Damping Performance of Axial Turbine Stages With Loosely Assembled Friction Bolts: The Nonlinear Dynamic Assessment

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
J. Szwedowicz ◽  
Th. Secall-Wimmel ◽  
P. Dünck-Kerst
Keyword(s):  
Nonlinear Dynamic ◽  
Dynamic Assessment ◽  
Contact Condition ◽  
Operating Conditions ◽  
Friction Forces ◽  
Axial Turbine ◽  
Resonance Frequencies ◽  
Wide Range ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses

An entire family of twisted and tapered low pressure steam turbine fast rotating condensation blading (SK) blades with pinned radial root and loosely assembled conical bolts is designed by scaling the aerodynamic and mechanical properties of the smallest airfoil. For SK blades operating with variable speed, the friction bolts, mounted in the upper airfoil part, provide either damping or coupling capabilities for the blades with respect to resonance conditions. The damping and coupling performance have been proven experimentally in the test rig of the real turbine. The measurements of the smallest SK-disk assembly under different operating conditions have allowed us to understand the dynamic and damping behavior of the bolts that are either friction dampers or coupling devices for the vibrating blades depending on the excitation level. In this paper, nonlinear dynamic analyses of the smallest and large SK-turbine stage are performed and compared with the experimental data. The modal blade dynamics is defined by 30 complex finite element (FE) mode shapes of the freestanding blades coupled by the disk whereby the bolt’s motion is described by six rigid body modes. The sticking contact condition between the blades and bolts is represented by the normal and tangential contact stiffnesses. These values are firstly estimated analytically with Hertz’s formulas for the FE reaction forces and contact areas. More realistic contact stiffness values are obtained from the iterative process, in which the resonance frequencies are calculated with the steady-state simulations and compared to the FE nodal diameter curves for sticking contact conditions that meet the experimental frequencies very well (Szwedowicz, J. et al., 2007, “Scaling Concept for Axial Turbine Stages With Loosely Assembled Friction Bolts: The Linear Dynamic Assessment Part 1,” Proceedings of ASME Turbo Expo 2007, Montreal, Canada, May 14–17, ASME Paper No. GT2007-27502). In nonlinear simulations, in case of exceeding the sticking contact condition, the induced friction forces are linearized by the harmonic balance method. In this manner, the microslipping and sticking contact behavior at all contact points are calculated iteratively for the specified excitation amplitudes, friction coefficient, contact roughness, and aerodamping values that are known from the experiment. The computed results of the tuned smallest SK blades agree with the experimental resonance stresses of 12 measured blades. Differences between the computed and measured stresses are caused by mistuning, which was not quantified in the experiment. The nonlinear dynamic analyses provide evidence of good damping performance for the smallest and large SK blades with respect to a wide range of excitation forces, different friction coefficients, and various aerodynamic damping values. For the analyzed resonances of the eighth engine order, the scalability of damping performance is found for the SK blades of different sizes.

Damping Performance of Axial Turbine Stages With Loosely Assembled Friction Bolts: The Non-Linear Dynamic Assessment — Part II

2007 ◽  
Author(s):  
J. Szwedowicz ◽  
Th. Secall-Wimmel ◽  
P. Du¨nck-Kerst
Keyword(s):  
Contact Stiffness ◽  
Contact Condition ◽  
Operating Conditions ◽  
Friction Forces ◽  
Linear Dynamic ◽  
Resonance Frequencies ◽  
Contact Behaviour ◽  
Wide Range ◽  
Dynamic Analyses ◽  
Non Linear

An entire family of twisted and tapered low pressure steam turbine SK-blades with pinned radial root and loosely assembled conical bolts is designed by scaling of the aerodynamic and mechanical properties of the smallest airfoil. For SK-blades operating with variable speed, the friction bolts, mounted in the upper airfoil part, provide either damping or coupling capabilities for the blades with respect to resonance conditions. The damping and coupling performance have been proved experimentally in the test rig of the real turbine. The measurements of the smallest SK-disc assembly under different operating conditions have allowed understanding the dynamic and damping behaviour of the bolts that are either friction dampers or coupling devices for the vibrating blades depending on the excitation level. In this paper, non-linear dynamic analyses of the smallest and large SK-turbine stage are performed and compared with the experimental data. The modal blade dynamics is defined by 30 complex FE mode shapes of the freestanding blades coupled by the disc whereby the bolt’s motion is described by 6 rigid body modes. The sticking contact condition between the blades and bolts is represented by the normal and tangential contact stiffness. These values are firstly estimated analytically with the Hertz’s formulas for the FE reaction forces and contact areas. More realistic contact stiffness values are obtained from the iterative process, in which the resonance frequencies are calculated with the steady-state simulations and compared to the FE nodal diameter curves for sticking contact conditions that meet the experimental frequencies very well (GT2007-27502). In non-linear simulations, in case of exceeding the sticking contact condition, the induced friction forces are linearized by the Harmonic Balance Method. In this manner, the micro-slipping and sticking contact behaviour at all contact points are calculated iteratively for the specified excitation amplitudes, friction coefficient, contact roughness and aerodamping values that are known from the experiment. The computed results of the tuned smallest SK-blades agree with the experimental resonance stresses of 12 measured blades. Differences between the computed and measured stresses are caused by mistuning, which was not quantified in the experiment. The non-linear dynamic analyses provide evidence of good damping performance for the smallest and large SK-blades with respect to wide range of excitation forces, different friction coefficients and various aerodynamic damping values. For the analyzed resonances of the 8th engine order, the scalability of damping performance is found for the SK-blades of different sizes.

