scholarly journals MOORED SHIP RESPONSE IN IRREGULAR WAVES

1982 ◽  
Vol 1 (18) ◽  
pp. 159
Author(s):  
E.P.D. Mansard ◽  
B.D. Pratte
Keyword(s):  
National Research Council ◽  
Irregular Waves ◽  
Experimental Investigations ◽  
Special Technique ◽  
Test Results ◽  
Sea State ◽  
Traditional Concept ◽  
Slow Drift ◽  
Vessel Response ◽  
Hydraulics Laboratory

The traditional concept of representing a "random" sea state by just a variance spectral density has been found to be insufficient for modelling the slow drift oscillations of large moored ships. This paper illustrates, through experimental investigations, the importance of including wave grouping as an additional design parameter. A special technique called SIWEH, developed by the Hydraulics Laboratory of the National Research Council Canada, for the generation of realistic wave climates which include wave grouping, is presented. However, when generating the grouped sea state, one also has to properly create the group-bound long wave components. The effect of proper compensation for the spurious free wave components is illustrated by the test results on the moored vessel response.

Experimental Study on Hydrodynamics of Hybrid Deep-V Monohull With Different Built-Up Appendages

2018 ◽  
Author(s):  
Shuzheng Sun ◽  
Hui Li ◽  
Muk Chen Ong
Keyword(s):  
Model Test ◽  
Performance Model ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Hydrodynamic Characteristics ◽  
Vertical Acceleration ◽  
Test Results ◽  
Regular Waves ◽  
Sea State ◽  
Seakeeping Performance

The hydrodynamic characteristics of a hybrid deep-V monohull with different built-up appendages are investigated experimentally in order to improve the resistance and seakeeping performance. Model tests have been carried out to study the hydrodynamic performance between a bare deep-V vessel and a deep-V monohull with different built-up appendage configurations (i.e. a hybrid deep-V monohull). From the model test results, it is found that the existence of the appendages will reduce the amplitude of pitching angle and bow vertical acceleration compared to that of the bare deep-V vessel in heading regular waves. However, the resistances for the hybrid deep-V monohull with built-up appendages are increased 15.6% for Fn = 0.264, and 0.1% for Fn = 0.441 compared to the resistance of the bare deep-V vessel. The model test results of seakeeping performance in irregular waves show that the hybrid deep-V monohull gives a better seakeeping performance than the deep-V vessel. The pitching angle and bow vertical acceleration of the hybrid deep-V monohull containing a built-up appendage are reduced 15.3% and 20.6% compared to the deep-V monohull in irregular waves at Fn = 0.441 in 6th class sea state (H1/3 = 6m).

Alternative Methodologies for Subsea Flexible Strength Analysis

2018 ◽  
Author(s):  
Anskey A. Miranda ◽  
Fred P. Turner ◽  
Nigel Barltrop
Keyword(s):  
Real World ◽  
Wave Train ◽  
Irregular Waves ◽  
Wave Crest ◽  
Strength Analysis ◽  
New Wave ◽  
Regular Wave ◽  
Wave Analysis ◽  
Sea State ◽  
Irregular Wave

This paper presents a study of the analysis methodologies used to predict the most likely response of flexibles in a subsea environment, with the aim of determining an efficient and reliable prediction methodology. The most accurate method involves simulating multiple wave realisations of a real world sea state, i.e. irregular waves, and post-processing the results to determine the most probable maximum (MPM). Due to the computationally intensive nature of this approach, however, regular wave analysis is typically used to determine flexible response. This approach considers the maximum wave within a design storm at a desired period; the choice of periods may leave room for uncertainty in the conservatism of the approach. With proper screening, regular wave analysis can be a valid yet overly conservative approach resulting in over design and additional cost. However, if screened incorrectly, there is a possibility that the choice of periods could give results that are under conservative. In addition to regular wave analysis, the paper presents two alternative methodologies to determine the most likely response, with the focus on reducing the computational resources required. The first alternative is an ‘Irregular Wave Screen’ approach in which the wave train is screened at areas of interest for waves within a user defined threshold of the maximum wave height, in addition to other user defined parameters. Only waves within these parameters are simulated to determine responses. The second alternative is the ‘New Wave’ approach, which models the most probable wave elevation around the maximum wave crest. The calculated new wave is then placed at the desired location to determine responses. The responses of the Regular, Irregular Wave Screen and New Wave methodologies are compared with the Irregular MPM approach to determine their feasibility to predict the response of flexibles in a real world irregular sea state with lower computational requirements.

