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What is the viscous damping percentage of critical damping for twin hull vessels such as swath, catamaran etc?
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Hi Mohamed,
Did you find an answer to this? If so I would be interested in what that was.
Thanks,
Ali
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Currently I'm working on a project related surface ship simulation. We need to simulate a plenty of ship types. I modeled propeller, rudder etc. But hydrodynamic forces are modeled as hyrodynamic derivatives (hyrodynamic coefficients, maneuvering coefficients ). For some ships, we generate our hyrodynamics data, but as I said, we need lot more. We dont want to spend time on CFD. We need direct data of Hydrodynamic of some ships. Is there such a company/institute/university/organization etc.? Any suggestion?
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Thanks for your contribution Liliia Kondratieva .
"How many variable input values do you have for creation of necessity data? " I did not get this question . I think, you mean the test data. If so, I don't have any :) That's point though. If I had some test data of some ships (turning circle, accelration, zig-zag, pullout,...) I could make an parameter identification.
I need all coefficients (lets say 4DOF, not 6DOF). There are papers for some. Example:
Ex: Son, K. H. and Nomoto, K. (1981). On the Coupled Motion of Steering and Rol ling of a High Speed Container Ship, J.S.N.A., Japan, Vol. 150
But I need a lot more.
The data you supplied, for which ship are they?
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Hi everyone,
I am trying to simulate turning circle and zig-zag maneuvering tests for a mariner class vessel using Star CCM+ (hull, rudder, and propeller come into the picture) using a set of overset meshes. I have made a few attempts and not yet succeeded. I would like to know if anyone in the community has done it or attempted it. If yes, kindly give me some suggestions.
Thank you.
Following links will be helpful.
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For simulate this, if surge ignored, you can use morphing mesh But it is very slow. for Zig Zag motion you need to define 2 DFBI, one for body and one for rudders, and then in angular velocity for rudders, you can define Sin field functions. attention if your surge velocity assigns to DFBI, in second DFBI you need also to define translation velocity as well as first DFBI.
Best Regards
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Which analysis could use for this problem?
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hi Iarly Vanderlei da Silveira
please call me in: seyed.reza.991@gmail.com
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I am using conformal mapping for calculating hydrodynamic coefficients but yet i have no good result. i am using c++ for writing conformal mapping code.
if there is a person that has used this method i have some questions.
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with hardship and trusting in god
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I am struggling to find any experiments which correctly satisfy the above question. I have looked through many online papers as well as various text books and papers in the university library. Any advice would be much appreciated!
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You can perform forced oscillation at any period requested using a hydraulic or electric moving arm forcing a vertical sinusoidal motion
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I'm looking for reference and formulae widely used for calculating emission of NOx and SOx in marine diesel engine, medium speed mainly
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The SOx emission depends on the sulfur content of the oil and not on the load of the engine. Hence you can calculate this easily with a mass balance. For NOx you will need a suitable model for the combustion process which is more difficult to deduce. At least you can look for some data in the literature to get an idea of how many NOx approximately you will have.
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I need information about the propeller used with the hull DTMB 5415. I need the 3-D geometry if possible.
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Dear Ali
Sorry but I cannot; I left DTMB 4 years ago, and in addition never did any work with propellers
Francis
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I am simulating flow over an elliptic cross-section at Re = 150. And by analyzing the time series of the transverse forces I calculate the vortex shedding frequency. My results indicate that as the thickness to cord length ratio decrease the shedding frequency increase. However the frequency peaks and begins to decline when the t/c ratio is less than 1/sqrt(2).  My questions therefore are as followed:
1) Is it correct that the vortex shedding should increase when the thickness to cord length ratio decreases.
2) Is there a thickness to cord length ratio for which the shedding frequency will peak, and further decrease will cause the shedding to drop.
I am grateful for any feedback on the matter. And apologizes for presenting a problem about fundamental knowledge.
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Thank you for your feedback.   I define my Reynolds number on the thickness of the ellipse, which I keep constant. After reading some articles  thoroughly I discovered that they define their Reynolds number based on the cord length, which is kept constant. This lead to two different Reynolds numbers, and my results compared much better to literature when recalculating my Reynolds numbers to their standards.
Mr Weymouth.  your claim that the Strouhal number is less consistent at lower Reynolds numbers is of interest. And it will most helpful to explain why my lower Reynolds numbers does not follow the same trends as seen for the range 10³-10⁵. If any literature where this is stated comes to mind please let me know. 
