Name: rigid body rotation in euler’s frame
Uploaded: 2024-03-07T13:22:28.000Z
Duration: 1 min 19 s
Channel: JoVE

慣性座標系で角速度 ω で回転する剛体を考えてみます。
別の回転フレームがボディに取り付けられており、これはボディとともにΩ角速度で移動します。
総モーメントの合計は、回転フレームに対する重心周りの角運動量の変化率と、物体の角速度とその角運動量の対積の合計に等しくなります。
回転軸の角速度が物体の角速度と等しい場合、回転軸に対するモーメントと慣性の積は一定になります。
角運動量のスカラー成分を思い出すと、全モーメント方程式はスカラー成分で表すことができます。
回転軸が慣性の主軸として選択されると、慣性項の積は消え、全モーメント方程式のスカラー形式が単純化されます。
これらは、回転する物体のオイラーの運動方程式として知られています。

 オイラーの運動方程式

Euler Equations of Motion

慣性座標系内で角速度 ω で回転する剛体を想像してください。 これに加えて、本体自体に取り付けられた 2 番目の回転フレームをイメージしてください。 このフレームは身体とともに動き、角速度 Ω を持ちます。 質量中心の周りの合計モーメントは、回転フレームに対する質量中心の周りの角運動量の変化率と、物体の角速度と角運動量の外積を加算することによって計算されます。

ここで、これらの回転軸の角速度が物体自体の角速度に等しい状況を考えてみましょう。 このようなシナリオでは、回転軸に関する慣性モーメントと慣性積は一定のままになります。 角運動量のスカラー成分を思い出し、これらを使用すると、スカラー成分の観点から合計モーメントの方程式を表すことができます。

回転軸を慣性の主軸として選択すると、慣性項の積はなくなります。 この単純化により、総モーメント方程式がより管理しやすいスカラー形式になります。 これらの原理と方程式は、回転体のオイラーの運動方程式を構成します。 これらの方程式は、回転剛体の力学に関する貴重な洞察を提供し、さまざまな条件下での剛体の挙動を理解し、予測できるようにします。

慣性座標系で角速度 ω で回転する剛体を考えてみます。
もう一つ回転フレームが本体に取り付けられており......

Education

JoVE Core

Mechanical Engineering

機械工学

Unit 1

ユニット1

3-Dimensional Kinetics of a Rigid Body

剛体の三次元動力学

KEY TERMS AND CONCEPTS

主要用語および概念

rigid body rotation in euler’s frame

Euler’s equations of motion describe how a rigid body rotates when measured in a moving frame attached to the body. The body rotates with angular velocity ω in an inertial frame, and the attached frame rotates with angular velocity Ω. Together, these two frames help describe the motion of the rigid body around its center of mass.

The total moment about the center of mass is found by adding two parts. One part is the rate of change of angular momentum about the center of mass in the rotating frame. The other part is the cross product of the body’s angular velocity and its angular momentum.

A useful simplification appears when the angular velocity of the rotating axes equals the angular velocity of the body. In that case, the moments of inertia and product of inertia about those rotating axes remain constant. The scalar components of angular momentum can then be used to write the total moment in a simpler form.

If the rotating axes are chosen as the principal axes of inertia, the product of inertia term disappears. This gives a more manageable scalar form of the total moment equation. These steps lead to Euler’s equations of motion for rotating rigid bodies, which help describe and predict how they behave under different conditions.

Rigid Body Rotation in Euler’s Frame

moments and product of inertia

Moment and Product of Inertia Basics

Moment of inertia and product of inertia describe how mass is distributed in a rigid body. They help show how the body responds about coordinate axes and planes. For a small mass element, the moment of inertia is found by multiplying the element's mass by the square of the shortest distance to one of the three coordinate axes. That same idea is extended to the whole body by integration. Adding the contributions of all the small mass elements gives the body's moment of inertia about that axis.

inertia tensor

Principal Axes and Moments of Inertia

The inertia tensor describes how mass is spread out in a rigid body and how that body resists rotation. It is written as a 3×3 matrix, and each entry represents a moment of inertia about a particular axis. This makes the tensor a compact way to study rotational behavior in three dimensions. The diagonal entries show the moments of inertia about the principal axes. These principal axes are the directions where the object has the least resistance to rotation. A smaller moment of inertia along...

