High frequency hydrodynamic coefficients of vertical cylinders

1992 ◽  
Vol 19 (4) ◽  
pp. 606-615
Author(s):  
Michael Isaacson ◽  
Thomas Mathai
Keyword(s):  
High Frequency ◽  
Scattering Problem ◽  
Offshore Structures ◽  
Short Wave ◽  
Alternative Methods ◽  
Local Form ◽  
Ocean Engineering ◽  
Damping Coefficients ◽  
Added Masses ◽  
Vertical Cylinders

Alternative methods of calculating high frequency added masses and damping coefficients of vertical cylinders of arbitrary section are described. Damping coefficients are calculated by a short-wave approximation relating to the local form of waves generated by the oscillating structure. As an alternative, they are also obtained from the exciting forces of the related scattering problem, with these forces obtained by a geometrical optics approximation. Added masses are obtained by discarding the propagating mode and using only the evanescent modes which are free of irregular frequencies. They are also obtained by an application of the Kramers–Kronig relations, which require the infinite frequency added masses and the damping coefficients at all frequencies. Numerical results obtained by the various methods are compared with corresponding analytical results for vertical circular and elliptic cylinders. The practical application of the proposed approach is indicated. Key words: added mass, cylinders, damping, hydrodynamics, ocean engineering, offshore structures, waves.

Hydrodynamic Coefficients of Vertical Cylinders of Arbitrary Section

1991 ◽  
Vol 113 (2) ◽  
pp. 109-116 ◽  
Author(s):  
M. Isaacson ◽  
T. Mathai
Keyword(s):  
Vertical Cylinder ◽  
Vertical Direction ◽  
Numerical Approach ◽  
Offshore Structures ◽  
Three Dimensions ◽  
Method Of Integral Equations ◽  
Square Cylinders ◽  
Added Masses ◽  
Arbitrary Section ◽  
Vertical Cylinders

The calculation of added masses and damping coefficients of a large surface-piercing vertical cylinder of arbitrary section extending to the seabed and undergoing harmonic oscillations is described. The linear radiation problem in three dimensions is reduced to a series of two-dimensional problems in the horizontal plane by the use of appropriate eigenfunctions that represent the variation of the velocity potential in the vertical direction. Each of these is solved by a numerical approach based on the method of integral equations. Comparisons are made with an analytic solution available for the case of a circular cylinder. Results are also provided for square cylinders, and the application to typical offshore structures subject to base motions is discussed.

Hydrodynamic coefficients of a vertical circular cylinder

1990 ◽  
Vol 17 (3) ◽  
pp. 302-310 ◽  
Author(s):  
Michael Isaacson ◽  
Thomas Mathai ◽  
Carol Mihelcic
Keyword(s):  
Circular Cylinder ◽  
High Frequency ◽  
Closed Form Solution ◽  
Added Mass ◽  
Offshore Structures ◽  
Form Solution ◽  
Ocean Engineering ◽  
Radiation Problem ◽  
The Vertical Distribution ◽  
Linear Radiation

The added mass and the damping coefficient of a large surface-piercing circular cylinder extending to the seabed and undergoing horizontal oscillations are described. A closed-form solution to the corresponding linear radiation problem is obtained by the use of eigenfunction expansions. Attention is given to the vertical distribution of these coefficients and to their high-frequency asymptotic behaviour. Comparisons are made with experimental measurements. The application to typical offshore structures is discussed. Key words: added mass, cylinders, damping, hydrodynamics, ocean engineering.

Influence of hydrodynamic effects on iceberg collisions

1990 ◽  
Vol 17 (3) ◽  
pp. 329-337 ◽  
Author(s):  
Michael Isaacson ◽  
Kevin McTaggart
Keyword(s):  
Added Mass ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Iceberg Drift ◽  
Added Masses ◽  
Waves And Currents ◽  
Fixed Structure ◽  
Wave Induced ◽  
Hydrodynamic Effects ◽  
Selection Of

This paper examines various hydrodynamic effects which should be considered when analyzing iceberg collisions with a fixed structure. Iceberg added mass is among the hydrodynamic parameters that must be known to evaluate collision severity. Effective added mass is shown to vary with collision duration and recommendations are made for the selection of added masses to be used in iceberg collision design. Iceberg impact velocities are influenced by waves and currents, which can both be significantly influenced by the presence of a large structure. Wave-driven iceberg drift motions are shown to be more sensitive than current-driven motions to the presence of a structure. The contribution of wave-induced oscillatory motions to impact velocity is also discussed. Key words: added mass, hydrodynamics, ice impact, icebergs, ocean engineering, offshore structures.