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Fixed seat rowing introduces pitching and heaving motions, especially at the start of the recovery, as well as a surge. How does the magnitude of the thus added resistance compare to the linear motion resistance at the mean speed? Is anyone aware of research into the dynamics and resistance associated with fixed seat rowing? Rudimentary experiments with an 8 oarsmen open water fixed rowing boat showed a longitudinal "surge" of +/- 15% compared to the average rowing speed.
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There have been several attempts to measure and model the effects of surge, and other motions in sliding-seat rowing. I don't know of any that have been made with fixed-seat rowing.
Day et al used the unsteady form of Michell's thin-ship theory to estimate wave resistance. The theory was quite successful at low stroke rates, but was very poor for the rates typically used in Olympic class events.
See:
Day A., Campbell I., Clelland D., Doctors L.J., Cichowicz J.,
"Realistic evaluation of hull performance for rowing shells, canoes, and kayaks in unsteady flow",
J Sports Sci. 2011 Jul;29(10):1059-69. doi: 10.1080/02640414.2011.576691.
The theory might be useful for fixed-seat rowing because the stroke rates are typically far lower than with sliding seats.
I released a (free) program named FIRM that allows users to model fixed- and sliding seat rowing. See:
The program accounts for the effects of hull motions on the wave resistance and viscous drag of the hulls for all Olympic classes of rowing (singles to eights).
Another alternative is to use a CFD code. There have been a few attempts to do this with kayaks, canoes and rowing, but I don't know if they have been used with fixed-seat rowing.
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I used to different methods to #control pressure in pump unit in #Power-take off system in #WEC. Obviously, the overall performance of the system is different.
I appreciate if you send me an article comparing two different control approaches applied for a same model.
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Dear Mojtaba
I recommend you two article entitled: "An overview of control performance assessment technology and industrial applications" and "Control performance assessment for nonlinear systems".
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I know added mass should taken into account, so undamped eigenfrequency can be calculated, but how to deal with damping? Is depth of water an important parameter?
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I hope that you already found a solution since it has been almost a year since your question. There are several well accepted software tools used in industry for marine structures (jackets). Depending on the site conditions there will be an interest for either wave - wind - current loading condition or seismic ground motion induced loads. From Kasiphon K comment you will see that soil induced damping if far higher than hydrodynamic. I believe today you can model fully "interconnected" jacket - foundation analysis with soil - structure interaction tools available through commercial software (SACS, Abaqus, etc).
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When the ratio D/6 for 2 inch sch. XXS pipeline is estimated, it was found greater than the pipeline thickness , which implies that more consideration should be required rated to theory of failure as in ASME B31.3. So I want to know, the reason to consider the ratio D/6 as the  limiting ration in such calculation
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Thanks Sirous , I want a clarification about your appreciated answer ,
Firstly, as per ASME B31.3: ,for, t ≥ D/6 : Y = (d + 2c)/(D+d+2c), it is not clear in the code that is  still valid to use the thickness equation only with calculated  Y coefficient without changing in the remaining  terms ,or there is another equation ,and if not can you please send me UK code covering this issue?.
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Dear all,
I would like to read about the turbulence intensity differences between onshore and offshore. Therefore would you please recommend me any papers to read.
I appreciate your kind support.
Regards,
Teklehaimanot
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You could also refer to trends of turbulence intensity deduced during experimental works. We carried out some investigation in a wave channel at our lab, for both cases of regular and irregular waves. If interested, try the following link
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I am studying the effect of design coefficients in the establishment of hull design. I am overwhelmed with all the information available, but I fail to find practical design guides...at least in what I've been able to download...perhaps someone with more experience can steer me in the right direction? ...I would be very grateful...meanwhile - Happy New Year to all my fellow colleagues out there...Gene.
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Additional to the very good recommendations you already got, there is a classic by German authors:
Ship design for efficiency and economy,
Herbert Schneekluth ; Volker Bertram
2. ed., Oxford [u.a.] : Butterworth-Heinemann, 1998
More general point to enter the topic could be:
Basic Ship Theory (Vol. 1 & 2)
K.J. Rawson ; E.C. Tupper
5. ed., Oxford [u.a.] : Butterworth-Heinemann, 2001
or as an introduction:
Practical ship design
David G. M. Watson
1. ed., Amsterdam [u.a.] : Elsevier, 1998
If you are interested rather in small crafts, I liked this book (eventhough outdated):
The Naval Architecture of Small Craft, D. Phillips-Birt, Hutchinson scientific & technical, 1957
Have fun!
