Thesis (M. P. A.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M. P. A.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M. P. A.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

This thesis reports the methods to simulate flows withcomplex boundary such as orifice flow. The method is forgeneral purposes so that it has been tested on different flowsincluding orifice flow. Also it contains a chapter about theexperiment of orifice flow. Higher-order precision interpolation schemes are used inumerical simulation to improve prediction at acceptable gridrefinement. Because higher-order schemes cause instability inconvection-diffusion problems or involve a large computationalkernel, they are implemented with deferred correction method. Alower-order scheme such as upwind numerical scheme is used tomake preliminary guess. A deferred (defect) correction term isadded to maintain precision. This avoids the conflict betweenprecision order and implementation difficulty. The authorproposes a shifting between upwind scheme and centraldifference scheme for the preliminary guess. This has beenproven to improve convergence while higher order schemes havewider range of stability. Non-orthogonal grid is a necessity for complex flow. Usuallyone can map coordinate of such a grid to a transformed domainwhere the grid is regular. The cost is that differentialequations get much more complex form. If calculated directly innon-orthogonal grid, the equations keep simple forms. However,it is difficult to make interpolation in a non-orthogonal grid.Three methods can be used: local correction, shape function andcurvilinear interpolation. The local correction method cannotinsure second-order precision. The shape function method uses alarge computational molecule. The curvilinear interpolationthis author proposes imports the advantage of coordinatetransformation method: easy to do interpolation. A coordinatesystem staggered half control volume used in the coordinatetransformation method is used as accessory to deriveinterpolation schemes. The calculation in physical domain withnon-orthogonal grid becomes as easy as that in a Cartesianorthogonal grid. The author applies this method to calculate turbulentorifice flow. The usual under-prediction of eddy length isimproved with the ULTRA-QUICK scheme to reflect the highgradients in orifice flow. In the last chapter, the author quantifies hydraulicabruptness to describe orifice geometry. The abruptness canhelp engineers to interpolate existing data to a new orifice,which saves detailed experiments

Denna uppsats handlar om en debatt, som fördes i en brytningstid, då den gifta kvinnans rätt till yrkesarbete ifrågasattes. Ett funktionalistiskt förslag om kollektivhus, där hushållsarbetet och en del av barnavården skulle skötas av kollektivt anställd personal, avsåg att underlätta kvinnans yrkesarbete. Den gällande normen förutsatte, att den gifta kvinnan var hemarbetande och mannen försörjare. Debatten kom att kretsa kring hustruns plikter mot familjen och barnens liv i det kollektiva huset. Här stod bevarare av traditionen mot anhängare av ett nytt familjemönster. Syftet har varit att fokusera anhängare och motståndare och analysera deras argument och strategier. Analysen har skett mot bakgrund av den pågående moderniseringsprocessen och den modernitet, som innebar nya livsvillkor för kvinnan och familjen. Yvonne Hirdmans genuskontraktsteori med endast ett dominerande husmoderskontrakt under mellankrigstiden diskuteras och ifrågasätts.

