Rotor Whirl Measurements on a Long Rotating Cylinder Partially Filled With Liquid

1993 ◽  
Vol 115 (2) ◽  
pp. 141-144 ◽  
Author(s):  
J. Colding-Jo̸rgensen
Keyword(s):  
Theoretical Analysis ◽  
Nonlinear Analysis ◽  
Dynamic Stability ◽  
Limit Cycle ◽  
Rotational Speed ◽  
Fluid Motion ◽  
Rotating Cylinder ◽  
Whirl Speed ◽  
Frequency Ratios ◽  
Further Development

A theoretical analysis of a long flexibly suspended, rotating cylinder partially filled with liquid has been presented earlier (Colding-Jo̸rgensen, 1990). Special emphasis has been placed on dynamic stability, application in centrifuges, and the influence of external damping. The present paper presents experimental results for comparison with the theoretical analysis, especially in regard to unstable speed ranges, whirl speed relative to rotational speed, and limit cycle amplitudes with external damping. The theory agrees quantitatively with regard to speed ranges and whirl frequency ratios but only qualitatively with regard to whirl amplitudes, indicating the need for further development of the nonlinear analysis of the fluid motion with external damping.

Rotor Whirl Measurements on a Long Rotating Cylinder Partially Filled With Liquid

1991 ◽  
Author(s):  
Jorgen Colding-Jorgensen
Keyword(s):  
Theoretical Analysis ◽  
Dynamic Stability ◽  
Limit Cycle ◽  
Rotational Speed ◽  
Fluid Motion ◽  
Rotating Cylinder ◽  
Linear Analysis ◽  
Whirl Speed ◽  
Frequency Ratios ◽  
Further Development

Abstract A theoretical analysis of a long flexibly suspended, rotating cylinder partially filled with liquid has been presented earlier (Colding-Jørgensen, 1990). Special emphasis has been placed on dynamic stability, application in centrifuges, and the influence of external damping. The present paper presents, experimental results for comparison with the theoretical analysis, especially in regard to unstable speed ranges, whirl speed relative to rotational speed, and limit cycle amplitudes with external damping. The theory agrees quantitatively with regard to speed ranges and whirl frequency ratios but only qualitatively with regard to whirl amplitudes, indicating the need for further development of the non-linear analysis of the fluid motion with external damping.

Field Vibration Tests and Dynamic Stability Analysis of a Full-Scaled Tainter-Gate

2004 ◽  
Author(s):  
Keiko Anami ◽  
Noriaki Ishii ◽  
Charles W. Knisely
Keyword(s):  
Theoretical Analysis ◽  
Dynamic Stability ◽  
Natural Frequencies ◽  
Hydrodynamic Pressure ◽  
Flowing Water ◽  
Rotational Vibration ◽  
Water Field ◽  
Vibration Tests ◽  
Frequency Ratios ◽  
Theoretical Analyses

This study presents results from in-air and in-water field vibration tests of a 29-ton full-scaled Tainter-gate installed on a river in Japan. These tests were conducted to confirm the validity of our theoretical analyses especially for a large value of Froude number. First, with the gate raised, an in-air experimental modal analyses, using an impact hammer and accelerometers, was conducted to determine the natural frequencies and the damping ratios for two modes of gate vibration. These two modes corresponded to the rigid body vibration of the whole gate around the trunnion pin and the streamwise rotational vibration of the skinplate. Subsequently, with the gate again lowered and exposed to flowing water, the gate vibration characteristics were carefully measured. Only weak, unsynchronized vibrations were recorded and the gate was found to be dynamically stable. A theoretical analysis developed to predict the hydrodynamic pressure, the vibration frequency ratios and the dynamic stability were applied to the full-scaled gate. The theoretical analysis correctly predicted both the measured frequency ratios and the gate’s dynamic stability.

scholarly journals Water Jet Applicator for Interface Tissue Removal in Minimally Invasive Hip Refixation: Testing the Principle and Design of Prototype

2019 ◽  
Vol 13 (2) ◽  
Author(s):  
Gert Kraaij ◽  
Arjo J. Loeve ◽  
Jenny Dankelman ◽  
Rob G. H. H. Nelissen ◽  
Edward R. Valstar
Keyword(s):  
Theoretical Analysis ◽  
Minimally Invasive ◽  
Water Pressure ◽  
Minimal Invasive ◽  
Outer Diameter ◽  
Experimental Setup ◽  
Technical Requirements ◽  
Tissue Removal ◽  
Further Development

Mechanical loosening of implants is in the majority accompanied with a periprosthetic interface membrane, which has to be removed during revision surgery. The same is true if a minimal invasive (percutaneous) refixation of a loose implant is done. We describe the requirements for a waterjet applicator for interface tissue removal for this percutaneous hip refixation technique. The technical requirements were either obtained from a literature review, a theoretical analysis, or by experimental setup. Based on the requirements, a waterjet applicator is designed which is basically a flexible tube (outer diameter 3 mm) with two channels. One channel for the water supply (diameter 0.9 mm) and one for suction to evacuate water and morcellated interface tissue from the periprosthetic cavity. The applicator has a rigid tip (length 6 mm), which directs the water flow to create two waterjets (diameter 0.2 mm), both focused into the suction channel. The functionality of this new applicator is demonstrated by testing a prototype of the applicator tip in an in vitro experimental setup. This testing has shown that the designed applicator for interface tissue removal will eliminate the risk of water pressure buildup; the ejected water was immediately evacuated from the periprosthetic cavity. Blocking of the suction opening was prevented because the jets cut through interface tissue that gets in front of the suction channel. Although further development of the water applicator is necessary, the presented design of the applicator is suitable for interface tissue removal in a minimally invasive hip refixation procedure.

