Effect of Special Outermost Module Designs on the Hydrodynamic Responses of a Modular Multi-Purpose Floating Structure System

2019 ◽  
Author(s):  
Nianxin Ren ◽  
Chi Zhang ◽  
Allan Ross Magee ◽  
Xiao Liu ◽  
Øyvind Hellan ◽  
...  
Keyword(s):  
Bending Moment ◽  
Structural Deformation ◽  
Special Design ◽  
Floating Structure ◽  
Mechanical Coupling ◽  
Maximum Deformation ◽  
Heave Plate ◽  
The Time Domain ◽  
Extreme Responses ◽  
Vertical Bending Moment

Abstract The present work investigates the effect of different outermost module designs on the hydrodynamic responses of a modular multi-purpose floating structure (MMFS) system. The MMFS system is initially designed for a mild sea zone. As the entire system consists of more than 20 bodies, a simplified system with seven interconnected standardized modules is proposed for numerical and experimental study. In this simplified system, each module is assumed as a rigid body. Both hydrodynamic interactions and mechanical coupling among modules are taken into consideration in the time-domain numerical analysis. The structural deformation of the MMFS system mainly occurs in the connectors among adjacent modules. The maximum deformation appears at the connectors between outermost modules with the internal modules. To reduce the deformation and improve the concept, two special design, outermost module of deeper draft and outermost module with additional heave plate are proposed and investigated for the MMFS system. The numerical results indicate that the two proposed designs for the outermost module can significantly reduce the hydrodynamic responses of the MMFS system, especially the motion of the outermost module and the vertical bending moment on the connector. The extreme responses of the MMFS system with different outermost module designs are also studied and compared.

scholarly journals Hydrodynamic Analysis of a Modular Floating Structure with Tension-Leg Platforms and Wave Energy Converters

2021 ◽  
Vol 9 (4) ◽  
pp. 424
Author(s):  
Nianxin Ren ◽  
Hongbo Wu ◽  
Kun Liu ◽  
Daocheng Zhou ◽  
Jinping Ou
Keyword(s):  
Wave Energy ◽  
Coupling Effect ◽  
Bending Moment ◽  
Large Degree ◽  
Hydrodynamic Performance ◽  
Floating Structure ◽  
Mechanical Coupling ◽  
Wave Energy Converters ◽  
Energy Converters ◽  
Inner Tension

This work presents a modular floating structure, which consists of five inner tension-leg platforms and two outermost wave energy converters (denoted as MTLPW). The hydrodynamic interaction effect and the mechanical coupling effect between the five inner tension-leg platforms (TLP) and the two outermost wave energy converters (WEC) are taken into consideration. The effects of the connection modes and power take-off (PTO) parameters of the WECs on the hydrodynamic performance of the MTLPW system are investigated under both operational and extreme sea conditions. The results indicate that the hydrodynamic responses of the MTLPW system are sensitive to the connection type of the outermost WECs. The extreme responses of the bending moment of connectors depend on the number of continuously fixed modules. By properly utilizing hinge-type connectors to optimize the connection mode for the MTLPW system, the effect of more inner TLP modules on the hydrodynamic responses of the MTLPW system can be limited to be acceptable. Therefore, the MTLPW system can be potentially expanded to a large degree.

Time Domain Comparison With Experiments for Ship Motions and Structural Loads on a Container Ship in Abnormal Waves

2011 ◽  
Author(s):  
Suresh Rajendran ◽  
Nuno Fonseca ◽  
C. Guedes Soares ◽  
Gu¨nther F. Clauss ◽  
Marco Klein
Keyword(s):  
Time Domain ◽  
Bending Moment ◽  
Green Water ◽  
Ship Motions ◽  
Container Ship ◽  
Wave Elevation ◽  
Strip Theory ◽  
The Time Domain ◽  
Vertical Bending Moment ◽  
Comparison With Experiments

The paper presents experimental results from model tests with a containership advancing in abnormal wave conditions and comparisons with numerical simulations. A nonlinear time domain method based on strip theory is used for the calculation of vertical ship responses induced by abnormal waves. This code combines the linear diffraction and radiation forces with dominant nonlinear forces associated with vertical response arising from Froude-Krylov forces, hydrostatic forces and shipping of green water. The time domain simulations are compared directly with experimental records from tests with a model of a container ship in deterministic waves for a range of Froude numbers. Extreme sea conditions were replicated by the reproduction of realistic abnormal waves like the New Year Wave and abnormal wave from North Alwyn. Head sea condition is considered and the comparisons include the wave elevation, the vertical motions of the ship and the vertical bending moment at midship.

