• 한국항만학회지
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• 제12권1호
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• pp.75-86
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• 1998

To design a coastal structure in the nearshore region, engineers must have means to estimate wave climate. Waves, approaching the surf zone from offshore, experience changes caused by combined effects of bathymetric variations, interference of man-made structure, and nonlinear interactions among wave trains. This paper has attempted to find out the effects of two of the more subtle phenomena involving nonlinear shallow water waves, amplitude dispersion and secondary wave generation. Boussinesq-type equations can be used to model the nonlinear transformation of surface waves in shallow water due to effect of shoaling, refraction, diffraction, and reflection. In this paper, generalized Boussinesq equations under the complex bottom condition is derived using the depth averaged velocity with the series expansion of the velocity potential as a product of powers of the depth of flow. A time stepping finite difference method is used to solve the derived equation. Numerical results are compared to hydraulic model results. The result with the non-linear dispersive wave equation can describe an interesting transformation a sinusoidal wave to one with a cnoidal aspect of a rapid degradation into modulated high frequency waves and transient secondary waves in an intermediate region. The amplitude dispersion of the primary wave crest results in a convex wave front after passing through the shoal and the secondary waves generated by the shoal diffracted in a radial manner into surrounding waters.

• 대한안전경영과학회:학술대회논문집
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• 대한안전경영과학회 2002년도 춘계학술대회
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• pp.221-225
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• 2002

Machinability improvement by the use of liquid nitrogen in cryogenic machining has been reported in various studies. This has been mostly attributed to the cooling effect of liquid nitrogen. However, No study has been found in discussion on whether liquid nitrogen possesses lubrication effect in cryogenic cutting. This paper presents lubrication mechanism related to chip microstructure. The friction reduction was further reflected In larger shear angle and less secondary deformation in the chip microstructures.

• 한국터널지하공간학회 논문집
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• 제8권4호
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• pp.365-375
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• 2006

일반적으로 터널2차라이닝의 구조해석에는 골조해석모델이 적용되고 있다. 본 모델은 경험적 방법에 의한 지반 이완하중을 고려하고 있으나 주관적이고 과대평가되는 경향이 있다. 2차라이닝에 작용하는 지반하중은 숏크리트 및 록볼트와 같은1차지보재의 지지력 상실에 기인한다. 그러므로 2차라이닝에 작용하는 지반하중 산정에는 1차지보재와 지반의 평형상태가 고려되어야 한다. 지반-라이닝 상호작용(Ground-Lining Interaction, GLI)모델은1차지보재의 지지력 상실에 의해 야기된 지반의 변형을2차라이닝이 지지하는 개념을 토대로 수립되었다. 따라서 GLI모델은 복잡한 지반조건과 1차 지보재의 설치조건을 합리적으로 반영한 지반하중을 고려할 수 있다. 2차라이닝에 작용하는 하중은 지반하중 외에 지하수압, 지진하중 등이 있다. 극한강도 설계법을 이용한 라이닝 구조보강을 위해서는 계수하중 및 다양한 하중조합이 고려되어야 한다. GLI모델은 계수하중을 고려하기 곤란하기 때문에 개별 하중에 대해 산정된2차라이닝 단면력에 하중계수를 곱하는 중첩의 원리를 적용하였다. 끝으로, 본 연구에서 제시된 GLI모델을 이용한 2차라이닝 설계방법을 저심도 지하철 터널에 적용하였다.

