Analysis of the Motion Response of Trimaran Based on Directional Spectrum

2016 ◽  
Author(s):  
Shuzheng Sun ◽  
Hui Sun ◽  
Jide Li ◽  
Xiyang Liu ◽  
Wenlei Du
Keyword(s):  
Wave Theory ◽  
Operating Conditions ◽  
Analysis Method ◽  
Towing Tank ◽  
Motion Response ◽  
Directional Spectrum ◽  
Irregular Wave ◽  
Motion Responses ◽  
Seakeeping Performance ◽  
Comparison Of The Results

The seakeeping performance of trimaran is crucial to its design and development. A series of trimaran model tests for seakeeping performance are conducted in towing tank. Directional spectrum theory and long-crested wave theory are introduced to the spectrum analysis method so as to analyze the motion response of trimaran. The comparison of the results gaining from two theories and those achieving from the long-crested irregular wave tests is carried out. By statistical analysis, there is a big difference between the motion responses of trimaran according to different wave theories in several operating conditions. The characteristics of trimaran motion responses under different course angles are studied. Compared with long-crested wave theory, directional spectrum theory is introduced as a more accurate approach to research the seakeeping performance of trimaran.

scholarly journals Investigation of Focused Wave Impact on Floating Platform for Offshore Floating Wind Turbine: A CFD Study

2019 ◽  
Author(s):  
Yang Zhou ◽  
Qing Xiao ◽  
Yuanchuan Liu ◽  
Atilla Incecik ◽  
Christophe Peyrard
Keyword(s):  
Potential Theory ◽  
Wave Theory ◽  
Second Order ◽  
Floating Platform ◽  
Wave Impact ◽  
Pitch Motion ◽  
Irregular Wave ◽  
Wave Parameters ◽  
Motion Responses ◽  
Focused Wave

Abstract Most existing research related to a semi-submersible offshore floating platform focuses on the wave-structure interaction under either a regular or irregular wave condition. In order to numerically model the irregular wave impact on a semi-submersible platform hydrodynamic response with a low computational cost, in this study, a focused wave is utilized. The platform under this consideration is the DeepCwind semi-submersible platform. A high fidelity CFD numerical solver based on solving Navier-Stokes equations is adopted to estimate the dynamic response and the hydrodynamic loading of the platform. The focused wave is firstly generated based on a first order irregular wave theory in a numerical wave tank and validated against the linear wave theory results. Next, for CFD coding validation, the surface elevation of a fixed FPSO model associated with a focused wave is calculated and compared with the benchmark results. At last, the dynamic responses of the platform are numerically simulated under various focused wave parameters, and the results are compared with those obtained from an in-house potential flow theory tool at Électricité de France (EDF). It is found that the predicted CFD surge motion responses are close to those achieved with the second order potential theory while differ from the results obtained using linear potential theory. As to the pitch motion, differences are observed between two results, due to the different methods used for second order loads and viscous effects calculation. Turning to the results under different wave parameters, the surge and heave motion responses increase as the wave period goes up. However, the pitch motion is not affected significantly by varying wave periods. It may be due to the fact that the low-frequency effects have limited impact on the pitch motion. The strong nonlinearity at extremely large wave amplitude will be the task in our near future study.

Interaction Between Two Closely Spaced Azimuthing Thrusters

1998 ◽  
Vol 42 (01) ◽  
pp. 15-32 ◽  
Author(s):  
Paul Brandner ◽  
Martin Renilson
Keyword(s):  
Mathematical Model ◽  
Satisfactory Agreement ◽  
Vehicle Dynamics ◽  
Operating Conditions ◽  
Towing Tank ◽  
Empirical Relations ◽  
Series Of Experiments ◽  
Flow Effects ◽  
Semi Empirical

To assist in predicting the performance of omni-directional propelled vehicles a series of experiments has been conducted to measure the interaction between two closely spaced ductedazimuthing thrusters. The thrusters were tested below a shallow draft ground board in a towing tank at a spacing of approximately 2 propeller diameters. Measurements were made of forces acting on a single thruster for a range of operating conditions and similarly on two thrusters for a range of relative positions. The results show that forces from the trailing thruster are heavily affected by interaction, particularly due to impingement of the race from the leading thruster, where as forces from the leading thruster remain essentially unaffected despite its proximity to the trailing thruster. A semi-empirical mathematical model suitable for simulation of omni-directional vehicle dynamics is presented. The model is based on the trajectory of the race from the leading thruster derived from momentum considerations with additional empirical relations to account for other more minor flow effects. Comparison of the predicted and measured results show satisfactory agreement.

