Search results

The purpose of this paper is to present a solution space searching method to study the initial design of interplanetary low thrust gravity assist trajectory.

For reducing the complexity and nonlinearity of the initial design problem, a sixth degree inverse polynomial shape based approach is brought. Then some improvements are provided for solving the parameters in the shape function and a quasi‐lambert solver is brought through the shape based method, the thrust profile can be generated under the given time of flight, boundary states including positions and velocities for low thrust phase. Combining gravity assist model, the problem is summarized and an improved pruning technique is used for searching the feasible solution space for low thrust gravity assist trajectory.

Using the solution space searching method, the feasible solution region would be generated under the given mission condition. The treatment about gravity assist demonstrates more accurate than previous method. Also another advantage is that the searching method can be used to design different types of mission trajectory, including flyby and rendezvous trajectories.

The method can be used as an efficient approach to search the feasible region for the complex low thrust gravity assist trajectory, and it can provide appropriate initial guesses for the low thrust gravity assist trajectory in mission design phase.

Feasible solution space would be obtained through the searching method. The quasi‐Lambert solver in the paper is found under the shape‐based method and relative improvement, and it shows its availability during the searching process. Through mission trajectory design, the effectiveness of the method is shown.

The purpose of this paper is to study the application of the planetary aerogravity‐assist (AGA) technique to the interplanetary transfer mission with low‐thrust engine, and the design and optimization approach of low‐thrust AGA trajectory.

In the research, the transfer trajectory with planetary AGA maneuver is analyzed first, the maximum atmospheric turn angle and the matching condition for AGA trajectory is derived out, which is the significant principle for AGA trajectory design and studies. Then, a design and optimization approach for interplanetary low‐thrust trajectory with AGA maneuver is developed. The complicated design problem is transformed into a parameter optimization problem with multiple nonlinear constraints by using calculus of variations and the matching condition associated with AGA trajectory. Furthermore, since the optimization problem is very sensitive to the launch date and AGA maneuver parameters, three ordinal sub‐problems are reformulated to reduce the sensitivity. Finally, a direct/indirect hybrid approach is utilized to solve these sub‐problems.

The planetary AGA maneuver is feasible and effective in decreasing the propellant consumption and flight time for interplanetary low‐thrust mission and provides better performance than pure planetary gravity assist. Moreover, the proposed approach is effective to design and optimize the low‐thrust transfer mission with AGA maneuver.

In further research, some simple preliminary design approaches for interplanetary low‐thrust trajectory with AGA maneuver are required to developed, which can provide a good initial conjecture for a hybrid optimization algorithm.

The paper provides the matching condition for interplanetary AGA transfer trajectory by analyzing some characteristics of planetary AGA maneuver, and presents an effective approach to design and optimize interplanetary low‐thrust AGA trajectory.

In this paper, we present a concept for multi‐material solid freeform fabrication of heterogeneous components. This concept features hopper‐nozzles designed for depositing thin layers of multiple patterned materials followed by selective laser sintering for consolidation to desired densities. Although prior work on the design of small‐scale nozzles for powder delivery is lacking, our design is guided by background theory for particle flow through industrial hoppers. Experimental guidelines for the delivery of powders in the 10 to 125 μm range from 0.5 to 2 mm hopper‐nozzle orifices are presented.

The high viscosity of heavy oil is a serious problem for the recovery efficiency of this resource by conventional methods. Since a few past years, the vapour extraction process (VAPEX) has emerged as a promising technology for the recovery of heavy oils and bitumen in reservoirs where thermal methods, such as steam-assisted gravity drainage cannot be applied. Recently, the use of CO₂ as a solvent is believed to make the VAPEX process more economical and environmentally and technically attractive. Convective mixing at the edge of the solvent chamber enhances mass and heat transfer rates which increases oil mobility and production rate. The objective of this study is to analysis the influence of the main controlling parameters, such as buoyancy ratio and Prandtl number on the flow patterns and mass transfer mechanism, in order to understand the thermal effect on the dissolution of carbon dioxide through natural convection at the boundary layer of solvent chamber of CO₂-VAPEX process. The numerical results obtained by lattice Boltzmann method show that the flow structure and the mass transfer mechanism are strongly depend on the buoyancy ratio and Prandtl number. So, the performances of CO₂-VAPEX process are strongly influenced by thermal effect; and we found that it has negative consequences on this process.

IN a departure from usual practice this issue concentrates to a large extent upon a single subject — Mechanical Handling. It coincides with that industry's exhibition at Earls Court from the 9th to 19th of this month, to be opened by the Rt. Hon. Christopher Chataway, M.P., Minister for Industrial Development. In consequence it was necessary to defer some regular features for a time, for which we apologise.

Vision systems are achieving the ultimate respectability by adoption in the motor car industry. This linescan application checks bolts going into an assembly machine at Ford Bridgend.

THE subject of retractable undercarriages has already been dealt with before the Royal Aeronautical Society as well as in numerous technical articles. This article endeavours therefore to deal with some aspects of the matter which have not been discussed very widely in the past. Reference is made to the problem as it affects the aircraft designer rather than the specialist undercarriage or hydraulic engineer, and stress is laid on the geometrical and installational problems rather than the mechanical design aspects of the equipment itself.

Given the current global climate change concerns, environmental goods (EGs) exported from developing countries have been declining in recent years despite the growing economic importance of these nations. Researchers believe that the problem lies in the nature of technology and border-related constraints.

This research work considers a relatively modern approach known as the “stochastic frontier gravity-type model” to examine opportunities and challenges involving Bangladesh EGs exports.

It is evident that Bangladesh, despite its close links to the other East Asian economies, has not realized the true potential of EGs exported between 2001 and 2015.

This study highlights the removal of border-related constraints that will improve the country’s exports. The findings will make it possible to explain the constraints of the export of environmental goods.

An aircraft landing gear bracing strut comprises two arms, pivoted to the aircraft and the landing gear, respectively, and also pivoted together about an axis lying outside the plane containing the pivotal axes of the two arms to the aircraft and landing gear when the latter is extended, wherein one of the arms constitutes the body of a fluid operated jack, of which the piston rod is coupled to the other arm through a connecting link. In FIG. 1, the wheel strut 1 is pivoted to an aircraft wing at C, and braced by a strut 3 breakable at D and pivoted to the wing at A and to the strut 1 at B. In FIG. 2, the strut 3 comprises two arms 4, 5 hinged on a pin 6. The arm 4 forms a cylinder in which works a piston 12, the rod 13 of which is universally jointed to a coupling rod 15 pivoted to the arm 5 at 16. The universal joint runs on a roller 17 in a guide 18 formed in the arm 4. Admission of fluid under pressure to port 21 and connexion of port 22 exhaust breaks and folds the strut, retracting the undercarriage, and vice versa. An abutment 19 on arm 5 abuts a strengthened portion 20 on arm 4 when the strut is extended. The cylinder is formed with members 23, and the piston with a sliding portion 24 as in Specification 527,225 to form a down‐lock. When the strut is fully opened, the piston actuates a member 26 to give an indication to the pilot. Specification 551,673 also is referred to.