ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677239

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The problem of laminar mixed convection in a horizontal dimensional channel with one or two protruded heat sources on one of the walls is studied numerically. The top surface of the protruding heat source is assumed to be isothermal while the rest of the surfaces and the walls are assumed to be adiabatic. The governing dimensionless equations in terms of vorticity, stream function and temperature are solved numerically by the cubic spline collocation method. The effects of the mixed convection parameter,Gr/Re2, height of thermal sources,D/H, and the interaction of the protruded heat sources on fluid and heat transfer characteristics of air in a horizontal channel are presented. The results show that the heat transfer rates increase as theGr/Re2andD/Hare increased because of the increase of the buoyancy effects. The results also show that the effects of the interaction of the two protruding heat sources are remarkably affected by the flow field and temperature field in the horizontal channel.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677240

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A language called aFP, which is a dialect of FP containing many desirable parallel constructs, is used to derive systolic algorithms. We view aFP programs from three levels. Programs at the object level map objects to objects. The structure level deals with the structures of objects, mapping structures to structures. The sequencing level programs map sequenced structures to sequenced structures and have corresponding systolic algorithms. Sequenced structures provide information about the moving sequencing of the objects (I/O data). These three levels help the synthesis of systolic algorithms. Families of complex systolic arrays can be constructed from simpler ones systematically. Examples are given to illustrate the derivation of systolic algorithms from aFP programs.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677241

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Numerical experiments were performed by a computer program TRUBAL, a discrete element model, to study the effect of particle friction and initial fabric on the evolution of fabric during shear deformation. Assemblies with lower inter‐particle friction had lower stiffness and yielded at lower shear stresses as compared with those with higher ones. Assemblies with lower inter‐particle friction dilated less and slower than those with higher ones. The anisotropic level that a fabric could reach depended on the inter‐particle friction. Assemblies with higher inter‐particle friction developed more anisotropic fabric. Depending on the shearing direction relative to the fabric axis, initial fabric influenced the mechanical behavior and fabric evolution of assemblies.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677242

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper proposes a penalty function to be used for constrained optimization problems. The proposed penalty function is based on two special types of the hyperbolic curve. For the equality constraint, the penalty function is√x2+t2, wherex= pg(X), g(X)=0 is the constraint,tis a shape parameter,pis a scale factor, andXcontains the design variables. For the inequality constraint, the penalty function is√x2+t2– x, wherex=pg(X), andp >0 is the constraint forg(X) > 0, orp <0 forg(X)≤0. These penalty functions have the advantages of being defined everywhere, accurate and differentiable. Two extended penalty functions are also proposed to dominate the infinite negative objective function in some cases. One is of the power type, another is of the exponential type. These two extended penalty functions are continuous up to their second derivatives. Therefore, they can be used in almost all of the optimization methods.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677243

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This study presents an electrochemical investigation of the corrosion (CF) behavior of 2024‐T3 aluminum alloy, under a constant deflection bending condition with a pulsating tension stress form. The investigation was conducted using both specimens that were anodized in a 3.5% NaCl solution to form a thick porous film and un‐anodized specimens. The Ecorrvariations of both types of specimens during the CF process show similarities and differences, and apparent differences also exist between the two types of 2024‐T3 alloy and the high carbon steel. Their behavior presumably can be explained by the ‘cracking of the anodic film’ and the theory of ‘imperfect recovery of the surface film’. It is suggested that the Ecorrmonitoring technique can be useful for estimating the remaining CF life of existing structural parts made of this alloy or other Al alloys, anodized or unanodized. Furthermore, the T3 temper provides a microstructure which may retard main crack formation and penetration in the CF process of the anodized alloy. This partly lessens the negative effect of the anodic film, for being readily‐crackable.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677244

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper addresses the problem of assigning a task with precedence constraints to a distributed computing system. A cost function considering communication overhead and idle time is adopted to measure the performance of the task assignment. The task assignment in this paper determines not only the assignment of modules but also the sequence of messages transmission to balance processor loading and diminish communication overhead. The search for the optimal task assignment with precedence constraints is known to be NP‐complete [7] in the strong sense. A heuristic algorithm with polynomial time complexity is proposed in order to effectively solve the task assignment problem. The experimental results reveal that the proposed approach is able to obtain a near‐optimal or even the optimal task assignment.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677245

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A robust nonlinear control strategy is proposed to deal with the control problem of robotic manipulators with second order nonlinear actuator dynamics. The control scheme is composed of two stages: the nominal dynamics stage and the perturbed dynamics stage. The control at the nominal dynamics stage and the perturbed dynamics stage. The control at the nominal dynamics stage is aimed at exact linearization and input/output decoupling of the nonlinear actuator‐manipulator system in the task space by nonlinear feedback and nonlinear state space diffeomorphic transformations. The resulting closed‐loop nominal system is capable of precise trajectory following in a desired second‐order linear behavior. To compensate uncertainties in a practical situation, an optimal error correcting compensator is designed to achieve some robustness at the perturbed dynamics stage. Simulation study of a cylindrical robot is given to illustrate the effectiveness of the proposed scheme.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677246

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

It is well‐known that bank‐to‐turn (BTT) control offers potential improvement in missile performance. For a highly maneuverable bank‐to‐turn missile, the dynamics of the pitch, roll, and yaw axes are not only cross‐coupled but also nonlinear, especially when high roll rates are involved. However, most BTT autopilots proposed to date rely on linear methods, either the classical SISO techniques or the state‐space methods of modern control theory. These linear approaches restrict their applicability to either small or slowly varying roll rates. The unmodelled effects of severe non‐linearities inherent in missile dynamics, particularly for asymmetric air‐frames, still remain one of the most critical issues in BTT autopilot design. In this paper, an optimal nonlinear tracking control using polynomial feedback is developed for BTT autopilots. Numerical simulations based on a 6 DOF nonlinear missile model are presented to demonstrate the effectiveness of the proposed nonlinear control technique.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677247

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The dynamic model of a manipulator system is a time‐varying highly nonlinear coupling equation set. When the moving speed increases or the payload, compared to its own weight, is no longer small, the performance of the conventional control schemes is not satisfactory for precision industrial application. Here a new adaptive control approach is developed for the manipulators to solve these problems. This algorithm directly uses a nonlinear dynamic model in the controller design to account for the nonlinear effects of the system. The least‐square time‐varying parameter identification scheme has been used to identify the change in configuration and payload. The simulation results show that this new approach has a very good trajectory tracking performance.

ISSN:0253-3839    

DOI:10.1080/02533839.1990.9677248

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor