Equivalent Mass-spring Model Research Articles

Damping Characteristics of Bladed Disk with Continuous Ring Type Structure (Effects of Friction Damping on Self-Excited Vibration)

Recently, bladed disks with the continuous ring type structure have been used in many kinds of turbomachinery due to its high reliability. The vibration characteristics of the bladed disk with continuous ring type structure have been studied extensively, and the effect of the friction damping on the forced vibration is almost clarified. On the other hand, few studies have been done on the effect of the friction damping on the blade flutter. In this paper, the stability analysis of the bladed disk with the continuous ring type structure is carried out using the equivalent spring mass model, and the effect of the friction damping on the blade flutter is clarified. From the results of analysis, it is concluded that the stable steady vibration or the flutter occurs when the aerodynamic damping of the blade becomes negative. Whether the blade vibration is stable or unstable depends on the magnitude of the aerodynamic damping and the initial condition. In other words, when the friction damping can not suppress the self-excited vibration due to the large aerodynamic damping and the large initial amplitude, the amplitude of the blade vibration becomes larger and the flutter occurs.

Damping Characteristics of Bladed Disk with Continuous Ring Type Structure (Effects of Friction Damping on Self-Excited Vibration)

Recently, bladed disks with continuous ring type structure have been used in many kinds of turbomachinery due to its high reliability. The vibration characteristics of the bladed disk with continuous ring type structure have been studied extensively, and the effect of the friction damping on the forced vibration is almost clarified. On the other hand, few studies have been done on the effect of the friction damping on the blade flutter. In this paper, the stability analysis of the bladed disk with continuous ring type structure is carried out using the equivalent spring-mass model, and the effect of the friction damping on the blade flutter is clarified. From the results of the analysis, it is concluded that the stable steady vibration or the flutter always occurs when the aerodynamic damping of the blade becomes negative. Whether the blade vibration is stable or unstable depends on the magnitude of the aerodynamic damping and the initial condition. In other words, when the friction damping cannot suppress the self-excited vibration due to the large aerodynamic damping and the large initial amplitude, the amplitude of the blade vibration becomes larger and the flutter occurs.

Seismic evaluation of fluid-elevated tank-foundation/soil systems in frequency domain

An efficient methodology is presented to evaluate the seismic behavior of a Fluid-Elevated Tank-Foundation/Soil system taking the embedment effects into accounts. The frequency-dependent cone model is used for considering the elevated tank-foundation/soil interaction and the equivalent spring-mass model given in the Eurocode-8 is used for fluid-elevated tank interaction. Both models are combined to obtain the seismic response of the systems considering the sloshing effects of the fluid and frequency-dependent properties of soil. The analysis is carried out in the frequency domain with a modal analysis procedure. The presented methodology with less computational efforts takes account of; the soil and fluid interactions, the material and radiation damping effects of the elastic half-space, and the embedment effects. Some conclusions may be summarized as follows; the sloshing response is not practically affected by the change of properties in stiff soil such as S1 and S2 and embedment but affected in soft soil. On the other hand, these responses are not affected by embedment in stiff soils but affected in soft soils.

Vibration Analysis on FRP Considering Damping Effect. Simple Calculation Method for Dynamic Design.

When a Fiber Reinforced Plastics(FRP) is used as a structure, it is necessary to design the dynamic property of FRP easily and accurately. In this paper, a natural frequency and loss factor of FRP is calculated by our equivalent mass-spring method. The FRP is expressed as equivalent homogeneous elements by the rule of mixture. The equivalent mass-spring model is expressed by shear springs of fiber and matrix resin which connect in series. The spring coefficients are identified by the sensitivity analysis. Then matrix resin is viscoelastic, the shear spring is presented by kmj(1+ηmi). Therefore, the loss factor of FRP is calculated by dividing imaginary part of the total shear spring coefficient by real one. When the parameters or size of FRP are changed, the natural frequency and loss factor is calculated by corrected spring coefficients of fiber and resin. This method is sufficiently reliable and easy to predict the vibration characteristics of FRP.

An Equivalent Reduced Modelling Method and its Application to Shaft—Blade Coupled Torsional Vibration Analysis of a Turbine—Generator Set

A coupled vibrating system (for example turbine-generator set), consisting of a main system (for example shaft system) and a sub-system (for example blade system) which are connected at bonding points (for example the centre boss of a blade), is equivalently reduced to a model suitable for analysis. According to this modelling technique, the eigenvalue analysis of the uncoupled flexible sub-system is done first under the assumption of the fixed bonding point. Then, an equivalent mass-spring system is produced for each eigenmode of the uncoupled subsystem. In this way, the main system plus the additional equivalent mass-spring model of the sub-system is combined into a global system model. This modelling technique is applied to the shaft-blade coupled vibration problems in an actual turbine-generator set and its effectiveness is provided with experimental test results.

Multi-Mode Stabilization of Torsional Oscillations Using Output Feedback Excitation Control

The paper presents an output feedback excitation control to stabilize the torsional oscillations due to subsynchronous Resonance of a capacitor-compensated power system. The control design is based on an equivalent mass-spring model, modern control laws, and eigenvalue sensitivity technique. With a multiple signal feedback synthesized from a minimum number of system outputs, the control provides proper damping to all torsional modes. Computer simulation tests show that all oscillating modes can be stabilized simultanously for a wide range of capacitor compensation.