Developments in the calculation of the wavemaking resistance of ships

1988 ◽  
Vol 416 (1850) ◽  
pp. 115-147 ◽  
Keyword(s):  
Three Dimensional ◽  
Source Distribution ◽  
Rectilinear Motion ◽  
Kelvin Wave ◽  
Distribution Method ◽  
Wave Source ◽  
Qualitative And Quantitative ◽  
Theoretical Predictions ◽  
Computational Aspects ◽  
Quantitative Manner

The wavemaking resistance of a rigid ship in steady rectilinear motion at the free surface of a previously calm ocean is evaluated by means of a linearized three-dimensional potential-flow formulation. Solutions to the disturbance potential of the steady perturbed flow about the moving ship are obtained by means of a Kelvin wave source distribution method. Particular emphasis is placed on computational aspects and accurate and efficient algorithms for the evaluation of the fundamental Kelvin wave source potential function are discussed. To illustrate the proposed method, experimental and theoretical predictions are compared for a variety of ship forms. In general, this approach shows the correct behaviour of the variation of the wavemaking resistance with forward speed in both a qualitative and quantitative manner.

Study on the Motions and Stress of Immersing Tunnel Element under Wave Actions

2013 ◽  
Vol 328 ◽  
pp. 614-622
Author(s):  
Hong Da Shi ◽  
Shui Yu Li ◽  
Dong Wang
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Diffraction Theory ◽  
Wave Force ◽  
Source Distribution ◽  
Wave Forces ◽  
Linear Wave ◽  
Wave Loads ◽  
Distribution Method ◽  
Motion Responses

The dynamic characteristics of large-scale tunnel element are very important for the process of immersion. In the paper, the motions and stress of the element under wave actions were studied. The linear wave diffraction theory and the three-dimensional source distribution method were applied to calculate the wave loads and motion responses of the tunnel element under different incident wave conditions. In the study, there have no cable on the element. On the basis of the above theories, the stress and the motions of the element were studied. The first order wave forces and the second order wave force were deduced, and the motions equation was made.

Calculation and Analysis of Components of Added Resistance of Ships in Waves

2015 ◽  
Author(s):  
Hong Liang ◽  
Zhu Chuan ◽  
Miao Ping
Keyword(s):  
Frequency Domain ◽  
Present Method ◽  
Three Dimensional ◽  
Wave Resistance ◽  
Source Distribution ◽  
Ship Motions ◽  
Hydrodynamic Coefficients ◽  
Added Resistance ◽  
Distribution Method ◽  
Different Types

Ship motions and its hydrodynamic coefficients are solved by three dimensional frequency domain potential theories with a translating and pulsating source distribution method. Furthermore, components of added wave resistance of ships advancing in waves due to the radiation and diffraction waves are obtained respectively. Added wave resistances of Wigley III hull and S175 containership with various forward speeds are carried out and analyzed in frequency domain. The numerical results are validated for the models by comparing them with experimental data. Its percentage of components of the total ship added wave resistance varying with frequency is investigated and discussed. The present method provides a rapid and efficient approach to predict added resistance of different types of ships in waves.

The Prediction of the Added Resistance for the Trimaran Ship With Different Side Hull Arrangements in Waves

2009 ◽  
Vol 53 (04) ◽  
pp. 227-235
Author(s):  
Ming-Chung Fang ◽  
Yi-Chin Wu ◽  
Deng-Kai Hu ◽  
Zi-Yi Lee
Keyword(s):  
Steady State ◽  
Steady Flow ◽  
Three Dimensional ◽  
Prediction Method ◽  
Source Distribution ◽  
Added Resistance ◽  
Distribution Method ◽  
Related Data ◽  
Head Waves ◽  
Flow Potential

In this paper, a second-order steady-state approach and a three-dimensional pulsating source distribution method are applied to derive the added resistance on a trimaran ship advancing in waves. The added resistance treated here is the secondorder steady-state hydrodynamic force, which can be expressed as products of the ship-motion responses, the radiation potential, diffraction potential, and the incident wave potential, and all related velocity potentials are in three-dimensional form. The steady flow potential is also included in the motion response calculation to investigate its effect on the added resistance. In order to validate the prediction method, the experiments for measuring the added resistance of a trimaran model in head waves were also handled in a National Cheng Kung University (NCKU) towing tank, and the related data are adopted to compare with the theoretical results. The comparisons show that the prediction results obtained in the paper generally agree well with experimental data; the validity of the prediction method applied here can be regarded as acceptable, and the effect of the steady flow potential on the added resistance of the trimaran ship can be neglected.

