We have many years experience with optimal structures!

 

3-d model of midship section includes plates, stiffeners, frames, girders

   

 

We can help your company design optimal thin-shell structures.

 

For the past 20 years, our company has worked with marine and industrial design, especially 3-D modelling, structural analyses, and optimal solutions.

 

Building optimal structures is not easy. For most large scale or long series projects, the potential cost savings are dramatic.

 

Finite-element analyses usually give better solutions, provide a better overview of structural response, and costs are often the same as 'manual' calculations (typical jobs here).

 

For large and complex structures, it is often best to use a global design model of the complete structure. This is because it is essential, after applying the correct loads to all components, to look at deflections, stresses and possible buckling or collapse of all structural members in one operation. Only in this way is it possible to safely reduce scantlings and/or to fix problem areas and identify potential damages.

 

Global finite element models are the best means to verify ship and other thin-shell structures. Everyone benefits. Arrangements can be varied, with confidence in the adequacy of the final structure. Non-critical areas can be identified. Costs can be cut. And the technical results can be used directly in the certification process.

 

Random checking of stresses in structural members, panel buckling or stiffener collapse, is a risky business. Failures in lightweight structures can occur anywhere. There are usually just too many structural elements which can go wrong. Design spreadsheets and empirical rules and formulas are OK up to a point. We use them too, but spreadsheets may not give optimal global design.

 

Hull modell contains plates, stiffeners, frames, girders, pillars, brackets, tanks, bulkheads

 

These days 'everyone' uses finite-element analyses, or so you would think. But it is not always the case in classification societies and certification authorities.

 

If certifying authorities are involved, of course they always want to have the last say (it's their job). They want to be sure that safety margins are adequate. So do you, and so do I. Sometimes their initial decisions can be extremely frustrating, but they are obliged to listen to arguments based on engineering fact. It is always worth discussing 'wrong' decisions with them, and it certainly helps to know how their approval process works.

 

Some classification society guidelines are very conservative. Most of my practical experience has been with DNV in Oslo, and it helps to be able to go down the road and discuss problems with their plan approval people. 

 

You wonder what level of structural weight savings we are talking about? To be honest, it is not unusual (or surprising) when we document designs from experienced ship- and boatyards to find that their scantlings are 'spot on'. In other optimisation projects, the designed structural weight may even increase slightly in local areas (miracles are scarce in this business). This is not uncommon in large aluminium vessels where buckling in upper decks, and potential shear failure near large openings, is a problem.

 

On the other hand, we have seen 7-8% steel weight savings for a ro-ro ship designed according to DNV rules with their software (and on that one we picked up bow-flare failures that class approval had missed - info on another page), and 15% for a supply vessel. For conventional g.r.p. and sandwich vessels, 30-40% weight savings, just by using different class rules, are not unusual. Obviously, unnecessary weight has a big bearing on costs for  newbuilding and in-service operation.

 

Cross section of VPSO

 

We try to follow up our structural designs, and have no record of any failures, even in high-speed ferries. We have been designing ship and boat structures for many years, and take pride in doing a good job in a positive atmosphere with clients. Proper documentation of analysis methods and structural models, loads and responses lets your own clients and the authorities make well-founded final decisions. All can then be sure that the final structure is not just minimum weight, but reliable.

 

Experience is important. Over the years, those of us working with these analyses tend to develop a 'feel' for reasonable answers, and that of course is an important aid to normal quality control processes. 


It is easy to be blinded by the nice plots and colours of finite-element analyses. We have reviewed for clients, and trashed some very thick, very expensive reports with a fundamental error on page 1. We are very much aware how easy it is to make mistakes. That fact just makes us careful.

 

For bigger projects, and depending on workload and whether it is desirable, it may be possible for me to work onsite. Working 'in the background' is quite OK, and it doesn't bother us if our reports are presented with someone else's logo or company name. We never discuss or release information about particular projects with other clients, and we are careful not to abuse proprietary information, even if we don't have a specific non-disclosure agreement. 

 

It is not easy to give a price or time indications now, since job complexity can vary so much. But if you have a definite project and scope of work, we can give you a quote. Our overheads are low, and hourly rates are reasonable. Small design jobs are no problem either.

 

We have worked with many types of project, from optimisation of deck panel details, small component design and local frame analyses to complete global optimisation for barges, large catamaran ferries and ships, and analysis of tankers.

 

Please get in touch if we can be of assistance.

   

Best regards,

Barry Spradbrow

 

Engine room details including bearers, pillars and hatch openings

 

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