scholarly journals STATISTICAL PROPERTIES OF THE MAXIMUM RUN OF IRREGULAR SEA WAVES

1988 ◽  
Vol 1 (21) ◽  
pp. 48 ◽  
Author(s):  
Akira Kimura
Keyword(s):  
Probability Distribution ◽  
Wave Height ◽  
Probability Distributions ◽  
Confidence Regions ◽  
Statistical Properties ◽  
Irregular Waves ◽  
Sea Waves ◽  
Sea State ◽  
Irregular Wave ◽  
Distribution Of The Maximum

The probability distribution of the maximum run of irregular wave height is introduced theoretically. Probability distributions for the 2nd maximum, 3rd maximum and further maximum runs are also introduced. Their statistical properties, including the means and their confidence regions, are applied to the verification of experiments with irregular waves in the realization of a "severe sea state" in the test.

Experimental Investigations on the Seismic Behavior of Precast Concrete Columns with Novel Box Connections

2019 ◽  
Vol 14 (02) ◽  
pp. 2050007
Author(s):  
Xizhi Zhang ◽  
Shengbo Xu ◽  
Shaohua Zhang ◽  
Gaodong Xu
Keyword(s):  
Energy Dissipation ◽  
Bearing Capacity ◽  
Failure Mode ◽  
Seismic Behavior ◽  
Load Transfer ◽  
Precast Concrete ◽  
Hysteretic Behavior ◽  
Experimental Investigations ◽  
Test Results ◽  
Energy Dissipation Capacity

In this study, two types of novel box connections were developed to connect precast concrete (PC) columns and to ensure load transfer integrity. Cyclic loading tests were conducted to investigate the seismic behavior of the PC columns with proposed connections as well as the feasibility and reliability of novel box connections. The failure mode, hysteretic behavior, bearing capacity, ductility, stiffness degradation and energy dissipation were obtained and discussed. The test results indicated that the all PC columns exhibited the ductile flexural failure mode and that the proposed connections could transfer the force effectively. The adoption of novel box connections could improve the deformation capacity and energy dissipation capacity of PC columns. A higher axial compression ratio could enhance the bearing capacity of PC column with proposed connection but would significantly deteriorate the ductility and energy dissipation capacity. Finite element models were developed and the feasibility of the models was verified by the comparison with the test results.

Current Effects on a Moored Floating Platform in a Sea State

2008 ◽  
Author(s):  
Carl Trygve Stansberg
Keyword(s):  
Irregular Waves ◽  
Mooring Line ◽  
Viscous Effects ◽  
Floating Platform ◽  
Sea State ◽  
Scaled Model ◽  
Wave Drift ◽  
Wave Basin ◽  
Wave Drift Damping ◽  
Non Gaussian

The significance of current-induced forces and effects on a moored semisubmersible production platform in various sea state conditions is explored, with emphasis on surge motions. Experimental data from 1:55 scaled model tests in a 50m × 80m wave basin are investigated. A description of the current generation is given first. The current in the actual basin is modelled by use of a return current under a false bottom. The importance of modelling a “real” physical current for the proper reproduction of platform responses is pointed out. The semisubmersible tests are carried out with the platform in current only, in irregular waves only, and in combined waves and current conditions. The effects from the current on platform motions and mooring line tensions are investigated. Vortex-Induced motions (VIM) are observed in pure current, depending on the actual combination of current velocity and natural sway period. In combined waves and current the VIM seems to be more or less disappearing. A large effect is seen on the wave drift responses. Both drift forces, non-Gaussian properties and resulting extreme motions and line tensions are significantly increased, especially in high sea states. This is explained through a combination of wave drift damping and viscous effects. At the same time the damping is also increased, but this only partly compensates for the increased forces.

Interaction of Waves With a Moored Semisubmersible

1984 ◽  
Vol 106 (4) ◽  
pp. 419-425 ◽  
Author(s):  
S. K. Chakrabarti ◽  
D. C. Cotter
Keyword(s):  
Diffraction Theory ◽  
Nonlinear Damping ◽  
Irregular Waves ◽  
Test Results ◽  
Regular Waves ◽  
Mooring Lines ◽  
Wave Groups ◽  
First Order ◽  
Oscillating Motion ◽  
Theoretical Results

A semisubmersible moored in waves experiences a steady offset and two types of motion—a first-order motion at frequencies corresponding to the incident wave frequencies and a slowly oscillating motion near the natural frequency of the semisubmersible/mooring system. An extensive wave tank testing of a semisubmersible model was undertaken in which the motions of the semisubmersible and the loads in the mooring lines were measured. The semisubmersible was tested in the tank in a head sea as well as a beam sea heading in a series of regular waves, regular wave groups and irregular waves. The test results of the steady offset and first-order and slowly oscillating motions are presented for each heading and for each of these wave series as functions of the wave period. The experimental results are correlated with theoretical results based on a 3-D diffraction theory which takes into account the appropriate first and second-order terms. It is found that the nonlinear damping terms are quite important in explaining the behavior of the moored semisubmersible in waves and that the steady drift loads in wave groups can be determined from results based on regular waves.

