Choice and Limits of a Fluid Model for the Numerical Study in Dynamic Fluid Structure Interaction Problems

This paper is related to the study of a nuclear propulsion reactor prototype for the French Navy. This prototype is built on ground and is to be dimensioned toward seismic loading. The dynamic analysis takes the coupled fluid structure analysis into account. The basic fluid models used by design engineers are inviscid incompressible or compressible. The fluid can be described in a bidimensional by slice or a three-dimensional approach. A numerical study is carried out on a generic problem for the linear FSI dynamic problem. The results of this study are presented and discussed. As a conclusion, the three-dimensional inviscid incompressible fluid appears to be the best compromise between the description of physical phenomena and the cost of modeling. The geometry of the reactor is such that large displacements of the structure in the fluid can occur. Therefore, the linearity hypothesis might not be longer valid. The case of large amplitude imposed oscillating motion of a cylinder in a confined fluid is numerically studied. A CFD code is used to investigate the fluid behavior solving the NAVIER-STOKES equations. The forces induced on the cylinder by the fluid are computed and compared to the linear solution. The limit of the linear model can then be exhibited.

Modeling of Sleeved Taylor Impact Specimens

Recently experimental studies have been conducted using a novel form of the Taylor impact test consisting of sleeved cylinders. A soft material of known properties (OFHC Cu) was used for the core and the tight fitting sleeve was fabricated from the material of interest (AF1410 steel). On impact the mushrooming and sliding core places the sleeve in a stress state not normally found in Taylor impact testing. This paper describes a study conducted to evaluate the feasibility of backing out Johnson-Cook strength model coefficients from measured (post-test) deformed geometries of sleeved specimens using an explicit impact code (EPIC). In addition, modifications to the sleeved concept geometry (tapered and capped core) are also explored numerically as well as the sleeve/core sliding friction coefficient.

Discussion on Two Times Integral Displacements of Strong Ground Motion Records and Shaking Table Data

In this paper, two times integral of acceleration record was discussed by the use of strong earthquake motion data; recorded in the 1999 Kocaeli (Turkey) Earthquake data. Usually, the two times integral displacements of horizontal seismic acceleration records will diverge. It was estimated for the integral displacement to diverge by the baseline shift caused on sensor tilting during quake. The data was simulated in 3 dimensional and 6 freedom shaking table. The divergent process of seismic data and shaking table data were studied.

Effects of Damper Force Ranges and Ground Motion Pulse Periods on the Performance of Semi-Active Isolation Systems

A large-scale base-isolated steel structural frame was tested at the shaking table laboratory of the National Research Institute for Earth Sciences and Disaster Prevention. These collaborative experiments featured auto-adaptive media and devices to enhance the performance of passive base isolation systems. The planning of these experiments involved determining appropriate device control methods, the development of a controllable damping device with fail-safe characteristics, and the evaluation of the performance of the controlled isolation system subjected to strong ground motion with pronounced near-field effects. The results of the planning study and their large-scale experimental confirmation provide guidelines for the development and implementation of auto-adaptive damping devices for full scale structures.

An Unsteady Analysis on Thermal Stratification in the SCS Piping Branched Off the RCS Piping

A numerical study is performed to estimate on an unsteady thermal stratification phenomenon in the Shutdown Cooling System (SCS) piping branched off the Reactor Coolant System (RCS) piping of Nuclear Power Plant. In the results, turbulent penetration reaches to the 1st isolation valve. At 500sec, the maximum temperature difference between top and bottom inner wall in piping is observed at the starting point of horizontal piping passing elbow. The temperature of coolant in the rear side of the 1st isolation valve disk is very slowly increased and the inflection point in temperature difference curve for time is observed at 2700sec. At the beginning of turbulent penetration from RCS piping, the fast inflow generates the higher temperature for the inner wall than the outer wall in the SCS piping. In the case the hot-leg injection piping and the drain piping are connected to the SCS piping, the effect of thermal stratification in the SCS piping is decreased due to an increase of heat loss compared with no connection case. The hot-leg injection piping affected by turbulent penetration from the SCS piping has a severe temperature difference that exceeds criterion temperature stated in reference. But the drain piping located in the rear compared with the hot-leg injection piping shows a tiny temperature difference. In a viewpoint of designer, for the purpose of decreasing the thermal stratification effect, it is necessary to increase the length of vertical piping in the SCS piping, and to move the position of the hot-leg injection piping backward.

Blast-Resistant Window Concepts

Terrorist bombs threaten American civilians and military personnel both at home and abroad. Analysis of data from previous terror attacks indicates the largest number of injuries result from projected glass shards from shattered windows and facades. Three key issues have led to increased interest in new window materials, as well as changes in building design codes: (1) actual terror attacks; (2) the threat of future terror attacks; and (3) monetary losses due to hurricanes. New protective products include a wide variation of films and laminated glasses for retrofit / replacement. Air Force Research Laboratory (AFRL) research has shown that these protective films will reduce the fragmentation of the enclosed glass. However, protective films that are not anchored will not provide retention of the film/glass system under the severe blast loadings expected from terror bombs. The paper introduces the Flex window, a patent-pending blast-resistant window developed at AFRL, along with key design concepts. In addition, the paper presents results from actual blast tests of the Flex window. Tabular data and photo-documentation is used to illustrate the ability of the Flex window to handle blast pressures a full order of magnitude greater than the typical commercial “blast proof” window. New AFRL methods for modeling both exterior and interior loading functions are presented. In addition, possible response modes are discussed, based on observations of high-speed video recordings.

Fatigue Effect of RCS Branch Line by Thermal Stratification

Recent events reported at a number of nuclear power plants worldwide have shown that thermal stratification, cycling, and striping in piping can cause excessive thermal stress and fatigue on the piping material. These phenomena are diverse and complicated because of the wide variety of geometry and thermal hydraulic conditions encountered in reactor coolant system. Thermal stratification effect of re-branched lines is not yet considered in the fatigue evaluation. To evaluate the thermal load due to turbulent penetration, this paper presents a fatigue evaluation methodology for a branch line of reactor coolant system with the re-branch line. The locations of fatigue monitoring and supplemented inspections are discussed as a result of fatigue evaluations by Interim Fatigue Management Guideline (ITFMG) and detail finite element analysis. Although the revised CUF was increased less than 50 %, the CUF values for some locations was greater than the ASME Code limits.

Flow-Induced Vibration Characteristics of Steam Generator U-Tubes With Defect

This paper investigates the fluidelastic instability characteristics of steam generator (SG) U-tubes with defect. The operating SG shell-side flow field conditions for determining the fluidelastic instability parameters such as damping ratio and added mass are obtained from three-dimensional SG flow calculation. Modal analyses are performed for the U-tubes either with axial or circumferential flaw with different sizes. Special emphases are on the effects of flaw orientation and size on the modal and instability characteristics of tubes, which are expressed in terms of the natural frequency, corresponding mode shape and stability ratio.

Study of the Dynamic Response of Large Scale Buildings Using Simplified Approaches

The dynamic response of large scale concrete buildings submitted to an explosion cannot always be obtained by means of classical FE analysis codes at reasonable costs. Indeed, the precision level required to predict efficiently the local failure of structural elements needs very fine meshes, which rapidly becomes unaffordable especially in the case of dynamics. The approach presented in this paper relies on a partitioning of the phenomena and their study by simplified methods: (1) The loading of the structure resulting from the detonation of an explosive charge is computed by a numerical implementation of semi-empirical formulas (Kinney and Graham, 1985, Baker et al., 1983); (2) The response of external walls elements, directly impacted by the aerial shock wave, is studied by a modal projection method, based on the use of analytical solutions from the thin plate theory; (3) Longitudinal propagation of the shock through the floors and walls of the building, including material and structural damping, is modeled by a 1D approach. This allows to determine finally whether the resistance limit of the constituting material is locally exceeded or not. Examples taken from a representative building study are presented in order to illustrate the approach.

Behavior of Facilities Under Explosive Loading Due to Malevolent Acts

As required in the French regulations, the behavior of the nuclear fuel reprocessing or fabrication plants and nuclear power plants must be assessed for a set of various normal and accidental situations including explosions due to operation hazards or malevolent acts. In this last case, the assessment gathers both safety and security aspects and lead to undertake studies accounting for loads due either to an explosion resulting from an aggression with a large amount of explosive or to an attack with a High Energy Density Device as a conical shaped charge. In order to provide the Authority with elements of appreciation and in support of the expertise of the studies performed by the operators, the Institut de Radioprotection et de Suˆrete´ Nucle´aire (IRSN) has initiated a program including experiments and development of numerical models concerning the evaluation of the consequences of such aggression in terms of mechanical damage to the plants and radiological release in the environment. The French approach for assessing the consequences of malevolent acts is based on a sensitivity study aiming at determining the critical components, followed by a vulnerability study for assessing the behavior of the facilities, depending on the type of weapons chosen in compliance with the threats. So for introduction, this approach will be briefly recall. The paper will focus on the technical tools to perform the vulnerability study in the case of an aggression by explosion.