| 1. |
- Asadi, Saeed, 1987, et al.
(författare)
-
Global Sensitivity Analysis of High Speed Shaft Subsystem of a Wind Turbine Drive Train
- 2018
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; 2018
-
Tidskriftsartikel (refereegranskat)abstract
- The wind turbine dynamics are complex and critical area of study for the wind industry. Quantification of the effective factors to wind turbine performance is valuable for making improvements to both power performance and turbine health. In this paper, the global sensitivity analysis of validated mathematical model for high speed shaft drive train test rig has been developed in order to evaluate the contribution of systems input parameters to the specified objective functions.Thedrive train in this study consists of a 3- phase induction motor, flexible shafts, shafts’ coupling, bearing housing, and disk with an eccentric mass.The governing equations were derived by using the Lagrangian formalism and were solved numerically by Newmark method. The variance based global sensitivity indices are introduced to evaluate the contribution of input structural parameters correlated to the objective functions. The conclusion from the current research provides informative beneficial data in terms of design and optimization of a drive train setup and also can provide better understanding of wind turbine drive train system dynamics with respect to different structural parameters, ultimately designing more efficient drive trains. Finally, the proposed global sensitivity analysis (GSA) methodology demonstrates the detectability of faults in different components.
|
|
| 2. |
- Felicetti, Roberto, 1972-, et al.
(författare)
-
A Synchronous Machine Transient Model Based upon an Algebraic Loop Accounting for Nonlinearity and Cross-Magnetization
- 2023
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Publishing Corporation. - 1023-621X .- 1542-3034. ; 2023
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to carry out an alternative to the present transient models for field wound synchronous machines, which is able to take into account the nonlinearity of the magnetic materials as well as the cross-magnetization. After presenting the principal model structures according to the state variables, a model based on two lookup tables for the magnetizing flux linkages is introduced and built step by step. The resulting signal flowchart shows an algebraic loop within the model, where the main flux linkage rapidly converges to its instantaneous value by simple iteration. The proof of this convergence is given for both saturated and unsaturated machine. Even though the proposed model uses the total linkage flux as state variable, as many alternative models do, it does not require the inversion of the current to flux linkage function (i.e., of lookup tables). This can spare a heavy computational task, especially with very large lookup tables. In the proposed model, the computational effort in the worst case scenario is reduced to few iterations (<10). Finally, the nonlinear behavior of the model is verified in four different transient scenarios by comparing its outcomes with those of a linear model for the same test machine.
|
|
| 3. |
- Karlberg, Magnus
(författare)
-
Approximated stiffness coefficients in rotor systems supported by bearings with clearance
- 2010
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1023-621X .- 1542-3034. ; 2010:Article ID 540101
-
Tidskriftsartikel (refereegranskat)abstract
- Many kinds of rotating machinery are supported by bearings with clearance, which are further clamped in a supporting structure. When designing such machinery it is important to be able to predict dynamics and hence valid models are needed. Due to gravity, the shaft often vibrates close to a static equilibrium position leading to a possibility to linearise the equation of motion. Although several studies on bearings with clearance exist, there are still no reports on how such clearances affects the stiffness coefficients close to a static equilibrium position. Therefore, analytical expressions for such approximated pedestal stiffness coefficients have been derived in this paper. By using such approximated pedestals in simple rotordynamical models, it was found that the eigenfrequencies decrease significantly with clearance. It is further shown that the approximated pedestal stiffness coefficients only will be valid for vibrations close to the static equilibrium position.
|
|
| 4. |
- Karlsson, Martin, et al.
(författare)
-
Numerical estimation of torsional dynamic coefficients of a hydraulic turbine
- 2009
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1023-621X .- 1542-3034.
