• Steel and Composite Structures
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• 제33권3호
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• pp.445-461
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• 2019

The ultrasonic guided wave-based technique has become one of the most promising methods in non-destructive evaluation and structural health monitoring, because of its advantages of large area inspection, evaluating inaccessible areas on the structure and high sensitivity to small damage. To further advance the development of damage detection technologies using ultrasonic guided waves for the inspection of welded components in structures, the transmission characteristics of the ultrasonic guided waves propagating through welded joints with various types of defects or damage in steel plates are studied and presented in this paper. A three-dimensional (3D) finite element (FE) model considering the different material properties of the mild steel, high strength steel and austenitic stainless steel plates and their corresponding welded joints as well as the interaction condition of the steel plate and welded joint, is developed. The FE model is validated against analytical solutions and experimental results reported in the literature and is demonstrated to be capable of providing a reliable prediction on the features of ultrasonic guided wave propagating through steel plates with welded joints and interacting with defects. Mode conversion and scattering analysis of guided waves transmitted through the different types of weld defects in steel plates are performed by using the validated FE model. Parametric studies are undertaken to elucidate the effects of several basic parameters for various types of weld defects on the transmission performance of guided waves. The findings of this research can provide a better understanding of the transmission behaviour of ultrasonic guided waves propagating through welded joints with defects. The method could be used for improving the performance of guided wave damage detection methods.

• 한국항만경제학회지
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• 제23권2호
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• pp.41-61
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• 2007

중국의 WTO 가입 이후 급속한 물동량의 증가와 중국항만의 급성장 추세는 대 중국 교역항으로서 성장하고 있는 평택 당진항에 있어서는 기회이자 위기가 될 수 있으며 또한 항만 발전의 전환점이 될 수 있다. 이러한 시점에서 해당 항만을 이용하는 북중국 화주의 정확한 요구파악은 항만 활성화의 주요한 전략적 요소로 고려될 수 있다. 본 연구에서는 평택 당진항에 대한 중국 현지 업체를 대상으로 설문조사를 실시하여 고객의 요구를 파악함으로서 평택 당진항의 활성화 전략을 제시하는데 목적이 있다. 연구결과 평택 당진항은 높은 지리적 강점을 보유하고 있으나 항만배후지 개발 지연, 다양한 항로의 부족, 마케팅 전략의 부재 등이 항만 활성화에 부정적 요인들로 나타났으며, 이를 위해 단순한 화물의존형 항만이 아닌 화물창출형의 항만으로 발전해야 신설항만으로서의 한계점을 극복하고 항만 활성화를 도모 할 수 있을 것이다.

• 한국방재학회 논문집
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• 제11권2호
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• pp.67-73
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• 2011

본 연구의 목적은 공기 단축과 초기 공사비를 절감하기 위해 PC 긴장재를 사용하지 않고, 슬리브와 일반 철근만으로 구성된 경제적이면서 시공성이 우수한 프리캐스트 교각 공법 개발에 있다. 이를 위해 본 연구에서는 신형식 철근이음 장치인 그라우팅형(形) 슬리브(Splice sleeve, 이하 슬리브)를 제안하고 최적의 슬리브를 개발하기 위하여 슬리브 길이, 철근직경, 양생방법 등을 변수로 하여 유한요소해석 및 인장실험을 수행하였다. 슬리브의 유한요소해석을 통하여 최적의 형상을 도출하였으며, 인장 성능 검토 결과, 철근의 인발에 의한 파괴는 발생하지 않았으며, 철근의 인장 파괴 혹은 슬리브의 기계적 결함에 의한 볼트 파단만이 관찰되었다. 제안된 슬리브는 우수한 인장성능을 갖고 있음을 확인하였으며 프리캐스트 교각에 무리 없이 적용할 수 있음을 검증하였다.

