scholarly journals The Hydrodynamic Moment of a Floating Structure in Finite Flowing Water

Fluids ◽  
2021 ◽  
Vol 6 (9) ◽  
pp. 307
Author(s):  
Zhen Cui ◽  
Shi-Yang Pan ◽  
Yue-Jun Chen
Keyword(s):  
Flood Control ◽  
Least Squares Method ◽  
Mathematical Expression ◽  
Experimental Results ◽  
Hydrodynamic Theory ◽  
Floating Structure ◽  
Floating Structures ◽  
Physical Model Tests ◽  
Hydraulic Conditions ◽  
Hydrodynamic Factors

The implementation of floating structures has increased with the construction of new sluices for flood control, and the hydrodynamic moment of a floating structure affects the safety and operation of that structure. Based on basic hydrodynamic theory, theoretical analysis and 121 physical model tests were conducted to study the relationships between the hydrodynamic moment and the influencing factors of floating structures, namely, the shape parameter, hydraulic conditions, and draft depth. Stepwise regression fitting based on the least squares method was performed to obtain a mathematical expression of the hydrodynamic moment, and the experimental results show that hydrodynamic factors significantly influence the hydrodynamic moment of such structures. The results predicted by the mathematical expression agree with the experimental results, and thus, the proposed expression can be used to comprehensively analyze and study the safety of a floating structure under the action of flow in finite water.

Image Reconstruction on Quincunx Patterned Green Channel

2013 ◽  
Vol 717 ◽  
pp. 493-496
Author(s):  
Gwang Gil Jeon
Keyword(s):  
Image Reconstruction ◽  
Least Squares ◽  
Least Squares Method ◽  
Interpolation Method ◽  
Experimental Results ◽  
Color Filter ◽  
Image Artifacts ◽  
Green Channel ◽  
Filter Array ◽  
Single Sensor

This paper addresses the issue of the quincunx patterned green channel interpolation method that is obtained by single sensor cameras. Our goal is to reconstruct the green channel in Bayer color filter array (CFA) data. We present a new filter-based method for the reduction of image artifacts in green channel. To reconstruct green channel, we trained a filter using least squares method. Experimental results confirm the effectiveness of the proposed method. Compared to other bilinear and bicubic filters, the improvement in quality has been achieved.

A Numerically Efficient Method for Analysis of Very Large Articulated Floating Structures

1998 ◽  
Vol 42 (03) ◽  
pp. 174-186
Author(s):  
C. J. Garrison
Keyword(s):  
Hydrodynamic Interaction ◽  
Near Field ◽  
Three Dimensional ◽  
Computational Effort ◽  
Floating Structure ◽  
Complete Structure ◽  
Field Interaction ◽  
Floating Structures ◽  
Computing Effort ◽  
The Individual

A method is presented for evaluation of the motion of long structures composed of interconnected barges, or modules, of arbitrary shape. Such structures are being proposed in the construction of offshore airports or other large offshore floating structures. It is known that the evaluation of the motion of jointed or otherwise interconnected modules which make up a long floating structure may be evaluated by three dimensional radiation/diffraction analysis. However, the computing effort increases rapidly as the complexity of the geometric shape of the individual modules and the total number of modules increases. This paper describes an approximate method which drastically reduces the computational effort without major effects on accuracy. The method relies on accounting for hydrodynamic interaction effects between only adjacent modules within the structure rather than between all of the modules since the near-field interaction is by far the more important. This approximation reduces the computational effort to that of solving the two-module problem regardless of the total number of modules in the complete structure.

