Showing papers on "Added mass published in 1977"

The added mass of two-dimensional cylinders heaving in water of finite depth

Abstract: This paper presents numerical results for the added-mass and damping coefficients of semi-submerged two-dimensional heaving cylinders in water of finite depth. A simple proof is given which shows that the added mass is bounded for all frequencies in water of finite depth. The limits of the added-mass and damping coefficients are studied as the frequency tends to zero and to infinity. A new formulation valid in the low-frequency limit is constructed by using a perturbation expansion in the wavenumber parameter. For the limiting cases, dual extremum principles are used, which consist of two variational principles: a minimum principle for a functional and a maximum principle for a different but related functional. These two functionals are used to obtain lower and upper bounds on the added mass in the limiting cases. However, the functionals constructed (Bai & Yeung 1974) for the general frequency range (excluding the limiting cases) have neither a minimum nor a maximum. In this case, the approximate solution cannot be proved to be bounded either below or above by the true solution. To illustrate these methods, the added-mass and damping coefficients are computed for a circular cylinder oscillating in water of several different depths. Results are also presented for rectangular cylinders with three different beamdraft ratios at several water depths.

Vibration of a Group of Circular Cylinders in a Confined Fluid

Abstract: Understanding and modeling fluid/structure interaction in cylinder bundles is a basic requirement in the development of analytical methods and guidelines for designing LMFBR heat exchanger and reactor fuel assemblies that are free from component vibration problems. As a step toward satisfying this requirement, a method of analysis based on the potential flow theory is developed for analyzing free vibration of a group of cylinders immersed in a fluid contained in a cylinder. The method of analysis presented can determine the added mass coefficients and natural frequencies of coupled cylinder-fluid systems. To demonstrate the method the coupled natural frequencies for two eccentrically located cylinders with a fluid-filled gap are calculated and discussed. A few other examples are also given to show the added mass coefficients.

Vibration of a group of circular cylinders in a confined fluid

Abstract: Understanding and modeling fluid/structure interaction in cylinder bundles is a basic requirement in the development of analytical methods and guidelines for designing LMFBR heat exchanger and reactor fuel assemblies that are free from component vibration problems. As a step toward satisfying this requirement, a method of analysis based on the potential flow theory is developed for analyzing free vibration of a group of cylinders immersed in a fluid contained in a cylinder. The method of analysis presented can determine the added mass coefficients and natural frequencies of coupled cylinder-fluid systems. To demonstrate the method the coupled natural frequencies for two eccentrically located cylinders with a fluid-filled gap are calculated and discussed. A few other examples are also given to show the added mass coefficients.

Inertial balanced dipole hydrophone

Abstract: A dipole hydrophone which includes a piezoelectric bender bar having at the ends thereof two identical disks having high added mass and low actual mass, and a single mass at the center with low added mass and high actual mass. Support wires are connected to the unit at the bender nodes so that movement of the support causes no electrical output. Another configuration includes a piezoelectric bender disk having an annular ring near the edge portion thereof and a single mass at the center of the disk with the ring and central mass having the same relationship as the disk and central mass of the other embodiment.

Added mass of pile group

Abstract: Through laboratory investigation, it is shown that when a pile group is arranged in a cluster, the added mass (or inertial force) increases sharply after the spacing between piles falls below a certain critical value. Two configurations of pile group arrangement—circular and square shapes of approximately the same base diameter—were tested. The experimental results reveal that when the spacing between piles is smaller than two times the pile diameter, or the solidification ratio becomes larger than 0.5, the added mass of the pile group increases drastically. For pile groups with individual pile spacing less than this critical value, the volume enclosed, rather than the volume displaced, by the pile cluster should be used as bases for added mass computation.

2-dimensional Hydrodynamic Forces of Heaving, Swaying and Rolling Cylinders on a Free Surface of a Water of Finite Depth.

Abstract: The hydrodynamic forces acting on a forced oscillating 2-dimensional cylinder on a free surface of a fluid of a finite depth are calculated by distributing singularities on the immersed body surface. And the Haskind-Newman relation in a fluid of a finite depth is derived. The wave exciting force of the cylinder to an oscillation is also calculated by using the above relation. The method is applied to a circular cylinder swaying in a water of finite depth, and then, to a rectangular cylinder heaving, swaying, and rolling. The results of above cases give a good agreement with those by earlier investigators such as Bai, Keil, and Yeung. Also, this method is applied to a Lewis form cylinder with a half beam-to-draft ratio of 1.0 and a sectional area coefficient of 0.941, and to a bulbous section cylinder which is hard to represent by a mapping function. The results reveal that the hydrodynamic forces in heave increase as the depth of a water decrease, but in sway or roll, the tendency of the hydrodynamic forces is difficult to say in a few words. The exciting force to heave for a bulbous section cylinder becomes zero at two frequencies. The added mass moment of inertia for roll is seemed to mainly depend on the sectional shape than the water depth.

Added Mass of Sphere Starting Upward Near Floor

Abstract: A method for suddenly releasing a buoyant sphere under water and measuring its acceleration was used to get experimental added-mass coefficients a short time after release. To show the effect of a plane boundary, the sphere was released zero to six diameters above a rigid floor. By definition the fluid force on an accelerating object may be divided into two parts — that due to viscosity and that which would occur if the fluid had no viscosity. A work-energy method applied to the boundary layers developing on the sphere and floor gave the viscous force at the instant the acceleration was measured. When this was subtracted from the known total force, the resulting experimental added-mass coefficients ranged from 0.83 (sphere very close to floor) to 0.50 (six diameters away). For the same set of starting positions, potential flow calculations gave coefficients from 0.8030 to 0.5000.

The Motion of an Ideal Fluid

Abstract: This chapter contains sections titled: Irrotational Flows, The Velocity Potential, Bernoulli's Equations, Boundary Conditions, Simple Potential Flows, The Stream Function, The Complex Potential, ConformaI Mapping, Separation of Variables, Fixed Bodies and Moving Bodies, Green's Theorem and Distributions of Singularities, Hydrodynamic Pressure Forces, Force on a Moving Body in an Unbounded Fluid, General Properties of the Added-Mass Coefficients, The Added Mass of Simple Forms, The Body-Mass Force, Force on a Body in a Nonuniform Stream, The Method of Images, Problems, References

Response Analysis of Floating Structures

Abstract: The dynamic response of a floating structure may be obtained either by analyzing the complete fluid-structure system or by a simpler method, in which the hydrodynamic effects are accounted for by the inclusion of added mass. Since the added mass of a floating structure is dependent on the frequency of its oscillation, the traditional use of a constant added mass is large over the frequency range of interest. Such a situation may arise when the floating body is acted upon by transient loads or when the body is enclosed in a basin having resonant frequencies, or both. A method to construct an equivalent model for the fluid-structure system in such cases, for the time domain response analysis of the floating structure, is presented in this paper. For construction of this model the frequency dependence of the added mass is assumed to be known.