• Journal of the Korean Wood Science and Technology
• /
• 제12권4호
• /
• pp.31-35
• /
• 1984

우리 나라 특산(特産) 수종(樹種)인 개나리속(屬)의 해부학적(解剖學的) 성질(性質)을 조사(調査)한 결과(結果)는 다음과 같다. 횡단면상(橫斷面上)의 도관(導管)은 거의 단일도관(單一導管)이었고, 2~3개(個)로 복합(複合)된 복합도관(複合導管)도 가끔 나타나고, 도관(導管)의 배열상태(排列狀態)는 복사공성(輻射孔性) 환공재(環孔材)이었다. 도관(導管)의 평균(平均) 길이는 개나리 $539.98{\pm}154.71{\mu}$, 만리화 $602.22{\pm}157.38{\mu}$, 장수만리화 $465.50{\pm}83.02{\mu}$이었다. 목섬유(木纖維)의 평균(平均) 길이는 개나리 $387.40{\pm}68.23{\mu}$, 만리화 $533.90{\pm}106.77{\mu}$, 장수만리화 $482.40{\pm}72.33{\mu}$ 이었다. 방사조직(放射組織)의 형(型)은 이성공형(異性工型)이었다.

• 임산에너지
• /
• 제20권1호
• /
• pp.62-72
• /
• 2001

목재의 알칼리 팽윤특성을ㄹ 해명하기 위해 국내산 주요 침·활엽수 4수종의 주요 구성요소의 알칼리 팽윤 거동을 횡단면 절편을 이용하여 조사하였다. 그 결과, 일본잎갈나무의 가도관 직경은 잣나무보다 크게 팽윤하였으며, 가도관의 벽두께는 10% 이상의 알칼리 수용액에 처리시 높은 팽윤율을 나타냈다. 알칼리 처리에 의해 도관의 직경은 방사방향으로 수축하였고, 접선방향으로 다소 팽윤하였다. 목섬유의 세코벽두께는 5%의 알칼리처리에서도 수분팽윤에 비해 3배 이상의 높은 팽윤성을 나타앴고, 알칼리 처리후 일본잎갈나무의 가도관 직경, 목섬유 직경 및 세포벽두께는 거의 등방적인 수축현상을 보여주었다. 또한 미처리 시료에 비해 머서화 처리 구성요소의 세포직경은 수축되었고, 세포벽은 팽윤되었다. 알칼리처리 과정에서 셀룰로오스 결정형의 변화는 없었지만 상대결정화도와 미결정의 폭이 다소 증가되었다. 결론적으로 알칼리의 농도, 수종, 세포의 종류가 목재의 알칼리 팽윤 특성에 크게 관여하는 것으로 생각되었다.

• Journal of the Korean Wood Science and Technology
• /
• 제34권3호
• /
• pp.8-14
• /
• 2006

목재의 탄화기구를 이해하기 위하여 굴참나무재를 사용하여 $250{\sim}740^{\circ}C$의 온도조건에서 탄화하였다. 탄화온도가 높아질수록 시험체의 부피는 수축하였고, 방사 방향으로 할렬이 발생하였다. 탄화온도가 증가함에 따라 목탄의 중량감소율은 증가되었으며, 특히 탄화온도 $300{\sim}340^{\circ}C$에서 급격히 증가하는 경향이 나타났다. 목재의 도관은 탄화 시 방사방향보다 접선방향으로 매우 크게 수축하였다. 탄화온도 $250{\sim}300^{\circ}C$의 경우, 목섬유나 도관 주위의 유세포들이 탄화되지 않은 세포벽 형태를 보여주었다. 그러나 탄화온도 $340^{\circ}C$이상에서는 세포벽층이 매끄러운 비결정형인 목탄의 형태가 관찰되기 시작하였다. 탄화온도 $300^{\circ}C$까지는 목재 셀룰로오스의 결정성이 남아있었으나 $340^{\circ}C$ 이상에서는 비결정성으로 변화되고 있는 것이 관찰되었다.

