• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.13 no.5
• /
• pp.77-83
• /
• 1993

A modified Lanczos method combined with a substructure analysis technique was used for calculating natural frequencies and mode shapes of large structural systems. The method does not require generation and storage of stiffness and mass matrices of the entire structure. It only uses the stiffness and mass matrices of each substucture. No approximating assumptions are required other than the usual assumption of linear elastic system modelled by finite elements. Thus, natural frequencies and mode shapes for the finite element model employed are the same as those with or without the suhstructuring algorithm. To check the efficiency of the proposed method, first ten natural frequencies and the corresponding mode shapes of an open truss helicopter tail-boom structure are calculated by using it.

• Journal of the Korea Society for Simulation
• /
• v.23 no.4
• /
• pp.75-83
• /
• 2014

Most warship combat systems inquire human operator to control several sensor and another equipments as well as decision-modeling. For this reason, many researches with multi-agent based M&S (Modeling and Simulation) have been increasingly conducted. However there cannot find any researches of M&S based analysis for anti-submarine warfare that requires a high level of mission complexity between multiple platforms. In this research, we have been developed various combat platform models such as warship, submarine and helicopter, etc. In order to apply the multi-agent-based M&S technology to the anti-submarine warfare i.e. a HVU (High Value Unit) escort mission scenario. Then we have successfully analyzed the measures of effectiveness according to the different tactics and different situations. In future, the defence engineer maybe employ our methodology and tools to analyze actual tactical problem by simply inserting actual data into our agent model.

• Composites Research
• /
• v.30 no.1
• /
• pp.52-58
• /
• 2017

This paper presents the optimum design methodology for composite wing structure which automatically calculates the safety margin using optimization framework integrating failure modes. Particularly, its framework is possible to optimize sizing procedure to prevent failure mode which has the greatest effect on reducing the sizing time of composite structure. The main failure mode was set as the first ply failure, buckling failure mode, and bolted joint stress field, and the margin was calculated to minimize the weight. The design variable is a laminate sequence database and the responses are strain, buckling, bolted joint stress field. The objective function is the mass of the wing structure. The results of buckling analysis were compared using the finite element model to verify the robustness and reliability of Composite Optimizer.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.5
• /
• pp.1-9
• /
• 2003

Detailed flow of a shrouded tail rotor in hover is studied by using a compressible inviscid flow solver on unstructured meshes. The numerical method is based on a cell-centered finite-volume discretization and an implicit Gauss-Seidel time integration. Numerical simulation is made for a single blade attached to the center body and guide by the duct by imposing a periodic boundary condition between adjacent rotor blades. The results show that the performance of an isolated rotor without shroud compares well with experiment. In case of a shrouded rotor, correction of the collective pitch angle is made such that the overall performance matches with experiment to account for the uncertainties of the experimental model configuration. Details of the flow field compare well with the experiment confirming the validity of the present method.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.33 no.1
• /
• pp.20-25
• /
• 2005

The thickness, loading, and broadband noise generated from the trailing edge of the UH-1H main rotor are numerically compared each other. The Kocureck and Tangler's prescribed wake model is adopted to represent the wake geometry during the hovering motion. Three tip Mach numbers of $M_{T}$ = 0.2, 0.4, and 0.8, are selected to analyze the effects of different tip Mach numbers. At $M_{T}$ = 0.8, in considering the A-weighting and audible frequency band, the random noise is smaller than the tonal noises such as the thickness and the loading noise which have the low frequency characteristics. Especially most of the random noise frequency spread on the ultrasound region. On the other hand, below $M_{T}$ = 0.4, the band of random noise moves to the audible frequency region, and the random noise becomes larger than the tonal noise. It turns out that the random noise analysis of the rotor should be necessary at low speed operating condition.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.20 no.6
• /
• pp.743-751
• /
• 2017

