• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 52
  • 31
  • 21
  • 15
  • 9
  • 5
  • 3
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 155
  • 27
  • 25
  • 25
  • 25
  • 24
  • 22
  • 19
  • 18
  • 18
  • 16
  • 16
  • 16
  • 14
  • 14
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

CFD Based External Heat Transfer Coefficient Predictions on a Transonic Film-Cooled Gas Turbine Guide Vane : A Computational Fluid Dynamics Study on the Von Karman Institute LS94 Test Case

Johnsson, Rosalie, Asiegbu, Lilian January 2022 (has links)
The turbine inlet guide vanes of a gas-turbine are subjected to extreme hot gas temperatures which increases the risk of mechanical failure and overall reduces the component lifespan. Hence, it is of great interest for gas-turbine manufacturers to establish methods for accurately estimating the temperature distribution along the vane surface. Due to the three-dimensional nature of turbine flow, it is of interest to establish Computational Fluid Dynamics (CFD) methodology which capture these three-dimensional effects. This thesis is one in a collection of theses conducted at Siemens Energy AB on the subject. Previous studies have investigated and validated the implementation of RANS simulations on non-cooled turbine vanes and endwalls. In this study, the focus is on studying a film cooled vane and establishing one RANS as well as one hybrid modelling strategy for heat transfer coefficient (HTC) predictions. The HTC prediction capabilities are compared and validated against experimental data presented in the doctoral thesis by Fabrizio Fontaneto on the LS94 vane at Von Karman Institute. The chosen RANS modelling method was the Shear Stress Transport (SST) k-ω turbulence model, with γ-Reθ transition modelling, based on the findings by Enico (2021) and Daugulis (2022). The model proved capable in estimating the HTC well on mainly the suction side of the vane. The pressure side HTC was largely under-predicted, a common issue with the SST model also seen in the previous theses as well as the hybrid simulations. The strength of the SST k-ω turbulence model, with γ-Reθ transition modelling, is in accurately capturing the HTC magnitude, most likely due to the well-predicted turbulence intensity decay at the inlet. However, it largely under-predicts the HTC along the suction side film-coolant layer, implying that it may be over-estimating the film-cooling capabilities. The hybrid model chosen was the Scale Resolving Hybrid (SRH) model, with underlying RANS SST k-ω. Compared to RANS, hybrid results were under-estimated, seemingly offset from the experimental data by a constant 200 units along the entire vane midspan. This is likely due to the inaccurate turbulence intensity presented in the SRH simulations, which decays quickly along the inlet compared to RANS and experimental data. Yet still, the hybrid model showed potential in capturing certain results not seen with RANS, such as the secondary flow effects by the vane endwalls, as well as arguably capturing the general HTC trend at midspan seen in the experimental data. Additionally, the section of severely under-predicted HTC by the suction side film-coolant seen with RANS is not present in the hybrid results. Although the hybrid model has proven promising in many aspects, in its current state it is not a viable method for HTC predictions due to its general under-prediction of HTC. Largely, the authors suspect this is due to the undesirably coarse mesh around the cooling holes, which leads to RANS computation in regions where SRH is desired. Thus, improvements would need to be made to the model, where, for example, implementing a zonal hybrid RANS-LES model would be an option. Considering the hybrid model in its current state, RANS is the preferred method, especially when considering the greater computational cost and the labor associated with hybrid simulations which were experienced during this study. In conclusion, it is evident that the correct capture of inlet turbulence intensity decay as well as suitable mesh refinement by the cooling holes are crucial for obtaining the correct magnitudes of HTC, and thus, the capture of it should be of utmost priority in future work within the field.
142