Feasibility of Using Stress Joint in an Existing Flexible Joint Receptacle for a Deepwater SCR

2009 ◽  
Author(s):  
Basim Mekha ◽  
Alok Kumar ◽  
Mike Stark ◽  
Paul Barnett
Keyword(s):  
Bending Moment ◽  
Flexible Joints ◽  
Floating Structure ◽  
Element Analysis ◽  
Flexible Joint ◽  
Floating Structures ◽  
Operational Problem ◽  
Hull Structure ◽  
Hull Design ◽  
Titanium Material

In recent years, most fluid produced or exported has been transported using steel catenary risers (SCRs) attached to deepwater floating structures. The SCRs are terminated at the floating structures using Top Termination Units (TTUs) such as flexible joints or tapered stress joints. The flexible joints are usually designed to allow the riser to rotate with the floating structure motion and reduce the amount of moments transferred to the hull structure. The flexible joints depend on the flexibility and compressibility of the elastomer layers to allow for the rotation of the SCR. The stress joints, alternatively, provide fixed support at the hull and thus larger bending moment that has to be accounted for in the hull design. The stress joints can be made of steel or titanium material. The SCR TTU’s receptacle, which will be welded to the hull porch and contains the TTU basket, has to be designed to meet the force and reaction requirements associated with the selected TTU type. However, in some cases which could be due to failure of the TTU to meet the expected life or the operational requirements, the operators may have to replace the damaged TTU with another one or with a different TTU type. A few examples are available in the Gulf of Mexico. Recently the Flexible Joint TTU of the Independent Hub 20-inch export SCR had an operational problem. During the course of investigating the related issues and studying possible solutions, one option considered was the feasibility of replacing the Flexible Joint (FJ) with Titanium Tapered Stress Joint (TSJ). This paper highlights the issues that have to be considered in the design of the FJ existing receptacle to accommodate the force reactions of a Titanium TSJ. These issues are addressed and the results of the detailed finite element analysis performed are provided. The analysis conclusions, which are related to the feasibility of the existing receptacle to receive the loads imposed by TSJ and the modifications required to achieve this, are presented.

Very Large Floating Structures

2007 ◽  
Author(s):  
H. Suzuki ◽  
H. R. Riggs ◽  
M. Fujikubo ◽  
T. A. Shugar ◽  
H. Seto ◽  
...  
Keyword(s):  
Design Procedure ◽  
Offshore Structures ◽  
Floating Structure ◽  
Floating Structures ◽  
Design Procedures ◽  
Novel Technology ◽  
Hydroelastic Analysis ◽  
Behavior Design ◽  
Hydroelastic Response ◽  
Near Future

Very Large Floating Structure (VLFS) is a unique concept of ocean structures primary because of their unprecedented length, displacement cost and associated hydroelastic response. International Ship and Offshore Structures Congress (ISSC) had paid attention to the emerging novel technology and launched Special Task Committee to investigate the state of the art in the technology. This paper summarizes the activities of the committee. A brief overview of VLFS is given first for readers new to the subject. History, application and uniqueness with regard to engineering implication are presented. The Mobile Offshore Base (MOB) and Mega-Float, which are typical VLFS projects that have been investigated in detail and are aimed to be realized in the near future, are introduced. Uniqueness of VLFS, such as differences in behavior of VLFS from conventional ships and offshore structures, are described. The engineering challenges associated with behavior, design procedure, environment, and the structural analysis of VLFS are introduced. A comparative study of hydroelastic analysis tools that were independently developed for MOB and Mega-Float is made in terms of accuracy of global behavior. The effect of structural modeling on the accuracy of stress analysis is also discussed. VLFS entails innovative design methods and procedure. Development of design criteria and design procedures are described and application of reliability-based approaches are documented and discussed.