Investigation of the 2D Behavior of a Rotating Cylinder in Flow Using the Discrete Vortex Method

2019 ◽  
Author(s):  
Chang-Kyu Rheem
Keyword(s):  
Rotational Speed ◽  
Vortex Method ◽  
Rotating Cylinder ◽  
Discrete Vortex ◽  
Discrete Vortex Method ◽  
Drag Forces ◽  
Runge Kutta Method ◽  
Speed Dependence ◽  
Three Stages ◽  
Lift And Drag

Abstract The influence of rotation on the behavior of a two-dimensional rotating cylinder in flow was investigated by using the discrete vortex method combined with the 4th order Runge-Kutta method. There are three stages for rotational speed dependence of hydrodynamic force on a fixed rotating cylinder, the stage where lift force increases and drag force decreases, the stage where lift and drag forces increase in proportion to the square of rotation ratio, and the stage where lift and drag forces increase in proportion to rotation ratio. As a fixed rotating cylinder begins to rotate and the rotational speed increases, the vortex train that causes VIV weakens and disappears. When the cylinder is mounted on a spring, the vibration frequency of the spring mounted rotating cylinder becomes lower. This indicates that the added mass of the rotating cylinder is increasing as the rotation ratio increases.

A Study on the Dynamic Stability of Observation Antenna Considering Rotational Speed by Payload Drive Motor

2016 ◽  
Vol 33 (8) ◽  
pp. 617-622
Author(s):  
Chae Sil Kim ◽  
Min Jae Shin ◽  
Chang Min Keum ◽  
Jae Min Kim ◽  
Hun Oh Choi
Keyword(s):  
Dynamic Stability ◽  
Rotational Speed ◽  
Drive Motor

scholarly journals Parametric instability in a rotating cylinder of gas subject to sinusoidal axial compression. Part 2. Weakly nonlinear theory

2008 ◽  
Vol 595 ◽  
pp. 291-321 ◽  
Author(s):  
J.-P. RACZ ◽  
J. F. SCOTT
Keyword(s):  
Fixed Point ◽  
Limit Cycle ◽  
Axial Compression ◽  
Local Stability ◽  
Small Amplitude ◽  
Parametric Instability ◽  
Rotating Cylinder ◽  
Basic Flow ◽  
Weakly Nonlinear ◽  
Primary Mode

A weakly nonlinear analysis is presented of parametric instability in a rotating cylinder subject to periodic axial compression by small sinusoidal oscillations of one of its ends (‘the piston’). Amplitude equations are derived for the pair of parametrically resonant (primary) inertial modes which were found to arise from linear instability in Part 1. These equations introduce an infinity of geostrophic mode amplitudes, representing a nonlinear modification of the mean flow, for which evolution equations are also derived. Consequences of the total system of equations are investigated for axisymmetric modes. Different possible outcomes are found at large times: (a) a fixed point, representing a saturated state in which the oscillatory toroidal vortices of the primary mode are phase-locked to the piston motion with half its frequency; (b) a limit cycle or chaotic attractor, corresponding to slow-time oscillations of the primary mode; or (c) exponential divergence of the amplitudes to infinity. The latter outcome, a necessary condition for which is derived in the form of a threshold piston amplitude for divergence, invalidates the theory, inducing a gross change in the character of the flow and providing a route out of the weakly nonlinear regime. Non-zero fixed-point branches arise via bifurcations from both sides of the linear neutral curve, where the basic flow changes local stability. The lower-amplitude branch is shown to be unstable, while the upper one may lose local stability, resulting in a Hopf bifurcation to a limit cycle, which can subsequently become aperiodic via a series of further bifurcations. Typically, during the resulting oscillations, whether periodic or not, the perturbation first grows from small amplitude owing to basic-flow instability, then nonlinear detuning of the parametric resonance causes decay back to small amplitude in the second half of the cycle, which then restarts.

scholarly journals Miniaturized substrate-integrated coaxial line bandpass filter with improved upper stopband

2017 ◽  
Vol 9 (7) ◽  
pp. 1441-1445 ◽  
Author(s):  
Yunlong Lu ◽  
Yi Wang ◽  
Taijun Liu ◽  
Bo Yu ◽  
Kai Li
Keyword(s):  
Theoretical Analysis ◽  
Fundamental Frequency ◽  
Bandpass Filter ◽  
Spiral Structure ◽  
Coaxial Line ◽  
Space Filling ◽  
Resonance Property ◽  
Circuit Structure ◽  
Frequency Ratios ◽  
Rejection Band

A miniaturized substrate-integrated coaxial line (SICL) bandpass filter with improved upper stopband using asymmetrical spiral stub-loaded resonators is presented in this paper. Owing to the space-filling feature of the spiral structure, the size of the proposed filter is significantly reduced. A theoretical analysis is carried out to examine the resonance property of the proposed resonator. It is found that the frequency ratios of the second and third harmonics to the fundamental frequency can be extended to 2.86 and 4.4. Benefiting from the circuit structure and SICL technology, the designed filter has a small size, wide stopband, low crosstalk, and high-density integration ability. The measured results show that the proposed filter, with dimensions of 0.051λ0 × 0.044λ0, operates at 1.056 GHz and the 20-dB rejection band is extended to 3.94f0.

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