I SHOULD like first to say how much I appreciate the honour of being invited to deliver the Wright Brothers Lecture. To anyone whose work is associated in any way with the…
Abstract
I SHOULD like first to say how much I appreciate the honour of being invited to deliver the Wright Brothers Lecture. To anyone whose work is associated in any way with the aeronautical sciences, it must be a source of pride and gratification to be invited to be a chief participant in one of the greatest occasions in the world of aeronautical research, an occasion designed in honour of the two great pioneers, Wilbur and Orville Wright. In my own case these feelings are shared with a feeling of humility and of my own unworthiness for the task.
Abstract
Purpose
Siphon-based deadlock control in a flexible manufacturing system (FMS) suffers from the problems of computational and structural complexity since the number of siphons grows exponentially with respect to the size of its Petri net model. In order to reduce structural complexity of a supervisor, a set of elementary siphons derived from all strict minimal siphons (SMS) is explicitly controlled. The purpose of this paper is through fully investigating the structure of a class of generalized Petri nets, WS3PR, to compute all SMS and a compact set of elementary siphons.
Design/methodology/approach
Based on graph theory, the concepts of initial resource weighted digraphs and restricted subgraphs are proposed. Moreover, the concept of augmented siphons is proposed to extend the application of elementary siphons theory for WS3PR. Consequently, the set of elementary siphons obtained by the proposed method is more compact and well suits for WS3PR.
Findings
In order to demonstrate the proposed method, an FMS example is presented. All SMS and elementary siphons can be derived from initial resource weighted digraphs. Compared with those obtained by the method in Li and Zhou, the presented method is more effective to design a structural simple liveness-enforcing supervisor for WS3PR.
Originality/value
This work presents an effective method of computing SMS and elementary siphons for WS3PR. Monitors are added for the elementary siphons only, and the controllability of every dependent siphon is ensured by properly supervising its elementary ones. A same set of elementary siphons can be admitted by different WS3PR with isomorphic structures.
Details
Keywords
Jinghan Xu, Shengguo Xia, Lixue Chen, Anbang Gu, Hongdan Yang and Chengxian Li
The purpose of this paper is to investigate the moving boundary conditions on the sliding armature and rail (A/R) interface. As the computational domains involve both moving and…
Abstract
Purpose
The purpose of this paper is to investigate the moving boundary conditions on the sliding armature and rail (A/R) interface. As the computational domains involve both moving and stationary conductors, Lagrangian description and backward difference schemes are adopted for spatial and temporal discretization, arising discontinuities in variables. The proposed formulation can compute the current distribution under high velocities (∼km/s) without numerical oscillations and avoids mesh re-generation, saving computational resources.
Design/methodology/approach
The governing equations in Lagrangian description, backward difference schemes and derivations of moving boundary conditions are shown in detail. The interface matrix is explicitly enforced on the whole domain matrix and pseudocodes are presented for implementation. Moreover, shifted interpolated quantity method is proposed to deal with unevenly sized mesh, which can calculate acceleration scenarios and save computation resources under high velocities. Comparative calculations with previous methods under low velocities are conducted to verify the correctness of computational and physical models.
Findings
The current distributions with constant velocities are consistent with previous two-dimensional and low-velocity studies, further verifying the correctness of the method. The three-dimensional high-velocity results show that the current tends to concentrate near the trailing edge of A/R interface and diffuses into the bulks over time, with higher velocity contributing to less significant current diffusion. The velocity skin effect precedes the magnetic diffusion, conductivity and other factors that influence the current distribution.
Originality/value
The proposed methods can compute the current distributions in railgun under velocity accelerated to over 2,000 m/s, and the results provide more comprehensive understandings of the current evolution process under velocity skin effect in railgun.
Details
Keywords
Shiqian Ni, Yanqin Zhang and Zhen Quan
When the clearance oil film of hydrostatic bearing friction pair is in critical lubrication state, the phenomenon of zero flow of local lubricating oil will aggravate the oil film…
Abstract
Purpose
When the clearance oil film of hydrostatic bearing friction pair is in critical lubrication state, the phenomenon of zero flow of local lubricating oil will aggravate the oil film temperature rise, which needs to be solved.
Design/methodology/approach
In this paper, the critical lubrication parameter equation and the oil film temperature rise mathematical model are derived for the new type q1-205 double rectangular cavity hydrostatic bearing. Based on a combination of theoretical analysis, simulation and experimental verification, this paper analyzes the flow characteristics and temperature rise characteristics of the lubricating oil when the hydrostatic bearing is in a critical lubrication state under different operating conditions and finally obtains the critical lubrication state of the oil film.
