A force-free field (FFF) is determined solely by the normal components of magnetic field and current density on the entire boundary of the domain. Methods employing three components of magnetic field suffer from overspecification of boundary conditions and/or a nonzero divergence-B problem. A vector potential formulation eliminates the latter issue, but introduces difficulties in imposing the normal component of current density at the boundary. This paper proposes four different boundary treatment methods within the vector potential formulation. We conduct a comparative analysis of the vector potential FFF solvers that we have developed incorporating these methods against other FFF codes in different magnetic field representations. Although the vector potential solvers with the new boundary treatments do not outperform our poloidal-toroidal formulation code, they demonstrate comparable or superior performance compared to the optimization code in SolarSoftWare. The methods developed here are expected to be readily applied not only to force-free field computations but also to time-dependent data-driven simulations.

The paper studied the climbing structure and magnet selection method of exploration platform utilized for large-scale steel structures such as vessel surface. With respect to wall climbing robots, the study proposed a stable operation structure even in rapid incline change of vessel surface. Since the wheel-based operating method is hard to work flexibly in inclination changes, we employed joints and designed the robot to have a rotation joint in the center. The arrangement of wheels is an important aspect of this structure. Viewed from the side, the robot wheels should overlap with each other to have intersection points. The wheels here are ring-type permanent magnets and serve as a tool of attachment on walls. Based on the conditions identified through formula modeling, we proposed the required magnetic force. Important factors needed for magnetic force setup include platform weight, angle between ground and inclined plane, and friction coefficient. We considered only the required magnetic force for the stable adhesion of circular magnet while making not a separate mention about the necessary force for directional locomotion. The analysis results of ANSYS Maxwell are applied to magnetic attachment. Based on the final analysis results, we built a platform and found it did not slip and stayed attached on steel plate.

본 논문에서는 안정적인 전력공급이 어려운 실제 현장에 적용하기 위해서 PSC 내부 텐던의 긴장력 관리를 위한 저전압 EM센싱기법을 검증하였다. 지난 국내외 PSC 구조물 사고 사례를 볼 수 있듯이, 공용간 구조적 안정성을 확보하기 위해서는 PS텐던의 긴장력 관리가 매우 중요함을 알 수 있었다. 이에 본 논문에서는 EM센서를 통해 탄성-자기이론을 기반한 강자성 체의 자기변형과 응력의 관계를 이용하여 전압 크기에 따른 긴장력에 대한 자기이력곡선을 계측하고자 하였다. 이를 위해 이중 원통코일형태의 EM센서를 제작하고 유압식 인장기를 이용한 PS텐던 인장 실험 장비를 구성하였다. 실험은 단계적으 로 전압을 감소시켜 긴장력 크기에 따른 자기이력곡선의 변화를 계측하면서 최대/최소 전압값에 대한 계측결과에 따른 투자 율의 변화와 긴장력의 관계를 비교·분석하였다. 그 결과, 전압이 감소하여 자기장의 크기가 작아짐에 따라 추정식에 대한 상수는 상이하지만 유사한 형태의 자기이력곡선 투자율의 변화를 확인할 수 있었다. 이를 통해 본 연구에서는 저전압 상태에 서 EM센싱기법을 이용한 PSC 내부 텐던에 대한 긴장력 관리가 가능할 것으로 판단된다.

본 논문에서는 PSC 거더의 긴장력을 계측하기 위한 EM 센싱 기법을 다양한 PS 텐던에 적용하기 위하여 PS 강종별 긴장력 변화에 따른 자기이력 모니터링 결과를 소개한다. PSC 교량의 성능평가에 있어 PS 텐던의 긴장력은 매우 중요한 인자이나 현재는 시공시 설계 긴장력의 도입 여부만을 검증하고 그 이후에는 긴장력 관리가 이루어지지 않는 실정이다. 이를 계측하기 위하여 EM 센서를 이용하여 긴장력을 계측하는 기법에 대한 연구가 이루어지고 있으나 PSC 거더에 사용되는 모든 PS 텐던에 대한 연구는 이루어지지 않았다. 이에 본 연구에서는 PSC 교량에 주로 사용되는 B, C, D종 PS 텐던에 대해 EM 센싱 기법을 적용하기 위하여 각 강종별 긴장력에 따른 자기 이력 변화를 모니터링하였다. 이를 위해 B종 12.7mm, C종 15.2mm, D종 15.2mm PS 텐던 시편에 50, 100, 150, 180kN의 긴장력을 도입하고 각 긴장력 단계마다 자기 이력 곡선을 EM 센서를 통하여 계측하였다. 계측 결과 각 긴장력 단계마다 그 투자율이 정량적으로 변화하는 것을 확인할 수 있었다. 특히 B, C 종의 경우 단면적이 달라 선형회귀분석식의 상수는 상이하지만 유사한 기울기를 가지고 변화하고 D종의 경우 다른 강종과 다른 기울기를 가지고 변화하는 것을 확인하였다.

