Taylor’s Series Expansion - 2.2 | 17. Cylindrical Coordinate System | Solid Mechanics
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2.2 - Taylor’s Series Expansion

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Interactive Audio Lesson

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Introduction to Taylor's Series Expansion

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0:00
Teacher
Teacher

Today, we’ll analyze how we can apply Taylor's series expansion to stress components in cylindrical coordinates. Why do you think we need Taylor’s expansion here?

Student 1
Student 1

To simplify the stress calculations around a central point?

Teacher
Teacher

Exactly! It helps us approximate the stress variation around a cylinder's centroid.

Student 2
Student 2

So, does it mean we ignore higher-order terms?

Teacher
Teacher

Yes! By ignoring them, we can focus on the most significant contributions.

Student 3
Student 3

And how do basis vectors play into this?

Teacher
Teacher

Great question. Basis vectors change with the angle θ, but remain constant with r and z. This fact significantly influences how we calculate forces.

Student 4
Student 4

Can you summarize the key points we've discussed?

Teacher
Teacher

Certainly! Taylor's expansion is applied for approximation, higher-order terms are ignored, and basis vectors influence calculations based on θ.

Derivatives of Basis Vectors

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0:00
Teacher
Teacher

Now, let's focus on how we derive the changes in basis vectors with respect to θ. Anyone want to explain what that means?

Student 1
Student 1

It means understanding how the vectors e_r and e_θ behave as θ changes?

Teacher
Teacher

Precisely! We can visualize this through geometry.

Student 2
Student 2

So, is it related to how we transport radial vectors?

Teacher
Teacher

Exactly! By translating them to a common point, we can measure the angle change.

Student 3
Student 3

And how do we conclude the direction of e_θ?

Teacher
Teacher

Using the defined angle bisector, we can deduce the relationship of e_θ with e_r.

Student 4
Student 4

Can you wrap this up?

Teacher
Teacher

Of course! We explored the geometrical approach to derive how basis vectors adjust to changes in θ.

Application to Linear Momentum Balance

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Teacher
Teacher

Let’s discuss how to apply these expansions in the context of the linear momentum balance. Can anyone describe our next steps?

Student 2
Student 2

We’ll plug in the derivatives we found into our equations for stress!

Teacher
Teacher

Correct! This allows us to better approximate the forces acting on the cylindrical face.

Student 3
Student 3

What about the forces on the z-planes?

Teacher
Teacher

Good point! Each face's calculation helps us establish a complete balance. We must consider both +z and -z planes.

Student 4
Student 4

Can you summarize again?

Teacher
Teacher

Great recap! We learned that the Taylor’s expansion simplifies integration for calculating forces affecting momentum balance.

Introduction & Overview

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Quick Overview

This section delves into the application of Taylor's series expansion for stress components in cylindrical coordinates, illustrating its significance in deriving linear momentum balances.

Standard

The section outlines the use of Taylor's series expansion to analyze varying stress components within cylindrical elements. It emphasizes the simplification of terms through derivatives and illustrates how these derivatives are utilized in the context of linear momentum balance.

Detailed

In this section, we explore the Taylor’s series expansion as applied to stress components within a cylindrical coordinate framework. As stress varies across the cylindrical element, the use of Taylor's expansion allows for approximating these variations around the centroid of the cylindrical element at coordinates (r, θ, z). We ignore higher-order terms to simplify our calculations, which leads us to understand how basis vectors change with respect to the angular coordinate θ, while maintaining constant values along the radial and vertical coordinates. The calculations yield crucial insights into the interactions of these variables within the linear momentum balance framework.

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Introduction to Taylor's Series Expansion

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As the stress components are varying in the domain of integration, we can use Taylor’s expansion about the center of the cylindrical element, i.e., at (r,θ,z).

Detailed Explanation

In this chunk, we are discussing the context in which Taylor's series is applied. When evaluating the stress components in a cylindrical element, these stresses vary across the element. To simplify the calculations, we can employ Taylor's series, which allows us to approximate complex functions using polynomials. Specifically, we expand the stress components around a certain point—here, the center of the cylindrical element—characterized by coordinates (r, θ, z). The expansion helps in managing the variations in stress across the element, providing a way to analyze these variations mathematically.

Examples & Analogies

Think of a curved surface, like a hill. If you want to analyze changes in elevation at various points on the hill, you can start at a specific point (the center) and use a simple mathematical model (like a straight line) to represent the slope around that point. Similarly, the Taylor series expansion allows us to create a simple model that represents the changes in stress at the center of the cylindrical element, making calculations more manageable.

Expanding Stress Components and Basis Vectors

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In equation (3), e.g., we need to Taylor expand both the stress components as well as basis vectors. Ignoring higher order terms, we get...

Detailed Explanation

This chunk carries forward the idea of applying the Taylor series. Here, we not only expand the stress components but also the basis vectors associated with the cylindrical coordinates. The Taylor expansion involves disregarding the higher-order terms (those that are very small compared to the first few terms) to simplify our calculations. This means we will focus on the primary terms that will have the most significant effect on the results, which allows us to capture the essential behavior of the system without getting bogged down in complicated calculations.

Examples & Analogies

Imagine you are trying to predict the temperature changes in a room throughout the day. Instead of looking at every slight fluctuation, you might take an average and only focus on the most significant changes—like the times when the sun shines through the window or when the air conditioning kicks in. By simplifying the situation like this, you gain insights without overwhelming details. The same principle applies in engineering when we simplify stress calculations.

Partial Derivatives with Respect to Coordinates

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As e and e change only with θ, their partial derivatives with respect to r and z will be zero...

Detailed Explanation

In this chunk, we delve into the nature of how the basis vectors e_r and e_θ change. The statement highlights that their variation is only dependent on the angular coordinate θ, which allows us to state that their partial derivatives with respect to the other coordinates (r and z) are zero. This simplification is critical as it greatly reduces the complexity when we want to differentiate these vectors in our equations, focusing solely on their dependency on the angle.

Examples & Analogies

Consider a spinning top, where the position of the top changes along a circular path based on its angle. However, the distance from the center (like the radius) doesn’t affect its spin speed—the spin depends entirely on the angle. Just like that, here the basis vectors' adjustment is reliant only on the angle θ, simplifying our understanding and analysis in the calculations.

Definitions & Key Concepts

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Key Concepts

  • Taylor's Series: Used for function approximation in stress components.

  • Cylindrical Coordinates: Important for analyzing 3D stress in cylindrical elements.

  • Basis Vectors: Their change with θ is crucial for accurate calculations.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • A cylindrical element may have varying stress depending on the angle θ, necessitating the use of Taylor’s expansion for accuracy in calculations.

  • When assessing forces, consider both the +z and -z planes of a cylindrical element for a complete momentum balance.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • For a series that expands, close to a point it stands, stress varies here, just see it clear.

📖 Fascinating Stories

  • Imagine a cylindrical can rolling; as it moves, the stress at different points shifts, just like we adjust our plans using Taylor’s method.

🧠 Other Memory Gems

  • Remember CAR for Cylindrical coordinates: Change in basis, Angle considerations, Radial assessment.

🎯 Super Acronyms

STA

  • Simplifying Taylor for Approximations around a point.

Flash Cards

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Glossary of Terms

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  • Term: Taylor's Series Expansion

    Definition:

    A mathematical method for approximating functions by polynomials at a given point.

  • Term: Cylindrical Coordinates

    Definition:

    A coordinate system that extends polar coordinates to three dimensions using (r, θ, z) coordinates.

  • Term: Basis Vectors

    Definition:

    Vectors that form the basis of the coordinate system, which can change in cylindrical coordinates depending on position.