Multiphase Fluid Structure Interaction in Bends and T-Joints

Air-water experiments were carried out in a horizontal 1″ pipe system to measure the magnitude of the forces induced by the multiphase flow. Forces and accelerations were measured on a number of bends and T-joint configurations for a wide range of operating conditions. Five different configurations were measured: a baseline case consisting of straight pipe only, a sharp edged bend, a large radius bend, a symmetric T-joint and a T-joint with one of the arms closed off. The gas flow was varied from a superficial velocity of 0.1 to 30 m/s and the liquid flow was varied from 0.05 to 2 m/s. This operating range ensures that the experiment encompasses all possible flow regimes. In general, the slug velocity and frequency presented a reasonable agreement with classical models. However, for high mixture velocity the measured frequency deviated from literature models. The magnitude of the measured forces was found to vary over a wide range depending on the flow regime. For slug flow conditions very high force levels were measured, up to 4 orders of magnitude higher than in single phase flow for comparable velocities. The annular flow regime resulted in the (relative) lowest forces, although the absolute amplitude is of the same order as in the case of slug flow. These results from a one inch pipe were compared to data obtained previously from similar experiments on a 6mm setup, to evaluate the scaling effects. The results for the one inch rig experiments agreed with the model proposed by Riverin, with the same scaling factor. A modification of this scaling factor is needed for the model to predict the forces measured on the 6mm rig. The validity of the theories developed based on the 6mm experiments were tested for validity at larger scales. In case of slug flow, the measured results can be described assuming a simple slug unit model. In annular and stratified flow a different model is required, since no slug unit is present. Instead, excitation force can be estimated using mixture properties. This mixture approach also describes the forces for the slug regime relatively well. Only the single phase flow is not described properly with this mixture model, as would be expected.

Computational Study of Flow Resonances and Forces on a Cylinder Vibrating In-Line to a Steady Flow

We present computational results of the flow dynamics and forces on a circular cylinder oscillating in-line with respect to a steady uniform stream. A wide range of oscillation frequencies is considered, from 0.5fs to 3fs, where fs is the natural Strouhal frequency of the Karman street. The oscillation amplitude is varied up to half the cylinder diameter. The Reynolds number value is 180, corresponding to two-dimensional flow. Simulations utilize a spectral element method. The computed flow states are characterized based on processed lift signals, and flow visualization. We find that the response of the flow is very sensitive to variations of the cylinder oscillation frequency. At low oscillation frequency, the lift signal and vortex patterns remain regular for low oscillation amplitudes, i.e. correspond to a 2S type of vortex street, and become complex at high oscillation amplitudes. Cylinder oscillation at the Strouhal frequency gives a window of chaotic flow at intermediate amplitudes, while at higher amplitudes 2S wakes are generated, with the sub-harmonic fs/2 and the higher harmonic 3fs/2 dominating the lift spectrum. Oscillation at twice the Strouhal frequency results in symmetric shedding, for oscillation amplitudes close to 30% of the cylinder diameter, and higher. Finally, at an oscillation frequency equal to three times the Strouhal frequency, the flow dynamics is very rich, characterized by “islands” of symmetric and asymmetric shedding at increasing oscillation amplitude. Chaotic flow is obtained only when the excitation frequency is equal to fs or to 3fs.

Parametric Study on the Fluid Elastic Instability Factor of the Fuel Rod for a PWR Plant

The main objective of this study is to estimate the effects of some considerable fuel design parameters on the fluid elastic instability behavior of the fuel rod. For the estimation, 6 fuel design parameters which seem to have direct relation with fluid elastic instability behavior of the fuel rod have been selected and examined using the PLUS7 fuel rod for OPR1000 PWR plants in Korea. Those are fuel rod creep-down, spacer grid stiffness, spacer grid spring relaxation, inactive spacer grid spring, intermediate flow mixing grid effect and fuel rod damping. As a result, the fluid elastic instability factors are insensitive with spacer grid stiffness, relaxation and intermediate flow mixing grid effect, but the other parameters need to be controlled and evaluated appropriately to maintain stability with proper margins.

