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1.
This paper discusses the problem of the extraction of characteristic roots {λt}(λ012…) on Bessel-Neumann’s mixed equations. It gives the expressions and the evaluation of the minimum root. The advantage of the method has no use for the table of the multi-figure number Bessel function and it does not need computer but can calculate all the characteristic roots {λt}. The precision of these roots is still high.  相似文献   

2.
Some results are presented of experimental studies of the equilibrium temperature and heat transfer of a sphere in a supersonic rarefied air flow.The notations D sphere diameter - u, , T,,l, freestream parameters (u is velocity, density, T the thermodynamic temperature,l the molecular mean free path, the viscosity coefficient, the thermal conductivity) - T0 temperature of the adiabatically stagnated stream - Te mean equilibrium temperature of the sphere - Tw surface temperature of the cold sphere (Twe) - mean heat transfer coefficient - e air thermal conductivity at the temperature Te - P Prandtl number - M Mach number  相似文献   

3.
The boundary-layer flow generated on an impermeable vertical surface in a saturated porous medium is considered in the case when wall heating at a rate proportional tox is switched on at timet=0, (x measures distance along the wall and is a constant). The similarity equations which hold in the limit of larget are discussed and are shown to have a solution only for >–1. The behaviour of the solution as –1 and as is obtained. Numerical solutions of the initial value problem are then obtained for a range of values of . A direct numerical integration is possible for 1, while an iterative procedure is required for <1, with the numerical scheme becoming unstable for =–0.5.
Grenzschichtströmung an einer plötzlich aufgeheizten vertikalen Fläche, in einem gesättigten porösen Medium
Zusammenfassung Es wird die an einer undurchlässigen, vertikalen Fläche hervorgerufene Grenzschichtströmung im Falle eines Einschalten der Heizung beit=0 betrachtet. Die Stärke der Wandheizung is proportional zux , wobeix die Koordinate längs der Wand ist und eine Konstante. Die Ähnlichkeitsgleichungen werden für den Bereich von großen Zeitent besprochen und es wird gezeigt, daß eine Lösung nur für >–1 vorliegt. Es wird das Verhalten der Lösungen für –1 und erhalten. Numerische Lösungen für die Anfangsbedingungen des Problems werden für eine Reihe von -Werten errechnet. Eine direkte numerische Integration ist für 1 möglich, während für <1 eine Iteration erforderlich ist, wobei das numerische Verhalten für =–0.5 instabil wird.
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4.
Equations are derived for the gasdynamics of a dense plasma confined by a multiple-mirror magnetic field. The limiting cases of large and small mean free paths have been analyzed earlier: 0 and k, where is the length of an individual mirror machine, 0 is the size of the mirror, and k is the mirror ratio. The present work is devoted to a study of the intermediate range of mean free paths 0 k. It is shown that in this region of the parameters the process of expansion of the plasma has a diffusional nature, and the coefficients of transfer of the plasma along the magnetic field are calculated.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 14–19, November–December, 1974.The authors thank D. D. Ryutov for the statement of the problem and interest in the work.  相似文献   

5.
Summary It has been investigated whether constitutive equations, which have been proposed originally to describe the rheological behaviour of polymerlike materials, can be used to represent the rheology of dispersions. Such equations generally predict stresses that depend on both the shear () and a quantity ( ) which is the product of the shear rate ( ) and the time constant of the material ().The behaviour of dispersions depends in general on the concentration of the dispersed particles. The dissipative aspect of the rheological behaviour is almostNewtonian for very dilute dispersions while it becomes plastic for more densely packet dispersions. In the latter case the shear stress is practically independent of the shear rate at low shear rates. Such behaviour may be accounted for in the constitutive equations by assuming to be almost constant. This motivated us to choose the equation ofBogue where the relaxation time () depends on the shear rate ( ), according to 1/ = (1/ 0) + a , where 1/ 0 accounts for the viscous behaviour and a for the plastic behaviour.Comparing the actual rheological behaviour of dispersions of fat crystals in paraffin oil with the behaviour predicted by theBogue equation, it turns out that theBogue equation has some success in representing the stress overshoot in steady shear experiments. However, the predicted value of the normal stress for the concentrated dispersions is too low in comparison with the measured value. It is suggested that this discrepancy is due to the dilatant behaviour of these dispersions.Moreover, the values of the dynamic moduli measured in oscillatory shear are predicted incorrectly, due to considerable changes in particle network which already occur at very small deformations.With 10 figures  相似文献   

