小展弦比飞翼布局新型嵌入面航向控制特性研究

在小展弦比飞翼布局机翼外侧上/下表面分别设计了一组中等后掠角嵌入面,并对其跨声速时的航向控制效果及其流动机理进行了风洞试验和数值模拟研究。计算和试验结果表明,上嵌入面可在小迎角范围通过轴向力和侧向力的共同作用提供稳定的偏航力矩,实现航向控制;当α>6°时,由于嵌入面逐渐处于前缘涡的影响范围内,在前缘涡的吸力作用下,嵌入面航向控制效果迅速下降,直至失效,且进行航向控制时存在不利的滚转耦合;下嵌入面可在全迎角范围内提供稳定的偏航力矩,实现航向控制;通过在小迎角范围内使用上嵌入面,α>6°时使用下嵌入面,不仅可在全迎角实现航向控制,且不影响飞机的隐身性能。

完全二部图的少面数强嵌入

通过调整完全二部图G的少双圈覆盖中的某些圈 ,可得到一个强嵌入 ,不同的双圈覆盖可以得到不同的强嵌入 .最后作为推论 ,得到完全三部图Kn ,n ,n可以强嵌入到某一亏格的曲面上 .

极大平面图的面嵌入图

定义了极大平面图的面嵌入图的概念,分析了这类极大平面图的结构和性质,给出了一类最小度等于5的四可着色的极大平面图.

飞翼布局阻力类偏航操纵装置操纵特性分析

飞翼布局取消了常规的垂尾和方向舵,存在较严重的航向操纵与控制问题,需要重点掌握偏航操纵舵面的配置特点与操纵特性.针对飞翼布局最常采用的两种阻力类偏航操纵装置:开裂式方向舵和嵌入面,介绍了研究现状、受力特点,利用数值仿真方法,详细分析了偏航操纵特性、三轴操纵耦合特性以及对气动特性和稳定特性的影响规律,对比了这两种舵面在操纵特性方面的共同点和差异性,并揭示了内在的影响机理.可为解决飞翼布局偏航操纵问题以及阻力类偏航操纵装置的工程化应用提供基础.

小展弦比无尾飞翼式无人机控制律研究与仿真

无尾飞翼布局无人机具有高气动效率、结构强度以及良好隐身特性等突出优势,但也具有控制性能不佳的缺点。以某型小展弦比飞翼式无人机为研究对象,基于CFD仿真计算和风洞试验得到的气动数据,分析该型无人机的稳定特性,讨论了嵌入面式操纵面对小展弦比无人机的优劣。主要分析该无人机纵向模态,进而设计了飞行控制系统,搭建了飞机模型,并使用MATLAB仿真飞行过程,验证了控制系统的可行性,为飞翼无人机控制系统的设计提供参考。

无尾布局嵌入式舵面的大迎角纵向操纵能力研究

针对某前掠翼翼身融合无尾布局由鸭面与尾舵组成的纵向基本控制舵面在大迎角状态操纵效率降低的问题,采用数值模拟方法研究一种机身下表面嵌入式新概念纵向操纵舵面实施大迎角纵向操纵补充的可行性。提出了嵌入式舵面的设计思想,研究了嵌入式舵面高度、偏度及其与尾舵组合时的相对位置等参数影响,提出了嵌入式舵面的设计原则、流动机理以及提供低头力矩增量的作用原理。研究结果表明:嵌入式舵面是无尾布局飞机大迎角纵向操纵的高效补充措施,单独使用,最大可提供约平衡10°迎角的低头操纵力矩,并对升阻特性影响很小;与尾舵组合使用,在研究迎角范围内(迎角α≤32°),可提供约6°迎角的低头平衡力矩增量,且对升阻性能产生有利影响。本文工作可为其他翼身融合无尾布局的气动舵面设计提供借鉴。

无尾布局纵向操纵的嵌入式舵面概念研究

基于提高W型无尾翼身融合布局大迎角俯仰操纵能力的设想,探索一种机身下表面嵌入式俯仰操纵舵面的新概念。采用CFD方法,研究纵向两个位置、两种弦向长度组成的四种机身下表面嵌入式舵面构型对无尾气动布局性能的影响及其流动机理,分析了嵌入式舵面提供纵向操纵控制的作用原理。研究结果表明,下表面嵌入式舵面可作为无尾布局大迎角俯仰操纵的有效补充措施,为无尾布局大迎角俯仰操纵提供了新的技术途径,具有进一步深入研究的价值。