moment of inertia about an arbitrary axis

moment-of-inertia-about-an-arbitrary-axis

Calculating Moment of Inertia on Any Axis

Moment of inertia can be calculated about any chosen axis, not just a principal axis. It depends on the mass distribution of the object along that axis. This makes it useful when an object rotates in a real machine or other setup where balance and stability matter. To find the moment of inertia about an arbitrary axis, the perpendicular distance from the axis to each mass element is needed. That distance is obtained with a cross product between the unit vector that gives the axis direction and...

angular momentum about an arbitrary axis

Angular Momentum Relative to Point P

Angular momentum relative to point P is found by adding the motion of every mass element in a rigid body. The body has mass m and a center of mass at point G. It rotates in an inertial reference frame, and the angular momentum at P comes from the cross product of each position vector and its linear momentum. To build the full expression, the velocity of each mass element is written as two parts. One part is the translational velocity of the body. The other part is the relative velocity caused...

angular momentum and principle axes of inertia

angular-momentum-and-principle-axes-of-inertia

Angular Momentum in Principal Axes

Angular momentum in a rigid body can be written using rectangular coordinates. The body’s angular momentum comes from the cross-product of each mass element’s position vector with the cross-product of the body’s angular velocity and that position vector. This gives a compact way to describe how a solid structure moves in rotation. To work with the equation more easily, the XYZ axes can be chosen as a new set of rectangular axes. These axes may be inclined at any angle to the reference frame.

principle of impulse and moment

Impulse and Angular Momentum in Rigid Bodies

Impulse and angular momentum help describe a rigid body moving in a plane. This motion combines translation and rotation. The topic uses Newton's second law to connect force, momentum, and motion. For translational motion, the equation is written for the center of mass, labeled G. When this equation is multiplied by a small time interval, dt, and integrated, it gives the principle of linear impulse. This principle shows that a change in momentum is proportional to the impulse applied to the...

kinetic energy for a rigid body

Rigid Body Energy from Center and Rotation

Rigid body kinetic energy in planar motion can be written using the body’s center of mass and its rotation. The solid object moves in general planar motion, and its center of mass is marked at point G. To find the kinetic energy of the i-th particle, the relative velocity definition is used with the position vector rA from point A to that particle. The kinetic energy of the whole body is built from the particles. First, a scalar product is taken. Then the expression is written in integral form.

equation of motion for a rigid body

Rigid Body Motion: Force and Moment Balance

Rigid body motion is described with both translational motion and rotational motion about the center of mass, point G. The center of mass is the point where Newton's Second Law applies to translation. It gives the linear motion of the body. The same body also has rotational motion about point G. The combined moments about the center of mass equal the rate of change of angular momentum. A moment is the turning effect caused by a force, and an external force applied away from the center of mass...

euler equations of motion

Euler’s equations of motion describe how a rigid body rotates when measured in a moving frame attached to the body. The body rotates with angular velocity ω in an inertial frame, and the attached frame rotates with angular velocity Ω. Together, these two frames help describe the motion of the rigid body around its center of mass. The total moment about the center of mass is found by adding two parts. One part is the rate of change of angular momentum about the center of mass in the rotating...

torque free motion

Mars Spin Under No Torque

Torque-free motion describes the movement of a rigid body when no external torques act on it. It can be seen in places with no outside forces or friction, such as outer space. Mars is one example of this kind of motion because it rotates in space without external torque. Mars is an axisymmetric object, which means it has an axis of symmetry. That symmetry defines the rotating z-axis. The rotating frame is set so that Mars&amp;#39;s center of mass is at the origin. This setup makes the moments...

key terms and concepts

Explore how Euler’s equations use a rotating frame, angular momentum, and principal axes to describe rigid body rotation in a simpler scalar form.

Rigid Body Rotation in Euler’s Frame | JoVE K12

JoVE Core 機械工学は、平衡、力、トラス解析、構造力学などの重要なトピックをカバーする簡潔でわかりやすいアニメーション ビデオを提供します。実際のアプリケーションを探索し、科学者主導の実験を通じてこれらのコンセプトが実際に動作しているのを目撃してください。

mechanical engineering

Rigid Body Rotation in Euler’s Frame

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