Computation of Slowly Varying Second-Order Hydrodynamic Forces on Floating Structures in Irregular Waves

1989 ◽  
Vol 111 (3) ◽  
pp. 223-232 ◽  
Author(s):  
T. Matsui
Keyword(s):  
Velocity Potential ◽  
Near Field ◽  
Fluid Pressure ◽  
Hydrodynamic Forces ◽  
Second Order ◽  
Irregular Waves ◽  
Floating Structures ◽  
Slow Drift ◽  
Submerged Body ◽  
Element Technique

An exact second-order formulation is presented for computing the slowly varying second-order hydrodynamic forces on floating structures in irregular waves. The near-field approach based on direct integration of the fluid pressure on the submerged body surface is employed in conjunction with numerical first-order solutions by means of the hybrid finite element technique. Green’s second identity is exploited to evaluate the second-order forces due to the second-order velocity potential. Numerical results are presented for the slow drift excitation forces on an articulated column and a semi-submersible platform. It is shown that the contribution from the second-order velocity potential is more significant to the roll moment than to the sway and heave forces on the semi-submersible.

Experimental Investigations on Effects of Simulated Seismic Loading on LBB Assessment of High Energy Piping

2005 ◽  
Author(s):  
Suneel K. Gupta ◽  
Vivek Bhasin ◽  
K. K. Vaze ◽  
A. K. Ghosh ◽  
H. S. Kushwaha
Keyword(s):  
Cyclic Loading ◽  
Nuclear Power ◽  
Dynamic Effect ◽  
High Energy ◽  
Experimental Investigations ◽  
Test Results ◽  
Apparent Fracture Toughness ◽  
Tearing Instability ◽  
Heavy Water Reactor ◽  
Fracture Assessment

The current Leak Before Break (LBB) assessment is based primarily on the monotonic fracture tearing instability. In it the maximum design accident load is compared with the fracture-tearing resistance load. The effect of cyclic loading has generally not been considered in the fracture assessment of nuclear power plant piping. It is a well-known fact that the reversible cyclic loading decreases the fracture resistance of the material, which leads to increased crack growth. Indian nuclear power reactors consider Operational-Basis-Earthquake (OBE) and Safe-Shutdown-Earthquake (SSE) event in the design of various structures, systems and components. Keeping this in view a series of cyclic tearing test have been conducted on straight pipes, made of ASTM SA333 Gr.6 carbon steel. This is the material of primary heat transport (PHT) piping material of Indian Pressurised Heavy Water Reactor (PHWR). In this series 13 tests have been carried out on circumferentially through wall cracked seamless and circumferential seam welded straight pipes under reversible cyclic bending loading. All the tests have been conducted under quasi-static i.e. slow loading rates and the dynamic effect is not considered. The cyclic test results have been compared with the corresponding monotonic pipe fracture test results. These test results and its comparison with corresponding monotonic tearing clearly illustrates the need of addressing the reduction in apparent fracture toughness of material under reversible cyclic loading and safe number of load cycles in the LBB assessment.

scholarly journals THE EFFECT OF WAVE ENERGY SPECTRA ON WAVE RUN-UP

1968 ◽  
Vol 1 (11) ◽  
pp. 57 ◽  
Author(s):  
J.H. Van Oorschot ◽  
K. D'Angremond
Keyword(s):  
Energy Spectrum ◽  
Wave Energy ◽  
Irregular Waves ◽  
Energy Spectra ◽  
Wave Spectra ◽  
Hydraulic Actuators ◽  
Wave Generator ◽  
Run Up ◽  
Hydraulics Laboratory ◽  
Monochromatic Waves

Previous investigations carried out "by the Delft Hydraulics laboratory have shown the necessity of applying irregular waves m studies on wave run-up. The installation of a wave generator driven "by hydraulic actuators has created the possibility of producing irregular waves with arbitrary wave spectra. Investigations performed with this type of wave generator show the influence of the shape of the energy spectrum on the wave run-up on smooth straight slopes of 1:4 and 1:6. The results are compared with run-up figures derived from experiments with wind generated waves and with monochromatic waves.

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