In this study, to improve the performance of a solid oxide fuel cell based on a porous metal support, a fuel cell using a multi-layered anode functional layer was fabricated and electrochemical performance analysis was performed. Surface and cross-sectional microstructures according to particle size control were confirmed through FE-SEM. The pore size of the multi-layer anode functional layer was gradually reduced compared to that of a single-structure anode functional layer. As a result, it was confirmed that the surface roughness was lower than that of the single structure. This led to a reduction in polarization resistance through smooth transmission of gas generated from the electrode. As a result, it was confirmed that electrochemical performance was improved by more than 1.25 times in fuel cells using a multi-layered anode functional layer compared to that with a single structure.
The fast steering mirror is now being used in industries beyond precision processing, such as space and defense. The piezoelectric fast steering mirror (PFSM), which utilizes a piezoelectric actuator, is particularly suitable for these industries as they often require devices like electro-optic devices to withstand external vibrations and impacts. While the PFSM has inherent high stiffness, its complex structure makes it difficult to control. To address this, an accurate dynamic model is necessary. In this paper, we derived a dynamic model for the PFSM using a two-inertial system model that takes into account its structural characteristics. This dynamic model consists of both a mechanical system model and an electrical system model. We measured the frequency response function from electrical input to mechanical output and compared it with the derived frequency response model to verify its accuracy. The derived model can be used not only for control design, but also for instrument design and interpretation.
Automatic transmissions, which have the advantages of compact structure and smooth shifting, are installed in various vehicles with engines and hybrid power sources. Research and development are continuously being conducted to improve power and fuel efficiency. In this study, the influence of helix direction and helix angle of the planetary gear set on thrust-bearing power loss in an automatic transmission was analyzed. A sample automatic transmission model was constructed to analyze the axial load and bearing relative rotation speed, which are the main factors in thrust-bearing power loss. The relative rotation speed of the bearing was analyzed using the sample model, and the thrust-bearing load in the axial direction was analyzed according to the helix direction of the planetary gear set constituting the model and the helix angle of the planetary gear set. The power loss occurring in thrust-bearing was derived using the analysis results of relative rotational speed and load, and the influence of the helix direction and helix angle of the planetary gear set was analyzed.
Quick picking and heavy lifting are the most common problems in current workplaces. They can cause lumbar muscle damage. The operator then must spend energy, time, and money for recovery or rehabilitation. To solve this problem, we developed a passive-type assistive suit using air mesh material, elastic band, and wire. To determine the strength support effect of the passive-type assistive suit, electromyography (EMG) was performed for eight muscles and the maximum voluntary contraction (MVC) was analyzed when lifting weights of 0%, 15%, and 30% of the subject’s weight in a Semisquat motion. Results showed that MVC increased as the weight of the heavy object increased. However, its increase was not proportional to the decrease in MVC according to the presence or absence of assistive suits or the weight of the heavy object. The highest MVC was observed for the erector spinae muscle under all conditions. The greatest decrease in MVC according to working clothes was measured for the vastus lateralis muscle (lifting: 17.7±2.95%, lowering: 18.3±0.55%). These results show that lifting work performed while wearing a passive-type assistive suit using wires and elastic bands is effective in assisting muscle activity.
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EMG and Usability Assessment of Adjustable Stiffness Passive Waist-Assist Exoskeletons for Construction Workers Jung Sun Kang, Bo Ra Jeong, Eung-Pyo Hong, Bok Man Lim, Byung June Choi, Youn Baek Lee, Yun Hee Chang International Journal of Precision Engineering and Manufacturing.2025; 26(1): 227. CrossRef
With global warming leading to abnormal weather phenomena and increasing carbon emissions, countries are implementing carbon emission reduction policies. Europe’s Carbon Border Adjustment Mechanism (CBAM) aims to promote environmentally responsible practices while maintaining industrial competitiveness. To avoid potential tariffs in the European market, Korea must vigorously pursue carbon emission reduction. Emphasizing renewable energy adoption is crucial for achieving eco-friendly and sustainable energy production. This study conducted an economic feasibility assessment for constructing small hydroelectric power plants using discharged energy from Goseong Green Power Plant. By evaluating economic viability, decision-makers could assess potential benefits and costs to support effective planning and implementation. Findings of this study could encourage investments in renewable energy projects, fostering a greener and more sustainable energy landscape for the future.
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.
In this work, precise gas pressure control based on a closed pneumatic circuit was achieved with a mechanically driven gas pressure controller (MDGPC), consisting of a variable-volume bellows chamber and linear actuator. The linear actuator was employed to change an axial dimension of the bellows chamber with the proportional (P) and proportional-integral (PI) controls for fast, stable, and precise pressure control of the gas inside the bellows chamber. The pressure control stability and resolution of the MDGPC were approximately 1.5 Pa and 10 Pa for the P control and 1 Pa and 5 Pa for the PI control, respectively. Despite the more stable and precise control characteristics of the PI control method, overshoots and undershoots observed during the set-point pressure changes and recoveries from pressure disturbances rendered it unsuitable for the MDGPC control method. In contrast, the MDGPC operated under the P control did not show any significant overshoots or undershoots when the set-point pressure abruptly changed or when the MDGPC was exposed to pressure disturbances. Therefore, it was concluded that a fast, precise, and stable gas pressure control in a closed manner was attainable with the MDGPC under the P control.