Efficient seakeeping performance predictions with CFD

Lagemann, Benjamin January 2019 (has links)
With steadily increasing computational power, computational fluid dynamics (CFD) can be applied to unsteady problems such as seakeeping simulations. Therefore, a good balance between accuracy and computational speed is required. This thesis investigates the application of CFD to seakeeping performance predictions and aims to propose a best-practice procedure for efficient seakeeping simulations. The widely used KVLCC2 research vessel serves as a test case for this thesis and FINEŠ/Marine software package is used for CFD computations. In order to validate the simulations, results are compared to recent experimental data from SSPA as well as predictions with potential ˛ow code SHIPFLOW® Motions. As for the calm water simulations, both inviscid and viscous ˛ow computations are performed in combination with three mesh refinement levels. Seakeeping simulations with regular head waves of different wavelengths are set-up correspondingly. Furthermore, different strategies for time discretization are investigated. With the given computational resources, it is not feasible to complete seakeeping simulations with a ˝ne mesh. However, already the coarse meshes give good agreement to experiments and SHIPFLOW® Motions' predictions. Viscous ˛ow simulations turn out to be more robust than Euler ˛ow computations and thus should be preferred. Regarding the time discretization, a fixed time discretization of 150 steps per wave period has shown the best balance between accuracy and speed. Based on these findings, a best-practice procedure for seakeeping performance predictions in FINEŠ/Marine is established. Taking the most efficient settings obtained from head wave simulations, the vessel is subjected to oblique waves with 160° encounter angle. Under similar wave conditions, CFD predictions of a similar thesis show close agreement in terms of added wave resistance. Compared to the previous head wave conditions of this study, added resistance in 160° oblique waves is found to be significantly higher. This underlines that oblique bow quartering waves represent a relevant case for determining the maximum required power of a ship. CFD and potential ˛ow show similar accuracy with respect to ship motions and added wave resistance, albeit potential ˛ow outperforms CFD in terms of computational speed. Hence, CFD should be applied in cases where viscous effects are known to have large influence on a vessel's seakeeping behavior. This can be the case if motion control and damping devices are to be evaluated, for instance. / Tack vare den stadigt ökande beräkningskraften kan beräkningsuiddynamik (CFD) idag användas på beräkningsintensiva problem som sjöegenskapssimulationer. Den här rapporten undersöker användning av CFD på sjöegenskapsprestanda och syftar till att foreslå ett best-practice förfaringssätt för effektiv sjöegenskapssimulationer. Forskningsskrovet KVLCC2 fungerar som ett testfall för denna rapport och FINE—/Marine-mjukvarupaketet används för CFD-beräkningar. Viktiga parametrar, såsom ödestyp, beräkningsnät och tidssteg varierars systematiskt. Resultaten jämförs med experiment gjorda vid SSPA. Baserat på resultaten förelås en best-practice. Den föreslagna best-practice användas vidare för berökningar av sjöegenskaper i sneda vågor. Jämförelse av resultaten med liknande studier visar god överensstämmelse. Genom att använda det föreslagna förfarandet för best-practice kan CFD-sjöegenskapssimulationer användas på fall där viskösa krafter måste beaktas, till exempel rörelseregleringsanordningar.
143

Forward Modelling of Ground Based SST Telescope Images

Hidalgo Larsson, Anna January 2021 (has links)
Space debris is becoming an increased threat to the future use of space orbits. In order to counteract this threat, the field of Space Situational Awareness (SSA), and the sub-field Space Surveillance and Tracking (SST), have been developed to gather knowledge about the space debris and satellites surrounding Earth. The orbit of a satellite can be determined by acquiring images of the satellite using a telescope and a sensor. During this thesis, a tool has been programmed in Python. This tool can simulate these types of images of satellite passes, at a given time and location. The simulator takes the system parameters of the telescope and camera sensor into account, together with several different types of disturbances which affect these images. The project has been carried out at the Swedish Space Corporation (SSC), which recently launched an SSA initiative. They plan to use these images to learn more about their upcoming observations, and possibly to test an orbit determination software. / Rymdskrot är ett allt mer påtagligt hot mot den framtida användningen av om-loppsbanor i rymden. För att motverka detta hot har det blivit viktigt att kartlägga rymdlägesbilden och de objekt som ligger i omloppsbana runt jorden. Detta görs genom att observera, identifiera och banbestämma satelliter. En satellits omlopps-bana kan bestämmas genom att ta bilder av satelliten med hjälp av ett teleskop och en sensor. Under detta examensarbete har ett verktyg för att kunna simulera sådana bilder utvecklats. Simuleringsverktyget har programmerats i Python och kan simulera bilder av satellitpass vid en given tidpunkt och från en given plats. Verktyget tar hänsyn till systemparametrarna för teleskopet och kamerasensorn, samt effekterna av ett flertal olika typer av störningar som påverkar dessa bilder. Projektet har genomförts hos företaget Swedish Space Corporation (SSC), som nyligen lanserade ett initiativ för att bättre förstå rymdlägesbilden. De planerar att använda dessa bilder för att lära sig mer om deras kommande observationer, samt att eventuellt testa en programvara för att bestämma banparametrar.
144

