前川 晃

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. [DOI: 10.1115/1.4001915]

This paper describes residual stress measurements and analysis of austenitic stainless steel pipe with a butt-welded joint. The measurements were done with neutron diffraction and strain gauge techniques. The measured results had typical characteristics of butt-welded pipe regarding both the decline of stress along the axial direction and the bending distribution of axial stress along the radial direction. The measured residual stress distribution by neutron diffraction was shifted more to the tensile side than that by the finite element method simulation. However, the measured radial and axial strains, except for the hoop strain determined by neutron diffraction, coincided well with analysis strains. The hoop strain was actually equivalent strain converted by a correction method because a different lattice plane had to be used to measure hoop strain. This might be one reason why the difference occurred. Therefore, future study of the correction method would be desirable.

A three-dimensional and elastic-plastic dynamic buckling analysis method that takes into consideration fluid-structure coupling and large deformation is proposed in order to accurately simulate the seismic response of cylindrical liquid storage tanks. The results of a dynamic buckling experiment of a tank using seismic motions closely match those of numerical simulation by the proposed method. The mesh size of the analytical model greatly influences the buckling analysis results. Optimization of the size is also discussed.

Vibration experiments for pressure pulsation behavior were made using actual size mock-up piping of nuclear power facilities. The mock-up was a closed loop consisting of a three-strand plunger pump, tanks, piping and valves. It was 40 m long to allow interaction of the acoustic resonance frequency of fluid inside with the mechanical natural frequency of the piping. The influence of valve closing and opening operations to change inner pressure during pump operations on the pulsation boundary condition was investigated in this study. A drastic change in the boundary condition of the acoustic resonance behavior by using a slightly different valve opening ratio to set a different inner pressure was shown in the experimental results. The phenomenon was numerically simulated by using the method of characteristics. The simulation results showed that the boundary condition of the acoustic resonance changed from the closing opening condition to the closing closing condition when the valve opening ratio was changed slightly from 10 % to 15 %. This indicated that the boundary condition of the acoustic resonance had a pulsed change. Therefore, the boundary condition of the acoustic resonance was sensitive to a slight change of the valve opening ratio.

This paper proposes a dynamic buckling analysis method which can accurately simulate the buckling behavior of cylindrical water storage tanks during an earthquake. The proposed method takes into account the behavior of oval-type vibration as well as beam-type vibration, which are coupled vibrations between the shell structure of the tank and the water stored in the tank. In the proposed method, both the tank and the stored water are three-dimensionally modeled by finite elements and time history analysis is conducted. Moreover, coupled analysis between the fluid and structure and large deformation analysis to the shell structure of the tank are also considered. The analytical results by the proposed method agreed well with those of experiments regarding occurrence of oval-type vibration, mode of buckling and buckling load. The method can accurately simulate the seismic response including the coupled vibrations and the process of damage such as buckling of the cylindrical water storage tank during an earthquake In conclusion, the proposed dynamic buckling analysis method can quantitatively evaluate the seismic performance of water storage tanks such as seismic safety margin.

This study describes a nonlinear vibration analysis for a cylindrical water storage tank considering oval-type vibration, which is a higher-order vibration mode (axial wave number m :l and circumferential wave number n >= ). Oval- type vibration occurs in the sidewall of cylindrical tanks when a coupled vibration system forms between the sidewall and the contained liquid. Recently, it was found that oval-type vibration causes the nonlinear vibration response of the tanks. Hence, it would be useful for future seismic design methods to conduct a nonlinear dynamic analysis of water storage tanks considering the influence of oval-type vibration.This study proposes a nonlinear dynamic analysis method concerning the coupled vibration between fluid and structure using an explicit method. The proposed method uses a shell element which can take into account the geometric nonlinearity characteristics and a solid element which follows Euler's equation. The ALE method is applied to the coupling analysis between fluid and structure, and the explicit time integration method is used for the time-history response analysis.Next, the proposed method is used to conduct a numerical simulation of the dynamic response of oval-type vibration and the nonlinear vibration behavior of the tank, and the analytical results are compared with the experimental ones. Both results are in good agreement concerning the occurrence and modes of oval-type vibration in addition to the nonlinear vibration response of the tank. Regarding the dynamic fluid pressure, the local pressure by oval-type vibration as well as the main pressure by beam-type vibration can be calculated accurately. These results confirm that the proposed method achieves a more accurate analysis for the nonlinear vibration response of the tank considering the influence of oval-type vibration.

