Set a support condition
set_supportWrite a nodal support (boundary condition) and point one or more nodes at it: creates or overwrites an entry in model.nodal_supports and sets node.nodal_support on every node you name. Returns the updated model — feed it to solve_model.
All 7 DOFs are set independently, in the GLOBAL frame: X/Y/Z (translations), RX/RY/RZ (rotations about the global axes) and warping (the 7th DOF, only live when analysis.options.include_warping is true and the section has i_w). Condition types are case-sensitive: Fixed (rigid), Free (no restraint), Spring (needs the matching _stiffness > 0 — N/m for translations, N*m/rad for rotations), PositiveOnly (one-way: may only push in the +global direction, i.e. lift-off) and NegativeOnly (the mirror image). A one-way condition may also carry a _stiffness, which from engine 0.2.65 is the bedding stiffness it acts through while in contact — a base plate on a slab is not infinitely stiff. Released, it is free regardless. On 0.2.64 and earlier that number was accepted, range-checked and then silently discarded, so the model solved as rigid contact.
THERE IS NO "FREE BY OMISSION". Once a node references a support, any DOF you leave out is treated by the solver as FULLY FIXED — a support of literally {"id":1} is an encastre, and the OpenAPI text claiming an absent field means free is wrong. This tool therefore always writes all six translation/rotation conditions explicitly, and anything you do not name is written as Free. Use preset to fill them in one go: fixed (encastre), pinned (X/Y/Z fixed, rotations free), free, roller_x/roller_y/roller_z (ONLY that translation fixed, everything else free), ground_contact_y (X/Z fixed, Y PositiveOnly, rotations free — a base plate that can lift off). Per-DOF fields are applied on top of the preset. Warping is the one exception: leaving it out really does mean free.
ONE-WAY SUPPORTS have a prerequisite this tool checks for you: analysis.options.rigid_strategy must be RigidMember (LinearMpc is a hard validation error). Tension/Compression members are fine alongside them from engine 0.2.65 -- before that the combination was refused at validation, so if you are reading advice written against an older engine, that restriction is gone. There is also a SILENT prerequisite — the release tolerance is 0.5*axial_slack in force units, so a coarse axial_slack leaves the DOF engaged while still reporting its reaction as 0, and the printed reactions stop summing to the applied load. This tool lowers axial_slack to 1e-3 when it writes a one-way condition (set keep_axial_slack to skip that). Beware that a support which lifts off can leave the structure unrestrained, and that a one-way support can break an eigen solve if the model also has a modal or buckling block.
Reactions use ONE SIGN CONVENTION for every support type from engine 0.2.60: each row is the force the support applies to the structure, so reactions can be summed against the applied load without checking which kind of support produced each one. (Up to 0.2.59 a Spring DOF reported the spring force k*u, the negative of what a Fixed DOF reported for the same physical situation. If you are reading results solved on an older engine, that flip is still in them.) A stiffness curve (stiffness_curves) makes the spring load-dependent, forces the DOF to Spring and requires a NONLINEAR analysis order — and note its driver is the EXTERNAL nodal load at that node, not the reaction, so a base-plate curve with no direct nodal load degenerates to the first point's stiffness.
Tool call template
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"node_ids": "<node_ids>"
},
"name": "set_support"
}
}Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| X | No | Fixed | Free | Spring | PositiveOnly | NegativeOnly (global X translation). | |
| Y | No | Same, global Y (vertical in these models). | |
| Z | No | Same, global Z. | |
| RX | No | Same, rotation about global X. | |
| RY | No | Same, rotation about global Y. | |
| RZ | No | Same, rotation about global Z. | |
| model | No | Stringified FERS model JSON | |
| preset | No | fixed | pinned | free | roller_x | roller_y | roller_z | ground_contact_y. Applied first; the per-DOF fields below then override it. | |
| warping | No | Warping DOF condition. | |
| node_ids | Yes | JSON array of node ids to support, e.g. [1,2], or the string "all". They all share one support definition. | |
| model_ref | No | Handle from stash_model, used INSTEAD of `model`. Avoids sending the whole document on every step; the tool returns the same handle back. | |
| support_id | No | Overwrite this existing nodal_supports entry; omit to allocate a new one. | |
| X_stiffness | No | N/m — required when X is Spring. | |
| Y_stiffness | No | N/m — required when Y is Spring. | |
| Z_stiffness | No | N/m — required when Z is Spring. | |
| RX_stiffness | No | N·m/rad — required when RX is Spring. | |
| RY_stiffness | No | N·m/rad — required when RY is Spring. | |
| RZ_stiffness | No | N·m/rad — required when RZ is Spring. | |
| classification | No | Free-text label. | |
| keep_axial_slack | No | Leave analysis.options.axial_slack untouched when writing a one-way support. | |
| stiffness_curves | No | Nonlinear support springs: {"Y":{"depends_on":"Fy","points":[[0,1e5],[10000,1e6]]}}. Forces that DOF to Spring and the analysis to NONLINEAR. | |
| warping_stiffness | No | Required when warping is Spring. |