A Numerical Investigation on Hydrodynamic Interaction Coefficients for a Group of Truncated Composite Cylinders Floating in Waves

2021 ◽  
Author(s):  
Mir Tareque Ali
Keyword(s):  
Hydrodynamic Interaction ◽  
Three Dimensional ◽  
Computer Code ◽  
Source Distribution ◽  
Floating Body ◽  
Body System ◽  
Floating Bodies ◽  
Interaction Coefficients ◽  
Distribution Method ◽  
Multi Body

Abstract When a group of bodies are floating closely in waves, the fluid loading on these bodies will be influenced due to the presence of the neighboring bodies. The wave loading on each of these bodies are affected, because of the sheltering or wave-reflection effects due to the presence of surrounding floating bodies, while additional loads are exerted by the radiated waves produced by the motions of the nearby floating bodies. For a multiple floating body system, it is important to precisely compute the hydrodynamic interaction coefficients, since these parameters will be used later to solve the 6xN simultaneous equations to predict the motion responses (where N is the number of freely floating bodies in the multi-body system). On the other hand, the hydrodynamic interaction coefficients are absent for an isolated floating body case. This paper investigates the hydrodynamic interaction coefficients for a group of three dimensional (3-D) bodies floating freely in each other’s vicinity. Since the nature of hydrodynamic interaction is rather complex, it is usually recommended to study this complicated phenomenon using numerically accurate scheme. A computer code developed using 3-D source distribution method which is based on linear three-dimensional potential theory is used and the validation of the computer code has been justified by comparing the present results with that of the published ones for the hydrodynamic interaction coefficients of multiple bodies. The agreement between the calculated results with those of the published ones is quite satisfactory. Numerical simulations are further conducted for a group of identical truncated composite circular cylinders floating vertically at close proximity in regular waves. During the computations of hydrodynamic interaction coefficients of this multi-body model for different groups, the number of members in the group as well as the gap width among them has been varied. The paper also examines the occurrence of hydrodynamic resonances in the gap among the floating bodies and the presence of spikes with rapid fluctuation in the results of the diagonal and coupling terms for interaction coefficients. Finally, some conclusions are drawn on the basis of the present analysis.

Shallow-Water Effect on the Motions of Three-Dimensional Bodies in Waves

1987 ◽  
Vol 31 (01) ◽  
pp. 34-40
Author(s):  
Hideichi Endo
Keyword(s):  
Green Function ◽  
Shallow Water ◽  
Three Dimensional ◽  
Source Distribution ◽  
Linear Wave ◽  
Water Effect ◽  
Surface Source ◽  
Distribution Method ◽  
The Green Function ◽  
Shallow Water Effect

The motions of three-dimensional bodies of arbitrary shape freely floating in waves in shallow water are studied. The wave loads on and hydrodynamic forces of a rigid body are calculated by applying the surface source distribution method (Green's function method) in the framework of linear wave potential theory. Special attention is paid to the numerical evaluation of the Green function for finite water depth; namely, an improper integral containing a singularity in the Green function is obtained by Gauss-Laguerre quadrature, and the ∫1 lr* ds term obtained is by numerical quadrature. Computational results of wave exciting forces, hydrodynamic coefficients, and motions of freely floating structures in shallow and deep water are compared with those obtained in the literature. Furthermore, the shallow-water effect on the motions of a large structure is examined.

scholarly journals A Proof-of-Concept Algorithm for the Retrieval of Total Column Amount of Trace Gases in a Multi-Dimensional Atmosphere

2021 ◽  
Vol 13 (2) ◽  
pp. 270
Author(s):  
Adrian Doicu ◽  
Dmitry S. Efremenko ◽  
Thomas Trautmann
Keyword(s):  
Trace Gases ◽  
Three Dimensional ◽  
Principal Component ◽  
Radiative Transfer Model ◽  
Computational Time ◽  
Transfer Model ◽  
Proof Of Concept ◽  
Discrete Ordinate ◽  
Distribution Method ◽  
Total Column

An algorithm for the retrieval of total column amount of trace gases in a multi-dimensional atmosphere is designed. The algorithm uses (i) certain differential radiance models with internal and external closures as inversion models, (ii) the iteratively regularized Gauss–Newton method as a regularization tool, and (iii) the spherical harmonics discrete ordinate method (SHDOM) as linearized radiative transfer model. For efficiency reasons, SHDOM is equipped with a spectral acceleration approach that combines the correlated k-distribution method with the principal component analysis. The algorithm is used to retrieve the total column amount of nitrogen for two- and three-dimensional cloudy scenes. Although for three-dimensional geometries, the computational time is high, the main concepts of the algorithm are correct and the retrieval results are accurate.