6.
The relaxation behavior of polymers with long linear flexible chains of uniform length has been investigated by means of dynamic mechanical analysis. The relaxation time spectrum (H()) follows a scaling relationship with two self-similar regions, one for the entanglement and terminal zone, and a second one for the transition to the glass. This can be described in its most general form (termed BSW spectrum) as H() = H e ne + H g n g for < max and H() = 0 for max < , where H e , H g , n e , n g are material constants and max is the molecular weight dependent cut-off of the self-similar behavior. In this study, the dynamic mechanical response has been measured and analyzed for four highly entangled, nearly monodisperse polybutadienes with molecular weights from 20000 to 200000. The data are well represented by the BSW spectrum with scaling exponents of n e = 0.23 and n g = 0.67. The values of the exponents obtained in this work are about the same as those found for polystyrene samples in a previous study. This suggests that the two types of polymers have a similar relaxation pattern. However, at this point further refinement of the experiments is needed before being able to draw definite conclusions about the universality of the exponents.Dedicated to Professor Arthur S. Lodge on the occasion of his 70th birthday and his retirement from the University of Wisconsin.  相似文献   

7.
Conclusions We have investigated solutions of equation (3) when 2 is an eigenvalue of the linearized operator (13) and when it is not. In Section 4 we have shown that for 0 and 2 = i 2 we have exactly two nontrivial solutions which bifurcate to the right of i 2 ; these solutions are shown to exist in an interval ( i 2 , i 2 + 0). The method of Section 3 may then be used to extend these two solutions to the right of i 2 + 0 providing that 2= i 2 + 0 is not an eigenvalue of the linear operator (13) evaluated at = ± 1. Either a solution can be uniquely extended, or there exists a value of 2where the bifurcation method must be applied again3.While the method used here gives the exact number of solutions bifurcating from i 2 , other problems remain open; for example, it is still not proven that the two bifurcating branches have i zeros, as is the case for Hammerstein operators with oscillation kernels [4]. The conjecture of Odeh and Tadjbakhsh that there are exactly 2(i+1) nontrivial solutions in the interval i 2 < i +1/2 remains un-answered, although it would be proven if one could show that there is no secondary bifurcation as in the cases of Kolodner [7] and Coffman [8].  相似文献   

8.
An experimental investigation of scaling laws in turbulence generated by a biplane grid for low Reynolds numbers (Re ) is presented. The present study covers a wide range of flow field conditions (from Re 2.5 to Re 36) that have not been analyzed from this point of view. It is shown that following the Kolmogorov theory a scaling range can not be observed since the separation between the energy production scales and the dissipative scales is too short. On the other hand, an extended form of scaling, the Extended Self-Similarity (ESS), permits the identification of a range of scales characterized by the same scaling exponent much wider than the one previously examined. Thus the scaling laws for the first six moments of the velocity structure function are accurately calculated by means of the ESS and an anomalous scaling with respect to the Kolmogorov theory is observed for Re down to the order of 10. As a matter of fact the scaling exponents are in good agreement with the ones that were determined at higher Re by previous experimental and numerical investigations. For Re 6 a regularization of the scaling exponents is observed as an effect of the dissipation. We also present an analysis of the universality properties of the ESS form of scaling by means of the form function and an analysis of the sensitivity of the scaling range to the Re .  相似文献   

9.
Summary The subject of this article is the thermodynamics of perfect elastic-plastic materials undergoing unidimensional, but not necessarily isothermal, deformations. The first and second laws of thermodynamics are employed in a form in which only the following quantities appear: the temperature , the elastic strain e, the plastic strain p, the elastic modulus (gq), the yield strain (gq), the heat capacity (e, p,), the latent elastic heat e(e, p, ), and the latent plastic heat p(e, p, ). Relations among the response functions , , , e, and p are derived, and it is shown that a set of these relations gives a necessary and sufficient condition for compliance with the laws of thermodynamics. Some observations are made about the existence and uniqueness of energy and entropy as functions of state.Dedicated to Clifford Truesdell on the occasion of his 60th birthdayThis research was supported by the U.S. National Science Foundation.  相似文献   

10.
In this paper we consider the asymptotic behavior of solutions of the quasilinear equation of filtration as t. We prove that similar solutions of the equation u t = (u )xx asymptotically represent solutions of the Cauchy problem for the full equation u t = [(u)]xx if (u) is close to u for small u.  相似文献   

