Bouncing-Ball Model of ‘Dry’ Motions of a Tethered Buoy

2000 ◽  
Vol 123 (3) ◽  
pp. 333-339 ◽  
Author(s):  
R. H. Plaut ◽  
A. L. Farmer ◽  
M. M. Holland
Keyword(s):  
Coefficient Of Restitution ◽  
Critical Force ◽  
Mooring Line ◽  
Wave Forces ◽  
Axial Component ◽  
Rigid Surface ◽  
Fluid Inertia ◽  
Sea Floor ◽  
Ball Bouncing ◽  
The Impact

The motions of a buoy moored to the sea floor by a cable are considered. The buoy is modeled both as a point mass and as a sphere. It is assumed that the mooring line has no effect when it is slack, and that when it becomes taut it exerts an instantaneous impulsive force on the buoy, analogous to the impact of a ball bouncing on a rigid surface. The magnitude of the axial component of the velocity is reduced at this time. Fluid inertia and damping are not included, and the wave forces are assumed to be harmonic. The effects of the coefficient of restitution and the forcing frequency on two types of critical force are examined. Trajectories of the motion are plotted and the impact velocities are computed and analyzed. Knowledge of the number and magnitude of these impacts is useful in assessing fatigue of the mooring line.

scholarly journals THE DESIGN AMD CONSTRUCTION OF THE NEW OIL PORT IN DALIAN, C.P.R.

1980 ◽  
Vol 1 (17) ◽  
pp. 125
Author(s):  
Zhu Zhuang
Keyword(s):  
Mooring Line ◽  
Wave Forces ◽  
Exciting Forces ◽  
The Impact ◽  
Design And Construction

The construction of New Oil Port in Dalian, C.P.R., was started around the end 1974 and completed in autumn 1976.In this paper a summary of the essential considerations in design and construction of this oil port, such as the planning of the pier, the determination of exciting forces (namely wave forces, forces due to earthquake, mooring line forces and berthing forces due to the impact of tanker on the fenders)on structures, the design of the large cylindrical cassion with a diameter of 9m and a height up to 19.7m and the construction of connecting bridges by two types, is presented.

Second-Order Low-Frequency Wave Forces on a SPM Offloading Tanker in Shallow Water

2008 ◽  
Author(s):  
S. Ma ◽  
S. Shi ◽  
M. H. Kim
Keyword(s):  
Shallow Water ◽  
Transfer Functions ◽  
Low Frequency ◽  
Wave Force ◽  
Second Order ◽  
Dynamic Responses ◽  
Mooring Line ◽  
Wave Forces ◽  
Frequency Wave ◽  
The Impact

This paper studies the influence of three different calculation methods of the second-order low-frequency (LF) wave forces on the tanker responses and hawser/mooring tensions in relatively shallow water region. The vessel-mooring-riser coupled dynamic analysis computer program HARP is used to simulate the coupled dynamic responses of offloading tanker moored to a SPM (Single Point Mooring). Because the SPM is supposed to be deployed in shallow water and the slowly varying drift motions of the tanker are to dominate the motion responses in typical operational conditions, the accurate calculation of LF wave-force quadratic transfer functions (QTFs) becomes important especially for mooring and hawser tensions. Like common practice, the so-called Newman’s approximation and another approximation method without including complicated free-surface integrals are first used to calculate the LF QTFs on the offloading tanker and they are compared with the complete QTF results. Further comparison is performed by calculating the resulting LF wave-force spectra and response time series by using the three different methods. The impact of the three different approaches on vessel surge motions and hawser/mooring line tensions is also addressed.

Modelling of tennis ball impacts on a rigid surface

2004 ◽  
Vol 218 (10) ◽  
pp. 1139-1153 ◽  
Author(s):  
S R Goodwill ◽  
S J Haake
Keyword(s):  
Contact Time ◽  
Momentum Flux ◽  
Viscoelastic Model ◽  
Coefficient Of Restitution ◽  
Model Parameters ◽  
Total Force ◽  
Tennis Ball ◽  
Rigid Surface ◽  
Ball Impact ◽  
The Impact

A viscoelastic model of a tennis ball impact at normal incidence on a rigid surface is presented in this study. The ball model has three discrete elements that account for the structural stiffness, material damping and momentum flux loading. Experiments using a force platform are performed to determine the force that acts on the ball during impact, for a range of ball inbound velocities. The inbound and rebound velocities of the ball are measured using speed gates. The contact time and coefficient of restitution for the impact are also determined in these experiments. The model parameters are determined such that the values of the coefficient of restitution and contact time that are calculated by the model are consistent with those values determined experimentally. The model can be used to calculate the force that acts on the ball during impact. Generally, the force-time plots calculated by the model were consistent with those determined experimentally. Furthermore, the model can be used to calculate the three components of the force that acts on the ball during impact. It is shown that the main component of the force during the first 0.6 ms of impact is that due to momentum flux loading. This is approximately equal in magnitude for each ball type and explains why the total force acting on each ball is very similar during this period.