Structure and properties of compact articles from high-alloyed iron powder with adding of boron nitride

2020 ◽  
pp. 39-48
Author(s):  
B. O. Bolshakov ◽  
◽  
R. F. Galiakbarov ◽  
A. M. Smyslov ◽  
◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Boron Nitride ◽  
Grain Boundary ◽  
Bending Strength ◽  
Physical And Mechanical Properties ◽  
Operating Conditions ◽  
Structure And Properties ◽  
Steam Turbines ◽  
Friction Forces ◽  
Wide Range

The results of the research of structure and properties of a composite compact from 13 Cr – 2 Мо and BN powders depending on the concentration of boron nitride are provided. It is shown that adding boron nitride in an amount of more than 2% by weight of the charge mixture leads to the formation of extended grain boundary porosity and finely dispersed BN layers in the structure, which provides a high level of wearing properties of the material. The effect of boron nitride concentration on physical and mechanical properties is determined. It was found that the introduction of a small amount of BN (up to 2 % by weight) into the compacts leads to an increase in plasticity, bending strength, and toughness by reducing the friction forces between the metal powder particles during pressing and a more complete grain boundary diffusion process during sintering. The formation of a regulated structure-phase composition of powder compacts of 13 Cr – 2 Mо – BN when the content of boron nitride changes in them allows us to provide the specified physical and mechanical properties in a wide range. The obtained results of studies of the physical and mechanical characteristics of the developed material allow us to reasonably choose the necessary composition of the powder compact for sealing structures of the flow part of steam turbines, depending on their operating conditions.

Numerical Investigations on the Seismic Response of Masonry Building Aggregates

2010 ◽  
Vol 133-134 ◽  
pp. 715-720 ◽  
Author(s):  
Ilaria Senaldi ◽  
Guido Magenes ◽  
Andrea Penna
Keyword(s):  
Seismic Response ◽  
Nonlinear Dynamic ◽  
Masonry Building ◽  
Structural Units ◽  
Numerical Investigations ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses ◽  
Building Aggregates

The work focuses on the analysis of the seismic response of masonry building aggregates for a better understanding of the vulnerability of single structural units and of their behaviour within the aggregates. Idealized representative models are developed based on the typical characteristics of the row conglomeration typology. The seismic response of the models is evaluated and discussed by means of nonlinear dynamic analyses.

Implications of cumulated seismic damage on the seismic performance of unreinforced masonry buildings

2014 ◽  
Vol 47 (2) ◽  
pp. 157-170 ◽  
Author(s):  
Amaryllis Mouyiannou ◽  
Andrea Penna ◽  
Maria Rota ◽  
Francesco Graziotti ◽  
Guido Magenes
Keyword(s):  
Nonlinear Dynamic ◽  
Fragility Curves ◽  
Seismic Damage ◽  
Unreinforced Masonry ◽  
Masonry Building ◽  
Masonry Buildings ◽  
Seismic Capacity ◽  
Building Stock ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses

The seismic capacity of a structure is a function of the characteristics of the system as well as of its state, which is mainly affected by previous damage and deterioration. The cumulative damage from repeated shocks (for example during a seismic sequence or due to multiple events affecting an unrepaired building stock) affects the vulnerability of masonry buildings for subsequent events. This paper proposes an analytical methodology for the derivation of state-dependent fragility curves, taking into account cumulated seismic damage, whilst neglecting possible ageing effects. The methodology is based on nonlinear dynamic analyses of an equivalent single degree of freedom system, properly calibrated to reproduce the static and dynamic behaviour of the structure. An application of the proposed methodology to an unreinforced masonry case study building is also presented. The effect of cumulated damage on the seismic response of this prototype masonry building is further studied by means of nonlinear dynamic analyses with the accelerograms recorded during a real earthquake sequence that occurred in Canterbury (New Zealand) between 2010 and 2012.

INFLUENCE OF ADDED VISCOUS DAMPERS ON THE PROBABILISTIC SEISMIC PERFORMANCE EVALUATION OF RC FRAMES

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Luca Landi ◽  
Cristina Vorabbi ◽  
Pier Paolo Diotallevi
Keyword(s):  
Nonlinear Dynamic ◽  
Ground Motions ◽  
Frame Structures ◽  
Rc Frame ◽  
Viscous Dampers ◽  
Fluid Viscous Dampers ◽  
Hazard Curve ◽  
Dynamic Analyses ◽  
Nonlinear Dynamic Analyses ◽  
Rc Frame Structures

This paper deals with the parameters which influence the probability of reaching the near collapse limit state of RC frame structures equipped with nonlinear fluid viscous dampers. The study can be divided into two steps. The first aims to assess how the median and the dispersion of seismic demand can vary in the RC frame structures with and without dampers, considering a wide set of ground motions. The second step evaluates the expression in closed form, given by 2000 SAC/FEMA method, to assess the annual probability of failure of RC structures. This probability has been estimated considering a wide set of ground motions and different methods to approximate the hazard curve. The evaluations have been made on the basis of the results of a large number of nonlinear dynamic analyses; in particular, 180 nonlinear dynamic analyses have been made for the case studies with and without dampers. In conclusion, it has been noticed that the probabilistic assessment depends on the number of records considered and that the simplified formula provided by the 2000 SAC-FEMA method is strongly sensitive to the variation of the hazard curve and the dispersion.

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