Measuring the exact cable tension force is important to cable supported bridge under construction and on service. This study was planned to propose EM(electro-magnetic) sensor-based method for measuring the tension force of MS(multi-strand) cable in cable-stayed and extradosed bridge. The tension force in each strand is the same due to MS cable construction using Iso-tensioning system. Therefore, In this prosed method, EM sensor was installed directly at a strand and the measurement model was established for estimating the tension force of strand via EM sensor by experiments. The measurement model was derived from the relation of tension force and magnetic permeability. Also, the magnetic permeability is shown to be different according to the magnetization characteristic of 1860MPa and 2200MPa high-strength strand. The difference is increased as tension force increases. Additional experiment was conducted to verify the measurement model. As a result, the distribution of strand tension calculated upon the EM sensor is similar to those of tension measured by load cell. This proposed approach can be an effective tool for monitoring and measuring the cable force of MS cable.

This study investigates on the tuning stainless steel(STS630) to understand for groove cutting characteristics. For this purpose, we observed the cutting force according to feed rate and cutting speed variation and performed the computational analysis due to groove cutting depth. In groove cutting of stainless steel, there were principal force, feed force and radial force by arranging the highest cutting force in order. In case of wall thicknesses of 0.3mm and 0.5mm at groove cutting, principal force increases according to the increase of feed rate but it is not related to cutting speed. We found the unstable region of cutting force that is caused to the friction resistance of cutting tool and elastic deformation of groove wall. In computational analysis, we confirmed that the more feed rate increases, the more strain increases around the tooth root.

This paper studies the repulsion occurring between the permanent magnet by the simulation analysis. Nowadays, there are many cases such as magnetic levitation, safety bumper device and so on using the properties of the permanent magnet. As the neodymium magnet of the powerful ferromagnetic material is less expensive by comparing with the strong magnetic force for industrial, medical areas and etc., it can be used at the various applications. The prediction of the magnetic force is becoming increasingly important in order to be used effectively permanent magnet in various fields. Therefore, the results of the magnetostatics by Ansys and the MAXWELL of commercial electromagnetic analysis software are analyzed and compared. Magnetic force is inversely proportional to the distance and power. In this paper, the permanent magnet was simulated and compared by the two permanent magnets of the small sizes with the diameter of 4mm and the length of 8mm. In addition, the forces between the ferromagnetic iron and permanent magnets are simulated.

면진장치 중에서 최근 많은 연구가 이루어지고 있는 마찰진자 베어링은 적절한 마찰력을 얻기 위해 PTFE(Polytetrafluoroethylene) 마찰재가 이용되고 있다. 본 연구에서는 자력의 반발력을 이용해 재료의 성질을 대체하여 면진성능을 향상 시킬 수 있는 자력을 이용한 마찰진자 베어링을 제안하였다. 제안된 시스템은 자력에 의한 반발력이 수직력을 줄여줌으로써 재료에 의한 마찰계수의 영향을 줄일 수 있음을 가정하였다. 또한 자력의 영향을 가정하기 위해서 간단한 실험을 구성해 보았으며, 자력이 작용을 할 때 마찰계수(\mu)를 약 20%정도 줄여줄 수 있었다. 실험 결과를 적용한 수치해석을 통해 다양한 지진에 대해서 기존의 마찰진자 베어링보다 향상된 성능을 보여주었고, 특히 지진으로 인해 구조물의 파괴에 작용하는 주된 요소인 최상층의 가속도와 구조물의 상대변위를 비교함으로써 제안된 시스템이 면진장치로서의 기능을 가지고 있음을 확인하였다. 자력을 이용하여 기존의 PTFE 마찰재를 대체할 수 있는 자력을 이용한 마찰진자 베어링의 구조적 설계를 할 수 있다면 마찰진자 베어링의 문제점을 보완한 기초격리장치로서 적용될 수 있을 것으로 사료된다.

In this paper, an magnetic hysteresis monitoring result for various PS tendon is indtoduced to apply the EM sensing technique to measure the tensile force of PSC bridge. The tensile force of PS tendon is a very important factor in the performance evaluation of PSC bridges. To measure the tensile force of PS tendons, the EM sensing based NDT method was developed but the proposed method cannot be applied to various class of PS tendons. The permeability of specimen was gradually decreased according to increase of tensile force.

To maintain the tension force of PS members is a very important issue for the safety of PSC structures. In practice many cases of corrosions and tensile force reduction in PC tendons, however, are reported from various causes. In the near future, thus the estimation of tensile forces in PC tendons would be major work of maintaining PSC structures. In this study, the approach using magnetic characteristics of PC tendons to estimate tensile force was investigated. Using simple but reasonable test procedures, the possibility of the approach like this was verified.