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A Comparative Assessment of Aerodynamic Models for Buffeting and Flutter of Long-Span Bridges 被引量:3
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作者 Igor Kavrakov Guido Morgenthal 《Engineering》 SCIE EI 2017年第6期823-838,共16页
Wind-induced vibrations commonly represent the leading criterion in the design of long-span bridges. The aerodynamic forces in bridge aerodynamics are mainly based on the quasi-steady and linear unsteady theory. This ... Wind-induced vibrations commonly represent the leading criterion in the design of long-span bridges. The aerodynamic forces in bridge aerodynamics are mainly based on the quasi-steady and linear unsteady theory. This paper aims to investigate different formulations of self-excited and buffeting forces in the time domain by comparing the dynamic response of a multi-span cable-stayed bridge during the critical erection condition. The bridge is selected to represent a typical reference object with a bluff con- crete box girder for large river crossings. The models are viewed from a perspective of model complexity, comparing the influence of the aerodynamic properties implied in the aerodynamic models, such as aerodynamic damping and stiffness, fluid memory in the buffeting and self-excited forces, aerodynamic nonlinearity, and aerodynamic coupling on the bridge response. The selected models are studied for a windspeed range that is typical for the construction stage for two levels of turbulence intensity. Furthermore, a simplified method for the computation of buffeting forces including the aerodynamic admittance is presented, in which rational approximation is avoided. The critical flutter velocities are also compared for the selected models under laminar flow. 展开更多
关键词 BUFFETING FlutterLong-span bridges Bridge aerodynamics Bridge aeroelasticity Erection stage
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Directly Simulation of Second Order Hyperbolic Systems in Second Order Form via the Regularization Concept
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作者 Hassan Yousefi Seyed Shahram Ghorashi Timon Rabczuk 《Communications in Computational Physics》 SCIE 2016年第6期86-135,共50页
We present an efficient and robustmethod for stresswave propagation problems(second order hyperbolic systems)having discontinuities directly in their second order form.Due to the numerical dispersion around discontinu... We present an efficient and robustmethod for stresswave propagation problems(second order hyperbolic systems)having discontinuities directly in their second order form.Due to the numerical dispersion around discontinuities and lack of the inherent dissipation in hyperbolic systems,proper simulation of such problems are challenging.The proposed idea is to denoise spurious oscillations by a post-processing stage from solutions obtained from higher-order grid-based methods(e.g.,high-order collocation or finite-difference schemes).The denoising is done so that the solutions remain higher-order(here,second order)around discontinuities and are still free from spurious oscillations.For this purpose,improved Tikhonov regularization approach is advised.This means to let data themselves select proper denoised solutions(since there is no pre-assumptions about regularized results).The improved approach can directly be done on uniform or non-uniform sampled data in a way that the regularized results maintenance continuous derivatives up to some desired order.It is shown how to improve the smoothing method so that it remains conservative and has local estimating feature.To confirm effectiveness of the proposed approach,finally,some one and two dimensional examples will be provided.It will be shown how both the numerical(artificial)dispersion and dissipation can be controlled around discontinuous solutions and stochastic-like results. 展开更多
关键词 Second order hyperbolic systems Tikhonov regularization Numerical(artificial)dispersion
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Disruption of orbitofrontal-hypothalamic projections in a murine ALS model and in human patients
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作者 David Bayer Stefano Antonucci +7 位作者 Hans-Peter Muller Rami Saad Luc Dupuis Volker Rasche Tobias M.Bockers Albert C.Ludolph Jan Kassubek Francesco Roselli 《Translational Neurodegeneration》 2021年第2期213-229,共17页
Background:Increased catabolism has recently been recognized as a clinical manifestation of amyotrophic lateral sclerosis(ALS).The hypothalamic systems have been shown to be involved in the metabolic dysfunction in AL... Background:Increased catabolism has recently been recognized as a clinical manifestation of amyotrophic lateral sclerosis(ALS).The hypothalamic systems have been shown to be involved in the metabolic dysfunction in ALS,but the exact extent of hypothalamic circuit alterations in ALS is yet to be determined.Here we explored the integrity of large-scale cortico-hypothalamic circuits involved in energy homeostasis in murine models and in ALS patients.Methods:The rAAV2-based large-scale projection mapping and image analysis pipeline based on Wholebrain and Ilastik software suites were used to identify and quantify projections from the forebrain to the lateral hypothalamus in the SOD1(G93A)ALS mouse model(hypermetabolic)and the FusΔNLS ALS mouse model(normo-metabolic).3 T diffusion tensor imaging(DTI)-magnetic resonance imaging(MRI)was performed on 83 ALS and 65 control cases to investigate cortical projections to the lateral hypothalamus(LHA)in ALS.Results:Symptomatic SOD1(G93A)mice displayed an expansion of projections from agranular insula,ventrolateral orbitofrontal and secondary motor cortex to the LHA.These findings were reproduced in an independent cohort by using a different analytic approach.In contrast,in the FusΔNLS ALS mouse model hypothalamic inputs from insula and orbitofrontal cortex were maintained while the projections from motor cortex were lost.The DTI-MRI data confirmed the disruption of the orbitofrontal-hypothalamic tract in ALS patients.Conclusion:This study provides converging murine and human data demonstrating the selective structural disruption of hypothalamic inputs in ALS as a promising factor contributing to the origin of the hypermetabolic phenotype. 展开更多
关键词 RAAV2 Agranular insula Orbitofrontal cortex Lateral hypothalamus HYPERMETABOLISM Amyotrophic lateral sclerosis
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