Nonreflective Conditions for Perfectly Matched Layer in Computational Aeroacoustics

Choung, Hanahchim,Jang, Seokjong,Lee, Soogab The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

In computational aeroacoustics, boundary conditions such as radiation, outflow, or absorbing boundary conditions are critical issues in that they can affect the entire solution of the computation. Among these types of boundary conditions, the perfectly matched layer boundary condition, which has been widely used in computational fluid dynamics and computational aeroacoustics, is developed by augmenting the additional term in the original governing equations by an absorption function so as to stably absorb the outgoing waves. Even if the perfectly matched layer is analytically a perfectly nonreflective boundary condition, spurious waves occur at the interface, since the analysis is performed in discretized space. Hence, this study is focused on factors that affect numerical errors from perfectly matched layer to find the optimum conditions for nonreflective PML. Through a mathematical approach, a minimum width of perfectly matched layer and an optimum absorption coefficient are suggested. To validate the prediction of the analysis, numerical simulations are performed in a generalized coordinate system, as well as in a Cartesian coordinate system.

Development of the KARI Space Debris Collision Risk Management System (KARISMA)

Kim, Hae-Dong,Lee, Sang-Cherl,Cho, Dong-Hyun,Seong, Jae-Dong The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

Korea has been operating multi-purpose low-earth orbit (LEO) satellites such as the Korea multi-purpose satellite (KOMPSAT) since 1999 and the Communication, Ocean, and Meteorological Satellite (COMS), which was launched into geostationary orbit in 2006. The Korea Aerospace Research Institute (KARI) consequently became concerned about the deteriorating space debris environment. This led to the instigation, in 2011, of a project to develop the KARI space debris collision risk management system (KARISMA). In 2014, KARISMA was adopted as an official tool at the KARI ground station and is operated to mitigate collision risks while being continuously upgraded with input from satellite operators. The characteristics and architecture of KARISMA are described with detailed operational views. The user-friendly user interfaces including 2D and 3D displays of the results, conjunction geometries, and so on, are described in detail. The results of our analysis of the space collision risk faced by the KOMPSAT satellites as determined using KARISMA are presented, as well as optimized collision avoidance maneuver planning with maneuvering strategies for several conjunction events. Consequently, the development of KARISMA to provide detailed descriptions is expected to contribute significantly to satellite operators and owners who require tools with many useful functions to mitigate collision risk.

An Online Tilt Estimation and Compensation Algorithm for a Small Satellite Camera

Lee, Da-Hyun,Hwang, Jai-hyuk The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

In the case of a satellite camera designed to execute an Earth observation mission, even after a pre-launch precision alignment process has been carried out, misalignment will occur due to external factors during the launch and in the operating environment. In particular, for high-resolution satellite cameras, which require submicron accuracy for alignment between optical components, misalignment is a major cause of image quality degradation. To compensate for this, most high-resolution satellite cameras undergo a precise realignment process called refocusing before and during the operation process. However, conventional Earth observation satellites only execute refocusing upon de-space. Thus, in this paper, an online tilt estimation and compensation algorithm that can be utilized after de-space correction is executed. Although the sensitivity of the optical performance degradation due to the misalignment is highest in de-space, the MTF can be additionally increased by correcting tilt after refocusing. The algorithm proposed in this research can be used to estimate the amount of tilt that occurs by taking star images, and it can also be used to carry out automatic tilt corrections by employing a compensation mechanism that gives angular motion to the secondary mirror. Crucially, this algorithm is developed using an online processing system so that it can operate without communication with the ground.

Artificial Neural Network Based Mission Planning Mechanism for Spacecraft

Li, Zhaoyu,Xu, Rui,Cui, Pingyuan,Zhu, Shengying The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

The ability to plan and react fast in dynamic space environments is central to intelligent behavior of spacecraft. For space and robotic applications, many planners have been used. But it is difficult to encode the domain knowledge and directly use existing techniques such as heuristic to improve the performance of the application systems. Therefore, regarding planning as an advanced control problem, this paper first proposes an autonomous mission planning and action selection mechanism through a multiple layer perceptron neural network approach to select actions in planning process and improve efficiency. To prove the availability and effectiveness, we use autonomous mission planning problems of the spacecraft, which is a sophisticated system with complex subsystems and constraints as an example. Simulation results have shown that artificial neural networks (ANNs) are usable for planning problems. Compared with the existing planning method in EUROPA, the mechanism using ANNs is more efficient and can guarantee stable performance. Therefore, the mechanism proposed in this paper is more suitable for planning problems of spacecraft that require real time and stability.

Adaptation Method for Overall and Local Performances of Gas Turbine Engine Model

Kim, Sangjo,Kim, Kuisoon,Son, Changmin The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

An adaptation method was proposed to improve the modeling accuracy of overall and local performances of gas turbine engine. The adaptation method was divided into two steps. First, the overall performance parameters such as engine thrust, thermal efficiency, and pressure ratio were adapted by calibrating compressor maps, and second, the local performance parameters such as temperature of component intersection and shaft speed were adjusted by additional adaptation factors. An optimization technique was used to find the correlation equation of adaptation factors for compressor performance maps. The multi-island genetic algorithm (MIGA) was employed in the present optimization. The correlations of local adaptation factors were generated based on the difference between the first adapted engine model and performance test data. The proposed adaptation method applied to a low-bypass ratio turbofan engine of 12,000 lb thrust. The gas turbine engine model was generated and validated based on the performance test data in the sea-level static condition. In flight condition at 20,000 ft and 0.9 Mach number, the result of adapted engine model showed improved prediction in engine thrust (overall performance parameter) by reducing the difference from 14.5 to 3.3%. Moreover, there was further improvement in the comparison of low-pressure turbine exit temperature (local performance parameter) as the difference is reduced from 3.2 to 0.4%.

