• Computers and Concrete
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• v.34 no.3
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• pp.307-328
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• 2024

The concrete damage plasticity (CDP) model is widely used to simulate concrete behaviour using either implicit or explicit analysis methods. To effectively execute the models and resolve convergence issues in implicit analysis, activating the viscosity parameter of this material model is a common practice. Despite the frequent application of implicit analysis to analyse concrete structures with the CDP model, the viscosity parameter significantly varies among available models and lacks consistency. The adjustment of the viscosity parameter at the element/structural level disregards its indirect impact on the material. Therefore, the accuracy of the numerical model is confined to the validated range and might not hold true for other values, often explored in parametric studies subsequent to validations. To address these challenges and develop a unified numerical model for varied conditions, a quasi-static analysis using the explicit solver was conducted in this study. Fifteen thick flat plates tested under load control with different geometries and different eccentric loads were considered to verify the accuracy of the model. The study first investigated various concrete material behaviours under compression and tension as well as the concrete tensile strength to identify the most reliable models from previous methodologies. The study compared the results using both implicit and explicit analysis. It was found that, in implicit analysis, the viscosity parameter should be as low as 0.0001 to avoid affecting material properties. However, at the structural level, the optimum value may need adjustment between 0.00001 to 0.0001 with changing geometries and loading type. This observation raises concerns about further parametric study if the specific value of the viscosity parameter is used. Additionally, activating the viscosity parameter in load control simulations confirmed its inability to capture the peak load. Conversely, the unified explicit model accurately simulated the behaviour of the test specimens under varying geometries, load eccentricities, and column sizes. This study recommends restricting implicit solutions to the viscosity values proposed in this research. Alternatively, for highly nonlinear problems under load control simulation, explicit analysis stands as an effective approach, ensuring unified parameters across a wide range of applications without convergence problems.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.91-104
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• 2008

In tunnels, safety factor concept has been suggested to estimate their stability quantitatively. It is merely limited in the framework of mechanical analysis. However safety factor concept has not been applied in hydro-mechanical coupled analyses due to their modelling complexity. Recently studies on this topic are being actively made. In this study, induced drainage modelling methods for hydro-mechanical coupled analyses are compared and analyzed to estimate safety factor of a subsea tunnel exactly. To this end, methods both controlling hydraulic characteristic of shotcrete and using a drainage well are considered. Sensitivity analysis were carried out on rock class, thickness of shotcrete, and hydraulic properties of rock mass. As the results of this study, it turned out that the induced drainage modelling using a drainage well would give more reliable results than that of controlling hydraulic characteristic of shotcrete in estimating tunnel stability in hydro-mechanical coupled analyses.

• Geomechanics and Engineering
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• v.2 no.2
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• pp.141-156
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• 2010

In the framework of meshfree methods, a new methodology is developed based on radial point interpolation method (RPIM). This methodology is applied to a one-dimensional contaminant transport modelling in the saturated porous media. The one-dimensional form of advection-dispersion equation involving reactive contaminant is considered in the analysis. The Galerkin weak form of the governing equation is formulated using 1D meshfree shape functions constructed using thin plate spline radial basis functions. MATLAB code is developed to obtain the numerical solution. Numerical examples representing various phenomena, which occur during migration of contaminants, are presented to illustrate the applicability of the proposed method and the results are compared with those obtained from the analytical and finite element solutions. The proposed RPIM has generated results with no oscillations and they are insensitive to Peclet constraints. In order to test the practical applicability and performance of the RPIM, three case studies of contaminant transport through the landfill liners are presented. A good agreement is obtained between the results of the RPIM and the field investigation data.

• Journal of the Korean Society of Safety
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• v.33 no.2
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• pp.132-137
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• 2018

Compared with general rivers, fluctuations of the water level and the river bed are severe in the tidal river. In hydro-dynamic aspect, such fluctuation gives different river-bed data to us according to observing period. The time-dependent river-bed data and pre-estimation of the Manning's roughness coefficient which is the key factor of numerical modelling induces uncertainty of evaluating the design flood level. Thus it is necessary to pay more attention to calculate the flood level at tidal rivers than at general rivers. In this study, downstream of the Imjin River where is affected by tide of the West Sea selected as a study site. From the numerical modelling, it was shown that the unsteady simulation gave considerable mitigation of the water level from the starting point to 15 km upstream compared to the steady simulation. Either making a detention pond or optional dredging was not effective to mitigate the flood level at Gugok - Majung region where is located in the downstream of the Imjin River. Therefore, a more sophisticated approach is required to evaluate the design flood level estimation before constructive measures adopted in general rivers when establishing the flood control plan in a tidal river.

• Geomechanics and Engineering
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• v.11 no.4
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• pp.471-492
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• 2016

Underground tunnelling is one of the sustainable construction methods which can facilitate the increasing passenger transportation in the urban areas and benefit the community in the long term. Tunnelling in various ground conditions requires careful consideration of the stability factor. This paper investigates three dimensional stability of a shallow circular tunnel in a layered soil. Upper bound theorem of limit analysis was utilised to solve the tunnel face stability problem. A three dimensional kinematic admissible failure mechanism was improved to model a layered soil and limiting assumptions of the previous studies were resolved. The study includes calculation of the minimum support pressure acting on the face of the excavation in closed-face excavations. The effects of the characteristics of the layers on the minimum support pressure were examined. It was found that the ratio of the thickness of cover layers particularly when a weak layer is overlying a stronger layer, has the most significant influence on the minimum tunnel support pressure. Comparisons have been made with the results of the numerical modelling using FLAC3D software. Results of the current study were in a remarkable agreement with those of numerical modelling.