Findings
This study found that the numerical simulations and the derived formulas agree with the results. When the oil film is in critical lubrication, the cross-section side flow of the oil side is almost zero. The heat cannot be taken away in time, resulting in the local temperature rise of the oil film, which causes serious heat accumulation.
Originality/value
It is concluded that the operating condition parameters corresponding to the critical lubrication state provide a theoretical basis for the selection of actual hydrostatic bearing operating conditions, which is of great scientific significance.
Details
Keywords
Chang N. Zhang and Cungang Yang
Information flow analysis is a necessary step to determine the information security for a given system. In this paper, we introduce an object oriented role‐based access control…
Abstract
Information flow analysis is a necessary step to determine the information security for a given system. In this paper, we introduce an object oriented role‐based access control model (ORBAC) and illustrate that the confinement problem may occur on the ORBAC based system. In order to deal with the problem, a technique called information flow analysis is proposed. Moreover, under the principle of mandatory access control (MAC) security policy, a role set assignment method is developed and proved to solve the confinement problem on ORBAC.
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Keywords
M.K. Loganathan and O.P. Gandhi
Reliability assessment does require an effective structural modelling approach for systems, in general and manufacturing systems are no exception. This paper aims to develop it…
Abstract
Purpose
Reliability assessment does require an effective structural modelling approach for systems, in general and manufacturing systems are no exception. This paper aims to develop it for large manufacturing systems using graph models, a systems approach.
Design/methodology/approach
Structural graph models for reliability at various hierarchical levels are developed by considering a CNC cam shaft grinding machine. The system reliability expression is obtained by converting the reliability graphs into equivalent matrices, which helps to evaluate and analyse system.
Findings
Using the obtained reliability expressions at various hierarchical levels of the system, it is possible not only to evaluate its reliability from structure point of view but also to identify weak structural elements from reliability point of view.
Research limitations/implications
The approach can be extended to include the influence of other parameters, such as human, component and environment, etc., on the system reliability.
Practical implications
The approach helps to design and develop manufacturing systems from reliability consideration by assessing their possible alternatives among these.
Originality/value
The suggested methodology is useful for reliability evaluation of large and complex manufacturing systems.
Details
Keywords
Varsha Bhambhani, Luis Valbuena‐Reyes and Herbert Tanner
The purpose of this paper is to develop a methodology for the design of cellular neural networks with interconnection topologies optimized and suitable for spatially distributed…
Abstract
Purpose
The purpose of this paper is to develop a methodology for the design of cellular neural networks with interconnection topologies optimized and suitable for spatially distributed implementation.
Design/methodology/approach
The authors perform combinatorial optimization on the neural network's topology to obtain a sparser network, in which the links between the components of the network that reside in different physical locations are minimized. The approach builds on existing computationally efficient tools for the design of cellular neural networks and uses the concept of the network's stability parameters to assess the performance of the network prior to testing.
Findings
It turns out that the sparser cellular neural networks thus produced exhibit performance that can be on par with that of networks with full connectivity, and that for implementations of modest size, communication delays are not that significant to affect the stability of the dynamical system.
Originality/value
The novelty of the proposed approach lies in the formulation of the combinatorial optimization problem in a way that trades‐off network performance for communication overhead, and the use of this method for the physical implementation of associative memories across different interconnected processors.
Details
Keywords
Use of film at the R.A.E. cinematography is indispensable in research and development, particularly in a field such as aeronautics. For purposes of recording and analysis…
Abstract
Use of film at the R.A.E. cinematography is indispensable in research and development, particularly in a field such as aeronautics. For purposes of recording and analysis, especially in circumstances where the human eye is likely to err or is unable to be present (for example the interior of a wind tunnel), the cine film provides a permanent assessable record of exactly what happens, which is invaluable in terms of ease of reference and scope of coverage.
AERONAUTICS owes much to the selfless devotion and enthusiasm of its early pioneers. As was noted by the author in the Fourth Lanchester Memorial Lecture,1 Queen Mary College can…
Abstract
AERONAUTICS owes much to the selfless devotion and enthusiasm of its early pioneers. As was noted by the author in the Fourth Lanchester Memorial Lecture,1 Queen Mary College can claim to have the oldest established University Department of Aeronautical Engineering in the country due to the pioneer work of Dr A. P. Thurston, a graduate of the College, t It was in 1908 that he decided to establish an Aeronautical Laboratory there. He inspired the interest and support of like‐minded friends and Mr P. Y. Alexander, in particular, contributed a major part of the funds required to equip the laboratory. From Professor J. L. S. Hatton, the then Principal of the College, Dr Thurston received warm encouragement and the space for the venture, but College funds were then less than adequate for its longer established activities, and so the College could not afford to offer financial support to the new venture in its early days.