CFD-Tool for Thermal-Hydraulics Pressurised Thermal Shock Analysis: Qualification of the Code_Saturne

This paper explains the numerical program concerning the new thermalhydraulic Code_Saturne qualification for Safety Injection studies. Within the frame of the plant life time project, an analysis has shown that the most severe loading conditions are generated by a pressurised injection of cold water in the downcomer of a Reactor Pressure Vessel. For this kind of transients, a thermal hydraulics study has to be carried out in order to better adjust the accurate distribution of the fluid temperature in the downcomer. For that, the numerical tools have to be able to simulate the physical phenomena present during the Pressurised Thermal Shock. (PTS). For this qualification task, we have investigated one configuration related to an injection of cold water particularly in cold leg but also in a downcomer. One experiment test case has been studied and this paper gives a comparison between experiment and numerical results in terms of temperature field.

Solution Adaptive Grids Applied to Low Reynolds Number Flow

A numerical study has been undertaken to investigate the use of a solution adaptive grid for flow around a cylinder in the laminar flow regime. The main purpose of this work is twofold. The first aim is to investigate the suitability of a grid adaptation algorithm and the reduction in mesh size that can be obtained. Secondly, the uniform asymmetric flow structures are ideal to validate the mesh structures due to mesh refinement and consequently the selected refinement criteria. The refinement criteria in this work are derived from turbulent viscosity, which is not applied to the flow simulation, but instead used as a measure for grid refinement.

Fluid-Structure Interaction for Hydrodynamic Problems: Impact Between a Tanker Bow Flare and a Submarine

A methodology to predict the capacity of a nuclear submarine hull to act as a protective container and energy absorber under impact by an another underwater structure is needed. Principia Marine, company of Research in Shipbuilding (formerly IRCN, Institut de Recherche en Construction Navale), is responding to this need by developing an underwater impact crash prediction methodology based upon LS-DYNA3D software. Several physical phenomena with their own characteristic times follow one another at the time of the shock. So different but complementary tasks to develop this methodology were worked individually. This paper deals with contribution to this ongoing program that breaks up into two objectives. The first goal aims to highlight the effect of water on the structural deformation at the time of the collision between a nuclear submarine and a tanker ram bow, which is generally plane. The two-dimensional modelling of this collision uses an Eulerian formulation for the fluid and a Lagrangian formulation for the structure. The fluid-structure interaction is treated by an Euler/Lagrange penalty coupling. This method of coupling, which makes it possible to transmit the efforts in pressure of the Eulerian grid to the Lagrangian grid and conversely, is relatively a recent algorithmic development. It was successfully used in many scientific and industrial applications: the modelling of the attack of birds on the fuselage of a Jet for the Boeing Corporation, the underwater explosion shaking the oil platforms, and airbag simulation… The requirements of modelling for this algorithm are increasingly pointed. Thus, the second objective of this paper is to compare the results in pressures and velocities near the bulb for two cases, in the first one, the bulb is modelled by a slip boundary condition, in the second one, the bulb is a rigid Lagrangian structure, which involves the use of the Euler/Lagrange penalty coupling.

Design of Tunnels in Swelling Soils: Determination of Swelling Soil Properties

This paper includes a study of soil swelling for tunnels projects. It is performed using a flexible odometer which authorizes a lateral deformation of the soil sample during swelling and allows the measurement of the lateral swell pressure. The paper is composed of three parts. The first one concerns analysis of swelling phenomenon in tunnel projects. The second one presents the swelling odometer which was used in this work. The last one presents results obtained on clay and discusses the influence of the swelling condition on both axial and lateral soils expansion.

CFD Simulation of Soil Flow Over Augers

The modelling of soil as an engineering material is confined, in the most part, to the investigation of how it behaves under loading and unloading. A key assumption made in existing models is that the soil is similar in behaviour to a solid and is generally elastic-perfectly plastic and has a linear stress strain relationship. The rapid displacement of soil, such as flow, has been studied far less. The aim of this paper is to study such behaviour and present the initial results of the flow around a rotating auger assuming the soil acts as a fluid. These initial simulations rely on the governing equations of fluid flow assuming Newtonian viscosity. Although evidence points to soil not having constant coefficient of viscosity, this study and a further study by Tardos [1] shows that for loose soils with a low angle of internal friction, such as liquefied sand, the Newtonian viscosity is an acceptable assumption. The patterns of soil movement around the auger are shown over two different drilling tools. Visual and numerical results of soil movement are presented.

