Asymmetric stokes flow past a spherical cap

Ranger's solution of the asymmetric streating Stokes' flow past a spherical cap is analyzed in detail. It is found that most caps exhibit wakes within their concavities, but the dividing streamsurface does not always emanate from the rim. Drag and torque formulae valid for all cap angles are derived and these are in agreement with the known results in the limiting cases when the cap becomes a sphere and a circular disc.

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Zusammenfassung Die Lösung von Ranger für die unsymmetrische Stokes-Strömung um eine Kugelhaube wurde im Detail analysiert. Es wurde gefunden, dass die meisten Kugelhauben in ihrem Hohlraum Albösungsgebiete aufweisen, doch beginnt die Ablösungs-Stromfläche nicht immer am Rand der Haube. Widerstand und Moment wurde für alle Haubenformen berechnet; die bekannten Resultate der Kugel und der Kreisscheibe ergeben sich als Grenzfälle.

     

Stokes flow past a two-dimensional lens

Summary Two problems involving uniform Stokes flow past a two-dimensional lens are considered in an attempt to determine those geometric characteristics which cause separation and theresultant formation of large Stokes eddies. Criteria are derived which identify lenses having this property. It is found that a necessary condition for separation is that the lens be convex-concave.

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Zusammenfassung Zwei Probleme werden untersucht, die die gleichförmige Stokes-Strömung über eine zweidimensionale Linse betreffen, als ein Versuch, die geometrischen Eigenschaften fetzustellen, die die Ablösung und die resultierende Formation von grossen Stokes-Wirbeln verursachen. Kriterien werden abgeleitet, welche Linsen, die diese Chharakteristik haben, identifizieren. Es zeigte sich, dass die konvex-konkave Form der Linse eine notwendige Bedingung ist.

     

Boundary integral method for Stokes flow past a porous body

In this paper we obtain an indirect boundary integral method in order to prove existence and uniqueness of the classical solution to a boundary value problem for the Stokes–Brinkman-coupled system, which describes an unbounded Stokes flow past a porous body in terms of Brinkman's model. Therefore, one assumes that the flow inside the body is governed by the continuity and Brinkman equations. Some asymptotic results in both cases of large and, respectively, of low permeability are also obtained. Copyright © 2007 John Wiley & Sons, Ltd.     

Stokes flow past a slightly deformed fluid sphere

Summary The Stokes flow past a fluid spheroid whose shape deviates slightly from that of a sphere, is examined. To the first order in the small parameter characterizing the deformation, an exact solution is obtained. As an application, the case of a fluid oblate spheroid is considered and the drag experienced by it is evaluated. Special well-known cases are then deduced.

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Zusammenfassung Die Stokes-Strömung um einen Flüssigkeitstropfen, der nur leicht von einer perfekten Kugel abweicht, wird untersucht. Eine Lösung wird gefunden, die exakt ist bis zur ersten Ordnung im Deformations-Parameter. Als Beispiel wird der Strömungswiderstand eines abgeplatteten Flüssigkeits-Sphäroids berechnet. Die Methode liefert für bekannte Spezialfälle korrekte Lösungen.

     

On axisymmetric Stokes flow past a finite circular pipe

The axisymmetric streaming Stokes flow past a hollow boundary of arc cross-section leads to a mixed boundary value problem that has only been solved for a hollow sphere with equal caps removed. Here a finite circular cylinder is considered and the solution is obtained via dual integral equations, involving modified Bessel functions, arising from Fourier transforms. Numerical values for the flux and drag are obtained, with particular interest accruing to the case of small pipelength for comparison with the spherical hollow boundary.

