Michiaki Suzuki

Proposal of a new estimation method for the thermal ratchetting of a cylinder subjected to a moving temperature distribution

Abstract In the structural design of an FBR component, thermal ratchetting without primary stress must be prevented. In this paper, thermal ratchetting of a hollow cylinder subjected to an axial movement of temperature distribution is focused on as a typical ratchetting mechanism of an FBR component. The basic estimation equations for this type of ratchetting are improved by using a theoretical model considering the effects of axial bending stress. The propriety of the proposed model is verified by comparing the predicted stress and strain with numerical results by FEM. Lastly, a new design procedure based on the improved estimation equation is proposed.

Development of Evaluation Method of Vibrational Stress in Piping System Applying Multiple Laser Displacement Sensors

Many damages of the piping system in the nuclear power plants have occurred due to the vibration fatigue induced by the mechanical vibration of pumps and so on. One of the preventive measures for the problem of vibration is the evaluation of vibrational stress, which is the methods using the strain gauge and the accelerometer. However, these evaluation methods require highly specialized skills and many man-hours, and nuclear plants are awaiting the development of vibration-measuring techniques and evaluation techniques that are easy to perform and produce accurate results promptly. The purpose of this study is the development of the method and the device measuring the vibrational stress directory using the laser displacement sensor. The proposed method evaluates the vibrational stress as follows: Three laser displacement sensors measure the displacement of the piping induced by vibrating, and the strain of the piping is calculated from the difference among the sensor-measured displacements to determine vibrational stress. The measurement equipment isn’t direct contact with the piping evaluated, can be easily reduced in size, and can realize quick and accurate measurement. This paper describes the concept of the proposed evaluation method of vibrational stress in the piping system using three laser displacement sensors, along with its theory and measurement procedure. And then, refer to the proposal of the evaluation method of torsional vibration using six laser displacement sensors. This paper also compares the stress values calculated based on the cantilever vibration identified by this method and the stress values calculated based on material mechanics, and discusses the applicability of the method in actual plants.Copyright

Methods of Evaluating Vibration Induced Stress of Small-Bore Piping

The vibration induced fatigue failure of small-bore piping is one of the common causes of failure trouble at nuclear power plants. This failure used to be prevented by calculating and screening vibration induced stresses using the accelerations measured by portable vibrometers, which are easy to handle in the working areas. Though the conventional evaluation method for calculating the vibration induced stress of small-bore piping often adopts the single-mass model, the stresses calculated by the model may be different from the actual ones because of being too simplified. So the purpose of this study is to develop the calculation methods of vibration induced stress for the screening preventing from fatigue failure troubles of small-bore piping using portable vibrometers. Firstly, for comparatively simple small-bore piping using the mock-up model simulating actual simple small-bore piping, shaking table experiments are conducted using sine wave and the field response wave measured on-site. By comparing the vibration induced stresses measured by the strain gauges and calculated using the accelerations, at first the validity of a single-mass model was conducted, and then the evaluation of a two-mass model developed as an improvement calculation model was conducted. As results of comparison, the single-mass model was found to be useful only for screening although the calculated stresses had the deviations and the tendency of an underestimate, and the two-mass model was found to be utilized as better screening because the calculated stresses had better agreement with the measured ones. Next, for small-bore piping with typical pattern configurations consisted of several masses and supports, the model considering the supports and the center of gravity being out of pipe centerline was developed and proposed. Finally, for the more complex small-bore piping with general piping configurations consisted of many bends, branches or joints, the method based on the finite element method analysis and the values measured by a portable vibrometer was developed. In this method, the analytical model was optimized, and the stresses were obtained considering vibration modes as dynamically. Judging from the results checked by numerical analysis, this method was found to be accuracy enough to use for screening, because the analytical model was optimized smoothly and the estimated stresses became to be from 1.1 to 1.4 times to the original true ones that corresponds to the actual ones measured in site.Copyright

Nonlinear Vibration Response of a Cylindrical Water Storage Tank Caused by Coupling Effect Between Beam-Type Vibration and Oval-Type Vibration: Part 1 — Vibration Experiment