• Geomechanics and Engineering
• /
• 제11권3호
• /
• pp.401-420
• /
• 2016

The stability of deep coal roadways with large sections and thick top coal is a typical challenge in many coal mines in China. The innovative Universal Discrete Element Code (UDEC) trigon block is adopted to create a numerical model based on a case study at the Dongtan coal mine in China to better understand the failure mechanism and stability control mechanism of this kind of roadway. The failure process of an unsupported roadway is simulated, and the results suggest that the deformation of the roof is more serious than that of the sides and floor, especially in the center of the roof. The radial stress that is released is more intense than the tangential stress, while a large zone of relaxation appears around the roadway. The failure process begins from partial failure at roadway corners, and then propagates deeper into the roof and sides, finally resulting in large deformation in the roadway. A combined support system is proposed to support roadways based on an analysis of the simulation results. The numerical simulation and field monitoring suggest that the availability of this support method is feasible both in theory and practice, which can provide helpful references for research on the failure mechanisms and scientific support designing of engineering in deep coal mines.

• Journal of the Korean Wood Science and Technology
• /
• 제44권4호
• /
• pp.607-615
• /
• 2016

The delamination along the annual ring on the cross-section of laminae and the bonding strength according to the tangential angle between laminae were evaluated for the production of 3-ply cross-laminated timber (CLT) using domestic larch. Since there is no standard for CLT in Korea, the production and test of specimens for bonding strength followed the standard procedure of "Structural glued laminated timber" (KS F 3021). The standard specifies to exclude any measurement from the cracks of timbers resulted from drying or knots during delamination test of the glued laminated timbers. However, the failure of cross-sectional tissues along the annual rings was observed near the glue-line of all specimens during the delamination test. Because this phenomenon can generate defects in the CLT that may be exposed to various temperatures and relative humidities after the actual construction, the delamination percentage was measured by including this wood failure. As a result, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed inward was the lowest, which was around 13%, regardless of the annual ring direction of the middle lamina. On the other hand, the delamination percentage of the CLT which had been combined in such a way that the annual rings of outer lamina were directed outward was the highest, which was around 26%. Furthermore, end-split occurred in the outer lamina during the drying process of the boiling delamination test, which affected the delamination percentage. Therefore, the soaking delamination test was found to be more appropriate for evaluating the delamination strength of CLT. The block shear strength of larch CLT was $3.9{\pm}0.9$ MPa on average, which was 46% lower than the block shear strength requirement (7.1 MPa) of the standard, but satisfied the criteria of the block shear strength (3.5 MPa) of the European Standard (prEN 16351: 2013).

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2000년도 사면안정 학술발표회
• /
• pp.3-38
• /
• 2000

Slope draperies in soil and rock are a well known method to avoid rockfalls into the roads or onto housings. Common wire mesh or a combination of wire mesh and wire rope nets are pinned to the slope by the means of fully grouted nails or anchors. Most of these installations have not been designed to stabilize the slope, but simply avoid the rocks from bouncing. The combination of soil- or rocknailing with a designable flexible facing system offers the advantage of a longterm stabilization of slopes and can replace other standard methods for slope stabilization. The capability to transfer axial and shear loads from the flexible facing system to the anchor points is most decisive for the design of the stabilization system. But the transfer of forces by mesh as pure surface protection devices is limited on account of their tensile strength and above all also by the possible force transmission to the anchoring points. Strong wire rope nets increase the performance for slope stabilizations with greater distances between nails and anchors and are widely used in Europe. However, they are comparatively expensive in relation to the protected surface. Today, special processes enable the production of diagonally structured mesh from high-tensile steel wire. These mesh provide tensile strengths comparable to wire rope nets. The interaction of mesh and fastening to nail / anchor has been investigated in comprehensive laboratory tests. This also in an effort to find a suitable fastening plates which allows an optimal utilization of the strength of the mesh in tangential (slope-parallel) as well as in vertical direction (perpendicular to the slope). The trials also confirmed that these new mesh, in combination with suitable plates, enable substantial pretensioning of the system. Such pretensioning increases the efficiency of the protection system. This restricts deformations in the surface section of critical slopes which might otherwise cause slides and movements as a result of dilatation. Suitable dimensioning models permit to correctly dimension such systems. The new mesh with the adapted fastening elements have already been installed in first pilot projects in Switzerland and Germany and provide useful information on handling and effects.