Microstructure evolution of hot pressed AZ91D alloy chips reheated to semi-solid state

AZ91D magnesium alloy chips, which were directly collected on the spot of machining process, were recycled to prepare billet via hot pressing for semi-solid processing. The semi-solid microstructure evolution of the billet during reheating was investigated. The results indicate that there are three stages during reheating to semi-solid state: the dissolution of Mg17Al12 and diffusion of Al into α-Mg matrix, the melting of the region with high content of solute and formation of isolated solid particles, and spheroidization and growth of solid particles. Meanwhile, a number of entrapped liquid droplets form within solid particles. In addition, the number and size of entrapped liquid droplets rely on the holding time in the semi-solid temperature range. With increasing isothermal holding time, the solid fraction remains unchanged when the solid-liquid system reaches the dynamic equilibrium at last, while the solid particles become more globular and the average size of solid particles increases owing to the decreasing of interfacial energy and the effect of interfacial tension.

Flexibility of Embeddings of a Halin Graph in the Torus

In this paper we show that the face-width of any embedding of a Halin graph（a type of planar graph） in the torus is one, and give a formula for determining the number of all nonequivalent embeddings of a Halin graph in the torus.

Structures of Facial Cycles and C-bridges of Embedded Graphs with Locally LEW-embedding Properties

In this paper, we show that for a locally LEW-embedded 3-connected graph G in orientable surface, the following results hold： 1） Each of such embeddings is minimum genus embedding; 2） The facial cycles are precisely the induced nonseparating cycles which implies the uniqueness of such embeddings; 3） Every overlap graph O（G, C） is a bipartite graph and G has only one C-bridge H such that C U H is nonplanar provided C is a contractible cycle shorter than every noncontractible cycle containing an edge of C. This extends the results of C Thomassen＇s work on LEW-embedded graphs.

3-D Scattering of Obliquely Incident Plane P Waves by Alluvial Valley Embedded in Layered Half-Space

The indirect boundary element method(IBEM) was established to solve the problem of 3-D seismic responses of 2-D topographies,by calculating the free-field responses with the direct-stiffness method and simulating the scattering wave fields with the dynamic Green's functions of moving distributed loads.The proposed method yields accurate results,because the 3-D dynamic stiffness matrixes used are exact and the fictitious moving distributed loads can be acted directly on the interface between the alluvial valley and the layered half-space without singularity.The comparison with the published methods verifies the validity of the proposed method.And the numerical analyses are performed to give some beneficial conclusions.The study shows that 3-D scattering by an alluvial valley is essentially different from the 2-D case,and that the presence of soil layer affects not only the amplitude value of surface displacements but also the distribution of surface displacements.

Performances of Flat Plate Pulsating Heat Pipes

Flat plate pulsating heat pipe is useful for hot spot heat spreader. Two kinds of flat plate spreader of pulsating heat pipe are designed, fabricated and experimented. For the embedded circular capillary type, the transferred heat flux could reach 32 W/cm2, the smallest thermal resistance for acetone, methanol and FC-72 were respectively 0.50, 0.57 and 0.40℃/W. While for the square capillary type, the transferred heat flux could reach 26 W/cm2, the equivalent thermal conductivity could reach 3211 W/（m. ℃）. There are ranges of optimal transferred power and filling ratio for different working liquid. If the transferred power is constant, changing the heating area and the place has little effects on the performance.

An Interpolation Theorem for Near-Triangulations

A near-triangular embedding is an embedded graph into some surface whose all but one facial walks are 3-gons. In this paper we show that if a graph G is a triangulation of an orientable surface Sh, then G has a near-triangular embedding into Sk for k=h, h＋1,...1,[β（G）/2], where β（G） is the Betti number of G.

The semi-global isometric embedding of surfaces with Gaussian curvature changing sign cleanly

A new method to solve the Gauss-Codazzi system is given in which we transform the linearized system to a partial differential equation of second order, and by the method we solve the problem of semi-global isometric embedding of surfaces with Gaussian curvature changing sign cleanly.

