The Experts below are selected from a list of 66 Experts worldwide ranked by ideXlab platform
Marko Zirk - One of the best experts on this subject based on the ideXlab platform.
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numerical Buoyancy Wave model for Wave stress and drag simulations in the atmosphere
Communications in Computational Physics, 2014Co-Authors: Marko Zirk, Aarne Mannik, Andres Luhamaa, Marko Kaasik, S TraudAbstract:Orographic drag formation is investigated using a numerical Wave model (NWM), based on the pressure-coordinate dynamics of non-hydrostatic HIRLAM. The surface drag, Wave stress (vertical flux of horizontal momentum), and Wave drag are split to the longitudinal and transverse components and presented as Fourier sums of their spectral amplitudes weighted with the power spectrum of relative orographic height. The NWM is accomplished, enabling a spectral investigation of the Buoyancy Wave stress, and drag generation by orography and is then applied to a cold front, characterised by low static stability of the upper troposphere, large vertical and di- rectional wind variations, and intensive trapped Wave generation downstream of ob- stacles. Resonances are discovered in the stress and drag spectra in the form of high narrow peaks. The stress conservation problem is revisited. Longitudinal stress con- serves in unidirectional flow, 2D orography conditions, but becomes convergent for rotating wind or 3D orography. Even in the convergent case the vertical momentum flux from the troposphere to stratosphere remains substantial. The transverse stress never conserves. Disappearing at the surface and on the top, it realises the main mo- mentum exchange between lower an upper parts of the troposphere. Existence of sta- tionary stratospheric quasi-turbulence (SQT) is established above wind minimum in the stratosphere.
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An Efficient Solution Method for the Buoyancy Wave Equation at Variable Wind and Temperature
Monthly Weather Review, 2007Co-Authors: Rein Rõõm, Marko ZirkAbstract:Abstract To solve a horizontally spectral, vertically discrete Buoyancy Wave equation in conditions of arbitrary wind and temperature distribution with height, a novel method is applied, which consists of a presentation of the solution in the form of a cumulative product of complex decrease factors. For decrease factors, a nonlinear, inhomogeneous, two-member recurrence formula follows that is initiated, assuming the radiative condition at the top. Singularities of the Wave equation, corresponding to a critical layer in the vicinity of evanescent wind, are eliminated by turbulent friction. The estimation of minimal vertical resolution is derived, enabling solution stability and accuracy. The areas of application of the developed numerical scheme are the high-precision modeling of orographic Waves for arbitrary orography in general atmospheric stratification conditions and testing of adiabatic kernels of numerical weather prediction models.
S Traud - One of the best experts on this subject based on the ideXlab platform.
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numerical Buoyancy Wave model for Wave stress and drag simulations in the atmosphere
Communications in Computational Physics, 2014Co-Authors: Marko Zirk, Aarne Mannik, Andres Luhamaa, Marko Kaasik, S TraudAbstract:Orographic drag formation is investigated using a numerical Wave model (NWM), based on the pressure-coordinate dynamics of non-hydrostatic HIRLAM. The surface drag, Wave stress (vertical flux of horizontal momentum), and Wave drag are split to the longitudinal and transverse components and presented as Fourier sums of their spectral amplitudes weighted with the power spectrum of relative orographic height. The NWM is accomplished, enabling a spectral investigation of the Buoyancy Wave stress, and drag generation by orography and is then applied to a cold front, characterised by low static stability of the upper troposphere, large vertical and di- rectional wind variations, and intensive trapped Wave generation downstream of ob- stacles. Resonances are discovered in the stress and drag spectra in the form of high narrow peaks. The stress conservation problem is revisited. Longitudinal stress con- serves in unidirectional flow, 2D orography conditions, but becomes convergent for rotating wind or 3D orography. Even in the convergent case the vertical momentum flux from the troposphere to stratosphere remains substantial. The transverse stress never conserves. Disappearing at the surface and on the top, it realises the main mo- mentum exchange between lower an upper parts of the troposphere. Existence of sta- tionary stratospheric quasi-turbulence (SQT) is established above wind minimum in the stratosphere.