The first report, “Part 1 - Vibration experiment”, has revealed that the nonlinear vibration response phenomena of beam-type vibration of a cylindrical water storage tank are caused by the coupling effect of beam-type vibration and oval-type vibration. This paper describes the modeling of the above phenomena into a nonlinear equivalent single-degree-of-freedom system and the results of the simulation analysis to investigate the mechanism of the nonlinear vibration responses of the tank when these two types of vibration are coupled. The conventional linear seismic response analysis method of the tank generally considers only beam-type vibration because the participation factor of oval-type vibration due to seismic excitations is theoretically zero. However, oval-type vibration was found to be generated and accompanied by the out-of-plane deformation of the tank sidewall when the test tank was experimentally subjected to large input acceleration excitations. So, it was considered that the geometrical nonlinearity due to oval-type vibrations was the main reason why the beam-type vibration response was nonlinear. Therefore, a static large-deformation analysis by the finite element method was conducted for the tank model whose sidewall had the oval-type vibration mode shape as the out-of-plane deformation in order to calculate the flexural rigidity of the tank. As a result, the flexural rigidity of the tank was found to decrease as the displacement of oval-type vibration increased. In other words, the geometrical nonlinearity caused by the oval-type vibration affects the flexural rigidity of the tank and generates the nonlinear vibration response. Furthermore, an equivalent single-degree-of-freedom system model was made to understand the nonlinear vibration response behavior of the tank, assuming that the flexural rigidity depended on the displacement of the oval-type vibration. Simulation of the frequency sweep test using this model showed that the resonance frequency decreased as the displacement of the oval-type vibration became larger. These results demonstrate the validity of the results mentioned in the first report, “Part 1 - Vibration experiment”.Copyright

Vibration Test of a 1/10 Reduced Scale Model of Cylindrical Water Storage Tank

This paper describes the results of vibration tests using a 1/10 reduced scale model of large-scale cylindrical water storage tanks to clarify their dynamic behavior under seismic excitation. The thin sidewall of the tanks is not so rigid that the vibration modes (sloshing and bulging) induced by earthquake can affect the distribution of their liquid pressure and seismic load. It is, therefore, important for the seismic design of water storage tanks to consider such elastic deformation theoretically and experimentally. In this study, vibration tests by shaking table are conducted using a reduced scale tank model partially filled with water to investigate the dynamic fluid pressure behavior and seismic-proof safety of the tanks. A small sinusoidal excitation test, large amplitude sinusoidal excitation test and seismic excitation test are conducted. The measured values are compared with the calculated ones by some conventional seismic design methods. The results reveal that the distribution shape and magnitude of the dynamic fluid pressure are different between under positive and negative pressures and depend on the magnitude of input acceleration. Further examination concludes that the oval-type vibration, which is a high-order vibration mode, occurring on the sidewall of the tanks affects the distribution shape and magnitude of dynamic fluid pressure. However, it is demonstrated that the vibration does not act as a seismic load in the conventional evaluation of seismic-proof safety.

Experimental Study of Coupling Vibration Characteristics Between a Thin Cylindrical Water Storage Tank and Its Contained Liquid

A large cylindrical water storage tank typically has a thin sidewall. When such a tank is under an earthquake, the vibrations of the water inside are coupled with the vibrations of the sidewall, producing a phenomenon called fluid-structure coupled vibration. The fluid-structure coupled vibration is an important issue for a tank like this to achieve reasonable seismic-proof design. Even though there have been many studies on fluid-structure coupled vibrations, only a few of them have examined the dynamic fluid pressure and oval vibrations. This paper reports on the investigations into the characteristics of oval vibrations exhibited by a cylindrical water storage tank, in which a vibration test was conducted using a shaking table, the correlation of changes in the excitation force and behaviors of dynamic fluid pressure with the appearance and growth of oval vibrations were analyzed, and the modes of oval vibrations that appeared were identified. The vibration test was conducted using a scale model tank of a large cylindrical water storage tank and a shaking table. The input vibrations were sinusoidal waves of 53 Hz, a frequency that was in the vicinity of the resonance frequency. The test took the form of a large amplitude excitation test, which increased the acceleration of the input vibrations gradually. The response acceleration of the tank and the dynamic fluid pressure were measured. Strain gages attached around the trunk of the tank were used to identify oval vibration modes. The frequency analysis of the dynamic fluid pressure revealed two major peaks, one at 53 Hz which matched the excitation frequency and the other at 106 Hz which was double the excitation frequency. It showed that the dynamic fluid pressure has nonlinear behavior like higher-harmonic resonance. The frequency analysis of the responses on the trunk of the tank arising from oval vibrations also revealed two major peaks, one at 53Hz and the other at 106Hz. The behavior of dynamic fluid pressure and the behavior of oval vibrations were coupled. It was found that a certain magnitude of the response acceleration of the tank that gave rise to oval vibrations were in proportion to the rate of increase of the response acceleration of the tank. In other words, oval vibrations appeared at a relatively low response acceleration if the response acceleration increased slowly, whereas oval vibrations appeared only at a relatively high response acceleration if the response acceleration increased quickly. An analysis of the circumferential distribution of circumferential strains around the trunk of the tank revealed the presence of two oval vibration modes with different circumferential wave numbers: 14 and 16, which have not been predicted by the FEM analysis. None of the natural frequencies determined by the FEM analysis of the two different vibration modes matched 106 Hz; however, a half of the sum of the two natural frequencies was close to 106 Hz. Thus oval vibrations were found to have a nonlinear characteristics experimentally.Copyright

