done to validate the present findings.
Nonlinear Longitudinal Controller Implementation and Comparison for Automated Cars
Authors: Lu Xiao-Yun , Tan Han-Shue , Shladover Steven , Hedrick J. Karl
Published: July 2002

This paper presents the implementation and comparison of nonlinear controllers in the longitudinal control of cars for platooning. Based on the previous implementation of adaptive sliding mode controller, a dynamic sliding mode controller and a dynamic back-stepping multiple surface controller have been implemented. These three controllers have been compared with the test results. Realtime run shows that each controller has its own characteristics. Emphasis has been put on the dynamic back-stepping multiple surface controller.
Some Aspects of Modeling Compressor Behavior in Gas Turbine Performance Calculations
Authors: Riegler Claus , Bauer Michael , Kurzke Joachim
Published: July 2002

Performance calculation procedures for gas turbine engines are usually based on the performance characteristics of the engine components, and especially the turbo components are of major interest. In this paper methods of modelling compressors in gas turbine performance calculations are discussed. The basic methodologies based on Mach number similarity are summarized briefly including some second order effects. Under extreme engine partload conditions, as for example subidle or windmilling, the operating points in the compressor map are located in a region which is usually not covered by rig tests. In addition the parameters usually used in compressor maps are no longer appropriate. For these operating conditions a method is presented to extrapolate compressor maps towards very low spool speed down to the locked rotor. Instead of the efficiency more appropriate parameters as for example specific work or specific torque are suggested. A compressor map prepared with the proposed methods is presented and discussed. As another relevant topic the performance modelling of fans for low bypass ratio turbofans is covered. Due to the flow splitter downstream of such a fan the core and bypass stream may be throttled independently during engine operation and bypass ratio becomes a third independent parameter in the map. Because testing a fan on the rig for various bypass ratios is a very costly task, a simplified method has been developed which accounts for the effects of bypass ratio.
A General Model for Analyzing the Thermal Performance of the Heat Charging and Discharging Processes of Latent Heat Thermal Energy Storage Systems*
Authors: Zhang Yinping , Su Yan , Zhu Yingxin , Hu Xianxu
Published: July 2002

During melting of phase change materials (PCM) encapsulated in a container, the solid PCM sinks to the bottom or floats to the top of the container according to the gravitational force and buoyancy resulting from the difference between solid and liquid densities. Compared with the solidification process, the melting process has a quite different behavior. Although the heat transfer characteristics of melting processes in various typical kinds of containers have been studied, the general model for analyzing the thermal performance of both melting and solidification processes of latent heat thermal energy storage (LHTES) systems composed of PCM capsules has not been presented in the literature. The present paper describes such a model which can be used to analyze the instantaneous temperature distribution, instantaneous heat transfer rate, and thermal storage capacity of a LHTES system. For solidification, the model is validated with the results in the literature. The thermal performance during melting of a LHTES system composed of PCM spheres is analyzed as an example. The model is not limited to a specific system or a specific PCM, so it can be used to select and optimize system design and to simulate the thermal behavior of various typical LHTES systems.
Probabilistic Failure of a Cracked Submarine Pipeline Subjected to the Underwater Shock
Authors: Lam K. Y. , Zong Z. , Wang Q. X.
Published: July 2002

The failure of a cracked submarine pipeline subjected to the underwater explosion shock is probabilistically analyzed in this paper. A simple procedure is presented, in which the Monte Carlo method is used to estimate the bending stress distribution, and an analytical method is used to estimate the fracture failure probability. The results obtained from the present method are compared with those obtained from direct Monte Carlo simulations. Both are in good agreement. From the studies in this paper, it is concluded that the most dangerous case is that the crack is perpendicular to the tension stress. The influence of crack model uncertainty is significant. FOSM method is also used, which greatly underestimates the failure probabilities for the problem studied in this paper.
Kinematic Analysis and Synthesis of Deterministic 3-2-1 Locator Schemes for Machining Fixtures
Authors: Marin Rodrigo A. , Ferreira Placid M.
Published: July 2002