11.
The drag coefficient for bubbles with mobile or immobile interface rising in shear-thinning elastic fluids described by an Ellis or a Carreau model is discussed. Approximate solutions based on linearization of the equations of motion are presented for the highly elastic region of flow. These solutions are in reasonably good agreement with the theoretical predictions based on variational principles and with published experimental data. C D Drag coefficient - E * Differential operator [E * 2 = 2/2 + (sin/ 2)/(1/sin /)] - El Ellis number - F D Drag force - K Consistency index in the power-law model for non-Newtonian fluid - n Flow behaviour index in the Carreau and power-law models - P Dimensionless pressure [=(p – p 0)/0 (U /R)] - p Pressure - R Bubble radius - Re 0 Reynolds number [= 2R U /0] - Re Reynolds number defined for the power-law fluid [= (2R) n U 2–n /K] - r Spherical coordinate - t Time - U Terminal velocity of a bubble - u Velocity - Wi Weissenberg number - Ellis model parameter - Rate of deformation - Apparent viscosity - 0 Zero shear rate viscosity - Infinite shear rate viscosity - Spherical coordinate - Parameter in the Carreau model - * Dimensionless time [=/(U /R)] - Dimensionless length [=r/R] - Second invariant of rate of deformation tensors - * Dimensionless second invariant of rate of deformation tensors [=/(U /R)2] - Second invariant of stress tensors - * Dimensionless second invariant of second invariant of stress tensor [= / 0 2 (U /R)2] - Fluid density - Shear stress - * Dimensionless shear stress [=/ 0 (U /R)] - 1/2 Ellis model parameter - 1 2/* Dimensionless Ellis model parameter [= 1/2/ 0(U /R)] - Stream function - * Dimensionless stream function [=/U R 2]  相似文献   

12.
The relaxation of polymers with linear flexible chains of uniform length   总被引:2,自引:8,他引:2  
The analysis of dynamic mechanical data indicates that linear flexible polymer chains of uniform length follow a scaling relation during their relaxation, having a linear viscoelastic relaxation spectrum of the formH() = n 1 G N 0 × (/ max) n1 for max. Data are well represented with a scaling exponent of about 0.22 for polystyrene and 0.42 for polybutadiene. The plateau modulusG N 0 is a material-specific constant and the longest relaxation time depends on the molecular weight in the expected way. At high frequencies, the scaling behavior is masked by the transition to the glassy response. Surprisingly, this transition seems to follow a Chambon-Winter spectrumH() = C–n2, which was previously adopted for describing other liquid/solid transitions. The analysis shows that the Rouse spectrum is most suitable for low molecular-weight polymersM M c , and that the de Gennes-Doi-Edwards spectrum clearly predicts terminal relaxation, but deviates from the observed behavior in the plateau region.Dedicated to Prof. Richard S. Stein on the occasion of his 65th birthday.On sabbatical leave from the University of Linz, Austria.  相似文献   

13.
Zusammenfassung Die Wärmeleitfähigkeit des Systems J22 J wurde experimentell und theoretisch im Bereich 400 °K<T<1200 °K und 10 Torr<p<380 Torr untersucht. Unter Verwendung des Begriffs der Diffusionslänge wurde eine Theorie entwickelt, welche die Wärmeleitfähigkeit in Übereinstimmung mit den Versuchsergebnissen zu berechnen gestattet.
Thermal conductivity of partially dissociated iodine vapour
The thermal conductivity of the system J2 2 J has been studied experimentally and theoretically in the range 400 °K<T<1200 °K and 10 Torr<p<380 Torr. Starting from the definition of the diffusion length a theory is presented which describes the thermal conductivity in agreement to the experimental results.

Bezeichnungen 0 gaskinetische Wärmeleitfähigkeit - D Dissoziationsanteil der Wärmeleitfähigkeit, Gleichgewichtswert - gesamte Wärmeleitfähigkeit - Gesamtdichte - W p molare Dissoziationsenthalpie - p Gesamtdruck - D Diffusionskoeffizient - Dissoziationsgrad - K p Massenwirkungskonstante des Systems J22 J - R allg. Gaskonstante - T abs. Temperatur - Z 3 Zahl der Dreierstöße je Zeiteinheit - Z 2 Zahl der Zweierstöße je Zeiteinheit - Moleküldurchmesser - mittlere Geschwindigkeit - mittlere freie Weglänge - S Diffusionslänge - Relaxationszeit - r 2 Radius des Heizdrahtes mit Quarzmantel - r 1 Meßzellenradius - l Länge der Meßzelle - Molenbruch des einatomigen Jodes - , 10 Gleichgewichtswert von - c molare Gesamtkonzentration - c v molare Wärmekapazität - M Molmasse - 20 Molenbruch des zweiatomigen Jodes, Gleichgewichtswert - 3 Molenbruch des Xenons - c 1,c 2,c 3 molare Konzentration von J, J2, Xe - k 1,k 2, ...,k 6 Reaktionsgeschwindigkeitskoeffizienten - /k Wechselwirkungsparameter des Lennard-Jones-Potentials - Viskosität Mitteilung aus der Physikalisch-Technischen Bundesanstalt  相似文献   