• Physical Therapy Rehabilitation Science
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• 제8권2호
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• pp.61-66
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• 2019

Objective: The purpose of this study was to investigate the effects of resistance applied in various directions on lower extremity muscle activity and balance during squat exercise performance. Design: Cross-sectional study. Methods: Forty-one adults (19 males and 22 females) agreed to the study purpose and procedures. All subjects randomly performed squat exercises with an intensity of overcoming 10% of body weight resistance pulled forward, backward and general squats with $60^{\circ}$ of knee joint flexion. Electromyography was used to measure muscle activity of the vastus medialis oblique (VMO), rectus femoris (RF), vastus lateralis oblique (VLO), biceps femoris (BF), and semitendinosus (ST) muscles. The Wii Balance Board was used to assess balance during the three-method squat operation. Each operation was measured three times for 10 seconds. Results: There were significant differences in muscle activities of the VMO, RF, VLO, ST and balance ability with the application of three directions of resistance (p<0.05). Post hoc comparisons revealed that squats performed with resistance pulled in the backward direction resulted in higher VMO, RF and VLO activity than with the resistance placed in a pulled forward direction (p<0.05). In the ST, resistance applied in the pulled forward direction showed greater muscle activity compared to the pulled backward direction (p<0.05). With balance, squats performed with resistance pulled in the forward direction showed greater muscle activity than with resistance applied in the pulled backward direction and during general squat performance (p<0.05). Conclusions: In this study, squat exercises performed with resistance applied in the direction of pulling backwards was found to be the most effective in improving quadriceps muscle strength and balance. It is effective to provide resistance that is placed in the forward when it is difficult to perform a general squat due to weakness of the quadriceps.

• 대한정형도수물리치료학회지
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• 제25권1호
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• pp.71-76
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• 2019

Background: An 8-year-old girl had severe neck pain and stiffness after trauma. CT scan showed atlantoaxial rotatory subluxation (AARS). She had conservative treatment because she did not have neurological symptoms and spinal basilar artery dysfunction. Conservative therapy was halter traction twice for 4 weeks. However, pain and stiffness persisted. She had been recommended to have surgery from her physician, but she received manual therapy for non-surgical procedures. Methods: The joint mobilization, muscle energy technique, motor control exercise, and deep neck flexor (DNF) endurance exercise were applied as manual therapy and 10 session for 2weeks. Results: Clinical outcomes were measured at initial baseline, after 2 weeks, and after 6weeks. Active range of motion was completely restored after 6weeks and numeric pain rating scale was completely reduced after 2 weeks. The strength of neck flexor muscle recovered to normal after 2 weeks, and the DNF endurance was improved to 25 seconds after 2 weeks and to 42 seconds after 6weeks. Motor control capacity recovered to 30 ㎜Hg after 2 weeks. Conclusions: This case report describes the immediate and short-term clinical outcomes for a patient presenting with symptoms of neck pain following AARS. Clinical rationale and patient preference aided the decision to incorporate manual therapy as a treatment for this patient. Manual therapy has shown a successful recovery in AARS patients, more research is needed to validate the inference of this case report.

• Biomedical Engineering Letters
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• 제8권4호
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• pp.337-344
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• 2018

Additive manufacturing (AM) is an alternative metal fabrication technology. The outstanding advantage of AM (3D-printing, direct manufacturing), is the ability to form shapes that cannot be formed with any other traditional technology. 3D-printing began as a new method of prototyping in plastics. Nowadays, AM in metals allows to realize not only net-shape geometry, but also high fatigue strength and corrosion resistant parts. This success of AM in metals enables new applications of the technology in important fields, such as production of medical implants. The 3D-printing of medical implants is an extremely rapidly developing application. The success of this development lies in the fact that patient-specific implants can promote patient recovery, as often it is the only alternative to amputation. The production of AM implants provides a relatively fast and effective solution for complex surgical cases. However, there are still numerous challenging open issues in medical 3D-printing. The goal of the current research review is to explain the whole technological and design chain of bio-medical bone implant production from the computed tomography that is performed by the surgeon, to conversion to a computer aided drawing file, to production of implants, including the necessary post-processing procedures and certification. The current work presents examples that were produced by joint work of Polygon Medical Engineering, Russia and by TechMed, the AM Center of Israel Institute of Metals. Polygon provided 3D-planning and 3D-modelling specifically for the implants production. TechMed were in charge of the optimization of models and they manufactured the implants by Electron-Beam Melting ($EBM^{(R)}$), using an Arcam $EBM^{(R)}$ A2X machine.

