Flexible Weir Research Articles

Self-Excited Oscillations of Dual Cylindrical Flexible Weir Shells Due to Overflow Fluid

Self-excited oscillations of the structure coupled with inner fluid occurred in the insulation wall cooling system of the fast breeder reactor Super-Phenix-1 (SPX-1) in France during test operations. In this system, lower temperature sodium going up along the inside of the main vessel in a feeding plenum brims over a cylindrical flexible weir shell and flows into a restitution plenum. It is reported that the self-excited oscillations were found to occur at the same natural frequency of the sloshing in the restitution plenum, the free surface of the fluid in both feeding and restitution plenums oscillated at large amplitudes, and the cylindrical shell was found to oscillate with an oval vibration mode instability. Such an instability is called a coupled sloshing mode. In this study, the authors analyzed and performed experiments on the instability of a multiple cylindrical structure system that has dual flexible weir shells. They measured self-excited oscillations changing various parameters such as discharge flow rate, difference of the liquid heights between feeding and restitution plenums, and so on. In the experiment, it was found that dual cylindrical shells oscillate in and out of phase with each other with an oval vibration mode under the specific conditions. Comparison between theoretically and experimentally obtained instability regions was made showing good agreement.

Self-Excited Sloshing due to the Fluid Discharge Over a Flexible Plate Weir

This paper presents an analytical model for the self-excited sloshing due to the fluid discharge over a flexible weir, as observed in the cooling circuit of the French fast breeder reactor, Super-Phenix-1. To clarify the instability mechanism, we analyzed the case in which a rectangular reservoir was divided into an upstream and a downstream plenum by a flexible plate weir. The kinematic and dynamic effects of the discharged fluid on downstream plenum sloshing are discussed in details. Calculations are presented for the rectangular fluid-structure model with successively increasing fluid level difference between the upstream and downstream plenums, and the instability mechanism is examined. [S0094-9930(00)00302-4]

Self-Excited Sloshing due to the Fluid Discharge Over a Flexible Cylindrical Weir

This paper presents an analytical model for the self-excited sloshing due to the fluid discharge over a flexible weir, as observed in the cooling circuit of the French fast breeder reactor, Super-Phenix-1. To clarify the instability mechanism, we analyzed the case in which an annular reservoir was divided into an upstream and a downstream plenum by a flexible cylindrical weir. The kinematic and dynamic effects of the discharged fluid on downstream plenum sloshing are discussed in details. Calculations are presented for the cylindrical fluid-structure model with successively increasing fluid level difference between the upstream and downstream plenums, and the instability mechanism is examined. [S0094-9930(00)00901-X]

Analytical Model for Self-Excited Vibration of an Overflow Flexible Plate Weir

An analytical model for the self-excited vibration of an overflow flexible weir as observed in the French demonstration fast breeder reactor, Super Phenix-1, is proposed. The instability condition was derived for the case in which the plate vibrates at the frequency of the downstream tank sloshing. In this analysis, the flexible plate weir is modeled as a simply supported-free-simply supported-clamped rectangular plate. Eigenfunction expansions were applied for analyzing both plate vibrations and the downstream tank sloshing. The effect of an overflow liquid is formulated based on the assumption that the momentum change due to the collision of an overflow liquid partly transmitted to the pressure rise on the free surface. As a result, the characteristic equation of the system yielding the theoretical stability boundary was obtained. The stability boundary thus derived agreed well with experimental results.

Self-Excited Oscillations of Dual Cylindrical Flexible Weir Shells due to Over-Flow Fluid.

This paper deals with self excited oscillations of the structure coupled with inner fluid occurred in the insulation wail cooling system of fast breeder reactor Super-Phenix-1 (SPX-1) in France during test operations. We analyzed and performed experiments on the instability of multiple cylindrical structure system which has dual flexible weir shells. We measured self excited oscillations changing various parameters such as discharge flow rate, gap of the liquid height between feeding and restitution plenums. In the experiment, it was found out that dual cylindrical shells oscillate in the inverse phase each other with an oval vibration mode under the specific conditions. Comparison between theoretically and experimentally obtained instability region was made, which shows good agreement.

Self-Excited Sloshing Due to the Fluid Discharge over a Flexible Weir. 2nd Report. Excitation Mechanism of Instability in the Cylindrical Model.

This paper presents an analytical model for the fluid elastic instability as observed in Super Phenix-1 LMFBR. This fluid-structure system is constituted by the flexible cylindrical weir and adjoining annular fluid plenums, and the fluid is discharged from the upstream plenum to the downstream plenum over the flexible weir. In this report, we analyzed the case in which the annular reservior was divided into the upstream and the downstream plenums by a flexible cylindrical weir. The characteristic equation of the system is derived. The effects of the discharged fluid on the downstream plenum sloshing and the effects of the fluid level difference between the upstream and the downstream plenum are examined, and the mechanism for instability is discussed.

Self-Excited Sloshing Due to the Fluid Discharge over a Flexible Weir. 1st Report. Excitation Mechanism of Instability in the Rectangular Model.

This paper presents an analytical model for the fluid-elastic instability as observed in Super-Phenix-1 LMFBR. This fluid-structure system is constituted by the flexible cylindrical weir and adjoining annular fluid plenums, and the fluid is discharged from the upstream plenum to the downstream plenum over the flexible weir. In this report, to clarify the mechanism for instability, we analyzed the case in which the rectangular reservior was divided into the upstream and the down-stream plenums by a flexible plate weir. The characteristic equation of the system is derived. The effects of the discharged fluid on the downstream plenum sloshing and the effects of the fluid level difference between the upstream and the downstream plenums are examined, and the mechanism for instability is discussed.