-
Tidskriftsartikel (refereegranskat)abstract
- The rotordynamic behavior of a hydraulic turbine is influenced by fluid-rotor interactions at the turbine runner. In this paper computational fluid dynamics (CFDs) are used to numerically predict the torsional dynamic coefficients due to added polar inertia, damping, and stiffness of a Kaplan turbine runner. The simulations are carried out for three operating conditions, one at about 35% load, one at about 60% load (near best efficiency), and one at about 70% load. The runner rotational speed is perturbed with a sinusoidal function with different frequencies in order to estimate the coefficients of added polar inertia and damping. It is shown that the added coefficients are dependent of the load and the oscillation frequency of the runner. This affect the system's eigenfrequencies and damping. The eigenfrequency is reduced with up to 65% compared to the eigenfrequency of the mechanical system without the fluid interaction. The contribution to the damping ratio varies between 30-80% depending on the load. Hence, it is important to consider these added coefficients while carrying out dynamic analysis of the mechanical system.
|
|
| 5. |
- Nässelqvist, Mattias, et al.
(författare)
-
Experimental and numerical simulation of unbalance response in vertical test rig with tilting-pad bearings
- 2014
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1023-621X .- 1542-3034. ; 2014
-
Tidskriftsartikel (refereegranskat)abstract
- In vertically oriented machines with journal bearing, there are no predefined static radial loads, such as dead weight for horizontal rotor. Most of the commercial software is designed to calculate rotordynamic and bearing properties based on machines with a horizontally oriented rotor; that is, the bearing properties are calculated at a static eccentricity. For tilting-pad bearings, there are no existing analytical expressions for bearing parameters and the bearing parameters are dependent on eccentricity and load angle. The objective of this paper is to present a simplified method to perform numerical simulations on vertical rotors including bearing parameters. Instead of recalculating the bearing parameters in each time step polynomials are used to represent the bearing parameters for present eccentricities and load angles. Numerical results are compared with results from tests performed in a test rig. The test rig consists of two guide bearings and a midspan rotor. The guide bearings are 4-pad tilting-pad bearings. Shaft displacement and strains in the bearing bracket are measured to determine the test rig's properties. The comparison between measurements and simulated results shows small deviations in absolute displacement and load levels, which can be expected due to difficulties in calculating exact bearing parameters.
|
|
| 6. |
- Petit, Olivier, 1980, et al.
(författare)
-
Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser
- 2013
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1542-3034 .- 1023-621X. ; Volume 2013
-
Tidskriftsartikel (refereegranskat)abstract
- Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTACcentrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test caseconsists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number ofmeasurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numericalmethods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and fourdifferent turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses afully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadinessof the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flowcomputations.The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for acrude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.
|
|
| 7. |
- Tabatabaei, Narges, et al.
(författare)
-
Time-Dependent Effects of Glaze Ice on the Aerodynamic Characteristics of an Airfoil
- 2018
-
Ingår i: International Journal of Rotating Machinery. - : Hindawi Limited. - 1023-621X .- 1542-3034. ; 2018:2981739, s. 527-544
-
Tidskriftsartikel (refereegranskat)abstract
- The main objective of this study is to estimate the dynamic loads acting over a glaze-iced airfoil. This work studies the performance of unsteady Reynolds-averaged Navier-Stokes (URANS) simulations in predicting the oscillations over an iced airfoil. The structure and size of time-averaged vortices are compared to measurements. Furthermore, the accuracy of a two-equation eddy viscosity turbulence model, the shear stress transport (SST) model, is investigated in the case of the dynamic load analysis over a glaze-iced airfoil. The computational fluid dynamic analysis was conducted to investigate the effect of critical ice accretions on a 0.610 m chord NACA 0011 airfoil. Leading edge glaze ice accretion was simulated with flat plates (spoiler-ice) extending along the span of the blade. Aerodynamic performance coefficients and pressure profiles were calculated and validated for the Reynolds number of 1.83 × 106. Furthermore, turbulent separation bubbles were studied. The numerical results confirm both time-dependent phenomena observed in previous similar measurements: (1) low-frequency mode, with a Strouhal number Sth≈0,013–0.02, and (2) higher frequency mode with a Strouhal number StL≈0,059–0.69. The higher frequency motion has the same characteristics as the shedding mode and the lower frequency motion has the flapping mode characteristics.
|
|
| 8. |
|
|