Less=Moor: A Time-Efficient Computational Tool to Assess the Behavior of Moored Ships in Waves

2017 ◽  
Author(s):  
Yijun Wang ◽  
Alex van Deyzen ◽  
Benno Beimers
Keyword(s):  
Dynamic Response ◽  
Research Effort ◽  
Equations Of Motion ◽  
Line Tension ◽  
Mooring Line ◽  
Induced Response ◽  
Wave Forces ◽  
Computational Tool ◽  
The Time Domain ◽  
Nonlinear Equations Of Motion

In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.

SIMULATION OF DYNAMIC EVENT OF IMPACT USING EXPLICIT 3D FEM MODEL AND VALIDATION BY EXPERIMENT AND CONTACT MODELS

2021 ◽  
Vol 6 (3) ◽  
Author(s):  
Akshay Mallikarjuna ◽  
Dan Marghitu ◽  
P.K. Raju
Keyword(s):  
Material Properties ◽  
Permanent Deformation ◽  
Oblique Impact ◽  
Coefficient Of Restitution ◽  
Impact Behavior ◽  
3D Fem ◽  
Dynamic Event ◽  
Contact Models ◽  
Explicit Dynamic ◽  
The Impact

— In this study, an optimized method to simulate the dynamic 3D event of the impact of a rod with a flat surface has been presented. Unlike the 2D FEM based contact models, in this study both the bodies undergoing the impact are considered elastic(deformable) and simulation is the dynamic event of the impact, instead of predefined 2D symmetric contact analysis. Prominent contact models and plasticity models to define material properties in ANSYS are reviewed. Experimentation results of normal and oblique impact of the rod for different rods provided the coefficient of restitution. Experimental results of permanent deformation on the base for different impact velocity is derived out of a prominent impact study. The simulation results are in co-relation with experiment and both indentation and flattening models on the coefficient of restitution (COR) and permanent deformation of the base and rod after the impact. Thus, the presented 3D Explicit Dynamic simulation of impact is validated to analyze the impact behavior of the 2 bodies without any predefined assumptions with respect to boundary conditions or material properties.

scholarly journals A Comprehensive Set of Impact Data for Common Aerospace Metals

2017 ◽  
Vol 12 (6) ◽  
Author(s):  
M. R. W. Brake ◽  
P. L. Reu ◽  
D. S. Aragon
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Model Development ◽  
Coefficient Of Restitution ◽  
Image Correlation ◽  
Plastic Behavior ◽  
Data Set ◽  
Force Resolution ◽  
Impact Data ◽  
The Impact

The results of two sets of impact experiments are reported within. To assist with model development using the impact data reported, the materials are mechanically characterized using a series of standard experiments. The first set of impact data comes from a series of coefficient of restitution (COR) experiments, in which a 2 m long pendulum is used to study “in-context” measurements of the coefficient of restitution for eight different materials (6061-T6 aluminum, phosphor bronze alloy 510, Hiperco, nitronic 60A, stainless steel 304, titanium, copper, and annealed copper). The coefficient of restitution is measured via two different techniques: digital image correlation (DIC) and laser Doppler vibrometry (LDV). Due to the strong agreement of the two different methods, only results from the digital image correlation are reported. The coefficient of restitution experiments are in context as the scales of the geometry and impact velocities are representative of common features in the motivating application for this research. Finally, a series of compliance measurements are detailed for the same set of materials. The compliance measurements are conducted using both nano-indentation and micro-indentation machines, providing sub-nm displacement resolution and μN force resolution. Good agreement is seen for load levels spanned by both machines. As the transition from elastic to plastic behavior occurs at contact displacements on the order of 30 nm, this data set provides a unique insight into the transitionary region.

AN OCEAN BOTTOM, D COMPONENT MAGNETOMETER

Geophysics ◽  
1967 ◽  
Vol 32 (6) ◽  
pp. 978-987 ◽  
Author(s):  
J. H. Filloux
Keyword(s):  
Electric Field ◽  
Dynamic Range ◽  
North Pacific Ocean ◽  
Mooring Line ◽  
Ocean Bottom ◽  
Magnetic Fluctuations ◽  
Sea Floor ◽  
The North ◽  
Low Profile ◽  
Optical Lever

