127 research outputs found
A Continuum Mechanics based Beam Finite Element for Elastoplastic Large Displacement Analysis.
No full text"In this paper, a total Lagrangian formulation of three-dimensional continuum mechanics based beam finite elements is presented for general nonlinear analysis. Warping displacements are continuously interpolated with a corresponding warping director vector and a warping degree of freedom. The beam element has seven degrees of freedom at each beam node. The beam element provides excellent nonlinear performance to predict the large twisting behaviour of beams with complicated three-dimensional geometry. The Green-Lagrange strain obtained implicitly includes the Wagner strain coupled with other strain components. Thus, the present element can successfully simulate complex nonlinear phenomena. The performance of the continuum mechanics based beam finite element in general nonlinear analysis is demonstrated using two post-buckling problems with elastic and elasto-plastic materials."
Deep learned finite elements
No full textIn this paper, we propose a method that employs deep learning, an artificial intelligence technique, to generate stiffness matrices of finite elements. The proposed method is used to develop 4- and 8-node 2D solid finite elements. The deep learned finite elements practically pass the patch tests and the zero energy mode tests. Through various numerical examples, the performance of the developed elements is investigated and compared with those of existing elements. Computation efficiency is also studied. It was confirmed that the deep learned finite elements can potentially outperform existing finite elements. The proposed method can be applied to generate various types of finite elements in the future.
Nonlinear torsional analysis of 3D composite beams using the extended St. Venant solution
No full textWe present in this paper a finite element formulation for nonlinear torsional analysis of 3D beams with arbitrary composite cross-sections. Since the proposed formulation employs a continuum mechanics based beam element with kinematics enriched by the extended St. Venant solutions, it can precisely account higher order warping effect and its 3D couplings. We propose a numerical procedure to calculate the extended St. Venant equation and the twisting center of an arbitrary composite cross-section simultaneously. The accuracy and efficiency of the proposed formulation are thoroughly investigated through representative numerical examples.
Development of the enriched MITC3 shell element
No full text유한요소법은 쉘 구조물의 선형 및 비선형 해석에 가장 널리 사용되는 수치해석기법이며, 지난 수십 년 동안 보다 더 정확하고 일관된 수치적 결과를 얻기 위한 연구가 활발하게 진행되었다. 하지만 응력이 집중되거나 singular 해가 존재하는 특정영역에서의 수치결과는 상당한 오차를 보여 주며 이러한 문제를 해결하기 위한 노력은 지속적으로 진행 중이다. 본 논문에서는 기존 형상 데이터의 변경없이 새로운 자유도를 추가 함으로써 정교한 수치 해를 얻을 수 있는 PU기반 3 절점 삼각형 쉘 요소를 제안하였으며 다양한 benchmark 문제를 해석함으로써 제안된 삼각형 쉘 요소의 성능을 비교 검증 하였다
Hydroelastic analysis of submerged floating tunnels under seismic loads
No full textWe present in this paper a theory for a continuum mechanics based beams and associated mixed finite element formulation for geometric nonlinear analysis. The kinematic description is directly derived by degenerating from the assemblage of the 3-D solid finite elements. The exact material position vector is given by enriching the torsional warping deformation with the corresponding warping direction. Thus, the Wagner strain is automatically and appropriately accounted. MITC formulation is adopted in order to circumvent shear locking and to improve nonlinear performance. We evaluate the remarkable nonlinear performance and the excellent modeling capabilities of the derived formulation through the means of several numerical examples
Ballasting plan optimization for Accuracy control on Offshore Floating Dock
No full textIn this paper, we propose and validate an accuracy control system for an Offshore Floating Dock (OFD) developed by Samsung Heavy Industries (SHI). The OFD was developed for constructing offshore structures on floating docks, and has a rectangular shape. Since the offshore structures are very heavy, the erection of offshore blocks causes global and local deformations of the OFD, which in turn adversely affects the alignment of the erection blocks. We propose a ballast plan optimization system for accuracy control. The proposed system was used and validated with data from the Jack & Saint Malo (JSM) offshore plant project that was being constructed on the OFD
Computational and Histological Analyses for Investigating Mechanical Interaction of Thermally Drawn Fiber Implants with Brain Tissue
