Journal of the Korean Society for Precision Engineering

Aerodynamic Flow Characteristics Inducing Centrifugal Compressor Noise Generation in High-speed Turbomachinery: Jihun Song, Chang Ho Son, Dong-Ryul Lee; J. Korean Soc. Precis. Eng. 2025;42(9):763-770.
Published online September 1, 2025; DOI: https://doi.org/10.7736/JKSPE.025.088

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Centrifugal compressor is a device that converts kinetic energy to increase the air pressure. It rotates at a high speed of up to 200,000 RPM and directly affects aerodynamic noise. Various studies have already been conducted, but the direct calculation method of acoustics based on the unsteady solution is inefficient because it requires a lot of resources and time. Therefore, flow characteristics and numerical comparison according to various aerodynamic factors predicted as a cause of noise generation were analyzed in this study based on the steady solution. High-frequency noise was calculated locally near the asymmetric flow properties. Vortex and turbulent kinetic energy were generated at similar locations. Among static components, a large-sized vortex of 3.48×10⁷ s^-1 was distributed at the location where the rotational flow around the compressor wheel combined with the inlet suction flow. In addition, a locally high vortex of 8.16×10⁵ s^-1 was distributed around the balancing cutting configurations that cause asymmetric flow characteristics. Analysis of these factors and causes that directly affect noise can be efficiently improved in the pre-design stage. Therefore, the efficient design methodology for centrifugal compressors that considers both performance and noise is expected based on the results of this study.

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Bending and Compressive Performance of Strut Tower Braces based on Finite Element Analysis for Improvement of Vehicle Safety and Stability: Jeong Bin Bae, Jung Jin Kim; J. Korean Soc. Precis. Eng. 2024;41(11):817-825.
Published online November 1, 2024; DOI: https://doi.org/10.7736/JKSPE.024.047

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A strut tower brace is one of the components that can improve the driving stability of a vehicle. This component has received steady attention for a long time due to its affordable price and easy installation. However, strut tower braces sold in the market have different structures. Moreover, most of them do not contain sufficient information related to safety or stability. Thus, this study aimed to analyze and compare structural behaviors of strut tower braces having various body shapes under bending and compressive scenarios. For this purpose, this study selected six representative models in the market and calculated structural behaviors (stress and deformation) using finite element analysis. Results revealed the body shape had a decisive effect not only on the durability of the strut tower brace, but also on the safety and stability of the vehicle. Among the six models tested, the model having a body shape with a single-axis form utilizing a wide rectangular cross-sectional showed the best bending and compressive performances. This study also confirmed that bending and compressive performances could be simultaneously improved depending on body shape.

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Structural Analysis and Optimization of Electrochemical Hydrogen Compressor End Plate Using Taguchi Method and Gray Relational Analysis: Sang Duk Seo, Won Tae Kwon; J. Korean Soc. Precis. Eng. 2023;40(12):955-964.
Published online December 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.083

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The Electrochemical Hydrogen Compressor is an optimal device for compressing low-pressure hydrogen to high-pressure hydrogen. It has a similar structure to the Proton Exchange Membrane Fuel Cell but operates at extremely high pressures, requiring multiple cells sealed with End Plates. The End Plate design must provide initial cell activation support, withstand maximum operating pressure within the stack, and prevent internal gas leakage. This study applies a multi-objective optimization method and grey relation analysis to determine the optimal design parameters for the End Plate based on the activation area of Dummy Cells. Finite Element Method (FEM) analysis is conducted to verify the effectiveness of the optimized End Plate design, considering the uniform pressure distribution with stacked Dummy Cells (1, 3, 6, 12). The analysis reveals that the parameters affecting the uniform pressure distribution include the End Plate design, stack sealing pressure, individual Cell design parameters, and the number of Cell stack layers.

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Study on Fabrication of Closed-cell Aluminum Foam Using Directed Energy Deposition: Hwa-Jeong Kim, Do-Sik Shim; J. Korean Soc. Precis. Eng. 2023;40(10):787-796.
Published online October 1, 2023; DOI: https://doi.org/10.7736/JKSPE.023.076

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In this study, based on directed energy deposition (DED) technology, one of the additive manufacturing technologies, a porous material fabricated by mixing various aluminum alloys and foaming agent was manufactured. First, the foaming agent formed pores inside the deposited materials and differences in foaming characteristics were observed depending on the type of aluminum. Also, the foaming characteristics according to the laser power, which is a representative process variable, were analyzed. As a result, a closed-cell porous material with a maximum porosity at a laser power of 1,100 W was manufactured. Results of the compression test showed that the porous material made by the pores generated therein collapses to absorb energy, and the internal pores disappear to become high density. Therefore, Young’s modulus and yield stress were reduced by the pores inside the sample of pure aluminum and Al6063. However, it was found that the specific energy absorption, which is an advantage of the foamed materials, increased compared to non-porous materials. The findings of this study confirmed that it was possible to manufacture DED-applied foam materials using aluminum powder and a foaming agent.

