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The core melt accidents at Fukushima Daiichi Units 1-2-3 have occurred due to the tsunami of the Great East Japan Earthquake at March 11, 2011. Now a coolant of approximately 100t is injected into each Reactor Vessel (RPV) in order to cool the fuel debris, and a part of the coolant leaks out from the water. The contaminated water is collected, and it is stored in the contaminated water storage tanks more than approximately 1,000 and the total amounts of coolant exceeds 1,000,000 t. Although the contaminated water is purified by ALPS, it is still in high nuclear pollution density. According to the homepage of Nuclear Regulation Authority (NRA) in Japan, the storage tanks have been placed on the concrete bed without any anchor. Tokyo Electric Company (TEPCO) reported to NRA in 2015 that the design acceleration used for the overturning evaluation of the tanks have 0.3G. At the Fukushima Daiichi Power Station in the Great East Japan Earthquake, the maximum horizontal acceleration was 0.6G, the maximum vertical acceleration was 0.326 G at the time of the Great East Japan Earthquake. Even if an earthquake that is a fraction of this earthquake comes back, there is a possibility that this tank will fall over. The temporary special design guideline is adopted. These tanks have already stored the contaminated water for 6 years. However, it is thought that the more long term countermeasures is necessary for preventing the contaminated water from flowing out into the Pacific Ocean when another great earthquake will attack this area in future. In this paper, we propose a drastic structure to add a foundation without causing ground to the present tank. In the past, the member fastening the steel plate of the upper structure of the tank and the concrete of the lower structure is a foundation bolt, but this time it is a stud welded to the tank side plate. This made it possible to flexibly design and reinforce the foundation itself even after tank installation.

To improve design and troubleshooting techniques of piping systems for operating power plants, it is necessary to investigate, by experiment and simulation, the behavior of fluid inside the piping system in detail. This study was conducted using full-scale piping system under conditions that could seriously threaten the plant operation, by matching pressure pulsations, acoustic resonance, and piping natural frequency. Although piping vibration is reported to influence fluid pressure pulsations, there were no such examples of influence in this experiment. Knowing that the opening ratio of the pressure control valve affects the boundary condition for acoustic resonance, experiment and simulation at different opening ratios were conducted. It has been suggested that the cases in which a valve partially open at 25% or less should not be taken as a closed end. This finding conflicts with such a widespread design assumption.

In this study, the applicability of a previously developed optimal seismic design methodology, which can consider the structural integrity of not only piping systems but also elasto-plastic supporting devices, is studied for seismic waves with various frequency characteristics. This methodology employs a genetic algorithm and can search the optimal conditions such as the supporting location and the capacity and stiffness of the supporting devices. Here, a lead extrusion damper is treated as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model. As a result, it is shown that the proposed optimal seismic design methodology is applicable to the seismic design of piping systems subjected to seismic waves with various frequency characteristics. The mechanism of optimization is also clarified.

The seismic-proof design of a large-scale cylindrical water storage tank has been an important issue for enormous earthquake. For enhancing its reliability, it is necessary to study the vibration behavior of the tank in more detail. This paper describes the results of a vibration test with a 1/10 reduced scale model of a large-scale cylindrical water storage tank, and also refers to the dynamic fluid pressure distribution and its influence on the seismic-proof design. Considering the differences between the experimental values and numerical design ones, it becomes obvious that there is a discrepancy between the positive and the negative pressures of the dynamic fluid pressure and that the dynamic fluid pressure depends on the acceleration magnitude. And it is suggested that such phenomena are caused by oval-type vibrations. They, however, have little effect on the seismic-proof design of the tank in the range of acceleration used in this study.