• 대한기계학회논문집B
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• 제37권5호
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• pp.489-494
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• 2013

본 연구는 주기적인 강제 진동이 가해지는 액적의 모드 특성을 실험적으로 이해하는 것을 목적으로 하고 있다. 액적의 공진 주파수 예측을 수행하여 이론 및 실험적 해석을 통해 두 접근방법의 타당성을 파악하였으며, 초고속카메라를 사용하여 액적의 다양한 변형 특성-모드 형상, 분리, 미소 액적의 발생, 그리고 비틀림의 특성을 관찰하였다. 이론 해석 및 실험결과와의 비교에 있어 공진 주파수 값의 차이가 약 15% 이하라는 것이 도출되었으며 이러한 차이의 발생 원인으로 접촉선 마찰, 비선형벽 고착, 실험의 불확실성 등에 큰 영향을 받는 것으로 판단된다. 접촉선이 고정되어있을 경우와 작은 진폭 조건 하에서 액적의 모양은 대칭형상을 가졌으며, 공진 주파수에서의 로브의 크기는 주변부 주파수에서의 로브 크기보다 더 크게 된다는 점을 확인하였다.

• 대한기계학회논문집A
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• 제26권1호
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• pp.55-60
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• 2002

For the development of a new creep test technique, the availability of SP-Creep test is discussed for 1Cr-0.5Mo boiler header material. And some results are also compared with those of 2.25Cr- 1Mo steel which widely uses as boiler superheater tube. The results can be summarized as follows. The load exponents(n) obtained by SP-Creep test for 1Cr-0.5Mo steel are decreased with increasing creep temperature and the values are 15.67, 13.89, and 17.13 at 550$^{circ}C$ ,575$^{circ}C$ and 600$^{circ}C$, respectively. The temperature dependence of the load exponent is given by n = 107.19 - 0.1108T. This reason that load exponents show the extensive range of 10∼16 is attributed to the fine carbide such as M$_{23}$C$_{6}$ in lath tempered martensitic structures. At the same creep condition, the secondary creep rate of 1Cr-0.5Mo steel is lower than the 2.25Cr-1Mo steel1 due to the strengthening microstructure composed by normalizing and tempering treatments. Through a SEM observation, it can be summarized that the primary, secondary, and tertiary creep regions of SP-Creep specimen are corresponding to plastic bending, plastic membrane stretching, and plastic instability regions among the deformation behavior of four steps in SP test, respectively.y.

• Earthquakes and Structures
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• 제26권5호
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• pp.383-400
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• 2024

For a conventionally repaired frame-supported-transfer-slab (FSTS) reinforced concrete (RC) structure, both the transfer slab and the beam-to-column and transfer slab-to-column joints remain vulnerable to secondary earthquakes. Aimed at improving the seismic performance of a damaged FSTS RC structure, an innovative retrofitting scheme is proposed, which adopts the sector lead rubber dampers (SLRDs) at joints after the damaged FSTS RC structure is repaired by conventional approaches. In this paper, a series of quasi-static cyclic tests was conducted on a large-scale retrofitted FSTS RC structure. The seismic performance was evaluated and the key test results, including deformation characteristics, damage pattern, hysteretic behaviour, bearing capacity and strains on key components, were reported in detail. The test results indicated that the SLRDs started to dissipate energy under the service level earthquake, and thus prevented damages on the beam-to-column and transfer slab-to-column joints during the secondary earthquakes and shifted the plastic hinges away from the beam ends. The retrofitting scheme of using SLRDs also achieved the seismic design concept of 'strong joint, weak component'. The FSTS RC structure retrofitted by the SLRDs could recover more than 85% bearing capacity of its undamaged counterpart. The hysteresis curves were featured by the inverse "S" shape, indicating good bearing capacity and hysteresis performance. The deformation capacity of the damaged FSTS RC structure retrofitted by the SLRDs met the corresponding codified requirements for the case of the maximum considered earthquake, as set out in the Chinese seismic design code. The stability of the FSTS RC structure retrofitted by the SLRDs, which was revealed by the developed stains of the RC frame and transfer slab, was improved compared with the undamaged FSTS RC structure.