Evgeny V. Morozov - One of the best experts on this subject based on the ideXlab platform.
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Global design and analysis of deep sea FRP composite risers under combined environmental loads
Advanced Composite Materials, 2015Co-Authors: Chunguang Wang, Krishnakumar Shankar, Evgeny V. MorozovAbstract:The use of composite materials in offshore engineering for deep sea oil production riser systems has drawn considerable interest due to the potential weight savings and improvement in durability that can be achieved. The design of composite risers consists of two stages: (1) local design based on critical local load cases (LCs) to obtain the geometric configuration of the riser which will be analysed in the global design stage, and (2) global analysis of the full length composite riser under global loads including top tension force, platform motion, hydrostatic pressure, gravity, Buoyancy, Wave and current loads to determine and assess critical locations. This study describes the methodology, LCs, analysis procedure and results of the global design of the composite riser based on the geometries of the tubular optimised in the local design stage. The results show that a careful local design of the tubular using inclined reinforcements in addition to axial and hoop reinforcements can offer substantial weigh...
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Tailored local design of deep sea FRP composite risers
Advanced Composite Materials, 2014Co-Authors: Chunguang Wang, Krishnakumar Shankar, Evgeny V. MorozovAbstract:The use of fibre reinforced polymer (FRP) composite materials in offshore engineering for deep sea riser systems has drawn considerable interest due to the potential weight savings and improvement in durability that can be achieved. The design of FRP composite risers consists of two stages: (1) preliminary local design based on critical local load cases (LCs) and (2) global analysis of the full length composite riser under global loads including platform motion, hydrostatic pressure, gravity, Buoyancy, Wave and current loads to determine and assess critical locations. The preliminary local design stage is necessary to obtain a first estimate of the laminate configuration – fibre orientations and layer thicknesses of the tube wall, since the deformations and hence the forces and bending moments due to the global loads, depend on the geometric configuration. This paper describes the methodology, LCs, analysis procedure and results of the first stage, the local design of the composite riser. The local design...
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Numerical Analysis of Deep Sea Steel Risers under Combined Loads
2010Co-Authors: Chunguang Wang, Krishna Shankar, Evgeny V. MorozovAbstract:The marine riser plays an indispensable role in offshore energy exploitation. It connects the floating drilling/production facility with subsea wells, and is used to guide the drill stem when drilling and to transport oil and gas to the floating platform or ship from the seabed during production. Thus the structural integrity of risers is critical to safe field operations. Under operational situation in the sea, risers are subject to variety of loads such as hydrostatic pressure, internal fluid pressure, gravity, Buoyancy, Wave and current loads, drifting of floating platform or ship. Many of these loads act simultaneously, which requires the analysis to consider combined load cases. In this paper, Top- Tension Steel Risers for deep water applications are analysed using finite element modelling under different boundary conditions and load cases in line with recommendations by American and European Standards. The boundary conditions considered are: simple support at either ends, ball support at the top and built in at the bottom, and with both ends built in. Initially modal analysis is conducted to determine the natural frequencies of the riser under various boundary conditions and top tension values. Subsequently a large deflection analysis of the riser is performed to study the effects of various boundary conditions including different support types and differing top-tension ratios on the maximum stress values of the riser under different load cases. Factors of Usage are determined for each riser configuration and compared to those recommended by the Standards.