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Zusammenfassung Die axisymmetrische Stokes-Strömung um (und durch) eine hohle Begrenzung mit bogenförmigem Querschnitt führt auf eine Randwertaufgabe vom gemischten Typus, welche bis jetzt nur für eine Hohlkugel (mit zwei identischen Kugelkappen entfernt) gelöst wurde. Hier wird ein endlicher Kreiszylinder behandelt und die Lösung wird mit Hilfe von dualen Integralgleichungen erhalten; diese enthalten modifizierte Besselfunktionen, die sich durch Fourier-Transformationen ergeben. Numerische Ergebnisse werden für den Fluss und den Widerstand angegeben, wobei das sehr kurze Rohr besonders interessant ist für den Vergleich mit dem Fall der Hohlkugel.

     

Stokes flow past a porous sphere using Brinkman's model

A general non-axisymmetric Stokes flow past a porous sphere in a viscous, incompressible fluid is considered. The flow inside the sphere is governed by Brinkman's equations. A representation for velocity and pressure for the Brinkman's equations is suggested and a method of finding the flow quantities is given. Faxén's laws for drag and torque for the flow past a porous sphere are also given.     

The first eigenvalue of a spherical cap

We find upper and lower bounds for the first eigenvalue of the Laplacian on the two-sphere from which a disk has been removed, with Dirichlet conditions imposed on the resulting boundary. When the radius of the disk tends to zero our lower bound is sharper than that obtained by Del Grosso, Gerardi, and Marchetti in the preceding paper.     

Stability of critical shapes for the drag minimization problem in Stokes flow

We study the stability of some critical (or equilibrium) shapes in the minimization problem of the energy dissipated by a fluid (i.e. the drag minimization problem) governed by the Stokes equations. We first compute the shape derivative up to the second order, then provide a sufficient condition for the shape Hessian of the energy functional to be coercive at a critical shape. Under this condition, the existence of such a local strict minimum is then proved using a precise upper bound for the variations of the second order shape derivative of the functional with respect to the coercivity and differentiability norms. Finally, for smooth domains, a lower bound of the variations of the drag is obtained in terms of the measure of the symmetric difference of domains.     

Stokes flow past an assemblage of slip eccentric spherical particle‐in‐cell models

The quasisteady axisymmetrical flow of an incompressible viscous fluid past an assemblage of slip eccentric spherical particle‐in‐cell models with Happel and Kuwabara boundary conditions is investigated. A linear slip, Basset type, boundary condition on the surface of the spherical particle is used. Under the Stokesian approximation, a general solution is constructed from the superposition of the basic solutions in the two spherical coordinate systems based on the particle and fictitious spherical envelope. The boundary conditions on the particle's surface and fictitious spherical envelope are satisfied by a collocation technique. Numerical results for the normalized drag force acting on the particle are obtained with good convergence for various values of the volume fraction, the relative distance between the centers of the particle and fictitious envelope and the slip coefficient of the particle. In the limits of the motions of the spherical particle in the concentric position with cell surface and near the cell surface with a small curvature, the numerical values of the normalized drag force are in good agreement with the available values in the literature. Copyright © 2011 John Wiley & Sons, Ltd.     

Stokes flow inside a porous spherical shell: Stress jump boundary condition

An arbitrary Stokes flow of a viscous, incompressible fluid inside a sphere with internal singularities, enclosed by a porous spherical shell, using Brinkmans equation for the flow in the porous region is discussed. At the interface of the clear fluid and porous region stress jump boundary condition for tangential stresses is used. The drag and torque are found by deriving the corresponding Faxens laws. It is found that drag and torque not only change with the varying permeability, but also change for different values of stress jump coefficient. Critical permeability is found for which drag and torque change their behavior. As a limiting case the corresponding Faxens laws for the rigid spherical shell with internal singularities has been obtained.Received: December 17, 2002; revised: February 3, 2004     

A note on plane Stokes flow past a shear free impermeable cylinder

Summary The slow steady two-dimensional motion of a viscous incompressible fluid in the unbounded region exterior to a shear free circular cylinder which is impermeable is examined. It is shown that the above problem requires a certain consistency condition for the existence of a solution. In addition, a circle theorem for the biharmonic equation is presented, for the above plane Stokes flow. Some examples are also given.     