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Evaluation of Thin-Shell Properties of Self-Healing Microcapsules by Reinforcement of Carbon Nanotubes: Jeong Keun Jang, Hyeon Ji Kim, Sung Ho Yoon; J. Korean Soc. Precis. Eng. 2023;40(1):71-77.
Published online January 1, 2023; DOI: https://doi.org/10.7736/JKSPE.022.089

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In this study, thin-shell surface observation, storage capability test, and micro-compressive test were performed for self-healing microcapsules using a field emission scanning electron microscope (FE-SEM) and a micro-compressive testing machine. A microcapsule having a melamine-urea-formaldehyde thin-shell and a microcapsule having a melamine-urea-formaldehyde thin-shell reinforced with carbon nanotubes were used. Two carbon nanotube contents were considered: 0.17 wt% and 0.50 wt%. Thin-wall shell state was relatively smooth when microcapsules were not reinforced with carbon nanotubes. It was uneven when microcapsules were reinforced with carbon nanotubes. Prepared microcapsules showed little decreases of weights even when the exposure time was increased regardless of whether they were reinforced with carbon nanotubes. Thus, their storage capability was good. When carbon nanotube content was the same, the fracture load was almost constant without being affected by the diameter of the microcapsule. However, fracture displacement increased with increasing diameter of the microcapsule. When diameters of microcapsules were similar, fracture load and fracture displacement increased when carbon nanotube content increased. It was found that self-healing microcapsules had good storage capability and mechanical properties. Thus, they could be applied to repair damage to composite materials if thin-shell formation mechanism for adding carbon nanotubes is supplemented.

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Analysis of mechanical properties and stress distribution in self-healing microcapsules using micro-compressive test, nanoindentation test, and finite element analysis
Hyeon Ji Kim, Sung Ho Yoon
Functional Composites and Structures.2024; 6(4): 045001. CrossRef
A simplified predictive model for the compression behavior of self-healing microcapsules using an empirical coefficient
Jaeho Cha, Sungho Yoon
Functional Composites and Structures.2024; 6(3): 035010. CrossRef

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Finite Element Analysis of the Difference of Bone-Conducted Responses according to the Young’s Modulus of Skull: Jongwoo Lim, Soomin Lee, Namkeun Kim; J. Korean Soc. Precis. Eng. 2022;39(9):663-667.
Published online September 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.078

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The bone compression and the inertia from cochlear fluid or middle ear (ME) ossicles, are generally considered to be important components inducing bone-conducted (BC) hearing. To clarify the bone compression effect on the BC hearing caused by variation of Young’s modulus of skull, two different types of three-dimensional finite-element models were used in this study. The FE models were (1) Isolated cochlea model comprising ME and cochlea containing basilar membrane (BM) and (2) Head model comprising the isolated cochlea structure. The model was validated by comparison of cochlear responses such as BM velocities with those of otosclerosis patients’ clinical data. Additionally, results showed that the bone compression effects on a BC hearing is highly depended on the Young’s modulus of a skull. Also, the bone compression effects could be underestimated at low frequencies in temporal bone experiments, whereas the effects could be overestimated at high frequencies in cadaver experiments.

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Energy Saving of Rubber Forming by Direct Heating Press Mold Development: Young Tae Cho; J. Korean Soc. Precis. Eng. 2022;39(7):485-491.
Published online July 1, 2022; DOI: https://doi.org/10.7736/JKSPE.022.049

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Rubber is positioned as an important material and essential tool and means for mass production of products in all industries due to its unique properties such as sealing, elasticity and shock absorption. However, in the case of conventional press rubber molding, its energy efficiency is low due to considerable heat loss, and the deviation of the temperature distribution of the molding mold is high due to the indirect heating method in which heat is transferred to the upper and lower molds installed on hot plates. The upper and lower heating plates were heated by several heaters installed on the hot plates. The high deviation of the temperature distribution causes unformed defects. Among the rubber mold working methods that consume considerable energy, this study attempted to reduce energy consumption by directly heating the mold via installing a heater inside the upper and lower molds in a compression mold with large energy loss. As a result, compared to the conventional method of transferring heat to the mold by heating the hot plate of the press, energy was saved by 30%, the initial mold heating time was shortened by 20 minutes, and the product defect was reduced with a rate of 25%.