This paper addresses the problem of generating a well-conditioned, near-optimal deterministic 3-2-1 location scheme. Given are a workpart with identified planar datum faces, each with an associated convex region of admissible locator positions, and a set of disturbing twists (resulting from the processing operations on the workpart). First, screw theory is used to identify easily implementable necessary and sufficient conditions for deterministic positioning of the workpart in a 3-2-1 locator scheme. Next, the conditioning of a location scheme is studied and combinatorial algorithms are developed for synthesizing near-optimally conditioned locator schemes. Interesting decomposition and restrictions on the search space are identified to make the synthesis procedure efficient.
Designing the Dynamic Behavior of an Engine Suspension System Through Genetic Algorithms
Authors: Baldanzini Niccolo` , Caprioli Davide , Pierini Marco
Published: July 2002

This work presents an innovative approach to dynamic design that has the significant advantage of allowing the dynamic requirements to be specified from the earliest design stage. The method applies genetic algorithms to optimize the dynamic behavior of the engine-subframe system and its links to the chassis. The optimization minimizes the sum of the amplitudes of the forces transmitted to the chassis from each mounting, while complying with the static and dynamic constraints. The genetic algorithm was applied to a multibody system model of the engine-subframe system and its links to derive new, improved configurations.
A Numerical Investigation on the Volute/Diffuser Interaction Due to the Axial Distortion at the Impeller Exit
Authors: Gu Fahua , Engeda Abraham , Cave Mike , Di Liberti Jean-Luc
Published: July 2002

A numerical simulation is performed on a single-stage centrifugal compressor using the commercially available CFD software, CFX-TASCflow. The steady flow is obtained by circumferentially averaging the exit fluxes of the impeller. Three runs are made at the design condition and off-design conditions. The predicted performance is in agreement with experimental data. The flow details inside the stationary components are investigated, resulting in a flow model describing the volute/diffuser interaction at design and off-design conditions. The recirculation and twin vortex structure are found to explain the volute loss increase at lower and higher mass flows, respectively.
Structural Modification for the Assignment of Zeros Using Measured Receptances
Authors: Mottershead J. E.
Published: July 2002

In many engineering applications it is desirable to assign the zeros of point or cross receptances to particular frequencies. This means that at the chosen coordinate no vibration will be experienced at those frequencies. It is shown how such an objective can be achieved by means of passive stiffness, damping, and mass modifications to the structure. The frequency responses of a subsidiary eigenvalue problem, the eigenvalue problem of the zeros, are determined in order that the methods of inverse structural modification may be applied. The technique requires only a small number of measurements from the structure in its unmodified condition. Numerical and physical experiments are carried out to illustrate the application of the method.
Tool Point Frequency Response Prediction for High-Speed Machining by RCSA
Authors: Schmitz Tony L. , Davies Matthew A. , Kennedy Michael D.
Published: July 2002

The implementation of high-speed machining for the manufacture of discrete parts requires accurate knowledge of the system dynamics. We describe the application of receptance coupling substructure analysis (RCSA) to the analytic prediction of the tool point dynamic response by combining frequency response measurements of individual components through appropriate connections. Experimental verification of the receptance coupling method for various tool geometries (e.g., diameter and length) and holders (HSK 63A collet and shrink fit) is given. Several experimental results are presented to demonstrate the practical applicability of the proposed method for chatter stability prediction in milling.
Failure Analysis of Tubular Hydroforming
Authors: Xia Z. C.
Published: July 2002

A mathematical analysis of failure developments for tubular hydroforming under combined internal pressure and end feeding is presented in this paper. Under considerations are two distinct failure modes, namely, the bursting and the wrinkling. Bursting is an instability phenomenon where the tube can’t sustain any increased tensile loading. Splitting usually follows due to extreme deformations in the bursting area. Wrinkling is due to high compression load, which deteriorates the quality of the final product. The deformation theory of plasticity is utilized in this study and the material anisotropy is accounted for in the constitutive model. The governing equations for the onset of both failure modes are established. The results are presented as Hydroforming Failure Diagram in the End Feed—Internal Pressure space. A parametric study of the failure criteria for a variety of materials and process parameters is performed. It is shown that the material anisotropy plays a significant role. The results provide guidelines for product designers and process engineers for the avoidance of failure during hydroforming. The validity and applicability of current study are also discussed.
Flow and Heat Transfer in an Industrial Rotor-Stator Rim Sealing Cavity
Authors: Mirzamoghadam A. V. , Xiao Z.
Published: July 2002