scholarly journals Drops bouncing off macro-textured superhydrophobic surfaces

2017 ◽  
Vol 824 ◽  
pp. 866-885 ◽  
Author(s):  
Ali Mazloomi Moqaddam ◽  
Shyam S. Chikatamarla ◽  
Iliya V. Karlin
Keyword(s):  
Contact Time ◽  
Numerical Study ◽  
Three Dimensional ◽  
Superhydrophobic Surfaces ◽  
Nonlinear Behaviour ◽  
Textured Surfaces ◽  
Texture Density ◽  
Wide Range ◽  
Quantitative Manner ◽  
The Impact

Recent experiments with droplets impacting macro-textured superhydrophobic surfaces revealed new regimes of bouncing with a remarkable reduction of the contact time. Here we present a comprehensive numerical study that reveals the physics behind these new bouncing regimes and quantifies the roles played by various external and internal forces. For the first time, accurate three-dimensional simulations involving realistic macro-textured surfaces are performed. After demonstrating that simulations reproduce experiments in a quantitative manner, the study is focused on analysing the flow situations beyond current experiments. We show that the experimentally observed reduction of contact time extends to higher Weber numbers, and analyse the role played by the texture density. Moreover, we report a nonlinear behaviour of the contact time with the increase of the Weber number for imperfectly coated textures, and study the impact on tilted surfaces in a wide range of Weber numbers. Finally, we present novel energy analysis techniques that elaborate and quantify the interplay between the kinetic and surface energy, and the role played by the dissipation for various Weber numbers.

The Effect of the Steady Flow Potential on the Motions of a Moving Ship in Waves

2000 ◽  
Vol 44 (01) ◽  
pp. 14-32
Author(s):  
Ming-Chung Fang
Keyword(s):  
Steady Flow ◽  
Present Method ◽  
Three Dimensional ◽  
Source Distribution ◽  
Series Expansions ◽  
Ship Motions ◽  
Double Integral ◽  
Flow Potential ◽  
Principal Value ◽  
Good Agreement

A three-dimensional method to analyze the motions of a ship running in waves is presented, including the effects of the steady-flow potential. Basically, the general formulations are based on the source distribution technique by which the ship hull surface is regarded as the assembly of many panels. The present study includes three algorithms for treating the corresponding Green function:the Hess & Smith algorithm for the part of simple source I/r,the complex plane contour integral of the Shen & Farell algorithm for the double integral of steady flow, andthe series expansions of the Telste & Noblesse algorithm for the Cauchy principal value integral of unsteady flow. The study reveals that the effect of steady flow on ship motions is generally small, but it still cannot be neglected in some cases, especially for the ship running in oblique waves. The effect also depends on the fore-aft configuration of the ship. The results predicted by the present method are found to be in fairly good agreement with existing experiments and other theories.

Evaluation of science and mathematics books used for students with visual impairment in inclusive classrooms in Tanzania

2021 ◽  
pp. 026461962110364
Author(s):  
Francis William
Keyword(s):  
Secondary Schools ◽  
Visual Impairment ◽  
Special Needs ◽  
Three Dimensional ◽  
3D Models ◽  
Inclusive Classrooms ◽  
Qualitative And Quantitative ◽  
Limited Knowledge ◽  
And Mathematics ◽  
Quantitative Approaches

This study evaluated the adapted science and mathematics books for students with visual impairment in inclusive classrooms in Tanzania secondary schools. It was conducted in 14 regions using qualitative and quantitative approaches. Data were generated from a sample of 19 heads of school, 103 students, and 77 teachers. The findings of the study show that the books are appropriate for students with visual impairment. However, they lacked enough tactile illustrations and pictures. Further findings revealed that lack of braille knowledge among some teachers limited them from using the books. As such, a few teachers who had braille knowledge had started to use the books while those with limited knowledge did not. Most teachers reported lack of appropriate pedagogy for handling special needs in inclusive classrooms. Therefore, although the books are appropriate, a lot needs to be desired in building teachers’ capacity to use the books. Various inclusive methodological knowledge to teachers needs to be ensured. Furthermore, the books must be improved to include more tactile graphics and pictures to make them more reader-friendly for students with visual impairment. Other educational books, including three-dimensional (3D) models, should be part of the adapted books.

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