11,190 research outputs found
Entropy splitting for high-order numerical simulation of compressible turbulence
No full textA stable high-order numerical scheme for direct numerical simulation (DNS) of shock-free compressible turbulence is presented. The method is applicable to general geometries. It contains no upwinding, artificial dissipation, or filtering. Instead the method relies on the stabilizing mechanisms of an appropriate conditioning of the governing equations and the use of compatible spatial difference operators for the interior points (interior scheme) as well as the boundary points (boundary scheme). An entropy-splitting approach splits the inviscid flux derivatives into conservative and nonconservative portions. The spatial difference operators satisfy a summation-by-parts condition, leading to a stable scheme (combined interior and boundary schemes) for the initial boundary value problem using a generalized energy estimate. A Laplacian formulation of the viscous and heat conduction terms on the right hand side of the Navier–Stokes equations is used to ensure that any tendency to odd–even decoupling associated with central schemes can be countered by the fluid viscosity. The resulting methods are able to minimize the spurious high-frequency oscillations associated with pure central schemes, especially for long time integration applications such as DNS. For validation purposes, the methods are tested in a DNS of compressible turbulent plane channel flow at low values of friction Mach number, where reference turbulence data bases exist. It is demonstrated that the methods are robust in terms of grid resolution, and in good agreement with published channel data. Accurate turbulence statistics can be obtained with moderate grid sizes. Stability limits on the range of the splitting parameter are determined from numerical tests
Progress in the development of a class of efficient low dissipative high order shock capturing methods
No full textIn a series of papers, Olsson (1994, 1995), Olsson & Oliger (1994), Strand (1994), Gerritsen & Olsson (1996), Yee et al. (1999a,b, 2000) and Sandham & Yee (2000), the issue of nonlinear stability of the compressible Euler and Navier-Stokes Equations, including physical boundaries, and the corresponding development of the discrete analogue of nonlinear stable high order schemes, including boundary schemes, were developed, extended and evaluated for various fluid flows. High order here refers to spatial schemes that are essentially fourth-order or higher away from shock and shear regions. The objective of this paper is to give an overview of the progress of the low dissipative high order shock-capturing schemes proposed by Yee et al. (1999a,b, 2000). This class of schemes consists of simple non-dissipative high order compact or non-compact central spatial differencings and adaptive nonlinear numerical dissipation operators to minimize the use of numerical dissipation. The amount of numerical dissipation is further minimized by applying the scheme to the entropy splitting form of the inviscid flux derivatives, and by rewriting the viscous terms to minimize odd-even decoupling before the application of the central scheme (Sandham & Yee). The efficiency and accuracy of these schemes are compared with spectral, TVD and fifth-order WENO schemes. A new approach of Sjogreen & Yee (2000) utilizing non-orthogonal multi-resolution wavelet basis functions as sensors to dynamically determine the appropriate amount of numerical dissipation to be added to the non-dissipative high order spatial scheme at each grid point will be discussed. Numerical experiments of long time integration of smooth flows, shock-turbulence interactions, direct numerical simulations of a 3-D compressible turbulent plane channel flow, and various mixing layer problems indicate that these schemes are especially suitable for practical complex problems in nonlinear aeroacoustics, rotorcraft dynamics, direct numerical simulation or large eddy simulation of compressible turbulent flows at various speeds including high-speed shock-turbulence interactions, and general long time wave propagation problems. These schemes, including entropy splitting, have also been extended to freestream preserving schemes on curvilinear moving grids for a thermally perfect gas (Vinokur & Yee 2000).<br/
Diomus roseicollis
No full textDiomus roseicollis (Mulsant, 1853) (Coleoptera: Coccinellidae: Coccinellinae: Diomini) Hawai‘i (new state record), Honolulu County, O‘ahu Island, Barbers Point, 0–5 ft elev., 27-III to 5-IV-2017, W. D. Perreira and D. A. Yee, YSBT, 1 ♀; Honolulu County, O‘ahu Island, Barbers Point, 0–5 ft elev., 5-12-IV-2017, W. D. Perreira and D. A. Yee, YSBT, 1 ♀; Honolulu County, O‘ahu Island, Barbers Point, 0–5 ft elev., 28- VI to - 2-VIII-2017, W. D. Perreira and D. A. Yee, YSBT, 1 ♀; Honolulu County, O‘ahu Island, Waimanalo, UH Ag Res Sta, 70 ft elev., 25-VIII-2017, W. D. Perreira and D. A. Yee, 1 ♀ (Figure 1).Published as part of Hesler, Louis S., Perreira, William D., Yee, Dana Anne & Silva, Joshua H. S., 2020, New state and island records of Coccinellidae (Coleoptera) in Hawai'i, USA, pp. 1-4 in Insecta Mundi 2020 (795) on page 2, DOI: 10.5281/zenodo.456513
