共查询到20条相似文献,搜索用时 22 毫秒
1.
A. Schausberger 《Rheologica Acta》1986,25(6):596-605
In the search for a workable mixing rule, use was made of experimental data for complex moduli of melts of narrow molar mass distribution polystyrenes and their homogeneous blends. In the course of this work two basic observations were made as to the nature of the relaxation time spectra of these blends:
- The relaxation strength (a product of the weight fraction and the plateau modulus) of a component of large molecules is reduced by the presence of shorter molecules, the latter molecules acting like ordinary diluent molecules even if their molar masses are larger thenM c .
- The relaxation time of a molecule (known from measurements on the respective monodisperse component) is considerably changed by the blending. The width of the distribution of relaxation times, as expected from the known composition of the blend, is significantly reduced.
2.
K. N. Katyal 《Flow, Turbulence and Combustion》1971,23(1):281-294
The flow of a dipolar fluid between two parallel plates with and without heat transfer is studied. The following cases are discussed:
- Isothermal flow due to the relative motion of the plates,
- Isothermal flow due to a constant pressure gradient with the plates at rest,
- Nonisothermal flow with linearly varying plate temperatures.
3.
W. J. Beranek 《Experimental Mechanics》1968,8(6):249-256
The paper describes the possibilities of rapidly and conveniently obtaining results by means of the reflection moiré method. The moiré photographs are produced with the aid of a screen provided with a finely ruled grid. The contrast of the photographs is increased by optical means. By displacement of two equal moiré photographs, moiré fringes of second order for the curvature or the twist are obtained. It is shown how charts can be produced which indicate:
- The distribution of the bending moments
- The distribution of the bending moments for which the reinforcement should be designed
- The distribution of the shear forces and the magnitude of the bearing reactions.
4.
For aqueousn-heptanol solutions and in a nearly two-dimensional flow, two strikingfeatures have been detected:
- a shift of the minimum of the surface tension
- a discrepancy between the observed Marangoni flow velocities and the expected ones from static surface tension values.
5.
Prof. Dr. A. P. Szumowski Prof. Dr. F. Obermeier Prof. Dr. G. E. A. Meier 《Experiments in fluids》1995,18(3):145-152
Experimental investigations of Laval nozzle flow show for relatively low supply to exit pressure ratios, which correspond to shock wave positions close to the nozzle throat, three different, oscillatory instabilities.
- Shock pattern oscillations where the root of a λ-like shock front remains nearly in constant position, but where the proportion between the normal part and the oblique part of the shock changes periodically.
- Shock wave and separation bubble oscillations where the motion of the shock wave is accompanied by displacements of the separation bubble.
- Flow rate oscillations where the shock waves leave periodically through the nozzle throat in upstream direction.
6.
Milton M. Leven 《Experimental Mechanics》1973,13(9):353-372
Twenty tests were performed on a 1 Cr?1 Mo?1/4 V rotor steel at 1000° F (538°C) to determine the interaction of creep and low-cycle fatigue. These tests involved five different types of strain-controlled cycling: creep at constant tensile stress; linearly varying strain at different frequencies; and hold periods at maximum compressive strain, maximum tensile strain, or both. The experimental data were then used to characterize the interaction of creep and fatigue by the:
- Frequency-modified strain-range approach of Coffin;
- Total time to fracture vs. the time of one cycle relation as proposed by Conway and Berling;
- Total time to fracture vs. the number of cycles to fracture characterization of Ellis and Esztergar;
- Summation of damage fractions obtained from tests using interspersed creep and fatigue as proposed by the Metal Properties Council;
- Strain-range-partitioning method of Manson, Halford, and Hirschberg.
7.
Dr.-Ing. H. M. Sofrata 《Heat and Mass Transfer》1980,14(2):119-129
The aim of this paper is to develop a fast and simple accurate graphical method for designing the required cooling coil for an air conditioning system in which both the sensible and latent heat are transferred. The method has the following advantages:
- Direct solution utilizing only Psychrometer charts.
- Solution of combined heat and mass transfer problems occuring at pressures other than that of atmosphere.
- Direct determination of boundary temperature at which dehumidification begins for that type of problem where a portion of the surface is in a dry condition.
- Less effort required than trial and error method in determination of air condition leaving a counterflow coil of a given area.
8.
