Application of seismic analysis methodology to small modular integral reactor internals

This paper presents a comparison between experimental results and numerical simulations of a reactor pressure vessel internals response due to a rapid depressurization associated to a pipe break. The experiment is designed to fulfil conditions relative to a Pressurised Water Reactor (PWR). The numerical simulation is performed with the computer program package ADINA. The calculations are performed both with and without Fluid Structure Interaction (FSI) effects. It is shown that FSI effects are very important for this problem. The comparison between experimental and numerical results is performed for local pressure in the water and displacements and strains in the reactor vessel and internals. Our experience is that good numerical results can be achieved for this type of loading for all compared quantities. Note that the experiment was set up to show the importance of FSI-phenomena, the effect of this could then be stronger in the experiment compared to a “real” case.

In a previous paper, ambient vibration tests were conducted on a cable stayed bridge with resilient-friction base isolation systems (R-FBI) to extract the dynamic characteristics of the bridge and compare the results with a seismic analysis model. In this paper, a nonlinear seismic analysis model was established for analysis of the bridge to compare the difference in seismic responses between nonlinear time history analysis and multi-mode spectral analysis methods in the seismic design phase of cable supported bridges. Through these studies, it was confirmed that the seismic design procedures of the “Korean Highway Bridge Design Code (Limit State Design) for Cable Supported Bridges” is not suitable for cable supported bridges installed with R-FBI. Therefore, to reflect the actual dynamic characteristics of the R-FBI installed on cable-supported bridges, an improved seismic design procedure is proposed that applies the seismic analysis method differently depending on the seismic isolation effect of the R-FBI for each seismic performance level.

Dynamic characteristics of a perforated cylindrical shell for flow distribution in SMART

Seismic facies analysis plays a key role in stratigraphy and has developed rapidly in the context of deep learning methods. However, seismic facies analysis cannot only be regarded as an image segmentation or classification task because this would exclude prior knowledge of geophysicists on seismic interpretation. Seismic parameters summarized by geophysicists were included in the seismic facies analysis model. Seismic parameters were used to calibrate the different seismic facies units, and well logging data and sequence stratigraphy were integrated to perform geological interpretation and to establish a training dataset. A multi-head seismic parameter classification (MSPC) model was then established to divide the seismic facies units. A seismic facies geological interpretation (SFGI) model was constructed for the geological interpretation of seismic facies units, and an end-to-end seismic facies analysis model was designed based on the MSPC model and the SFGI model. The proposed model effectively improves the accuracy of the seismic interpretation, solves the intra-facies noise problem, and is easy to train and use.

<sec>Fluid-structure interaction pipeline systems are extensively adopted to transfer matter, energy and momentum, which are widely used in various fields. Due to the fluid-structure interaction effect, the pipe wall proves to produce strong vibration and noise under fluid action, which has a serious influence on the safety and concealment of the equipment, even leading to serious damages. Therefore, it is of great significance to study the vibration characteristics of fluid-structure interaction pipeline and methods to reduce the vibration of pipeline both in theory and in practice. </sec><sec>Phononic crystal can suppress the propagation of elastic waves in a specific frequency range by their special band-gap characteristics, which have wide application prospects in the field of vibration and noise reduction. Especially, the band gap characteristics of phononic crystal pipeline used to design fluid-structure interaction pipeline system have been widely studied, thus providing a new technical approach to reducing the vibration and noise of the pipeline. </sec><sec>In this paper, based on the theory of phononic crystal, the vibration transfer characteristics of the Bragg phononic crystal pipeline under fluid-structure interaction are studied. Combining the transfer matrix method and the finite element method, the band structure and band gap characteristics are calculated. Using the finite element method, the vibration characteristics of the phononic crystal pipeline under fluid-structure interaction effect, the shock excitation of pipe wall and the shock excitation of the fluid are considered. The influence of the fluid-structure interaction on the vibration transmission characteristics of the phononic crystal pipeline is also analyzed. </sec><sec>The research results indicate that when the fluid velocity in the fluid-structure interaction pipeline system is small the Bragg phononic crystal pipeline has a good attenuation effect on the shock excitation of pipe wall in the band gap range, and that when the fluid velocity increases the fluid-structure interaction effect becomes significant, the attenuation effect becoming weaker. Bragg phononic crystal pipeline has a certain attenuation effect on the pipe wall vibration caused by the fluid shock excitation near the band gap. The research results are expected to be able to provide a technical reference for the vibration control of pipeline systems under fluid-structure interaction conditions. </sec>

