The goal of the work described in this report was the experimental investigation of the mixing of coolant with different quality (temperature, boron concentration) in nuclear reactors on the way from the cold leg through the downcomer and lower plenum to the core inlet in a systematic way. The obtained data were used for the clarification of the mixing mechanisms and form a data basis for the validation of computational fluid dynamics (CFD) codes. For these purposes, experiments on slug mixing have been performed at two test facilities, modelling different reactor types in scale 1:5, the Rossendorf and Vattenfall test facilities. The corresponding accident scenario is the start-up of first main coolant pump (MCP) after formation of a slug of lower borated water during the reflux-condenser mode phase of a small break loss of coolant accident (LOCA). The matrices for the experiments were elaborated on the basis of the key phenomena, being responsible for the coolant mixing during pump start-up. Slug mixing tests have also been performed at the VVER-1000 facility of EDO Gidropress to meet the specifics of this reactor type. The mixing of slugs of water of different quality is also very important for pre-stressed thermal shock (PTS) situations. In emergency core cooling (ECC) situations after a LOCA, cold ECC water is injected into the hot water in the cold leg and downcomer. Due to the large temperature differences, thermal shocks are induced at the reactor pressure vessel (RPV) wall. Temperature distributions near the wall and temperature gradients in time are important to be known for the assessment of thermal stresses. One of the important phenomena in connection with PTS is thermal stratification, a flow condition with a vertical temperature profile in a horizontal pipe. Due to the fluctuating character of the flow, this may cause thermal fatigue in the pipe. Besides of thermal fatigue, a single thermal shock can also be relevant for structural integrity, if it is large enough, especially in the case, that the brittle fracture temperature of the RPV material is reduced due to radiation embrittlement. Therefore, additional to the investigations of slug mixing during re-start of coolant circulation, the mixing of slugs or streams of water with higher density with the ambient fluid in the RPV was investigated. The aim of these investigations was to study the process of turbulent mixing under the influence of buoyancy forces caused by the temperature differences. Heat transfer to the wall and thermal conductivity in the wall material have not been considered. Experiments on density driven mixing were carried out at the Rossendorf and the Fortum PTS facilities.

The goal of the work described in this report was the experimental investigation of the mixing of coolant with different quality (temperature, boron concentration) in nuclear reactors on the way from the cold leg through the downcomer and lower plenum to the core inlet in a systematic way. The obtained data were used for the clarification of the mixing mechanisms and form a data basis for the validation of computational fluid dynamics (CFD) codes. For these purposes, experiments on slug mixing have been performed at two test facilities, modelling different reactor types in scale 1:5, the Rossendorf and Vattenfall test facilities. The corresponding accident scenario is the start-up of first main coolant pump (MCP) after formation of a slug of lower borated water during the reflux-condenser mode phase of a small break loss of coolant accident (LOCA). The matrices for the experiments were elaborated on the basis of the key phenomena, being responsible for the coolant mixing during pump start-up. Slug mixing tests have also been performed at the VVER-1000 facility of EDO Gidropress to meet the specifics of this reactor type. The mixing of slugs of water of different quality is also very important for pre-stressed thermal shock (PTS) situations. In emergency core cooling (ECC) situations after a LOCA, cold ECC water is injected into the hot water in the cold leg and downcomer. Due to the large temperature differences, thermal shocks are induced at the reactor pressure vessel (RPV) wall. Temperature distributions near the wall and temperature gradients in time are important to be known for the assessment of thermal stresses. One of the important phenomena in connection with PTS is thermal stratification, a flow condition with a vertical temperature profile in a horizontal pipe. Due to the fluctuating character of the flow, this may cause thermal fatigue in the pipe. Besides of thermal fatigue, a single thermal shock can also be relevant for structural integrity, if it is large enough, especially in the case, that the brittle fracture temperature of the RPV material is reduced due to radiation embrittlement. Therefore, additional to the investigations of slug mixing during re-start of coolant circulation, the mixing of slugs or streams of water with higher density with the ambient fluid in the RPV was investigated. The aim of these investigations was to study the process of turbulent mixing under the influence of buoyancy forces caused by the temperature differences. Heat transfer to the wall and thermal conductivity in the wall material have not been considered. Experiments on density driven mixing were carried out at the Rossendorf and the Fortum PTS facilities.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1966 M848 / Master of Science

