Glossary

Geometry generated from a few inputs by rules, rather than drawn one part at a time.

The rules of the product are written down once: which dimension follows which, and which check happens when. After that only the inputs change from order to order, and the geometry, the checks and the documents follow. It pays where the product is custom in its dimensions but fixed in its rules: tanks, boilers, frames, enclosures.

Handing the routine an engineer repeats on every order over to software.

Parametric design as it shows up in a business. The test is not whether the product is complicated, but whether the same decisions are being made again on every order. If an engineer can explain the procedure at a whiteboard in ten minutes, it can be automated.

The repeating dimension a product is built on. For panel tanks, 1080 mm.

In a bolted panel tank every panel is 1080 mm square and the tank is built in multiples of it. That is why the tank is sized in panels rather than millimetres: 4 × 3 × 2 panels means 4.32 × 3.24 × 2.16 metres outside. Halves are allowed.

A water tank assembled from standard panels bolted edge to edge, with no site welding.

The panels are made in the factory and bolted together on site with a gasket between them. That is the difference from a welded tank: nothing is welded on site, and the tank can be dismantled, moved or extended. Designing one is largely counting, because the volume falls out of the panel count.

A panel tank in the shape of a rectangular box.

The common form. It gives more volume than a cylinder in the same footprint, and the regular panel grid makes the arithmetic simple. Taller tanks need internal or external support.

The total length of gasket in the panel joints, measured in metres.

Gasket in a panel tank is counted by the metre rather than by the piece: side gasket and base gasket separately, with a T gasket where runs cross. As the grid grows the gasket length rises faster than the panel count, because every new panel brings four more edges.

The space left above the water line.

The shell volume of a tank and its usable water volume are not the same number. Room is left at the top for venting, overflow and surge. So the volume you get from a tank's outside dimensions is more than the water it will hold.

Every part the job needs, with its quantity.

Panels, bolts, gaskets, connections and supports. It is only worth anything if it comes off the same model as the drawing; a list kept separately goes quietly wrong the moment the customer changes a dimension.

The scaled drawing that goes to production. For a panel tank, four A0 pages.

Front and side elevations, the roof plate layout, a dimensioned isometric and the title block. This is the document that actually reaches the site and the drawing office, and the quote and the bill of materials have to come from the same model.

The box in the corner of a drawing that identifies the job and the firm.

Job name, customer, date, revision, scale and who drew it. In white-labelled software the title block is the customer's own: the name of whoever wrote the software does not appear on the document.

A file format for moving drawings between CAD programs.

A vector format published by Autodesk that nearly every CAD and CAM program reads. Software that produces drawings is expected to export it, so the drawing office can open the result in its own program and carry on.

Software that appears under the brand of the company using it.

Every drawing, report and quote carries that company's logo and title block. The name of whoever built the software does not appear. It is the only arrangement a manufacturer will accept for documents that go out with their name on them.

Computational fluid dynamics: solving a flow numerically on a computer.

It works out how air or water moves around a body by dividing the space into small cells and solving the equations in each. It does not replace a wind tunnel; it is for comparing shapes at the design stage, not for final validation.

Reynolds-averaged Navier-Stokes: solving for the average of a turbulent flow.

Rather than resolving every eddy, it solves for the average and represents the effect of turbulence with a model. It is what most engineering work uses, because resolving the flow directly does not finish in a sensible amount of time.

The equations that stand in for turbulence in a RANS solution.

Spalart-Allmaras uses one equation, runs fast, and is common in external aerodynamics. SST uses two, does better where the flow separates, and costs more. Which one to use depends on the geometry and on what you are looking at.

The angle of a body relative to the oncoming flow.

The angle a wing, a spoiler or a helmet makes with the flow direction. Lift and drag change quickly with it, which is why the same geometry is run at several angles.

The forces on a body, with the size and the speed divided out.

CD is drag, CL is lift. The raw force cannot be compared directly because it depends on speed and area; the coefficient removes that dependence and lets two shapes be compared.

A simple 3D file format that describes a surface as triangles.

Almost every CAD program exports it. It carries surface geometry only, with no material, dimension or tolerance information. It is the usual input for analysis and for 3D printing.

Dividing the space around a body into small cells.

The equations are solved in each cell, so cell size and shape affect the answer directly. The mesh is made finer near the surface, because that is where the flow changes fastest.

A measure of how far a solution still is from settling.

It should fall as the run proceeds. If it stops falling or oscillates, the solution has not converged and the numbers are not trustworthy. Watching it live is what lets a run that is going nowhere be stopped in the first minute rather than the twentieth.

A fire-tube steam boiler with a cylindrical shell.

Combustion happens in a furnace tube inside the shell, and the hot gas passes through smoke tubes, giving up its heat to the water around them. It is one of the most common types in industrial steam.

The curved end that closes a pressure vessel.

A curve is used instead of a flat plate because under pressure it turns force into membrane stress, doing the same job in much thinner steel. The shape is defined by the standards.

A vessel holding fluid above atmospheric pressure.

Its design and manufacture follow standards, because failure is sudden and dangerous. Wall thickness, weld detail and inspection steps all come out of the calculation.

The set of rules defining how a product is calculated and built.

In tanks, boilers and pressure vessels the calculation is not a free choice: which load is taken how, and which thickness follows from it, is written down. That is also where a parametric model earns its keep. You encode the rule correctly once, and every job applies it the same way.