• Journal of KSNVE
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• v.8 no.2
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• pp.251-259
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• 1998

The motion of an aircraft landing gear over rough runway at variable speed is nonstationary. In this paper, a method for the computation of nonstationary response variance is presented which uses a state space form for the combination of landing gear and runway excitation. The dynamic characteristics of the landing gear under nonstationary random excitations has also been analyzed using the proposed method. The formulation is for linear systems of arbitrary order and allows any deterministic velocity history. It has been found by a series of simulation that correlation parameter, damping coefficients of landing gear and tire, and velocity profiles play a prominent role on the dynamic characteristics.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.67.5-67
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• 2001

A closed loop system with a linear plant and nonlinearity in the feedback connection is analyzed for its quasi-static orbital stability by a state-space approach. First a periodic orbit is assumed to exist in the loop which is determined by describing function method for the given nonlinearity. This is possible by selecting a proper nonlinearity and a rigorous justification of the describing function method.[1-3, 18, 20]. Then by introducing residual operator, a linear perturbed model can be formulated. Using various transformations like a modified eigenstructure decomposition, periodic-averaging, charge of variables and coordinate transformation, the stability of the periodic orbit, as a solution of harmonic balance, can be shown by investigating a simple scalar function and result of linear algebra. This is ...

• Journal of Institute of Control, Robotics and Systems
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• v.4 no.5
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• pp.644-650
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• 1998

In this paper , a state space model for flexible beam is presented using the assumed-modes approach. The state space equation is derived for a flexible beam in which one end is connected to a motor and is driven by a torque equation and the other end is free. Many of the transfer function proposed thus far use the torque to the flexible beam as the input and the tip deflection of the flexible beam as the output. The Technique for the analysis and synthesis of the dual-input describing function(DIDF) is introduced here and the construction of a non-linear compensator, based on this technique, is proposed. This non-linear compensator, properly connected in the direct path of a closed-loop linear or non-linear control system. The above non-linear network is used to compensate linear and non-linear systems for instability, limit cycles, low speed of response and static accuracy. The effectiveness of the proposed scheme is demonstrated through computer simulation and experimental results.

• Structural Engineering and Mechanics
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• v.23 no.1
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• pp.97-113
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• 2006

A simply supported hybrid plate consisting of top and bottom functionally graded elastic layers and an intermediate actuating or sensing homogeneous piezoelectric layer is investigated by an elasticity (piezoelasticity) method, which is based on state space formulations. The general spring layer model is adopted to consider the effect of bonding adhesives between the piezoelectric layer and the two functionally graded ones. The two functionally graded layers are inhomogeneous along the thickness direction, which are approached by laminate models. The effect of interlaminar bonding imperfections on the static bending and free vibration of the smart plate is discussed in the numerical examples.

• Journal of KIISE:Software and Applications
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• v.27 no.1
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• pp.41-49
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• 2000

This paper describes a method of generating MPHFs(Minimal Perfect Hash Functions) for large static search key sets. The MOS(Mapping-Ordering-Searching) approach is widely used presently in MPHF generation. In this research, the MOS approach is improved and a SOMS(Selecting-Ordering-Mapping-Searching) approach is proposed, where the Selecting step is newly introduced and the Orderng step is performed before the Mapping step to generate MPHFs more effectively. The MPHF generation algorithm proposed in this research is probabilistic and the expected processing time is linear to the number of keys. Experimental results show that MPHFs are generated fast and the space needed to represent the hash functions is small.

• KIPS Transactions on Software and Data Engineering
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• v.12 no.5
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• pp.199-206
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• 2023

The current software becomes the huge size of source codes. Therefore it is increasing the importance and necessity of static analysis for high-quality product. With static analysis of the code, it needs to identify the defect and complexity of the code. Through visualizing these problems, we make it guild for developers and stakeholders to understand these problems in the source codes. Our previous visualization research focused only on the process of storing information of the results of static analysis into the Database tables, querying the calculations for quality indicators (CK Metrics, Coupling, Number of function calls, Bad-smell), and then finally visualizing the extracted information. This approach has some limitations in that it takes a lot of time and space to analyze a code using information extracted from it through static analysis. That is since the tables are not normalized, it may occur to spend space and time when the tables(classes, functions, attributes, Etc.) are joined to extract information inside the code. To solve these problems, we propose a regularized design of the database tables, an extraction mechanism for quality metric indicators inside the code, and then a visualization with the extracted quality indicators on the code. Through this mechanism, we expect that the code visualization process will be optimized and that developers will be able to guide the modules that need refactoring. In the future, we will conduct learning of some parts of this process.