Quantized Consensus Control for Second-Order Nonlinear Multi-agent Systems with Sliding Mode Iterative Learning Approach

Deng, Xiongfeng,Sun, Xiuxia,Liu, Ri The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

In this paper, the consensus problem of second-order nonlinear multi-agent systems with directed communication topology is discussed. Information for the states of neighbour agents is quantized using a uniform quantizer. The sliding mode control law is designed based on quantized state information and the stability analyzed by using Lyapunov theory. Additionally, an iterative learning control law based on sliding mode errors is developed. Thereby, a novel consensus control protocol consisting of a sliding mode control law and an iterative learning approach is achieved, where the purpose of applying the sliding mode control law is to eliminate non-repeatable uncertainties and the iterative learning control law is to remove repeatable disturbances. Also, the convergence of the proposed control protocol is analyzed in the frequency domain. Finally, two cases are provided to illustrate the effectiveness of theoretical analysis.

The Experimental Study about the Effect of Operating Conditions on Multi-tube Pulse Detonation Engine Performance

Kim, Jung-Min,Han, Hyung-Seok,Choi, Jeong-Yeol The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

This study examines a multi-tube pulse detonation engine (PDE) which has a type of constant volume combustion. We designed and made the multi-tube PDE and then conducted an experiment in various operating frequencies and equivalence ratios. First, experiments with operating frequencies of 40, 80, 120, 160, and 200 Hz resulted in an average thrust and specific impulse 23.14 N and 42.34 s. The next experiment resulted in the equivalence ratio varying from 0.81 to 1.38, which resulted in an average thrust and specific impulse 22.36 N and 40.11 s. The average detonation velocity was 8% lower than that calculated according to C-J theory. The incidence ratios of the detonation wave were stable with the exception of the operating frequency of 200 Hz. However, at 200 Hz, the incidence ratio was less than 50%. We assumed that a low fill fraction occurred for this problem. The thrust of the PDE increased with the operating frequency. However, the thrust increase was at a lower rate than in previous studies, because of a lost thrust output result from the slow response time of the load cell amplifier.

Steady Aerodynamic Characteristics of Two-Dimensional NACA0012 Airfoil for One Revolution Angle of Attack

Park, Byung Ho,Han, Yong Oun The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.2

Steady variations in aerodynamic forces and flow behaviors of two-dimensional NACA0012 airfoil were investigated using a numerical method for One Revolution Angle of Attack (AOA) at Reynolds number of $10^5$. The profiles of lift coefficients, drag coefficients, and pressure coefficients were compared with those of the experimental data. The AERODAS model was used to analyze the profiles of lift and drag coefficients. Wake characteristics were given along with the deficit profiles of incoming velocity components. Both the characteristics of normal and reverse airfoil models were compared with the basic aerodynamic data for the same range of AOA. The results show that two peaks of the lift coefficients appeared at $11.5^{\circ}$ and $42^{\circ}$ and are in good agreement with the pre-stall and post-stall models, respectively. Counter-rotating vortex flows originated from the leading and trailing edges at a high AOA, which formed an impermeable zone over the suction surface and made reattachments in the wake. Moreover, the acceleration of inflow along the boundary of the vortex wrap appeared in the profile of the wake velocity. The drag profile was found to be independent of the airfoil mode, but the lift profile was quite sensitive to the airfoil mode.

Panel Flutter Emulation Using a Few Concentrated Forces

Dhital, Kailash,Han, Jae-Hung The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

The objective of this paper is to study the feasibility of panel flutter emulation using a few concentrated forces. The concentrated forces are considered to be equivalent to aerodynamic forces. The equivalence is carried out using surface spline method and principle of virtual work. The structural modeling of the plate is based on the classical plate theory and the aerodynamic modeling is based on the piston theory. The present approach differs from the linear panel flutter analysis in scheming the modal aerodynamics forces with unchanged structural properties. The solutions for the flutter problem are obtained numerically using the standard eigenvalue procedure. A few concentrated forces were considered with an optimization effort to decide their optimal locations. The optimization process is based on minimizing the error between the flutter bounds from emulated and linear flutter analysis method. The emulated flutter results for the square plate of four different boundary conditions using six concentrated forces are obtained with minimal error to the reference value. The results demonstrated the workability and viability of using concentrated forces in emulating real panel flutter. In addition, the paper includes the parametric studies of linear panel flutter whose proper literatures are not available.

Provisional-Ideal-Point-Based Multi-objective Optimization Method for Drone Delivery Problem

Omagari, Hiroki,Higashino, Shin-Ichiro The Korean Society for Aeronautical Space Sciences 2018 International Journal of Aeronautical and Space Sc Vol.19 No.1

In this paper, we proposed a new evolutionary multi-objective optimization method for solving drone delivery problems (DDP). It can be formulated as a constrained multi-objective optimization problem. In our previous research, we proposed the "aspiration-point-based method" to solve multi-objective optimization problems. However, this method needs to calculate the optimal values of each objective function value in advance. Moreover, it does not consider the constraint conditions except for the objective functions. Therefore, it cannot apply to DDP which has many constraint conditions. To solve these issues, we proposed "provisional-ideal-point-based method." The proposed method defines a "penalty value" to search for feasible solutions. It also defines a new reference solution named "provisional-ideal point" to search for the preferred solution for a decision maker. In this way, we can eliminate the preliminary calculations and its limited application scope. The results of the benchmark test problems show that the proposed method can generate the preferred solution efficiently. The usefulness of the proposed method is also demonstrated by applying it to DDP. As a result, the delivery path when combining one drone and one truck drastically reduces the traveling distance and the delivery time compared with the case of using only one truck.