Ring Gaps Research Articles

Fluid–structure interaction modeling of clusters of spacecraft parachutes with modified geometric porosity

To increase aerodynamic performance, the geometric porosity of a ringsail spacecraft parachute canopy is sometimes increased, beyond the "rings" and "sails" with hundreds of "ring gaps" and "sail slits." This creates extra computational challenges for fluid---structure interaction (FSI) modeling of clusters of such parachutes, beyond those created by the lightness of the canopy structure, geometric complexities of hundreds of gaps and slits, and the contact between the parachutes of the cluster. In FSI computation of parachutes with such "modified geometric porosity," the flow through the "windows" created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the Homogenized Modeling of Geometric Porosity (HMGP), which was introduced to deal with the hundreds of gaps and slits. The flow needs to be actually resolved. All these computational challenges need to be addressed simultaneously in FSI modeling of clusters of spacecraft parachutes with modified geometric porosity. The core numerical technology is the Stabilized Space---Time FSI (SSTFSI) technique, and the contact between the parachutes is handled with the Surface-Edge-Node Contact Tracking (SENCT) technique. In the computations reported here, in addition to the SSTFSI and SENCT techniques and HMGP, we use the special techniques we have developed for removing the numerical spinning component of the parachute motion and for restoring the mesh integrity without a remesh. We present results for 2- and 3-parachute clusters with two different payload models.

Fluid–structure interaction modeling of ringsail parachutes with disreefing and modified geometric porosity

Fluid---structure interaction (FSI) modeling of parachutes poses a number of computational challenges. These include the lightness of the parachute canopy compared to the air masses involved in the parachute dynamics, in the case of ringsail parachutes the geometric porosity created by the construction of the canopy from "rings" and "sails" with hundreds of "ring gaps" and "sail slits," in the case of parachute clusters the contact between the parachutes, and "disreefing" from one stage to another when the parachute is used in multiple stages. The Team for Advanced Flow Simulation and Modeling (T?AFSM) has been successfully addressing these computational challenges with the Stabilized Space---Time FSI (SSTFSI) technique, which was developed and improved over the years by the T?AFSM and serves as the core numerical technology, and a number of special techniques developed in conjunction with the SSTFSI technique. The quasi-direct and direct coupling techniques developed by the T?AFSM, which are applicable to cases with nonmatching fluid and structure meshes at the interface, yield more robust algorithms for FSI computations where the structure is light. The special technique used in dealing with the geometric complexities of the rings and sails is the homogenized modeling of geometric porosity (HMGP), which was developed and improved in recent years by the T?AFSM. The surface-edge-node contact tracking (SENCT) technique was introduced by the T?AFSM as a contact algorithm where the objective is to prevent the structural surfaces from coming closer than a minimum distance in an FSI computation. The recently-introduced conservative version of the SENCT technique is more robust and is now an essential technology in the parachute cluster computations carried out by the T?AFSM. As an additional computational challenge, the parachute canopy might, by design, have some of its panels and sails removed. In FSI computation of parachutes with such "modified geometric porosity," the flow through the "windows" created by the removal of the panels and the wider gaps created by the removal of the sails cannot be accurately modeled with the HMGP and needs to be actually resolved during the FSI computation. In this paper we focus on parachute disreefing, including the disreefing of parachute clusters, and parachutes with modified geometric porosity, including the reefed stages of such parachutes. We describe the additional special techniques we have developed to address the challenges involved and report FSI computations for parachutes and parachute clusters with disreefing and modified geometric porosity.

Fluid–structure interaction modeling and performance analysis of the Orion spacecraft parachutes

AbstractWe focus on fluid–structure interaction (FSI) modeling and performance analysis of the ringsail parachutes to be used with the Orion spacecraft. We address the computational challenges with the latest techniques developed by the T★AFSM (Team for Advanced Flow Simulation and Modeling) in conjunction with the SSTFSI (Stabilized Space–Time Fluid–Structure Interaction) technique. The challenges involved in FSI modeling include the geometric porosity of the ringsail parachutes with ring gaps and sail slits. We investigate the performance of three possible design configurations of the parachute canopy. We also describe the techniques developed recently for building a consistent starting condition for the FSI computations, discuss rotational periodicity techniques for improving the geometric‐porosity modeling, and introduce a new version of the HMGP (Homogenized Modeling of Geometric Porosity). Copyright © 2010 John Wiley & Sons, Ltd.