• Advances in aircraft and spacecraft science
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• v.1 no.2
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• pp.197-218
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• 2014

Quite a demanding task frequently arises in space engineering, when dealing with the cargo accommodation of modules and vehicles. The objective of this effort usually aims at maximizing the loaded cargo, or, at least, at meeting the logistic requirements posed by the space agencies. Complex accommodation rules are supposed to be taken into account, in compliance with strict balancing conditions and very tight operational restrictions. The context of the International Space Station (ISS) has paved the way for a relevant research and development activity, providing the company with a remarkable expertise in the field. CAST (Cargo Accommodation Support Tool) is a dedicated in-house software package (funded by the European Space Agency, ESA, and achieved by Thales Alenia Space), to carry out the whole loading of the Automated Transfer Vehicle (ATV). An ad hoc version, tailored to the Columbus (ISS attached laboratory) on-board stowage issue, has been further implemented and is to be used from now on. This article surveys the overall approach followed, highlighting the advantages of the methodology put forward, both in terms of solution quality and time saving, through an overview of the outcomes obtained to date. Insights on possible extensions to further space applications, especially in the perspective of the paramount challenges of the near future, are, in addition, presented.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.5
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• pp.12-18
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• 2006

A new steady approach has been developed to predict the transonic buffet onset of a high speed aircraft. In this paper, the flow is assumed to be steady for the buffet onset. The present study involves the analysis of a distinct change in the variation of various static aerodynamic parameters. These distinct changes indicates the onset of transonic buffet. Among the various aerodynamic parameters considered in this study, the variation in the center of pressure has shown to provide a clearest indicator of transonic buffet onset. This new steady approach can be applied to predict the transonic buffet onset for airfoils with shock induced separation bubble and for large swept wings with small aspect ratios. Good agreements have been obtained compared with unsteady wind tunnel buffet test data. Based on the results obtained the new steady approach, it can be newly suggested that the distinct slope changes of the center of pressure curve can be used as an indicator of buffet onset for the steady experimental method on a full aircraft configuration.

• Structural Engineering and Mechanics
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• v.85 no.2
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• pp.147-161
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• 2023

Based on the ideas of variational differential quadrature (VDQ) and finite element method (FEM), a numerical approach named as VDQFEM is applied herein to study the large deformations of plate-type structures under static loading with arbitrary shape hole made of functionally graded graphene platelet-reinforced composite (FG-GPLRC) in the context of higher-order shear deformation theory (HSDT). The material properties of composite are approximated based upon the modified Halpin-Tsai model and rule of mixture. Furthermore, various FG distribution patterns are considered along the thickness direction of plate for GPLs. Using novel vector/matrix relations, the governing equations are derived through a variational approach. The matricized formulation can be efficiently employed in the coding process of numerical methods. In VDQFEM, the space domain of structure is first transformed into a number of finite elements. Then, the VDQ discretization technique is implemented within each element. As the last step, the assemblage procedure is performed to derive the set of governing equations which is solved via the pseudo arc-length continuation algorithm. Also, since HSDT is used herein, the mixed formulation approach is proposed to accommodate the continuity of first-order derivatives on the common boundaries of elements. Rectangular and circular plates under various boundary conditions with circular/rectangular/elliptical cutout are selected to generate the numerical results. In the numerical examples, the effects of geometrical properties and reinforcement with GPL on the nonlinear maximum deflection-transverse load amplitude curve are studied.

• Tunnel and Underground Space
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• v.13 no.3
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• pp.180-186
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• 2003

The fracture processes under dynamic loading in tension were simulated using a proposed numerical approach and analyzed to determine dynamic tensile strength. The dynamic tensile strength and the scatter of the strength data decreased with increasing uniformity coefficients. The differences of static and dynamic tensile strength were due to the stress concentrations and redistribution mechanisms in the rock specimen. Although there were different mechanisms for the static and dynamic fracture processes, the static and dynamic tensile strengths were close to the mean microscopic tensile strength at high values of the uniformity coefficient. This paper shows that the rock inhomogeneity has an effect on dynamic tensile strength and is a factor that contributes to the different specimen strengths under dynamic and static loading conditions.