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There have been some empirical calculation of roll damping for monohull already. However these simple prediction formulas are not suitable for catamaran. Can I use these formulas to predict a catamaran's viscous dampening? If not, how can I predict it in a simple way?
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I think the book below is a very useful for you if you wish to understand the hydrodynamics of catamaran
"Molland and Trunock, Ship Resistance and Propulsin, Camb. Univ. Press".
However, if you can't go for experimental tests it is better to use CFD to study the viscous damping of your unit.
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Offshore jacket structures are supported on steel piles. Is there any criteria regarding the maximum permissible lateral deflection or rotation of the pile at mudline specified in design codes?
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No explicit criteria are provided for deflection in standards. Some infromation can be found in API RP 2A / 2GEO or Iso 19901 series.
Traditional procedure is to perform global analysis of the jacket structure considering foundations with PY curves and superstructure and to check final results w.r.t geotechnical strength and structural strength, not forgetting group action for the foundation part.  
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Hello experts,
I'm trying to apply one-step nonlinear model predictive control (NMPC) for 3 degree of freedom nonlinear model of the ships(the system is nonlinear affine). The state weighting matrix  is selected to be diagonal. The problem i face is that the controller can not track the position states due to the zeros corresponding to them in the control matrix g(x) (see the attachment). 
i think changing the matrix Q, may lead to a solution but i couldn't do that by trail and error and i don't know any technique for selecting it.
Thanks in advance
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As a general advice I would say: when you are setting your MPC problem up you should choose your weighting matrices based on the following criteria:
- stability and feasibility of the underlying problem should be achieved. 
- elements of the weighting matrices should be first normalized and then magnified based on their importance.
Generally for the first criterion there is no solid theory in the context of "NMPC" based on my best knowledge, although some results may be found in the literature.
Regarding the second factor the simplest way is to consider physical features of all states and obtain the maximum and minimum values they will achieve in the normal operations. Alternatively, you can first design a simple controller (e.g. PID) and run the system in different points, then you can estimate min/max of each state. Finally, you can first normalize all states and so on....
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Currently i'm working on issues related to high-speed craft design; I'm wondering how do Maxsurf  modules like MaxSurf { modeler, stability, structure, motion, resistance, etc} handle errors(I don't only use Maxsurf modeler) , I mean is there a report or research about each modules error ranges in real world projects and in practice? any help or suggestions would be appreciated;
btw thanks in advance;
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Maxsurf software is very good, but my advise for resistance the program is simply estimate the resistance and not so accurate. It better to use CFD for the resistance analysis. 
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I have used "Hydrodynamics of High-Speed Marine Vehicles by Faltinsen". I need some numerical examples.
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It is too wide definition of a ship. As a minimum, you need for the ship type selection, dimension correlation and shape of hull(s). 
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I have drift QTFs for a vessel estimated in a water depth using a hydrodynamic software (linear). Now I would like to estimate drift QTF for the same vessel but for significantly different water depth. Is there any simple 'good' way to do this without running the analysis since I don't have the model? any references? Thanks
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In my bachelor thesis I studied with fluent program and appropriate boundary conditions gave me approximate results. But I only studied with ships. If you are researching a submarine or some vessel in deep sea, you have to analyse the vessel like an obstacle in a pipe.
Regards.
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I want to do some calculations for two diesel engines drive a ship propeller through a gearbox. I want to know the speed reduction ratio, total inertia of the system, torque ratio, etc.
I know that the power delivered at the propeller which rotates at 150 rpm will be equal to the sum of power of the two engines running at 750 rpm.
P(load) = 2*p(eng)
T(laod) * 150 = 2*750*T(eng)
Is the speed reduction ratio is different from torque ratio ? is (2*750)/150 the correct reduction ratio ? or it is just 750/150 ?
Also, to model the shaft dynamics, i will use the following equation:
2*pi*Inertia of rotating parts*(dn/dt)= T(eng) - T(propeller) - T(friction)
The total system inertia at the shaft = inertia of propeller including entrained water + shaft + gearbox + engine inertia*(reduction ratio^2) ???? 
