• Tribology and Lubricants
• /
• v.36 no.2
• /
• pp.105-115
• /
• 2020

This paper presents a numerical study on the rotordynamic analysis of a dual-spool turbofan engine in the context of blade defect events. The blades of an axial-type aeroengine are typically well aligned during the compressor and turbine stages. However, they are sometimes exposed to damage, partially or entirely, for several operational reasons, such as cracks due to foreign objects, burns from the combustion gas, and corrosion due to oxygen in the air. Herein, we designed a dual-spool rotor using the commercial 3D modeling software CATIA to simulate blade defects in the turbofan engine. We utilized the rotordynamic parameters to create two finite element Euler-Bernoulli beam models connected by means of an inter-rotor bearing. We then applied the unbalanced forces induced by the mass eccentricities of the blades to the following selected scenarios: 1) fully balanced, 2) crack in the low-pressure compressor (LPC) and high pressure compressor (HPC), 3) burn on the high-pressure turbine (HPT) and low pressure compressor, 4) corrosion of the LPC, and 5) corrosion of the HPC. Additionally, we obtained the transient and steady-state responses of the overall rotor nodes using the Runge-Kutta numerical integration method, and employed model reduction techniques such as component mode synthesis to enhance the computational efficiency of the process. The simulation results indicate that the high-vibration status of the rotor commences beyond 10,000 rpm, which is identified as the first critical speed of the lower speed rotor. Moreover, we monitored the unbalanced stages near the inter-rotor bearing, which prominently influences the overall rotordynamic status, and the corrosion of the HPC to prevent further instability. The high-speed range operation (>13,000 rpm) coupled with HPC/HPT blade defects possibly presents a rotor-case contact problem that can lead to catastrophic failure.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.51 no.6
• /
• pp.78-86
• /
• 2014

In this paper, a novel intensity-based fiber optic vibration sensor using a mass-spring structure, which consists of four serpentine flexure springs and a rectangular aperture within a proof mass, is proposed and its feasibility test is given by the simulation and experiment. An optical collimator is used to broaden the beam which is modulated by the displacement of the rectangular aperture within the proof mass. The proposed fiber optic vibration sensor has been analyzed and designed in terms of the optical and mechanical parts. A mechanical structure has been designed using theoretical analysis, mathematical modeling, and 3D FEM (Finite Element Method) simulation. The relative aperture displacement according to the base vibration is given using FEM simulation, while the output beam power according to the relative displacement is measured by experiment. The simulated sensor sensitivity of $15.731{\mu}W/G$ and detection range of ${\pm}6.087G$ are given. By using reference signal, the output signal with 0.75% relative error shows a good stability. The proposed vibration sensor structure has the advantages of a simple structure, low cost, and multi-point sensing characteristic. It also has the potential to be made by MEMS (Micro-Electro-Mechanical System) technology.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.3
• /
• pp.163-172
• /
• 2017

Porous insulation have been frequently used in a number of industries by minimizing thermal insulation space because of excellent performance of their thermal insulation. This paper devices an effective thermal conductivity prediction model. First of all, we perform literature survey on traditional effective thermal conductivity prediction models and compare each other model with heat transfer experimental results. Furthermore this research defines advanced effective thermal conductivity prediction models model based on heat transfer experimental results, the Zehner-Schlunder model. Finally we verify that the newly defined effective thermal conductivity prediction model has better performance prediction than other models. Finally, this research performs a transient heat transfer analysis of thermal protection system with a porous insulation using the finite element method and confirms validity of the effective thermal conductivity prediction model.

• Composites Research
• /
• v.29 no.2
• /
• pp.53-59
• /
• 2016

Aircraft wing structure is used as a fuel tank containing the fluid. Fuel tank and joint parts are consists of composite structure. Hydrodynamic Ram(HRAM) effect occurs when the high speed object pass through the aircraft wing or explosion and the high pressure are generated in the fuel tank by HRAM effect. High pressure can cause failure of the fuel tank and the joint parts as well as the aircraft wing structure. To ensure the aircraft survivability design, we shall examine the behavior of the joint parts in HRAM effect. In this study, static tensile tests were conducted on four kind of the composite T-Joints. The failure behavior of the composite T-joint was examined by strain gauges and high speed camera. We examine the validity of the Finite Element Modeling by comparing the results of FEA and static tensile tests. The failure stresses and failure pressure of the composite T-Joint were calculated by FEA.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.7 no.2
• /
• pp.52-59
• /
• 2008

The objective of this study is to develop an automatic object changer unit to improve processing problems existed in the conventional horizontal machining center. To achieve this goal, this study designed a horizontal transfer as the second project continued to the first project that designed a upward and downward traverse unit. A horizontal traverse unit shows a symmetric structure and consists of frame, which consists of four unit tools, motor and reducer, which are fixed at a frame, operation unit with pinions, first traverse unit, and second traverse unit. Constraint conditions based on the operation mechanism with these elements were configured and obtained following results after modeling a model for a traverse motor. In the kinematic expression of sliding motion with one degree of freedom, the sliding motion is constrained. Also, the rack 3 installed at a frame is used to configure possible kinematic constraint conditions of the rack 2 according to the rolling motion of the pinion 2 in the first traverse unit. In addition, the moment of inertia that is a type of kinetic energy in a converted horizontal traverse unit in the side of the reducer can be applied to introduce the moment of inertia of a converted horizontal traverse unit in the side of the reducer by using the sum of kinetic energy in the rack and pinion, which is a part of the horizontal traverse unit. Also, the equation of motion of the converted upward and downward traverse unit in the side of the motor using the equation of motion of the motor. Furthermore, the horizontal traverse unit predetermines the mass of the first and second traverse unit and applied load including the radius and reduction ratio of the pitch circle in the pinion 1 and applied load to the rack 2. Then, a proper motor can be determined using several parameters in the upward and downward traverse unit in order to verify such predetermined specifications. In future studies later this study, a simulation that verifies the results of the previous two stages of studies using a finite element method.