We prove short-time well-posedness of the Cauchy problem for incompressible strongly elliptic hyperelastic materials. Our method consists in:
- Reformulating the classical equations in order to solve for the pressure gradient (The pressure is the Lagrange multiplier corresponding to the constraint of incompressibility.) This formulation uses both spatial and material variables.
- Solving the reformulated equations by using techniques which are common for symmetric hyperbolic systems. These are:
- Using energy estimates to bound the growth of various Sobolev norms of solutions.
- Finding the solution as the limit of a sequence of solutions of linearized problems.
9.
It is shown that the well-known variational principles for the ideal compressible fluid model in Eulerian coordinates have the following deficiencies:
- They are not related to the corresponding variational principles in Lagrangian coordinates;
- The variation procedure in these variational problems does not lead to the equations of motion themselves in the Euler form; rather it leads to relations which correspond to definite classes of solutions of the Euler equations. Here allowance for the equations of the constraints imposed by the adiabaticity and continuity conditions limits the region of application of these variational principles to only potential flows;
- More general results, involving flows other than potential, are achieved by artificial selection of certain additional constraint conditions imposed on the quantities being varied, and in this case additional clarification is required to ascertain whether any inviscid compressible fluid flow is the extremum of the corresponding variational problem.
10.
Joseph Der Hovanesian 《Experimental Mechanics》1974,14(6):233-236
This paper presents a new “hybrid” method whereby the ratio of the isochromatic-fringe visibility/isopachic-fringe visibility may be easily and continuously varied. This simple procedure merely combines a conventional polariscope with a holographic system. A variable beam splitter permits an incoherent superposition of the reconstruction of a doubly exposed hologram with real-time isochromatics, either dark or light field. By varying the ratios of the above two, in the image plane, numerous interesting results may be obtained including:
- Isochromatics only, without errors in position
- Isochromatics-isopachic fringes identical to those obtained through classical interferometry
- Isochromatic-isopachic fringes whereby the amplitude modulation between the two may be minimized
- Continuously variable isopachic/isochromatic-fringe visibility.
11.
A numerical procedure on the basis of the Marker and Cell-method [1] was developed in order to solve the conservation equations for mass, momentum and energy for the case of bubble growth on a heating surface. This procedure was used to calculate steam bubble growth on a horizontal stainless steel heating surface under saturated pool boiling conditions at a system pressure of 1 bar and different superheatings. The essential results obtained are: -Good agreement was found between calculations and experiments concerning bubble growth rates, bubble shape and temperature field in the liquid surrounding the bubble. -During its growth the bubble penetrates the temperature boundary layer formed in the liquid on the heating surface, simultaneously liquid is displaced aside. -The microlayer evaporation fraction of the total bubble growth increases with growth time from 20 % to 50%. 相似文献
12.
Rolf P. Häggström 《Experimental Mechanics》1982,22(3):106-110
Today's demand to preserve energy, to optimally utilize limited resources and to still increase quality calls for more-precise measurements in virtually all manufacturing processes. One such field is the measurement of tension in, for instance, paper machines, printing presses, machines for the manufacturing of rubber, plastics, fabrics, etc. Newspaper-printing presses produce today an impressive number of paper breaks. Measurement of the web tension at critical positions could give an early warning when the tension in the paper is growing to dangerous values. In a paper macnine, it is necessary to introduce webtension measurements at many positions to optimize quality, to prevent paper breaks and to reduce wear. Measurements have been carried out with a particular force transducer that can be easily built into an existing, as well as a new machine. Several installations, mainly in paper machines and newspaper-printing presses, show that - the number of paper breaks are drastically reduced - a more-uniform quality of the paper can be achieved - the lifetime of machine parts, such as wires and felts, can be increased. 相似文献
13.
Test results are reported for a recently completed experimental research program on rocks subjected to triaxial compression. Sandstone, marble, granite and shale specimens were tested at confining pressures as high as 90,000 psi corresponding to mean stresses of up to 143,000 psi. Recognizing that the largest potential experimental error in such tests results from making strain and load measurements external to the vessel, special load and strain-measuring devices were designed and fabricated for use inside the pressure vessel. The specimens were carefully machined cylinders with length-to-diameter ratios of two and with diameters ranging from 4/16 in. to 1 in. The confining pressure was held constant during each run, but varied from 0 to 90,000 psi over the tests. Results are reported in the form of:
- Stress-strain curves for individual specimens
- Maximum shear stress at fracture vs. mean-stress curves for each rock type tested
- Tabulation of results for 59 specimens
14.
