Large-Scale Disturbances and Their Mitigation Downstream of Shallow Cavities Covered by a Perforated Lid

Flow past cavities covered by perforated lids pose a challenging problem for design engineers. Kelvin–Helmholtz waves appear early in the separated shear layers above the perforations that quickly mature into large-scale coherent structures far downstream. This evolution is sustained by a hydrodynamic feedback mechanism within the cavity even when its aft wall is far removed from the lid. Herein, the results from large-eddy simulations show analogous fundamental characteristics between open and perforated-cover cavities. Both adequately scale the fundamental frequency of the large-scale disturbance using the freestream velocity and the cavity width (or lid length). Moreover, the dimensionless frequencies jump to higher modes at equivalent length scales. Unlike the open cavity, one can invoke certain conditions that instigate the instability above the perforations but not a simultaneous long-term feedback mechanism necessary to fully sustain the periodic oscillation. The lid itself offers options for mitigating (or even eliminating) the instability. Results (for laminar separation) show the perforation spacing as the key factor. While maintaining the same fundamental frequency, one can easily dampen its spectral peak to complete disappearance by extending the perforation spacing.

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Mitigation of the Large-Scale Oscillation Self-Sustained by Shallow Cavities With a Perforated Lid

Volume 2, Parts A and B ◽

10.1115/ht-fed2004-56508 ◽

2004 ◽

Author(s):

Stephen A. Jordan

Keyword(s):

Fundamental Frequency ◽

Large Scale ◽

Periodic Oscillation ◽

Feedback Mechanism ◽

Complete Disappearance ◽

Freestream Velocity ◽

Design Engineers ◽

Large Scale Disturbance ◽

Key Factor ◽

Shallow Cavities

Flow past cavities covered by perforated lids pose a challenging problem for design engineers. Kelvin-Helmholtz waves appear early in the separated shear layers above the perforations that quickly mature into large-scale coherent structures far downstream. This evolution is sustained by a hydrodynamic feedback mechanism within the cavity even when its aft wall is far removed from the lid. Herein, the results from large-eddy simulations show analogous fundamental characteristics between open and perforated-cover cavities. Both adequately scale the fundamental frequency of the large-scale disturbance using the freestream velocity and the cavity width (or lid length). Moreover, the dimensionless frequencies jump to higher modes at equivalent length scales. Unlike the open cavity, one can invoke certain conditions that instigate the instability above the perforations but not a simultaneous long-term feedback mechanism necessary to fully sustain the periodic oscillation. The lid itself offers options for mitigating (or even eliminating) the instability. Results (for laminar separation) show the perforation spacing as the key factor. While maintaining the same fundamental frequency, one can easily dampen its spectral peak to complete disappearance by extending the perforation spacing.

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Going the Distance

10.23943/princeton/9780691150772.001.0001 ◽

2020 ◽

Author(s):

Ron Harris

Keyword(s):

Large Scale ◽

Western Europe ◽

Family Firms ◽

Global Trade ◽

Long Distance ◽

Business Corporation ◽

Modern Economy ◽

Key Factor ◽

Silk Route ◽

Passive Investors

Before the seventeenth century, trade across Eurasia was mostly conducted in short segments along the Silk Route and Indian Ocean. Business was organized in family firms, merchant networks, and state-owned enterprises, and dominated by Chinese, Indian, and Arabic traders. However, around 1600 the first two joint-stock corporations, the English and Dutch East India Companies, were established. This book tells the story of overland and maritime trade without Europeans, of European Cape Route trade without corporations, and of how new, large-scale, and impersonal organizations arose in Europe to control long-distance trade for more than three centuries. It shows that by 1700, the scene and methods for global trade had dramatically changed: Dutch and English merchants shepherded goods directly from China and India to northwestern Europe. To understand this transformation, the book compares the organizational forms used in four major regions: China, India, the Middle East, and Western Europe. The English and Dutch were the last to leap into Eurasian trade, and they innovated in order to compete. They raised capital from passive investors through impersonal stock markets and their joint-stock corporations deployed more capital, ships, and agents to deliver goods from their origins to consumers. The book explores the history behind a cornerstone of the modern economy, and how this organizational revolution contributed to the formation of global trade and the creation of the business corporation as a key factor in Europe's economic rise.