The seismic design of thin cylindrical water storage tanks takes 1,710 account beam-type vibration but not simultaneous oval-type vibration. In this study, an experimental and analytical investigation was conducted on the nonlinear response of beam-type vibration upon the generation and growth of oval-type vibration. The resonance frequency of the beam-type vibration shifted to a lower region and the magnification factor decreased with the increase in oval-type vibration by large input excitation. The application of a nonlinear single-degree-of-freedom system model revealed that this response was due to coupling between the beam-type vibration and oval-type vibration. In addition, a nonlinear finite element method capable of accurately simulating oval-type vibration is proposed. The new method simulates the nonlinear response of beam-type vibration with a high degree of accuracy.

In the pipe line installed in the nuclear power plant, there are many reports of damage caused by fatigue as a result of machine vibration of a pump etc. Vibrational stress evaluation by the method using the strain-gauge method or the accelerometer as one of the preventive measures of these oscillating troubles etc. is performed. However, since many special skill and working hours are required for these methods, the development of vibration measurement and stress evaluation technology which operates quickly and easily at the spot is desired. The purpose of this research is the development of a technique and equipment which measures vibrational stress immediately using a laser displacement sensor. In the measurement technique proposed, displacement by the bending vibration of piping which vibrates using three sets of laser displacement sensors is measured, and vibrational stress is obtained by calculating the strain produced from those displacement differences for piping. This measuring instrument is a non-contact system, and a miniaturization and short-time measurement of equipment are easy.This paper deals with the concept of the vibrational stress measurement technique, the theory of the measuring method, and the procedure, the authors propose, using three sets of the laser displacement sensors. Furthermore, using a cantilever model, vibration experiments are conducted, displacements and strain are measured. Next, comparison with the stress by using the displacement measured by the experiment based on this technique and the stress from the strain measured by the experiment is performed. The application possibility of the technique is described.

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.

This study reports on the dynamic buckling experiment of a 1/10 reduced scale model of a large-scale cylindrical water storage tank by using a shaking table, and the buckling analysis by using both the simplified method and the finite element method.The dynamic buckling experiment is performed by using the reduced scale tank model whose initial imperfection has been measured. The tank model is filled with water up to 95% of the full level, and puts 200-weight on its top, overcoming the response reduction induced by the oval-type vibration. The sinusoidal waves are used as the input. As a result of the experiment, the bucking occurs on the tank and plastic deformation is observed on the side and bottom of the tank.Two methods of the buckling analysis are carried out. At first, the buckling load is estimated by using a simplified method adopted in the current Japanese guideline. The analytical result shows this method is conservative despite using the tank with initial imperfection.Secondly, the static buckling analysis with the finite element method is conducted. There is an issue how to treat the dynamic fluid pressure distribution of the contained water in the tank with regard to the static analysis, because the coupling between fluid and structure cannot be taken into consideration. In this study, the distribution of the dynamic fluid pressure is calculated in accordance with the Fischer's method. The buckling load calculated by using the dynamic fluid pressure distribution agrees with that of the experiment approximately. Therefore, it is appropriate to apply this proposed static analytical method to seismic design.

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.