• 한국결정성장학회지
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• 제28권6호
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• pp.250-255
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• 2018

본 연구에서는 3D-프린팅 적층 공정으로 제조한 인공관절용 CoCrMo 합금 소재의 HIP 처리를 포함한 복합열처리 후 소재의 인장특성, 내마모 특성 등의 기계적 특성과 결정구조 및 미세조직 등의 재료특성 변화를 고찰하였다. 내부마이크로 기공을 제거하기 위한 HIP 열처리와 금속탄화물 생성을 위한 상압열처리 및 금속탄화물의 균질화를 위한 용체화 열처리를 거치는 복합열처리 공정을 실시하여 인공관절 소재로서의 특성을 부여하고자 하였다. 3D-프린팅 적층 공정으로 제조한 인공관절용 CoCrMo 합금 소재의 복합열처리 효과는 HIP 공정중의 치밀화 과정, 상압열처리 중의 금속탄화물 생성 및 용체화 열처리 과정중의 금속탄화물의 균질화 효과임을 XRD, FE-SEM, EDS 분석으로 확인하였다.

• Advances in Computational Design
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• 제4권1호
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• pp.53-72
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• 2019

Safety measures for tower cranes are extremely important among the seismic countermeasures at high-rise building construction sites. In particular, the collapse of a tower crane from a high position is a very serious catastrophe. An example of such an accident due to an earthquake is the case of the Taipei 101 Building (the author was the project director), which occurred on March 31, 2002. Failure of the bolted joints of the tower-crane mast was the direct cause of the collapse. Therefore, it is necessary to design for this eventuality and to take the necessary measures on construction sites. This can only be done by understanding the precise dynamic behavior of mast joints during an earthquake. Consequently, we created a new hybrid-element model (using beam, shell, and solid elements) that not only expressed the detailed behavior of the site joints of a tower-crane mast during an earthquake but also suppressed any increase in the total calculation time and revealed its behavior through computer simulations. Using the proposed structural model and simulation method, effective information for designing safe joints during earthquakes can be provided by considering workability (control of the bolt pretension axial force and other factors) and less construction cost. Notably, this analysis showed that the joint behavior of the initial pretension axial force of a bolt is considerably reduced after the axial force of the bolt exceeds the yield strength. A maximum decrease of 50% in the initial pretension axial force under the El Centro N-S Wave ($v_{max}=100cm/s$) was observed. Furthermore, this method can be applied to analyze the seismic responses of general temporary structures in construction sites.

• Composites Research
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• 제33권6호
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• pp.401-407
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• 2020

공학 및 산업 분야에서는 구조적인 부분들에서 경량 복합 소재가 강과 같은 금속 소재를 대체해 오고 있다. 이러한 복합 소재는 리벳, 용접이나 볼트 및 너트를 이용한 체결 방법을 대신하여 접착제 체결 방법을 적용하고 있다. 복합 소재에 접착제 체결 방법을 적용하기 위해서는 접착계면에 대한 강도 특성 연구가 필수적으로 요구된다. 섬유 강화 플라스틱 복합 소재인 CFRP를 용이하게 가공하여 본 연구를 수행하였다. CFRP와 알루미늄(Al6061), 알루미늄 폼(Al-foam)을 가진 이종 복합 소재로 된 경사진 이중외팔보(TDCB) 시험편들로서 면내 전단과 면외 전단의 하중 조건들하에서 정적 실험을 수행하였다. 본 연구 결과를 통하여 이중외팔보들의 파괴 특성과 그 파단 시점을 파악하여 접착계면을 가진 이종 복합 소재 구조물에 관한 내구성을 검토하였다.

• 한국지반환경공학회 논문집
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• 제12권1호
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• pp.5-12
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• 2011

본 연구에서는 10개 현장에서 실시한 공내재하시험을 통하여 얻은 변형계수와 RMR과의 상관관계를 분석하여 기존에 사용하고 있는 제안식의 적용성을 평가하였다. RMR이 40보다 작은 경우에는 변형계수와 RMR과의 상관관계가 김교원, Aydan, Serafim과 Pereira의 식과 잘 일치하였지만 RMR이 40보다 큰 경우에는 상관관계가 낮았다. 이것은 RMR 분류 시 일축압축강도나 RQD보다 절리의 상태와 절리의 틈새가 상대적으로 가중치가 크기 때문이며 공학자의 개인적 차이뿐만 아니라 암반의 종류와 다른 풍화도 때문에 정성적으로 평가되는 경향이 있기 때문이다. 퇴적암 중 사암은 제안식과 비교적 잘 일치하지만 다른 사암은 분산이 커서 상관관계가 낮다. 본 연구에서는 현장시험결과를 근거로 새로운 지수함수 형태의 식을 제안하였다.