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Trace element catalyses mineral replacement reactions and facilitates ore formation

Nature Communications ◽

10.1038/s41467-021-21684-5 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Yanlu Xing ◽

Joël Brugger ◽

Barbara Etschmann ◽

Andrew G. Tomkins ◽

Andrew J. Frierdich ◽

...

Keyword(s):

Mass Transfer ◽

Trace Elements ◽

Fluid Flow ◽

Large Scale ◽

Metal Accumulation ◽

Nucleation And Growth ◽

Reaction Interface ◽

Ore Formation ◽

Key Factor ◽

Mineral Replacement

AbstractReaction-induced porosity is a key factor enabling protracted fluid-rock interactions in the Earth’s crust, promoting large-scale mineralogical changes during diagenesis, metamorphism, and ore formation. Here, we show experimentally that the presence of trace amounts of dissolved cerium increases the porosity of hematite (Fe2O3) formed via fluid-induced, redox-independent replacement of magnetite (Fe3O4), thereby increasing the efficiency of coupled magnetite replacement, fluid flow, and element mass transfer. Cerium acts as a catalyst affecting the nucleation and growth of hematite by modifying the Fe2+(aq)/Fe3+(aq) ratio at the reaction interface. Our results demonstrate that trace elements can enhance fluid-mediated mineral replacement reactions, ultimately controlling the kinetics, texture, and composition of fluid-mineral systems. Applied to some of the world’s most valuable orebodies, these results provide new insights into how early formation of extensive magnetite alteration may have preconditioned these ore systems for later enhanced metal accumulation, contributing to their sizes and metal endowment.

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Ecological processes maintaining differential tree species distributions in an Australian subtropical rain forest: implications for models of species coexistence

Journal of Tropical Ecology ◽

10.1017/s0266467400001474 ◽

2000 ◽

Vol 16 (3) ◽

pp. 387-415 ◽

Cited By ~ 20

Author(s):

Igor Debski ◽

David F. R. P. Burslem ◽

David Lamb

Keyword(s):

Species Composition ◽

Tree Species ◽

Rain Forest ◽

Large Scale ◽

Species Coexistence ◽

Common Species ◽

Size Class ◽

Differential Mortality ◽

Mixed Composition ◽

Large Scale Disturbance

All stems ≥ 1 cm dbh were measured, tagged, mapped and identified on a 1-ha plot of rain forest at Gambubal State Forest, south-east Queensland, Australia. The spatial patterns and size class distributions of 11 common tree species on the plot were assessed to search for mechanisms determining their distribution and abundance. The forest was species-poor in comparison to many lowland tropical forests and the common species are therefore present at relatively high densities. Despite this, only limited evidence was found for the operation of density-dependent processes at Gambubal. Daphnandra micrantha saplings were clumped towards randomly spaced adults, indicating a shift of distribution over time caused by differential mortality of saplings in these adult associated clumps. Ordination of the species composition in 25-m × 25-m subplots revealed vegetation gradients at that scale, which corresponded to slope across the plot. Adult basal area was dominated by a few large individuals of Sloanea woollsii but the comparative size class distributions and replacement probabilities of the 11 common species suggest that the forest will undergo a transition to a more mixed composition if current conditions persist. The current cohort of large S. woollsii individuals probably established after a large-scale disturbance event and the forest has not attained an equilibrium species composition.