Determination of the added masses and damping coefficients during coupled motions of two ships in shallow water parallel to the vertical wall

2021 ◽  
pp. 16-25
Author(s):  
В.Ю. Семенова ◽  
К.И. Баканов
Keyword(s):  
Shallow Water ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Hydrodynamic Coefficients ◽  
Damping Coefficients ◽  
Added Masses ◽  
Joint Motions ◽  
National Practice ◽  
Simultaneous Influence

В статье рассматривается определение коэффициентов демпфирования и присоединенных масс, возникающих при совместной качке двух судов в условиях мелководья параллельно вертикальной стенке на основании решения трехмерной потенциальной задачи. Определение гидродинамических коэффициентов осуществляется на основании методов интегральных уравнений и зеркальных отображений. Представленное решение в отечественной практике является новым. В статье приводятся результаты расчетов коэффициентов присоединенных масс и демпфирования, возникающих при качке двух одинаковых судов, расположенных лагом к волнению и параллельно вертикальной стенке в зависимости от изменения расстояний как между судами, так и между судами и вертикальной стенкой. Проводится исследование влияния различных фарватеров на величины гидродинамических коэффициентов, а именно: мелководного фарватера, мелководного фарватера с вертикальной стенкой, мелководного фарватера со вторым параллельно качающимся судном и мелководного фарватера с вертикальной стенкой и вторым судном. Таким образом, в работе учитывается одновременное влияния мелководья, вертикальной стенки и второго судна. Показано увеличение значений коэффициентов присоединенных масс и демпфирования при уменьшении расстояний между судами и между судами и вертикальной стенкой. Также показано значительное совместное влияние вертикальной стенки и второго судна на коэффициенты присоединенных масс и демпфирования по сравнению с другими видами стесненных фарватеров. The article discusses the determination of damping coefficients and added masses arising from the joint motions of two ships in shallow water conditions parallel to the vertical wall based on the solution of a three-dimensional potential problem. Determination of hydrodynamic coefficients is carried out on the basis of the methods of integral equations and mirror images. The solution presented in the national practice is new The article presents the results of calculating the coefficients of added masses and damping arising from the motions of two identical ships located lagged to the sea and parallel to the vertical wall, depending on the change in the distances between the ships and between the ships and the vertical wall. A study is being made of the influence of various waterways on the values ​​of hydrodynamic coefficients, namely: a shallow waterway, a shallow waterway with a vertical wall, a shallow waterway with a second parallel oscillating ship and a shallow waterway with a vertical wall and a second ship. Thus, the work takes into account the simultaneous influence of shallow water, vertical wall and the second ship. An increase in the values of the coefficients of added masses and damping with a decrease in the distances between ships and between ships and the vertical wall is shown. It also shows a significant combined effect of the vertical wall and the second ship on the added mass and damping coefficients in comparison with other types of constrained waterways.

Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower

2016 ◽  
Author(s):  
Chinsu Mereena Joy ◽  
Anitha Joseph ◽  
Lalu Mangal
Keyword(s):  
Dynamic Response ◽  
Wind Turbine ◽  
Renewable Energy Sources ◽  
Offshore Structures ◽  
Dynamic Responses ◽  
Offshore Wind ◽  
Experimental Investigations ◽  
Offshore Wind Turbine ◽  
Ocean Engineering ◽  
Study Results

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.

Effect of rail pad stiffness on the wheel/rail force intensity in a railway slab track with short-wave irregularity

2019 ◽  
Vol 233 (10) ◽  
pp. 1038-1049 ◽  
Author(s):  
Amin Khajehdezfuly
Keyword(s):  
High Frequency ◽  
Critical Speed ◽  
Concrete Slab ◽  
Low Frequency ◽  
Short Wave ◽  
Vehicle Speed ◽  
Frequency Range ◽  
Slab Track ◽  
High Frequency Excitation ◽  
Frequency Excitation

In this paper, a two-dimensional numerical model is developed to investigate the effect of rail pad stiffness on the wheel/rail force in a slab track with harmonic irregularity. The model consists of a vehicle, nonlinear Hertz spring, rail, rail pad, concrete slab, resilient layer, concrete base, and subgrade. The rail is simulated using the Timoshenko beam element for considering the effects of high-frequency excitation produced by short-wave irregularity. The results obtained from the model are compared with those available in the literature and from the field to prove the validity of the model. Through a parametric study, the effect of variations in rail pad stiffness, vehicle speed, and harmonic irregularity on the wheel/rail force is investigated. For the slab track without any irregularity, the wheel/rail force is at maximum when the vehicle speed reaches the critical speed. As the rail pad stiffness increases, the critical speed increases. When the amplitude of irregularity is high, wheel jumping phenomenon may occur. In this situation, as the vehicle speed and rail pad stiffness are increased, the dynamic wheel/rail force is increased. In the low-frequency range, the wheel/rail force increases as the rail pad stiffness increases. In the high-frequency range, the wheel/rail force increases as the rail pad stiffness is decreased.