4812 ピストンリング合口部からのオイル上がりに関する研究(G07-2 エンジンシステム(2),G07 エンジンシステム)

Oil consumption is caused by the evaporation of oil film left on the cylinder wall or by the combustion of oil flowing out to the combustion camber through the piston ring gap. This study focusedd on oil outflow through the piston ring gap under a high vacuum operating condition in the intake manifold. Moreover, the oil film was visualized to determine oil film thickness. As a result, the oil flowed out steadily from the piston ring gaps at this operating condition, and moved through the surface of the top land to the combustion chamber. It was also found that the amount of oil outflow and the oil consumption were affected by the end gap design of the top ring.

Cassini Drops In

### Contents #### Viewpoints How Long Is the Day on Saturn? A. Sanchez-Lavega [Saturn's Variable Magnetosphere][1] T. I. Gombosi and K. C. Hansen Research Articles and Reports Cassini Imaging Science: Initial Results on Saturn's Rings and Small Satellites C. C. Porco et al. Cassini Imaging Science: Initial Results on Phoebe and Iapetus C. C. Porco et al. [Cassini Imaging Science: Initial Results on Saturn's Atmosphere][2] C. C. Porco et al. [Temperatures, Winds, and Composition in the Saturnian System][3] F. M. Flasar et al. Ultraviolet Imaging Spectroscopy Shows an Active Saturnian System L. W. Esposito et al. Radio and Plasma Wave Observations at Saturn from Cassini's Approach and First Orbit D. A. Gurnett et al. [Oxygen Ions Observed Near Saturn's A Ring][4] J. H. Waite Jr. et al. Composition and Dynamics of Plasma in Saturn's Magnetosphere D. T. Young et al. Cassini Magnetometer Observations During Saturn Orbit Insertion M. K. Dougherty et al. Dynamics of Saturn's Magnetosphere from MIMI During Cassini's Orbital Insertion S. M. Krimigis et al. [Composition of Saturnian Stream Particles][5] S. Kempf et al. A fter 23 years of limited Earth-based observations, a spacecraft has returned to Saturn and, unlike the Pioneer 11, Voyager 1, and Voyager 2 flybys from 1979 to 1981, Cassini intends to stay awhile, at least 4 years or 74 orbits, to collect information about the planet's atmosphere, its elusive magnetosphere and ionosphere, the rings, and the moons. This special issue covers the observations made during approach (December 2003 to June 2004), during the ring plane crossing and orbit insertion (1 July 2004), and the first few orbits (July through December 2004). The Cassini spacecraft (with 12 instruments) with its companion, the Huygens probe (with 6 instruments), was launched from Cape Canaveral on 15 October 1997. The massive mission, about 5650 kg, needed three major gravity assists and 7 years to reach Saturn. It looped around the Sun twice, boosting its orbit for a final gravity assist from a close flyby of Jupiter in December 2000. During the Jupiter flyby, the Cassini instruments were turned on to measure properties of the jovian system, with spectacular results. After the flyby, Cassini began its fall toward the ringed planet. On 11 June 2004, Cassini flew within 2071 km of the outermost moon of Saturn, Phoebe: its closest and only approach to this satellite. Phoebe is covered with craters signifying an ancient surface and consists of a mixture of rock and water ice with an unexpectedly high porosity. On 1 July 2004 Cassini fired its main rocket engines to slow down the spacecraft, so it could drop into a stable orbit. As the spacecraft was slowing down, it glided over the rings and obtained unprecedented details of their structure and chemistry during the only close ring plane crossing of the entire mission. New moons were found within ring gaps; new rings were mapped; fine-scale ring structures were puzzled over; clouds of oxygen suggested tenuous ring atmospheres; and other data suggested that the rings formed from recycled bits of the moons, making the rings second- or perhaps even third-generation offspring of their parent planet. During the ring plane crossing, Cassini also made its closest approach to Saturn, coming within 18,000 km of the gas giant. Before, during, and after this close approach, instruments tracked lightning associated with storms, clouds, vertical wind shears, and thermal variations in the atmosphere. These observations enigmatically imply that Saturn's rotation rate has slowed by about 6 min since 1981. Saturn's atmosphere is richer in carbon than Jupiter's atmosphere, which is consistent with planet formation by core accretion. A radiation belt was discovered inside of the D ring, the external magnetic field has changed, the current sheet within the magnetosphere is thinner and more extended, and ion cyclotron waves indicate a dynamic plasma. After Cassini's closest approach to Saturn, the spacecraft dropped down through the large gap between the F and the G rings into a stable orbit. The size and angle of this orbit will change over time to allow Cassini to visit many moons and sample the rest of the saturnian system to develop a more complete three-dimensional model of the system's dynamics. Cassini plans to do more than drop by; it will stay awhile. [1]: /lookup/doi/10.1126/science.1108226 [2]: /lookup/doi/10.1126/science.1107691 [3]: /lookup/doi/10.1126/science.1105806 [4]: /lookup/doi/10.1126/science.1105734 [5]: /lookup/doi/10.1126/science.1106218

