• Structural Engineering and Mechanics
• /
• 제58권3호
• /
• pp.577-596
• /
• 2016

FRP-concrete interfacial mechanical properties determine the strengthening effect of RC beams strengthened with FRP. In this paper, the model experiments were carried out with eight specimens to study the failure modes and the strengthening effect of RC beams strengthened with FRP. Then a theoretical model based on interfacial performances was proposed and interfacial mechanical behaviors were studied. Finite element analysis confirmed the theoretical results. The results showed that RC beams strengthened with FRP had three loading stages and that the FRP strengthening effects were mainly exerted in the Stage III after the yielding of steel bars, including the improvement of the bearing capacity, the decreased ultimate deformation due to the sudden failure of FRP and the improvement of stiffness in this stage. The mechanical formulae of the interfacial shear stress and FRP stress were established and the key influence factors included FRP length, interfacial bond-slip parameter, FRP thickness, etc. According to the theoretical analysis and experimental data, the calculation methods of interfacial shear stress at FRP end and FRP strain at midspan were proposed. When FRP bonding length was shorter, interfacial shear stress at FRP end was larger that led to concrete cover peeling failure. When FRP was longer, FRP reached the ultimate strain and the fracture failure of FRP occurred. The theoretical results were well consistent with the experimental data.

• Geomechanics and Engineering
• /
• 제24권4호
• /
• pp.307-321
• /
• 2021

In an earlier publication (Serrano et al. 2014), the theoretical basis for evaluating the shear strength in rock joints was presented and used to derive an equation that governs the relationship between tangential and normal stresses on the joint during slippage between the joint faces. In this paper, the theoretical equation is applied to two non-linear failure criteria by using non-associated flow laws, including the modified Hoek and Brown and modified Mohr-Coulomb equations. The theoretical model considers the geometric dilatancy, the instantaneous friction angle, and a parameter that considers joint surface roughness as dependent variables. This model uses a similar equation structure to the empirical law that was proposed by Barton in 1973. However, a good correlation with the empirical values and, therefore, Barton's equation is necessary to incorporate a non-associated flow law that governs breakage processes in rock masses and becomes more significant in highly fractured media, which can be induced in a rock joint. A linear law of dilatancy is used to assess the importance of the non-associated flow to obtain very close values for different roughness states, so the best results are obtained for null material dilatancy, which considers significant changes that correspond to soft rock masses or altered zones of weakness.

• 한국음향학회지
• /
• 제43권4호
• /
• pp.391-399
• /
• 2024

란주반 트랜스듀서에 의해 강제 진동되는 원형 진동판으로부터 방사되는 음장의 분포를 해석하기 위하여 L. Rayleigh에 의해 도출된 진동 원판의 운동방정식을 기초로 구동 영역 및 고정 경계영역의 경계 조건을 적절히 적용하여 이론적 해석모델을 도출하였다. 도출된 해석모델을 이용하여 진동 원판의 표면에 분포하는 진동 변위를 계산하고 이로부터 방사되는 초음파에 의해 형성되는 음장을 계산한 결과, 진동 원판의 넓이에 따라 방사 특성이 크게 변함을 확인할 수 있었다. 비교를 위하여 유한요소법인 COMSOL 프로그램을 사용하여 동일한 시스템에 대한 시뮬레이션을 수행한 결과 이론 계산 결과와 좋은 일치를 보여 본 연구에서 도출한 이론적 해석모델의 유효성을 확인할 수 있었다. 본 연구에서 도출한 이론적 해석모델은 초음파 화학분야 등 관련 디바이스의 설계 및 개발에 활용될 수 있을 것으로 기대된다.

• 수산해양기술연구
• /
• 제50권4호
• /
• pp.427-434
• /
• 2014

Although ex situ target strength (TS) measurements using dual- and split-beam systems have become the primary approach of estimating fish abundance, theoretical model estimation is a powerful tool for verifying the measurements, as well as for providing values when making direct measurements is difficult. TS values for 20 samples of live bambooleaf wrasse (Pseudolabrus japonicus) whose target length (TL) ranged between 13.7 and 21.3 cm were estimated theoretically using the Kirchhoff-ray mode model, and the TS values for 18 live fish samples were additionally measured at ${\sim}0^{\circ}$ tilt angle to the swimming aspect using a tethered method at a frequency of 120 kHz to verify the theoretical values. The digitizing intervals used to extract the fish body and swim bladder morphology in the X-ray photographs significantly affected the calculated TS patterns, but variations based on the speed of sound and density ratio values for the general range of fish flesh were relatively small (within 1 dB). Close agreement was observed between the measured and theoretical TS values, and the correlation between the average TS and body length of the fish could be calculated accurately as <$TS_{120kHz}$>= 20logTL (cm) -71.6 using the theoretical method.