Propuesta de mejora en la gestión de SST basado en la norma G-050 para reducir costos laborales en una constructora

Morales Sipion, Lucas Antonio January 2024 (has links)
En la empresa MATE IRL han ocurrido problemas referidos al bienestar del trabajador. Por ello se propuso una mejora en la gestión de SST basado en la Norma G050 para reducir costos laborales en la constructora. Asimismo, se diagnosticó la situación actual de la seguridad y salud en el trabajo, encontrándose que el personal no estaba capacitado ni tenía experiencia, ya que se encontró un I.G.M que alcanzó los 380 días perdidos por horas trabajadas; los equipos de seguridad colectiva y personal estaban incompletos y desgastados, el área de trabajo se encontraba desordenada y la empresa no tenía metas u objetivos relacionados con la seguridad. Se registraron gastos percibidos de problemas referidos a accidentes en el trabajo, que ascienden a S/ 13 149,8 y los gastos no percibidos en el que caso de que la empresa sea denunciada por un trabajador son de S/ 60 931,00. Por lo tanto, se elaboró la propuesta de mejora en la gestión de Seguridad y Salud en el Trabajo basada en la norma G-050, específica para el rubro de la empresa, incluyendo métodos como la implementación adecuada de señalizaciones, controles administrativos que conciernen capacitaciones y diversos formatos específicos para la evaluación de la seguridad y salud en el trabajo, compra de elementos de protección personal y de protección colectiva. Se evaluó el impacto económico de la propuesta planteada, donde se demostró que el proyecto es viable al poseer una TIR de 64,2%, un VAN de S/46 631,00 y un costo beneficio de S/. 1,26. / In the company of this investigation there have been problems related to the welfare of the worker. For this reason, an improvement in the management of SST based on the G-050 Standard was proposed to reduce labor costs in the construction company MATE EIRL. Likewise, as specific objectives, the current situation of safety and health at work in the company MATE EIRL was diagnosed, where after carrying out the initial evaluation it was found that the personnel was not trained or had much experience, the collective security teams and personal they were incomplete and with what they had was already worn out, the work area was messy and the company did not have goals or objectives related to safety-The proposal for improvement in the management of Safety and Health at Work was also elaborated based on the G-050 standard in the company MATE EIRL, including methods such as the proper implementation of signs, administrative controls that concern training and various specific formats for the evaluation of safety and health at work in the company, purchase of personal protection elements and collective protection. Finally, the economic impact of the proposed proposal was evaluated, where it was shown that the project is viable by having an IRR of 64.2%, a NPV of S/46,631.00 and a benefit cost of S/. 1.26.
145

Implementación del sistema de gestión de seguridad y salud en el trabajo para reducir riesgos en la oficina criminalística

