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A link object connects two joints, i and j, separated by length L, such that specialized structural behavior may be modeled. Linear, nonlinear, and frequency-dependent properties may be assigned to each of the six deformational degrees-of-freedom
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(DOF)
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which
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are
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internal
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to
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a
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link,
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including
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axial,
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shear,
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torsion,
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and
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pure
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bending.
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Internal
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deformation
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is
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then
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calculated
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from
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joint
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j
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displacement
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relative
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to
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joint
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i
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,
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where
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i
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may
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be
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grounded
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to
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simulate
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a
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support
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point.
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To
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utilize
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nonlinear
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and
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frequency-dependent
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properties,
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corresponding
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analysis
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must
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be
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defined
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and
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run.
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Link
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(F-D)
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relationships
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may
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be
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specified
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for
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each
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of
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the
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6-DOF
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to
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simulate:
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- Multi-linear
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- springs
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- (uniaxial
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- elasticity)
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- Wen
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- behavior
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- (uniaxial
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- plasticity)
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- Kinematic,
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- Takeda,
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- and
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- pivot
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- behavior
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- (multi-linear
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- uniaxial
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- plasticity)
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- Gap
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- (compression-only)
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- and
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- hook
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- (tension-only)
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- elements
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- Isolation
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- devices
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- (biaxial-plasticity
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- and
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- friction-pendulum
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- isolators
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- with
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- optional
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- uplift)
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- Viscoelastic damping is specified in Force/Velocity
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- units
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All
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shear
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deformation
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is
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assumed
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to
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occur
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within
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a
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shear
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spring.
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Shear-spring
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location
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may
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be
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specified
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in
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terms
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of
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distance
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from
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joint
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j
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,
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where
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dj2
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is
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the
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major-axis
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shear-spring
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location,
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and
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dj3,
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the
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minor-axis.
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As
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such,
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dj2
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represents
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the
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location
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for
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1-2
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plane
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shearing
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and
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1-3
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plane
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bending,
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while
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dj3
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is
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the
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reverse.
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Either
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translation
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or
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rotation
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may
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induce
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shear
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deformation.
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Each
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of
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the
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six
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springs
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and
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hinges
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which
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correlate
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with
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internal
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link
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deformation
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may
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actually
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be
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several
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coincident
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components
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which
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form
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a
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system
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of
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springs
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and
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dashpots.
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F-D
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relationships
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within
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a
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single
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DOF,
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or
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among
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multiple
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DOF,
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may
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be
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coupled
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or
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independent.
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Each
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F-D
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relationship
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is
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defined
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within
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a
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local
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coordinate
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system
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which
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is
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specific
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to
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that
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link.
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Links
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may
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be
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of
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zero
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length,
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as
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is
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the
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case
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with
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links
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grounded
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at
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support
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points.
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For
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dynamic
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analysis,
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numerical
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solution
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requires
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that
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m
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,
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and
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mass
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moments
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of
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inertia
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mr1
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,
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mr2
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,
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and
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mr3
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,
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be
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assigned
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to
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a
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link
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such
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that
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response
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captures
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translational
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and
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rotational
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inertia.
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Half
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of
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each
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of
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these
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values
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will
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be
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assigned
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to
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each
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joint
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within
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a
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link.
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Internal
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deformation
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and
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internal
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forces
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are
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then
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reported
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as
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output
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local
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to
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each
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joint.
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Additional
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information
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is
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available
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in
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the
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...
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(The
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Link/Support
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Element
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Basic,
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page
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229)
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and
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(The
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Link/Support
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Element
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Advanced,
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page
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253).
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