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폴리비닐알콜/히드록시아파타이트 동결융해 젤의 납 이온 흡착제거 특성 연구
박재하,민병길,Park, Jae-Ha,Min, Byung Gil 한국섬유공학회 2012 한국섬유공학회지 Vol.49 No.5
A new adsorbent for removing heavy metal lead ions from wastewater, poly(vinyl alcohol)/hydroxyapatite (PVA/HAp) composite cryogel, has been investigated. The PVA/HAp cryogel was prepared through a clean process by using water and freeze-thawing. The PVA/HAp cryogel is provided with interconnected macropores varying from 0.1 um to several um and well dispersed and immobilized HAp in cryogel. Continuous column tests of lead ion sorption were carried out to test the sorption ability of PVA/HAp cryogel. Moreover, it was found that the porosity of the cryogels was increased by adding water-soluble poly(vinyl pyrrolidone) (PVP) followed by its extraction after cryogellation. The maximum sorption capacity of the cryogels was 69 mg/g HAp for the cryogel having 20 wt% of HAp based on PVA. On the other hand, the maximum capacity was increased to 108 mg/g HAp when 15 wt% PVP based on PVA was added and extracted due to the increase of the effective HAp amount exposed to the aqueous lead ion.
음향방출 파형 파라미터 필터링 기법을 이용한 실시간 음원 분류
조승현(Seung Hyun Cho),박재하(Jae Ha Park),안봉영(Bongyoung Ahn) 한국비파괴검사학회 2011 한국비파괴검사학회지 Vol.31 No.2
음향방출기법은 대형 구조물의 구조건전성감시(SHM)를 위한 매우 효율적인 방법이지만, 롤러코스터 지지구조물처럼 승용물의 운행으로 인한 매우 큰 잡음이 일상적으로 존재하는 경우에는 균열 진전 신호만을 분류하여 실시간 감시를 수행하기가 쉽지 않다. 이와 같은 문제의 해결을 위해 본 연구에서는 실시간으로 음원의 분류가 가능한 파형 파라미터 필터링 기법을 제안하였다. 파형 파라미터 필터링 기법은 음향방출 신호의 파형 파라미터를 이용하여 음향방출 히트를 사전에 필터링함으로써 실시간으로 감시하고자 하는 대상 음원만을 분류해내는데 매우 유리한 점이 있다. 다양한 음원에 대해 음향방출 파형 파라미터를 측정 및 분석하여 제안한 기법의 타당성을 살펴보았다. 또한, 파형 파라미터 필터가 내장된 음향 방출 시스템을 구축하고 이를 실제 롤러코스터 지지구조물에 적용하여 실시간 균열진전 감시를 위한 가능성을 타진하였다. The acoustic emission(AE) technique is a well established method to carry out structural health monitoring(SHM) of large structures. However, the real-time monitoring of the crack growth in the roller coaster support structures is not easy since the vehicle operation produces very large noise as well as crack growth. In this investigation, we present the waveform parameter filtering method to classify acoustic sources in real-time. This method filtrates only the AE hits by the target acoustic source as passing hits in a specific parameter band. According to various acoustic sources, the waveform parameters were measured and analyzed to verify the present filtering method. Also, the AE system employing the waveform parameter filter was manufactured and applied to the roller coaster support structure in an actual amusement park.
박재하 ( Park Jae Ha ),승홍민 ( Seung Hong Min ),조승현 ( Cho Seung Hyun ) 한국구조물진단유지관리공학회 2018 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.22 No.1
The loss of prestress in cable supported structure is a direct cause of structural deterioration of the structure. Thus, measurement and evaluation of the tensile force acted on a strand consist of the cable system have been a significant technological factor. However, a measurement method of tension for each of strands is not proposed, as well as conservative assessment of cable system is bing adopted in industrial application. This paper proposes a new and effective method for measurement of tensile force in a strand based on ultrasound. Electromagnetic acoustic transducer(EMAT) is used for generation of ultrasound. Tensile force acting on a strand can be measured by characterization of guided waves that propagate along the boundary of geometry. Consequently, proposed method is experimentally verified by some experiments using seven-wire strand.
철-코발트 합금 패치로 구성된 자기변형 트랜스듀서를 이용한 체적 전단파 발생 및 측정
박재하(Jae Ha Park),조승현(Seung Hyun Cho),안봉영(Bongyoung Ahn),권휴상(Hyu-Sang Kwon) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.8
최근 가공성이 우수하고 강한 자기변형성을 가진 강자성 패치가 소개되면서, 이를 이용한 탄성초음파 변환 연구가 활발하다. 이러한 자기변형 패치 트랜스듀서는 SH 파와 비틀림파 등 전단파 변환 성능이 우수하여 비파괴평가 분야에서 많은 주목을 받고 있지만, 지금까지 관련 연구가 유도초음파 변환에 집중된 반면 체적초음파에는 아직 적용이 된 예가 없다. 본 연구에서는, 자기변형성이 큰 재질 중 하나인 철-코발트 합금을 이용한 체적전단파 트랜스듀서를 제안하고자 한다. 제안한 트랜스듀서는 강자성 패치, 코일, 영구자석, 요크를 포함하여 모듈형으로 설계되었고, 실험을 통해서 파형 및 방사 패턴 등을 측정하였다. 결과적으로, 제안한 트랜스듀서는 신호대잡음비 및 방사패턴 면에서 상당히 우수한 성능을 보임을 확인하였다. Recently, the results of many studies have clarified the successful performance of magnetostrictive transducers in which a ferromagnetic patch is used for the transduction of guided shear waves; this is because a thin ferromagnetic patch with strong magnetostriction is very useful for generating and detecting shear wave. This investigation deals with bulk shear wave transduction by means of magnetostriction; on the other hand, the existing studies have been focused on guided shear waves. A modular transducer was developed; this transducer comprised a coil, magnets, and a thin ferromagnetic patch that was made of Fe?Co alloy. Some experiments were conducted to verify the performance of the developed transducer. Radiation directivity pattern of the developed transducer was obtained, and a test to detect the damage on a side drill hole of a steel block specimen was carried out. From the results of these tests, the good performance of the transducer for nondestructive testing was verified on the basis of the signal-to-noise ratio and narrow beam directivity.
단면 초음파공진 거동 변화에 기반한 PWS형 케이블 강선 긴장력 측정 타당성 연구
박재하 ( Park Jae-ha ),지봉규 ( Ji Bonggyu ),조승현 ( Cho Seung-hyun ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.1
The main objective of this paper is a feasibility Study for measuring tensile forces in the steel wire which are widely used in various types of prestressed structures. A steel wire serves as a load-bearing element, and electromagnetic-acoustic transducers are used to excite and detect resonant vibrational modes. The results show a promising feasibility on measurement of tensile forces in the steel wire.
박재하 ( Park Jae-ha ),조승현 ( Cho Seung-hyun ) 한국구조물진단유지관리공학회 2019 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.23 No.1
The evaluation for the status and levels of tension acting on a cable supported structure has been a issue due to the structural stability. Each of strands comprising that structures is adopted prestress, the tension level of the strand during the operation is a significant factor for structural integrity of the system. However, a suitable alternative for measurement of tension acting on a strand is not proposed, as well as conservative assessment of cable system is bing adopted in industrial application. Thus, in this paper, a new method is proposed for measurement of tensile forces in a strand using guided waves. This method use a dispersion characteristic of guided waves with variation of stiffness between each of wires. Proposed method is experimentally verified by some experiments using a seven-wire strand.