The next generation of nuclear safety analysis computer codes will require detailed modeling of two-phase fluid flow. The most complete and fundamental model used for these calculations is known as the two-fluid model. It is the most accurate of the two-phase models since it considers each phase independently and links the two phases together with six conservation equations. A major drawback is that the current two-fluid model, when area-averaged to create a one-dimensional model, becomes ill-posed as an initial value problem when the gas and liquid velocities are not equal. The importance of this research lies in obtaining a model that overcomes this difficulty. It is desired to develop a modified one-dimensional two-fluid model for horizontal flow that accounts for the pressure difference between the two phases, due to hydrostatic head, with the implementation of a void fraction distribution parameter. With proper improvement of the one-dimensional two-fluid model, the next generation of nuclear safety analysis computer codes will be able to predict, with greater precision, the key safety parameters of an accident scenario. As part of this research, an improved version of the one-dimensional two-fluid model for horizontal flows was developed. The model was developed from a theoretical point of view with the three original distribution parameters simplified down to a single parameter. The model was found to greatly enhance the numerical stability (hyperbolicity) of the solution method. With proper modeling of the phase distribution parameter, a wide range of flow regimes can be modeled. This parameter could also be used in the future to eliminate the more subjective flow regime maps that are currently implemented in today's multiphase computer codes. By incorporating the distribution parameter and eliminating the flow regime maps, a hyperbolic model is formed with smooth transitions between various flow regimes, eliminating the unphysical oscillations that may occur near transition boundaries in today's multiphase computer codes. / Graduation date:2006

This dissertation reported on the findings of the characteristics of the pedestrian flows in Chinese New Year Eve Fair in Hong Kong and, the recommendations to its crowd control measures. Since most of the pedestrian flow models were developed for general purposes under normal condition, special models developed specifically for major events such as bazaars, fairs and festivals in Hong Kong were required to understand their pedestrian flow patterns. In this dissertation, pedestrian flows in the Fair were videotaped and data was extracted for calibrating several pedestrian flow models. These included the conventional models developed by Greenshields, Greenberg, Pipes-Munjal, Underwood, Drake, Wong et al. and four modifications of these models for simulating isotropic and bi-directional pedestrian flow scenarios. The free flow speed of the pedestrians in the Chinese New Year Eve Fair was found to be around 0.69-0.84 m/s, slower than those identified in other researches. Besides, the results of these models showed the relationships between walking speed, density and flow of the pedestrians in the Fair. Also, the effects of bi-directional flow to pedestrian flows were assessed and quantified. These findings obtained from models were then used as a basis for formulating crowd control strategy of major events in Hong Kong. / published_or_final_version / Transport Policy and Planning / Master / Master of Arts in Transport Policy and Planning

Walking is an environmentally friendly mode of transportation. A better understanding of pedestrian activities and effective planning of walking facilities are particularly important for densely populated Asian cities like Hong Kong. Empirical studies on pedestrian flows can be classified as controlled experiments and observational surveys. Controlled experiments are flexible and can be designed to fulfill the requirements of specific studies and eliminate influence from unrelated factors. Observational surveys provide data for pedestrian movements in different types of walking facilities. This thesis aims to develop a mathematical model for multidirectional pedestrian flows based on knowledge obtained from both a controlled experiment and observational surveys on three different walking facilities. Bayesian inference is adopted for model calibration, as it can combine the prior information from the controlled experiment and the observed data from the observational surveys. The proposed model is based on Drake’s (1967) model of traffic flow. However, multidirectional pedestrian flows are much more complicated than the unidirectional and bidirectional flows. Therefore, instead of relating the speed of a pedestrian stream solely to pedestrian density, the flow ratio and intersecting angles between streams are introduced as factors that may influence stream speed. The proposed model takes the form of a set of structural equations rather than a single deterministic function. By applying Bayesian inference, the proposed model is calibrated with the three sets of observed data respectively, based on the prior distribution specified by the controlled experiment results. Finally, pedestrian movements in three different walking facilities are analyzed based on the properties of the calibrated model. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