14.
An equation is derived for the ascent velocity of large gas bubbles in a liquid. This velocity is assumed to be governed by the propagation of a wavelike perturbation caused by the bubble in the liquid.Notation w bubble (or drop) velocity - specific gravity - dynamic viscosity - kinematic viscosity - r bubble (or drop) radius - surface tension - coefficient of friction - g gravitational acceleration - D bubble (or drop) diameter - p pressure - c propagation velocity of the wavelike perturbation - wavelength  相似文献   

15.
Summary Two-dimensional stress singularities in wedges have already drawn attention since a long time. An inverse square-root stress singularity (in a 360° wedge) plays an important role in fracture mechanics.Recently some similar three-dimensional singularities in conical regions have been investigated, from which one may be also important in fracture mechanics.Spherical coordinates are r, , . The conical region occupied by the elastic homogeneous body (and possible anisotropic) has its vertex at r=0. The mantle of the cone is described by an arbitrary function f(, )=0. The displacement components be u. For special values of (eigenvalues) there exist states of displacements (eigenstates) % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakabbaaa6daaahjxzL5gapeqa% aiaadwhadaWgaaWcbaGaeqOVdGhabeaakiabg2da9iaadkhadaahaa% WcbeqaaiabeU7aSbaakiaadAgadaWgaaWcbaGaeqOVdGhabeaakiaa% cIcacqaH7oaBcaGGSaGaeqiUdeNaaiilaiabfA6agjaacMcaaaa!582B!\[u_\xi = r^\lambda f_\xi (\lambda ,\theta ,\Phi )\],which may satisfy rather arbitrary homogeneous boundary conditions along the generators.The paper brings a theorem which expresses that if is an eigenvalue, then also-1- is an eigenvalue. Though the theorem is related to a known theorem in Potential Theory (Kelvin's theorem), the proof has to be given along quite another line.
Zusammenfassung Zwei-dimensionale Spannungssingularitäten in keilförmigen Gebieten sind schon längere Zeit untersucht worden und neuerdings auch ähnliche drei-dimensionale Singularitäten in konischen Gebieten.Kugelkoordinaten sind r, , . Das konische Gebiet hat seine Spitze in r=0. Der Mantel des Kegels lässt sich beschreiben mittels einer willkürlichen Funktion f(, )=0. Die Verschiebungskomponenten seien u. Für spezielle Werte von (Eigenwerte) bestehen Verschiebunszustände % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakabbaaa6daaahjxzL5gapeqa% aiaadwhadaWgaaWcbaGaeqOVdGhabeaakiabg2da9iaadkhadaahaa% WcbeqaaiabeU7aSbaakiaadAgadaWgaaWcbaGaeqOVdGhabeaakiaa% cIcacqaH7oaBcaGGSaGaeqiUdeNaaiilaiabfA6agjaacMcaaaa!582B!\[u_\xi = r^\lambda f_\xi (\lambda ,\theta ,\Phi )\],welche homogene Randwerte der Beschreibenden des Kegels entlang genügen.Das Bericht bringt ein Theorem, welches aussagt, das und =–1– beide Eigenwerte sind.
  相似文献   

16.
For many solid materials the stress relaxation process obeys the universal relationF = – (d/d lnt)max = (0.1 ± 0.01) ( 0 i ), regardless of the structure of the material. Here denotes the stress,t the time, 0 the initial stress of the experiment and i the internal stress. A cooperative model accounting for the similarity in relaxation behaviour between different materials was developed earlier. Since this model has a spectral character, the concepts of linear viscoelasticity are used here to evaluate the corresponding prediction of the dynamic mechanical properties, i.e. the frequency dependence of the storageE () and lossE () moduli. Useful numerical approximations ofE () andE () are also evaluated. It is noted that the universal relation in stress relaxation had a counterpart in the frequency dependence ofE (). The theoretical prediction of the loss factor for high-density polyethylene is compared with experimental results. The agreement is good.  相似文献   