• Korean Journal of Agricultural Science
• /
• v.23 no.1
• /
• pp.13-24
• /
• 1996

The following results were obtained by analyzing the displacement, strain and stability of ground at the soft ground excavation using sheet pile. 1. Before setting the strut, the horizontal displacement was large on the upper part of excavated side, but after setting the strut, it showed concentrated phenomenon while being moved to go down to the excavated side. 2. After setting the strut, the displacement of sheet pile was rapidly decreased about a half compared with before setting the strut. The limitation of excavation depth was shown approximately GL-8m after setting double stair strut. 3. Maximum shear strain was gradually increased with depth of excavation, and local failure possibility due to shear deformation at the bottom of excavation was decreased by reinforcement of strut. 4. Maximum horizontal displacement of sheet pile at GL-7.5m was shown 0.2% of excavation depth in elasto-plastic method, and 0.6% in finite-element methods, and the maximum displacement was occurred around the bottom of excavation. 5. To secure the safety factor about penetration depth in the ground of modeling, D/H should be more than 0.89 in the case of one stair strut, and more than 0.77 in the case of double stair strut. 6. The relation of safety factor and D/H about the penetration depth was appeared, Fs=0.736(D/H) + 0.54 in the case of one stair strut, and Fs=0.750(D/H) + 0.62 in the case of double stair strut.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.145-153
• /
• 2003

The resonant column testing determines the shear modulus and material damping factor dependent on the shear strain magnitude, based on the wave-propagation theory. The determination of the dynamic soil properties requires the theoretical formulation of the dynamic behavior of the resonant column testing system. One of the theoretical formulations is the use of the wave equation for the soil specimen in the resonant column testing device. Wood, Richart and Hall derived the wave equation by assuming the linear elastic soil, and didn't take the material damping into consideration. Hardin incorporated the viscoelastic damping of soil in the wave equation, but he had to assume the material damping factor for the determination of the shear modulus. For the better theoretical formulation of the resonant column testing, this study derived a new wave equation to include the viscosity of soil, and proposed an approach for the solution. Also, in this study, the equation of motion for the testing system, which is another approach of the theoretical formulation of the resonant column testing, was also derived. The equation of motion leads to the better understanding of the resonant column testing, which includes the dynamic magnification factor and the phase angle of the response. For the verification of the proposed equation of motion for the resonant column testing, the finite element analysis was performed for the resonant column testing. The comparison of the dynamic magnification factors and the phase angles far the system response were performed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.2
• /
• pp.610-619
• /
• 2016

Digital manufacturing (DM) technology helps engineers design products promptly and reliably at low production cost by simulating a manufacturing process and the material behavior of a product in use, based on three-dimensional digital modeling. The computing infrastructure for digital manufacturing, however, is usually expensive and, at present, the number of professional design engineers who can take advantage of this technology to a product design accurately is insufficient, particularly in small and medium manufacturing companies. Considering this, the Korea Institute of Science and Technology Information (KISTI) and H University is operating a DM track in the form of Industry-University-Research Institute collaboration to train high-performance-computing-based DM professionals. In this paper, a series of courses to train students to work directly into DM practice in industry after graduation is reported. The operating cases of the DM track for two years since 2013 are presented by focusing on the progress in establishment, lecture and practice contents, evaluation of students, and course quality improvement. Overall, the track management, curriculum management, learning achievement of students have been successful. By expediting more active participation of the students in the track and providing more internship and job offers in the participating companies in addition to collaborative capstone design projects, the track can be expanded by fostering a nationwide training network.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.9
• /
• pp.596-603
• /
• 2020

'Electro-Mechanical Brake (EMB) is a novel braking system for automobiles and railway vehicles, and research in this area is actively underway. The current braking system for railway vehicles generates a braking force using a pneumatic cylinder, but the EMB system generates the force through a combination of an electric motor and gears. In this study, the design of an EMB system that meets the domestic standards was conducted through the finite element modeling and fatigue analysis of an eccentric rotating shaft-based EMB system capable of generating a high clamping force. At this time, to improve the accuracy of fatigue analysis, three types of fatigue test specimens, which were subjected to the same heat treatment as the materials used in the prototype, were produced, and the fatigue tests were performed for each material. The fatigue properties (S-N curves) were obtained from the fatigue test results for each material and reflected in the analysis model. The results of fatigue analysis confirmed that the design of the EMB prototype could satisfy the maximum commercial braking/relaxation of 530,000 times, which was the endurance life condition for domestic railway vehicles. In addition, based on this design, a prototype will be manufactured, and endurance testing will be completed to demonstrate the durability characteristics of the developed prototype.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.27 no.5
• /
• pp.339-344
• /
• 2015

Suction piles have been widely used as foundations and anchor systems in offshore industry, and recently, it have been tried to be used as foundations for offshore wind turbines. Many researches have shown that stiffness of a foundation could effect dynamic responses of a offshore wind turbine so that appropriate modeling application of wind turbine foundations is recommended. In this paper, we calculate a stiffness matrix of a suction foundation through 3D FEM analysis and compare the results with the ones calculated by conventional formula for estimating stiffness of shallow foundations. And then we carry out integrated load analysis for the evaluation of dynamic responses and natural frequencies of the structure using the calculated stiffness matrix. The results shows that the effect of load in the mudline is not large, but in the case of assuming the foundation as a fixed support, the natural frequency is over-estimated up to 10%. Therefore, considering stiffness of foundations is recommended when you evaluate the natural frequencies of wind turbine structures.