Embedding Generalized Petersen Graph in Books

A book embedding of a graph G consists of placing the vertices of G on a spine and assigning edges of the graph to pages so that edges in the same page do not cross each other. The page number is a measure of the quality of a book embedding which is the minimum number of pages in which the graph G can be embedded. In this paper, the authors discuss the embedding of the generalized Petersen graph and determine that the page number of the generalized Petersen graph is three in some situations, which is best possible.

Embedding Periodic Maps on Surfaces into Those on S^3

Call a periodic map h on the closed orientable surface Σg extendable if h extends to a periodic map over the pair(S3, Σg) for possible embeddings e : Σg→ S3. The authors determine the extendabilities for all periodical maps on Σ2. The results involve various orientation preserving/reversing behalves of the periodical maps on the pair(S3, Σg). To do this the authors first list all periodic maps on Σ2, and indeed the authors exhibit each of them as a composition of primary and explicit symmetries, like rotations, reflections and antipodal maps, which itself should be interesting. A by-product is that for each even g,the maximum order periodic map on Σg is extendable, which contrasts sharply with the situation in the orientation preserving category.

A CHARACTERIZATION OF THE EMBEDDABILITY OF GRAPHS ON THE SURFACE OF GIVEN GENUS

The embedding technique based on an operator appeared in [Liu, Y. P., Scientia Sinica, Special Issue on Math,1 (1979),191-201 (in Chinese)] for determining the maximum non-orientable genus of a graph is developed to obtain the general theorem which presents a necessary and sufficient condition for a graph to be embeddable into either the orientable or the non-orientable surface of genus k. Furthermore,the greatest lower bound of the lengths of genus ranges of the class of nonplanar graphs which are up-embeddable is also obtained.

Pfaffian graphs embedding on the torus

An orientation of a graph G with even number of vertices is Pfaffian if every even cycle C such that G-V(C) has a perfect matching has an odd number of edges directed in either direction of the cycle. The significance of Pfaffian orientations stems from the fact that if a graph G has one, then the number of perfect matchings of G can be computed in polynomial time. There is a classical result of Kasteleyn that every planar graph has a Pfaffian orientation. Little proved an elegant characterization of bipartite graphs that admit a Pfaffian orientation. Robertson, Seymour and Thomas (1999) gave a polynomial-time recognition algorithm to test whether a bipartite graph is Pfaffian by a structural description of bipartite graphs. In this paper, we consider the Pfaffian property of graphs embedding on the orientable surface with genus one (i.e., the torus). Some sufficient conditions for Pfaffian graphs on the torus are obtained. Furthermore, we show that all quadrilateral tilings on the torus are Pfaffian if and only if they are not bipartite graphs.

Embedding compact surfaces into the 3-dimensional Euclidean space with maximum symmetry

The symmetries of surfaces which can be embedded into the symmetries of the 3-dimensional Euclidean space R3 are easier to feel by human＇s intuition. We give the maximum order of finite group actions on （R3 E） among all possible embedded closed/bordered surfaces with given geometric/algebraic genus greater than 1 in R3. We also identify the topological types of the bordered surfaces realizing the maximum order, and findsimple representative embeddings for such surfaces.

Embedded Surfaces for Symplectic Circle Actions

The purpose of this article is to characterize symplectic and Hamiltonian circle actions on symplectic manifolds in terms of symplectic embeddings of Riemann surfaces.More precisely, it is shown that(1) if(M, ω) admits a Hamiltonian S^1-action, then there exists a two-sphere S in M with positive symplectic area satisfying c1(M, ω), [S] > 0,and(2) if the action is non-Hamiltonian, then there exists an S^1-invariant symplectic2-torus T in(M, ω) such that c1(M, ω), [T] = 0. As applications, the authors give a very simple proof of the following well-known theorem which was proved by Atiyah-Bott,Lupton-Oprea, and Ono: Suppose that(M, ω) is a smooth closed symplectic manifold satisfying c1(M, ω) = λ· [ω] for some λ∈ R and G is a compact connected Lie group acting effectively on M preserving ω. Then(1) if λ < 0, then G must be trivial,(2) if λ = 0, then the G-action is non-Hamiltonian, and(3) if λ > 0, then the G-action is Hamiltonian.