Numerical procedures for predicting reinforced concrete (RC) frames behavior, subjected to severe solicitation in particular earthquake, is nowadays a very important challenge in earthquake engineering field. The development of finite element (FE) codes generated multiple models of discretization associated to various rules of concrete and steel materials behavior. Indeed, both the coupling of these highly heterogeneous materials requires a fairly extensive behavior study including a maximum of parameters for better structure response simulation under seismic actions. Although, theoretically the most satisfying RC frames seismic analysis model involves the application of inelastic time-history dynamic analysis of three dimensional model of RC frames. Nowadays, this model seems to be too expensive or impractical due to the structures size and complexity. However, the simplified models applied to nonlinear static method can offer a good damage and safety evaluation of buildings' dynamic behavior. Other aims for RC structures seismic analysis are to be noticed, either for safety margins determination of the existing structures or the new buildings design. This work aims to expose the most used existing approaches in seismic numerical analysis and carry out a comparative study with the goal of evaluating the capacity of each method. Four models of seismic analyses are considered: dynamic, static, linear and nonlinear. Predictions are confronted with experimental results obtained from shake table tests. Furthermore, aiming to have a complete seismic analysis, three FE discretization models were studied for different scales. Hence, detailed knowledge of each approach was gotten from this procedure, deducing as a result the advantages and disadvantages of each model (reliability, computational time and domain of applicability), and providing a full database for reliability development and numerical methods robustness in earthquake, complying with the seismic design European standard recommendations. Comparing numerical and experimental results, a satisfying concordance is obtained when considering the initial structure damage. These results will be a good asset to assess the impact of uncertain parameters on seismic hazard and nonlinear response, through robust and simplified approach development of RC structures vulnerability estimating in civil engineering.

As composite materials have been used for marine structures such as boats, ships, offshore structures, etc., the effect of FSI should be understood.In particular, FSI effect is expected to be significant for polymer composites because the water density is very comparable to the composites' densities.For example, the density of a carbon composite is approximately 50% greater than the water density.Sandwich composites consisting of very low densities of core materials have lower densities than that of water.As a result, the hydrodynamic mass associated with FSI would be very critical to composite structures under water.The growing use of composites in ship masts, superstructures, deck grates, piping, ducting, rudders, propellers, stacks, and various submarine structures requires extensive modeling and testing to help designers, builders and operators better understand composite response [Mouritz, et al., 2001].These materials are subjected to a wide spectrum of loads during manufacturing and service life.Dynamic loadings, in particular, impact type event, represent a serious design concern for use of composite.Composite structures are more susceptible to impact damage than similar metallic structures which are more ductile in nature and can absorb typically large amounts of energy without failure.Furthermore, the damage in composites from impact can go undetected even when the mechanical properties may be drastically reduced from an impact.For these reasons, numerous experimental and analytical studies have been conducted to study the dynamic response of composites subjected to impact loading [Abrate, 1994;Aslan, et al., 2003;Kwon & Wojcik, 1998].According to the review of past works, most of the research effort has been focused on low velocity impact damage, specifically, the damage predictions, and the evaluation and prediction of residual properties of damaged laminates.All of the research completed thus far has focused on damage in composites under impact loading in dry environments to support development of composites in aircraft structures.As far as dynamic response of structures under water is concerned, a great deal amount of analytical and experimental studies have been conducted on the effect of fluid force on the natural frequencies, damping ratios and mode shapes of vibrating structures in contact with fluid.This is commonly known as the Fluid Structure Interaction (FSI) problem.FSI investigations have supported many problems in submarine signaling, offshore oil structure stability, and ship structure vibrations.Through these studies, many numerical and analytical methods have been developed in order to predict the added mass and the www.intechopen.com Advances in Composites Materials -Ecodesign and Analysis 338resulting changes in natural frequency of a structure in contact with fluid.It has been determined and widely proven that the effect of fluid surrounding a structure decreases the natural frequency of a structure due to the increase in total kinetic energy of the vibrating structure and fluid from the addition of kinetic energy of the fluid.This effect can be interpreted as an added mass to the vibrating structure in the analysis of the dynamic response.Essentially as the structure vibrates, its mass is increased by the mass of the vibrating fluid with which it is in contact, consequently decreasing its natural frequency.Studies of fluid structure interaction and the added mass effect, also known as virtual mass effect, hydrodynamic mass, and hydroelastic vibration of structures, started with Lamb [Lamb, 1921] who calculated the first bending mode of a submerged circular plate.In response to a problem of submarine signaling, Lamb investigated the vibrations of a thin elastic circular plate in contact with water.In his investigation he discovered that the natural frequencies for structures in contact with fluid are lower than the frequencies in air, based on the assumption that the modes shapes are virtually the same in water as in a vacuum.The resonant frequency was determined using Rayleigh's method.Lamb's theortical results were verified experimentally [Powell & Roberts, 1923].Much later, more research was conducted for measuing and calculating natural frequencies of free vibartions of beams and plates under water [Lindholm, et al., 1965; Fu & price, 1979;Kwak, 1996].Another branch of FSI studies is underwater explosion.Both experimental and numerical studies have been conducted for metallic structures [

The paper considers the problem of simultaneous modeling of structure and flow in a piping system. It takes a middle road between full coupled analysis on the one hand, and the simplified case of treating the liquid as a rigid mass. The suggested method allows the use of standard beam and rod elements for the analysis. Two approaches to the problem of dynamic interaction between pipe and medium are compared in the given paper: 1) The first one treats medium as mass rigidly connected to the pipe finite-element model’s nodes. 2) In the second one medium is modeled by the finite-element system of rod-elements. In this case the basic fluid-structure interaction (FSI) effects are taken into account. The main techniques for FE modeling of some pipeline elements are presented in the paper. The second approach can be implemented by the use of general purpose FE programs. A model of a feed water pipeline of VVER-440 type NPP has been developed to study how the FSI affects on pipeline response. The results of the analysis which allow estimation of inaccuracy arising from medium dynamics neglecting are as follows: • calculation of eigen frequency and mode shapes; • seismic analysis using the response-spectrum method; • accidental blast impact assessment with the use of time history analysis; • operating vibration assessment on the basis of harmonic analysis. It has become apparent that the way of medium modeling has an essential influence on the dynamic behavior of pipelines.

