Signie Cantly Research Articles

Design Optimization of Springback in a Deepdrawing Process

The design optimization of springback in a deepdrawing process is proposed to control the e nal shape of the workpiece. The manufacturing process design problem is formulated to minimize the difference between the shape of the desired workpiece geometry and the e nal analysis result after elastic springback. The rigid die shape and the workpiece thickness are treated as design variables. A nonlinear structural problem that includes e nitedeformation elastoplasticity withfrictional contactissolved usinga mesh-freemethod in which thestructural domain is discretized by a set of particles. Continuum-based design sensitivity analysis is carried out to obtain gradient information for the optimization efe ciently. The accuracy of the sensitivity result is compared with the e nite difference result with excellent agreement. The optimum deepdrawing process signie cantly improves the quality of the e nal product. ESPITE signie cant simulation and design capability developments in modern technology, gaps still remain between the simulation-based design and the manufacturing process itself. One major reason for these gaps is the lack of efe cient and accurate numerical methods in the design process. First, accurate numerical methods have to be used to simulate manufacturing processes, and these methods must take into account large deformations, complicated constitutive relations, and a sliding contact between workpiece and die. Second, efe cient numerical methods have to be used to make the deepdrawing optimization process practical. It is the purpose of this paper to demonstrate that these two obstacles can be resolved by using accurate numerical methods and an efe cient design sensitivity analysis (DSA). The deepdrawingprocessinvolvesa large degree ofplastic deformation and rigid-body rotations, as well as a complicated contact between workpiece and die. Many simplie ed approaches have been proposedinsimulationanddesignofthemetalformingprocess.One

Liver Fibrosis: What's the Beginning of Autonomic Deficit?

Histologic diagnoses were made using standard criteria and two independent observers scored all samples using the Scheuer staging system (3). We distinguished between patients affected by moderate e brosis (scores 2 and 3) and those affected by severe e brosis, corresponding to cirrhosis (score 4). Cardiac index was determined using pulsed-wave Doppler echocardiography (Hewlett-Packard Sonos 2000, Andover, Mass., USA). Peripheral vascular resistance (PVR) was calculated as the mean arterialpressure/cardiacoutput £80.Heartratevariabilitywas evaluated in the frequency domain using appropriate software (Rozinn Electronics H4W 3.6F, Glendale, N.Y., USA). A series of consecutive 5-min intervals was calculated from the Holter ECG as a function of beat numbers. Power spectral analysis of the intervals between adjacent R waves of the electrocardiogram (RR) was performed using the fast Fourier transform mathematical function (5). Low frequency (LF; 0.04‐0.15 Hz) and high frequency (HF; 0.15‐0.40 Hz) spectral powers and the ratio of LF to HF (LF/HF) were calculated and expressed in normalized units (nU). The recordings were obtained with 5 min in the supine position and 5 min in passive head-up tilt (70°). Statistical analysis was performed using an appropriate t test. P values lower than 0.05 were regarded as statistically signie cant. None of the patients included in this study, with either chronic viral hepatitis or with cirrhosis, showed evidence of hyperdynamic circulation. Cardiac index and peripheral vascular resistances were not signie cantly different from those of healthy subjects. Moreover, our results showed no differences between patients and controls in mean systolic and diastolic arterial pressures, either in the supine or in the tilt position. The power spectral analysis showed the occurrence of a

Numerical Simulation of Three-Dimensional Augmented Burnett Equations for Hypersonic Flow

For computation of hypersonic e owe elds about space vehicles in low Earth orbits, where the local Knudsen numbers Kn lie in the continuum-transition regime, a set of extended three-dimensional hydrodynamic equations is required that is more accurate than the Navier ‐Stokes equations and computationally more efe cient than the direct simulation Monte Carlo (DSMC) computations. The three-dimensional augmented Burnett equations are derived from the Chapman ‐Enskog expansion of the Boltzmann equation to O(Kn 2) and adding the augmented terms (linear third-order super Burnett terms with coefe cients determined from linearized stability analysis to ensure stability of the augmented Burnett equations to small wavelength disturbances ). The three-dimensional augmentedBurnettequationsareappliedtocomputethehypersonicblunt-bodye owsforvariousrangeofKnudsen numbers (0:0884 < ‐ Kn < ‐ 0:227) and Mach numbers (10 < ‐ M < ‐ 25:3). The computational results are compared with the Navier ‐Stokes solutions, the existing augmented Burnett solutions, and the available DSMC results. The comparisons show that the difference between the Navier ‐Stokes and the augmented Burnett solutions is very small (less than 3% for the shock layer thickness ) at Knudsen numbers less than 0.01; the difference becomes signie cant as the Knudsen number increases. The comparisons also show that the augmented Burnett solutions are signie cantly closer to the DSMC results for the temperature distributions in the continuum-transition regime than the Navier ‐Stokes calculations.