As systems/structures get smaller we need to take into account noise and quantum effects and so, we need to develop some quantum devices. Quantum devices work using quantum principles like qubits that have already been developed, i.e., superconducting qubits that are going to be discussed in chapter 1. Initially, scientists wanted to use qubits to do quantum computations, this is not easy so scientists developed methods to do something different, e.g. quantum metamaterials. Here in this thesis we describe two examples of quantum devices. Our first device is the parametric quantum amplifier. Used when we need to amplify very weak signals. Amplifying a weak signal on the nanoscale is a very big challenge, this is due to classical and quantum noise, and so, we need to employ quantum physics to resolve this issue. The proposed two-qubit system amplifies weak signals at very small scales. We have shown that we can construct a multitude of novel devices on the nano-scale with the use of qubits Our second device uses harmonic mixing. It can be used where rectification is needed, for example, when we need to rectify some fluctuations and in principle some quantum fluctuations in order to pump either an excited or ground state of the two qubit device. In this thesis we propose how to do this. Firstly, we propose that if we apply harmonic mixing of two signals for two qubits, using the structure of the equation and basically the structure of quantum mechanics we can pump a desirable quantum state. We can pump either the upper or ground state by changing the signal.

published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

Road slips are common in Northland Allochthon residual clay soil, and are commonly mitigated using deep soil mixing (DSM). A deficiency in laboratory investigations on Northland Allochthon residual clay and a need for a better understanding of the numerical modelling of DSM columns used to mitigate unstable slopes in this soil type is evident in literature, and has been highlighted by practitioners. This research has aimed to fill aspects of these deficiencies. Field testing and classification tests have provided insight into how the soil varies between sites and with depth, and how in situ testing methods compare to one another. Field testing has also demonstrated that soil property changes around DSM columns have been shown to exist through seismic flat plate dilatometer testing before and after column installation, which has not previously been proven using an in situ method. This is important for practitioners who use DSM to demonstrate the additional soil improvements provided by the columns. The testing of reconstituted soil is fundamental in examining soil behaviour, and this study is the first to examine the triaxial behaviour of reconstituted specimens of Northland Allochthon soil. Laboratory triaxial testing and oedometer testing have allowed for a normalized comparison of the intact strength of Northland Allochthon residual clay soil to its reconstituted state. This work provides an answer to the important question regarding the role of soil structure in this soil type. It was revealed that soil structure results in increased shear strength of the soil, and that this increase is primarily cohesive in nature. The near coincidence of the post-rupture strength of intact specimens with the critical state angle of internal shearing resistance provides support for its use in examining first time slope failures in this soil type. This is an important finding for practitioners, as it demonstrates the value of testing reconstituted specimens, which are much easier to obtain than high quality intact specimens. In addition, relationships between the plasticity index (PI) of the soil and certain soil parameters (and soil behaviour) have been demonstrated to be relevant and useful for this soil type. Soil properties acquired in this study were tabulated along with those from other field sites in Northland Allochthon soil. It was found that there is significant variation between field sites, likely due to varying degrees of weathering, which is an important consideration for practitioners dealing with this soil type. A brief examination of constitutive models for representation of Northland Allochthon residual clay soil have shown that several different models can sufficiently represent the behaviour of this soil. The Mohr-Coulomb model was selected for use in subsequent finite element numerical models. A case study of a road slip at a field site in Northland Allochthon residual clay soil, mitigated using DSM columns, revealed that the use of a pre-existing slip surface after first time failure leads to an improved match between observed field behaviour and the behaviour of the slope as exhibited in a numerical model. This type of failure mechanism has not been previously examined in this soil type, and this case study demonstrates it is a useful approach that should be considered when dealing with second time failure in Northland Allochthon slopes. This numerical model also introduces the replacement ratio method (RRM), a technique used to represent the three dimensional (3D) geometry of the DSM columns in the more commonly used two dimensional (2D) analysis. Examination of laterally loaded DSM columns in plan view, which has not previously been performed in the context of DSM columns, has illustrated how installation effects and column shape influence load displacement curves, and demonstrates the effects of soil arching. This analysis provides practitioners with evidence that improved soil property changes, found to occur around DSM columns, lead to improved DSM column performance. A simplified 3D numerical model of laterally loaded DSM columns, which builds on the ideas developed in the previous two 2D models, has been compared to an identical 2D model. It is shown that the commonly used RRM results in an overestimation of the resisting force provided by the columns as compared to the 3D model. However, this does not necessarily imply that the use of the RRM in an analysis will always result in a safe slope. The degree to which its use will affect the results will depend on the slope geometry, location of the DSM columns, and the type of analysis performed (i.e. factor of safety or deformation based). A modification to the RRM has been proposed. It is recommended that when the DSM column diameter and soil properties are similar to those used in this study, the MRRM developed in this study should be utilized. In circumstances where they differ, it is recommended that practitioners perform a sensitivity analysis using the MRRM developed here as a basis for modifying the RRM in order to determine the extent to which their results are influenced. If the influence is significant, the use of a 3D model should be considered.