Lopez Campos, Kelly Doity January 2023 (has links)
La presente investigación tiene como finalidad implementar un Sistema de Gestión de Seguridad y Salud en el Trabajo para reducir el nivel de riesgo en la oficina de Criminalística. La metodología es de tipo aplicada, nivel descriptivo y carácter pre-experimental, contando como población y muestra a 52 efectivos de la PNP. Mediante el análisis inicial de datos se estableció un cumplimiento del Sistema de Gestión de SST de 6,6% considerado como desaprobado, bajo los lineamientos del basado en la Ley 29783. Paralelamente los resultados de la matriz IPERC detectaron alto porcentaje de peligros Mecánicos y físicos (21.1% respectivamente) y locativos (15.8%), así como un alto porcentaje de riesgos importantes e intolerables (37% y 21% respectivamente), los mismos que requieren una inmediata atención. Determinado los riesgos y sus factores se procedió a diseñar el SGSST a fin de reducir los riegos encontrados a nivel tolerable. La implementación se viene realizando de forma paulatina debido a que requiere de una asignación presupuestal anual por parte del estado para ejecución y mantenimiento, las implementaciones realizadas con el presupuesto actual abarco conformación del CSST, elaboración del RISST, mapa de riegos, plan de emergencia, capacitaciones, adquisición de EPPs, entre otros. Aplicando nuevamente los mismos instrumentos ha permitido obtener como resultado un cumplimiento de los lineamientos del SGSST del 77% considerado aprobado y se logró reducir los riesgos intolerables e importantes y moderados a triviales y tolerables. Finalmente, se analizó la viabilidad económica de la presente implementación logrando obtener un costo beneficio de 1,48 un VAN de S/. 38,692.48 y un TIR del 77%, haciéndolo económicamente rentable y aplicable en la presente institución. / The purpose of this research is to implement an Occupational Health and Safety Management System to reduce the level of risk in the Criminalistics office. The methodology is applied, descriptive and pre-experimental, with 52 PNP personnel as population and sample. By means of the initial data analysis, a 6.6% compliance with the OSH Management System was established, considered as disapproved, under the guidelines based on Law 29783. At the same time, the results of the IPERC matrix detected a high percentage of mechanical and physical hazards (21.1%, respectively) and local hazards (15.8%), as well as a high percentage of important and intolerable risks (37% and 21%, respectively), which require immediate attention. Having determined the risks and their factors, the company proceeded to design the SGSST in order to reduce the risks found to a tolerable level. The implementation has been carried out gradually because it requires an annual budget allocation from the state for execution and maintenance. The implementations carried out with the current budget included the creation of the CSST, preparation of the RISST, risk map, emergency plan, training, acquisition of PPE, among others. Reapplying the same instruments has resulted in a 77% compliance with the SGSST guidelines, which are considered approved, and it was possible to reduce intolerable, important and moderate risks to trivial and tolerable risks. Finally, the economic viability of the present implementation was analyzed, obtaining a cost benefit of 1.48, an NPV of S/. 38,692.48 and an IRR of 77%, making it economically profitable and applicable in the present institution.
146

Customer Value Co-Creation Through Self-Service Technology : Qualitative Research on SST in Large Chain Supermarkets / Customer Value Co-Creation Through Self-Service Technology : Qualitative Research on SST in Large Chain Supermarkets

Kulsoom, Kulsoom January 2024 (has links)
Self-service technologies are rapidly increasing in the retailing industries as retailers aim to streamline transactions and enhance efficiency for both consumers and themselves. Despite various studies on SSTs, exploring their usability, impact, and influence on consumers' value co-creation was still lacking. Through this study, the influence of SSTs on consumers' value co-creation has been investigated by a qualitative approach, consisting of interviews and observational studies. The gathered data has helped this study to gain insights into the subjective dimensions of consumers' experiences, behaviors, and interactions with SSTs in a supermarket in East London.  Thematic analysis of the data reveals four key dimensions of value co-creation through SSTs: Value-Driven Efficiency, Autonomous Value Co-Creation, Value-Enriched Shopping Experience, and Value-Driven Refinement. Applying Service-Dominant (S-D) logic, the study finds that SSTs significantly enhance shopping experiences by providing convenience, efficiency, and autonomy, especially for small purchases. Consumers engage actively with SSTs, making informed decisions and navigating independently, with assistance available as needed. Common challenges include scanning items without barcodes, purchasing age-restricted items, and SSTs malfunctioning. Despite these issues, the overall impact of SSTs remains positive.
147

Numerische und experimentelle Untersuchung der fluiddynamischen Eigenschaften von Strahlströmungen in begrenzten Räumen