Many Thanks in advance
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Assuming same speed of both engines, same speed ratio and same orientation of the torque, the torque of both engines add up, meaning you are right.
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I have a PhD student working on developing a model for estimating overhead cost of building ships.  He has many good papers but they all date to 1990s and early 2000s. He needs more recent papers on ABC and their advantages on conventional cost systems and models. Thank you. 
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REZA:
GARY has provided you with his work -- and this may be all  you require.  However, you might also consider simply contacting the earlier authors -- by phone or e-mail and ask if they have any suggestions [Gary has given you what he had, so the other authors remain to "chase."}  This technically-termed  "informal literature search" approach is often surprisingly effective.  Personally, however,  I have found it usually more effective to first do a "formal literature search" that is aimed at articles that have cited the  either the earlier articles at hand, or those provided by Gary.    Looking at these in turn, you may then identify cites of their work and further continue until you have citations and even pre-prints of work in press.   This "follow-the-citations-forward" process is well-known to research librarians (aka, "Information Scientists")....                                                                                                              One way to start the process is to Google the word Scholar  and in the resulting scholar related articles find and open "Google Scholar."   When this is opened, then type in the authors names for any article you have at hand in the format: Cokins G, Nextauthor H (or whatever).   I did this entering Cokins G and added terms "and up front costs of building ships"   My second result [orders may be slightly different with each person] was that below which is Cited by 114 which you then click-on, and sort through for articles of interest to further click-on...  
ALVAH
[BOOK] Performance management: finding the missing pieces (to close the intelligence gap)
G Cokins - 2004 - books.google.com
... 85 Activity-Based Management Model Design and Principles: Key to Success 98 Operational
(Local) Activity-Based Management for Continuous ... Gary Cokins garyfarrns@aol.com (I welcome
your e-mail.) ... modeling the data into information, and Web-reporting it to users. ...
Cited by 114 Related articles All 3 versions Cite Save More
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I am trying to simulate the Natural circulation loop with rolling motion. How can one incorporate this motion in fluent?
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Hello Mayur,
To model the rolling motion of a ship in Fluent, you either have to use the 6DOF solver inside the solver and define the properties of your vessel (like displacement, moment of inertia etc.) or write a UDF to solve for the fluid-structure interaction between the ship and the surrounding fluid.
I have heard that Star-CCM+ is easier to use for these types of simulations but I have never tried it myself. You might want to learn more about it if you will be doing ship motion simulations a lot in the future.
Good luck with your simulations.
Kemal
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I am trying to understand the vessel motions at sea and what affects them.
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The low-frequency responses are the motions caused mainly by second-order wave loads, current, mean wind component, mooring systems and thrusters.
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i am researching on seakeeping optimization and I want to use BEM for hydrodynamic calculations to find hydrodynamic coefficients.
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u can ask D.r reza, i sure he can help u
have good night
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I have had some luck with the USPTO database searching on "permafrost" but that will not lead, I think, to ship/boats/ etc. technologies.  I think what I really need is to know what the classification numbers might be.  Looked at the 2013 WIPO Indicators publication. I have not gone looking via the Intl Maritime Organization.
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Yes, the broad ways that something could be ice capable was the problem when I looked at the database.  Ice capable fixed structures in the Arctic would be a good category, but that, too, is a giant set of potential technologies.  I'm working on a little paper where I've taken 5 'factors' that two energy experts used in a 2009 article to assess how likely it is the Arctic will get exploited as environmental change moves along. I'm looking at whether any of the factors are further along now than then. I thought the article's factors were general enough to cover lots in the Arctic and they were not specific to energy production.  New technologies might also prove useful for adapting things for those who live there all the time.  Stands to reason that technological adaptation to change would grow fast there.  But it is hard to show that. Any suggestion are welcome.  I have a former student who works North Slope, he's a field engineer.  He's trying to help me think about it, too.  But, I see you have a lot on this.  I'm not an engineer.  Any suggestions would be welcome.
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I want to study design offshore structures including Submarine pipelines and oil platforms in different types.
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Hi Hadi,
Here are a few that may help:
Introduction to Offshore Structures: Design, Fabrication, InstallationOct 1981
by W.J. Graff
Offshore Installation PracticeNov 1987
by J. Crawford
Construction of Marine and Offshore Structures, Third Edition5 Mar 2007
by Ben C. Gerwick Jr
Subsea Pipeline Design, Analysis, and Installation14 Mar 2014
by Qiang Bai and Yong Bai
Good luck!