Flow and heat transfer in the row-1 upstream rotor-stator disk cavity of a large 3600-rpm industrial gas turbine was investigated using an integrated approach. A two dimensional axisymmetric transient thermal analysis using aeroengine-based correlations was performed to predict the steady-state metal temperatures and hot running seal clearances at ISO rated power condition. The cooling mass flow and the flow pattern assumption for the thermal model were obtained from the steady-state two dimensional axisymmetric CFD study. The CFD model with wall heat transfer was validated using cavity steady-state air temperatures and static pressures measured at inlet to the labyrinth seal and four cavity radial positions in an engine test which included the mean annulus static pressure at hub radius. The predicted wall temperature distribution from the matched thermal model was used in the CFD model by incorporating wall temperature curve-fit polynomial functions. Results indicate that although the high rim seal effectiveness prevents ingestion from entering the cavity, the disk pumping flow draws air from within the cavity to satisfy entrainment leading to an inflow along the stator. The supplied cooling flow exceeds the minimum sealing flow predicted from both the rotational Reynolds-number-based correlation and the annulus Reynolds number correlation. However, the minimum disk pumping flow was found to be based on a modified entrainment expression with a turbulent flow parameter of 0.08. The predicted coefficient of discharge (Cd) of the industrial labyrinth seal from CFD was confirmed by modifying the carryover effect of a correlation reported recently in the literature. Moreover, the relative effects of seal windage and heat transfer were obtained and it was found that contrary to what was expected, the universal windage correlation was more applicable than the aeroengine-based labyrinth seal windage correlation. The CFD predicted disk heat flux profile showed reasonably good agreement with the free disk calculated heat flux. The irregular cavity shape and high rotational Reynolds number (in the order of 7×107) leads to entrance effects that produce a thicker turbulent boundary layer profile compared to that predicted by the 1/7 power velocity profile assumption.
Numerical Simulation of Engagement of a Wet Clutch With Skewed Surface Roughness
Authors: Gao H. , Barber G. C. , Shillor M.
Published: July 2002

The engagement of a wet clutch with skewed surface roughness was investigated. A Weibull asperity height distribution rather than a Gaussian one was utilized in the asperity contact pressure model. The combined effects of surface roughness and skewness on the friction coefficient were studied for new, run-in and glazed wet friction materials. The results show that the engagement time predicted by the Weibull distribution is greater than that obtained using the Gaussian distribution. A torque spike at the beginning of engagement occurs using the Weibull distribution by taking the skewness into account. A positively sloped curve of friction coefficient versus velocity can reduce the torque increase near the end of the engagement. The strain value at the end of engagement obtained by including the skewness is lower than that predicted by excluding it. The surface topography and the friction characteristics change with the engagement wear and thermal glazing. The torque response and the phase plane are presented for the run-in and the glazed wet friction materials as a function of surface roughness, skewness, and friction characteristic.
On the Solution of Multidimensional Inverse Heat Conduction Problems Using an Efficient Sequential Method
Authors: Park H. M. , Jung W. S.
Published: July 2002

An efficient real-time scheme is developed to estimate the unsteady, spatially varying wall heat flux in a two-dimensional heat conduction system from the temperature measurement inside the domain. The algorithm is based on the Kalman filtering and the Karhunen-Loe`ve Galerkin procedure. Although the employment of the Kalman filtering technique allows the derivation of a set of sequential estimation equations, the real-time implementation of these equations is never feasible due to the tremendous requirement of computer time and memory. In the present scheme, this difficulty is circumvented by means of the Karhunen-Loe`ve Galerkin procedure that reduces the governing partial differential equation to a minimal set of ordinary differential equations. The performance of the present technique of inverse heat conduction problems is evaluated by several numerical experiments, and it is found to be very accurate as well as efficient.
Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade
Authors: Schreiber Heinz-Adolf , Steinert Wolfgang , Ku¨sters Bernhard
Published: July 2002