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Enabling Technologies for Thermal Management During Permanent Mold Casting: A Critical Review
Cheolmin Ahn, Carl Söderhjelm, Diran Apelian
International Journal of Metalcasting.2025;[Epub] CrossRef

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Deep Learning-Based Analysis for Abnormal Diagnosis of Air Compressors: Mingyu Kang, Yohwan Hyun, Chibum Lee; J. Korean Soc. Precis. Eng. 2022;39(3):209-215.
Published online March 1, 2022; DOI: https://doi.org/10.7736/JKSPE.021.117

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Due to recent development of sensor technology and IoT, research is being actively conducted on PHM (Prognostics and Health Management), a methodology that collects equipment or system status information and determines maintenance using diagnosis and prediction techniques. Among various research studies, research on anomaly detection technology that detects abnormalities in assets through data is becoming more important due to the nature of industrial sites where it is difficult to obtain failure data. Conventional machine learning-based and statistical-based models such as PCA, KNN, MD, and iForest involve human intervention in the data preprocessing process. Thus, they are not suitable for time series data. Recently, deep learning-based anomaly detection models with better performances than conventional machine learning models are being developed. In particular, several models with improved performance by fusing time series data with LSTM, AE (Autoencoder), VAE (Variational Auto Encoder), and GAN (Generative Adversarial Network) are attracting attention as anomaly detection models for time series data. In the present study, we present a method that uses Likelihood to improve the evaluation method of existing models.

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Analysis of Compression Behavior on 3D Microlattices Coated with Metal Nanoparticle-Polymer Composites: Seo Rim Park, Do Hyeog Kim, Seok Kim, Young Tae Cho; J. Korean Soc. Precis. Eng. 2021;38(9):631-637.
Published online September 1, 2021; DOI: https://doi.org/10.7736/JKSPE.021.071

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Microlattice is well known as an efficient structure having a low density which maintains mechanical properties, so microlattice is being applied to the structural design of lightweight material in many industrial fields. In this study, we proposed a core-shell microlattice structure by the conformal coating of a metal nanoparticle-polymer composite in order to enhance the mechanical properties of polymeric microlattice printed by light-based 3D printing method. Polymeric architected microlattice was fabricated using digital light printing, which enabled the printing of complex structures with good surface smoothness. Then, the polymeric microlattice was conformally coated with aluminum nanoparticle-polymer composites. To investigate the effect of the metal nanoparticle-polymer composite coating on the mechanical properties of the microlattice, we studied the compressive behavior of cubic and octet-truss microlattices. As a result, we confirmed that both compressive strength and toughness of the two types of microlattices were effectively increased by coating with aluminum nanoparticle-polymer composites.

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Robust catalyst 3D microarchitectures by digital light printing with ceramic particle–polymer composites
Do Hyeog Kim, Sang-Hoon Nam, Gina Han, Seo Rim Park, Gwang Ho Jeong, Seok Kim, Young Tae Cho, Nicholas Xuanlai Fang
APL Materials.2024;[Epub] CrossRef
Study on Mechanical Properties of MWCNT Reinforced Photocurable Urethane Acrylate for Additive Manufacturing
Hyunjun Jo, Bum-Joo Lee
Journal of the Korean Society for Precision Engineering.2024; 41(3): 199. CrossRef

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Effect of Heat-Treatment Temperature on the Corrosion Behaviour of Cold Worked 6111 Aluminium Alloy: Jamal Nayief Sultan, Majid Khaleel Najem, Emad Toma Karash; J. Korean Soc. Precis. Eng. 2021;38(6):385-395.
Published online June 1, 2021; DOI: https://doi.org/10.7736/JKSPE.020.114

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The present investigation studies the effects of heat treatment temperature on the corrosion behavior of cold worked 6111 aluminum alloy. The specimens were cold worked at different cold working ratios, namely, 10, 20, and 40%. They were then heat treated at 100, 200, and 400°C. Corrosion tests were performed using tap water with 0.01 M sodium hydroxide, as a corrosive medium, and the weight loss of the corroded specimens plus the corrosion rates were then calculated. Experimental results showed that corrosion rates depended on the amount of cold working percentage and the heat treatment temperature. Corroded surfaces were also photographed and analyzed. The graphs revealed large numbers of corrosion pits, in addition to crevice corrosion and fine grains of rust, and these rusts were cultivated to scales that were detached from the surfaces and were subjected to corrosive medium.

