Abstract
A new approximate method for the determination of natural frequencies of a cantilever beam in free bending vibration by a rigid multibody system is proposed. Uniform Euler-Bernoulli cantilever beams with and without a lumped mass at the tips are considered. The modelling method consists of two steps. In the first step, the cantilever beam is replaced by lumped masses interconnected by massless flexible beams. In the second step, the massless flexible beams are replaced by massless rigid beams connected through revolute and prismatic joints with corresponding springs in them. Elastic properties of the massless flexible beams are modelled by the springs introduced. The method proposed is compared with similar ones in the literature.
Zusammenfassung
Es wird eine neue Methode angezeigt, für die approximative Bestimmung der Kreisfrequenz der elastischen, transversal schwingenden Konsole. Diese Methode stützt sich auf die Theorie des Mehrkörpersystems. Es wird eine homogene Konsole betrachtet, mit und ohne konzentrierte Masse auf ihrer freien Ende. Diese Methode besteht aus zwei Schritten. In erstem Schritt wird die Traverse durch ein System von konzentrierten Massen, die gegenseitig mit elastischen, leichten Kolben verbunden sind, ersetzt. Im zweiten Schritt werden die elastischen Kolben durch leichte, steife Kolben ersetzt, die gegenseitig mit rotierenden und prismenförmigen Gelenken mit entsprechenden Federn verbunden sind. Durch diese Federn werden die elastischen Merkmale der leichten, flexiblen Kolben modelliert. Diese Methode wurde auch mit verwandten Methoden in der Literatur verglichen.
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Abbreviations
- x, y, z :
-
Axes of the inertial coordinate frame
- F :
-
Force [N]
- M :
-
Torque of a couple [Nm]
- u :
-
Deflection [m]
- L :
-
Length [m]
- E :
-
Young’s modulus of elasticity [N/m2]
- I z :
-
Axial moment of inertia for the principal axis z [m4]
- i, j, k :
-
Unit vectors of axes x, y, and z, respectively
- u, u P :
-
Displacement vectors of points B and P, respectively
- p i :
-
Local vector of the ith massless beam
- K B , K P :
-
Stiffness matrices corresponding to points B and P
- q i :
-
Displacement in the ith joint
- c i :
-
Stiffness of the spring in the ith joint
- m :
-
Mass of the beam [kg]
- m i :
-
Mass of the particle M i [kg]
- m T :
-
Lumped mass at the tip of the cantilever beam
- n :
-
Number of equal parts
- e i :
-
Unit vector of the axis of the ith joint
- T :
-
Kinetic energy [J]
- \(\mathbf{V}_{M_{\alpha}}\) :
-
Velocity of the particle M α
- \(\mathbf{r}_{M_{\alpha}}\) :
-
Position vector of the particle M α
- q :
-
Vector of generalized coordinates
- q 0 :
-
Vector of zero values of generalized coordinates
- \(\dot{\mathbf{q}}\), \(\ddot{\mathbf{q}}\) :
-
First and second time derivatives of the vector q
- \(\mathbf{\overline{q}}_{1}\) :
-
Vector of odd generalized coordinates
- \(\overline{\mathbf{q}}_{2}\) :
-
Vector of even generalized coordinates
- \(\ddot{\mathbf{\overline{q}}_{1}}\), \(\ddot{\mathbf{\overline{q}}_{2}}\) :
-
Second time derivatives of the vectors \(\mathbf{\overline{q}}_{1}\) and \(\overline{\mathbf{q}}_{2}\)
- M :
-
Mass matrix
- m ij :
-
Components of the mass matrix M
- K, \(\overline{\mathbf{K}}\), K ⋆ :
-
Stiffness matrices of the system
- 0 :
-
Zero matrix
- I :
-
Identity matrix
- \(\overline{\mathbf{M}}_{ij}\) :
-
Block matrices of the matrix \(\overline{\mathbf{M}}\)
- \(\overline{\mathbf{K}}_{ij}\) :
-
Block matrices of the matrix \(\overline{\mathbf{K}}\)
- \(\mathbf{K}_{ij}^{\star}\) :
-
Block matrices of the matrix K ⋆
- \(\mathbf{T}_{\varLambda}, \mathbf{T}_{\varPi}, \tilde{\mathbf{B}}, \tilde{\tilde{\mathbf{B}}}\) :
-
Matrices
- v :
-
Eigenvector
- w i :
-
The ith root of the transcendental equation
- θ :
-
Slope
- Π :
-
Potential energy of the cantilever beam
- Π c :
-
Potential energy of the system of springs in the joints
- \(\overline{\chi}_{i}\), χ i :
-
Identifiers of the joint type
- ω i :
-
The ith natural frequency [rad/s]
- \(\overline{\omega}_{i}\) :
-
The ith non-dimensional natural frequency
- T :
-
Matrix transposition operation
- −1:
-
Inverse matrix operation
- q 0 :
-
Zero values of generalized coordinates
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Acknowledgements
This research was supported under grants no. TR35006 and no. ON174016 by the Ministry of Education, Science and Technological Development of the Republic of Serbia. This support is gratefully acknowledged.
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Šalinić, S., Nikolić, A. On the determination of natural frequencies of a cantilever beam in free bending vibration: a rigid multibody approach. Forsch Ingenieurwes 77, 95–104 (2013). https://doi.org/10.1007/s10010-013-0168-0
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DOI: https://doi.org/10.1007/s10010-013-0168-0