8/11/2019 Idei Principale Articole Si Teze

1/4

1. Turbine speed governor PID gains play a very important role in hydraulic transients cause

by load changes. By optimal tun- ing of PID gains, the dynamic performance of the gener

unit can be well improved.

2.

The Effect of Inlet Swirl on the Rotordynamic Shroud Forces in a Centrifugal PumA. GUINZBURG, C. E. BRENNEN, A. J. ACOSTA and T. K. CAUGHEY

The present research investigates the contributions to the rotordynamic forces from the discharge-to-suction leakage flows between the front shroud of the rotating imp

and the stationary pump casing. In particular, the dependency of the rotordynamic characteristics of leakage flows on the swirl a t the inlet to the leakage path was exam

An inlet guide vane was designed for the experiment so that swirl could be introduced at the leakage flow inlet. The data demonstrates substantial rotordynamic effectsdestabilizing tangential force for small positive whirl ratios; this force decreased with increasing flow rate. The effect of swirl on the rotordynamic forces was found to

destabilizing.

3. The impulse response function and ship motionsW.E. Cummins 1962

4. COMPUTATION OF ADDED MASS AND DAMPING COEFFICIENTS DUE TO A HEAVING CYLINDER

DAMBARU D BHATTA 2007

We present the boundary value problem (BVP) for the heave motion due to a vertical circular cylinder in water of finite depth . The BVP is presented

terms of velocity potential function. The velocity potential is obtained by considering two regions, namely, interior region and exterior region. The

solutions for these two regions are obtained by the method of separation of variables. The analytical expressions for the hydrodynamic coefficients

derived. Computational results are presented for various depth to radius and draft to radius ratios.

5. Vibrations in Nonlinear Rotordynamics Modelling, Simulation, and Analysis

Jan Rubel 2009 phdThe two most common problems in rotordynamics of turbomachinery are the occurrence of large amplitude steady state synchronous vibrations and the occurrence of

subharmonic instabilities (San Andres, 2006). The former have their source in the unbalance of the rotor due to inevitable production inaccuracies. If e.g. the centerof gravity is not aligned with the rotation axis, the centrifugal forces will lead to a periodic forcing of the system. Resonances occur for rotational speeds equal to one orotors eigenfrequencies. These angular velocities are called critical speeds. These undesirable oscillations cause noise, wear, material fatigue and failure due to

contact, which can have serious consequences since the rotational energy contained in the system is very high. A common countermeasure to unbalance oscillation is thbalancing of the rotor to reduce the total unbalance or the introduction of damping. Another possibility is to change the geometry of the rotor-bearing system, such that

the resonance frequencies are tuned out of the operation range of the device under consideration. This can be done by shape optimization of the rotor and finding optima

positions of the bearings as has been shown in a related parallel project (Strau, 2005; Strau et al., 2007).The subharmonic vibrations have their source in the nonlinear reaction forces of the fluid bearings, seals and fly wheels interacting with the rotor. These vibrations can

also have very high amplitudes and therefore cause noise and wear. Their suppression can be achieved again by changing the geometry of the systemto tune the frequen

or by introducing damping. The most desirable option is the elimination of the source of instability. The instability caused by oil lubricated bearings is called oil whirl acan be partially suppressed by using e.g. elliptical bearings instead of circular bearings (San Andres, 2006).

6. Experimental investigation of added mass effects on a Francis turbine runner in still water

C.G. Rodrigueza, E. Egusquizaa,_, X. Escalera, Q.W. Lianga, F. Avellanb 2006

8/11/2019 Idei Principale Articole Si Teze

2/4

An experimental investigation in a reduced scale model of a turbine runner, using modal analysis, was

carried out. Several impact tests with the runner freely suspended in air and in water were done. The respwas measured with accelerometers located in different positions of the runner. From the modal analysis,

natural frequencies, damping ratios, and mode-shapes were determined. The same mode-shapes obtained

air were obtained in water but with lower natural frequencies and higher damping ratios in water. Thedifference in the natural frequencies is shown to be dependant basically on the added mass effect of the w

and not on its added damping. This difference also depends on the geometry of the mode, presenting

different values for different mode-shapes. Using nondimensional values, the reduction in the naturalfrequencies can be extrapolated to other Francis runners presenting similar geometrical characteristics.