Slamming Simulations in a Conditional Wave

2012 ◽  
Author(s):  
Sopheak Seng ◽  
Jørgen Juncher Jensen
Keyword(s):  
Bending Moment ◽  
Body Motion ◽  
Correction Coefficient ◽  
Container Ship ◽  
Cfd Simulations ◽  
Strip Theory ◽  
Structural Responses ◽  
Cfd Method ◽  
Extreme Responses ◽  
Vertical Bending Moment

A study of slamming events in conditional waves is presented in this paper. The ship is sailing in head sea and the motion is solved for under the assumption of rigid body motion constrained to two degree-of-freedom i.e. heave and pitch. Based on a time domain non-linear strip theory most probable conditional waves are generated to induce short term extreme responses of 4500 MNm sagging and hogging vertical bending moment (VBM) amidships on a modern 9,400-TEU post-Panamax container ship and 3000 MNm (sag) on a Panamax container ship. The results of the strip theory are compared to the results of free surface NS/VOF CFD simulations under the same wave conditions. In moderate seas and no occurrence of slamming the structural responses predicted by the methods agree well. When slamming occurs the strip theory overpredicts VBM but the peak values of VBM occurs at approximately the same time as predicted by the CFD method implying the possibility to use the more accurate CFD results to improve the estimation of slamming loads in the strip theory through a rational correction coefficient.

Calculation of Vertical Bending Moment Acting on an Ultra Large Containership in Large Amplitude Waves

2015 ◽  
Author(s):  
Suresh Rajendran ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Large Amplitude ◽  
Bending Moment ◽  
Regular Waves ◽  
Structural Dynamic ◽  
Strip Theory ◽  
Structural Dynamic Characteristics ◽  
Wetted Surface Area ◽  
The Time Domain ◽  
Hydroelastic Response ◽  
Vertical Bending Moment

The time domain method is further extended here in order to calculate the hydroelastic response of an ultra large containership in regular waves. Based on strip theory, the hydrodynamic and the hydrostatic forces are calculated for the instantaneous wetted surface area. Slamming forces are calculated using a Von Karman approach in which the water pile up during slamming is neglected. Timoshenko beam which takes into account the shear deformation and rotary inertia is used to model the structural dynamic characteristics of the hull. The beam is discretized using the finite element method and the ship vibration is solved using the modal analysis. The method is used to calculate the vertical bending moment acting on an ultra large containership in large amplitude regular waves. The results are compared with the experimental results measured in wave tank.

scholarly journals Load calculation and strength analysis of floating garbage cleaning equipment

2021 ◽  
Vol 261 ◽  
pp. 03024
Author(s):  
Weiyao Xu ◽  
Jianting Guo ◽  
Chunyan Ji
Keyword(s):  
High Stress ◽  
Bending Moment ◽  
Strength Analysis ◽  
Floating Structure ◽  
Cleaning Equipment ◽  
Load Calculation ◽  
Calculation Results ◽  
Torque Load ◽  
Design Requirements ◽  
Vertical Bending Moment

In order to alleviate the problem that there is increasingly floating garbage pollution on the sea, this paper proposes a new design of floating garbage cleaning equipment. This equipment is a slender structure, and whether its structural strength can meet the design requirements requires special attention. In order to ensure the rationality and safety of the design, load calculation and strength analysis are carried out based on the design wave method. The calculation results show that the longitudinal torque load of this equipment is the largest, which is 2.5 times of the second largest vertical bending moment. At the same time, there are three large stress areas in the floating structure, which are the connection between the pontoon and the connecting buntons, the connecting buntons intersecting with the Y axis and the pontoons on both sides. For the abovementioned high-stress areas, a structural strengthening plan is proposed. After the improvement, the stress in the high-stress areas of the structure is significantly reduced, with a maximum reduction of 52%. The strength of the improved structure meets the design requirements. The research results of this paper can provide relevant references for the development of floating garbage cleaning equipment in the future.

Post-Ultimate Strength Behavior of Very Large Floating Structure Subjected to Extreme Wave Loads

2012 ◽  
Author(s):  
Kazuhiro Iijima ◽  
Masahiko Fujikubo
Keyword(s):  
Ultimate Strength ◽  
Cross Section ◽  
Simple Formula ◽  
Bending Moment ◽  
Wave Loads ◽  
Extreme Wave ◽  
Floating Structure ◽  
Strength Behavior ◽  
Wave Induced ◽  
Vertical Bending Moment

In this paper, post-ultimate strength behavior of VLFS to extreme wave-induced loads is investigated. A mathematical model to describe the post-ultimate strength behavior of VLFS is developed taking the hydroelasticity into account. The whole VLFS is modeled by two beams on an elastic foundation connected via a nonliner rotational spring assuming that VLFS collapses amidship under severe bending moment. The model is solved numerically by using FEM. It is shown that the extent of collapse of VLFS is smaller than that of ship structures for given amplitude of vertical bending moment on condition that the structures have the same cross section and the same moment-displacement relationship. A simple formula to represent the extent of collapse of VLFS is derived. Its efficacy is shown.