Peter R. Bannon - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Atmospheric Adjustment to Thermal Forcing
Journal of the Atmospheric Sciences, 2005Co-Authors: Paul F. Fanelli, Peter R. BannonAbstract:A nonlinear, numerical model of a compressible atmosphere is used to simulate the hydrostatic and geostrophic adjustment to a localized prescribed heating applied over five minutes with a size characteristic of an isolated, deep, cumulus cloud. This thermal forcing generates both Buoyancy Waves and a horizontally propagating Lamb Wave packet as well as a steady state rich in potential vorticity. The adjustments in three model atmospheres (an isothermal, a constant lapse rate, and one with a stratosphere) are studied. The Lamb Wave packet and the two lowest-order Buoyancy Waves are relatively unaffected by nonlinearities but the higher-order modes and the steady state are. The heating generates a vertically stacked dipole of potential vorticity with a cyclonic perturbation below an anticyclonic perturbation. In contrast to the linear results, the nonlinear dipole is severely distorted by vertical and horizontal advections. In addition, the Lamb Wave packet contains some weak positive perturbation potential vorticity. The energetics is examined using traditional and Eulerian available energetics. Traditional energetics consists of kinetic, internal, and potential energies. It is shown that the Lamb Wave packet contains more total traditional energy than that input to the atmosphere by the heating. The traditional energy in the packet resides primarily in the form of internal energy and only secondarily in the form of potential energy. The passage of the Lamb Wave packet produces an atmosphere that, overall, is cooler, less dense, and with less total traditional energy than the initial atmosphere. Eulerian available energetics consists of kinetic, available potential, and available elastic energies. The heating generates both available elastic and potential energy that is then converted into kinetic energy. Most of the available elastic energy projects onto the Lamb packet, while almost all of the available potential energy is associated with the Buoyancy Waves and the steady state. The effects of varying the spatial and temporal scale of the heating, while keeping the net heating the same, are examined. As the duration of the heating decreases, the amount of energy projected onto the Waves increases. Increasing the size of the heating decreases the amount of energy projected onto the Waves. The adjustment is kinetically more vigorous in the nonisothermal atmospheres because of the reduction in the base-state static stability. The presence of a stratosphere produces large anomalies at and above the tropopause that are linked to the vertical motions of the Buoyancy Wave field.
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Adjustment to Injections of Mass, Momentum, and Heat in a Compressible Atmosphere
Journal of the Atmospheric Sciences, 2005Co-Authors: Jeffrey M. Chagnon, Peter R. BannonAbstract:This study compares the response to injections of mass, heat, and momentum during hydrostatic and geostrophic adjustment in a compressible atmosphere. The sensitivity of the adjustment to these different injection types is examined at varying spatial and temporal scales through analysis of the transient evolution of the fields as well as the partitioning of total energy between acoustic Waves, Buoyancy Waves, Lamb Waves, and the steady state. The effect of a cumulus cloud on its larger-scale environment may be represented as a vertical mass source/sink and a localized warming. To examine how the response to such injections may differ, injections of mass and heat that generate identical potential vorticity (PV) distributions and, hence, identical steady states, are compared. When the duration of the injection is very short (e.g., a minute or less), the injection of mass generates a very large acoustic Wave response relative to the PV-equivalent injection of heat. However, the Buoyancy Wave response to these two injection types is quite similar. The responses to injections of divergent momentum in the vertical and horizontal directions are also compared. It is shown that neither divergent momentum injection generates any PV and, thus, there is no steady-state response to these injections. The Waves excited by these injections generally propagate their energy in the direction of the injection. Consequently, an injection of vertical momentum is an efficient generator of vertically propagating, horizontally trapped, high-frequency Buoyancy Waves. Such Waves have a short time scale and are therefore very sensitive to the injection duration. Analogously, an injection of divergent horizontal momentum is an efficient generator of horizontally propagating, vertically trapped low-frequency Buoyancy Waves that are relatively insensitive to the injection duration. Because of this difference in the response to horizontal and vertical injections of momentum, the response to the injection of an isolated updraft differs depending on whether a compensating horizontal inflow/outflow is also specified. This additional specification of inflow/outflow helps filter acoustic Waves and encourages a stronger updraft that is not removed as rapidly by the Buoyancy Waves. This finding is relevant to the initialization of updrafts in compressible numerical weather prediction models. Injection of nondivergent momentum generates Waves in the regions of convergence/divergence produced by the deflection of the current by Coriolis forces. The energy partitioning for such an injection is sensitive to the width and depth of the current relative to the Rossby radius of deformation, but the response is insensitive to the duration of injection for time scales shorter than several hours.