Design of readout IC for photoelectron detector of short-wave high frequency IRFPA

2013 ◽  
Author(s):  
Pan Wang ◽  
Rui-jun Ding ◽  
Guo-qiang Chen ◽  
Honglei Chen
Keyword(s):  
High Frequency ◽  
Short Wave

Wave Interaction With an Infinite Long Horizontal Elliptical Cylinder

2011 ◽  
Author(s):  
Hao Song ◽  
Longbin Tao
Keyword(s):  
Wave Interaction ◽  
Wave Structure ◽  
Offshore Structures ◽  
Elliptical Cylinder ◽  
Ocean Engineering ◽  
Parallel Side ◽  
Matrix Differential Equations ◽  
Unsteady Loading ◽  
Matrix Differential ◽  
Wave Structure Interaction

Wave-structure interaction in ocean engineering is a major source of unsteady loading and vibration of offshore structures including platforms, risers and long cables. Many efforts focus on vertical structures in which solution procedures can usually be simplified in the plane of mean free surface as the variable in the direction of gravity can be separated. In this paper, wave interaction with an infinite long horizontal elliptical cylinder is solved by a semi-analytical method, namely, the scaled boundary finite-element method (SBFEM). The solution domain is divided into two bounded domains and two unbounded domains with parallel side-faces. The governing partial differential equation (Helmholtz equation) is weakened and transformed to ordinary matrix differential equations in radial direction and are then solved analytically by SBFEM.

scholarly journals High-frequency Direct Somatic Embryogenesis and Plantlet Regeneration from Leaves Derived from In Vitro-Germinated Seedlings of a Coffea arabica Hybrid Cultivar

HortScience ◽  
2016 ◽  
Vol 51 (9) ◽  
pp. 1148-1152 ◽  
Author(s):  
Jane Kahia ◽  
Margaret Kirika ◽  
Hudson Lubabali ◽  
Sinclair Mantell
Keyword(s):  
Tissue Culture ◽  
High Frequency ◽  
Somatic Embryos ◽  
Coffea Arabica ◽  
Alternative Methods ◽  
Direct Somatic Embryogenesis ◽  
Ms Medium ◽  
Embryogenic Cultures ◽  
Half Strength

Breeding work carried out during the period 1971–85 by the Coffee Research Institute, Ruiru, Kenya resulted in the release of a new improved hybrid Coffea arabica named Ruiru 11. The cultivar combines resistance to coffee berry disease (CBD) and leaf rust, with high yield and good cup quality attributes. The propagation by F1 hybrid seeds production, cuttings, and tip grafting do not produce enough planting materials. There was a need to explore alternative methods and tissue culture offers potential options. The objective of the study was to evaluate the effect of explant sources and cytokinins on induction and regeneration of somatic embryos. Eight different explants were cultured on half-strength Murashige and Skoog (MS) medium supplemented with 10 µm benzylaminopurine (BAP). The effect of kinetin, N6-(2-isopentyl) adenine (2iP) evaluated at (0, 0.5, 5, or 25 µm) or thidiazuron (TDZ) (0, 0.5, 1.0, or 5 µm) added in separate experiments was also evaluated. The percentage of embryogenic cultures and the numbers of embryos per explant were determined after 3 months’ culture. The explant type had a significant effect (P > 0.05) on the induction of somatic embryos. Explants from in vitro-germinated seedlings produced the highest embryogenic cultures (90%) and the highest mean number of embryos (19.36) per explant. Cytokinins strongly enhanced induction and regeneration of somatic embryos. TDZ at 1 µm produced the highest embryogenic cultures (100%) and the highest mean number of embryos (24.2). The embryos were germinated on half-strength MS medium without any hormones. A high (98%) survival rate of the regenerated plantlets was recorded over all the treatments in the greenhouse. This is the first report on induction of high-frequency direct somatic embryos from coffee juvenile tissues. This is of great significance in tissue culture and indeed molecular biology manipulations because it allows regeneration of coffee from several explants.

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