Maximizing the Performance of Cased Munitions Under Realistic Constraints

In order to make the process of fragmentation of warhead cases more systematic, we have developed a procedure that makes use of nonlinear optimization to derive optimal values for case design parameters subject to various design constraints. A framework has been developed that makes use of the optimization software package LS-OPT driving the hydrocode CTH (CTH is developed and maintained at Sandia National Laboratories, LS-OPT is commercially available from Livermore Software Technology Corp.). CTH was used to model the explosive detonation and determine the resultant kinetic energy delivered to the case by the energetic material. As an example of application of the framework, a test problem was run using a case configuration consisting alternating titanium alloy and polymer layers.

On the Penetrator Nose Drag Measurements

In the current study, a rigid body penetrator nose shape that is optimized for minimum penetration drag [1] has been tested to determine the aerodynamic drag of such a penetrator in comparison to three additional nose shapes. Other nose shapes tested were an ogive cylinder, a 3/4 power series nose, and a standard cone. Fineness ratio for the studied nose geometries was chosen as l/d = 1 to maximize variation of the aerodynamic drag forces acting on the nose shapes. This paper discusses the measurements carried out in the University of Alabama’s 6″ × 6″ supersonic wind tunnel, using a 4 component force balance system. In separate experiments, drop tests were made in a viscous fluid to determine the skin-friction effects on these nose shapes. Supersonic wind-tunnel experiments were performed on each of the nose shapes at nine different Mach numbers ranging from 2 to 3.65. Results show that the nose shape optimized for penetration has the lowest drag coefficient of all the shapes at each Mach number within an uncertainty of 5.75%. In the viscous flow drop-test experiments, each nose shape was dropped from rest through water and then separately through viscous fluid (Nu-Calgon vacuum pump oil) under freefall conditions. Each drop was recorded via videotape, and the video was then analyzed to find the terminal velocity of each individual nose shape. Using classical dynamics equations, the weight, buoyant force, and experimentally determined terminal velocity are used to determine the drag force applied to each nose cone shape. Results indicate that while the optimal shape has a lesser drag coefficient than tangent ogive and the cone, the 3/4 power series shape is observed to have the least drag coefficient. In addition to the experiments performed, results on further investigation of the optimal nose shape for penetration are presented. The nose shape has been split into a series of line segments, and a program written has been utilized to search through numerical space for the combination of line segment slopes that produces the nose geometry with the lowest nose shape factor. The results of the numerical analysis in this study point to a different nose shape than the “optimal nose” shape tested in the current study.

Fluid Structure Interactions for Tube Bundles: Physical Meaning of a Rayleigh Damping

It is well known that a fluid may strongly influence the dynamic behaviour of a structure. Many different physical phenomena may take place, depending on the conditions: fluid flow, fluid at rest, small or high displacements of the structure. Inertial effects can take place, with lower vibration frequencies, dissipative effects also, with damping, instabilities due to the fluid flow (Fluid Induced Vibration). In this last case the structure is excited by the fluid. The paper deals with the vibration of tube bundles under a seismic excitation or an impact. In this case the structure moves under an external excitation, and the movement is influenced by the fluid. The main point in such system is that the geometry is complex, and could lead to very huge sizes for a numerical analysis. Important developments have been made in the last years to develop homogenization methods for the dynamic behaviour of tube bundles. The numerical size of the problem is reduced, and it is possible to make numerical simulations on large tube bundles with reasonable computer times. These methods consider that the fluid movement is governed by the Euler equations for the fluid. They are based on an analysis on an elementary cell, corresponding to one tube, and on an expression of the forces applied by the fluid to the structure. This force only depends on the fluid’s and tube’s acceleration. Only “inertial effects” will theoretically take place, with globally lower frequencies. A research program is under progress to take into account dissipative effects also, with a homogenization of the Navier-Stokes equations in the tube bundle. It is common, in numerical simulations, to add a damping for the structures by using a global Rayleigh damping. The paper deals with the physical meaning of this Rayleigh damping in the Euler homogenized equations. It can be demonstrated that this damping corresponds to a force applied by the fluid to the structure depending not only on the acceleration, but on the fluid and structure velocity also. This Rayleigh damping is a first step to take into account the dissipative effects for FSI in tube bundles.