This study describes the vibration experiment which examines the vibration characteristics of a cylindrical water storage tank caused by the coupling between the beam-type and the oval-type vibrations in detail.A small or large acceleration excitation test is performed by a shaking table using a 1/10 reduced scale model of a large-scale tank The sinusoidal waves with the resonance frequency of the beam-type vibration are used as the input. By using accelerometers, displacement sensors and strain gauges, the vibration characteristics and the vibration modes of the tank model are investigated.The beam-type and the oval-type vibrations are excited simultaneously and the oval-type vibration of fundamental harmonics is excited in the small or large acceleration excitation test. In the large acceleration excitation test, however, the oval-type vibration of subharmonics of order one-half appears suddenly and grows rapidly when the amplitude of the oval-type vibration of fundamental harmonics increases to some magnitude. At the same time, the response of the beam-type vibration of the tank is reduced rapidly. This result shows that the occurrence of the oval-type vibration of subhanmonics of order one-half and the response reduction of the beam-type vibration are in close relationship.

A large cylindrical water storage tank, widely used at power stations and chemical plants, typically has a large radius/wall-thickness ratio. The relatively thin sidewall of such a tank can deform easily during an earthquake due to vibrations of the tank structure. In order to improve the seismic-proof design practices for a water storage tank of flexible structure and to develop a new seismic resistance evaluation method to be adopted in future, it is important to understand the dynamic responses of such a tank to seismic motions including the nonlinearity of responses to large amplitude vibrations.This paper reports on the results of vibration test, in which sinusoidal wave excitations with large amplitude were conduced to the scale model tank of a thin-walled cylindrical water storage tank, and the theoretical analysis of the dynamics of the vibratory behaviors that were observed during the vibration test.First, a frequency sweep test was performed over the range that covered the natural frequency. The response of the test tank as a whole to given vibrations remained almost the same over the excitation frequency range. Frequency analysis of the response of the tank failed to locate any resonance points at or around frequencies that had been determined by the basic vibration characteristic test that we had conducted in advance.Next, a large amplitude excitation tests were carried out, in which the test tank was excited intensively by several tens of sinusoidal. waves of a fixed frequency that was in the vicinity of the resonant frequency. The response of the tank as a whole in the form of beam vibrations did not intensify in proportion to the input acceleration; it did not go beyond a certain level.Since both of the tests produced significant oval vibrations on the sidewall of tank, the influence of oval vibrations over beam vibrations was analyzed. The analysis concerning the deflection of the sidewall of tank by the additional appearance of oval vibrations in the presence of beam vibrations revealed that a major decrease in the flexural rigidity reduced the response (beam vibrations) of the whole tank. The phenomenon was modeled using a nonlinear equation of motion, assumed that the rigidity depended on the amplitude of oval vibrations. The analysis using this equation explained the results of the above-mentioned tests very well.Thus, it was demonstrated both empirically and analytically that beam vibrations of a cylindrical water storage tank are reduced by the appearance of oval vibrations that have the effect of lowering the natural frequency.

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 53 Hz and the other at 106 Hz. 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 tanks 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.

In order to develop an advanced ion exchange process for the reprocessing of spent nuclear fuels, a novel anion exchanger, AR-01 with the resin embedded in porous silica beads and benzimidazoles as functional groups has been manufactured. Adsorption behavior of various fission product elements (FPs) and uranium in nitric acid medium were investigated experimentally using this anion exchanger. Separation performance of FPs from U(VI) in simulated spent fuel solutions was demonstrated by column chromatography utilizing dilute HNO₃ and thiourea as eluents.<BR>Most FPs such as Cs(I), Sr(II), Mo(VI), Rh(III) and trivalent rare earths showed negligibly slight adsorption and could be separated from U(VI) satisfactorily. Cerium(IV) was strongly adsorbed, but was gradually reduced to non-adsorptive Ce(III) by the anion exchanger. Zirconium(IV) presented weak adsorption and its a part mixed with U(VI) in the column experiments. Ruthenium(III) exhibited quite strong adsorption in a broad HNO₃ concentration range as the form of anionic nitrosylnitrato-complexes, its most amount mixed with U(VI). Palladium(II) showed significantly strong adsorption probably due to complexes formation with the anion exchanger. The adsorbed Pd(II) was effectively eluted out by thiourea and separated from U(VI) and other FPs completely.