Ringleb, Ansgar 03 April 2018 (has links)
In der vorliegenden Arbeit wurden Strömungen räumlich begrenzter Strahlen untersucht. Zum einen wurde die Ausströmung eines runden Strahls in ein Rohr betrachtet, der sog. begrenzte Strahl. Zum anderen wurde die Ausströmung von 7 hexagonal angeordneten runden Strahlen in ein Rohr betrachtet, das sog. hexagonale Strahlbündel. Die Motivation zur vorliegenden Arbeit ergab sich aus der Entwicklung von Durchflussmessgeräten, die als Bypassapparaturen ausgeführt sind und stromabwärts des Staudruckkörpers ein Strömungsgebiet mit begrenzten Strahlen aufweisen. Dafür wurden mit Hilfe der Ähnlichkeitstheorie die zugrundeliegenden Kennzahlen bestimmt. Besonderes Augenmerk lag auf der Charakterisierung der instationären bzw. turbulenten Strömungseigenschaften für Reynolds-Zahlen zwischen 1.000 und 20.000. Es wurden die selbstähnlichen Eigenschaften der Strömungen untersucht, wobei sich insbesondere für den begrenzten Strahl wichtige Erkenntnisse ergaben. Für das hexagonale Strahlbündel wurden mit Hilfe der numerischen Strömungssimulation die grundlegenden Eigenschaften des Strömungsfeldes untersucht. Dabei weisen die Geometriekennzahlen einen dominierenden Einfluss auf. So konnten in Abhängigkeit zum Durchmesserverhältnis und Strahlabstand drei Strömungsformen identifiziert und experimentell mittels Laser-Doppler Anemometrie nachgewiesen werden. Eine wesentliche Fragestellung bestand in der Anwendung der numerischen Strömungssimulation, des RANS-Ansatzes und des SST-Turbulenzmodells. Dazu wurde die Anpassung der Modellkoeffizienten untersucht, wobei für den begrenzten Strahl ein allgemein gültiger Satz gefunden wurde. / In the present work flows of spatially limited radiation were investigated. On the one hand, the outflow of a round jet into a pipe was considered, the so-called confined jet. On the other hand, the outflow of 7 hexagonal arranged round jets into a pipe was con-sidered, the so-called hexagonal jet array. The motivation for the present work arose from the development of flowmeters which are designed as bypass apparatures that have a jet array flow downstream of the dynamic pressure body. For this purpose the underlying similarity parameters were determined. Special attention was paid to the cha-racterization of transient and turbulent flow properties for Reynolds numbers between 1,000 and 20,000. The self-similar properties of the flows were investigated with im-portant findings in particular for the confined jet. For the hexagonal jet array the basic properties of the flow field were investigated by using computational fluid dynamics. The geometric similarity parameters have a dominant influence. Thus, depending on the di-ameter ratio and jet distance ratio, three flow patterns could be identified and experimen-tally detected by the use of laser Doppler anemometry. An important question was the application of the computational fluid dynamic method, the RANS approach and the SST turbulence model. For this purpose a generally valid set of model coefficients was found for the confined jet flow.
148

Regionalização hidrológica de vazões e de cargas difusas de sólidos suspensos totais para o programa ProdutorES de Água e o pagamento de serviços ambientais. Estudo de caso: bacia hidrográfica do rio Benevente, ES / Hydrological regionalization of flows and loads of total suspend solids for the program Producers of Water and the payment of environmental services. Case study of river basin Benevente, ES