• Steel and Composite Structures
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• v.2 no.3
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• pp.171-194
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• 2002

In this paper, the behaviour of axially loaded partially encased composite columns made with light welded H steel shapes is examined using ABAQUS finite element modelling. The results of the numerical simulations are compared to the response observed in previous experimental studies on that column system. The steel shape of the specimens has transverse links attached to the flanges to improve its local buckling capacity and concrete is poured between the flanges only. The test specimens included 14 stubcolumns with a square cross section ranging from 300 mm to 600 mm in depth. The transverse link spacing varied from 0.5 to 1 times the depth and the width-to-thickness ratio of the flanges ranged from 23 to 35. The numerical model accounted for nonlinear stress-strain behaviour of materials, residual stresses in the steel shape, initial local imperfections of the flanges, and allowed for large rotations in the solution. A Riks displacement controlled strategy was used to carry out the analysis. Plastic analyses on the composite models reproduced accurately the capacity of the specimens, the failure mode, the axial strain at peak load, the transverse stresses in the web, and the axial stresses in the transverse links. The influence of applying a typical construction loading sequence could also be reproduced numerically. A design equation is proposed to determine the axial capacity of this type of column.

• Structural Engineering and Mechanics
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• v.43 no.3
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• pp.321-336
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• 2012

As an improvement on the isoparametric element method, the derivation presented in this paper is close to that done by Wang (1990) for the 2-D finite element. We extend this idea to solve 3-D crack problems in this paper. A new displacement modelling is constructed with local solutions of three-dimensional cracks and a quasi-compatible isoparametric element for three-dimensional fracture mechanics analysis is presented. The stress intensity factors can be solved directly by means of the present method without any post-processing. A new method for calculating the stress intensity factors of three-dimensional cracks with complex geometries and loads is obtained. Numerical examples are given to demonstrate the validity of the present method. The accuracy of the results obtained by the proposed element is demonstrated by solving several crack problems. The results illustrate that this method not only saves much calculating time but also increases the accuracy of solutions. Because this quasi-compatible finite element of 3-D cracks contains any singularities and easily meets the requirement of compatibility, it can be easily implemented and incorporated into existing finite element codes.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.71-80
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• 2005

More than 100 bridges have been annually collapsed or seriously damaged by scouring in Korea. It is extremely hard to understand the complicated scour mechanism and estimate the scour depth with accuracy in fields, however since scouring is a very complex manifestation of sediment transport unable to describe with a simple mathematical tool. In order to obtain the reasonable solution to bridge scouring, therefore, the interdisciplinary co-operation is strongly recommended. In this study the special task force team for the scour problems around Incheon 2nd bridge piers is made, in which all kinds of scour oriented researches such as oceangraphic survey, hydraulic model test, numerical simulation, scour rate test, real-time scour monitoring, etc will be carried out. This paper provides this interdisciplinary procedure in details.

• New & Renewable Energy
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• v.3 no.3
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• pp.45-53
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• 2007

This paper demonstrates a computational method in predicting aerodynamic noise generated from wind turbines. Low frequency noise due to displacement of fluid and leading fluctuation, according to the blade passing motion, is modelled on monopole and dipole sources. They are predicted by Farassat 1A equation. Airfoil self noise and turbulence ingestion noise are modelled upon quadrupole sources and are predicted by semi-empirical formulas composed on the groundwork of Brooks et al. and Lowson. Aerodynamic flow in the vicinity of the blade should be obtained first, while noise source modelling need them as numerical inputs. Vortex Lattice Method(VLM) is used to compute aerodynamic conditions near blade. In the use of program X-foil [M.Drela] boundary layer characteristics are calculated to obtain airfoil self noise. Wind turbine blades are divided into spanwise unit panels, and each panel is considered as an independent source. Retarded time is considered, not only in low frequency noise but also In turbulence ingestion noise and airfoil self noise prediction. Numerical modelling is validated with measurement from NREL [AOC15/50 Turbine) and ETSU [Markham's VS45] wind turbine noise measurements.

• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.105-112
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• 2011

This paper presents the numerical modelling technique for modeling the time-dependent behavior of geosynthetic reinforced soil wall under a sustained load. The applicability of power law-based creep models for modeling the creep deformations of geogrid and reinforced soil was first examined. The modeling approach was then used to simulate the long-term performance of a geosynthetic reinforced soil wall used in a bridge abutment. The results indicated that the power law-based models can be effectively used for modelling the long term behavior of geosynthetic reinforced walls under sustained loading. In addition, it was shown that, when using creep deformation susceptible backfill soils, the abutment wall and the sill beam may experience deformations exceeding allowable limits. Practical implications of the findings from this study are discussed in great detail.