Luiza
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The simple strip theory does not result in good prediction of  the motions of Surface effect ships. I want to know if there is a generalized strip theory or other procedure for prediction of the motions of surface effect ships(SES)?
Any suggestion is appreciated.
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The air cushion shouldn't be modelled with strip theory. The sidehull hydrodynamics might be modelled with strip theory while a simple mathematical model for the air cushion dynamics (assuming uniform pressure in space) can be included in terms of two extra degrees of freedom (pressure and density) in the equations of motion. The most easily available write-up of this is found in Faltinsen "Hydrodynamics of High Speed Marine Vehicles" (2005), Cambridge Univ. Press.
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We are looking into time series of vertical buoy (Datawell) or radar displacement measurements of the ocean surface and are trying to discriminate between outliers and extreme waves. Has anybody got experience with this task?
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... thanks a lot!
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River-sea ships sail from inner river channels and out to sea. Is it meaningful to account for hydroelastic effects when considering ship design?
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Dear Chi,
For answer this question, firstly we should know when Hydroelasticity is important. Hydroelasticity means that the fluid flow and the structural elastic reaction are considered simulaneously and that we have mutual interaction, that is,
1-The elastic vibrations cause a fluid flow with a pressure field
2-The hydrodynamic loading affects the structural elastic vibration
For study phenomenas due to Hydroelasticity, there is ways and criteria ,for example , Wagner and von Karman methods for slamming, drop test for Green water, comparison with standards (for example, DNV classification society for determine pressure loads due to Hydroelasticity in plate).
As example, for bottom slamming the Ochi (1964 ) criteria has offered. For more information, I think one of the best and classical reference is:
Hydroelasticity of ships , by Bishop and Price (1979)
Good Luck
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How can I estimate pdf of ship with advance speed (U) in a direction of encounter waves If I have a wave spectra ?
Thanks in advance.
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For all Owen Clarke Design projects, the common denominator is performance, regardless of whether the yacht is a cruising or racing design. Our designs always prove to be fast. This is partly due to the tools that we have available to us, the way in which we use them and our partnerships with some of the world’s leading engineers, designers and marine technology consultants.
As professional engineers and designers we offer our skills, experience and use of the tools at our disposal to individuals, yacht designers, boat-builders and other agencies as well as applying their use to our own designs. OCD have recruited qualified naval architects in recent years in order to expand this area of our business. We have continued to invest time and resources in the application of analytical methods such as Computational Fluid Dynamics (CFD) and Finite element analysis (FE) to fluid and structural engineering problems, expanding the use of these tools through our range of designs as the software and services have become more cost effective.
The starting point of any new design is to develop a set of hull lines which define the geometry of the boat. We’ve been using Maxsurf, the world’s leading yacht design software since drawing the lines of our first racing boat, the 35’ trimaran Fiery Cross, in 1987. Since then the product has also been developed for use in the design of commercial craft and ships. It remains however the most utilised yacht design software for designers the world over.
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I want to know about engine load fluctuations in waterjet propulsion system of boat, please help me if you have information/paper/suggestion etc.
Thanks in advance.
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another cases can help you are : 
1.Cavitation inside the inlet
2. Ventilation and penetration of air from
the free surface or from
entrained air in the boundary layer
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I have conducted a model tests of a moored CALM buoy in a towing tank.
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Dear James,
Surge added mass (a11) of a floating object, a11 approximately equals 10 % of its mass. But, regarding restoring force, there is not any restoring force for the surge motion. For floating objects, restoring force exist for heave, pitch, and roll. In this case, you have a damping force due to surge velocity, and you can write the motion equation in the form of (m+a11)d(u)/dt+(b11)*u = External Force, if the motion is pure surge. If you have the response of your object, you can estimate both a11 and b11.
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For my thesis I need to gather information on system control concepts applications in navigation/motion of surface effect ships.
I want to know if you have any links/sources/articles on the matter?
Thanks in advance.
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Hello Ehsan:
  I am not familiar with surface effect ships but if the porblem can be written as a non-linear ODE control systems, then our CPWL technique is suitable. Please let me know if you are interested to go into further details.
   Best regards,