Often, to restrain the lateral displacement of elastomeric bearings in slab-girder bridges, two retainers in the form of angles or welded plates are placed on each side of the bearings, with a slight clearance to allow for longitudinal movement of the elastomer. The existence of the gap introduces nonlinearity into the seismic analysis of the structure, which is commonly ignored. In addition, by considering the gap, the elastomer's stiffness in the transverse direction contributes to the overall stiffness of the system. This paper investigates the behavior of these retainers under earthquake forces. The retainers' stiffness, the gap distance, and the period of the bridge are used as variable parameters. It is shown that the seismic demand on retainers is nonlinear in nature and depends on the frequency content of the input motion. It is also proved that ignoring the gap in the seismic analysis model can lead to lower seismic demands on the retainers and substructure. Design recommendations are given for bridges with such retainers.

The shaking table experiments on sliding and overturning of CAP1400 spent fuel storage rack with the effect of FSI

The seismic response analysis model of a single-column pier surrounded by sea ice was established and it analyzed the nonlinear seismic response of the pier subject to different types of earthquakes. The results show that the maximum seismic responses of the pier occur when the mass of sea ice is about 5000~10000 ton, which should be used to design a pier. When the sea ice is considered, the curvature ductility demand coefficient，the maximum displacement and the maximum residual displacement of the pier are several times than those corresponding to without sea ice, and the M-Ø hysteretic curves of the cross-section of the pier subject to earthquakes present downfallen ‘S’ form significantly and the deformability and energy dissipation capability of the pier drop remarkably.

Performance-based seismic evaluation is usually done by considering simplified models for the liquid storage tanks therefore, it is important to validate those simplified models before conducting such evaluation. The purpose of this study is to compare the seismic response results of the FSI (fluid-structure interaction) model and the simplified models for the cylindrical liquid storage tanks and to verify the applicability of the simplified models for estimating failure probability. Seismic analyses were carried out for two types of storage tanks with different aspect ratios (H/D) of 0.45 and 0.86. FSI model represents detailed 3D fluid-structure interaction model and simplified models are modeled as cantilever mass-spring model, frame type mass-spring model and shell type mass-spring model, considering impulsive and convective components. Seismic analyses were performed with modal analysis followed by time history analysis. Analysis results from all the models were verified by comparing with the results calculated by the code and literature. The results from simplified models show good agreement with the ones from detailed FSI model and calculated results from code and literature, confirming that all three types of simplified models are very valid for conducting failure probability analysis of the cylindrical liquid storage tanks.

The gravity cooling water tank is a remarkable structural feature of third-generation pressurized water reactor nuclear power plant. To investigate the influence of fluid-structure interaction (FSI) on the seismic response of the structure, this study designed two 1 : 50 simplified models of the AP1000 shield building. A series of shaking table tests were conducted to study the seismic responses with and without FSI effect. The natural frequency, acceleration, strain, and hydrodynamic pressure of the two models were analyzed, and the seismic reduction effect of the water tank was evaluated. Moreover, the test data were compared with the results of numerical analysis using the ABAQUS software. The results show that the presence of water and the sloshing of water reduce the natural frequency and seismic response of the model structure. Thus, the gravity cooling water tank has a certain seismic reduction effect. The simplified model of water sloshing can be used to analyze the seismic response of the shield building.

This work presents results from a numerical investigation on the influence of fluid-structure interaction (FSI) on the dynamic response of thin steel plates subjected to blast loading. The loading was generated by a shock tube test facility designed to expose structures to blast-like loading conditions. The steel plates had an exposed area of 0.3 m × 0.3 m and experienced large deformations during the tests. Numerical simulations were performed using the finite element code EUROPLEXUS. An uncoupled FSI approach was compared to a coupled FSI approach in an attempt to investigate FSI effects. Reduced deformation was observed in the plates due to the occurrence of FSI during the dynamic response. The general trend was an increased FSI effect with increasing blast intensity. The numerical results were finally compared to the experimental data to validate their reliability in terms of deflections and velocities in the steel plates. A good agreement with the experimental data was found, and the numerical simulations were able to predict both the dynamic response of the plate and the pressure distribution in front of the plate with good accuracy. Hence, the numerical framework presented herein could be used to obtain more insight regarding the underlying physics observed in the experiments. The clear conclusion from this study is that FSI can be utilized to mitigate the blast load acting on a flexible, ductile plated structure, resulting in reduced deformations.

Simplified earthquake response analysis of rectangular liquid storage tanks considering fluid-structure interactions