Aircraft Engineering and Aerospace Technology

Local structural nonlinearities identification based on the minimum error linear frequency response function : Table of Contents

Hamed Kashani, A.S. Nobari — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to consider the dynamic characteristics identification of local structural nonlinearities. Design/methodology/approach – Proposed identification method is based on minimum error linear frequency response function (MELF). Two different techniques are developed to extract nonlinear element's dynamic behavior from MELF. The first method, in which no pre-assumed model is considered for the nonlinearity mechanism behavior, is called “direct identification method.” The second method is “model based identification method.” Findings – Cubic stiffness dynamic characteristics are identified using the proposed techniques as a case study. Originality/value – The paper shows that the proposed identification technique is simple and free of any sophisticated measurement hardwares and constraints, which is required by most of the methods proposed so far.

Atomistic simulation of micro-scale adiabatic piston problem : Table of Contents

Nevsan Sengil, Firat Oguz Edis — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to demonstrate the utilization of the direct simulation Monte Carlo (DSMC) method for moving-boundary/deforming-domain micro-scale gas flow problems. Furthermore, a hydrodynamic model, proposed in the literature, is used to compare its results with those obtained using the DSMC method. Design/methodology/approach – A micro-scale adiabatic piston problem is analyzed using a parallel DSMC implementation for deforming domains. Initially, pressures at both sides of the piston wall are different. Consequently, frictionless piston moves toward low-pressure compartment, keeps oscillating from one side to the other. Eventually, the piston reaches the “Mechanical equilibrium” state. Although the temperatures are different, pressures are equal at this state. The unsteady problem is analyzed until it reaches this state. Three test cases, all with the same initial conditions but different piston masses are analyzed. The time variation of the piston position, conditions in the compartments separated by the piston, are presented and compared with the results obtained from a hydrodynamic model proposed in the literature. Findings – The results show that the DSMC and hydrodynamic results agree for the case where the piston mass is much larger than the mass of the gas inside the cylinder. But for other two cases, where the piston mass is smaller, piston motion, and conditions in the compartments separated by the piston differ for the two methods. This is attributed to the linear velocity distribution assumption of the hydrodynamic model. The DSMC results demonstrate that this assumption is not valid for cases where the piston mass is equal or less than the mass of the gas inside the cylinder. Originality/value – Implementation of the DSMC method for problems with deforming domain is presented and a limitation for applicability of hydrodynamic model for these problems is shown.

Linearization-based attitude error regulation: multiplicative error case : Table of Contents

R. Ozgur Doruk — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to design and simulate a linearized attitude stabilizer based on linear quadratic regulator theory (LQR) using the multiplicative definition of the attitude. Design/methodology/approach – The attitude is modeled by the modified Rodriguez parameters that provide a minimal representation of attitude and always invertible kinematics. The nonlinear model of the satellite attitude dynamics is linearized around the origin and an LQR is proposed for the linearized design. They are also simulated using the original nonlinear satellite dynamics in order to verify that the controller is operating properly. Simulations include randomly selected initial conditions to justify the stability against various initial conditions. Findings – Theoretically, the resultant controllers are locally stable around the origin. However, the simulation results show that the attitude is well regulated in the presence of both inertia uncertainties and random initial conditions. Originality/value – The originality of this work is due to its demonstration that complicated attitude regulators are not the solution for proper satellite or spacecraft attitude stabilization.

Autonomous navigation and guidance scheme for precise and safe planetary landing : Table of Contents

Li Shuang, Zhang Liu — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to discuss the autonomous navigation and guidance scheme for future precise and safe planetary landing. Design/methodology/approach – Autonomous navigation and guidance schemes are proposed based on inertial measurement unit (IMU) and optical navigation sensors for precise and safe landing of spacecrafts on the moon and planetary bodies. First, vision-aided inertial navigation scheme is suggested to achieve precise relative navigation; second, two autonomous obstacle detection algorithms, based on grey image from optical navigation camera and digital elevation map form light detection and ranging sensor, respectively, are proposed; and third, flowchart of automatic obstacle avoidance maneuver is also given out. Findings – This paper finds that the performance of the proposed scheme precedes the traditional planetary landing navigation and guidance mode based on IMU and deep space network. Research limitations/implications – The presented schemes need to be further validated by the mathematical simulations and hardware-in-loop simulations, and then they can be used in the real flight missions. Practical implications – The presented schemes are applicable to both future planetary pin-point landing missions and sample return missions with little modification. Originality/value – This paper presents the new autonomous navigation and guidance scheme in order to achieve the precise and safe planetary landing.

Vibrations of an infinite plate placed in a circular channel containing fluid flow : Table of Contents

Erol Uzal, Sule Kapkin — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to investigate the linear vibrations of an elastic plate subject to irrotational, incompressible fluid flow bounded by a rigid cylinder. Design/methodology/approach – The plate is placed diametrically in the cylinder and extends along it, both infinite in length. The fluid flow is in the axial direction of the cylinder. Findings – The problem is solved analytically and the eigenfrequencies are obtained explicitly. Originality/value – The solution offered in this paper allows investigation of the instabilities and computation of the flutter velocity/minimum flow velocity at which the plate vibrations grow in time.

Research of an improved BP decoding arithmetic : Table of Contents

Guo-Qiang Wu, Zhao-Wei Sun, Xian-De Wu — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to research the traditional belief-propagation (BP) decoding algorithm of low-density parity-check code. The big computation load is a shortcoming of traditional BP decoding algorithm. Accordingly, the paper provides an improved BP decoding algorithm which raises the decoding efficiency and reduces decoding time delay. Design/methodology/approach – An improved BP decoding algorithm is studied and the error correction performance of the improved BP decoding algorithm in the Gaussian channel is provided. Findings – The simulation result shows the improved BP decoding algorithm has lower computational complexity and higher decoding speed based on the premise of a little decoding performance loss. Research limitations/implications – The improved BP decoding algorithm has lower computational complexity and higher decoding speed based on the premise of a little decoding performance loss. Practical implications – The improved BP decoding algorithm raises the decoding efficiency and reduces decoding time delay. Originality/value – The decoding algorithm only needs to update the wrong bit information which might arise, but not update the bit information whose reliability is very high. The improved BP decoding algorithm raises the decoding efficiency and reduces decoding time delay.

Linear correlations of principal parameters for the preliminary design of twin civil jet aircraft : Table of Contents

Yannis Kallinderis, Xenakis Vouvakos, Pinelopi Menounou — Sat Oct 17 08:00:42 BST 2009

Abstract:
Purpose – The purpose of this paper is to simplify the preliminary design process as well as the initial evaluation of existing design parameters of civil jet aircraft; to include noise level consideration right from the start of the design process; and to form a current database of civil jet aircraft design parameters. Design/methodology/approach – Simple (linear) correlations are found between key design parameters. Findings – Direct linear relationships are found between design parameters including noise levels. Simplified preliminary design process. Originality/value – New correlations which simplify the current procedures for preliminary design. In addition, the noise is included right from the beginning of the design. Finally, a new database is formed with specially selected aircraft that is current and covers a wide spectrum of sizes.