Chae Sil Kim

Cyclic Oxidation Behavior of Thermal Barrier Coatings Irradiated by High-Intensity Pulsed Ion Beam

High-temperature oxidation resistance of 7 wt.％Y2O3-ZrO2 thermal barrier coatings (TBCs) irradiated by high-intensity pulsed ion beam (HIPIB) has been investigated in a cyclic oxidation condition at 1050 °C ×1 h. The ceramic coating of a tetragonal ZrO2 phase structure was prepared on GH33 superalloy substrates with a NiCoCrAlY bond coat by using electron-beam physical-vapor deposition (EB-PVD). The ceramic coating is composed of columnar grains forming dense clusters spacing with several-μm gaps among grain clusters. The characteristics of the columnar grains disappeared after HIPIB irradiation at the ion current densities of 100-200 A/cm2, and the irradiated surface presented a smoothed, densified feature after the remelting and ablation due to the HIPIB irradiation. The thickness of the densified layer is about 1 μm. After oxidation with 15 cycles at 1050 °C ×1 h, the oxidation kinetics curves of the as-deposited and irradiated TBCs showed a parabolic shape. The weight gain of original sample is about 0.8-0.9 mg/cm2, while the values of the HIPIB-irradiated TBCs decreased to some extent. The lowest weight gain is obtained for the irradiated TBCs at 200 A/cm2 with one shot, being 0.3-0.4 mg/cm2, and those at 100 A/cm2 have a medium weight gain of 0.6-0.7 mg/cm2. The cross-sectional morphologies of HIPIB-irradiated TBCs show less oxidation of the NiCoCrAlY bonding layer, with a thinner thermally grown oxide (TGO) layer. The morphology observation is consistent with the results of cyclic oxidation test. It is found that the inward diffusion of oxygen through TBCs can be significantly impeded by the densified top layer by the HIPIB irradiation, thus limiting the oxidation of the bonding layer, improving the overall oxidation resistance of the irradiated TBCs.

An Experimental Study on the Prediction Control Technique for a Magnetic Bearing

Active vibration control methods are required in the high speed rotor systems supported by magnetic bearings. A prediction control technique is one of the control methods. Gain and phase angle are primarily chosen with analyzing the responses for a certain rotor speed. The feasibility of this technique has been reported for only analytical simulations. Therefore this paper constructs the test rig supported by ball bearings with a magnetic bearing type actuator and develops a prediction control system by using LabVIEW and Compact RIO. Finally as rotating speeds are modulated, the gains and phase angles for the speeds are determined with vibration control of the test rig. This leads that the prediction control technique may be applied to the rotor system with the magnetic bearing.

A Study on the Control of an Anchor Auto Drop System for Ship Windlass

In this research, we will perform a basic study to develop an Anchor Auto Drop System for Chain dia. Φ107mm/G3 (Refloat load 45ton) Windlass model. First of all, to evaluate the control characteristics of the Windlass, we made an analysis model using the commercial software ‘Simulation-X’. Then, we analyzed the control characteristics of the Anchor falling speed and used PID control to evaluate the falling speed control. Additionally, we analyzed the desired falling speeds of 2, 3, 4 m/s when the Anchor and all chains were a total of 44 tons in weight at 100 m distance. Also, we obtained results of Caliper brake loads and torque changes and we were able to determine that the braking pressure and torque are increased when the load is increased. We analyzed the gear load when the brake is implemented and the Anchor is at 200 m distance and has a total weight of 69 tons. And, for the winch structure design, we obtained a basic design method to develop the auto drop system for a Marine Windlass in terms of the important elements.

Analytical Estimation of Structural Integrity for a Thermocouple in Nuclear Power Plant

Thermocouples used for temperature measurement in nuclear power plants should meet the seismic qualification regulations of -IEEE Std 323 and 344 so as to withstand big vibrations such as earthquakes. In this paper, we establish a model for the estimation of the structural integrity of the thermocouples that are used in nuclear reactor building models. We then review the need for seismic measure using modal analysis and the boundary condition. If the natural frequency is less than 33 Hz for the installation environment, response spectrum analysis was carried out taking into consideration the weight of this interpretation and that of the seismic load models in the input response curves (Floor Response Spectra) OBE (Operation Base Earthquake), and SSE (Safe Shutdown Earthquake). Finally, analytical estimation of the structural integrity of a thermocouple is performed by making a comparison of the maximum stress and the allowable stress.