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What determines a boundary for navigating a complex street network: evidence from London taxi drivers

Journal of Navigation ◽

10.1017/s0373463321000679 ◽

2021 ◽

pp. 1-20

Author(s):

Eva-Maria Griesbauer ◽

Ed Manley ◽

Daniel McNamee ◽

Jeremy Morley ◽

Hugo Spiers

Keyword(s):

Urban Space ◽

Large Scale ◽

Route Planning ◽

Taxi Drivers ◽

Street Networks ◽

Planning Models ◽

Key Factor ◽

Efficient Planning ◽

Regent's Park ◽

Insight Into

Abstract Spatial boundaries play an important role in defining spaces, structuring memory and supporting planning during navigation. Recent models of hierarchical route planning use boundaries to plan efficiently first across regions and then within regions. However, it remains unclear which structures (e.g. parks, rivers, major streets, etc.) will form salient boundaries in real-world cities. This study tested licensed London taxi drivers, who are unique in their ability to navigate London flexibly without physical navigation aids. They were asked to indicate streets they considered as boundaries for London districts or dividing areas. It was found that agreement on boundary streets varied considerably, from some boundaries providing almost no consensus to some boundaries consistently noted as boundaries. Examining the properties of the streets revealed that a key factor in the consistent boundaries was the near rectilinear nature of the designated region (e.g. Mayfair and Soho) and the distinctiveness of parks (e.g. Regent's Park). Surprisingly, the River Thames was not consistently considered as a boundary. These findings provide insight into types of environmental features that lead to the perception of explicit boundaries in large-scale urban space. Because route planning models assume that boundaries are used to segregate the space for efficient planning, these results help make predictions of the likely planning demands of different routes in such complex large-scale street networks. Such predictions could be used to highlight information used for navigation guidance applications to enable more efficient hierarchical planning and learning of large-scale environments.

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Introducing systems oriented design for complex societal contexts in design engineering education

Form Akademisk - forskningstidsskrift for design og designdidaktikk ◽

10.7577/formakademisk.1460 ◽

2017 ◽

Vol 10 (1) ◽

Cited By ~ 2

Author(s):

Jairo da Costa Junior ◽

Ana Laura Rodrigues dos Santos ◽

Jan Carel Diehl

Keyword(s):

Large Scale ◽

Resource Depletion ◽

Point Of View ◽

Design Engineering ◽

Support Design ◽

Humanitarian Emergencies ◽

Study Approach ◽

Design Engineers ◽

Problem Solvers ◽

Societal Problems

As our society faces large-scale wicked problems like global warming, resource depletion, poverty and humanitarian emergencies, problem solvers are required to apply new reasoning models more appropriate to deal with these complex societal problems. Dealing with these problems poses unfamiliar challenges in contexts with poor financial and infrastructural resources. Systems Oriented Design (SOD) has been recognized in the literature as a promising approach, capable to support design engineers to deal with these complex societal problems. This paper explores the application of SOD in the development of Product-Service System (PSS) concepts by student teams in a multidisciplinary master course. The course resulted in twelve concepts that were analysed using a case study approach with the support of protocol analysis. The analysis results in a description of advantages, context- and process-related challenges of using SOD. From an education point-of-view, the results demonstrate that even though SOD provides students with a broad knowledge base and skills to deal with problems in complex societal contexts, there is still the need to introduce the appropriate scope and depth in the design engineering curricula, making the transition from traditional product design, a challenging one.

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Synthesis of the Sparse Uniform-Amplitude Concentric Ring Transmitting Array for Optimal Microwave Power Transmission

International Journal of Antennas and Propagation ◽

10.1155/2018/8075318 ◽

2018 ◽

Vol 2018 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Hua-Wei Zhou ◽

Xue-Xia Yang ◽

Sajjad Rahim

Keyword(s):