Influence of Compressor Exit Conditions on Combustor Annular Diffusers Part II: Flow Redistribution

In gas-turbine engines the velocity of air, issuing from the compressor, must be reduced in order to permit effective operation of the downstream combustor. This is partly achieved by locating an annular diffuser behind the compressor outlet guide vanes (OGVs) and, in modern systems, the inlet of this diffuser is usually located at the trailing edge of the blade row. This paper is concerned with some of the interactions that occur between these components and, in particular, the e ow redistribution that occurs along the diffuser length due to the e ows generatedbytheOGVbladepassageandupstreamrotor.Amainlyexperimentalinvestigationhasbeenundertaken, on a fully annular facility, which incorporates a single-stage axial e ow compressor and simulated e ame tube. In addition, immediately downstream of the OGV row a constant-area passage, ordiffusers of area ratio 1.45 or 1.60, can be incorporated. The OGV blade row produces a proe le that, as a result mainly of the blade wakes, contains an excess of kinetic energy relative to that of a uniform proe le. The mixing out of these wakes therefore enhances the pressure rise within the downstream diffuser. Measured mean velocity data are used to determine the path of streamlinesalongeachdiffuserandindicateregionswherehigh-energye uidisbeingconvected,towardeachcasing, and low-energy boundary layere uidisbeing removed.Thisisbecauseoftheremnantsofthee owsgeneratedwithin each OGV passage. The mean momentum equation along each diffuser is then used to indicate that such e ows signie cantly offset the changes in momentum, within each boundary layer, that are associated with the applied pressure gradient. Such effects are therefore thought signie cant in terms of reducing the boundary-layer growth and delaying e ow separation from the casings.

Fuel Regression Rate in Hydroxyl-Terminated-Polybutadiene/Gaseous-Oxygen Hybrid Rocket Motors

The results of a systematic experimental investigation on the methods of enhancing the regression rate in hydroxyl-terminated polybutadiene (HTPB) fuel used in an HTPB/gaseous oxygen hybrid motor are presented. The effects of the addition of ammonium perchlorate (AP) or aluminum in the fuel, the variation of oxidizer ‐fuel ratio, and the variation of characteristic dimensions of fuel grain are presented. For the extents of the parametric variations considered, while the addition of AP and/or Al and the reduction of grain port diameter enhance the regression rate, the effect due to the latter is the most signie cant one. Furthermore, the regression rate increases along theaxis, and it becomes essentially constant in the port region corresponding to a fuel-rich composition. The possible physical processes for all of these behaviors are discussed. The experimentally obtained exponents of the variables for regression rate (oxidizer mass e ux and port diameter ) are found to be signie cantly different from those of the conventional theory. The similarity between the fuel regression rate equation used in solid-fuel ramjet and that obtained in hybrid motor is discussed.

Quantitative Effects of Projectile-Launch Tube Wall Friction on Ballistic Range Operation

Theoretical and experimental studies are conducted on the quantitative evaluation of a friction force at the interface between a projectile and the launch tube wall in a ballistic range. From a mechanical balance relation applied to the projectile, the friction force is expressed theoretically as a function of the net acceleration of the projectile. With this formulation, experimentally measured in-bore projectile velocity proe les obtained using a velocity interferometer system for any ree ector are well interpreted. If the initial projectile motion is signie cantly suppressed by the friction force while the burning rate of the propellant remains signie cant, the base pressure becomes much higher than that with a negligibly small friction force, thereby enhancing the net acceleration. However, if the projectile-tube e t is excessively high, the main function of the friction force is to decrease the muzzle velocity.

SONG QUALITY DOES NOT INDICATE MALE PARENTAL ABILITIES IN THE PIED FLYCATCHER FICEDULA HYPOLEUCA

Summary Femalepied e ycatchers Ficedula hypoleuca prefer to mate with males having complex songs, but the benee ts of this preference are not known. One potential benee t might be that males with complex songs are of higher quality and thus contribute more to the feeding of the brood than males with simple songs. We tested this by recording the feeding rate of males in two different populations in Norway. Neither the feeding rate nor the male ¢s contribution to the feeding relative to his mate correlated signie cantly with song complexity (27 and 21 males studied, respectively). However, male feeding rate may beine uenced by femalefeeding effort. Therefore, we also recorded body mass change of 13-day-old nestlings of 30 males during a period of eight hours of enforced female absence. The males were matched in pairs according to brood size and, if necessary, nestlings were exchanged between broods to reduce initial differences in body mass. Both males in each pair were treated on the same day. The change in brood mass did not differ signie cantly between males with complex and simple songs, and the latter males did not lose more body mass than the former males during female absence. Thus, we conclude that female pied e ycatchers mated with males having large song repertoires do not seem to benee t in terms of increased feeding effort from their mates. 2) Helge Rinden is unfortunately not with us any longer. He had a tragic accident in the nature