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Wave Response during Hydrostatic and Geostrophic Adjustment. Part I: Transient Dynamics
Journal of the Atmospheric Sciences, 2005Co-Authors: Jeffrey M. Chagnon, Peter R. BannonAbstract:Abstract The adjustment of a compressible, stably stratified atmosphere to sources of hydrostatic and geostrophic imbalance is investigated using a linear model. Imbalance is produced by prescribed, time-dependent injections of mass, heat, or momentum that model those processes considered “external” to the scales of motion on which the linearization and other model assumptions are justifiable. Solutions are demonstrated in response to a localized warming characteristic of small isolated clouds, larger thunderstorms, and convective systems. For a semi-infinite atmosphere, solutions consist of a set of vertical modes of continuously varying Wavenumber, each of which contains time dependencies classified as steady, acoustic Wave, and Buoyancy Wave contributions. Additionally, a rigid lower-boundary condition implies the existence of a discrete mode—the Lamb mode— containing only a steady and acoustic Wave contribution. The forced solutions are generalized in terms of a temporal Green's function, which repres...
Michael T Montgomery - One of the best experts on this subject based on the ideXlab platform.
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damping and pumping of a vortex rossby Wave in a monotonic cyclone critical layer stirring versus inertia Buoyancy Wave emission
Physics of Fluids, 2004Co-Authors: David A Schecter, Michael T MontgomeryAbstract:This paper further examines the rate at which potential vorticity in the core of a monotonic cyclone becomes vertically aligned and horizontally axisymmetric. We consider the case in which symmetrization occurs by the damping of a discrete vortex Rossby (VR) Wave. The damping of the VR Wave is caused by its stirring of potential vorticity at a critical radius r*, outside the core of the cyclone. The decay rate generally increases with the radial gradient of potential vorticity at r*. Previous theories for the decay rate were based on “balance models” of the vortex dynamics. Such models filter out inertia–Buoyancy (IB) oscillations, i.e., gravity Waves. However, if the Rossby number is greater than unity, the core VR Wave can excite a frequency-matched outward propagating IB Wave, which has positive feedback. To accurately account for this radiation, we here develop a theory for the decay rate that is based on the hydrostatic primitive equations. Starting from conservation of Wave activity (angular pseudom...
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On the symmetrization rate of an intense geophysical vortex
Dynamics of Atmospheres and Oceans, 2003Co-Authors: David A Schecter, Michael T MontgomeryAbstract:Abstract Numerical models demonstrate that a broad class of geophysical vortices freely evolve toward vertically aligned, axisymmetric states. In principle, this intrinsic drive toward symmetry opposes destructive shearing by the environmental flow. This article examines the case in which a discrete vortex-Rossby-Wave dominates a perturbation from symmetry, and symmetrization occurs by decay of the Wave. The Wave is damped by a resonance with the fluid rotation frequency at a critical radius, r * . The damping rate is proportional to the radial derivative of potential vorticity at r * . Until now, the theory of resonantly damped vortex-Rossby-Waves (technically quasi-modes) was formally restricted to slowly rotating vortices, which obey quasigeostrophic (QG) dynamics. This article extends the theory to rapidly rotating vortices. The analysis makes use of the asymmetric balance (AB) approximation. Even at a modest Rossby number (unity), AB theory can predict damping rates that exceed extrapolated QG results by orders of magnitude. This finding is verified upon comparison of AB theory to numerical experiments, based on the primitive equations. The experiments focus on the decay of low azimuthal Wave-number asymmetries. A discrete vortex-Rossby-Wave can also resonate with an outward propagating inertia-Buoyancy Wave (Lighthill radiation), inducing both to grow . At large Rossby numbers, this growth mechanism can be dynamically relevant. All balance models, including AB theory, neglect inertia-Buoyancy Waves, and therefore ignore the possibility of a Rossby-inertia-Buoyancy (RIB) instability. This article shows that a large potential vorticity gradient (of the proper sign) at the critical radius r * can suppress the RIB instability, and thereby preserve balanced flow, even at large Rossby numbers.