Research Development and Key Technical on Floating Foundation for Offshore Wind Turbines

2012 ◽  
Vol 446-449 ◽  
pp. 1014-1019 ◽  
Author(s):  
Ruo Yu Zhang ◽  
Chao He Chen ◽  
You Gang Tang ◽  
Xiao Yan Huang
Keyword(s):  
Wind Energy ◽  
Wind Turbine ◽  
Water Area ◽  
Offshore Wind ◽  
Offshore Wind Energy ◽  
Floating Structure ◽  
Floating Structures ◽  
Floating Foundation ◽  
Set Up ◽  
Sea Area

The water area in which water depth is deeper than 50m has special advantage in wind turbine generation, because there are the stable wind speed and small Wind-shear. In such sea area, the offshore wind energy generating equipments should be set up on floating foundation structure. Therefore, it is of great significance to study the floating foundation structures that are available for offshore wind energy generation for the industrialization of the offshore wind power generation. In this paper, the basic type and working principles are reviewed for some novel floating structures developed in recent year. In addition, some key dynamical problems and risk factors of the floating structure are systemically analyzed for working load caused by turbine running and sea environment loads of floating structure. The results are valuable for designing the floating structures of wind turbine generation.

Yaw Drift Moment of a Floating Structure in Waves

2005 ◽  
Author(s):  
Dimitris Spanos ◽  
Apostolos Papanikolaou
Keyword(s):  
Hydrodynamic Forces ◽  
Computational Method ◽  
Irregular Waves ◽  
Linear Potential ◽  
Floating Bodies ◽  
Floating Structure ◽  
Natural Wave ◽  
Positioning Systems ◽  
Floating Structures ◽  
Wave Induced

The wave induced yaw drift moment on floating structures is of particular interest when the lateral yaw motion of the structure should be controlled by moorings and/or active dynamic positioning systems. In the present paper, the estimation of the yaw drift moment in the modeled natural wave environment is conducted by application of a nonlinear time domain numerical method accounting for the motion of arbitrarily shaped floating bodies in waves. The computational method is based on linear potential theory and includes the non-linear hydrostatic terms in an exact way, whereas the higher-order wave-induced effects are partly approximated. Despite the approximate modeling of the second order hydrodynamic forces, the method proved to satisfactorily approach the dominant part of the exerted hydrodynamic forces enabling the calculation of drift forces and of other drift effects in irregular waves. Hence, the subject yaw drift moment in the modeled natural wave environment is derived, resulting to a basic reference for the design of similar type floating structures.

A Study on Predictions of Fully Nonlinear Motion Aircushion Type Floating Structures Using 2D MPS Method

2008 ◽  
Author(s):  
Mitsuhiro Masuda ◽  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hisaaki Maeda
Keyword(s):  
Water Waves ◽  
Theoretical Calculations ◽  
Numerical Technique ◽  
Ocean Waves ◽  
Nonlinear Phenomena ◽  
Linear Potential ◽  
Floating Structure ◽  
Fully Nonlinear ◽  
Floating Structures ◽  
Mps Method

Very large floating structures (VLFSs) have been proposed for new ocean space utilization and many researches have been carried out. VLFSs are elastically deformed due to ocean waves because the rigidity of the structure decreases relatively. The authors examine the aircushion type floating structure in order to reduce hydroelastic motion. An aircushion type floating structure to which air-chambers are installed can reduce the wave drifting force and hydroelastic motion at the same time. Most theoretical calculations of motion of aircushion type floating structures in water waves have been done based on a linear potential theory so far. As a result, the utility of the aircushion has been proved. However fully nonlinear phenomena such as deck wetness, slamming and air-leakage cannot be investigated by using existing calculations based on the linear theory. In this study, a computer program code of the two-dimensional MPS method that can consider fully nonlinear influence is developed and then the air layer inside an aircushion is expressed with particles of the MPS. Moreover, the numerical technique for introducing directly the mooring force into the motion equation of the particle is developed. Motion response of aircushion type floating structures in a billow is computed. As a result, the usefulness of this numerical calculation method is confirmed.

