• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.3 no.2
• /
• pp.161-171
• /
• 1999

Aerodynamic sensitivity analysis codes are developed via the hand-differentiation using a direct differentiation method and an adjoint method respectively from discrete two-dimensional compressible Navier-Stokes equations. Unlike previous other researches, Baldwin-Lomax algebraic turbulence model is also differentiated by hand to obtain design sensitivities with respect to design variables of interest in turbulent flows. Discrete direct sensitivity equations and adjoint equations are efficiently solved by the same time integration scheme adopted in the flow solver routine. The required memory for the adjoint sensitivity code is greatly reduced at the cost of the computational time by allowing the large banded flux jacobian matrix unassembled. Direct sensitivity code results are found to be exactly coincident with sensitivity derivatives obtained by the finite difference. Adjoint code results of a turbulent flow case show slight deviations from the exact results due to the limitation of the algebraic turbulence model in implementing the adjoint formulation. However, current adjoint sensitivity code yields much more accurate sensitivity derivatives than the adjoint code with the turbulence eddy viscosity being kept constant, which is a usual assumption for the prior researches.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.11
• /
• pp.2245-2252
• /
• 2002

Design sensitivity analysis scheme is proposed in an elasto -plastic finite element method with explicit time integration using a direct differentiation method. The direct differentiation is concerned with large deformation, the elasto-plastic constitutive relation, shell elements with reduced integration and the contact scheme. The design sensitivities with respect to the process parameter are calculated with the direct analytical differentiation of the governing equation. The sensitivity results obtained from the present theory are compared with that obtained by the finite difference method in a class of sheet metal forming problems such as hemi-spherical stretching and cylindrical cup deep-drawing. The result shows good agreement with the finite difference method and demonstrates that the preposed sensitivity calculation scheme is a pplicable in the complicated sheet metal forming analysis and design.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2001.10a
• /
• pp.93-96
• /
• 2001

Design sensitivity is calculated in the sheet metal forming process with an elasto-plastic finite element analysis and a direct differentiation method The sensitivity analysis is concerned with the time integration the constitutive relation considering planar anisotropy, shell elements and the contact scheme. The present result is compared with the result obtained with the finite difference approach in deep drawing processes. The obtained sensitivity information is applied to the simple optimization process for the sheet metal forming process.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.11 s.242
• /
• pp.1455-1462
• /
• 2005

In this paper, we intend to introduce a nonlinear finite element method based on the fully nonlinear potential flow theory in order to simulate the large amplitude sloshing flow in two-dimensional baffled tank subject to horizontally forced excitation. The free surface is tracked by a direct time differentiation scheme with the four-step predictor-corrector time integration method. The flow velocity is accurately recovered from the velocity potential by second-order least square method. In order to maintain the finite element mesh regularity and total mass, the semi-Lagrangian surface tracking method with area conservation is applied. According to the numerical formulae, we perform the parametric experiments by varying the installation height and the opening width of baffles, in order to examine the effects of baffle on the nonlinear liquid sloshing. From the numerical results, the hydrodynamic characteristics of the large amplitude sloshing are investigated.

• Proceedings of the KSME Conference
• /
• 2001.06c
• /
• pp.402-407
• /
• 2001

Sensitivity analysis scheme is developed in the elasto-plastic finite element method with explicit time integration using direct differentiation method. The direct differentiation is concerned with the time integration, constitutive relation, shell element with reduced integration and the contact scheme. Sensitivity analysis results are mainly examined with the highly nonlinear and quasi-static problem with the complicated contact condition. The result shows stable sensitivity especially in the sheet metal forming analysis.

• 한국전산유체공학회:학술대회논문집
• /
• 2000.05a
• /
• pp.66-72
• /
• 2000

Aerodynamic sensitivity analysis is performed for the Navier-Stokes equations coupled with two-equation turbulence models using a discrete adjoint method and a direct differentiation method respectively. Like the mean flow equations, the turbulence model equations are also hand-differentiated to accurately calculate the sensitivity derivatives of flow quantities with respect to design variables in turbulent viscous flows. Both the direct differentiation code and the adjoint variable code adopt the same time integration scheme with the flow solver to efficiently solve the differentiated equations. The sensitivity codes are then compared with the flow solver in terms of solution accuracy, computing time and computer memory requirements. The sensitivity derivatives obtained from the sensitivity codes with different turbulence models are compared with each other. Using two-equation turbulence models, it is observed that a usual assumption of constant turbulent eddy viscosity in adjoint methods may lead to seriously inaccurate results in highly turbulent flows.