When slender pipes are subjected to internal flow, the pipes lose stability by flutter and divergence in increasing the fluid velocity. In addition, they also lose stability when they are subjected to external annular axial flow. In the development of a piping system in the field of ocean mining, and in the field of fluid energy utilization, and so forth, the double walled pipe structure system subjected to an internal flow and an external flow simultaneously is thought to be one of the important pipe structures. In this paper, the pipe structures are assumed to be composed of the cantilevered beam structure which shows the complicated dynamic behavior than the other supported conditions. For the analysis of the internal flow, the conventional inviscid stability analysis method is applied. For the analysis of the external annular axial flow, both the viscous solution using the Navier-Stokes equation of motion and the ideal fluid solution which viscous influence is added to are applied. Changing the flow direction and the fluid velocity of the internal flow and the external flow, and the specifications of modeling, the stability of the double walled pipes is investigated and discussed.Copyright © 2015 by ASME

A tuned mass damper is usually used to reduce wind-induced vibration of towers and high rise buildings. However it is not so effective for the structures of which the natural frequency is varied for the case of building up bridge-towers. For these structures the semi-active controlling method seems to be effective in reducing the vibration. This paper proposes a new semi-active vibration controlling method and an adaptive tuned mass damper ATMD consists of a pendulum and an analogue controlling system. In this system the tuning condition of the ATMD is realized by retaining the phase lag of the damper mass to the main structure to be 90°. The effectiveness of the proposed ATMD is evaluated analytically and experimentally.

This paper deals with new-type dynamic vibration absorber for structures such as piping systems, buildings and towers. This dynamic absorber consists of balls and ball cases. It makes use of ball rotation for reducing the vibration of structures. The characteristics are shown as follows : (1) It is simple composition composed of some balls and ball cases and so it is low-cost type; (2) The frequency tuning is unnecessary, and so a preliminary measurement for adjustment is not necessary; (3) It is possible to correspond to any frequency without tuning; (4) It is compact and easy to install on structures. We applied this self-tuning dynamic absorber to a pipe branch of piping system and a view tower as a large structure. The effects of vibration reduction were evaluated by simulation analysis and vibration test using a shaking table.

Hysteresis elements such as elasto-plastic dampers are important elements for mechanical structures, especially for earthquake-proof structures. When such nonlinear supports are utilized for piping systems, the nonlinearities of the hysteresis elements and the geometrical complexity of the piping systems lead to complicated seismic responses, and thus further studies are required in order to enhance the reliability of the earthquake-proof design. In the seismic response analysis, the method of time history response analysis is widely used. In this paper, a method of nonlinear seismic response analysis for a piping systems using a combination of the FEM and the Differential Algebraic Equations (DAE) is proposed. As it is well known, the DAE is suitable for numerical analysis of time history responses for mechanical structures and machinery elements. According to the advantage of the DAE, the numerical modeling and simulation of a complex piping systems supported by the hysteresis elements can be easily carried out by using the proposed method. In order to verify the usefulness of the method, the time history responses of piping systems supported by a elasto-plastic damper is examined for seismic excitation by using the proposed method. The damper is modeled as a bilinear model. The effects of the second stiffness and the stiffness associated with the plastic deformation of the damper on the seismic responses are investigated using an actually recorded earthquake motion.

Hysteresis elements such as elasto-plastic dampers are important for mechanical structures. They have nonlinearities and thus the vibration characteristics of mechanical structures with hysteresis elements are not clarified yet and need further studies. In this paper, the investigation of the dynamical stability of mechanical structures with a hysteresis element is performed by means of describing function method, which is on the basis of linear approximation of the hysteresis element. The nonlinear vibration system is composed of a linear spring-mass-damper structure system of any order and a hysteresis damper. The describing function of a hysteresis damper is derived and it is shown that the function remains upper half plane in the complex plane. According to the passivity of the linear structure system, this fact leads to the vibration system that is stable for any harmonic excitation. Next, the responses for seismic excitation are examined in simulation by using two typical models of the hysteresis element, a bilinear model and a Ramberg-Osgood model. The effects of the second stiffness of the dampers and the amplitude of the excitation motion are investigated using an actually recorded earthquake motion. The simulation results imply that the determination of the second stiffness requires the trade-off between an oscillation and a drift for designing earthquake-proof mechanical structures with the hysteresis damper.

To reduce wind-induced vibration of tall buildings and bridge towers, tuned mass dampers are often used. These dampers are called “passive type” while the methods which reduce the vibration by controlling the motion of a large mass with an actuator are called “active type”. For these types we have to change or control the structural vibration characteristics themselves, therefore they need very large exciting forces, and the system will become very large for large structures. In this view point, new concepts have just begun to be studied, where the driving forces themselves will be controlled. In this paper, we proposed a new system for reducing the flow-induced vibration of the structures by utilizing fluid excitation force itself. In this system, as we control the direction of the driving forces, this system does not need so large control forces and the system becomes smaller and simpler. We investigated the feasibility of this system when applied to a bridge, a building and evaluated the effectiveness of driving forces by the wind test using a reduced scale model.

