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1
Content available remote On the Shape of Eigen-Forms of Columns Under Non-Conservative Loads
Bogacz R., Kurnik W.
Machine Dynamics Research
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2016
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Vol. 40, No. 1
31--44
EN
In many structures of civil engineering, rotating machinery, flying objects with rocket propulsion and other systems, problems of stability arise and have to be addressed. The optimal cross-section layout in maximization of critical loads of such systems needs a deep knowledge concerning their modal properties and stability behavior, to enable one to effectively control them. The present paper is devoted to discussion of the relations between the eigenfrequencies and the eigen-modes of selected discrete and continuous models of columns subjected to conservative and non-conservative follower loads.
2
Content available An active electromagnetic stabilization of the Leipholz column
Szmidt T., Przybyłowicz P.
Archives of Control Sciences
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2012
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Vol. 22, no. 2
161-174
EN
We study the application of electromagnetic actuators for the active stabilization of the Leipholz column. The cases of the compressive and tensional load of the column placed in air and in water are considered. The partial differential equation of the column is discretized by Galerkin's procedure, and the stability of the obtained control system is evaluated by the eigenvalues of its linearization. Four different methods of active stabilization are investigated. They incorporate control systems based on feedback proportional to the transverse displacement of the column, its velocity and the current in the electromagnets. Conditions in which these strategies are effective in securing safe operation of the column are discussed in detail.
3
Content available remote Shear force allowance in lumbar spine under follower load in neutral standing posture
Kim K., Kim Y. H., Lee S.
Acta of Bioengineering and Biomechanics
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2010
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Vol. 12, no. 4
49-53
EN
It has been shown experimentally that the load carrying capacity of the spine significantly increases when compressive loads are carried along the follower load (FL) direction. However, it is necessary to modify the current FL concept because a certain amount of shear force is produced during activities in daily life. In this study, a clinically allowable range of shear force was investigated using the modified FL concept. The shear force allowance was defined as the maximum ratio of the shear force to the follower force at each vertebral body center. Then, it was shown that the appropriate shear force allowance was within approximately 0.2 ~ 0.5 from the investigation of the follower forces, the shear forces, and the muscle force coordination. The predicted shear force allowance indicated that the resultant joint force is directed to a certain inside region between a half vertebral body and whole vertebral body.
4
Content available remote Stability of Slender Non-Conservative Columns Made of Thermo-Active Gradient Materials
Kurnik W.
Machine Dynamics Problems
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2008
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Vol. 32, No. 4
50-66
EN
The paper is concerned with stability analysis of slender thin-walled cantilever beam subjected to axial distributed follower load, modelled as Leipholz columns and made of functionally gradient materials. Both transverse and longitudinal material gradients are studied as a result of different phase mixture with inclusion of thermo-active shape memory alloy (SMA). Attention is focused on the effect of phase transformation in SMA caused by increase of temperature and resulting in considerable changes of the local visco-elastic material properties which in turn affect system stability. Equivalent homogeneous beam stiffness and internal Kelvin-Voigt loss factor are determined using Kirchhoff's hypothesis and the visco-elastic principle. Partial equation of transverse column vibration is transformed to ordinary equations by means of two-mode Galerkin's discretisation based on the cantilever beam functions. Eigen-value behaviour and critical follower force are studied for various material gradient configurations. A concept of intelligent column is proposed utilizing longitudinal material functionality induced by non-uniform temperature distribution.
5
Content available remote Application of Sugiyama stability criterion to a geometrically non-linear system under follower load
Przybylski J.
Vibrations in Physical Systems
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2002
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Vol. 20
246--247
6
Content available remote Piezoelectric Stabilisation of Leipholz Columns
Kurnik W.
Machine Dynamics Problems
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2000
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Vol. 24, No. 1
121-129
EN
The paper is concerned with a concept of flutter suppression in slender columns subjected to tangential follower forces. The mechanism of self-excitation of such systems is more or less recognised what enables a designer to apply proper stabilisation methods including active techniques. Promissing results have been obtained in numerical experiments with distributed piezoelectric actuators contracting column curvature occurring as a disturbance of the strait-line equilibrium position. Piezoelements can also be used in what is called shunting effect to additionally dissipate energy of transverse vibration. The method has been successfully applied in reduction of resonat vibrations of transversely loaded beams and plates. In the present paper the shunting effect is modelled and examined from the point of view of application in a non-conservative self-excited system being the Leipholz column.
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