7.NUMERICAL SIMULATION OF FLUID ADDED MASS

EFFECT ON A KAPLAN TURBINE RUNNER WITH

EXPERIMENTAL VALIDATIONDanilo de Souza Braga

Daniel Freitas Coelho

Newton Sure Soeiro

Gustavo da Silva

Vieira de Melo

The effect of the added mass and damping of water can modify considerably the natural frequenc

of the runner. An experimental investigation in a Kaplan turbine runner, using modal analysis, w

carried out. Several tests with the runner freely suspended in air were perfomed. The response w

measured with accelerometers located in different positions of a runner blade. From the modal

analysis, the natural frequencies, damping ratios, and mode- shapes were determined. Therefore,

this paper, a numerical simulation to analyze the influence of the surrounding water in a turbine

runner has been carried out using finite element method (FEM). First, the sensitivity of the FEMmodel on the element shape and mesh density has been analysed and an optimized FEM model f

the modal behaviour with the runner vibrating in air and in water has been calculated. After, the

added mass effect by comparison of the natural frequencies and mode shapes in both cases has b

determined. The numerical results obtained have been compared with experimental results availa

The comparison shows a good agreement in the natural frequency values and in the mode shapes

The added mass effect due to the fluid structure interaction has been discussed in detail.

7. Investigation on fluid added mass effect in the modal

response of a pump-turbine runner

L Y He, Y He, Y Y Luo and Z W Wang

In this paper, numerical simulation to analyze the influence of the surrounding water in a pump-

turbine runner modal has been carried out by using finite element method. The modal behavior o

8/11/2019 Idei Principale Articole Si Teze

3/4

the runner in air and in water has been calculated. In addition, the added mass effect by comparin

the natural frequencies and mode shapes in both cases has been determined. The results show tha

due to the added mass effect of the surrounding water, natural frequencies are considerably reduc

The frequency reduction ratio (FRR) varies in a range of 0.06~0.43, depending on the mode shap

Vibration amplitude and complexity of modes are the two main factors that affect the reduction r

of runner natural frequencies.

8.

Added-mass estimation of flat membranes vibrating

Yuanqi Li, Lei Wang

In the case of a vibrating structure, a part of the surrounding fluid vibrates with it. For a concrete or

construction the added mass effect is neglected due to higher ratio of density of the material and the air. In the

of the vibrating membrane the effect cannot be neglected.

Based on the theory for the vibrating chord and considering that the membrane is vibrating in vacuum and t

movement around it is irotational and inviscid , it is obtained a relation for the added mass ma = 0.68l where

air density and the chord length l . It is studied the variation coefficient along the chord and it is seen tha

practically uniform except near the end points. The results are considered to be good for the case of a

dimensional membrane and thus are calculated for different air pressures for different modes of vibration o

membrane. The results obtained are compared with the experimental results in the case of a membrane inserte

a vacuum chamber and are believed to be consistent.

9.

Numerical estimation of torsional dynamic coefficients of a hydraulic turbine

Karllson, Nilsson

The behavior in terms of rotor dynamics is influenced by the interaction between fluid and rotor. Through th

Tool are estimated inertia coefficients, damping and stiffness for a Kaplan turbine rotor with five blades. Simula

are considered for the three loading cases 35, 60 and 70%.

CFD Simulation Tool is made with OpenFoam and for obtaining the coefficients a simple model was consider

which the generator is considered rigid and thus only the rotation of the rotor is considered. The equations w

describe the water action on the rotor are presented. Simulations are employed for three different angular sp

Stiffness is neglected and the results for the added mass and damping are presented for the cases analyzed.

The findings show that these coefficients vary with the workload of the turbine. The results indicate a reduct

frequency resonance with 5-65% and an increase in damping of 30-80%.

10.

Influence of inlet boundary conditions in the prediction of rotor dynamic forces and moments for hyd

turbine using CFD

Karlsson, Nilsson, Aidanpaa

8/11/2019 Idei Principale Articole Si Teze

4/4

The paper used CFD to estimate numeric values dynamic excitation forces due to water flow through the ru

Simulations are employed for three different boundary conditions: axial-symmetric inlet and two axial pe

(made by separate simulations of the flow through guide vans and spiral case).

The analysis is performed for Kaplan Holleforsen model with OpenFoam with a load of 60 %, close to the po

maximum efficiency. Basically it is intended to find the influence of the flow boundary conditions on the behaviothe rotor. Boundary conditions take into account the distribution of velocities from the spiral case and intera

between the guide vanes and fluid curent.

The results vary for each of the three different cases, forces and moments being larger on the runner blades obt

when using the spiral boundary conditions than in the case of axis symmetric flow. The model used in CFD doe

contain the spirale case or the draft tube.

11.

Numerical simulation of fluid added mass effect on a Francis turbine runner

Liang, Rodriguez

It aims to obtain the effect of a given volume of water that surrounds the rotor by finite element method.

The numerical model is based on the dynamic equation and the acoustic wave equation known as the Helm

equation and also making certain simplifications like is easy compressible fluid, inviscous, and the changes of d

and pressure are very small.

Added inertia effect is obtained by comparing the results obtained for the natural frequencies of the simulatio

water and air. Calculated frequencies in the two cases and are compared with the experimental ones. It analyze

the movement mode of the blade and the crown. Mode shapes between air and water are about the same e

frequency decreases significantly. Maximum displacement is found in areas of the blade edge.