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4 percent. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested, the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40 percent of chord. For high turbulence levels (Tu>3 percent) and high Reynolds numbers, the transition region moves upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably; at Tu=4 percent, bypass transition is observed near 7–10 percent of chord. Experimental results are compared to theoretical predictions using the transition model, which is implemented in the MISES code of Youngren and Drela. Overall, the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.
An Integrated Time-Domain Aeroelasticity Model for the Prediction of Fan Forced Response due to Inlet Distortion
Authors: Bre´ard C. , Vahdati M. , Sayma A. I. , Imregun M.
Published: July 2002

The forced response of a low aspect-ratio transonic fan due to different inlet distortions was predicted using an integrated time-domain aeroelasticity model. A time-accurate, nonlinear viscous, unsteady flow representation was coupled to a linear modal model obtained from a standard finite element formulation. The predictions were checked against the results obtained from a previous experimental program known as “Augmented Damping of Low-aspect-ratio Fans” (ADLARF). Unsteady blade surface pressures, due to inlet distortions created by screens mounted in the intake inlet duct, were measured along a streamline at 85 percent blade span. Three resonant conditions, namely 1F/3EO, 1T & 2F/8EO and 2S/8EO, were considered. Both the amplitude and the phase of the unsteady pressure fluctuations were predicted with and without the blade flexibility. The actual blade displacements and the amount of aerodynamic damping were also computed for the former case. A whole-assembly mesh with about 2,000,000 points was used in some of the computations. Although there were some uncertainties about the aerodynamic boundary conditions, the overall agreement between the experimental and predicted results was found to be reasonably good. The inclusion of the blade motion was shown to have an effect on the unsteady pressure distribution, especially for the 2F/1T case. It was concluded that a full representation of the blade forced response phenomenon should include this feature.
Viscous Dissipation in Finite Thin-Gap Couette Devices
Authors: Wendl Michael C. , Agarwal Ramesh K.
Published: July 2002

An analytical solution is reported for the temperature distribution in finite span thin-gap Couette devices which accounts for viscous dissipation. Taken in conjunction with an established solution for the stable velocity profile, this result describes the standard experimental configuration where no external heat fluxes are applied. We discuss physical aspects as well as conditions for which classical one-dimensional theory should be replaced by the present result.
Influence of Irradiation Time, Particle Sizes, and Initial Moisture Content During Microwave Drying of Multi-Layered Capillary Porous Materials
Authors: Ratanadecho P. , Aoki K. , Akahori M.
Published: July 2002

The drying of capillary porous materials by microwave with rectangular waveguide has been investigated numerically and experimentally. Most importantly, it focuses on the investigation of the distributions of electric field, temperature and moisture profiles within the capillary porous materials. The measurements of temperature and moisture distributions within the capillary porous materials provide a good basis for understanding of the microwave drying process. The mathematical model gives qualitatively comparable trends to experimental data. The calculations of electromagnetic fields inside the rectangular waveguide and the capillary porous materials show that the variation of particle sizes and initial moisture content changes the degree of penetration and rate of microwave power absorbed within the sample. Further, the small particle size leads to much higher capillary pressure resulting in a faster drying time.
Electromechanical Effects of a Screw Dislocation Around a Finite Crack in a Piezoelectric Material
Authors: Kwon J. H. , Lee K. Y.
Published: July 2002

The interaction between a screw dislocation and a finite crack in an unbounded piezoelectric medium is studied in the framework of linear piezoelectric theory. A straight screw dislocation with the Burgers vector, which is normal to the isotropic basal plane, positioned around the tip of a finite crack is considered. In addition to having a discontinuous electric potential across the slip plane, the dislocation is assumed to be subjected to a line force and a line charge at the core. The explicit solution is derived by means of complex variable and conformal mapping methods. All field variables such as stress, strain, electric field, electric displacement near the crack tip, and the forces on a screw dislocation, the field intensity factors, and the energy release rate are determined under the combined out-of-plane mechanical and in-plane electrical loads. Also, the effects of screw dislocation and electrical loads are numerically analyzed.
On Pressure Distributions of Drum Brakes
Authors: Huang Yuan Mao , Shyr J. S.
Published: July 2002