Wind transport and sublimation of snow particles are common phenomena across high altitude and latitude cold regions and play important roles in hydrological and atmospheric water and energy budgets. In spite of this, blowing snow processes have not been incorporated in many mesoscale hydrological models and land surface schemes. A physically based blowing snow model, the Prairie Blowing Snow Model (PBSM), initially developed for prairie environments was used to model snow redistribution and sublimation by wind over two sites representative of mountainous regions in Canada: Fisera Ridge in the Rocky Mountain Front Ranges in Alberta, and Granger Basin in the Yukon Territory. Two models were used to run PBSM: the object-oriented hydrological model, Cold Regions Hydrological Modelling Platform (CRHM) and Environment Canadas hydrological-land surface scheme, Modélisation Environmentale Communautaire Surface and Hydrology (MESH). PBSM was coupled with the snowcover energy and mass-balance model (SNOBAL) within CRHM. Blowing snow algorithms were also incorporated into MESH to create MESH-PBSM. CRHM, MESH and MESH-PBSM were used to simulate the evolution of snowcover in hydrological response units (HRUs) over both Fisera Ridge and Granger Basin.<p> To test the models of blowing snow redistribution and ablation over a relatively simple sequence of mountain topography, simulations were run from north to south over a linear ridge in the Canadian Rocky Mountains. Fisera Ridge snowcover simulations with CRHM were performed over two winters using two sets of wind speed forcing: (1) station observed wind speed, and (2) modelled wind speed from a widely applied empirical, terrain-based windflow model. Best results were obtained when using the site meteorological station wind speed data. The windflow model performed poorly when comparing the magnitude of modelled and observed wind speeds. Blowing snow sublimation, snowmelt and snowpack sublimation quantities were considerably overestimated when using the modelled wind speeds. As a result, end-of-winter snow accumulation was considerably underestimated on windswept HRUs. MESH and MESH-PBSM were also used to simulate snow accumulation and redistribution over these same HRUs. MESH-PBSM adequately simulated snow accumulation in the HRUs up until the spring snowmelt period. MESH without PBSM performed less well and overestimated accumulation on windward slopes and the ridge top whilst underestimating accumulation on lee slopes. Simulations in spring were degraded by a large overestimation of melt by MESH. The early and overestimated melt warrants a detailed examination that is outside the scope of this thesis.<p> To parameterize snow redistribution in a mountain alpine basin, snow redistribution and sublimation by wind were calculated for three winters over Granger Basin using CRHM. Snow transport fluxes were distributed amongst HRUs using inter-HRU snow redistribution allocation factors. Three snow redistribution schemes of varying complexity were evaluated. CRHM model results showed that end-of-winter snow accumulation can be most accurately simulated when the inter-HRU snow redistribution schemes take into account wind direction and speed and HRU aerodynamic characteristics, along with the spatial arrangement of HRUs in the catchment. As snow transport scales approximately with the fourth power of wind speed (u4), inter-HRU snow redistribution allocation factors can be established according to the predominant u4 direction over a simulation period or can change at each time step according to an input measured wind direction. MESH and MESH-PBSM were used to simulate snow accumulation and ablation over these same HRUs. MESH-PBSM provided markedly better results than MESH without blowing snow algorithms.<p> That snow redistribution by wind can be adequately simulated in computationally efficient HRUs over mountainous terrain has important implications for representing snow transport in large-scale hydrology models and land surface schemes. Snow redistribution by wind caused mountain snow accumulation to vary from 10% to 161% of seasonal snowfall within a headwater catchment in the Canadian Rocky Mountains, and blowing snow sublimation losses ranged from 10 to 37% of seasonal snowfall.

An <i>Interval Routing Scheme (IRS)</i> represents the routing tables in a network in a space-efficient way by labeling each vertex with an unique integer address and the outgoing edges at each vertex with disjoint subintervals of these addresses. An IRS that has at most <i>k</i> intervals per edge label is called a <i>k-IRS</i>. In this thesis, we propose a new type of interval routing scheme, called an <i>Ordered Interval Routing Scheme (OIRS)</i>, that uses an ordering of the outgoing edges at each vertex and allows nondisjoint intervals in the labels of those edges. Our results on a number of graphs show that using an OIRS instead of an IRS reduces the size of the routing tables in the case of <i>optimal</i> routing, i. e. , routing along shortest paths. We show that optimal routing in any <i>k</i>-tree is possible using an OIRS with at most 2^k-1 intervals per edge label, although the best known result for an IRS is 2^k+1 intervals per edge label. Any torus has an optimal 1-OIRS, although it may not have an optimal 1-IRS. We present similar results for the Petersen graph, <i>k</i>-garland graphs and a few other graphs.

