The thermodynamic efficiency of the stirling engine has a high theoretical efficiency closest to that of the Carnot cycle, and various heat sources can be used as an external combustion engine. In the early days of the invention, the sealing technology was not good, so it was pushed to the steam engine and was not put to practical use, and in modern times, it was not used due to the development of internal combustion engines. Sterling cryogenic refrigerators using linear compressors have advantages such as low vibration, small size, light weight, low required power, and sufficient durability compared to conventional cryogenic refrigerators, so they are widely used as infrared sensors for night vision goggles (0.5 to 1.9 W at 77 K) and superconducting filters for mobile communication wireless base stations (3 to 6 W at 77 K). By examining the characteristics of the refrigerator using such a stirling refrigerant refrigerator, the difference from the existing refrigeration air conditioning system using refrigerant gas can be seen, and this study showed that the manufacturing method of the motor part and the design of the inlet voltage and current and frequency of the motor greatly affect the performance of small linear stirling refrigerators when manufacturing a compressor of a linear stirling refrigerator.

본 연구에서는 내연적 시간적분법과 비선형 정적해석에서 발생하는 선형 시스템을 효율적으로 해결하기 위한 자체 솔버 프로그램 을 개발하고 이를 평가하였다. 희소행렬 연산에 유용한 반복법과 전처리기(preconditioner) 알고리즘을 구현하였으며, 자체 개발을 통 해 프로그램 코드의 수정 및 활용을 용이하게 하였다. 또한 메모리 사용량 절감 및 계산 효율성 향상을 위해 CSR(compressed sparse row) 형식 기반의 행렬 및 벡터 연산을 구현하였다. 개발된 솔버 성능 검증을 위해 Voronoi-cell 격자 모델 기반 선형시스템을 대상으 로 개별 반복법 알고리즘을 적용하였다. 아울러 선형/비선형 정적 구조 거동을 모두 고려하여 관련 대칭/비대칭 시스템 행렬을 도출 하고 이를 활용하였다. 보의 처짐 문제를 대상으로 각 반복법의 결과를 수렴성, 계산 시간, 행렬의 대칭성 및 크기에 따라 비교 분석하 였다. 이를 통해 자체 개발한 반복법 솔버의 수치적 성능을 검증하였고 내연적 구조해석 등에 수반되는 선형 시스템의 근사해 계산에 개발 코드를 효과적으로 활용할 수 있음을 확인하였다.

This study investigated the vertical displacement behavior caused by differential drying shrinkage in jointed concrete pavements. This study proposed a method to convert this behavior into an equivalent linear temperature difference for structural analysis. Controlled experiments were conducted under varying humidity and airflow conditions to simulate pavement environments. The test results showed that a lower relative humidity and added airflow significantly increased the vertical displacement, particularly at the slab edges. A 3D finite element model using ABAQUS was developed to analyze the behavior and derive the equivalent linear temperature difference that increased with curing age and varied notably with environmental conditions. These findings highlighted the impact of early-age environmental factors on the shrinkage behavior and suggested that the proposed method offered a practical approach for predicting deformation without repeated physical testing.

본 연구는 한국에서 시행 중인 탄소배출권 거래제도가 탄소중립을 달 성하는데 효과적으로 기여하고 효율적으로 작동할 수 있도록 정책적 시 사점을 제공하고자 한다. 이를 위해서, 탄소배출권 가격과 전산업생산지 수의 관계를 분석하였다. 즉, 탄소배출권 가격과 전산업생산지수의 선형 및 비선형 관계를 고려하여 경제학적 모형을 통해 추정 및 분석을 진행 하였다. 분석 방식은 구조변화를 반영한 방식과 임계값(문턱값)을 반영하 는 방식으로 나누어 모형을 구축하고 추정하였다. 그 결과, 한국의 탄소 배출권 가격과 전산업생산지수는 추정한 모형에서 비선형적 관계가 포착 되었다. 이러한 결과는 한국에서 시행 중인 탄소배출권 거래제도가 효율 적으로 작동할 수 있도록 추가적인 정책이 필요함을 시사한다. 예를 들 어, 산업 분야에서 저탄소 공정으로의 전환(또는 저탄소 경제로의 전환) 이 완전히 이루어지지 않은 현실을 고려할 때, 여전히 경제가 성장하는 상황에서 비선형 관계가 포착된다는 것은 탄소배출권 가격이 적정한 수 준을 유지하지 못하고 지속적으로 하락하는 추세를 나타낸다는 것이기 때문이다. 따라서, 탄소배출권 거래제도의 본래 취지인 탄소배출량의 감 축에 기여할 수 있도록 적정한 탄소배출권 가격이 배출권 거래제도하에 서 유지되도록 하는 정책을 고려해야 한다.

The Earth’s radiation belts, which extend from near the Earth to approximately geosynchronous orbit, contain highly energetic particles that actively interact with various plasma waves. This study reviews two numerical approaches to studying waveparticle interactions in the Earth’s radiation belts and discusses their respective advantages and limitations. The first approach involves diffusion simulations based on quasi-linear theory, which is well-suited for describing the collective dynamics of many particles from a statistical perspective. The second approach, test particle simulation, focuses on the detailed motion of individual particles, revealing nonlinear phenomena such as phase trapping and bunching. Both methods allow for the derivation of diffusion coefficients, which quantify the timescale of wave-particle interactions and help explain how particles either precipitate into the atmosphere or accelerate to higher energies in the Earth’s radiation belts. Additionally, these methodologies can be adapted to study the dynamics of planetary radiation belts, such as those around Jupiter and Saturn, by adjusting for the specific environmental parameters of each planet.

