DESCRIPTION OF SOME LINEAR AND NON-LINEAR MODELING ELEMENTS
Linear Elements
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Alford's force element
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The element allows computing of aerodynamic cross-coupling forces operating
in axial flow compressors and leading to instability of rotor system. It is based
on the correlation discovered by J.S. Alford.
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Wachel's force element
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The element allows computing aerodynamic cross-coupling forces acting in centrifugal
compressors and leading to instability of rotors. It is based on J.C. Wachel's empirically
derived correlation
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Block of code and elements for computation of shaft systems with gearings
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This allows computing shaft systems with cylindrical, bevel, helical and hypoid
gearings.
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Function of import of super elements from FEM systems
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The element gives an opportunity to combine solutions obtained in FEM program
and in DYNAMICS R4 by means of modal synthesis method. It allows to take into account
the complex configuration of separate assembly units, for example, cases and housings.
Non-linear Elements
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"Clearance" element ("Elastic Damping Lateral Restraint" element)
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This element allows to model different cases of full or partial rubbings of
rotating and non-rotating structures. This allows you to model most cases of instability
in rotating systems with clearances. It takes into account any kinds of contact
with external and internal damping, with friction in contact point, weight and circumferential
irregularity of clearance. The element is indispensable for educating engineers
in fundamental non-linear dynamics.
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Journal bearing element
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This element allows computing the rotating system with two notable cases of
plain bearing: "short" bearing and the "long" bearing. Different kinds of cavitation
of fluid film are considered: uncavitated (2-π film) damper and cavitated (π-film)
damper. It allows to compute dynamical systems in steady-state and non-steady state
conditions.
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Squeeze-film damper element
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This element models two well-known cases of hydrodynamic damper: the "short"
damper and the "long" damper. Combinations of these cases are also possible. Different
kinds of fluid film cavitations are considered: uncavitated (2-π film) damper
and cavitated (π-film) damper. Fluid inertia effects are also included in squeeze
film damper models. It allows to compute dynamical systems in steady-state and non-steady
state conditions. Any number of squeeze-film dampers in rotating system. Fast computation.
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User-programmable non-linear element
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It allows to use the user's own algorithms of nonlinear effects in rotating
machinery to program new elements and also to integrate them into DYNAMICS R4 program
system. The new element can be of any complexity and it can be used in a rotor model
in combination with other non-linear elements of DYNAMICS R4. The language of
programming is the script language Python (www.python.org) built-in in DYNAMICS
R program system and can be easily mastered by the user. This element is indispensable
for engineers and post-graduate students carrying out investigations in the rotor
dynamics field. By the user's request the new element which was made in a script
language can be adapted and included in program system by DYNAMICS R4 developers
(Alfa-Tranzit Co., Ltd). It will make it possible to speed up computation dozen
of times.
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Rolling bearing element
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This element allow to model the main types of rolling bearings - angular-contact
(ball) bearing , roller bearing, etc. The Hertz theory is used for computing speed
dependent stiffness and bearing forces. Clearances in bearings can also be taken
into account. The user has an opportunity to specify bearing linear and nonlinear
damping.
Individual options are offered for customers who have purchased the Dynamic R4.0
program system. Development of the following non-linear elements can be made according
to their needs:
- elliptical bearing
- multi-lobe bearing
- tilting-pad bearing
- trust journal bearing
- seals
- air-foil bearing
- magnetic bearing
- gear coupling
- tangential crack
- etc.
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ROTOR DYNAMICS OF TURBOMACHINERY