Tank Test and Numerical Simulation of Spar Type Floating OTEC

2021 ◽  
Author(s):  
Shunka C. Hirao ◽  
Jun Umeda ◽  
Kentaroh Kokubun ◽  
Toshifumi Fujiwara
Keyword(s):  
Numerical Simulations ◽  
Cold Water ◽  
Scaling Law ◽  
Internal Flow ◽  
Bending Moment ◽  
Floating Structure ◽  
Waves And Currents ◽  
Tank Test ◽  
Safety Assessments ◽  
Ocean Thermal Energy

Abstract National Maritime Research Institute, NMRI, had been studying the analytical method on safety assessments of floating power generation facilities for ten years more. As a part of these studies, an Ocean Thermal Energy Conversion (OTEC) was also studied in our institute. The OTEC normally has a very long and thick Cold-Water Pipe (CWP) with an unanchored end to pump up a large amount of cold-water continuously. From the viewpoints of the safety assessments of the OTEC operation, it is noteworthy to confirm the effect of the existing long pipe against a floating unit/body and an effect of internal flowing water. It is necessary, moreover, to consider the Vortex Induced Vibration (VIV) effect for floater motions and structural analysis of the pipe itself and a connecting point of the floating structure. In this paper, the results of model tests and numerical simulations of a spar type floating OTEC with a single CWP in waves and currents are presented. The CWP model was made of material fitting the scaling law for a planned full scale OTEC. The specific and unique phenomena of the floating OTEC were confirmed from the model test results. Based on the results of the tank tests and the numerical simulations, we confirmed the necessary items and arrangements for safety evaluations. In detail, the internal flow increased the bending moment at the connection point.

Load Combination for Fatigue Analysis of Ship Structures

2004 ◽  
Author(s):  
Yung S. Shin ◽  
Booki Kim ◽  
Alexander J. Fyfe
Keyword(s):  
Bending Moment ◽  
Linear Summation ◽  
Load Combination ◽  
Longitudinal Stiffeners ◽  
Stress Components ◽  
Tank Pressure ◽  
Wave Induced ◽  
Vertical Bending Moment ◽  
Oil Tanker

A methodology for calculating the correlation factors to combine the long-term dynamic stress components of ship structure from various loads in seas is presented. The methodology is based on a theory of a stationary ergodic narrow-banded Gaussian process. The total combined stress in short-tem sea states is expressed by linear summation of the component stresses with the corresponding combination factors. This expression is proven to be mathematically exact when applied to a single random sea. The long-term total stress is similarly expressed by linear summation of component stresses with appropriate combination factors. The stress components considered here are due to wave-induced vertical bending moment, wave-induced horizontal bending moment, external wave pressure and internal tank pressure. For application, the stress combination factors are calculated for longitudinal stiffeners in cargo and ballast tanks of a crude oil tanker at midship section. It is found that the combination factors strongly depend on wave heading and period in the short-term sea states. It is also found that the combination factors are not sensitive to the selected probability of exceedance level of the stress in the long-term sense.

scholarly journals Thermo-hydro-mechanical coupling analysis of a thermo-active diaphragm wall

2018 ◽  
Vol 55 (5) ◽  
pp. 720-735 ◽  
Author(s):  
Yi Rui ◽  
Mei Yin
Keyword(s):  
New Technologies ◽  
Bending Moment ◽  
Diaphragm Wall ◽  
Elastic Model ◽  
Element Analysis ◽  
Thermally Induced ◽  
Mechanical Coupling ◽  
Reversal Effect ◽  
Earth Pressures ◽  
Geotechnical Aspect

Thermo-active diaphragm walls that combine load bearing ability with a ground source heat pump (GSHP) are considered to be one of the new technologies in geotechnical engineering. Despite the vast range of potential applications, current thermo-active diaphragm wall designs have very limited use from a geotechnical aspect. This paper investigates the wall–soil interaction behaviour of a thermo-active diaphragm wall by conducting a thermo-hydro-mechanical finite element analysis. The GSHP operates by circulating cold coolant into the thermo-active diaphragm wall during winter. Soil contraction and small changes in the earth pressures acting on the wall are observed. The strain reversal effect makes the soil stiffness increase when the wall moves in the unexcavated side direction, and hence gives different trends for long-term wall movements compared to the linear elastic model. The GSHP operation makes the wall move in a cyclic manner, and the seasonal variation is approximately 0.5–1 mm, caused by two factors: the thermal effects on the deformation of the diaphragm wall itself and the thermally induced volume change of the soil and pore water. In addition, it is found that the change in bending moment of the wall due to the seasonal GSHP cycle is caused mainly by the thermal differential across the wall during the winter, because the seasonal changes in earth pressures acting on the diaphragm wall are very limited.

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