As the flexible plates, the papers in printing machines, the thin plastic and metal films, and the fluttering flag are enumerated. In this paper, the flexible plate is assumed to be stationary in an axial flow although both the stationary plate and the axially moving plate can be thought. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The coupled equation of motion of a flexible cantilevered plate is derived in consideration of the added mass, added damping and added stiffness, respectively. The velocity potential is obtained by assuming the unsteady axial fluid velocity to be zero at the trailing edge of a flexible cantilevered plate, neglecting the effect of a circulation. The complex eigenvalue analysis is performed for the stability analysis. In order to investigate the validity of the proposed analysis, another stability analysis is also performed by using the non-circulatory aerodynamic theory. The comparison between both solutions is investigated and discussed. Changing the velocities of a fluid and the specifications of a plate as parametric studies, the effects of these parameters on the stability of a flexible cantilevered plate are investigated.Copyright © 2014 by ASME

A herringbone-grooved gas-lubricated journal bearing can rotate silently at high speed with low friction, and moreover it can be small-sized. In this paper, the equation of motion of a herringbone-grooved gas-lubricated journal bearing is derived using the gas force which can be obtained by applying the Navier-Stokes equation to the grooved and the ridged parts of a journal. The stability analysis is performed by using the analysis method by Routh-Hurwitz, the root locus of complex eigenvalue analysis, and the transient time history response analysis. The physical meanings of the stability charts which have not been explained sufficiently in the conventional studies are clarified by considering the forward whirling motion and the backward whirling motion, and the more reasonable stability charts are proposed. In addition, it is reported that the present analysis results show a good agreement with the already reported experimental results. Furthermore, the parametric studies as for the specification of gas-lubricated bearing are performed, and it is shown that the stability charts are affected by the change of specifications intricately.Copyright © 2014 by ASME

Recently, the leakage-flow inside the mechanical structures such as rods in the cylinders, valves, seals and orifices, so on for controlling the flow volume and the fluid pressure tends to become larger aiming to increse the plant efficiency, which lead to the occurrence of the fluid-elastic instability of these structures. In this study, the fluid-elastic instability analysis procedure is proposed in order to establish the design criteria on protecting the key components from the flow-induced instability. The unsteady fluid force is derived theoretically for the simple segment and the equation of motion for the axisymmetric rods is conducted by the finite element method. Using these formulation the coupled equation of motion between fluid and structures is derived. The stability evaluation is performed using the Argand diagram obtained by plotting the real part and the imaginary part of the eigen value λ. Comparing the numerical values with the experimental values, this evaluation method is very efficient as the design criteria for the flow-induced instability.

The dynamic stability of a flexible plate subjected to a parallel flow is investigated when it moves in a flowing fluid. As the flexible flat plates, the papers in a high speed printing machine, the papers discharged by a paper machine, and the thin plastic and metal films, the fluttering flag and the oscillating doom roof caused by wind are enumerated. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The fluid-structure coupled equation of motion of a flexible flat plate supported simply at the both ends is derived into consideration with the added mass, added damping and added stiffness of a fluid, respectively. In addition, the effect of tension acting on a flexible plate, the influence of velocity of a moving plate and that of a fluid velocity, are also included into the coupled equation of motion respectively. The eigenvalue analysis is performed for the dynamic stability analysis. Changing the velocities of a plate and a fluid, and the specifications of a plate as parameter studies, the influences of these parameters on the dynamic stability of a plate are clarified. It is made clear that the plate moving in a still fluid becomes unstable at slightly lower velocity than the stationary plate subjected to a parallel flow. Moreover, it is found that the present solution shows a good agreement with the already reported experiments in which the flexible flat plate was a paper.Copyright © 2013 by ASME

In this paper, active vortex control in flow across a barrage is investigated experimentally and theoretically. The special feature of the presented control method is that the vortex is controlled by the vibration of the control element, which is the front edge of the barrage and the generation point of the vortex. In the experimental study, the front edge of the barrage is acted upon by an excitor perpendicular to the flow direction. Firstly, the transfer function between the vibration of the control element and the pressure in the wake is determined. Then the feedback control is carried out with consideration of the phase shift obtained by the transfer function. In the theoretical study, the vortex filament method is used and the flow across a barrage is analyzed as a two-dimensional flow. The feedback control theory is used and the behaviour of the vortex is simulated. It is shown experimentally and theoretically that the vortex is suppressed by the vibration of the control element in the case of the specified phase shift.