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The Effect of Stress Ratio on Fatigue Cracks Growth Rate in Aluminum Alloy
Emad Toma Karash
WSEAS TRANSACTIONS ON APPLIED AND THEORETICAL MECHANICS.2022; 17: 235. CrossRef
The Effect of Stress Ratio on Fatigue Cracks Growth Rate in Aluminum Alloy
Emad Toma Karash
International Journal on Applied Physics and Engineering.2022; 1: 35. CrossRef

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A Study on Aero-Acoustics of High-Speed Turbomachinery for Different Rotational Speeds: Ji-Hun Song, Dong-Ryul Lee; J. Korean Soc. Precis. Eng. 2020;37(12):897-904.
Published online December 1, 2020; DOI: https://doi.org/10.7736/JKSPE.020.072

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This study is to numerically investigate the Aero-Acoustics of Turbocharger compressor. The turbocharger compressor is high-speed turbomachinery that rotates faster than 200,000 RPM. The Aero-Acoustics with five different rotational speeds (120,000, 150,000, 180,000, 200,000, and 220,000 RPM) is used herein. The fluid domain is designed by CATIA V5R21 and analyzed by ANSYS FLUENT V19.1 with compressible momentum equation. The Pressure-velocity coupling method of the solver is the coupled algorithm and calculated by a pressure-based method. Numerical analysis of the aero-acoustics by broadband noise sources model provides calculated sound-source and acoustic-level based on steady RANS. At the industrial site, it is important to quickly analyze the noise source. APL (Acoustic Power Level) with five different rotational speeds and sound characteristics based on flow factor at the compressor wheel was numerically calculated for the noise-based design. The maximum APL is located at blade tips in case of 120,000, 150,000 and 180,000 RPM. In the case of 200,000 RPM, the maximum APL is located at splitter tips. At more than 220,000 RPM, the maximum APL is located at the balancing cutting section of the wheel. In order to optimally design the high-speed turbomachinery, cutting sections and side locations of the wheel are essential factors to reduce physical noise.

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A Review on Flow Regimes and Aeroacoustic Coupling in Subsonic Flow Around Flat Plates
Atef El Khatib, Ahmad Al Miaari, Hassan Assoum, Ahmad Salem, Ali Hammoud
Arabian Journal for Science and Engineering.2025; 50(12): 8753. CrossRef
Aerodynamic Flow Characteristics Inducing Centrifugal Compressor Noise Generation in High-speed Turbomachinery
Jihun Song, Chang Ho Son, Dong-Ryul Lee
Journal of the Korean Society for Precision Engineering.2025; 42(9): 763. CrossRef

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Controlling the Fluid Induced Instability of a Supercritical CO₂ Compressor Supported by Magnetic Bearing: Sheng-He Jin, Jae-Eun Cha, Jee-Uk Chang, Sang-Hyun Choi, Hyeong-Joon Ahn; J. Korean Soc. Precis. Eng. 2020;37(10):737-742.
Published online October 1, 2020; DOI: https://doi.org/10.7736/JKSPE.020.049

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Since sCO₂ (Supercritical Carbon Dioxide) turbomachinery are generally small and operate at high rotational speed, the bearings remain a significant challenge to the design of the turbomachinery for the sCO₂ power cycles. However, a fluid induced instability similar to the oil whirl may occur even with the magnetic bearing under high pressure and high speed conditions of the sCO₂ turbomachinery. This paper presents experimental investigation on the instability of a sCO₂ compressor supported by the magnetic bearing. First, we introduce the sCO₂ compressor supported by the magnetic bearing. The procedure to guarantee the rotordynamic performance of the sCO₂ compressor supported by the magnetic bearing is provided. Then, the effects of the working condition such as the pressure and rotating speed on the fluid induced instability are investigated experimentally. Finally, a strategy to resolve the fluid-induced instability with conventional PID control is proposed and experimentally verified.