• Journal of the Korean Operations Research and Management Science Society
• /
• v.31 no.2
• /
• pp.57-67
• /
• 2006

One of challenging issues of market oriented manufacturing organization is product proliferation. However, increasing product variety not only incurs additional direct and indirect production cost, but also aggravates production system performance such as inventory level, customer lead time and fill rate. Recently, as one of the most beneficial strategic choices to menage the risks associateed with product variety and uncertain sales, special attention is focused on the product/process redesign to delayed product differentiation. In this paper, we develop an analytical model to demonstrate the existence of an optimal level of product differentiation, which can be used to provide theoretical basis in establishing market oriented SCM strategy.

• Animal Bioscience
• /
• v.34 no.4
• /
• pp.533-538
• /
• 2021

Objective: Pluripotent stem cell-derived lymphatic endothelial cells (LECs) show great promise in their therapeutic application in the field of regenerative medicine related to lymphatic vessels. We tested the approach of forced differentiation of mouse embryonal stem cells into LECs using biodegradable poly lactic-co-glycolic acid (PLGA) nanospheres in conjugation with growth factors (vascular endothelial growth factors [VEGF-A and VEGF-C]). Methods: We evaluated the practical use of heparin-conjugated PLGA nanoparticles (molecular weight ~15,000) in conjugation with VEGF-A/C, embryoid body (EB) formation, and LEC differentiation using immunofluorescence staining followed by quantification and quantitative real-time polymerase chain reaction analysis. Results: We showed that formation and differentiation of EB with VEGF-A/C-conjugated PLGA nanospheres, compared to direct supplementation of VEGF-A/C to the EB differentiation media, greatly improved yield of LYVE1(+) LECs. Our analyses revealed that the enhanced potential of LEC differentiation using VEGF-A/C-conjugated PLGA nanospheres was mediated by elevation of expression of the genes that are important for lymphatic vessel formation. Conclusion: Together, we not only established an improved protocol for LEC differentiation using PLGA nanospheres but also provided a platform technology for the mechanistic study of LEC development in mammals.

• YAKHAK HOEJI
• /
• v.41 no.1
• /
• pp.81-85
• /
• 1997

Ceramide has been suggested as an important mediator of the effects of extracellular agonists on cell growth inhibition, differentiation, apoptosis. However the biochemical sign aling mechanism involved in transducing the effects of ceramide on leukemia cell differentiation is still unclear. In these respects, we examined the regulatory effects of ceramide on c-jun gene expression during differentiation. In U-937 cells. ceramide increased c-jun mRNA levels in a time-dependent manner. The half life, of c-jun mRNA was 30 min. In contrast, inhibition of protein synthesis with cycloheximide in the absence, of transcription with actinomycin D increased the half-life of c-jun mRNA in ceramide-treated U-937 cells to more than 90 min. In order to examine whether ceramide-inhibited c-jun gene expression is regulated through ceramide-activated protein phosphatase (CAPP), a direct target for the action of ceramide, okadaic acid were treated to the cells. Okadaic acid inhibited enhancement of c-jun mRNA induced by C2-ceramide in a dose-dependent manner. These results suggested that ceramide increases c-jun mRNA level during differentiation in U-937 cells and regulates the gene expression on posttranscriptional level. In addition, we provide the evidence that CAPP is involved in ceramide-induced c-jun gene expression in U-937 cells.

• BMB Reports
• /
• v.33 no.5
• /
• pp.402-406
• /
• 2000

In order to understand the role of AGP on the differentiation of promyelocytic leukemia cells, the AGP expression and its relation to cytokines were investigated during granulocytic or monocytic differentiation of HL-60 cells. When HL-60 cells were treated with all-trans-retinoic acid (ATRA) for 5 days, the cells were fully differentiated into granulocytes, and the AGP mRNA and protein levels were continuously increased up to 5 days in a dose- and time- dependent manner. However, in the case of the monocytic differentiation of HL-60 cells by tetradeanoyl phorbol acetate (TPA), the AGP gene expression was not induced. In addition, $IL-1{\alpha}$, $IL-1{\beta}$, IL-6 and $TNF-{\alpha}$ mRNAs were also enhanced during granulocytic differentiation. These cytokine transcripts showed a peak level 3 days after the ATRA treatment. It decreased gradually thereafter. However, direct addition of recombinant cytokines ($IL-1{\beta}$, IL-6 and $TNF-{\alpha}$) and dexamethasone to the HL-60 cell cultures showed no AGP induction. These findings suggest that the AGP and proinflammatory cytokines are expressed in ATRA-treated promyelocytic cells. However, these cytokines do not act as autocrine inducers on AGP expression. This fact implies that the AGP expression during granulocytic differentiation of HL-60 cells is induced through a signal pathway different from hepatocyte signaling in inflammation.