Vehicular communication networking is a promising approach for facilitating road safety, traffic management, and infotainment dissemination for drivers and passengers. However, it is subject to various malicious abuses and security attacks which hinder it from practical implementation. In this study, we propose a novel security protocol called GSIS based on group signature and identity-based signature schemes to meet the unique requirements of vehicular communication networks. The proposed protocol not only guarantees security and anonymity, but also provides easy traceability when the identity of the sender of a message has to be revealed by the authority. However, the cryptographic operations introduced in GSIS as well as the existing public key based message authentication protocols incur some computation and communication overhead which affect the system performance. Simulation results show that the GSIS security protocol is only applicable under light traffic conditions in terms of the message end to end delay and message loss ratio. Both the GSIS protocol and the existing public key based security protocols have to sign and verify all the received messages with asymmetric algorithms. The PKI based approach also has to attach a public key certificate in each packet. Therefore, to enhance the system performance and mitigate the message overhead without compromising the security requirement, this study further proposes an enhanced TESLA based Secure Vehicular Communication (TSVC) protocol. In TSVC, the communication overhead can be significantly reduced due to the MAC tag attached in each packet and only a fast hash operation is required to verify each packet. Simulation results show that TSVC maintains acceptable message latency, using a much smaller packet size, and significantly reduces the message loss ratio as compared to GSIS and existing PKI based protocols, especially when the traffic is denser. We conclude that the proposed approach could serve as good candidate for future vehicular communication networks.

An <i>Interval Routing Scheme (IRS)</i> represents the routing tables in a network in a space-efficient way by labeling each vertex with an unique integer address and the outgoing edges at each vertex with disjoint subintervals of these addresses. An IRS that has at most <i>k</i> intervals per edge label is called a <i>k-IRS</i>. In this thesis, we propose a new type of interval routing scheme, called an <i>Ordered Interval Routing Scheme (OIRS)</i>, that uses an ordering of the outgoing edges at each vertex and allows nondisjoint intervals in the labels of those edges. Our results on a number of graphs show that using an OIRS instead of an IRS reduces the size of the routing tables in the case of <i>optimal</i> routing, i. e. , routing along shortest paths. We show that optimal routing in any <i>k</i>-tree is possible using an OIRS with at most 2^k-1 intervals per edge label, although the best known result for an IRS is 2^k+1 intervals per edge label. Any torus has an optimal 1-OIRS, although it may not have an optimal 1-IRS. We present similar results for the Petersen graph, <i>k</i>-garland graphs and a few other graphs.

Vehicular communication networking is a promising approach for facilitating road safety, traffic management, and infotainment dissemination for drivers and passengers. However, it is subject to various malicious abuses and security attacks which hinder it from practical implementation. In this study, we propose a novel security protocol called GSIS based on group signature and identity-based signature schemes to meet the unique requirements of vehicular communication networks. The proposed protocol not only guarantees security and anonymity, but also provides easy traceability when the identity of the sender of a message has to be revealed by the authority. However, the cryptographic operations introduced in GSIS as well as the existing public key based message authentication protocols incur some computation and communication overhead which affect the system performance. Simulation results show that the GSIS security protocol is only applicable under light traffic conditions in terms of the message end to end delay and message loss ratio. Both the GSIS protocol and the existing public key based security protocols have to sign and verify all the received messages with asymmetric algorithms. The PKI based approach also has to attach a public key certificate in each packet. Therefore, to enhance the system performance and mitigate the message overhead without compromising the security requirement, this study further proposes an enhanced TESLA based Secure Vehicular Communication (TSVC) protocol. In TSVC, the communication overhead can be significantly reduced due to the MAC tag attached in each packet and only a fast hash operation is required to verify each packet. Simulation results show that TSVC maintains acceptable message latency, using a much smaller packet size, and significantly reduces the message loss ratio as compared to GSIS and existing PKI based protocols, especially when the traffic is denser. We conclude that the proposed approach could serve as good candidate for future vehicular communication networks.