To evaluate the structural integrity of the helicopter radome, we performed bird strike analysis using SPH (Smoothed Particle Hydrodynamics) technique. Since the SPH method is a meshfree method, there is no phenomenon such as mesh tangling and it is suitable to predict the dispersion behavior of debris and debris cloud generated by high-speed impact. In order to observe the scattering direction of fractured bolts, the analysis were performed under the condition that the fracture occurs at the proof load. As a result of bird strike analysis, there is no secondary damage as well as the damage due to, the dispersion behavior of the bird model, and the scattering of the fractured bolts and radome. From the additional analysis that were performed to determine the actual bolt fracture, only plastic deformation is predicted since the maximum stress of the bolt does not exceed the ultimate stress.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.2
• /
• pp.181-186
• /
• 2009

The objective of this study is ensuring safety of cabin when the blade impacts into a obstacle by verifying safety of the rotor mast and the transmission using impact loads calculated from the simulation. The rotor mast shall not fail and the transmission shall not be displaced into occupiable space when the main rotor composite blade impact into a 8 inch rigid cylinder in diameter on the outer 10% of the blade at operational rotor speed. To calculate the reaction loads at the spherical bearing and lead-lag damper, blade impact analysis was performed with FE model consist of composite blade, tree(or rigid cylinder) using elastic-plastic with damage material and several contact surfaces which were created to describe a progress of actual failure. Also, the reaction loads were investigated in change of blade rotation speed and pitch angle.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.37 no.3
• /
• pp.301-306
• /
• 2009

In this study a 3-component rotating balance, which is designed to measure the thrust (Fz) and two moment components (Mx, My) simultaneously for a rotor test jig, is designed and its performance is validated experimentally. The low voltage signal from the strain gages mounted on the balance is amplified with a rotating amplifier, which is then fed through a slip-ring unit into the data acquisition system. In order to validate the accuracy of the calibration matrix obtained from a static calibration test, an additional reaction type balance is used to measure the thrust from a model rotor simultaneously, and shows very good result. Finally, the expanded uncertainty value, which is obtained from ISO method is estimated to be $2.82\times10^{-1}$, and the balance turns out to be reliable.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.11 no.10
• /
• pp.1937-1943
• /
• 2007

Given the mountainous nature of Korea, cutting slopes are bound to happen. Every you, slope failures lead to enormous human and material losses. More recently, reckless development and subsequent degradation of forests has brought about soil erosion, which coupled with heavy rainfall, contaminates rivers, raises the level of river bottoms and thereby deteriorates their discharge capacity. In Korea, environmental impact assessments and disaster impact assessments have been conducted to come up with proper countermeasures. In order to perform quantitative analysis for this purpose, reliable slope information is quintessential. This study aims to obtain slope-related digital images using an RC model helicopter with a non-metric camera embedded, and to process these images to gain more accurate slope information. To this end, digital images obtained regarding cutting slopes were processed to gain numerical information of slopes and, on the basis of slope information gained here, reliable soil erosion factors were estimated.

• Journal of the Korea Institute of Military Science and Technology
• /
• v.24 no.4
• /
• pp.357-367
• /
• 2021

This paper studies the simulations of active airframe vibration controls for the Sikorsky X2 helicopter with a lift-offset coaxial rotor. The 4P hub vibratory loads of the X2TD rotor are obtained from the previous work using a rotorcraft comprehensive analysis code, CAMRAD II. The finite element analysis software, MSC.NASTRAN, is used to model the structural dynamics of the X2TD airframe and to analyze the 4P vibration responses of the airframe. A simulation study using Active Vibration Control System(AVCS) with Fx-LMS algorithm to reduce the airframe vibrations is conducted. The present AVCS is modeled using MATLAB Simulink. When AVCS is applied to the X2TD airframe at 250 knots, the 4P longitudinal and vertical vibration responses at the specified airframe positions, such as the pilot seat, co-pilot seat, engine deck, and prop gearbox, are reduced by 30.65 ~ 94.12 %.