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Turbomachine Operation with Magnetic Bearings in Supercritical Carbon Dioxide Environment
Alexander Johannes Hacks, Dieter Brillert
International Journal of Turbomachinery, Propulsion and Power.2022; 7(2): 18. CrossRef
A Study on the Efficient Optimization of Controller for Magnetic Bearings Supporting Oil-Free Turbo-Chiller Compressor
Eunsang Kwon, Myounggyu Noh, Namsoo Lee, Seongki Baek, Young-Woo Park
Journal of the Korean Society for Precision Engineering.2022; 39(2): 123. CrossRef

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Analysis on Deformation Behavior and Restructuring of Additive Manufactured Metal Lattice-Structures under Compressive Loading Condition: Jin Qing Ye, Dong Seok Kang, Si Mo Yeon, Yong Son, Sang Hu Park; J. Korean Soc. Precis. Eng. 2020;37(8):625-631.
Published online August 1, 2020; DOI: https://doi.org/10.7736/JKSPE.020.015

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We studied compressive behavior of two types of lattice structures having small-scale struts fabricated by utilizing a metal additive manufacturing process. Generally known, the lattice structure has some advantages such as lightweight and high specific mechanical strength, allowing diverse potential applications in the aerospace and mobility industries. In this work, we proposed two types of lattice such as body-centered truss (BCT) and octahedral truss (OCT) that were designed and fabricated for a compression test. From the experimental results, the OCT has much higher strength than the BCT, and all cases showed several buckling modes during the compressive behavior. Furthermore, ‘restructuring’ occurred with BCT, and the compressive force increased overall but fluctuated due to the restructuring by an increase of compression. Through this work, we found out that the BCT has the interesting compressive behaviors, and a repetitive bucking-restructuring was found. In fact, its strength could be increased continuously by the restructuring during compression. In conclusion, the BCT has key-characteristics of lightweight and re-strengthening, which are applicable to various applications in the industry.

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Numerical Study on the Quantitative Structure-Property Relation of Lattice Truss Metals
Jiyeon Kim, Dongmyoung Jung, Yongwoo Kwon
MATERIALS TRANSACTIONS.2022; 63(10): 1317. CrossRef
Analysis on Material Behavior of Metal Additive Manufactured Lattice Structures under Quarter Compression Test
Qingye Jin, Simo Yeon, Yong Son, Sanghu Park
Journal of the Korean Society for Precision Engineering.2021; 38(9): 667. CrossRef

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Design of Tip Clearance in the D.D.I. Process to Manufacture Pressure Vessel: Hyo Seo Kwak, Gun Young Park, Chul Kim; J. Korean Soc. Precis. Eng. 2018;35(7):715-720.
Published online July 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.7.715

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The liner of CNG pressure vessel was manufactured using a deep drawing and ironing (D.D.I.) process with a single punch. Tip clearance between billet and die suggested in the actual field has been widely used to reduce forming load and to improve die life. However, the analysis and design of tip clearance is necessary for the third stage of forming defect. In this study, the tip clearance of the third stage was determined to limit the ratio of reduction of cross-sectional area based on theoretical analysis. The proposed tip clearance was verified via finite element analysis. In addition, the simulation technique was established by comparing the forming load based on theoretical calculation with the load determined via FEM.

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Degradation Progression of Polyurethane Hydraulic Reciprocating Seal: Junho Bae, Koo-Hyun Chung; J. Korean Soc. Precis. Eng. 2018;35(7):701-706.
Published online July 1, 2018; DOI: https://doi.org/10.7736/KSPE.2018.35.7.701

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In this work, the degradation progression of a polyurethane (PU) hydraulic reciprocating seal with respect to the sliding distance were investigated using a pin-on-reciprocating tribo-tester. Also, the acceleration effect of alumina particles added in lubricant on degradation of PU seal were assessed, with an aim to contribute to the development of accelerated wear testing methods. As a result, It was shown that the height of PU specimens decreased drastically at the initial stage of sliding. Then, the height decrease was found to become gradual as sliding distance further increased. The result also shows that the height decrease of the PU specimen was mainly due to the effect of the compression set and wear. In addition, the noted abrasive wear of the PU specimens was found to be significantly accelerated due to the alumina particles in lubricant, which determined a further result in 50 % faster height decrease with increasing sliding distance, as compared to the normal lubricant. The outcome of this work may provide significant and useful information for the prediction of the lifetime of a hydraulic reciprocating seal, and for the continued development of accelerated wear testing of the hydraulic reciprocating seal.

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