The distribution of electric conductivity in the crustal and upper mantle materials beneath the ocean may be estimated from measurements of the relationship between the magnetic fluctuations and the induced electric field at the ocean bottom. Techniques for the measurement of the electric field have been available for a few years. The horizontal magnetic fluctuations to the magnetic east, usually called D, can be recorded with a simple instrument placed on the sea floor at any depth. This instrument uses a magnet pair which orients itself among the main horizontal field H. The coupling of the magnets to the mirror of a sensitive optical lever is delayed until the instrument has reached the bottom. There is no need to perform any orientation in situ. The instrument resolves 1 γ or less and has a dynamic range of at least 2500 γ. It is capable of recording for approximately 40 days at the rate of 30 readings per hour on self‐contained dry cells. It is lowered to the sea floor and recovered by means of a mooring line connected to a surface float. The low‐profile supporting tripod is effectively decoupled from the mooring tackle as evidenced by the lack of motion of the magnetometer during 26 days of recording. A sample of the observed fluctuations on the floor of the North Pacific Ocean, 600 km offshore, is given.

Analytical Study of the Oblique Impact of a Rod with a Flat Using an Elasto-Plastic Contact Model

2015 ◽  
Vol 801 ◽  
pp. 25-32
Author(s):  
Ozdes Cermik ◽  
Hamid Ghaednia ◽  
Dan B. Marghitu
Keyword(s):  
Impact Velocity ◽  
Contact Force ◽  
Analytical Study ◽  
Initial Conditions ◽  
Permanent Deformation ◽  
Oblique Impact ◽  
Coefficient Of Restitution ◽  
Contact Model ◽  
Impact Angles ◽  
The Impact

In the current study a flattening contact model, combined with a permanent deformation expression, has been analyzed for the oblique impact case. The model has been simulated for different initial conditions using MATLAB. The initial impact velocity used for the simulations ranges from 0.5 to 3 m/s. The results are compared theoretically for four different impact angles including 20, 45, 70, and 90 degrees. The contact force, the linear and the angular motion, the permanent deformation, and the coefficient of restitution have been analyzed. It is assumed that sliding occurs throughout the impact.

scholarly journals Non-Line Analysis of Stiffness in Compression Conditions

2018 ◽  
Vol 25 (2) ◽  
pp. 100-107
Author(s):  
Maciej Kahsin ◽  
Dawid Stecki
Keyword(s):  
Critical Force ◽  
Experimental Planning ◽  
Surface Method ◽  
Linear Buckling ◽  
Geometric Deviations ◽  
The Difference ◽  
The Impact ◽  
Linear Buckling Analysis ◽  
Simultaneous Influence ◽  
Line Analysis

Abstract The analyzes were aimed at demonstrating the influence of parameters describing the deformation of the structure on the uncertainty of critical force, and the impact of technological imperfections on stress uncertainty in compression conditions. In a linear buckling analysis, the problem is considered only for the initial, permanent state of the stiffness matrix. In the case of demonstrating the influence of initial deformations on the behavior of the structure under load, it is necessary to visualize changes in stiffness over time. To this end, a non-linear MES analysis was carried out, which will take into account local changes in the stiffness of the model through a gradual increase in the load. Thus, the difference in stiffness is taken into account, which in the linear problem is infinite. The analysis was used to examine the local and global sensitivity of the parameters describing: plating thickness as well as deformation caused by the technological process on the stress value reduced by Huber hypothesis, and the value of normal stress. To take into account the influence of non-specified values of the magnitude of geometric deviations, and their simultaneous influence on the range of obtained results, the Experimental Planning Method and the Surface Method of Answers were used.

Coupled Time-Domain Hydro-Elastic Simulation for Submerged Floating Tunnel Under Wave Excitations

2021 ◽  
Author(s):  
Chungkuk Jin ◽  
Sung-Jae Kim ◽  
MooHyun Kim
Keyword(s):  
Time Domain ◽  
Domain Model ◽  
Mooring Line ◽  
Wave Forces ◽  
Rod Theory ◽  
Discrete Module ◽  
Simulation Based ◽  
Submerged Floating Tunnel ◽  
The Time Domain ◽  
Elastic Simulation

Abstract We develop a fully-coupled time-domain hydro-elasticity model for the Submerged Floating Tunnel (SFT) based on the Discrete-Module-Beam (DMB) method. Frequency-domain simulation based on 3D potential theory results in multibody’s hydrodynamic coefficients and excitation forces for tunnel sections. Subsequently, we build the time-domain model with the multibody Cummins equation and external stiffness matrix from the Euler-Bernoulli and Saint-Venant torsion theories. We establish the mooring line model with rod theory and couple components with translational springs at their respective connection locations. We then compare the dynamic motions, wave forces, and mooring tensions between the present and Morison-equation-based elastic models under regular wave excitations at different submergence depths. The present model is especially important for the shallowly submerged tunnel in which the Morison model shows exaggerated motions, especially at high-frequency range.

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