Investigated is the coupled response of a tension leg platform (TLP) for random waves. Inferred are the mass matrix, coupling stiffness matrix, damping matrix in the vibration differential equation and external load of TLP in moving coordinating system. Infinitesimal method is applied to divide columns and pontoons into small parts. Time domain motion equation is solved by Runge-Kutta integration scheme. Jonswap spectrum is simulated in the random wave, current is simulated by linear interpolation, and NPD spectrum is applied as wind spectrum. The Monte Carlo method is used to simulate random waves and fluctuated wind. Coupling dynamic response, change of tendon tension and riser tension in different sea conditions are analyzed by power spectral density (PSD). The influence of approach angle on dynamic response of TLP and tendon tension is compared. 相似文献
The tilt angles of sunspot groups are defined, using the Mount Wilson data set. It is shown that groups with tilt angles greater
than or less than the average value (≈ 5 deg) show different latitude dependences. This effect is also seen in
synoptic magnetic field data defining plages. The fraction of the total sunspot group area that is found in the leading spots
is discussed as a parameter that can be useful in studying the dynamics of sunspot groups. This parameter is larger for low
tilt angles, and small for extreme tilt angles in either direction. The daily variations of sunspot group tilt angles are
discussed. The result that sunspot tilt angles tend to rotate toward the average value is reviewed. It is suggested that at
some depth, perhaps 50 Mm, there is a flow relative to the surface that results from a rotation rate faster than the surface
rate by about 60 m/sec and a meridional drift that is slower than the surface rate by about 5 m/sec. This results in a slanted
relative flow at that depth that is in the direction of the average tilt angle and may be responsible for the tendency for
sunspot groups (and plages) to rotate their magnetic axes in the direction of the average tilt angle. 相似文献
Concepts from projective geometry are used to provide a coherent framework for the determination of orbits from observation data comprising lines of sight at three known times. A novel way of presenting the results in a finite diagram is introduced, The effectiveness of the approach is demonstrated by an example, using a simple spreadsheet. A computer-graphic implementation is recommended. 相似文献
This paper analyzes the stability of the Llerin rockfill dam using Barton–Kjaernsli's shear criterion. To fit the parameters of this criterion, a direct shear test was designed that allows in situ calculation, using large-size samples of the shear stress at which failure is produced for different normal loads. These experimental values are then used to obtain more reliable values for the friction angle and the equivalent roughness of the rockfill material.The rockfill of Llerin dam is formed by a suitably ground gonfolite limestone rockfill that serves as a contention dam for a lagoon of mine tailings. The experimental results obtained in in situ tests were compared with those predicted by the shear criterion, subsequently determining the safety coefficient of the rockfill dam using the SLOPE computer program. We conclude that the values estimated via in situ testing permit the behaviour of the containment dam to be predicted more accurately. 相似文献
A computer program is developed for hull/mooring/riser coupled dynamic analysis of a tanker-based turret-moored FPSO (Floating Production Storage and Offloading) in waves, winds, and currents. In this computer program, the floating body is modeled as a rigid body with six degrees of freedom. The first- and second-order wave forces, added mass, and radiation damping at various yaw angles are calculated from the second-order diffraction/radiation panel program WAMIT. The wind and current forces for various yaw angles of FPSO are modeled following the empirical method suggested by OCIMF (Oil Company International Marine Forum).
The mooring/riser dynamics are modeled using a rod theory and finite element method (FEM), with the governing equations described in a generalized coordinate system. The dynamics of hull, mooring lines, and risers are solved simultaneously at each time step in a combined matrix for the specified connection condition. For illustration, semi-taut chain-steel wire-chain mooring lines and steel catenary risers are employed and their effects on global FPSO hull motions are investigated. To better understand the physics related to the motion characteristics of a turret-moored FPSO, the role of various hydrodynamic contributions is analyzed and assessed including the effects of hull and mooring/riser viscous damping, second-order difference-frequency wave-force quadratic transfer functions, and yaw-angle dependent wave forces and hydrodynamic coefficients. To see the effects of hull and mooring/riser coupling and mooring/riser damping more clearly, the case with no drag forces on those slender members is also investigated. The numerical results are compared with MARIN's wave basin experiments. 相似文献
DNA damage of aquatic organisms living in polluted environments can be used as a biomarker of the genotoxicity of toxic agents to organisms. This technique has been playing an important role in ecotoxicologlcal study and environmental risk assessment. In this article, main types of DNA damage caused by pollutants in water environments were reviewed; methods of detecting DNA damage were also documented for water environmental monitoring. 相似文献