A Study on the Dynamic Stability of Heavy Press Considering Rotational Speed

This article describes the determination of the dynamic stability for a heavy press, particularly considering rotational speed. A finite element model of the driving parts for the heavy press was generated. We also applied boundary conditions and dynamic loads considering the driving conditions. Modal analysis was conducted using the finite element construction model. Therefore, no resonance was identified with the comparison between the results of the modal analysis and vibration excitation frequency by the gear tooth. In addition, the stress distribution of the driving parts for press was determined using transient analysis. As compared to the yield strength of the material, the dynamic stability the heavy press was confirmed.

Design of Compressor Impeller Using Evolutionary Optimization Technique

Configuration design on an impeller using to the centrifugal compressor of turbocharger was conducted to improve its performance. Impeller shape was adjusted by changing its meridional contours and blade profile. Total nine design variables were chosen with constraints. ANN (Artificial Neural Net) was adopted as a main optimization algorithm with PSO (Particle Swarm Optimization) in order to reduce the optimization time. This ANN was learned and trained with the design variable sets which were obtained using DOE (Design of Experiment). This ANN was continuously improved its accuracy for each generation of which population was one hundred. New design variable set in each generation was selected using a non-gradient based method of PSO in order to obtain the global optimized result. After 7th generation, the difference of efficiency and pressure ratio predicted by ANN and CFD (Computational Fluid Dynamics) was less than 0.6%. From more than 1,200 design variable sets, a pareto of efficiency versus pressure ratio was obtained and an optimized result was selected based on the multi-objective function. On this optimized impeller, the efficiency and pressure ratio were improved by 1% and 9.3%, respectively.

A Design Technique for a Magnetic Bearing-Rotor in a Turbo Blower Considering Critical Speeds

This paper introduces a rotor design technique for a turbo blower supported by magnetic bearings that considers the critical speeds of the rotor. An important factor for rotor critical speeds is the stiffness of its bearings. The magnetic bearing acts as a negative spring, called the position stiffness prior to operation, and rotor systems are initially unstable until the stiffness (current stiffness) and damping in the active control rotating system are determined using closed loop control forces. This paper describes a finite element model for the rotor, derives the stiffness equations for the magnetic bearing, and defines the total magnetic bearing stiffness including the position stiffness and current stiffness. Finally, the magnetic bearing stiffness that avoids the rotor critical speeds is chosen.

Analytical Techniques of Case and Pad for 5-Pad Tilting Pad Bearing

As the pad of a tilting pad bearing has invisible, three dimensional complicated movements around its pivot point inside the bearing case, its contact surface is difficult to establish. The loading points inside the bearing case are also not easy to predict accurately. This paper presents practical analysis techniques and loading conditions for the pad and bearing case of a tilting pad bearing in the structural analysis to meet the actual operating conditions. The analysis for the pad is conducted by applying the pressure of lubricant to the whole pad surface and constraining the circumferential degrees of freedom at nodes around the pivot. Part of the pad of boundary condition is hydraulic of practically applied lubricant and contact area of pivot and the rotational degree of freedom in line with circumferential. It is proposed to using of external case boundary condition 4 pads and 5 pads. Points of the case, combined with the pad are applied to the actual load. The result of analysis, the reliability of the pad and the case was obtained, because stress distribution is nearly identical with the actual phenomenon.

Vibration Characteristic Prediction of a Heavy Machinery Suspension Seat Using Multi-Body Dynamic Analysis Method

This article proposes a novel simulation technique to predict the reasonable dynamic characteristics of a suspension seat for heavy machinery using a commercial multibody dynamic analysis code, ADAMS. The dynamic model is simulated with the specific condition such as sinusoidal and sweep input. The experiment test for actual suspension seat is conducted for reviewing the dynamic simulation model with same input condition. As the simulation results shows good agreements with experimental test results, the dynamic analysis model is reasonable and will be very helpful for predicting the dynamic characteristic for the suspension seat for heavy machinery and for designing the other type seats with the other suspension mechanism types.