Influence of Longitudinal Roughness on Friction in EHL Contacts

2004 ◽  
Vol 126 (3) ◽  
pp. 473-481 ◽  
Author(s):  
B. Jacod ◽  
C. H. Venner ◽  
P. M. Lugt
Keyword(s):  
Numerical Simulations ◽  
Operating Conditions ◽  
Simplified Approach ◽  
Curve Fit ◽  
Longitudinal Roughness ◽  
Wide Range ◽  
Equivalent Wave ◽  
Harmonic Components ◽  
Comparison Of The Results ◽  
Relative Friction

The effect of longitudinal roughness on the friction in EHL contacts is investigated by means of numerical simulations. In the theoretical model the Eyring equation is used to describe the rheological behavior of the lubricant. First the relative friction variation caused by a single harmonic roughness component is computed as a function of the amplitude and wavelength for a wide range of operating conditions. From the results a curve fit formula is derived for the relative friction variation as a function of the out-of-contact geometry of the waviness and a newly derived parameter characterizing the response of the lubricant to pressure variations. Subsequently, the case of a superposition of two harmonic components is considered. It is shown that for the effect on friction such a combined pattern can be represented by a single equivalent wave. The amplitude and the wavelength of the equivalent wave can be determined from a nonlinear relation in terms of the amplitudes and wavelengths of the individual harmonic components. Finally the approach is applied to the prediction of the effect of a real roughness profile (many components) on the friction. From a comparison of the results with full numerical simulations it appears that the simplified approach is quite accurate.

scholarly journals A comparative review of the resistance of a 37,000 dwt Chemical Tanker based on experimental tests and calculations

2020 ◽  
Vol 1 ◽  
pp. 59-66
Author(s):  
Liviu Crudu ◽  
Radu Bosoancă ◽  
Dan Obreja
Keyword(s):  
Energy Efficiency ◽  
Experimental Tests ◽  
Full Scale ◽  
The Other ◽  
Towing Tank ◽  
Ship Resistance ◽  
Comparative Review ◽  
Cfd Applications ◽  
Energy Efficiency Design Index ◽  
Comparison Of The Results

The evaluation of ship resistance is of paramount importance having a decisive impact on the economic performances and efficiency depending on mission. If new IMO requirements through the Energy Efficiency Design Index (EEDI) are taken into account the necessity to have more and more accurate tools capable to consider the influences of different parameters became mandatory. The availability of towing tank facilities and the full scale trials are the practical means in order to be able to confirm the accuracy of theoretical formulations and to define the limits of CFD applications. Based on the results of the towing tank tests, a direct comparison with the results provided by classical methods and CFD computations can be systematically can be performed. On the other hand, the influences of the modifications operated on the fore part of the ship aretheoretically evaluated and compared with the towing tank results. Consequently, the paper is focused on the comparison of the results evaluated using different tools which have been carried out for a Chemical Tanker built by Constanta Shipyard Romania.

Effect of Shallow Water on a Mathematical Hull at High Subcritical and Supercritical Speeds

1986 ◽  
Vol 30 (02) ◽  
pp. 85-93
Author(s):  
A. Millward ◽  
M. G. Bevan
Keyword(s):  
Shallow Water ◽  
Wave Theory ◽  
Hull Form ◽  
Towing Tank ◽  
Resistance Peak ◽  
Good Agreement ◽  
Made In

Experiments have been made in a towing tank to measure the resistance of a mathematical hull form in deepwater and in shallow water at high subcritical and supercritical speeds. The data have been compared with calculations using linearized wave theory for the same hull shape. The results have shown fairly good agreement, with the greatest differences occurring near the subcritical resistance peak.

Evaluation of a Small and Fast Planing Boat’s Seakeeping Performance at the Design Stage

2015 ◽  
Author(s):  
Dong Jin Kim ◽  
Sun Young Kim
Keyword(s):  
Model Tests ◽  
Full Scale ◽  
Scale Model ◽  
Design Stage ◽  
Small Scale ◽  
Irregular Wave ◽  
Seakeeping Performance ◽  
Head Waves ◽  
Scale Ratio ◽  
Free Running

Seakeeping performance of a planing boat should be sufficiently considered and evaluated at the design stage for its safe running in rough seas. Model tests in seakeeping model basins are often performed to predict the performance of full-scale planing boats. But, there are many limitations of tank size and wave maker capacity, in particular, for fast small planing boats due to small scale ratio and high Froude numbers of their scale models. In this research, scale model tests are tried in various test conditions, and results are summarized and analyzed to predict a 3 ton-class fast small planing boats designed. In a long and narrow tank, towing tests for a bare hull model are performed with regular head waves and long crested irregular head waves. Motion RAOs are derived from irregular wave tests, and they are in good agreements with RAOs in regular waves. Next, model ships with one water-jet propulsion system are built, and free running model tests are performed in ocean basins. Wave conditions such as significant heights, modal periods, and directions are varied for the free running tests. Motion RMS values, and RAOs are obtained through statistical approaches. They are compared with the results in captive tests for the bare hull model, and are used to predict the full-scale boat performances.

