Dynamic Stability of Initially Curved Columns under a Time Dependent Axial Displacement of their Support

1987 ◽  
pp. 56-71
Author(s):  
A. N. Kounadis ◽  
I. Mallis
Keyword(s):  
Dynamic Stability ◽  
Axial Displacement ◽  
Time Dependent

Analytical Treatment of In-Plane Parametrically Excited Undamped Vibrations of Simply Supported Parabolic Arches

2003 ◽  
Vol 125 (1) ◽  
pp. 73-79 ◽  
Author(s):  
Dimitris S. Sophianopoulos ◽  
George T. Michaltsos
Keyword(s):  
Differential Equations ◽  
Free Vibration ◽  
Dynamic Stability ◽  
Parametric Excitation ◽  
Stability Problem ◽  
Axial Loading ◽  
Time Dependent ◽  
Analytical Treatment ◽  
Simply Supported ◽  
Forced Motion

The present work offers a simple and efficient analytical treatment of the in-plane undamped vibrations of simply supported parabolic arches under parametric excitation. After thoroughly dealing with the free vibration characteristics of the structure dealt with, the differential equations of the forced motion caused by a time dependent axial loading of the form P=P0+Pt cos θt are reduced to a set of Mathieu-Hill type equations. These may be thereafter tackled and the dynamic stability problem comprehensively discussed. An illustrative example based on Bolotin’s approach produces results validating the proposed method.

DYNAMIC STABILITY OF CABLE-STAYED BRIDGE PYLONS

2008 ◽  
Vol 08 (04) ◽  
pp. 627-643 ◽  
Author(s):  
G. T. MICHALTSOS ◽  
I. G. RAFTOYIANNIS ◽  
T. G. KONSTANTAKOPOULOS
Keyword(s):  
Dynamic Stability ◽  
Dynamic Load ◽  
Solution Method ◽  
Bridge Deck ◽  
Nonlinear Problems ◽  
Time Dependent ◽  
Metal Structures ◽  
Cable Stayed Bridge ◽  
The Stability ◽  
Cable Stayed Bridges

This paper deals with the stability of the pylons of a cable-stayed bridge under the action of time-dependent loads, due to the vibration of the bridge deck. The stability of such problems of cable-stayed bridges is solved by a technique developed in the Laboratory of Metal Structures and Steel Bridges, of National Technical University of Athens (NTUA), as well as Bolotin's technique for the solution of nonlinear problems of dynamic stability. Three cases are studied: pylons with damping, pylons under forced vibration, and pylons subjected to an arbitrary external dynamic load. Useful relations are established by the aforementioned solution method, examples for a variety of pylons are presented, and interesting results regarding the stability of each case are given in diagrams.

scholarly journals Dynamic Electromechanical Response of a Viscoelastic Dielectric Elastomer under Cycle Electric Loads

2018 ◽  
Vol 2018 ◽  
pp. 1-14
Author(s):  
Junjie Sheng ◽  
Yuqing Zhang
Keyword(s):  
Dynamic Response ◽  
Dynamic Stability ◽  
Relaxation Times ◽  
Excitation Frequency ◽  
Dielectric Elastomer ◽  
Time Dependent ◽  
Electric Load ◽  
Single Cycle ◽  
Set Up ◽  
Electric Loads

Dielectric elastomer (DE) is able to produce large electromechanical deformation which is time-dependent due to the viscoelasticity. In the current study, a thermodynamic model is set up to characterize the influence of viscoelasticity on the electromechanical and dynamic response of a viscoelastic DE. The time-dependent dynamic deformation, the hysteresis, and the dynamic stability undergoing viscoelastic dissipative processes are investigated. The results show that the electromechanical stability has strong frequency dependence; the viscoelastic DE can attain a larger stretch in the dynamic response than the quasistatic actuation. Furthermore, with the decreasing frequency of the applied electric load, the viscoelastic DE system will present dynamic stability evolution from an aperiodic motion to the quasiperiodic motion. The DE system may also experience a stability evolution from a single cycle motion to multicycle motion with the increasing relaxation times. The value and variation trend of the amplitude of the stretch are highly dependent on the excitation frequency and the relaxation time.

Numerical Simulation of a Self-Stabilizing Rotor of a Centrifugal Pump

2003 ◽  
Author(s):  
Christian Steinbrecher ◽  
Romuald Skoda ◽  
Rudolf Schilling ◽  
Norbert Mu¨ller ◽  
Alexander Breitenbach ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Hydrodynamic Forces ◽  
Axial Displacement ◽  
Operating Conditions ◽  
Time Dependent ◽  
Navier Stokes ◽  
Axial Position ◽  
Rotating Disc ◽  
Time Step ◽  
Fluid Structure

The goal of this investigation is to contribute to the design of a centrifugal pump that can operate without bearings. This paper presents numerical studies of fluid-structure interactions on a rotating disc that can move axially unrestricted in a housing. This model mimics the gap flow between the rotor and the housing of a centrifugal pump, which stabilizes the rotor. Fluid-structure occur because of hydrodynamic forces that displace the rotor. First the effect responsible for stabilizing the rotor is described in detail. The next section presents the employed 3D Navier-Stokes Computational Fluid Dynamics (CFD) code. Special interest is given to a correct implementation of the Space-Conservation Law, where the time-dependent simulations use moving meshes. The code includes additional modules for grid generation and for calculation of the hydrodynamic forces acting on the rotor surfaces and the resulting displacement of the entire rotor. Newton’s second law is used for the coupling between hydrodynamic forces and resulting axial displacement. Results from stationary simulations are presented and compared with measurements, from the German Heart Center Munich, that show an axial displacement of the rotor results in a hydrodynamic force that pulls the rotor in the opposite direction. Finally, the results from time dependent simulations where the rotor can move unrestricted in axial position are discussed. Here, the influence of the time step is investigated, as well as the influence of geometric parameters and operating conditions.

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