Development of Double Metal Bellows Air Pressure Spring With Lead Rubber Bearing Type 3-Dimensional Seismic Isolator

A new simple 3-dimensional seismic isolator concept for a commercial fast breeder reactor (FBR) building was proposed. The isolator consists of common reliable industrial parts, metallic bellows and lead rubber bearing (LRB). Air pressurized metallic bellows is for vertical isolation and LRB is for horizontal. The isolation frequencies are 0.5Hz for horizontal and 0.56Hz for vertical respectively. The maximum vertical displacement to absorb is 400mm and the vertical load of 9807kN should be supported per each isolator. A conceptual design was performed for these design requirements and a scale model test was carried out to confirm the feasibility of the concept.© 2002 ASME

Vibration Test of 1/10 Scale Model of Cylindrical Water Storage Tank

Large-scale cylindrical water storage tanks have a large ratio of radius to thickness, which means their thickness is relatively thin compared with the radius. Regarding seismic responses, the deformation of a tank frame is significantly influenced by the sloshing of the water inside the tank and by the bulging vibration of the tank structure, therefore it is important to consider such deformation theoretically and experimentally. This paper describes the results of a vibration test with a 1/10 reduced scale model of a large-scale industrial cylindrical water storage tank, conducted particularly to clarify the dynamic behavior of the tank during a seismic excitation. First a sinusoidal wave excitation experiment was performed for the scale model tank, which measured axial distributions of dynamic fluid pressures, strains and accelerations. Ovaling vibration of the scale model tank also was examined by measuring the circumferential distribution of strains. Furthermore, the dependence of dynamic fluid pressure on the acceleration magnitude of the input excitation was investigated. Secondly, a seismic excitation experiment was conducted using typical seismic waves. Finally, the measuring results were compared with the values calculated using common seismic-proof design methods based on the Housner method or velocity potential theory and the finite element method. Considering the differences between the experiment values and numerical design ones, it became obvious that there was inconsistent between the positive and the negative pressures of the dynamic fluid pressure and that the dynamic fluid pressure was dependent on the acceleration magnitude. And it was suggested that such phenomena were caused by ovaling vibration. They, however, had little effect on the seismic-proof design of the tank in the range of acceleration used in this study.© 2004 ASME

Seismic Response Reduction Caused by Coupling Between Beam-Type and Oval-Type Vibrations of a Cylindrical Water Storage Tank Under Large Excitation

This study describes the response reduction caused by coupling between the beam-type and the oval-type vibrations of a cylindrical water storage tank under seismic excitation. In this study, the seismic response experiment is performed by using a 1/10 reduced scale model of an actual tank and then numerical simulation is performed by the simplified model. The authors conducted the sinusoidal response experiment for the tank and reported that the coupling between the beam-type and the oval-type vibrations causes the resonance frequency of the beam-type vibration to shift to the lower frequency and the response in the beam-type vibration (the response of the tank) to reduce. The seismic response experiment of the tank model filled with water up to 95% is performed by a shaking table. The El Centro 1940 NS and the improved standard seismic wave for Japanese LWR are used as the input seismic wave. The experimental results show that the maximum response acceleration does not enlarge linearly as the maximum input acceleration increases. The dominant resonance frequency slightly shifts to the lower frequency as the maximum input acceleration increases. It is concluded that the coupling between the beam-type and the oval-type vibrations make an influence on the beam-type vibration in seismic excitation. In the meantime, the authors propose the nonlinear single-degree-of-freedom system model to explain that the vibration response of the tank reduces. This model is based on geometric nonlinearity due to the out-of-plane deformation of the side-wall of the tank caused by the oval-type vibration. The numerical simulation of the seismic response is conducted using the nonlinear single-degree-of-freedom system model proposed by the authors. The analytical results agree with the experimental results as a general trend. Therefore, it is concluded that the response reduction of the tank is generated by coupling between the beam-type and the oval-type vibrations in the seismic excitation as well as the sinusoidal excitation. In addition, the response reduction rate of the tank under much larger seismic excitation can be estimated by using the nonlinear single-degree-of-freedom system model.Copyright