Reliable predictions of reservoir flow response corresponding to various recovery schemes require a realistic geological model of heterogeneity and an understanding of its relationship with the flow properties. This dissertation presents results on the implementation of a novel approach for the integration of dynamic data into reservoir models that combines stochastic techniques for simultaneous calibration of geological models and multiphase flow functions associated with porelevel spatial representations of porous media. In this probabilistic approach, a stochastic simulator is used to model the spatial distribution of a discrete number of rock types identified by rock/connectivity indexes (CIs). Each CI corresponds to a particular pore network structure with a characteristic connectivity. Primary drainage and imbibition displacement processes are modeled on the 3-D pore networks to generate multiphase flow functions corresponding to networks with different CIs. During history matching, the stochastic simulator perturbs the spatial distribution of the CIs to match the simulated pressures and flow rates to historic data, while preserving the geological model of heterogeneity. This goal is accomplished by applying a probabilistic approach for gradual deformation of spatial distribution of rock types characterized by different CIs. Perturbation of the CIs in turn results in the update of all the flow functions including the effective permeability, porosity of the rock, the relative permeabilities and capillary pressure. The convergence rate of the proposed method is comparable to other current techniques with the distinction of enabling consistent updates to all the flow functions. The resultant models are geologically consistent in terms of all the flow functions, and consequently, predictions obtained using these models are likely to be more accurate. To compare and contrast this comprehensive approach to reservoir modeling against other approaches that rely on modeling and perturbing only the permeability field, a realistic case study is presented with implementation of both approaches. Comparison is made with the history-matched model obtained only by perturbing permeability. It is argued that reliable predictions of future production can only be made when the entire suite of flow functions is consistent with the real reservoir.

No description available.

An intensive examination was conducted to test the credibility of current traffic signal change interval policies founded on a kinematic equation developed nearly 30 years ago. The investigation involved the review of relevant literature as well as an extensive collection of data. The literature review and data analysis revealed that current change interval policies rely on the disproven assumption that traffic decelerates at a constant rate. The data analysis also demonstrated that traffic approach speed and deceleration distance affect the manner in which deceleration occurs. Based on the data analysis, an alternative treatment of the kinematic equation is proposed using surrogate deceleration rates. The surrogate rates offer a pragmatic set of input for the kinematic equation. Therefore, rather than yielding a change interval based on an inaccurate assumption, agencies can implement change intervals which are responsive to local traffic.

Project Completion Report OWRT Project A- 076 -ARIZ The work upon which this publication is based was supported in part by the United States Department of the Interior as authorized under the Water Research Act of 1964, as amended. / Constant head borehole infiltration tests are widely used for the in situ evaluation of saturated hydraulic conductivities of unsaturated soils above the water table. The formulae employed in analyzing the results of such tests disregard the fact that some of the infiltrating water may flow under unsaturated conditions. Instead, these formulae are based on various approximations of the classical free surface theory which treats the flow region as if it were fully saturated and enclosed within a distinct envelope, the so- called "free surface." A finite element model capable of solving free surface problems is used to examine the mathematical accuracy of the borehole infiltration formulae. The results show that in the hypothetical case where unsaturated flow does not exist, the approximate formulae are reasonably accurate within a practical range of borehole conditions. To see what happens under conditions closer to those actually encountered in the field, the effect of unsaturated flow on borehole infiltration is investigated by means of two different numerical models: A mixed explicit - implicit finite element model, and a mixed explicit -implicit integrated finite difference model. Both of these models give nearly identical results; however, the integrated finite difference model is considerably faster than the finite element model. The relatively low computational efficiency of the finite element scheme is attributed to the large humber of operations required in order to reevaluate the conductivity (stiffness) matrix at each iteration in this highly nonlinear saturated -unsaturated flow problem. The saturated -unsaturated analysis demonstrates that the classical free surface approach provides a distorted picture of the flow pattern in the soil. Contrary to what one would expect on the basis of this theory, only a finite region of the soil in the immediate vicinity of the borehole is saturated, whereas a significant percentage of the flow takes place under unsaturated conditions. As a consequence of disregarding unsaturated flow, the available formulae may underestimate the saturated hydraulic conductivity of fine grained soils by a factor of two, three, or more. Our saturated -unsaturated analysis leads to an improved design of borehole infiltration tests and a more accurate method for interpreting the results of such tests. The analysis also shows how one can predict the steady state rate of infiltration as well as the saturated hydraulic conductivity from data collected during the early transient period of the test.