No description available.

The nonlinear interactions between a fundamental instability mode and both its harmonics and the changing mean flow are studied using the weakly nonlinear stability theory of Stuart and Watson, and numerical solutions of coupled nonlinear partial differential equations. The first part of this work focuses on incompressible cold (or isothermal; constant temperature throughout) mixing layers, and for these, the first and second Landau constants are calculated as functions of wavenumber and Reynolds number. It is found that the dominant contribution to the Landau constants arises from the mean flow changes and not from the higher harmonics. In order to establish the range of validity of the weakly nonlinear theory, the weakly nonlinear and numerical solutions are compared and the limitation of each is discussed. At small amplitudes and at low-to-moderate Reynolds numbers, the two results compare well in describing the saturation of the fundamental, the distortion of the mean flow, and the initial stages of vorticity roll-up. At larger amplitudes, the interaction between the fundamental, second harmonic, and the mean flow is strongly nonlinear and the numerical solution predicts flow oscillations, whereas the weakly nonlinear theory yields saturation. Beyond the region of exponential growth, the instability waves evolve into a periodic array of vortices. In the second part of this work, the weakly nonlinear theory is extended to heated (or nonisothermal mean temperature distribution) subsonic round jets where quadratic and cubic nonlinear interactions are present, and the Landau constants also depend on jet temperature ratio, Mach number and azimuthal mode number. Under exponential growth and nonlinear saturation, it is found that heating and compressibility suppress the growth of instability waves, that the first azimuthal mode is the dominant instability mode, and that the weakly nonlinear solution describes the early stages of the roll-up of an axisymmetric shear layer. The receptivity of a typical jet flow to pulse type input disturbances is also studied by solving the initial value problem and then examining the behavior of the long-time solution. The excitation produces a wave packet which consists of a few oscillations and is convected downstream by the mean flow. The magnitude of the disturbance in the jet depends on the location of the excitation and there is an optimum position at which little energy input will produce large perturbations. It is found that in order to generate the largest perturbations at any point in the jet, the disturbance should be deposited into the flow at a point where the phase velocity of the most amplified wave equals the fluid velocity (of the base flow).

The turbulent mixing process between two liquid streams in a standard tank stirred by a Rushton turbine has been studied. Experimental measurements of concentration and segregation (fluctuating concentration) have been made for both reacting and non-reacting flows. For the non-reacting case, one stream was marked with a fluorescent dye; the local concentration was measured using a fluorescence technique and a bifurcated fiber optic probe of custom design. Measurements were taken at two axial-radial planes within the tank. In the reacting case, the second-order reaction between sodium hydroxide and hydrochloric acid was studied, and urinine acted as a fluorescent indicator which became non-fluorescent as the reaction proceeded. Numerical studies of the mixing in the laboratory-scale vessel were made. FLUENT, a general-purpose fluid flow modelling program, was used to simulate the flow within the tank. This program uses a k-epsilon closure of the turbulent momentum equations. The program was modified to allow the inclusion of a segregation balance equation. Using this segregation balance technique, the turbulent species balance equations were solved. The results of these simulations agreed with the experimental measurements in all regions except the region near the entrance jets, where the model could not adequately predict the fluid behavior. This study has successfully predicted the behavior of reacting fluids in a bench-scale turbulently mixed stirred tank by the implementation of a segregation balance throughout the entire domain.