In this paper, numerical simulations of vortex-induced vibrations in a vertical top-tension riser with a length-to-diameter ratio of 500 using our in-house code viv-FOAM-SJTU are presented. The time-dependent hydrodyn...In this paper, numerical simulations of vortex-induced vibrations in a vertical top-tension riser with a length-to-diameter ratio of 500 using our in-house code viv-FOAM-SJTU are presented. The time-dependent hydrodynamic forces on two-dimensional strips are obtained by solving the Navier-Stokes equations, which are, in turn, integrated into a finite-element structural model to obtain the riser deflections. The riser is discretized into 80 elements with its two ends set as pinned and 20 strips are located equidistant along the risers. Flow and structure are coupled by hydrodynamic forces and structural displacements. In order to study the effects of the shear rate, of the current profiles on the vortex-induced vibrations in the riser, vibrations, with varying shear rates, in both the in-line and cross-flow directions, are simulated. In addition to the time domain analysis, spectral analysis was conducted in both the temporal and spatial domains. Multi-mode vibration characteristics were observed in the riser. The relationship between dominant vibration mode number and the shear rate of current profiles is discussed. In general, the overall vibrations in the riser pipe include contributions from several modes and each mode persists over a range of shear rates. Moreover, the results suggest that with a larger shear rate the position of the maximum in-line time-averaged displacement will move closer to the end where the largest velocity is located.展开更多
Even today, with the great progress that has been made in the scientific, technological and computational fields, we are still stunned by the devastating effects brought about by atmospheric phenomena. This paper aims...Even today, with the great progress that has been made in the scientific, technological and computational fields, we are still stunned by the devastating effects brought about by atmospheric phenomena. This paper aims to propose new hypotheses in the field of dynamics to enhance our understanding of the behaviour of atmospheric disturbances caused by rotating winds. I believe that the criteria of classical dynamics that are applied to vortex systems in the atmosphere should be rigorously reviewed. I propose to establish new hypotheses in the field of dynamics, in order to better interpret rotation in nature. These hypotheses have been structured into a new theory that has been tested experimentally by both ourselves and third parties, with positive results. I propose to use the Theory of Dynamic Interactions (TDI) to interpret the behaviour of systems undergoing successive rotations around different axes—which we will refer to as non-coaxial rotations. I hold that this theory applies to air masses and groups of particles in suspension that are accelerated by rotations. Accordingly, it should be used to interpret the behaviour of tornadoes, cyclones and hurricanes. I believe that this proposal could enhance our understanding of these atmospheric phenomena and improve predictions about them.展开更多
We give a brief review of the asymptotic theory of slender vortex filaments with emphases on (i) the choices of scalings and small parameters characterizing the physical problem,(ii) the key steps in the formulation o...We give a brief review of the asymptotic theory of slender vortex filaments with emphases on (i) the choices of scalings and small parameters characterizing the physical problem,(ii) the key steps in the formulation of the theory and (iii) the assumptions and/or restrictions on the theory of Callegari and Ting (1978).We present highlights of an extension of the 1978 asymptotic theory:the analyses for core structures with axial variation.Making use of the physical insights gained from the analyses,we present a new derivation of the evolution equations for the core structure.The new one is simpler and straightforward and shows the physics clearly.展开更多
基金Supported by the National Natural Science Foundation of China(51379125,51490675,11432009,51579145)Chang Jiang Scholars Program(T2014099)+3 种基金Shanghai Excellent Academic Leaders Program(17XD1402300)Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning(2013022)Innovative Special Project of Numerical Tank of Ministry of Industry and Information Technology of China(2016-23/09)Lloyd’s Register Foundation for Doctoral Student
文摘In this paper, numerical simulations of vortex-induced vibrations in a vertical top-tension riser with a length-to-diameter ratio of 500 using our in-house code viv-FOAM-SJTU are presented. The time-dependent hydrodynamic forces on two-dimensional strips are obtained by solving the Navier-Stokes equations, which are, in turn, integrated into a finite-element structural model to obtain the riser deflections. The riser is discretized into 80 elements with its two ends set as pinned and 20 strips are located equidistant along the risers. Flow and structure are coupled by hydrodynamic forces and structural displacements. In order to study the effects of the shear rate, of the current profiles on the vortex-induced vibrations in the riser, vibrations, with varying shear rates, in both the in-line and cross-flow directions, are simulated. In addition to the time domain analysis, spectral analysis was conducted in both the temporal and spatial domains. Multi-mode vibration characteristics were observed in the riser. The relationship between dominant vibration mode number and the shear rate of current profiles is discussed. In general, the overall vibrations in the riser pipe include contributions from several modes and each mode persists over a range of shear rates. Moreover, the results suggest that with a larger shear rate the position of the maximum in-line time-averaged displacement will move closer to the end where the largest velocity is located.
文摘Even today, with the great progress that has been made in the scientific, technological and computational fields, we are still stunned by the devastating effects brought about by atmospheric phenomena. This paper aims to propose new hypotheses in the field of dynamics to enhance our understanding of the behaviour of atmospheric disturbances caused by rotating winds. I believe that the criteria of classical dynamics that are applied to vortex systems in the atmosphere should be rigorously reviewed. I propose to establish new hypotheses in the field of dynamics, in order to better interpret rotation in nature. These hypotheses have been structured into a new theory that has been tested experimentally by both ourselves and third parties, with positive results. I propose to use the Theory of Dynamic Interactions (TDI) to interpret the behaviour of systems undergoing successive rotations around different axes—which we will refer to as non-coaxial rotations. I hold that this theory applies to air masses and groups of particles in suspension that are accelerated by rotations. Accordingly, it should be used to interpret the behaviour of tornadoes, cyclones and hurricanes. I believe that this proposal could enhance our understanding of these atmospheric phenomena and improve predictions about them.
文摘We give a brief review of the asymptotic theory of slender vortex filaments with emphases on (i) the choices of scalings and small parameters characterizing the physical problem,(ii) the key steps in the formulation of the theory and (iii) the assumptions and/or restrictions on the theory of Callegari and Ting (1978).We present highlights of an extension of the 1978 asymptotic theory:the analyses for core structures with axial variation.Making use of the physical insights gained from the analyses,we present a new derivation of the evolution equations for the core structure.The new one is simpler and straightforward and shows the physics clearly.
