Chapter 9: Vector Calculus
Section 9.8: Divergence Theorem
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Example 9.8.8
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Apply the Divergence theorem to the vector field and , the region bounded by the elliptic paraboloid and the plane .
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Solution
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Mathematical Solution
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The divergence of F:
Implement the integral of over the interior of :
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To compute the flux through , note that there are two boundaries, the upper elliptic paraboloid, and the ellipse and its interior that is the intersection of the paraboloid and the plane . To compute the flux through the upper surface, note that on that surface
If this be integrated over the ellipse , the result is
=
On the lower boundary (ellipse), the outward normal is , so , which becomes zero in the plane . Hence, the flux through the interior of the ellipse at the bottom of vanishes, and the flux through the upper surface matches the volume integral of the divergence.
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Maple Solution - Interactive
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The Student VectorCalculus package is needed for calculating the divergence, but it then conflicts with any multidimensional integral set from the Calculus palette. Hence, the Student MultivariateCalculus package is installed to gain Context Panel access to the MultiInt command.
Initialize
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Tools≻Load Package: Student Vector Calculus
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Loading Student:-VectorCalculus
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Tools≻Tasks≻Browse: Calculus - Vector≻
Vector Algebra and Settings≻
Display Format for Vectors
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Press the Access Settings button and select
"Display as Column Vector"
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Display Format for Vectors
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Define the vector field F
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Enter the components of F in a free vector.
Context Panel: Evaluate and Display Inline
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Context Panel: Student Vector Calculus≻Conversions≻To Vector Field
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Context Panel: Assign to a Name≻F
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Obtain , the divergence of F
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Common Symbols palette: Del and dot-product operators
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Context Panel: Evaluate and Display Inline
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Context Panel: Assign to a Name≻
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Obtain the volume integral of the divergence of F
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Tools≻Load Package:
Student Multivariate Calculus
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Loading Student:-MultivariateCalculus
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Context Panel: Assign to a Name≻Y
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Write the name given to the divergence and press the Enter key.
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Context Panel: Student Multivariate Calculus≻Integrate≻Iterated
Complete the dialogs as per the figures below.
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Context Panel: Evaluate Integral
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Calculus palette: Iterated triple-integral template
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Context Panel: Evaluate and Display Inline
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There are two parts to the boundary of , the surface of the upper hemisphere, and, in the plane , the interior and boundary of the ellipse . For the flux through the upper surface, use a task template.
Tools≻Tasks≻Browse:
Calculus - Vector≻Integration≻Flux≻3-D≻Through a Surface Defined over an Ellipse
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Flux through a Surface Defined over Interior of an Ellipse
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For the Vector Field:
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On the lower boundary (ellipse), the outward normal is , so , which becomes zero in the plane . Hence, the flux through the interior of the ellipse at the bottom of vanishes, and the flux through the upper surface matches the volume integral of the divergence.
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Maple Solution - Coded
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Initialize
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Install the Student VectorCalculus package.
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Obtain , the divergence of F
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Use the int command to integrate the divergence of F over
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Use the Flux command to obtain the flux of F through the hemispheric surface
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On the lower boundary (ellipse), the outward normal is , so , which becomes zero in the plane . Hence, the flux through the interior of the ellipse at the bottom of vanishes, and the flux through the upper surface matches the volume integral of the divergence.
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