Licensing and activation

The free tier

The free build is the same binary as the paid one. There is no separate download and no trial timer.

The authoritative list is docs/licensing/tiers.json in this repository — the application compiles it in, because the free tier has to work with no account and no network and so has nobody to ask.

Free is limited by scale, not by physics. Every analysis type, every turbulence model, every boundary condition and every cell zone is available without a licence. What a free user cannot do is run it big, run it wide, or run it somewhere else.

The application renders this list itself, from the entitlements actually in force, under WHAT THIS TIER ALLOWS on the Licence page of Settings. That is the copy to trust on your own machine.

Why nodes and not cells for the solid families

Finite volume stores the answer in the cell, so cells and degrees of freedom move together and a cell cap is a real resource limit. Finite element stores it at the nodes, and element order changes the node count without changing the element count — 100,000 linear tets carry about 18,000 nodes, 100,000 quadratic tets carry about 140,000. Quadratic is not exotic: linear tets are too stiff in bending, and real structural work uses them. An element cap would therefore be a budget you blow through while still appearing to sit under it, which is the worst shape a limit can have.

100,000 nodes is 300,000 degrees of freedom. It is deliberately not the fluids number scaled: the solid solvers are direct, and their memory grows far faster than the iterative ones OpenFOAM uses, so a matched cap would be met as a machine running out of RAM rather than as a limit.

The three workflow limits

Concurrent jobs, restart from a result and headless runs are booleans rather than numbers, and that is the deliberate exception to the rest of the list. There is no meaningful small version of running headless, so a boolean there refuses a convenience rather than an analysis.

Restart from a result is the one a free user meets most often. Initialising a case with mapFields from an earlier run puts an error in the Problems tab: "Starting from an earlier result is not part of the Free tier. Initialise from the field values instead, or upgrade — the run itself is not limited, only the head start."

An engineer who discovers a cap after installing is annoyed; one who read it and installed anyway is qualified. That is why the list is here and on the download page rather than in a footnote.

Activating a paid licence

Three routes, on the Licence page of Settings. All three end in the same place.

Sign in with my SHD account. A device-code flow, not a password prompt. The application asks the licence server for a code, opens the approval page in your browser, and then shows the code with the instruction "Enter this code in your browser", the URL, and how long it has left before it expires. Open the page again and Cancel sit underneath. The panel's own reassurance is the point of it: "Approve this computer in your browser — no password is typed into the app." Use this one — it attaches the machine to a person, which is what makes seat management work later.

Enter a licence key. Paste the key into the field marked SHDSIM-XXXX-XXXX-XXXX-XXXX and press Activate. This works with no browser and on a machine that cannot reach a sign-in page.

Import a licence file… A file dialog over *.lic, *.licence and *.txt. This is the air-gapped route, and it is a button on every tier: "Import a licence file is for machines with no internet access."

The difference between the first two matters when somebody leaves. A machine activated by signing in can be stopped by removing that person from the organisation; a machine activated by typing a key carries no identity, so it has to be deactivated from your account.

The licence server address

The Licence page also carries a LICENCE SERVER section with an editable Address field, hinted "Only change this if you have been told to - for an on-premises licence server, for instance." It defaults to https://api.shd-sim.com and can also be set with the SIMCFD_API_BASE environment variable. The machine identifies itself to that server by a hash; serial numbers and hardware addresses are hashed and never sent.

Working offline

Once activated, the application does not need the network to run. It holds a signed licence file and revalidates periodically; if it cannot reach the licence server it keeps working for a 14-day grace period.

Grace covers our failures, not revocation. An unreachable server, a timeout or a 5xx is honoured from the cached file for those fourteen days. A definitive 403 — a cancelled or revoked licence — is authoritative immediately, with no grace at all. Otherwise pulling the network cable would buy a cancelled subscription a free fortnight.

When a licence lapses, the application degrades to the free tier. It does not lock your cases, make them read-only, or delete anything. Your work stays openable.

Seats and devices

A licence is per seat, and a seat is either assigned to a person or drawn from a pool. Neither word appears in the application; you meet the distinction as an error if it bites — "Your account does not have a seat on this licence" for the first, "Every seat in the pool is in use" for the second.

Manage seats and devices at account.shd-sim.com, which the Account page button on the Licence page opens. Deactivating a device frees its seat immediately.

Moving to a new machine

Deactivate the old one first — Settings → Licence, then Deactivate this machine — or from your account. Then activate the new one normally.

If the old machine is gone — dead, wiped, stolen — deactivate it from your account. You do not need the machine to release its seat.