• Journal of the Korean GEO-environmental Society
• /
• v.21 no.8
• /
• pp.15-27
• /
• 2020

In the current paper, a series of advanced 3D finite element analyses have been performed on existing pieces of work of negative skin friction from a geotechnical centrifuge test and full-scale field measurements. From these analyses, key features of pile behaviour under the influence of negative skin friction which, previously, were not fully understood in existing studies, have been meticulously discussed. As such, it has been possible to successfully address several numerical modelling issues such as negative skin friction induced pile settlements and group effects (the shielding effect), the effect of sacrificial piles in groups and the interaction between the pile head and the cap, the effect of interface elements at the pile-soil interface and the time-dependent pile behaviour. During a geotechnical centrifuge test, substantial amounts of negative skin frictions were mobilised when centrifugal acceleration increased from 1g to a certain g-level due to an increase in the self-weight of soil. The behaviour of piles inside a group were heavily affected by the sacrificial piles and the connectivity between the pile head and the pile cap. In particular, as negative skin friction has time dependent qualities associated with consolidation, it was logical to perform coupled analyses when analysing piles in consolidating grounds. From the current work, several insufficiencies of previous researches have been addressed, and the engineering pile behaviour subjected to negative skin friction has been clarified.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
• /
• v.40 no.1
• /
• pp.3-10
• /
• 2014

Objectives: Although nerve growth factor (NGF) could promote the functional regeneration of an injured peripheral nerve, it is very difficult for NGF to sustain the therapeutic dose in the defect due to its short half-life. In this study, we loaded the NGF-bound heparin-conjugated fibrin (HCF) gel in the NGF-delivering implants and analyzed the time-dependent release of NGF and its bioactivity to evaluate the clinical effectiveness. Materials and Methods: NGF solution was made of 1.0 mg of NGF and 1.0 mL of phosphate buffered saline (PBS). Experimental group A consisted of three implants, in which $0.25{\mu}L$ of NGF solution, $0.75{\mu}L$ of HCF, $1.0{\mu}L$ of fibrinogen and $2.0{\mu}L$ of thrombin was injected via apex hole with micropipette and gelated, were put into the centrifuge tube. Three implants of experimental group B were prepared with the mixture of $0.5{\mu}L$ of NGF solution, $0.5{\mu}L$ HCF, $1.0{\mu}L$ of fibrinogen and $2.0{\mu}L$ of thrombin. These six centrifuge tubes were filled with 1.0 mL of PBS and stirred in the water-filled beaker at 50 rpm. At 1, 3, 5, 7, 10, and 14 days, 1.0 mL of solution in each tubes was collected and preserved at $-20^{\circ}C$ with adding same amount of fresh PBS. Enzyme-linked immunosorbent assay (ELISA) was done to determine in vitro release profile of NGF and its bioactivity was evaluated with neural differentiation of pheochromocytoma (PC12) cells. Results: The average concentration of released NGF in the group A and B increased for the first 5 days and then gradually decreased. Almost all of NGF was released during 10 days. Released NGF from two groups could promote neural differentiation and neurite outgrowth of PC12 cells and these bioactivity was maintained over 14 days. Conclusion: Controlled release system using NGF-HCF gel via NGF-delivering implant could be an another vehicle of delivering NGF to promote the nerve regeneration of dental implant related nerve damage.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.12
• /
• pp.57-71
• /
• 2021

The pile-supported wharf is the port structure in which the upper deck is supported by piles or columns. By installing batter piles in this structure, horizontal load such as earthquake loads can be partially delivered as axial forces. The codes suggests using the response spectrum analysis as a preliminary design method for seismic design of pile-supported wharf, and suggests modeling the piles using virtual fixed points or soil spring methods for this analysis. Recently, several studies have been conducted on pile-supported wharves composed of vertical piles to derive a modeling method that appropriately simulates the dynamic response of structures during response spectrum analysis. However, studies related to the response spectrum analysis of pile-supported wharves with batter piles are insufficient so far. Therefore, this study performed the dynamic centrifuge model test and response spectrum analysis to evaluate the seismic performance according to the modeling method of pile-supported wharves with batter piles. As a result of test and analysis, it is confirmed that modeling using the Terzaghi (1955) constant of horizontal subgrade reaction (n_h) most appropriately simulates the actual response in the case of the pile-supported wharf with batter piles.

• Journal of the Korean GEO-environmental Society
• /
• v.12 no.1
• /
• pp.61-70
• /
• 2011

The impact protection system consists of an arrangement of circular sheet pile cofferdams-denoted dolphin structuredeeply embedded in the seabed, filled with crushed rock and closed at the top with a robust concrete cap. Centrifuge model tests were performed to investigation the behaviors of dolphins in this study. Total 7 quasi-model tests and 11 dynamic model tests were performed. The main experimental results can be summarized as follows. Firstly, The experimental force-displacement results for quasi-static tests show a limited influence on the initial stiffness of the structure from the change in fill density and the related change in the stiffness of the fill. And by comparing the dissipation at the same dolphin displacement it was found that the denser fill increase the dissipation by 16% for the 20m dolphin and by 23% for the 30m dolphin. The larger sensitivity for the large dolphin is explained by a larger contribution to the dissipation from strain in the fill. In low level impacts the dynamic force-response is up to 26~58% larger than the quasi-static and the dissipation response is showed larger in small displacement. Hence, it is concluded conservative to use the quasi-static response characteristics in the approximation of the response, and it is further concluded that the dolphin resistance to low level impacts is demonstrated to be equivalent and even superior to the high level impacts.