• 한국수산과학회지
• /
• 제43권4호
• /
• pp.380-385
• /
• 2010

Several theoretical acoustic scattering models were applied to estimate the target strength (TS) for assessing the biomass of zooplankton, to overcome the difficulty of direct measurements. Acoustical scattering characteristics of copepods were estimated using three theoretical models, and the application of the models was evaluated for four frequencies of a scientific echo sounder. The scattering directivity by the body shapes of copepods at 200 kHz and 420 kHz was significantly affected by TS patterns. Averaged TS, however, were similar at higher frequencies. Consequently, a low frequency model, such as a truncated fluid sphere model, provides a good acoustical biomass estimation. The regressions of TS and 30 logL were < $TS_{200\;kHz}$ >= 30logL-118.4 ($R^2=0.716$) and < $TS_{420 kHz}$ > =30 logL-108.8 ($R^2=0.758$), respectively.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2007년도 추계 학술대회논문집
• /
• pp.236-242
• /
• 2007

A theoretical and numerical investigation is performed on the flow in a micronozzle for precision-controlled seal dispenser. The working fluid is a highly viscous epoxy used as sealant in producing LCD panels, which contains a number of tiny solid spacers. Flow analysis is conducted in order to achieve the optimal design oj internal geometry of a nozzle. A simplified design analysis methodology is proposed for predicting the flow in the nozzle based on the assumption that the Reynolds number is much less than O(1). The parallel numerical computations are performed by using a CFD package FLUENT. Comparison discloses that the theoretical model gives a good prediction on the distribution of pressure and wall shear stress in the nozzle. However, the theoretical model has a difficulty in predicting the maximum wall shear stress as found in a limited region near edge by numerical computation. The theoretical and numerical simulations provide the good guideline for designing a dispensing micronozzle.

• Computers and Concrete
• /
• 제19권5호
• /
• pp.501-507
• /
• 2017

The predictive utility of a damage model depends heavily on its particular choice of a damage variable, which serves as a macroscopic approximation in describing the underlying micromechanical processes of microdefects. In the case of spatially perfectly randomly distributed microcracks or microvoids in all directions, isotropic damage model is an appropriate choice, and scalar damage variables were widely used for isotropic or one-dimensional phenomenological damage models. The simplicity of a scalar damage representation is indeed very attractive. However, a scalar damage model is of somewhat limited use in practice. In order to entirely characterize the isotropic damage behaviors of damaged materials in multidimensional space, a system theory of isotropic double scalar damage variables, including the expressions of specific damage energy release rate, the coupled constitutive equations corresponding to damage, the conditions of admissibility for two scalar damage effective tensors within the framework of the thermodynamics of irreversible processes, was provided and analyzed in this study. Compared with the former studies, the theoretical formulations of double scalar damage variables in this study are given in the form of matrix, which has many features such as simpleness, directness, convenience and programmable characteristics. It is worth mentioning that the above-mentioned theoretical formulations are only logically reasonable. Owing to the limitations of time, conditions, funds, etc. they should be subject to multifaceted experiments before their innovative significance can be fully verified. The current level of research can be regarded as an exploratory attempt in this field.

• 한국전산유체공학회지
• /
• 제12권4호
• /
• pp.54-60
• /
• 2007

A theoretical and numerical investigation is performed on the flow in a micronozzle for precision-controlled sealant dispenser. The working fluid is a highly viscous epoxy used as sealant in producing LCD panels, which contains a number of tiny solid spacers. Flow analysis is conducted in order to achieve the optimal design of internal geometry of a nozzle. A simplified design analysis methodology is proposed for predicting the flow in the nozzle based on the assumption that the Reynolds number is much less than O(1). The parallel numerical computations are performed by using a CFD package FLUENT. Comparison discloses that the theoretical model gives a good prediction on the distribution of pressure and wall shear stress in the nozzle. However, the theoretical model has a difficulty in predicting the maximum wall shear stress as found in a limited region near edge by numerical computation. The theoretical and numerical simulations provide the good guideline for designing a dispensing micronozzle.

• 농촌지도와개발
• /
• 제4권1호
• /
• pp.317-327
• /
• 1997

The objectives of this study were to review studies on the community attachment and to identify it's related variables. Community attachment variables were divided into linear development model variables and system model variables. The theoretical base for linear development model originated from Ferdinand Toennies(1957) and system model was from Kasarda and Janowitz(1974). Linear development model variables were population size and density. And system model variables were age, education, income, number of children, marital status, length of residence, sex, and job. Recent studies on the community attachment were being carried out through system model than linear development model.

• Journal of the Korean Wood Science and Technology
• /
• 제30권4호
• /
• pp.96-105
• /
• 2002

전단벽은 현대식 경골목조건축에서 바람이나 지진 등에 의한 측방하중에 대한 저항력을 제공하는 가장 중요한 요소 중의 하나이다. 전단벽에서 건물에 전달된 측방하중은 벽의 스터드와 덮개재료 사이의 못접합부를 통하여 덮개재료로 전달되고 덮개재료에 전달된 하중은 판재의 면전단력에 의하여 지지된다. 따라서 실제 전단벽에서 측방하중에 대한 저항력을 결정하는 가장 중요한 요소는 못접합부라고 할 수 있을 것이다. 이 연구에서는 스터드와 판재 사이의 못접합부에 대한 강성 및 강도를 측정하였으며 이 값들은 전단벽의 찌그러짐 저항력을 예측하는 이론모형의 입력자료로 사용되었다. 이론모형의 예측치의 정확성을 검증하기 위하여 판재 한 장으로 구성된 전단벽의 전단시험을 수행하였다. 못접합부의 강성은 스터드 부재의 섬유방향에 의하여 영향을 받았으나 판재의 방향은 거의 영향을 미치지 않는 것으로 나타났다. 전단하중 하에서 못접합부나 전단벽의 거동은 3개의 직선구간으로 나나낼 수 있었으며 이론모형 I보다 이론모형 II의 예측치가 더 정확하였다.