When calculating the resonant response of bladed turbine disks, it has been expedient to assume that all blades on a given disk are identical. This leads to the prediction that all blades experience the same amplitude of displacement and stress when excited by forces harmonically related to the rotor speed. However, it has been shown experimentally that significant variations in these amplitudes occur for different blades on the same disk. These variations arise due to the effects of mistuning, which refers to small differences in blade characteristics. In this paper, effects of mistuning for free-standing blades and integral shroud blades are studied by means of Monte Carlo simulation and sensitivity analysis. It is found that weakly coupled systems with low damping are very sensitive to mistuning. Also, the validity of the lumped model used in this paper is examined by comparing the calculated results with experimental data.

A new active adaptive feedback control algorithm (F. B. LMS) was developed in this paper mainly for the purpose of reducing aerodynamically self-oscillating noises. This is an algorithm which reconstructs the Filtered-X-LMS to a feedback type and which needs only error signals. A simple experiment using a straight duct proved that this method could increase acoustic damping in a closed sound field by controlling the secondary source just like a sound-absorbing wall. This method was also proven to be effective for reducing periodic noises which had periodic causality. This method was applied to reduce a cavity tone and a resonant noise of a model tube bundle which were typical self-oscillating noises, and satisfactory results were obtained. It was also successfully applied to reduce periodic noises such as those in a cab of a construction machine radiating from engine, cooling fan and oil hydraulic pump.

The liquid storage container (tank) is listed as one of the facilities, which are apt to be damaged by an earthquake in industrial facilities. As for seismic damages of containers, the sloshing phenomenon of the liquid free surface and the bulging phenomenon which is due to the interaction between the container structure rigidity and the liquid pressure become problems. Here, we investigate a nonlinear sloshing. There are many papers, in which the perturbation method using the small parameter, and the Galerkin’s method are applied as a method of the nonlinear analysis. However, in this paper, a modal method which superposes the linear solutions using Fourier series’ representation is proposed. Furthermore, this method is applied to the seismic response analysis on the nonlinear sloshing of a rectangular liquid storage container.Copyright © 2011 by ASME

To improve condition-based maintenance (CBM) techniques for operating plants, it is necessary to investigate, by experiments and numerical simulations, on the behavior of fluid inside piping system in detail. This study was conducted using the full-scale piping system under conditions that could seriously threaten the plant operation, by matching pressure pulsation, acoustic resonance and piping natural frequency. Although piping vibration is reported to influence fluid pressure pulsation, there were few examples of such influence in the conditions of this experiment. Knowing that the opening ratio of the pressure control valve affects the boundary condition for acoustic resonance, the experiment and numerical simulation at different opening ratios were conducted. It was suggested that there are cases in which a valve partially open at 25% or less shouldn’t be taken as a closed end. This finding conflicts with widespread design assumption.Copyright © 2011 by ASME

In Japanese nuclear power plants, quantitative evaluation for seismic safety margin of the equipment is an important issue. In this study, the seismic safety margin of cylindrical liquid storage tanks used in nuclear power plants was investigated experimentally and analytically using test tanks with water inside. The buckling load of the tanks was examined because buckling was their dominant damage mode. The test tanks were reduced-scale models similar to the large-scale liquid storage tanks used in nuclear power plants. The experimental buckling load was compared with the design value. Furthermore, dynamic and static elastic-plastic buckling simulations by finite element analysis using a three-dimensional model were made and then the simulation results were compared with the experimental and design values. The simulated and experimental results agreed well, showing the values were the nearly-true buckling load, that is, proof stress. The design value was lower than the other values, indicating the difference was the seismic safety margin. The above results illustrated that existing actual tanks would have a bigger seismic safety margin.Copyright © 2011 by ASME

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the power plant, has been used in severe conditions where high loading is in effect. Therefore, for the purpose of increasing plant reliability, we must establish a precise calculation method and optimal design procedure of the blade, taking its specific characteristics into consideration. In this paper, an effective autotuning technique of the blade's natural frequencies by combining sensitivity analysis with nonlinear programming is presented, and its application is shown. In the blade design, many natural frequencies must be tuned between engine order frequencies, satisfying various constrained conditions which result from such requirements as thermal efficiency and manufacturing. The new optimal technique in this paper is very useful for such blade design because a blade profile having the required natural frequencies can be obtained automatically.