published_or_final_version / Physics / Master / Master of Philosophy

University of Macau / Faculty of Science and Technology. / Department of Computer and Information Science

Lee Kuen. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 123-128). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- The Minority Game: A Review --- p.3 / Chapter 2.1 --- The basic MG --- p.9 / Chapter 2.2 --- The basic features of MG --- p.11 / Chapter 2.3 --- Crowd-Anticrowd Theory --- p.15 / Chapter 2.4 --- Some variation on the Minority Game --- p.20 / Chapter 2.4.1 --- The Thermal Minority Game (TMG) --- p.20 / Chapter 2.4.2 --- The Evolutionary Minority Game (EMG) --- p.21 / Chapter 3 --- The Minority Game with different payoff functions --- p.23 / Chapter 3.1 --- Review --- p.24 / Chapter 3.1.1 --- Models of Savit et al [48] --- p.24 / Chapter 3.1.2 --- Results --- p.25 / Chapter 3.2 --- Applying Crowd-anticrowd theory to the models --- p.27 / Chapter 4 --- The Minority Game with k-sided imitation in regular net- works --- p.33 / Chapter 4.1 --- Review --- p.34 / Chapter 4.1.1 --- 1-sided follow-action model --- p.34 / Chapter 4.1.2 --- Results --- p.36 / Chapter 4.2 --- Follow-action model --- p.37 / Chapter 4.2.1 --- 2-sided model --- p.37 / Chapter 4.2.2 --- Results --- p.38 / Chapter 4.2.3 --- k-sided model and results --- p.40 / Chapter 4.3 --- Follow-strategy model --- p.43 / Chapter 4.3.1 --- 1-sided and 2-sided models --- p.43 / Chapter 4.3.2 --- Results --- p.45 / Chapter 4.3.3 --- k-sided model and results --- p.47 / Chapter 4.4 --- Summary --- p.51 / Chapter 5 --- One-lane traffic flow models --- p.53 / Chapter 5.1 --- Introduction --- p.54 / Chapter 5.2 --- NS dynamics --- p.56 / Chapter 5.3 --- FI dynamics --- p.60 / Chapter 6 --- One-lane traffic flow models with anticipation effects --- p.63 / Chapter 6.1 --- Review --- p.64 / Chapter 6.1.1 --- Model using NS dynamics --- p.64 / Chapter 6.1.2 --- Results --- p.65 / Chapter 6.2 --- Models using FI dynamics --- p.65 / Chapter 6.2.1 --- Models --- p.65 / Chapter 6.2.2 --- Results and Discussion --- p.68 / Chapter 6.2.3 --- Mean Field Theory --- p.76 / Chapter 6.3 --- Summary --- p.89 / Chapter 7 --- Two-route Models with Global Information --- p.91 / Chapter 7.1 --- Review: Two-route model with global information using NS dynamics --- p.92 / Chapter 7.1.1 --- Announcing transit time as global information --- p.92 / Chapter 7.1.2 --- Results --- p.93 / Chapter 7.2 --- Announcing instantaneous average speed model using NS dy- namics [87] --- p.95 / Chapter 7.2.1 --- Model --- p.95 / Chapter 7.2.2 --- Results --- p.95 / Chapter 7.2.3 --- Discussion --- p.99 / Chapter 7.3 --- Two-route models with global information using FI dynamics --- p.103 / Chapter 7.3.1 --- Models --- p.103 / Chapter 7.3.2 --- Results --- p.105 / Chapter 7.3.3 --- Discussion --- p.110 / Chapter 7.4 --- Summary --- p.120 / Chapter 8 --- Conclusion --- p.121 / Bibliography --- p.123