Stokes flow for the axisymmetric motion of several spherical particles perpendicular to a plane wall

The creeping flow around several spherical particles moving on a line perpendicular to a plane wall is calculated numerically using the boundary integral method. The locations of the point forces on the surfaces of the spheres are chosen so as to describe precisely the lubrication regions when the surfaces are close to one another. Earlier results are recovered for the cases of a single sphere and a wall and of two equal spheres far from a wall. New results are presented for two (equal or unequal) spheres close to a plane wall and several equal spheres far from a wall.     

A new approximate analytical solution for arbitrary Stokes flow past rigid bodies

A method of computing general Stokes flows in the presence of rigid boundaries of arbitrary shape is proposed. The solution satisfies the governing field equations exactly and the boundary conditions approximately. The method has been illustrated with three examples. The advantage of the method lies in the ease of implementation for rigid bodies of arbitrary shape, providing an approximate but analytical solution throughout the domain.     

Bounds for the First eigenvalue of a spherical cap

We study upper and lower bounds for the lowest eigenvalueλ of the Laplace operator on a spherical capC _θ inm-dimensional space (m ≥ 3). We prove that these bounds are sharp by finding asymptotic expressions forλ asθ → π and asθ → 0.     

The centrifugal instability of a Stokes layer: asymmetric disturbances

The centrifugal instability of a Stokes layer on a circular cylinder to non-axisymmetric disturbances is studied. The governing equations used previously for this problem are corrected, and numerical results are presented.

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Zusammenfassung Es wird die zentrifugale Instabilität einer Stokes'schen Grenzschicht an einem Kreiszylinder gegenüber nicht-axisymmetrischen Störungen untersucht. Die früher benützten Gleichungen für dieses Problem sind korrigiert und numerisch gelöst worden.

     

An upper bound for the first eigenvalue of a spherical cap

By working with suitable test functions, we obtain an upper bound for the principal eigenvalue of a geodesic ball on a sphere of arbitrary dimension. This bound is sharp in the limiting case when the radius of the ball approaches the diameter of the sphere.This research was supported by ARO Grant 28905-MA.     

Stokes drag on axially symmetric bodies: a new approach

In this paper a new approach to evaluate the drag force in a simple way on a restricted axially symmetric body placed in a uniform stream (i) parallel to its axis, (ii) transverse to its axis, is advanced when the flow is governed by the Stokes equations. The method exploits the well-known integral for evaluating the drag on a sphere. The method not only provides the value of the drag on prolate and oblate spheroids and a deformed sphere in axial flow which already exists in literature but also new results for a cycloidal body, an egg shaped body and a deformed sphere in transverse flow. The salient results are exhibited graphically. The limitations imposed on the analysis because of the lack of fore and aft symmetry in the case of an eggshaped body is also indicated. It is also seen that the analysis can be extended to calculate the couple on a body rotating about its axis of symmetry.     

Numerical integration with polynomial exactness over a spherical cap

This paper presents rules for numerical integration over spherical caps and discusses their properties. For a spherical cap on the unit sphere \mathbbS²\mathbb{S}^2, we discuss tensor product rules with n ²/2 + O(n) nodes in the cap, positive weights, which are exact for all spherical polynomials of degree ≤ n, and can be easily and inexpensively implemented. Numerical tests illustrate the performance of these rules. A similar derivation establishes the existence of equal weight rules with degree of polynomial exactness n and O(n ³) nodes for numerical integration over spherical caps on \mathbbS²\mathbb{S}^2. For arbitrary d ≥ 2, this strategy is extended to provide rules for numerical integration over spherical caps on \mathbbS^d\mathbb{S}^d that have O(n ^d ) nodes in the cap, positive weights, and are exact for all spherical polynomials of degree ≤ n. We also show that positive weight rules for numerical integration over spherical caps on \mathbbS^d\mathbb{S}^d that are exact for all spherical polynomials of degree ≤ n have at least O(n ^d ) nodes and possess a certain regularity property.