Optimisation of Loads in Piping Systems by Realistic Calculation Method Applying FSI and Dynamic Friction

To reduce costs and to extend the lifetime of piping systems their design loads due to valve action have to be optimised. To get the best effect the results of the fluiddynamic and structural calculations should be realistic as far as possible. Therefore the calculation programs were coupled to consider the fluid structure interaction and the effect of dynamic fluid friction was introduced to get realistic results of oscillations due to pressure surges. Detailed modelling of check valve behaviour allows to minimise the pressure surge loading by improving the valve function and adapting it to the system behaviour. The method was validated at measurements of load cases in power plant piping systems. Results with different load cases show the effectiveness of reducing the fluid forces on piping. Examples are given to prove the reduction of supports.

Fluid-Structure Interaction of Stirrers in Mixing Vessels: Part I — Development of the Mechanical Model

Mixing stirrers are subject to severe damages when the rotational speed approaches the Eigenfrequency. Damping due to fluid-structure interaction between the mixing stirrer and the fluid in the vessel has major influence on the Eigenfrequency. Therefore coupled analysis of the flow field within a mixing vessel and the structural dynamic response of the stirrer should be conducted in order to evaluate vibrational amplitudes to guarantee life time safety for the stirrer. In some previous works at our institute CFD analysis of mixing stirrers has been carried out for both one-phase and two-phase flow. In this paper a simplified numerical model based on Newmark’s integration scheme is developed for the stirrer dynamics that is suitable to be implemented in the CFD code as a user subroutine. Results in terms of Eigenfrequencies are compared to results of analytical formulae and FEM results and show excellent agreement. In the second part of the paper the fully fluid-structure coupled analysis is presented (Part II).

On Study of Free Metal Forming Using Underwater Shock Wave

In the material processing such as shock synthesis and powder consolidation by shock waves the method for generating dynamic pressure is of very importance for the final recovered materials. A general and convenient way for producing shock wave needed in such field is to take advantage of the explosion effect from high explosive. Therefore, it becomes an interest subject how to produce dynamic pressure as high as possible under the given high explosive. Starting from this motivation, we put forward a method of high-pressure generation by using the overdriven detonation of high explosive. The basic configuration for this device is summarized in the following. A metal flyer accelerated by the high explosive is used to impact another layer of high explosive to incur an overdriven detonation in this layer of explosive. The overdriven detonation of high explosive acts on the powder materials, providing the high dynamic pressure for it. To examine the efficiency of this combination, a numerical computation is performed to this system. The details on the illustration of this system and numerical treatment will be given.

Metal Pipe Forming Using Underwater Shock Wave

Recently, many metal pipes have been manufactured and used as various mechanical parts. Cross section of these parts has circular and oval shape. And then, a lot of kinds, but a small quantity production of these metal pipe increases. However, commonly, very expensive metal die are used in that case. Therefore, we considered the metal pipe forming method so that we can obtain the required deformation shape of metal pipes using the underwater shock wave generated by underwater explosion of explosive. We did some experiments of the metal pipe forming by that method. We used detonating cord as the explosive. The metal pipe and explosive was submerged into water and the detonating cord was detonated by electric detonator. We made some experiments by changing the explosive set-up position and inside the metal pipe filled with water, soil, air, and so on. In this paper, we have discussed these experimental results. And then, we have done the numerical simulation to this method and those results are also discussed.

Fluid-Structure Interaction of Stirrers in Mixing Vessels: Part II — Fully Coupled Simulation

Mixing Stirrers are subjected to severe damages [Strohmeier (1996), Strohmeier and Ho¨lzl (1998)] when the rotational speed approaches the critical rotational speed nkrit (eigenfrequency). Because of resonant vibrations, the stirrer deflection approaches infinity (no damping case). The possibilities of an accurate design of mixing stirrers with analytical calculations [Fischer and Strohmeier (2000)] are often very unsatisfactional, due to the complex effects of the fluid medium on the structure (impeller), and consequently its critical speed and its vibrational amplitudes cannot be readily defined. To consider transient fluid effects and out-of-balance forces, it is necessary to implement a coupled analysis of flow field and structural dynamic response of the stirrer in the CFD code as a user subroutine. As a new aspect, a rotating grid (sliding mesh) was combined with a deformable grid to simulate the impeller movement. The results are compared to experimental and analytical data and show good agreement.