As environmental concerns escalate, the increase in recycling of aluminum scrap is notable within the aluminum alloy production sector. Precise control of essential components such as Al, Cu, and Si is crucial in aluminum alloy production. However, recycled metal products comprise various metal components, leading to inherent uncertainty in component concentrations. Thus, meticulous determination of input quantities of recycled metal products is necessary to adjust the composition ratio of components. This study proposes a stable input determination heuristic algorithm considering the uncertainty arising from utilizing recycled metal products. The objective is to minimize total costs while satisfying the desired component ratio in aluminum manufacturing processes. The proposed algorithm is designed to handle increased complexity due to introduced uncertainty. Validation of the proposed heuristic algorithm's effectiveness is conducted by comparing its performance with an algorithm mimicking the input determination method used in the field. The proposed heuristic algorithm demonstrates superior results compared to the field-mimicking algorithm and is anticipated to serve as a useful tool for decision-making in realistic scenarios.

Non-uniform reinforced concrete brace facade systems are newly considered to improve seismic performance of reinforced concrete frame buildings under lateral load. For normal and high strength concrete of 30MPa, 80MPa, and 120MPa, the cross-sections of reinforced concrete brace facade systems were designed as different size with same amount of reinforcements. The strengthened frame systems were analyzed by a non-linear two-dimensional finite element technique which was considering material non-linearities of concrete and reinforcing bars under monotonic and cyclic loadings. From the study of non-linear analysis of the systems, therefore, it was provided that the proposed braced facade systems were reliable to improve laterally load-carrying capacity and minimize damages of concrete members through comparisons of load-displacement curves, crack patterns, and stress distributions of reinforcing bars predicted by current non-linear finite element analysis of frame specimens.

Cellulose has experienced a renaissance as a precursor for carbon fibers (CFs). However, cellulose possesses intrinsic challenges as precursor substrate such as typically low carbon yield. This study examines the interplay of strategies to increase the carbonization yield of (ligno-) cellulosic fibers manufactured via a coagulation process. Using Design of Experiments, this article assesses the individual and combined effects of diammonium hydrogen phosphate (DAP), lignin, and CO2 activation on the carbonization yield and properties of cellulose-based carbon fibers. Synergistic effects are identified using the response surface methodology. This paper evidences that DAP and lignin could affect cellulose pyrolysis positively in terms of carbonization yield. Nevertheless, DAP and lignin do not have an additive effect on increasing the yield. In fact, combined DAP and lignin can affect negatively the carbonization yield within a certain composition range. Further, the thermogravimetric CO2 adsorption of the respective CFs was measured, showing relatively high values (ca. 2 mmol/g) at unsaturated pressure conditions. The CFs were microporous materials with potential applications in gas separation membranes and CO2 storage systems.

In this study, a vibrating nozzle using the waste vibration energy of the compressor body was installed in the suction flow path to improve the efficiency of the compressor through the pre-compression. To this end, the behavior of the suction valve according to the vibrating nozzle and the mass flow rate of the refrigerant entering the compression chamber were numerically analyzed. The results showed that the mass flow rate increased proportionally as the angle of the vibration nozzle increased. Among the profile shapes of the vibration nozzle, the concave or straight shape showed the highest mass flow rate. Considering the ease of machining, the straight shape is more favorable. On the other hand, as the operating frequency and stroke of the vibration nozzle increased, the mass flow rate also increased proportionally. It can be seen that the largest nozzle angle, operating frequency, and stroke are favorable for pre-compression unless the suction flow is restricted.. In the future, it is necessary to apply the vibrating nozzle system to an actual compressor model to experimentally check the compressor's cooling power, compression work and EER.

In this research, a new piston pinhole boring machine for simultaneous 3-axis machining using linear motor and tilting unit is developed. We propose a new method that combines the linear motor and tilting unit to overcome the limitations of existing techniques. By using the linear motor, we suggest oval machining of piston pin holes. The horizontal reciprocating motion of the linear motor allows for oval machining, creating horizontal or vertical ovals on the pin holes based on the spindle tool's rotation angle. For profile machining of piston pin holes, we propose the use of a tilting unit that converts servo motor motion into linear motion. The vertical motion of the tilting unit enables profile machining, allowing the spindle tool connected to it to translate vertically during spindle rotation and shape the pin holes. To ensure simultaneous oval and profile machining, we suggest channel synchronization, separating the oval and profile machining channels. Synchronizing these channels enables both oval and profile machining to be performed simultaneously on the pin holes. In summary, this research aims to develop a piston pinhole boring machine that effectively utilizes the linear motor and tilting unit for accurate and productive pin hole machining, achieving simultaneous 3-axis machining.

In this research, a new structure of an asymmetric piston dedicated machining center is developed. By applying 2 linear motors in this machine, the slide unit structure could be simplified by comparing to the ball screw method, resulting in easier maintenance of the machine and enabling simultaneous machining in 2 axes and high-speed precision machining. In addition, a dedicated HMI for the asymmetric piston is developed to support efficient operation by workers, allowing them to verify product quality and take necessary actions. It is confirmed that by fully utilizing control libraries and productive programming languages, immediate response to future demands could be achieved. Through speed control loop performance testing, it is confirmed that applying feedforward function could improve the response speed, control accuracy, and stability of the speed control loop. The application of polynomial interpolation and Newton interpolation in the actual machining of asymmetric pistons confirmed the achievement of dynamic machining precision at high speeds. The developed machine and HMI are expected to contribute significantly to the efficiency, productivity, and improvement of product quality in the machining of asymmetric pistons.