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71.
The strain–stress state of the solid propellant rocket engines (SPREs) is simulated under impact. The effect of orientation of elastic and strength properties of orthotropic organoplastic shell material on the strain–stress state of the solid propellant is investigated. Normal and oblique impact of single steel cylinder projectiles, both simultaneous and at different times of multiple, converging steel spheric particles with SPRE are investigated in this study. The investigation is conducted numerically. The numerical modeling was carried out in a three-dimensional formulation by the method of finite elements for the continuous approach of the mechanics of a deformable solid. The destruction of the anisotropic material is described by the tensor-polynomial criterion of the fourth degree, which takes into account the influence of hydrostatic pressure. 相似文献
72.
Using a novel space platform-based manipulator with slewing and deployable links, the paper addresses two issues of considerable importance: (a) How important is it to model flexibility of the system? (b) How many modes are needed to adequately represent the elastic character? Results suggest that the fundamental mode is able to capture physics of the response quite accurately. Due to its massive character, the platform dynamics is virtually unaffected, even by severe maneuvers of the manipulator. Hence, treating the platform as rigid would save the computational cost without affecting the accuracy. Although the link flexibility does affect the manipulator's tip vibration, the joint and platform vibrations remain negligible. The revolute joint flexibility appears to be an important parameter affecting both the joint as well as tip responses. The information should prove useful in the design of this new class of manipulators. 相似文献
73.
L. M. Zelenyi M. S. Dolgonosov A. A. Bykov V. Yu. Popov Kh. V. Malova 《Cosmic Research》2002,40(4):357-366
Using both analytical and numerical models of the collisionless anisotropic current sheet generated by the impinging flows of transient ions, we have studied the self-consistent solutions taking the plasma trapped in the sheet into account. It is demonstrated that there exists a limited window in the space of system parameters where self-consistent solutions can exist. When the density of the quasi-trapped plasma is sufficiently large, a redistribution of the total current can be a cause of the sheet decay, when the local current of the trapped particles compensate (totally or in part) the main current in the center and at the edges of the sheet, while the total current generated by ions on the trapped trajectories vanishes. 相似文献
74.
Barmin I Bryukhanov N Egorov A Filatov I Markov A Senchenkov A Tsvetkov V 《Acta Astronautica》2002,51(1-9):255-259
The problem is considered of using the PROGRESS transport spacecraft, which will deliver the payload on the ISS, as a free flying platform for realization of space experiments. For maintenance of the ISS 5-6 PROGRESS flights per year are planned. Usually after delivery of the payload the PROGRESS undocks from the ISS and burns down in the Earth atmosphere. However, the operating conditions of its onboard systems allow to prolong operation and to make free flight near to the station and repeatedly to be docked to it. It is offered to use this possibility for performing experiments on Material Science. 相似文献
75.
Green AR Andrews HR Bennett LG Clifford ET Ing H Jonkmans G Lewis BJ Noulty RA Ough EA 《Acta Astronautica》2005,56(9-12):949-960
In light of the importance of the neutron contribution to the dose equivalent received by space workers in the near-Earth radiation environment, there is an increasing need for a personal dosimeter that is passive in nature and able to respond to this neutron field in real time. Recent Canadian technology has led to the development of a bubble detector, which is sensitive to neutrons, but insensitive to low linear energy transfer (LET) radiation. By changing the composition of the bubble detector fluid (or “superheat”), the detectors can be fabricated to respond to different types of radiation. This paper describes a preliminary ground-based research effort to better characterize the bubble detectors of different compositions at various charged-particle accelerator facilities, which are capable of simulating the space radiation field. 相似文献
76.