Stress Development in Wet Filament Wound Pipes

A computer based process model for wet filament winding has been developed. A software supplied by Stanford University has been modified for the numerical simulation. The model has been verified with manufacturing of glass fiber pipes including the industrially common case of pipes with mixed angle lay-up. Resin pressure in the composite during winding was measured and found to be relatively low supporting the assumption that it can be neglected for this process. Calculated final fiber fraction distribution agrees well with measured values on cured pipes. The model shows that fiber fraction is changed significantly during the winding stage due to compression forces. Mechanical and total strain measurements generally show good agreement with calculations. Analysis of ring gaps indicate that residual stresses are dominated by other effects than matrix shrinkage for the investigated parameter combination.

Paracellular barrier and junctional protein distribution depend on basolateral extracellular Ca 2+ in cultured epithelia

The polarised nature of the increase in paracellular permeability induced by Ca 2+-chelation with EGTA was investigated in several cultured epithelial cell lines. In strain I MDCK cells (canine kidney cells), a marked decrease (> 90%) in transepithelial electrical resistance ( R T) and increase in mannitol and inulin permeabilities were only observed after addition of EGTA (for 4 h) to either basolateral (basal) or both (apical + basal) bathing solutions; apical Ca 2+-chelation resulted in significant smaller changes (∼ 30%) in these variables. The increase in paracellular permeability upon basal EGTA addition was significantly lower than that produced by simultaneous apical and basal addition of 2 mM EGTA. A higher concentration of EGTA (20 mM) did not significantly eliminate this difference in potency between basal and apical + basal Ca 2+-chelation. The polarised Ca 2+-dependence of the paracellular barrier was associated with polarised effects on the junctional/cytoskeletal protein distribution. Basal or apical + basal EGTA addition induced substantial internalisation of uvomorulin with some cellular redistribution of the perijunctional actin ring and desmosomes and gaps in ZO-1 location between adjacent cells. In addition, polarised Ca 2+-dependence of the paracellular barrier (assessed by measuring R T) was observed also in strain II MDCK and two human adenocarcinoma intestinal cell lines, Caco-2 and HCT-8, demonstrating generality of the phenomenon. Therefore, the data show a polarity in the ability of EGTA to enhance epithelial permeability and induce cellular redistribution of cytoskeletal/junctional proteins in several epithelia. The basolateral membrane sensitivity to Ca 2+-chelation might be explained by the polarised distribution of uvomorulin.

Human glioblastoma cells persistently infected with simian virus 40 carry nondefective episomal viral DNA and acquire the transformed phenotype and numerous chromosomal abnormalities.

A stable, persistent infection of A172 human glioblastoma cells with simian virus 40 (SV40) was readily established after infection at an input of 450 PFU per cell. Only 11% of the cells were initially susceptible to SV40, as shown by indirect immunofluorescent staining for the SV40 T antigen at 48 h. However, all cells produced T antigen by week 11. In contrast, viral capsid proteins were made in only about 1% of the cells in the established carrier system. Weekly viral yields ranged between 10(4) and 10(6) PFU/ml. Most of the capsid protein-producing cells contained enormous aberrant (lobulated or multiple) nuclei. Persistent viral DNA appeared in an episomal or "free" state exclusively in Southern blots and was indistinguishable from standard SV40 DNA by restriction analysis. Viral autointerference activity was not detected, and yield reduction assays did not indicate defective interfering particle activity, further implying that variant viruses were not a factor in this carrier system. Interferon was also not a factor in the system, as shown by direct challenge with vesicular stomatitis virus. Persistent infection resulted in cellular growth changes (enhanced saturation density and plating efficiency) characteristic of SV40 transformation. Persistent infection also led to an increased frequency of cytogenetic effects. These included sister chromatid exchanges, a variety of chromosomal abnormalities (ring chromosomes, acentric fragments, breaks, and gaps), and an increase in the chromosome number. Nevertheless, the persistently infected cells continued to display a bipolar glial cell-like morphology with extensive process extension and intercellular contacts.