Many heat-exchange tubes in a shell-and-tube-type heat exchanger are oscillated by means of the flow . of fluid through the heat exchanger. This flow is often cross flow and gas-liquid two-phase flow. Here, a brief review of studies on two-phase cross-flow-induced vibration is presented, and a summary of our work in this area provides a design methodology. Three types of vibration have been studied for tubes in two-phase cross-flow conditions: First, resonance of a tube due to vortex shedding is important primarily in single-phase flow, but also has been observed in homogeneous flow and even in two-phase flow. However, this vibration disappears in the slug flow or froth flow regions, which are important in numerous heat exchangers. Therefore, the vortex shedding phenomenon is not considered in this paper. Secondly, turbulent buffeting vibration is considered as the dominant phenomenon in the slug flow and froth flow regions. A method for estimating this type of random vibration is explained in this paper. Thirdly, an unstable form of vibration, so-called fluid elastic vibration, is also considered. The common method for estimating the instability boundary is similar to that used for single-phase flow; however, new insights on the method for two-phase flow are given in this paper.

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.

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.Copyright © 2010 by ASME

We have applied H2 control to an electrohydraulic shaking table. In the application of H2 control to this device, we propose a method in which the H2 controller is designed based on a model of a whole analog feedback control system to make as much use as possible of a loop shaping function of robust control. This method is very practical because no changes in the analog feedback system are needed. As a result of the application to a 1-axis electrohydraulic shaking table of National Research Institute for Earth Science and Disaster Prevention, the Characteristics of a position control have been improved by 30% from 10.6 Hz to 13.6 Hz.

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.Copyright © 2009 by ASME

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the turbine, has been used in the severe condition. Especially the blade root, which is inserted into a disc groove, supports the excessive centrifugal force. In this paper, effective methods of calculating the peak stress of the blade root and disc groove are presented. Since the geometry of the blade root and disc groove is complicated, the three-dimensional finite-element method is applied, including the nonlinear effect due to slippage between the root and groove. By using the above nonlinear finite-element method, contact and slip analysis is performed to obtain the converged peak stress. The effective linear analysis procedure for replacing the nonlinear analysis is also examined by comparing the calculated results of both methods.

The on-line computer test method is a new type of research technique to study the earthquake response bohavior of various types of structural elements, assemblages, and systems. It combines the experiment and numerical analysis and utilizes the benefits of both experimental and analytical research. In this study, we applied substructuring concepts to the on-line computer test method and developed a new algorithm which increases the accuracy of the substructuring method. By using this algorithm, we can simulate a more realistic elasto plastic seismic response of structures. For the purpose of development and verification of this algorithm, we prepared a small-scale on-line computer test system and simulated the high-level seismic response of a liquid tank which had seismic isolation devices.

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 ≥ 1 and circumferential wave number n ≥ 2). Oval-type vibration occurs in the side wall 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.Copyright © 2008 by ASME

The present paper aims to verify the seismic safety of the base-isolated spent-fuel storage rack. A series of seismic tests has been conducted using a three-dimensional shaking table. A sliding-type base-isolation system was employed for the prototype rack considering environmental conditions in an actual plant. A non linear seismic response analysis was also performed, and it is verified that the prototype of a base-isolated spent-fuel storage rack has a sufticient seismic safety margin for design seismic conditions from the viewpoint of seismic response.