Being Chiang Yee: Feeling difference and storytelling
No full textChiang Yee was a Chinese writer, poet and painter who lived in England during the 1930s and 1940s. In his writing and drawings, there are many observations on the attention that his Chinese appearance provoked, all enabling him to tell stories about both Chinese and English cultures. The autobiographical persona of Silent Traveller, created by Chiang Yee in his writing, steered clear of controversial remarks, although he had strong feelings about Chinese politics, racism, and how Chinese people were regarded in Britain and America. This chapter explores how emotions, whether difficult or joyous, do not fit smoothly into linear narratives, and make personal memory an unreliable witness to history. Historians also may have a personal and emotional interest in the subjects they study. Indeed, I cannot think about Chiang Yee without resonances of my own family history, and experiences of being or embodying something of the Chinese in Britain. In a new analysis of The Silent Traveller in London (1945) and The Silent Traveller in Oxford (1946), the chapter explores what happens if we deepen rather than deny the historian’s role as storyteller, and pay closer attention to the differences and overlaps between Chiang Yee the author and Chiang Yee the Silent Traveller. Embracing the fragmented, the personal, the emotional, and the miss-remembered reveals a series of moments that speak about a Chinese physical presence in Oxford and London. These bring us closer to what it felt like to be a Chinese man in England during the 1940s, between the stories that were silenced and the things that could be said
Student Expectations in the New Millennium
No full textHigher education has experienced vast changes as a result of global political and economic developments. Cultural and social changes in the last decade have also added to the continuing evolution of higher education. These changes inevitably lead to changing expectations of students entering higher education. An adequate understanding of student expectations is crucial in ensuring a good fit between higher educational institutions and their students. This study attempts to carry out a baseline descriptive-quantitative research on student expectations in the higher education of Hong Kong. Four scales have been developed to measure students’ attitude toward: 1. job-oriented curriculum design, 2. user-friendly course delivery method, 3. opportunities for lifelong learning, and 4. student consumerism. Students’ priority of what makes a good university, their reasons for going to university, and their self-perception of ability to cope with university life are also explored. The Student Expectations Questionnaire (developed by the author) was used to gather data from 857 first-year undergrads from nine institutions of higher education in Hong Kong. Analyses include, among others, gender, age, major of study as well as institution comparisons
Self-consistent anisotropic kinetic effects of photoelectrons on the polar wind
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1996.Includes bibliographical references (leaves 155-160).by Wing Yee Sunny Tam.Ph.D
Radial Basis Function Assisted Turbo Equalization
No full textThis paper presents a turbo equalization (TEQ) scheme, which employs a radial basis function (RBF)-based equalizer instead of the conventional trellis-based equalizer of Douillard et al. Structural, computational complexity, and performance comparisons of the RBF-based and trellis-based TEQs are provided. The decision feedback-assisted RBF TEQ is capable of attaining a similar performance to the logarithmic maximum scheme in the context of both binary phase-shift keying (BPSK) and quaternary phase-shift keying (QPSK) modulation, while achieving a factor 2.5 and 3 lower computational complexity, respectively. However, there is a 2.5-dB performance loss in the context of 16 quadrature amplitude modulation (QAM), which suffers more dramatically from the phenomenon of erroneous decision-feedback effects. A novel element of our design, in order to further reduce the computational complexity of the RBF TEQ, is that symbol equalizations are invoked at current iterations only if the decoded symbol has a high error probability. This techniques provides 37% and 54% computational complexity reduction compared to the full-complexity RBF TEQ for the BPSK RBF TEQ and 16QAM RBF TEQ, respectively, with little performance degradation, when communicating over dispersive Rayleigh fading channels. Index Terms—Decision-feedback equalizer (DFE), Jacobian logarithm, neural network, radial basis function (RBF), turbo coding, turbo equalization (TEQ)
Stability and transient analysis of controlled longitudinal motion of aircraft with nonideal automatic controls
No full textThesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautical Engineering, 1941.Microfiche copy available in Barker.Vita.Includes bibliographical references.by Yee Jing Liu.Sc.D
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