检索结果-南通市图书馆

Computational Analysis of Surface Pressure Distribution over a 2D Wedge in the Supersonic and Hypersonic Flow Regimes

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Fluid Dynamics & Materials Processing 2023年第6期19卷 1637-1653页

作者： Javed S.Shaikh Krishna Kumar Khizar A.Pathan Sher A.Khan mit School of Engineering MIT ADT UniversityPune412201India Trinity College of Engineering and Research Pune411048India Department of Mechanical Engineering International Islamic University MalaysiaKuala Lumpur53100Malaysia

The complex fluid-dynamic instabilities and shock waves occurring along the surface of a two-dimensional wedge at high values of the Mach number are studied here through numerical solution of the governing ***,a regression model is implemented to determine the pressure distribution for various Mach numbers and angles of *** Mach number spans the interval from 1.5 to *** wedge angles(θ)are from 5°to 25°.The pressure ratio(P2/P1)is reported at various locations(x/L)along the 2D *** results of the numerical simulations are compared with the regression model showing good agreement.

关键词： CFD analysis supersonic wedge angle Mach number

Energetics Constraint for Linear Disturbances Development

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Advances in Atmospheric Sciences 1993年第3期10卷 273-286页

作者： Y.L.McHall Department of Earth Atmospheric and Planetary Sciences MIT MA 02139 USA

In development of baroclinic disturbances, baroclinity of basic temperature field varies with conversion of available potential energy. The growth rate which depends on the baroclinity varies as well. However, in previous linear theories, the growth rate was considered constant, so development of disturbances was not constrained by energy sources in the linear theories. In terms of energy conservation and conversion in an isolated atmosphere, we may study the variations in the baroclinity and growth rate and draw the corresponding pictures of perturbation developments in the varying environments. The amplification for the most unstable Eady wave is discussed as an example. It will be found that growth of baroclinic perturbations constrained by energy conservation is significantly different from the growth at the initial constant rate after mature stage.

关键词： Linear disturbance development Eddy mean-field interaction APE conversion Energetics constraint Eady waves

Multiagent Reinforcement Learning:Rollout and Policy Iteration

在线全文

学校读者我要写书评

暂无评论

IEEE/CAA Journal of Automatica Sinica 2021年第2期8卷 249-272页

作者： Dimitri Bertsekas the Arizona State University(ASU) TempeAZ 85281 USAand also with Massachusetts Institute of Technology(MIT)CambridgeMA 02139

We discuss the solution of complex multistage decision problems using methods that are based on the idea of policy iteration(PI),i.e.,start from some base policy and generate an improved *** is the simplest method of this type,where just one improved policy is *** can view PI as repeated application of rollout,where the rollout policy at each iteration serves as the base policy for the next *** contrast with PI,rollout has a robustness property:it can be applied on-line and is suitable for on-line ***,rollout can use as base policy one of the policies produced by PI,thereby improving on that *** is the type of scheme underlying the prominently successful Alpha Zero chess *** this paper we focus on rollout and PI-like methods for problems where the control consists of multiple components each selected(conceptually)by a separate *** is the class of multiagent problems where the agents have a shared objective function,and a shared and perfect state *** on a problem reformulation that trades off control space complexity with state space complexity,we develop an approach,whereby at every stage,the agents sequentially(one-at-a-time)execute a local rollout algorithm that uses a base policy,together with some coordinating information from the other *** amount of total computation required at every stage grows linearly with the number of *** contrast,in the standard rollout algorithm,the amount of total computation grows exponentially with the number of *** the dramatic reduction in required computation,we show that our multiagent rollout algorithm has the fundamental cost improvement property of standard rollout:it guarantees an improved performance relative to the base *** also discuss autonomous multiagent rollout schemes that allow the agents to make decisions autonomously through the use of precomputed signaling information,which is sufficient to maintain the c

关键词： Dynamic programming multiagent problems neuro-dynamic programming policy iteration reinforcement learning rollout

Group Velocity of Anisotropic Waves-Part Ⅱ: Conservative Properties

在线全文

学校读者我要写书评

暂无评论

Advances in Atmospheric Sciences 1993年第4期10卷 407-414页

作者： Yong L.McHall Department of Earth Atmospheric and Planetary Sciences MIT MA 02139 USA

It has been argued in Part I that traditional expression of multidimensional group velocity used in meteorology is only applicable for isotropic waves. While for anisotropic waves, it cannot manifest propagation of waves group along the trajectory of a reference wave point, and varies with rotation of coordinates. The general mathematical expression of group velocity which may be used also for anisotropic waves has been derived in Part I. It will be proved that the mean wave energy, momentum and wave action density are all conserved as a wave group propagates at the general group velocity. Since general group velocity represents the movement of a reference point in either isotropic or anisotropic wave trains, it may be used to define wave rays. The variations of wave parameters along the rays in a slowly varying environment are represented by ray-tracing equations. Using the general group velocity, we may derive the anisotropic ray-tracing equations, which give the traditional ray-tracing equations for isotropic waves.

关键词： Wave ray Wave energy Wave action Wave momentum Ray-tracing equations

Large Scale Perturbations in Extratropical Atmosphere-Part Ⅰ: On Rossby Waves

在线全文

学校读者我要写书评

暂无评论

Advances in Atmospheric Sciences 1993年第2期10卷 169-180页

作者： Y. L. McHall Department of Earth Atmospheric and Planetary Sciences MIT MA 02139 USA

This study reexamines the propagation mechanism and geostrophic property of the classical two-dimensional Rossby waves in a non-divergent barotropic atmosphere. It will be found that propagation of large scale atmospheric waves depends crucially on horizontal divergence. A small Rossby number in Rossby waves is not sufficient for the waves to have a small ageostrophic component, because the two-dimensional classical Rossby waves do not manifest the geostrophic balance as good as observed in the atmosphere.