• 전자공학회논문지
• /
• 제50권11호
• /
• pp.28-35
• /
• 2013

Krylov-Schur 반복법을 활용하여 2-차원 사각 도파관에서 나타나는 고유특성을 밝혔다. 고유 행렬 방정식은 삼각형 그물 요소의 접선을 기저벡터로 사용한 FEM(유한요소법)으로 구성하였다. 우선 Arnoldi 분해법을 이용하여 이 방정식에 대한 상위 Hessenberg 행렬을 구하였다. 그리고 QR 알골리즘을 통하여 이것을 삼각형 대각 행렬인 Shur 형태로 변형하였다. 수렴 조건에 부합된 몇몇 고유 값들이 삼각형 대각 행렬의 대각 요소에 나타났다. 이들에 대응하는 고유 모드들을 역-반복법으로 구하였다. 수렴조건에 부합되는 고유 값들은 Shur 행렬의 대각선 선두 부분으로 재배열시켰다. 이들은 나머지 고유값 및 고유모드의 쌍을 구하는 반복 과정에서 변형되지 않도록 배제되었다. 이 과정이 연속하여 서너 번 반복되었는데, 그 결과 충분한 신뢰도를 갖는 주요한 몇 개의 TM 및 TE 고유 쌍들이 구하여졌다.

• Wind and Structures
• /
• 제23권1호
• /
• pp.1-18
• /
• 2016

This work experimentally and numerically analyzes the flow configurations and the dynamic wind loads on panels of rectangular L/h 5:1 cross section mounted on a structural frame of rectangular bars of L/h 0.5:1, corresponding to a radar structure. The fluid dynamic interaction between panels and frame wakes imposes dynamic loads on the panels, with particular frequencies and Strouhal numbers, different from those of isolated elements. The numerical scheme is validated by comparison with mean forces and velocity spectra of a panel wake obtained by wind tunnel tests. The flow configuration is analyzed through images of the numerical simulations. For a large number of panels, as in the radar array, their wakes couple in either phase or counter-phase configurations, changing the resultant forces on each panel. Instantaneous normal and tangential force coefficients are reported; their spectra show two distinct peaks, caused by the interaction of the wakes. Finally, a scaled model of a rectangular structure comprised of panels and frame elements is tested in the boundary layer wind tunnel in order to determine the influence of the velocity variation with height and the three-dimensionality of the bulk flow around the structure. Results show that the unsteady aerodynamic loads, being strongly influenced by the vortex shedding of the supporting elements and by the global 3-D geometry of the array, differ considerably on a panel in this array from loads acting on an isolated panel, not only in magnitude, but also in frequency.

• Geomechanics and Engineering
• /
• 제21권2호
• /
• pp.201-206
• /
• 2020

A stress-induced brittle failure in deep tunneling generates spalling and slabbing, eventually causing a v-shaped notch formation. An empirical relationship for the depth of the notch to the maximum tangential stress assuming an equivalent circular cross-section was proposed (Martin et al. 1999). While this empirical approach has been well recognized in the industry and used as a design guideline in many projects, its applicability to a non-circular opening is worth revisiting due to the use of equivalent circular profile. Moreover, even though the extent of the notch also contributes to notch failure, it has not been estimated to date. When the estimate of both the depth and the extent of notch are combined, a practical and economically justifiable support design can be achieved. In this study, a new methodology to assess the depth as well as the extent of notch failure is developed. Field data and numerical simulations using the Cohesion Weakening Frictional Strengthening (CWFS) model were collected and correlated with the three most commonly accepted failure criteria (σ₁/σ₃, D_is=σ_max/σ_c, σ_dev/σ_cm). For the numerical analyses, the D-shaped tunnel was used since most civil tunnels are built to this profile. Inferential statistical analysis is applied to predict the failure range with a 95% confidence level. Considering its accuracy and simplicity, the new correlation can be used as an enhanced version of failure assessment.

• Journal of the Korean Wood Science and Technology
• /
• 제48권5호
• /
• pp.666-675
• /
• 2020

본 연구는 태백산맥을 기준으로 영동(고성군), 영서(홍천군), 영남(봉화군) 세 지역 간 소나무의 재질 차이 유무를 알기 위해 역학적 특성을 조사하였다. 측정한 역학적 성질은 압축강도, 경도 및 전단강도였다. 압축강도는 미성숙재에서 지역 간 차이가 없으며, 심재부와 변재부에서는 봉화, 홍천, 고성군 순으로 크게 나타났다. 경도는 횡단면에서는 봉화군이, 방사 및 접선 단면에서는 고성군이 크게 나타났다. 전단강도는 심재부에서는 차이가 없었으며, 변재부에서는 봉화군이 고성, 홍천군에 비해 높게 나타났다. 이는 지역 간 가도관장, 마이크로피브릴경각 차이에 의한 것으로 생각된다. 지역 간 재질특성의 차이 규명으로 국내산 소나무재를 효율적이고 선택적으로 사용하여 부가가치를 높이고, 또한 우수한 수형목을 선발하는데 활용될 수 있을 것으로 생각한다.