Microwave Power ◽

Large Scale ◽

Power Transmission ◽

Synthesis Method ◽

Pso Algorithm ◽

Practical Significance ◽

Concentric Ring ◽

Swarm Optimization ◽

Key Factor ◽

Feed Network

Beam capture efficiency (BCE) is one key factor of the overall efficiency for a microwave power transmission (MPT) system, while sparsification of a large-scale transmitting array has a practical significance. If all elements of the transmitting array are excited uniformly, the fabrication, maintenance, and feed network design would be greatly simplified. This paper describes the synthesis method of the sparse uniform-amplitude transmitting array with concentric ring layout using particle swarm optimization (PSO) algorithm while keeping a higher BCE. Based on this method, uniform exciting strategy, reduced number of elements, and a higher BCE are achieved simultaneously for optimal MPT. The numerical results of the sparse uniform-amplitude concentric ring arrays (SUACRAs) optimized by the proposed method are compared with those of the random-located uniform-amplitude array (RLUAA) and the stepped-amplitude array (SAA), both being reported in the literatures for the maximum BCE. Compared to the RLUAA, the SUACRA saves 32% elements with a 1.1% higher BCE. While compared to the SAA, the SUACRA saves 29.1% elements with a bit higher BCE. The proposed SUACRAs have higher BCEs, simple array arrangement and feed network, and could be used as the transmitting array for a large-scale MPT system.

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Performance and Benefit Analysis of Mining Accumulator Locomotive AC Speed System Based on DTC

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.328-330.1846 ◽

2011 ◽

Vol 328-330 ◽

pp. 1846-1850

Author(s):

Xi Zhang ◽

Jie Yang ◽

Wen Chao Chen ◽

Qi Zhou Huang

Keyword(s):

Large Scale ◽

Asynchronous Motor ◽

Speed Control ◽

Fast Response ◽

Efficient Operation ◽

Ac Drive ◽

Key Factor ◽

Large Scale Integration ◽

Overload Capacity ◽

Scale Integration

The traditional mine accumulator locomotive usually takes the DC motor for its power source. And the series-wound resistance method is usually used in its speed control. With the development of power electronics technology, the AC drive system based on power electronic converters can be realized. Especially after the realization of large-scale integration and compmer controling, the performance of AC variale speed has been improved a lot. In operation, the mine accumulator locomotive not only works in frequent starting, breaking, accelerating and decelerating conditions, but also has to adapt to the bad pavement. The AC asynchronous motor has simple stmcture, sturdy and durable, and it could save power by notusing resistance when it was used in speed control. With this characteristics, the AC speed control system has the feature of fast response and high overload capacity. The AC speed system is the key factor for efficient operation of mining accumulator locomotive. Compared with the traditional DC speed system, the principle of DTC is introduced in this paper. And the advantage of operating performance and economic benefit of mining accumulator locomotive with AC speed system based on DTC is analyzed from practical application.

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Effects of Weld Strength Heterogeneity on Crack Driving Force in Stress and Strain Based Design Scenarios

Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern and Offshore Environments; Strain-Based Design; Standards and Regulations ◽

10.1115/ipc2014-33454 ◽

2014 ◽

Author(s):

Stijn Hertelé ◽

Noel O’Dowd ◽

Matthias Verstraete ◽

Koen Van Minnebruggen ◽

Wim De Waele

Keyword(s):

Driving Force ◽

Large Scale ◽

Limit State ◽

Weld Strength ◽

Force Response ◽

Crack Driving Force ◽

Key Factor ◽

Weld Properties ◽

Girth Welds ◽

Strain Hardening Behavior

Weld strength mismatch is a key factor with respect to the assessment of a flawed girth weld. However, it is challenging to assign a single strength mismatch value to girth welds, which are generally heterogeneous in terms of constitutive behavior. The authors have recently developed a method (‘homogenization’) to account for weld strength property variations in the estimation of crack driving force response and the corresponding tensile limit state. This paper separately validates the approach for stress based and strain based assessments. Whereas homogenization is reliably applicable for stress based assessments, the strain based crack driving force response is highly sensitive to effects of actual heterogeneous weld properties. The sensitivity increases with increased weld width and decreased strain hardening behavior. For strain based design, a more accurate methodology is desirable, and large scale testing and/or advanced numerical modeling remain essential.

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