Trim and Floor Influence on Vibrational Response of an Aircraft Fuselage Model

The ine uence of the interior trim and the e oor partition on the vibratory response of the physical model of an aircraft fuselage model was investigated experimentally. The one-third scale model faithfully replicated the salient structural features of a rear-engine aircraft fuselage. Detailed modal analysis of the green fuselage, i.e., the bare fuselage skin without any e oor, trim, or lining, was e rst performed. The effects of adding a honeycomb e oor partition, a sound-absorbing blanket, and a thin plastic interior lining on the modal parameters of the structure were then determined. It was found that the addition of the sound-absorbing blanket signie cantly increased the structure’ s modal damping coefe cients for its e rst e ve modes of resonance. Notable changes in the structural responseat higher frequencieswere also observed. These results strongly suggest, in agreement with recent studies reported in the literature, that sound-absorbing blankets do add signie cant damping to the vibration response of the structure (in addition to absorbing sound energy from the cabin interior ). These damping properties may be used advantageously for the optimal design of skin-damping aircraft noise-control treatments for minimal added weight, and minimal cost.

Strategies for Pulsed Detonation Engine Performance Optimization

The pulsed detonation engine (PDE) concept is systematically analyzed with respect to design variations, and the potential performance is measured from computational e uid dynamics simulations. Variations in cone guration geometry are examined e rst through single-pulse computations. These show that the presence of a nozzle can greatly affect the performance of the PDE by increasing thrust delivery during the ignition phase. It is further shown that it is not necessary to e ll the entire tube with a fuel ‐ air mixture and that signie cant gains in specie c impulse can be obtained by appropriate fueling strategies. Multicycle computations are performed next and the effect of cycling parameters is studied. It is shown that the cycling frequency can be signie cantly increased by selecting the pressure parameters and the extent of refueling. We also show that multicycle performance can be very different from the single-pulse estimates, and that it is not possible to optimize separately the ignition phase from the injection phase. Finally, the question of open-end initiation is examined and a comparison between quasi-one-dimensional and two-dimensional computations is performed.

Numerical Study of Nozzle Exit Condition Effects on Jet Development

Numerical predictions of the ine uence of nozzle exit conditions on the development of an ideally expanded supersonic rectangular jet areperformed. The effects of theseconditions on the jet’ s development have been found to be signie cant in experimental investigations. A model for the initial conditions is developed. A higher-order accurate e nite difference algorithm for the solution of the full three-dimensional Navier ‐Stokes equations is used to generate results that isolate the impacts of excitation amplitude, modal excitation, and corner vortices on the jet character. Time-averaged, cross-correlation, and cross-spectral data are gathered from the simulation and compared to experimental data. The results indicate that, over the range of operating conditions considered here, the excitation amplitude does not signie cantly alter the jet development. The corner vortices, although prescribed ina sensethatshouldanticipateaxisswitching (asdeterminedby experimentalsubsonicresults ), arefound to delay it. This appears to be caused by the dominance of e ow instabilities in supersonic jets and the observed tendency of the corner vortices to reduce the mixing associated with this instability. Finally, independent of modal excitation, the lowest-order modes (of the large-scale turbulence structure ) are found to consist of a combination of e apping in the minor axis plane with varicose motion in the major axis plane.

Multidimensional Modeling of Fuel Effects and Split Injections on Diesel Engine Cold-Starting

A computational model has been developed for describing multicomponent fuel vaporization and ignition in diesel engines and was implemented in the KIVA-II computational e uid dynamics code. The model has been applied to understand diesel engine cold-starting and the parameters that signie cantly ine uence this phenomena. Typical diesel fuels are blends of various fuels species, i.e., multicomponent. Thus, the original single-component fuel vaporization model in KIVA-II was replaced by a multicomponent fuel vaporization model. Necessary modie cations were carried out in other spray submodels that describe droplet breakup and coalescence to account for multicomponent fuels. The autoignition process was modeled using a modie ed multistep kinetics Shell ignition model to account for fuel composition effects. The improved model was applied to simulate cold-starting in diesel engines. The effects of fuel residual left from previous cycles, injection timing, and duration were studied. Split injections, where a small pilot injection was introduced during the compression stroke, were found to have a signie cant and benee cial effect on cold-starting.