Benchmark of an Application of Acoustic FEA for Light Water Reactor Loss of Coolant Accident Acoustic Loads

A Recirculation Line Break Loss of Coolant Accident is a design basis event which must be considered for stress analyses of Boiling Water Reactor internal components such as Jet Pumps and Core Shrouds. This event causes acoustic and fluid drag loads on BWR internals. These loads must also be considered for fracture mechanics evaluations performed to assess allowable operating periods for flaws detected during inservice inspections. Acoustic loads methods generally utilized in the past have been 1-D or simplified 2-D models of the domain of interest. In a few cases sophisticated thermal-hydraulic codes are used to obtain the acoustic response to the LOCA event. The present paper describes the results of a benchmark study performed to validate use of acoustic finite elements available in many commercial general purpose finite element analysis software packages. Use of FEA to predict acoustic loading in the BWR is benchmarked against blow down testing performed by Pacific Northwest Laboratory on a simulated light water reactor vessel. The results of the benchmark demonstrate that use of acoustic FEA yields conservative results and can be considered a viable method for BWR LOCA acoustic load predictions.

Development of a Blood Flow Model Including Hypergravity and Validation Against an Analytical Model

Fluid structure interaction (FSI) appears in many areas of engineering, e.g. biomechanics, aerospace, medicine and other areas and is often motivated by the need to understand arterial blood flow. FSI plays a crucial role and cannot be neglected when the deformation of a solid boundary affects the fluid behavior and vice versa. This interaction plays an important role in the wave propagation in liquid filled flexible vessels. Additionally, the effect of hyper gravity under certain circumstances should be taken into account, since such exposure can cause alterations in the wave propagation underexposed. Typical examples in which hyper gravity occurs are rollercoaster rides and aircraft or spacecraft flights. This paper presents the development of an arterial blood flow model including hyper gravity. This model has been developed using the finite element method along with the ALE method. This method is used to couple the fluid and structure. In this paper straight and tapered aortic analogues are included. The obtained computational data for the pressure is compared with analytical data available.

Free Vibration Analysis of a Simply Supported Rectangular Tank Partially Filled With a Liquid

This paper presents a theoretical analysis for the hydroelastic vibration of a rectangular tank partially filled with an ideal liquid. The wet dynamic displacement of the tank is approximated by combining the orthogonal polynomials satisfying the simply supported boundary conditions, since the rectangular tank is composed of four rectangular plates. As the facing rectangular plates are geometrically identical, the vibration modes of the facing plates can be divided into two categories: symmetric modes and asymmetric modes with respect to the vertical centerlines of the plates. The liquid displacement potential satisfying the boundary conditions is derived and the wet dynamic modal functions of the four plates are expanded by the finite Fourier transformation for a compatibility requirement along the contacting surface between the tank and the liquid. The natural frequencies of the rectangular tank in the wet condition are calculated by using the Rayleigh-Ritz method. The proposed analytical method is verified by observing an excellent agreement with three-dimensional finite element analysis results.

Experimental and CFD Evaluation of a Bubble Column Reactor

During the scale-up design of a slurry bubble column reactor from a pilot demonstration facility to a production reactor, the design team used computational fluid dynamics (CFD) as a tool to quantify design variables, such as gas holdup and liquid velocities/structural pressures within the reactor. At the time of the analysis, all available physics models for modeling the multi-phase flow had significant limitations that would require “tuning” of the CFD input parameters to ensure confidence in the results. The authors initially conducted a literature search to find data that could be used to calibrate the model. While a wide variety of literature is available, none provided the exact data required for model calibration. For this reason, the authors constructed a test column and performed experiments to derive data for tuning the CFD models. Statistical analysis of the experimental data provided distributions on the input parameters of interest. CFD studies were then used to tune the CFD input parameters to match the experimental data. A correlation was developed, tested and verified. This correlation was then used to provide confidence in the results of the design analysis performed on the scaled up reactor.