Experimental Studies on the Hydroelastic Unstable Vibration of a Thin Cylindrical Weir. Unstable Vibration Characteristics.

Experimental studies have been conducted on the hydroelastic unstable vibration of a thin cylindrical weir. A test cylindrical weir made of polyester with radius R=100mm, length L=113mm, thickness h=0.244mm, and water was used in the experiment. In this paper, characteristics of the unstable vibation of the flexible weir due to a liquid flowing over it are presented. It was found that the vibration mode of the flexible weir varies with the volume of the liquid flow as well as with the height of the inner liquid inside the weir. This result may provide useful data for the theoretical investigation of this kind of unstable vibration.

Stability Analysis of Self-Excited Vibration of a Flexible Weir due to Fluid Discharge.

This paper deals with a theoretical analysis of dynamic instability of vibrations induced in a flexible weir subjected to fluid discharge over the weir top. We formulate the equation of motion for the coupling vibration of a flexible weir and sloshing liquid contained in upper and lower tanks by taking into accout the time lag generated by the fluid travel from the top of the weir to the surface of the liquid contained in the lower tank. The energy of the vibration of the weir produced by sloshing and dissipation energy are evaluated to find the instability conditions in terms of discharge height. The instability conditions are clarified with respect to important parameters of this fluid structure coupling system and are compared with experimental results.

Experimental Study on Self-Excited Vibration Characteristics of a Flexible Weir due to Fluid Discharge.

This paper deals with the characteristics of unstable self-excited vibrations of a rectangular, flexible weir installed in a tank, over which water in the upstream tank discharges into the down-stream one. Experiments were carried out for measuring the vibrational strains of the weir, and the oscillation of the water surface in the up-stream tank with changing inlet velocity of water and discharge height. We examined the vibration characteristics of the weir with changing tank ratio (defined as the down stream tank length/the upstream tank length), and found that the occurrence of unstable vibration depends strongly on the tank ratio. The phase relations of the weir vibration to the upstream tank water oscillation were experimentally investigated.

Self-excited oscillation due to the fluid discharge over a flexible weir. 2nd Report. Excitation mechanism of a hydroelastic mode.

The excitation mechanism of a self-excited oscillation due to the fluid discharge over a flexible werir was investigated both theoretically and experimentally. A new type of hydroelastic instability was discovered during test operations of the Super-Phenix LMFBR reactor in France. According to a recent report by Aita, this phenomenon includes two types of instability modes: one is the sloshing mode which means the oscillation of a weir associated with coupled sloshing modes of both feeding and restitution fluid collectors; the other is a hydroelastic mode which means the oscillation of a weir associated with fluid-shell modes. In this report, the excitation mechanism of a hydroelastic mode is discussed by calculating the excitation energy brought by discharge to the fluid-structure system. The theoretical results for the range of hydroelastic mode instability virtually agreed with the experimental data.

Fluid-elastic vibration of flexible overflow weir.

The present paper describes the fundamental feature of the fluid-elastic vibration of flexible overflow weir, as observed in the French demonstration fast breeder reactor, Super Phenix-1. In the experimental study, the instability criterion of the fluid-elastic vibration was investigated using a simple experimental apparatus of a rectangular tank separated by a flexible weir. A spring-mass model for sloshing motion of liquid contained in the tank was developed to clarify the mechanism of the instability. The instability condition was analytically derived from the equations of the spring-mass model. The equations of the spring-mass model were also computationally integrated in time to simulate the timewise evolution of the fluid-elastic vibration. The comparison between the experimental and theoretical results indicate that the present theoretical model is capable of predicting the general characteristics of the vibration observed in the experiment. The present study revealed that the lag-time of the water fall at the weir is the most influential parameter on the fluid-elastic instability of a flexible overflow weir.

Self-excited oscillation due to the fluid discharge over a flexible weir. (1st report. Excitation mechanism of a sloshing mode).

The excitation mechanism of a self-excited oscillation due to the fluid discharge over a flexible weir was investigated both theoretically and experimentally. A new type of hydroelastic instability was discovered during test operations of the Super-Phenix LMFBR reactor in France. According to the recent report by Aita, this phenomenon includes two types of instability modes : one is sloshing mode which means the oscillation of a weir associated with coupled sloshing modes of both feeding and restitution fluid collectors ; the other is a hydroelastic mode which means the oscillation of a weir associated with fluid-shell modes. In this report, the excitation mechanism of a sloshing mode is discussed by calculating the excitation energy brought by discharge to the fluid-structure system. The theoretical results for the range of sloshing mode instability almost agreed with the experimental data.

Experimental Study of Self-Excited Vibrations of a Flexible Weir due to Fluid Discharge

This paper deals with the characteristics of unstable self-excited vibrations of a rectangular, flexible weir installed between two tanks, over which the water in the upper tank discharges into the lower one. Experiments were done for measuring vibrational strains of the weir, oscillation of the overflow water thickness, and the oscillations of the water surface in the upper and lower tanks with changing inlet velocity of water into the upper tank and water discharge height. Four unstable vibration modes were found in our experiments. The 1st unstable vibration mode was sloshing-dominated weir vibration and its vibration frequency was almost equal to the sloshing one for the lower tank. The 2nd one was a high frequency vibration of the weir unrelated to the sloshing oscillation and the 3rd one was a torsional one of the weir with a high frequency different from the 2nd one. The 4th mode was peculiar to the experimental system due mostly to the coupling between the inlet water jet and the weir The phase relations between the weir vibration and overflow water thickness were experimentally investigated.