We describe steady two-dimensional flows of two immiscible fluids through an undulating porous medium of constant thickness, with impermeable or slightly permeable boundaries. Flows in the same or opposite directions are called, respectively, direct or counter flows. Three special classes of flow are determined:
- The pressure dominated case occurs for high direct flows and has the interface approximately a constant vertical distance from the impermeable boundaries.
- The gravity dominated case occurs for low direct flows and has the interface very close to the lower (upper) boundary for downward (upward) sloping boundaries except at crossovers.
- Counter flows require the interface to decrease in the direction of flow of the lower fluid.
15.
ATaylor-series correction to the maximum inplane shear stress was studied as a means of extending the data zone in photoelastic determination of stress-intensity factors beyond the singular region of a two-degree-of-freedom analysis. Convergence properties were obtained by comparing with several complete two-dimensional solutions. Experiments were performed on two kinds of three-dimensional problems, plates containing surface flows in both bending and extension. Results were analyzed by both a two-degree-of-freedom and aTaylor-series correction method (TSCM). Results were compared to theories of F. W. Smith and A. S. Kobayashi and R. C. Shah. It was concluded that:
- The TSCM program converges rapidly to accurateK I values and will accommodate the scatter inherent in experimental data if the series is properly truncated.
- The TSCM program is essentially equivalent to the two-parameter representation when only the crack-surface effects dominate.
- When effects other than crack surfaces are important, TSCM requires more terms but still predictsK I with reasonable accuracy.
16.
Conventional organic-epoxy adhesives outgas when exposed to ultra-high vacuum and, as operating temperatures are increased, they begin to exhibit plastic behavior causing hysteresis and zero instability in the transducer. The use of an inorganic glass as the bonding material has resulted in a significant advance in transducer-fabrication technology for the following reasons:
- The outgassing of transducers in high-vacuum applications is minimized.
- Mechanical properties of the transducer such as hysteresis and repeatability are improved.
- The electrical isolation of the strain gages from the metallic elements of the transducer is increased at high temperatures over that provided by epoxy. Also, the glass bond can survive and operate in severe radiation environments, wherein the epoxy adhesive will suffer either temporary or permanent loss of its dielectric strength.
- Glass-bonding techniques are particularly useful for the extension of the temperature range of operation of silicon-strain-gage transducers.
17.
This paper describes a technique of interferogram processing by the use of spatial-frequency filtering. Proper part of Fourier spectrum of the interferogram is blocked out by a matched mask located in the focal plane of the imaging system. Depending on the mask shape and dimensions one can obtain
- interferogram images with delineating fringes or
- interferogram images of one component of strain.
18.
A theoretical study has been made of the transport of mass, heat and momentum in a tube, in which at the inner surface a heterogenous not-equimolecular reaction takes place. The tube is flowed laminarly by the gaseous reacting components. The surface of the tube is heated or cooled. In the centre of attention are the effects of: heating or cooling the reactor and temperature dependent transport coefficient on the mass transfer. The calculations show, that the mass transfer is definitively depending on the time the gas stays in the tube. Heating or cooling of the reactor leads to a change in density and thus to a change of the residence time. Among the transport coefficients the diffusion depends very much on the temperature and has a great influence on the diffusion controlled mass transfer. 相似文献
19.
Modes of a vibrating disk, made of piezoelectric ceramic-type PZT-5A, were investigated by two optical coherent methods:
- Time-average holography (TAH).
- Speckle-shearing interferometry (SSI). It is shown how synthesis of data from the two methods can give a good picture of the modes of vibration, more exact than the picture one can derive from each method alone.
20.
We study supersonic flows of an electrically conductive gas in crossed electric and magnetic fields [1] in the presence of shock waves. It is shown that three steady flow regimes can exist, and that these are defined by the electrical conductivity of the gas as a function of temperature and density.
- The normal regime is characterized by a tendency for the shock to move toward the channel entrance on increase of the static pressure at the channel exit. The steady regime of this type exists and is stable.
- The anomalous regime (formally constructed) is characterized by a tendency for the shock to move toward the exit on increase of the static pressure at the channel exit. This regime is unstable and the flow in the MHD-channel may be either entirely supersonic or entirely subsonic.
- The limiting (boundary) regime is intermediate between the normal and anomalous regimes and is characterized by the fact that the stationary position of the shock wave and its amplitude are not uniquely defined. Steady flow in this case is not unique.