The adaptation of turbomolecular pumps to plasma etching processes

A summary of the requirements vacuum pumps have to meet during their application with plasma etchers is given. In particular the modification of turbomolecular pumps will be discussed. Two pumps with a pumping speed of 330 l s −1 and 510 l s −1 for N 2 have been adapted and extensively tested with plasma etchers under production conditions. The pumps have been equipped with a gas purge system. The purge gas is admitted directly into the rotor bearing area of the turbomolecular pump and generates a gas flow from there to the forevacuum port. Due to inbuilt restrictors, a laminar flow in the ring gaps of the bearing area by the corrosives is achieved. In addition the internal surfaces of the pump have special corrosion resistant coatings. The adapted turbomolecular pumps have shown a high operational life (up to now approx 7000 h without failures) and reliability. The pressure range of sputtering and plasma etching processes is above the optimum operating range of the high vacuum pumps used with these processes. These pumps, however, can be used in the 5 × 10 −3 mbar to 1 × 10 −1 mbar range by placing a throttle valve between the pump and the work chamber. The paper describes the design of a corrosion resistant conductance limiter, the flow conductance of which can be adjusted in the range from 0.1 to 1000 l s −1. This conductance limiter can be used as a pressure and a flow control, due to the high reproducibility of the positioning of the valve plate.

The Prediction of Gas Pressures within the Ring Packs of Large Bore Diesel Engines

The established orifice and volume method for predicting the gas pressures between piston rings in reciprocating machines is extended to take account of the energy loss due to wall friction in the circumferential gas flow between the piston and cylinder liner. The results show that such energy losses are significant when gas flow rates exceed 10-2 kg/s and that this is most likely to occur in engines of over 0·5 m bore with worn piston rings. Under these conditions the angular displacement of the ring gaps significantly affects ring pack gas flow. In particular, it is shown that the maximum resistance to the flow of gas through the ring pack occurs when adjacent ring gaps are separated by more than 90 degrees. In the analysis of piston ring lubrication in ring packs it is necessary to ascertain the inter-ring pressures and the present paper enables such pressures to be determined with greater accuracy and for a wider range of engines.

Instabilities in Dynamical Systems, Proceedings of the NATO Advanced Study Institute

During the dark age of nonlinear dynamics lying between Poincare and Kolmogorov-Arnold'd-Moser, astronomers were the sole keepers of the flame. In reading these proceedings through to the end, one hears again the annual Gregorian sonorities of the astronomically faithful gathered from their widely scattered monastic observatories. After some initial unsettling sermons regarding outside developments in Sec. I followed by a bow to numerical procedures in Sec. II, they safely return in Sec. III-V to the familiar ground of asteroid belt and Saturn ring gaps, Lagrange equilibrium points, and secular perturbation theory. Surely, these proceedings will be a balm to the faithful; however, to the unorthodox they are more likely to be a

Orbital Resonances in the Solar System

Orbital resonances are defined as any system of two or more satellites (including planets) orbiting the same primary and whose orbital mean motions are in a ratio of small whole numbers. Known orbital resonances in the solar system are identified, including those involving Jupiter's satellites Io, Europa, and Ganymede; Saturn's satellites Mimas and Tethys, Enceladus and Dione, and Titan and Hyperion; Saturn's ring gaps and Mimas; various asteroids and Jupiter; and the planets Neptune and Pluto. The stability of orbital resonances is examined, the origin of orbital commensurabilities is investigated, and a simple model of the simplest kind of eccentricity-type resonance is outlined. A method is described by which tides carry a noncommensurate pair of satellites into a stable libration, and current ideas concerning the formation of the gaps in Saturn's rings and the asteroid belt are discussed. Various approaches to the analysis of orbital resonances are laid out and illustrated. Three two-body commensurabilities in Saturn's satellite system are analyzed numerically.

The Effects of Age and Visual Capability on Performance with Plane and Convex Mirrors

Reaction times were measured for a detection task and a recognition task when using plane mirrors and when using convex mirrors. Three groups of nine drivers each (Young, Mature-with Bifocals, and Mature-No Glasses) were studied. The detection task consisted of reporting the number of Landolt Rings (0,1,2,3, or 4) that were made to appear in a mirror. The recognition task consisted of reporting the orientation (left, right, up, or down) of the Landolt Ring gaps. On both the detection and recognition tasks differences between types of subjects increased as the convexity of the mirror increased. The largest differences occured when the images were displayed in a 40 inch convex mirror. Here, Mature-No Glasses subjects took .77 seconds longer to report target orientation than Young subjects. On the same task Mature-Bifocaled subjects took only .18 seconds longer than the Young subjects. Since the longer reaction times of Mature-No Glasses subjects appears to be due to their poorer visual acuity it is recommended that states require higher visual standards with respect to far visual acuity.

915. Determination of gas leakage through ring gaps of liquid ring vacuum pumps: V F Lukoyanov et al,Vakuum Tekh, 2,Kazan 1970, 31–37 ( in Russian)

915. Determination of gas leakage through ring gaps of liquid ring vacuum pumps: V F Lukoyanov et al,Vakuum Tekh, 2,Kazan 1970, 31–37 ( in Russian)