• 한국지반공학회논문집
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• 제21권7호
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• pp.5-12
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• 2005

화강풍화토의 강도와 변형특성을 조사하기 위하여 불포화배수 삼축압축실험을 실시하였다. 본 실험을 위하여 야마구치현의 시모노세키에서 화강풍화토를 구하였으며 주응력방향과 다짐방향을 0,45, 90도의 세가지 방향성을 갖도록 하였다. 등방압축시 발생하는 압축변형률은 다짐각도에 따라 크게 영항을 받는다. 이차압축시의 변형거동에 관한 시간의존성은 다짐각도와 관계가 없다. 다짐각도가 압축강도와 변형에 미치는 영향은 특히 낮은 구속압력시에 크다. 다짐각도가 다르다 하더라도 다일러틴시 비율은 다일러턴시로 인한 강도증가와 상관하여 변화한다. 따라서 다짐풍화토는 초기 비등방성 조직을 갖고 있는 모래와 같이 비등방성 역학적 성질을 갖는다고 할 수 있다.

• 한국지반공학회논문집
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• 제26권6호
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• pp.21-28
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• 2010

화강풍화토는 가장 일반적인 흙의 종류이다. 비등방성 화강풍화토의 응력-변형-강도를 측정하는 것은 사면, 옹벽, 굴착의 변형과 안정을 위하여 매우 중요하다. 불포화 강도특성을 알기 위하여 일련의 불포화 배수삼축압축시험을 시행하였다. 시험시료는 다짐방향에 각각 0, 45, 90도의 축방향각을 갖도록 하였다. 등방압축을 받는 시료의 축변형률은 다짐방향에 의하여 크게 영향을 받으며 이차압축과정에는 시간의존성은 다짐방향과 관계가 거의 없다. 삼축압축강도와 변형에 미치는 다짐방향의 영향은 저구속압과 포화토에서 더 확연한것으로 나타났다. 다짐방향과의 각도를 고려하는 불포화화강풍화토의 강도를 추정하는 방법을 제안하였다.

• Advances in concrete construction
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• 제11권5호
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• pp.375-386
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• 2021

In this paper, a study of stability and health of a newly-built railway tunnel is presented. The field test was implemented to monitor the secondary lining due to the significant cracking behaviors influenced the stability and health of the tunnel structure. Surface strain gauges were installed for monitoring the status of crack openings, and the monitoring outputs demonstrated that the cracks were still in the developing stage. Additionally, adjacent tunnel and poor condition of surrounding rock were identified as the causes of the lining cracking by systematically characterizing the crack spatial distribution, tunnel site and surrounding rock conditions. Reconstruction of partial lining and reconstruction of the whole secondary lining were designed as the maintenance projects for different cracking regions based on the construction feasibility. For assessing the health conditions of the reinforced lining, embedded strain gauges were set up to continuously measure the strain and the internal force of the reconstructed structures. For the partially reconstructed lining, the outputs show the maximum tensile elongation is 0.018 mm during 227 days, which means the structure has no obvious deformation after maintenance. The one-year monitoring of full-section was implemented in the other two completely reconstructed cross-sections by embedded strain gauge. The outputs show the reconstructed secondary lining has undertaken the pressure of surrounding rock with the time passing. According to the calculated compressive and tensile safety factors, the completely reconstructed lining has been in reliable and safe condition during the past year after reinforcement. It can conclude that the aforementioned maintenance projects can effectively ensure the stability and health of this tunnel.

• 한국전기전자재료학회논문지
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• 제23권11호
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• pp.880-885
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• 2010

The Angle Ring and Cap which is called pressboard are settled at the primary and secondary coil winding of 154 kV transformer that can reduce effectively distance of insulation. As it has not manufactured pressboard of Angle Ring and Cap for high voltage grade, insulation components industry especially high voltage transformer has not participate in a competition with worldwide yet. That's why is difficult to make an specialized shape of insulation components of high voltage grade. Therefore it has finally completed to make an deformation manufacturing utility using an bellowed special analysis tools. This study that uses various analysis program determining optimum shape about insulation of Angle Ring and Cap which is related life of high voltage transformer. In addition to develop forming equipment with an specialized five steps pressing. That is also based on the mechanical strength evaluation and test, it is investigated optimized processing components.