Henrique, Cesar Sperchi 19 November 2009 (has links)
O sistema de pagamento por serviços ambientais de uma bacia hidrográfica pode ser economicamente atrativo e ecologicamente importante. Programas como o Produtor de Água compensam economicamente proprietários a montante da bacia que utilizam de manejo adequado do uso do solo, e do reflorestamento, para evitar a erosão hídrica, o aumento de cargas poluidoras difusas, e aumentar a disponibilidade e qualidade de água. Por conseqüência usuários de água, a jusante da bacia, são beneficiados, por exemplo, as estações de tratamento de água. Este trabalho tem como objetivo, a partir de metodologias de pagamentos de serviços ambientais, regionalizar hidrologicamente a quantidade e qualidade de água do rio Benevente para dar subsídios ao programa de produtores de água de sua bacia hidrográfica. O trabalho foi desenvolvido na parte média e alta da bacia hidrográfica do Benevente, localizada ao sul do Estado do Espírito Santo, com área de drenagem de aproximadamente 1260 \'KM POT.2\'. Á área de drenagem do local do estudo é de 825,24 \'KM POT.2\'. Parte da metodologia consistiu no levantamento de dados quantitativos e qualitativos de água ao longo do rio Benevente, nos últimos anos. De posse dos dados de vazão, concentração de SST e da área de drenagem, foram calculadas as cargas específicas difusas de SST, em termos de Kg/ha.ano e as cargas totais difusas em termos de ton/ano. A carga específica média de SST para a bacia foi de 194 Kg/ha.ano, a carga total média de SST foi de 11.238 ton/ano. A metodologia de regionalização hidrológica de cargas de SST por meio de curvas de permanência mostrou que há uma ampla variação de cargas produzidas na bacia sobre diferentes condições hidrológicas. Por exemplo, para uma faixa de permanências de 40% a 60% a variação de produção específica regional de SST foi de 58,54 a 825,14 Kg/ha.ano. A utilização da metodologia das curvas de permanência quali-quantitativas para a proposição de cenários ambientais em vista das mudanças de uso e ocupação do solo, propostos pelos programas de PSA, permitiu estimar o Percentual de Abatimento de Sedimentação (P.A.S) e consequentemente o Percentual de Abatimento de Erosão (P.A.E), na bacia. Encontrou-se um P.A.E de 36,9% entre o cenário atual e o cenário com amento de 20% da área florestal da bacia. Com este resultado estimou-se um total arrecadado na bacia pelo P.S.A de 825.195 R$/ano. Com as metodologias propostas também foi calculada a perda de solo atual da bacia, em relação à estação de amostragem mais a jusante. A taxa estimada foi de 200.123 ton/ano. / Systems of payment for environmental services of a catchment area can be economically attractive and ecologically important. Programs such as Producers of Water economically compensate owners upstream of the basin using the proper management of land use, and reforestation to prevent erosion, increased pollution loads diffuse and increase the availability and quality of water. Consequently water users downstream of the basin, are benefited, for example, sewage water treatment. This paper aims, methodologies from payments for environmental services, regionalization of hydrologically the quantity and quality of water from the river Benevente to aid the program producer of water from its watershed. The study was conducted in the middle and upper catchment of the Benevente, located south of Espírito Santo, with drainage area of approximately 1260 \'KM POT.2\'. The drainage area of the study is 825.24 \'KM POT.2\'. Part of the survey methodology consisted of qualitative and quantitative data of water along the river Benevente in recent years. With these data we calculated the diffuse specific loads of TSS, in terms of Kg/ha.year. The specific load average TSS for the basin was 194 Kg/ha.year, the total load average SST was 11,238 Ton/year. The methodology of regionalization of hydrological loads of TSS through curves of duration showed that there remain a wide range of loads in the basin produced on different hydrological conditions. For example, for a range of stays of 40% to 60% of the variation of specific regional production of TSS was 58.54 to 825.14 Kg/ha.year . Using the methodology of the curves remain qualitative and quantitative for the proposition environmental scenarios in view of land use change and land use, proposed by the PSA program, estimated the rate of reduction on Sedimentation (PAS) and consequently the rate Abatement of Erosion (PAE) in the basin. Found a PAE of 36.9% from the current scenario and the scenario with budget of 20% of the forest area of the basin. With this estimated result a total collected in the basin by the PSA for R$ 825,195/year. With the proposed methodology was also calculated the soil loss on the basin in relation to the sampling station further downstream. The rate was estimated at 200,123 ton/year.
149

Development and use of satellite-derived sea-surface temperature data for the nearshore North Pacific and Arctic Oceans : temperature pattern analysis and implications for climate change at ecoregional scale