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Pneumatic temperature control characteristics of a variable-load heat source with a pressure-controlled loop heat pipe Bomi Nam, Wukchul Joung International Communications in Heat and Mass Transfer.2025; 166: 109219. CrossRef
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SFT, which has a high glass fiber content, is one of the effective methods to replace metal and secure weight reduction and price competitiveness. Also, paintless injection molding in which a functional pattern is applied to the mold surface can eliminate the cost of painting. In this study, three types of SFTs were manufactured by adding round glass fibers measuring Φ7 and Φ10 μm and flat glass fiber measuring 27 × 10 μm for the experiment. DOE (Design of Experiment) was conducted to confirm the change in the warpage of the product and the gloss of the micro pattern due to the cross-sectional shape of glass fibers and the major injection conditions. Based on the results, it was identified that the flat SFT had a very small warpage compared to the round SFTs, and the holding pressure was the main factor in the warpage of all three SFTs. The Φ7 μm SFT had the largest gloss value, and the Φ10 μm SFT and the flat SFT had similar average values. All SFTs demonstrated an enormous change in gloss according to the change in mold temperature. The flat SFT had the smallest standard deviation in both warpage and gloss.
Controlling an optical sensor’s line of sight (LOS) with an inertial stabilization system carried out on a dynamic platform is a challenging engineering task. The LOS needs to track a target object accurately despite intentional maneuvers, inadvertent motions, and additional disturbances. In this study, a super-twisting sliding mode controller (STSMC) is implemented to overcome this problem. The controller is designed based on the analysis of system dynamics. The stability is then proved to be satisfactory by the Lyapunov theory. Then, the control law is validated through experimental studies. In addition, a comparison to the performance of a linear controller is derived so that the effectiveness of the proposed controller is validated.
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Farming is a typical task that includes repetitive tasks, incomplete working positions, and weight work, along with exposure to a number of musculoskeletal diseases and harmful factors. Therefore, in this study, work clothes were developed for older agricultural workers exposed to musculoskeletal diseases and alienated from the medical system. Work clothes can help in repetitive cropping and support the load on the work, preventing and mitigating farmers" diseases. To verify the effectiveness of the developed clothing, six men in their 20s were evaluated for muscle usage before and after wearing the clothing in two ways: stoop lifting and squat lifting. The results of this study showed that the mass of most muscles, except the gastrocnemius muscle, was reduced during lifting operations by stoop lifting after wearing work clothes. The reason why the gastrocnemius was more activated was that the ankle joint was greatly activated by dorsal flexion. For squatting and lifting, most of the muscle usage was reduced. In future research, we want to analyze the muscle characteristics of actual agricultural workers on wearing work clothes.
With the development of 3D printing technology, its applications are expanding. However, 3D printed parts present a challenge in achieving high-quality surface roughness because of stair stepping problems. With the recent application of 3D printing in electronics and the visibility of flow in microfluidic systems, high-quality surface roughness is needed. Chemical mechanical polishing (CMP), one of semiconductor fabrication processes, has the longest planarization length in terms of productivity among existing planarization methods. In this study, we investigate friction characteristics of polishing of ABSLike resin material printed by the Stereolithography Apparatus (SLA). At the polishing of ABS-Like resin, the friction force has a high value at the beginning of polishing, but it stabilizes as processing progresses because of the effect of waviness on the printed material. The surface roughness (Sa and Sz) reduction and the glossiness of ABS-Like resins after polishing appear to be related to the reduction of the Shore D hardness resulting from the rise in the polishing process temperature caused by friction during polishing.
This study proposed the proper detonation delay time of a main warhead after a precursor warhead detonation in an arbitrary tandem shaped charge missile as 407 μsec. In addition, the available detonation delay time range of the main warhead was proposed to be between 396 μsec and 418 μsec. The proposed figures were based on the analysis of the target protection capability and the scattering reactor behaviors of the explosive reactive armor with dual reactive panels. By virtue of this work, the determination of main warhead detonation delay time is more effective and convenient. Finally, the tandem shaped charge missile with more effective penetration performance also could be developed in the future.
Recently, the concern for safety is increasing as customers’ interest in Run-Flat tires, which can assure their safety in case of a puncture when driving, is growing. Run-Flat tires continues to evolve with the demands of customers who want the performance of general tires such as fuel-consumption and comfort from the basic Run-Flat function in the 1st generation. Run-flat tires are designed in various ways to cope with puncture in pneumatic tires. Currently, Run-flat tires in which Runflat Inserts are inserted into sidewalls of the tires are mainly used. In this study, we would like to propose a method to predict the temperature of sidewall of a Run-flat tires while running and how it affects the durability. We predicted the temperature distribution of sidewall during the running of Run-flat tires by calculating energy loss which is from the viscoelastic characteristic of rubber through deformation analysis of tires, and verified the prediction technique by comparing with the Run-flat endurance test.
Polyacrylamide (PAM) was used for matrix material to fabricate composite hydrogels reinforced with natural cellulose nanocrystal (CNC). Invoking in situ free-radical polymerization with different concentration of cellulose nanocrystal, polyacrylamide hydrogels were fabricated. The chemical structure, compression strength, morphology and dielectric properties of the composite hydrogels were investigated. The CNC played a role as a reinforcing filler and a multifunctional cross-linker in the hydrogel. The elastic modulus and dielectric property of the composite hydrogels increased as increasing the CNC concentration. The electrical actuation test of the PAM/CNC hydrogel shows its possibility for soft electro-active materials for active lens.
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A gas turbine is the main equipment used in a combined heat and power plant. It generates a high sound pressure noise level. To reduce the noise level, an enclosure is installed around the turbine. The sound insulation performance of the enclosure affects the amount of external noise reduction. In this study, a sound transmission loss analysis is performed using the boundary element method to predict sound insulation performance according to the numbers and shapes of the supporter. Radiated noise analysis is also performed for the main external points of the enclosure using ray-acoustics. The results of these analyses are presented and a design plan is proposed that reduces the sound pressure noise level of the enclosure.
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