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2013 | OriginalPaper | Buchkapitel

4. Rigid-Body Systems

verfasst von : Murilo G. Coutinho

Erschienen in: Guide to Dynamic Simulations of Rigid Bodies and Particle Systems

Verlag: Springer London

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Abstract

This chapter presents the theoretical and practical aspects of designing and implementing dynamic-simulation engines for rigid-body systems. It covers both generic and specialized algorithms for non-convex and convex objects, respectively, including the special cases of thin and fast moving objects. Special attention is given to one of the most difficult and least understood topics in physically based modeling, namely, the computational techniques needed for determining all impulsive and contact forces between bodies with multiple simultaneous collisions and contacts.

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Vorheriges Kapitel Particle Systems

Nächstes Kapitel Articulated Rigid-Body Systems

The algorithm presented in Appendix F (Chap. 11) limits the set of valid cut faces to simple polygons (without holes or double edges). This, in turn, makes the algorithm unsuitable for decomposing complex geometric shapes.

This issue has been already discussed in Sect. 1.4.4 of Chap. 1, but it is revisited here for completeness.

The direction defined by the line connecting the closest points at t _i.

Since an edge is shared by two faces, the underlying implementation data structure representing the rigid body’s face must have its own edge structure because the same edge has one direction for one of its faces, and the reverse of this direction for the adjacent face.

This owes to the fact that the bodies have convex shapes. Unfortunately, the same does not apply for the case in which the bodies have non-convex shapes.

There is no particular preference for which violated plane should be used in the event that there is more than one.

We shall use the parameter λ to index the points on edge b ₂.

Recall that \(\vec{p}_{2}\) is the point on b ₂ closest to b ₁.

Equation (4.33) is the same as Eq. (4.29), and is repeated here for convenience.

The plane in this case is defined as \(\pi_{\vec{p}_{i}, \vec{q}_{i}} = \{\vec{x}: (\vec {n}_{i} \cdot \vec{x} + d_{i}) = 0\}\), as opposed to \(\{\vec{x} : (\vec{n}_{i} \cdot \vec{x} - d_{i}) = 0\}\). The latter is the definition used in all other sections of this book.

We will use the vector-based notation as much as possible to keep the equations concise. However, there are cases in which we do need to rewrite the equations using the individual components of each vector, such as when computing the critical-friction coefficient covered later in this section.

Even though the use of the indexes is not particularly useful for the single-collision case, they will be extensively applied in the block-matrix representation of multiple collisions to distinguish between equations associated with collisions involving different rigid bodies.

If the actual coefficient of friction is equal to the critical coefficient of friction, then the sliding motion will stop exactly at the instant corresponding to the end of the collision.

Keep in mind that the velocities computed so far assume that the sliding motion continues throughout the collision.

The local-coordinate frame is defined by the collision normal and tangent plane.

Whenever a collision becomes a contact, the collision normal will be referred to as the contact normal.

Notice that F _t is zero if a _t(t) is zero.

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Titel: Rigid-Body Systems
verfasst von: Murilo G. Coutinho
Verlag: Springer London
Buch: Guide to Dynamic Simulations of Rigid Bodies and Particle Systems
Print ISBN: 978-1-4471-4416-8

Electronic ISBN: 978-1-4471-4417-5

Copyright-Jahr: 2013
DOI: https://doi.org/10.1007/978-1-4471-4417-5_4

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