Estimating Design Loads for Floating Structures Using Environmental Contours

2020 ◽  
Author(s):  
Yuliang Zhao ◽  
Sheng Dong ◽  
Zihao Yang ◽  
Lance Manuel
Keyword(s):  
Structural Response ◽  
Design Stage ◽  
Dependence Structure ◽  
Floating Structure ◽  
Zero Crossing ◽  
Floating Structures ◽  
Reliability Method ◽  
Extreme Response ◽  
Design Loads ◽  
Nataf Transformation

Abstract To ensure acceptable operation and/or survival of floating structures in extreme conditions, nonlinear time-domain simulations are often used to predict the structural response at the design stage. An environmental contour (EC) is commonly employed to identify critical sea states that serve as input for numerical simulations to assess the safety and performance of marine structures. In many studies, marginal and conditional distributions are defined to construct bivariate joint probability distributions for variables such as significant wave height and zero-crossing period; then, environmental contours can be constructed using the inverse first-order reliability method (IFORM). This study adopts alternative models to describe the generalized dependence structure between the environmental variables using copulas; the Nataf transformation is also discussed as a special case. Environmental contours are constructed, making use of measured wave data from moored buoys. Derived design loads are applied on a semi-submersible platform to assess possible differences. In addition, the long-term extremes of the tension of the mooring lines are estimated, considering uncertainties in the structural response using a 3D model (that includes response variability, ignored with the EC approach) to help establish more accurate design loads using Monte Carlo simulation. Results offer a clear indication of the extreme response of the floating structure based on the different models.

scholarly journals Prediction of dynamic responses of floating structures using NARX with mirroring technique

2018 ◽  
Vol 203 ◽  
pp. 01025
Author(s):  
Ruly Irawan ◽  
Mohd Shahir Liew ◽  
Montasir Osman Ahmed Ali ◽  
Ahmad Mohamad Al Yacouby
Keyword(s):  
Time Series ◽  
Time Series Data ◽  
Dynamic Network ◽  
Dynamic Responses ◽  
Series Data ◽  
Ann Model ◽  
Floating Structure ◽  
Floating Structures ◽  
Time Series Modelling ◽  
Mirroring Technique

Displacements, velocities and accelerations of Six Degree of freedom of a single floating structure was predicted using Time Series NARX feedback neural Networks. The nonlinear autoregressive network with exogenous inputs (NARX) is a recurrent dynamic network, with feedback connections enclosing several layers of the network is based on the linear ARX model, which is commonly used in time-series modelling is used in this study. Time series data of displacements of a single floating structure was used for training and testing the ANN model. In the training stage, this time series data of environment parameters was used as input and dynamic responses was used as target. Benchmarking result and error prediction was compared between two techniques of Neural Network training. The prediction result of the model responses can be concluded that NARX with mirroring technique increase the accuracy and can be used to predict time series of dynamic responses of floating structures.

scholarly journals Experimental Method for Plotting S-N Curve with a Small Number of Specimens

2016 ◽  
Vol 23 (4) ◽  
pp. 129-137 ◽  
Author(s):  
Przemysław Strzelecki ◽  
Janusz Sempruch
Keyword(s):  
Fatigue Life ◽  
Least Squares Method ◽  
Experimental Results ◽  
Bending Test ◽  
Likelihood Method ◽  
Staircase Method ◽  
Random Occurrence ◽  
Straight Line ◽  
Standard Documents ◽  
Time Required

Abstract The study presents two approaches to plotting an S-N curve based on the experimental results. The first approach is commonly used by researchers and presented in detail in many studies and standard documents. The model uses a linear regression whose parameters are estimated by using the least squares method. A staircase method is used for an unlimited fatigue life criterion. The second model combines the S-N curve defined as a straight line and the record of random occurrence of the fatigue limit. A maximum likelihood method is used to estimate the S-N curve parameters. Fatigue data for C45+C steel obtained in the torsional bending test were used to compare the estimated S-N curves. For pseudo-random numbers generated by using the Mersenne Twister algorithm, the estimated S-N curve for 10 experimental results plotted by using the second model, estimates the fatigue life in the scatter band of the factor 3. The result gives good approximation, especially regarding the time required to plot the S-N curve.

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