Flexibility of Seakeeping Simulation Tools for Landing Craft Hullforms

2017 ◽  
Author(s):  
Kevin Silva ◽  
Andrew Silver ◽  
Kenneth Weems ◽  
David Wundrow ◽  
Sheguang Zhang
Keyword(s):  
Surface Effect ◽  
Water Jet ◽  
Operating Conditions ◽  
Physical Models ◽  
Simulation Tools ◽  
Test Conditions ◽  
Seakeeping Performance ◽  
Surface Effect Ship ◽  
Analytical Tools ◽  
Large Amplitude Motion

As the operational requirements of landing craft expand to faster speeds and higher sea states, more complex hullforms are being proposed to meet these requirements. The seakeeping performance of such vessels can become difficult to predict. Analytical tools must be flexible in order to handle the variety of operating conditions, hull geometries, loading conditions, and other attributes. The analytical seakeeping models should be based on the physical models of the hydrodynamic phenomena rather than case-specific empirical tuning. This paper describes a study that evaluated the ability of the Large Amplitude Motion Program (LAMP) to simulate traditional and non-traditional landing craft hullforms in varying operating conditions. The hullforms include a traditional semi-planing monohull, a semi-planing water jet propelled “W” shaped hull, a water jet propelled catamaran, and a catamaran Surface Effect Ship (SES) style hull. The measures taken to model each hullform and test conditions in LAMP are discussed and the correlation between experimental data and LAMP predictions are presented through comparisons of motions and accelerations.

Response Time of Forested Mountainous Watersheds in Humid Regions

2000 ◽  
Vol 31 (3) ◽  
pp. 149-168 ◽  
Author(s):  
A. Loukas ◽  
N. R. Dalezios
Keyword(s):  
Field Experiments ◽  
Time Lag ◽  
Wave Theory ◽  
Roughness Coefficient ◽  
Stream Channel ◽  
Stream Channels ◽  
Mountainous Watersheds ◽  
Two Phases ◽  
Comparison Of The Results ◽  
Estimation Of Time

This study proposes an analytical method for the estimation of time lag for forested mountainous watersheds. The water flow in a watershed is separated and analyzed in two phases, the land or hillslope phase and the stream channel phase. In many areas around the globe the flow in a forested high gradient watershed is generated through subsurface pathways as several field experiments have shown. The kinematic wave theory is used to describe the generation of flow from steep forested hillslopes. This hillslope runoff is, then, used as input to the stream channels. The equations were developed by assuming kinematic conditions in the stream channel and that the stream slope and the roughness coefficient i) vary according to a second order polynomial with the distance from the mouth of the watershed, ii) vary linearly with the distance from the outlet of the watershed, and iii) are constant throughout the watershed. Comparison of the results of the proposed equation with data from two experimental watersheds in Coastal British Columbia indicates that the three expressions of the proposed equation, even the simplest one assuming constant stream slope and roughness coefficient, are reliable and give good approximation of the observed time lag.

Numerical Study on Seakeeping Performance of a Damaged Ship

2019 ◽  
Author(s):  
Lu-Ning Cui ◽  
Yi Zheng ◽  
Yinggang Li ◽  
Ling Zhu ◽  
Mingsheng Chen
Keyword(s):  
Numerical Study ◽  
Rolling Motion ◽  
Wave Direction ◽  
Regular Waves ◽  
Motion Responses ◽  
Seakeeping Performance ◽  
Property Losses ◽  
Hull Damage ◽  
Wave Induced ◽  
Damaged Ship

Abstract Ships sailing in the sea may encounter collision, grounding or projectile impacting accidents, which may cause hull damage and subsequent compartment flooding. Due to the effect of the flooding water induced moment and the restoring moment, the damaged ship may have inclination and rolling motion. When the inclination or the rolling motion is too large, it may affect the safety and survivability of ship in navigation and cause severe casualties and property losses. In order to increase the navigation safety and survivability of the damaged ship, a numerical model is established based on the potential flow theory to investigate the seakeeping performance of the damaged ship in two scenarios, i.e., the case before ship damaged, and the case when the damaged ship reaching a relatively stable floating state. The heave, pitch and roll motion responses and corresponding wave-induced loads acting on the ship are analyzed in regular waves. In addition, the effects of the navigation speed and the wave direction on the seakeeping performance are also investigated.

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