Payne, Meredith C. 12 March 2012 (has links)
The quantification and description of sea surface temperature (SST) is critically important because it can influence the distribution, migration, and invasion of marine species; furthermore, SSTs are expected to be affected by climate change. Recent research indicates that there has been a warming trend in ocean temperatures over the last 50 years. Hence, we sought to identify and demonstrate how a particularly germane SST dataset can be used within the scope of global climate change research. For this project we assembled a 29-year nearshore time series of mean monthly SSTs along the North Pacific coastline, as well as mean monthly SSTs for ice-free regions of the Arctic, using remotely-sensed satellite data collected with the Advanced Very High Resolution Radiometer (AVHRR) instrument. By providing detailed information concerning both dataset generation and data limitations, we aimed to make these data comprehensible to an expanded audience concentrating on life sciences rather than the traditionally physical science-based community. Furthermore, by making these data freely and publically available in multiple formats, including GIS (geographic information systems) layers, we expand their visibility and the extent of their use. We then used the dataset to describe SST patterns of nearshore (< 20 km offshore) regions of 16 North Pacific ecoregions, and of ice-free regions of 20 Arctic ecoregions, as delineated by the Marine Ecoregions of the World (MEOW) hierarchical schema. Our work creates a better understanding of present temperature regimes in these critically sensitive areas, from which we can draw several basic conclusions. 1) AVHRR SST measurements alone are sufficient to identify temperature patterns pertinent to determining health of ecosystems; 2) Within the nearshore North Pacific, ecoregions along the California Current System are most vulnerable to habitat-altering SST changes; 3) sea ice distribution is a major factor affecting SSTs in Arctic ecoregions, causing concern for the welfare of Arctic species. / Graduation date: 2012
150

A Ventilation Strategy Based on Confluent Jets : An Experimental and Numerical Study

Janbakhsh, Setareh January 2015 (has links)
This study presents air distribution systems that are based on confluent jets; this system can be of interest for the establishment of indoor environments, to fulfill the goals of indoor climate and energy-efficient usage. The main objective of this study is to provide deeper understanding of the flow field development of a supply device that is designed based on wall confluent jets and to investigate the ventilation performance by experimental and numerical methods. In this study, the supply device can be described as an array of round jets on a flat surface attached to a side wall. Multiple round jets that issue from supply device apertures are combined at a certain distance downstream from the device and behave as a united jet or so-called confluent jets. Multiple round jets that are generated from the supply device move downward and are attached to the wall at the primary region, due to the Coanda effect, and then they become wall confluent jets until the floor wall is reached. A wall jet in a secondary region is formed along the floor after the stagnation region. The characteristics of the flow field and the ventilation performance of conventional wall confluent jets and modified wall confluent jets supply devices are investigated experimentally in an office test room. The study of the modified wall confluent jets is intended to improve the efficiency of the conventional one while maintaining acceptable thermal comfort in an office environment. The results show that the modified wall confluent jets supply device can provide acceptable thermal comfort for the occupant with lower airflow rate compared to the conventional wall confluent jets supply device. Numerical predictions using three turbulence models (renormalization group (RNG k– ε), realizable (Re k– ε), and shear stress transport (SST k– ω) are evaluated by measurement results. The computational box and nozzle plate models are used to model the inlet boundary conditions of the nozzle device. In the isothermal study, the wall confluent jets in the primary region and the wall jet in the secondary region, when predicted by the three turbulence models, are in good agreement with the measurements. The non-isothermal validation studies show that the SST k– ω model is slightly better at predicting the wall confluent jets than the other two models. The SST k– ω model is used to investigate the effects of the nozzle diameter, number of nozzles, nozzle array configuration, and inlet discharge height on the ventilation performance of the proposed wall confluent jets supply device. The nozzle diameter and number of nozzles play important roles in determining the airflow pattern, temperature field, and draught distribution. Increased temperature stratification and less draught distribution are achieved by increasing the nozzle diameter and number of nozzles. The supply device with smaller nozzle diameters and fewer nozzles yields rather uniform temperature distribution due to the dominant effect of mixing. The flow behavior is nearly independent of the inlet discharge height for the studied range. The proposed wall confluent jets supply device is compared with a mixing supply device, impinging supply device and displacement supply device. The results show that the proposed wall confluent jets supply device has the combined behavior of both mixing and stratification principles. The proposed wall confluent jets supply device provides better overall ventilation performance than the mixing and displacement supply devices used in this study. This study covers also another application of confluent jets that is based on impinging technology. The supply device under consideration has an array of round jets on a curve. Multiple jets issue from the supply device aperture, in which the supply device is positioned vertically and the jets are directed against a target wall. The flow behavior and ventilation performance of the impinging confluent jets supply device is studied experimentally in an industrial premise. The results show that the impinging confluent jets supply device maintains acceptable thermal comfort in the occupied zone by creating well-distributed airflow during cold and hot seasons.

Page generated in 0.0202 seconds