Based on the assumptions that there is perfect contact at the interface between the brake drum and the lining plates, the friction coefficient is constant, the thermal effect is neglected, and the brake drum is a rigid body, the pressure distributions of drum brakes were studied by using the boundary element method. The constant element is used in the two-dimensional model of the drum brake for simplicity and economy. The friction force versus the effective lift at the actuation edge and the location of the maximum pressure are compared and indicate a good correlation with existing data. The effects of the Young’s modulus of elasticity of the metal shoe, the arc lengths of the metal shoe and lining plate, the location, the thickness, the friction coefficient, the Young’s modulus of elasticity of the lining plate, and the angle of actuation force on the pressure distributions were then studied. By selecting proper values of these parameters, a drum brake can be designed to have a more uniform pressure distribution and a longer life.
Multiphase Mechanics of Capsule Formation in Tumors
Authors: Lubkin S. R. , Jackson T.
Published: July 2002

The presence of a capsule around a tumor is known to be correlated with benign status, and the absence of a capsule often has negative implications for patient prognosis. A mechanical description is presented of the growth of a tumor and the resulting deformations of surrounding normal tissue. A mathematical model of the mechanics is analyzed using physical parameters measured in vivo and in vitro. The model has only three dimensionless parameters, and its results are very robust with respect to parameter variation. We show that the presence of contractility in the surrounding tissue, corresponding to a host defense, can make an existing capsule denser and constrain the tumor better, but cannot be responsible for the observed pressure gradients in encapsulated tumors. Some implications for treatment are discussed.
Mechanistic Model for Tapping Process With Emphasis on Process Faults and Hole Geometry
Authors: Dogra Ajit Pal S. , Kapoor Shiv G. , DeVor Richard E.
Published: July 2002

A mechanistic approach for modeling the tapping process is presented. A methodology for computing chip load is developed for an arbitrary tap geometry. The mechanics of cutting for tapping is analyzed, considering it as an oblique cutting phenomenon. The effects of tap geometry (tap diameter, thread pitch, number of flutes, flute helix angle, tooth rake angle, and thread type), workpiece geometry (hole diameter and hole depth), process parameters (spindle speed and tap penetration depth), and process faults (tap runout, axis misalignment, and drilled hole geometry) are incorporated in the model. The model is calibrated using drilling experiments and is validated by comparing experimental tapping results for aluminum 319, aluminum 356, and gray cast iron. In most cases, the tapping forces were predicted within 10 percent of the experimental values.
An Investigation of Flow Fields Over Multi-Element Aerofoils
Authors: Maddah S. R. , Bruun H. H.
Published: July 2002

This paper presents results obtained from a combined experimental and computational study of the flow field over a multi-element aerofoil with and without an advanced slat. Detailed measurements of the mean flow and turbulent quantities over a multi-element aerofoil model in a wind tunnel have been carried out using stationary and flying hot-wire (FHW) probes. The model configuration which spans the test section 600mm×600mm, is made of three parts: 1) an advanced (heel-less) slat, 2) a NACA 4412 main aerofoil and 3) a NACA 4415 flap. The chord lengths of the elements were 38, 250 and 83 mm, respectively. The results were obtained at a chord Reynolds number of 3×105 and a free Mach number of less than 0.1. The variations in the flow field are explained with reference to three distinct flow field regimes: attached flow, intermittent separated flow, and separated flow. Initial comparative results are presented for the single main aerofoil and the main aerofoil with a nondeflected flap at angles of attacks of 5, 10, and 15 deg. This is followed by the results for the three-element aerofoil with emphasis on the slat performance at angles of attack α=10, 15, 20, and 25 deg. Results are discussed both for a nondeflected flap δf=0deg and a deflected flap δf=25deg. The measurements presented are combined with other related aerofoil measurements to explain the main interaction of the slat/main aerofoil and main aerofoil/flap both for nondeflected and deflected flap conditions. These results are linked to numerically calculated variations in lift and drag coefficients with angle of attack and flap deflection angle.