关键词： Th Large Scale Perturbations in Extratropical Atmosphere-Part On Rossby Waves

The Dialectic of Cross-Cultural Learning:What I Learned from Chinese Fellows

在线全文

学校读者我要写书评

暂无评论

China City Planning Review 2018年第3期27卷 27-30页

作者： Bish Sanyal SPURS/Humphrey Program MIT

This brief article summarizes my positive impression of the Chinese scholars over the last fourteen years in the Special Program for Urban and Regional Studies(SPURS) at the Massachusetts Institute of Technology, Cambridge, Massachusetts. In particular, I highlight the fellows' intellectual humility and passion for continuous learning from others. The fellows are, however, very comprehensive in the way they analyze all aspects of design problems and quite bold in their design imagination, compared to United States' graduate students who are more cautious to propose any radical change in urban form. Surprisingly, the Chinese fellows rarely address social equity issues in project design and do not usually worry about project implementation challenges, perhaps because they assume that such issues are to be addressed by policy makers at higher levels. In contrast, the U.S. students frequently raise issues of social equity but are hesitant to propose radical changes because of limited power of public planning institutions in the United States. Such contrasts in design thinking is ideal for comparative and critical analysis which has enriched the SPURS program.

关键词： SPURS intellectual humility comprehensive thinking equity

CONSENSUS FORMATION OF TWO-LEVEL OPINION DYNAMICS

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Scientia 2014年第4期34卷 1029-1040页

作者： Yilun SHANG SUTD-mit International Design Center Singapore University of Technology and Design20 Dover Drive138682Singapore

Opinion dynamics have received significant attention in recent years. This paper proposes a bounded confidence opinion model for a group of agents with two different confidence levels. Each agent in the population is endowed with a confidence interval around her opinion wiih radius αd or （1 - α）d, where α∈ （0, 1/2] represents the differentiation of confidence levels. We analytically derived the critical confidence bound dc = 1/（4α） for the two-level opinion dynamics on Z. A single opinion cluster is formed with probability 1 above this critical value regardless of the ratio p of agents with high/low confidence. Extensive numerical simulations are performed to illustrate our theoretical results. Noticed is a clear impact of p on the collective behavior： more agents with high confidence lead to harder agreement. It is also experimentally revealed that the sharpness of the threshold dc increases with a but does not depend on p.

关键词： social dynamics bounded confidence phase transition Monte Carlo simulation

Effect of fiber orientation in uni-directional glass epoxy laminate using acoustic emission monitoring

在线全文

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English Letters) 2011年第5期24卷 351-364页

作者： V.Arumugam S.Barath Kumar C.Santulli A.Joseph Stanley Department of Aerospace Engineering Anna University Department of Chemical Engineering Materials and EnvironmentUniversità La Sapienza mit Campus Anna University

Acoustic emission （AE） can be used for in situ structural health monitoring of the composite laminates. One of the main issues of AE is to characterize different damage mechanisms from the detected AE signals. In the present work, pure resin and GFRP composites laminates with different stacking sequences such as 0°, 90°, angle ply[±45°], cross-ply [0°/90°] are used to trigger different failure mechanisms when subjected to tensile test with AE monitoring. The study of failure mechanisms is facilitated by the choice of different oriented specimens in which one or two such mechanisms predominate. Range of peak frequencies in each orientation is investigated using FFT analysis. Fast Fourier Transform （FFT） enabled calculating the frequency content of each damage mechanism. Randomly selected hits from each range of peak frequencies for the specimens with different orientations subjected to tensile test with AE monitoring are analyzed using short time FFT （STFFT） analysis. STFFT analysis is used to highlight the possible failure mechanism associated with each signal. The predominance of failure modes in each orientation is useful in the study of discrimination of failure modes in composite laminates from AE data.

关键词： Composite materials Failure mechanisms Acoustic emissionFFT analysis STFFT analysis

The Blow-up Locus of Heat Flows for Harmonic Maps

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2000年第1期16卷 29-62页

作者： Jiayu Li Institute of Mathematics,Academia Sinica,Beijing 100080,P.R.ChinaGang Tian Department of Mathematics,mit,Cambridge,MA 02139,USA Institute of Mathematics Academia Sinica Beijing 100080 P.R. China Department of Mathematics MIT Cambridge USA

Let M and N be two compact Riemannian *** uk（x,t）be a sequence of strong stationary weak heat flows from M×R+ to N with bounded *** that uk→u weakly in H1.2（M×R+,N）and that ∑t is the blow-up set for a fixed t>*** this paper we first prove ∑t is an Hm-2-rectifiable set for almost all t ∈ R+.And then we prove two blow-up formulas for the blow-up set and the limiting *** the formulas,we can see that if the limiting map u is also a strong stationary weak heat flow,∑t is a distance solution of the（m-2）-dimensional mean curvature flow[1]. If a smooth heat flow blows-up at a finite time,we derive a tangent map or a weakly quasi-harmonic sphere and a blow-up set ∪t∑t×{t}.We prove the blow-up map is stationary if and only if the blow-up locus is a Brakke motion.

关键词： Heat flow Mean curvature flow Brakke motion Blow-up locus