17.
Zusammenfassung Zur Berechnung der dynamischen Idealviskosität Ideal (T) und der Idealwärmeleitfähigkeit ideal (T) benötigt man die kritische TemperaturT kr, das kritische spezifische Volum kr, die MolmasseM, den kritischen Parameter kr und die molare isochore WärmekapazitätC v(T). Sowohl das theoretisch, als auch das empirisch abgeleitete erweiterte Korrespondenzgesetz ergeben eine für praktische Zwecke ausreichende Genauigkeit für die Meßwertwiedergabe, die bei den assoziierenden Stoffen und den Quantenstoffen jedoch geringer ist als bei den Normalstoffen.
The extended correspondence law for the ideal dynamic viscosity and the ideal thermal conductivity of pure substances
For the calculation of the ideal dynamic viscosity Ideal (T) and the ideal thermal conductivity ideal (T) the critical temperatureT kr, the critical specific volumev kr, the molecular massM, the critical parameter kr, and the molar isochoric heat capacityC v(T) is needed. Not only the theoretically determined but also the empirically determined extended correspondence law gives for practical use a good representation of the measured data, which for the associating substances and the quantum substances is not so good as for the normal substances.
  相似文献   

18.
A class of semilinear nonautonomous parabolic equations subjected to additive white noise is considered. The existence of a family of randomN-dimensional approximate inertial manifolds (AIMs) whose neighborhoods of thickness of order exp(- N+1 ) attract exponentially in the mean all the trajectories is proved forN large enough. Here N+1 is the (N+1)th eigenvalue of the corresponding linear problem, and and are positive constants. We also construct a sequence of AIMs which converges to the exact inertial manifold, when a spectral gap condition is satisfied. These results remain true for deterministic autonomous and nonautonomous cases.  相似文献   

19.
Übersicht Bei stark abklingenden Funktionen wird die Übertragungsmatrix U() aufgespalten in die Anteilc U 1() e und U 2() e. Der zweite Term spielt am Rand = 0 keinc Rolle. Die unbekannten Anfangswerte sind über die Matrix U 1(0) an die bekannten gebunden und eindeutig bestimmbar.
Summary For strongly decaying solution functions the transfer matrix U() is splitted into the parts U 1() e and U 2() e. The second term does not influence at the boundary = 0. The unknown initial values are related by the matrix U 1(0) to the known values and they can be uniquely determined.
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20.
The results of an analytical approximation method to predict the film vaporization are compared with the predictions of a finite difference method of Hermitian type. The analytically estimated rate of vaporization of different hydrocarbons, which is the most important value for practical applications, deviates only a few percents from the numerically estimated value.
Zur Berechnung der Filmverdunstung von Kohlenwasserstoffen in einem Heißluftstrom
Zusammenfassung Es wird ein Näherungsverfahren zur Berechnung der Filmverdunstung dargestellt, bei dem eine vollständige Lösung der miteinander gekoppelten Grenzschichtgleichungen entfallt. Die nach dieser analytischen Methode ermittelte Verdunstung verschiedener Kohlenwasserstoffe wird mit Werten verglichen, die nach einem Differenzenverfahren vom Hermiteschen Typ berechnet wurden. Es zeigt sich, daß die analytisch berechnete Verdunstungsrate, die für praktische Anwendungen wichtigste Größe, nur wenige Prozent von dem numerisch ermittelten Wert abweicht.

Formelzeichen c ew Konzentrationsdifferenz c1e -c 1w - c i Massenkonzentration der Komponentei - cp, cpi spezifische Wärmekapazität bei konstantem Druck des Gemisches — der Komponentei - D 12 binärer Diffusionskoeffizient - f dimensionslose Stromfunktion - f dimensionslose Geschwindigkeit - g () allgemeine Funktion - m 1 Massenstromdichte der Komponente 1 - m * dimensionslose Massenstromdichte, G1. (4.8) - M, Mi Molgewicht, — der Komponentei - P, P i Druck, Partialdruck der Komponentei - Pr Prandtlzahl,C p/ - q Wärmestromdichte - r 1 Verdampfungswärme - R allgemeine Gaskonstante - Sc Schmidtzahl/D 12 - T absolute Temperatur - u Geschwindigkeitskomponente inx-Richtung - v Geschwindigkeitskomponente iny-Richtung - x Längskoordinate - y Querkoordinate - z dimensionslose Konzentration - dimensionslose Funktion/ e e - transformierte Koordinatey - dimensionslose Temperatur (T-T w)/(Te-Tw) - Wärmeleitfähigkeit des Gemisches - Zähigkeit des Gemisches - transformierte Koordinate - Dichte des Gemisches - Stromfunktion Indizes e am Außenrand der Grenzschicht - i Stoffi - w an der Filmoberfläche - 1, 2 Komponente 1, 2 - () Ableitung ()/ n   相似文献   

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