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.Copyright © 2007 by ASME

In this study, the optimal seismic design methodology which can consider the structural integrity of both piping systems and elasto-plastic support devices are developed. This methodology employs genetic algorithm and can search the optimal conditions such as supporting locations, capacity and stiffness of supporting devices. A lead extrusion damper is treated here as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model for the various kinds of seismic waves with different frequency characteristics. As a result, it is shown that the optimal seismic design methodology proposed here is applicable to the seismic design of piping systems supported by elasto-plastic dampers subjected to the seismic waves with various kinds of frequency characteristics.Copyright © 2007 by ASME

In this study, the damping effects of an impact damper which consists of a vessel and elasto-plastic balls are evaluated. Lead is employed as an elasto-plastic material. Numerical simulations are performed based on a discrete element method. In the numerical simulations, the impact force modeling is modified so as that the elasto-plasticity of the material can be considered. And the rotation of a particle is also considered to simulate the actual particle behaviors at the collision. Frequency responses of the vessel and the damping effect of the damper are evaluated for 2 kinds of impact force models. Also, the effects of vessel dimensions, vessel configurations and the excitation directions are investigated. As a result, the effects of the above mentioned parameters are clarified.Copyright © 2007 by ASME

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 © 2006 by ASME

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 © 2006 by ASME

In this study, the optimal seismic design methodology which can consider the structural integrity of both the piping systems and the elasto-plastic supporting devices are developed. This methodology employs genetic algorithm and can search the optimal conditions such as the supporting location, the capacity and stiffness of the supporting devices. The lead extrusion damper is treated here as a typical elasto-plastic damper. Four kinds of evaluation functions; stress of piping systems, energy absorption, lead melt of dampers and energy absorbing balance are considered and each optimal condition is clarified and discussed. As the results, it is found that the optimal seismic design methodology proposed here is very effective and can be applied to the actual seismic designs for the piping systems supported by the elasto-plastic dampers, and can be also applied to the piping systems exposed to the actual earthquake waves which have various frequency components and the piping systems with a heavy local mass.Copyright © 2006 by ASME

Conventional impact dampers often utilize the steel balls because of its low cost and handling easiness. But the steel-ball impact dampers sometimes collapse or generate very large noise because of large shock at the impact. And as for the design of the impact damper, in the conventional approaches, the analytical modeling for the impact force is based on the contact theory proposed by H. Hertz, in which the restitution coefficient is assumed to be constant, i.e., the dependency on the relative velocity is not taken into consideration. However, some experimental results show that the restitution coefficient depends on the relative velocity at the impact. In this study, the elasto-plastic materials are employed as an impact damper material in order to suppress the large shock for the damper vessel and large impact noise. Therefore, the impact force modeling is modified so as that the elasto-plasticity of the material can be considered. This modeling can also consider the dependency of the restitution coefficient on the relative velocity. An impact damper which composed of a vessel and several particles made of elasto-plastic material such as lead is treated. The frequency response of the damper vessel and the damping effect of the damper are evaluated for the 2 kinds of impact force modeling by numerical simulations. Also, the effects of the particle number and the vessel configuration are evaluated. As a result, the effects of the above mentioned parameters are clarified.

We herein investigate the motion and vibration of multi-vehicles that follow complicated three-dimensional trajectories. A roller coaster is used as the multi-vehicle model. The equations of motion and the constraint conditions of the model are set up using a differential-algebraic equation (DAE). In previous reports, we examined the motion and vibration of a single-vehicle roller coaster. In the present paper, we examine a multi-vehicle roller coaster. We herein propose and analyze the constraint conditions between the vehicles. In the simulation, we investigate differences in motion and vibration among the coupled vehicles. The motions of multi-vehicles in the simulation and the experiment shared a number of similar tendencies. In addition, we propose a theory by which to evaluate the yaw angle, which is expressed in the x-y (s-u) plane defined as the ground surface, and analyze the influence on the yaw direction. Finally, we examine the validity of the proposed simulation method.Copyright © 2005 by ASME

In this paper, the vibrational behavior and unstable phenomena of multi-connected bodies supported by damper-spring elements moving in a narrow flow passage are investigated. These vibrational phenomena have been often observed in high-speed trains running in tunnels, cleaning robots going through pipings, medical machines in human blood vessels and core internal structures in nuclear reactor vessels. The fluid forces acting on the multi-connected rigid bodies are obtained analytically on the basis of the Navier-Stokes equations applied to a narrow flow passage. After the equations of coupled motion of the multi-connected bodies and fluid are derived, a stability analysis is performed, taking physical dimensions such as gaps etc. as parameters.Copyright © 2005 by ASME