• Asian-Australasian Journal of Animal Sciences
• /
• v.12 no.4
• /
• pp.544-547
• /
• 1999

The object of this study was to determine the influence of monensin and virginiamycin (VM) on in vitro ruminal fermentation of rice straw or ammoniated rice straw. Rumen fluid was collected from 4 wethers fed 200 g of concentrate supplement with 400 g of untreated (U) or ammoniated (A) rice straw once daily for 28 days. Mixed ruminal microorganisms were incubated in anaerobic media that contained 20% (vol/vol) ruminal fluid and 0.3 g of either U or A rice straw. Monensin and/or VM, dissolved in ethanol, were added in centrifuge tubes at final concentrations of 0, 15, 30, 15+15 and 30+30 ppm of culture fluid. The addition of monensin and VM combination to A rice straw fermentation decreased (p<0.05) the acetate to propionate ratio, total VFA and lactate production, but increased (p<0.05) pH. Total gas production tended to be decreased by the addition of monensin plus VM. Antimicrobial agents decreased $NH_3$ N concentration and dry matter digestibility.

• Journal of Industrial Technology
• /
• v.20 no.A
• /
• pp.101-111
• /
• 2000

This research is results of experimental and numerical works on characteristic of strength increase and bearing capacity in dredged and reclaimed soil due to desiccation shrinkage. For a soil sampled from southern coastal area in Korea, basic soil property tests and standard consolidation test with falling head permeability tests were carried out to obtain consolidational characteristics of soil. Double cone penetration test, laboratory vane test and unconfined compression test were also performed to investigate the change of shear strength with degree of desiccation. Model tests were performed in 1G environment and 30G level artificially accelerated condition by using the centrifuge model test facilities to investigate the bearing capacity of desiccated ground. Test results were analyzed by using the theoretical and load-settlement characteristics method proposed by Meyehof & Hanna(1978). On the other hands, the numerical technique, using the finite strain consolidation theory considering the effect of desiccation was used to estimate the appropriate time of using heavy construction equipments in field with respect to strength increase due to desiccation.

• Geomechanics and Engineering
• /
• v.21 no.5
• /
• pp.489-501
• /
• 2020

This paper conducts a complicated coupled effective stress analysis of X-section-in-place concrete (XCC) pile installation and consolidation processes using the dual-stage Eulerian-Lagrangian (DSEL) technique incorporating the modified Cam-clay model. The numerical model is verified by centrifuge data and field test results. The main objective of this study is to investigate the shape effect of XCC pile cross-section on radial total stress, excess pore pressure and time-dependent strength. The discrepancies of the penetration mechanism and set-up effects on pile shaft resistance between the XCC pile and circular pile are discussed. Particular attention is placed on the time-dependent strength around the XCC pile shaft. The results show that soil strength improved more significantly close to the flat side compared with the concave side. Additionally, the computed ultimate shaft resistance of XCC pile incorporating set-up effects is 1.45 times that of the circular pile. The present findings are likely helpful in facilitating the incorporation of set-up effects into XCC pile design practices.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09a
• /
• pp.201-204
• /
• 2010

Earthquake load to design a structure has been calculated from a fixed base SDOF model using amplified surface accelerations along soft soil layers. But the method dose not consider a soil-structure interaction. Centrifugal experiments that were consisted of soil, a shallow foundation and a structure were performed to find the effects of soil-structure interaction. The experiments showed that mass and stiffness of the foundation affected a response of the structure and nonlinear behavior of soil near the foundation. And a rocking displacement caused by overturning moment affected the response and increases a damping effect. In this study, the centrifugal experiment was simulated as a two dimensional finite element model. The finite element model was used for nonlinear time domain analysis of the OpenSees program. The numerical model accurately evaluated the behaviors of soil and the foundation, but the rocking effect and the behavior of structure were not described.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.9 no.2
• /
• pp.115-123
• /
• 1989

A computer program evaluating the pile downdrag is developed using the conventional elastic solid method. Modification of the conventional method has been performed by introducing the concept of critical relative displacement. A simple transfer function method which employes the critical relative displacement as a pile-soil slip criterion and calculates downdrag by Mohr-Coulomb equation, has also been developed. The results of three methods are all found to be in good agreement with field observations. When they are applied to a centrifuge modeling problem of pile downdrag to predict its result, however, diverse answers are obtained. Overall, the simple transfer function method developed in this study seems to be the most effective in the evaluation of pile downdrag, considering the quality of its result and its efficiency in computation.

• Wind and Structures
• /
• v.21 no.6
• /
• pp.677-691
• /
• 2015

In this study, the geometrical setup of a turbine blade is tracked. A research-scale rotating turbine blade system is setup with a single 3-axes accelerometer mounted on one of the blades. The turbine system is rotated by a controlled motor. The tilt and rolling angles of the rotating blade under operating conditions are determined from the response measurement of the single accelerometer. Data acquisition is achieved using a prototype wireless sensing system. First, the Rodrigues' rotation formula and an optimization algorithm are used to track the blade rolling angle and pitching angles of the turbine blade system. In addition, the blade flapwise natural frequency is identified by removing the rotation-related response induced by gravity and centrifuge force. To verify the result of calculations, a covariance-driven stochastic subspace identification method (SSI-COV) is applied to the vibration measurements of the blades to determine the system natural frequencies. It is thus proven that by using a single sensor and through a series of coordinate transformations and the Rodrigues' rotation formula, the geometrical setup of the blade can be tracked and the blade flapwise vibration frequency can be determined successfully.