Laser-Raman imagery is a non-intrusive, non-destructive analytical technique, recently introduced to Precambrian paleobiology, that can be used to demonstrate a one-to-one spatial correlation between the optically discernible morphology and kerogenous composition of permineralized fossil microorganisms. Made possible by the submicron-scale resolution of the technique and its high sensitivity to the Raman signal of carbonaceous matter, such analyses can be used to determine the chemical-structural characteristics of organic-walled microfossils and associated sapropelic carbonaceous matter in acid-resistant residues and petrographic thin sections. Here we use this technique to analyze kerogenous microscopic fossils and associated carbonaceous sapropel permineralized in 22 unmetamorphosed or little-metamorphosed fine-grained chert units ranging from approximately 400 to approximately 2,100 Ma old. The lineshapes of the Raman spectra acquired vary systematically with five indices of organic geochemical maturation: (1) the mineral-based metamorphic grade of the fossil-bearing units; (2) the fidelity of preservation of the fossils studied; (3) the color of the organic matter analyzed; and both the (4) H/C and (5) N/C ratios measured in particulate kerogens isolated from bulk samples of the fossil-bearing cherts. Deconvolution of relevant spectra shows that those of relatively well-preserved permineralized kerogens analyzed in situ exhibit a distinctive set of Raman bands that are identifiable also in hydrated organic-walled microfossils and particulate carbonaceous matter freed from the cherts by acid maceration. These distinctive Raman bands, however, become indeterminate upon dehydration of such specimens. To compare quantitatively the variations observed among the spectra measured, we introduce the Raman Index of Preservation, an approximate measure of the geochemical maturity of the kerogens studied that is consistent both with the five indices of organic geochemical alteration and with spectra acquired from fossils experimentally heated under controlled laboratory conditions. The results reported provide new insight into the chemical-structural characteristics of ancient carbonaceous matter, the physicochemical changes that accompany organic geochemical maturation, and a new criterion to be added to the suite of evidence by which to evaluate the origin of minute fossil-like objects of possible but uncertain biogenicity. 相似文献
77.
V. A. Kosmodemyanskii 《Cosmic Research》2004,42(1):84-91
The problem of optimum partitioning of a staged vehicle (SV) and determination of the minimal number of stages to provide for a maximum velocity in the vertical SV motion in a homogeneous gravity field is considered at a given value of payload mass. 相似文献
78.
An analytical model for calculation of the thrust and pressure modulation of a solid propellant rocket by means of a fluidic vortex valve with secondary combustion has been developed. Thrust control by the vortex valve method was found superior to the axial injection of control flow. Addition of oxygen in the injected flow improves the energetic performance of the system as well as the thrust modulation capability. Experiments have been conducted using a mixture of nitrogen and oxygen as the injection gas. The two main parameters investigated in a series of experiments were the oxygen percentage in the injection gas and the ratio between the mass flow rates of the control gas and the solid propellant combustion products. The results show an increase of thrust by a factor of 2 for a 25% addition in mass flow rate by secondary injection at optimal conditions. 相似文献
79.
Using the method of characteristics, the problem of breaking or non-breaking of waves is studied in a plane cylindrically or spherically symmetric flow of an ideal dissociating gas. It is investigated as to how the effects of dissociation and that of the wave front curvature influence the breaking or non-breaking of waves. In a symmetrical converging gas motion a remarkable difference between the behaviours of cylindrical and spherical waves is discovered. 相似文献
80.
If life ever existed, or still exists, on Mars, its record is likely to be found in minerals formed by, or in association with, microorganisms. An important concept regarding interpretation of the mineralogical record for evidence of life is that, broadly defined, life perturbs disequilibria that arise due to kinetic barriers and can impart unexpected structure to an abiotic system. Many features of minerals and mineral assemblages may serve as biosignatures even if life does not have a familiar terrestrial chemical basis. Biological impacts on minerals and mineral assemblages may be direct or indirect. Crystalline or amorphous biominerals, an important category of mineralogical biosignatures, precipitate under direct cellular control as part of the life cycle of the organism (shells, tests, phytoliths) or indirectly when cell surface layers provide sites for heterogeneous nucleation. Biominerals also form indirectly as by-products of metabolism due to changing mineral solubility. Mineralogical biosignatures include distinctive mineral surface structures or chemistry that arise when dissolution and/or crystal growth kinetics are influenced by metabolic by-products. Mineral assemblages themselves may be diagnostic of the prior activity of organisms where barriers to precipitation or dissolution of specific phases have been overcome. Critical to resolving the question of whether life exists, or existed, on Mars is knowing how to distinguish biologically induced structure and organization patterns from inorganic phenomena and inorganic self-organization. This task assumes special significance when it is acknowledged that the majority of, and perhaps the only, material to be returned from Mars will be mineralogical. 相似文献