No full textThe development of a compliant neural probe is necessary to achieve chronic implantation with minimal signal loss. Although fiber-based neural probes fabricated by the thermal drawing process have been proposed as a solution, their long-term effect on the brain has not been thoroughly investigated. Here, we examined the mechanical interaction of thermally drawn fiber implants with neural tissue through computational and histological analyses. Specifically, finite element analysis and immunohistochemistry were conducted to evaluate the biocompatibility of various fiber implants made with different base materials (steel, silica, polycarbonate, and hydrogel). Moreover, the effects of the coefficient of friction and geometric factors including aspect ratio and the shape of the cross-section on the strain were investigated with the finite element model. As a result, we observed that the fiber implants fabricated with extremely softer material such as hydrogel exhibited significantly lower strain distribution and elicited a reduced immune response. In addition, the implants with higher coefficient of friction (COF) and/or circular cross-sections showed a lower strain distribution and smaller critical volume. This work suggests the materials and design factors that need to be carefully considered to develop future fiber-based neural probes to minimize mechanical invasiveness
Testing for time stochastic dominance
No full text© 2022 Elsevier B.V.We propose nonparametric tests for the null hypothesis of time stochastic dominance. Time stochastic dominance makes a partial order of different prospects over time based on the net present value criteria for general utility and time discount function classes. For example, time stochastic dominance can be used for ranking investment strategies or environmental policies based on the expected net present value of the future benefits. We consider an Lp-type test statistic and derive its large sample distribution under standard panel data sampling scheme with fixed time dimension. We suggest a path-wise (or cluster) bootstrap procedure that allows individual time series dependence over the time horizon. We describe two approaches, the contact-set approach and the numerical delta method, that may lead to enhanced power compared to the conventional least-favorable-case based approach. We prove the asymptotic validity of our testing procedures. We investigate the finite sample performance of the tests in simulation studies. As an illustration, we apply the proposed tests to evaluate the Million Baht Village Fund Program in Thailand and carbon emission trading scheme in China.N
Exposure to several polychlorinated biphenyls (PCBs) is associated with chronic kidney disease among general adults: Korean National Environmental Health Survey (KoNEHS) 2015-2017
No full textWe investigated the association between major persistent organic pollutants (POPs) exposure and chronic kidney disease (CKD) among general adult population of Korea. For this purpose, a subset of the adult population (n = 1276) participated in Korean National Environmental Health Survey (KoNEHS) Cycle 3 (2015-2017) were analyzed for twenty-four POPs in serum, including organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs), and were derived for estimated glomerular filtration rate (eGFR) and urinary albumin-to-creatinine ratio (uACR). Multivariable linear regression was conducted to assess the association between POPs exposure and CKD-related parameters including eGFR and uACR. As sensitivity analyses, principal component analysis was conducted. Moreover, the U.S. National Health and Nutrition Examination Survey (NHANES) 1999-2004 data were chosen to compare with the observations of the Korean adults. Approximately 7.7% of the Korean adult population possessed CKD based on either eGFR (< 60 ml/min/1.73 m(2)) or uACR (>= 30 mg/g) criteria. Among the POPs that were detected in >= 70% of the subjects, PCB153 (beta =-1.61, 95% CI:-2.55,-0.67, P = 0.001) and PCB180 (beta =-1.47, 95% CI:-2.53,-0.40, P = 0.007) exhibited significant associations with decreased eGFR, especially in females. In male participants, hexachlorobenzene (HCB) was associated with eGFR (beta =-0.79, 95% CI:-1.53,-0.04, P = 0.040). Sex-dependent associations with eGFR were also shown in the PCA model. Moreover, the sex-dependent associations of PCBs were similarly observed in the adult populations of the US NHANES. However, POPs exposure was not associated with uACR, regardless of association model or population. The observed associations of PCBs are supported by several experimental studies reported elsewhere. To our knowledge, it is the first report that suggests significant associations of PCBs and HCB with eGFR among general population, and further validations in other populations are warranted.N
- …
