beam-mechanics

name	beam-mechanics
description	Run simple dimensionless 1D Euler-Bernoulli beam mechanics with selectable boundary conditions, point forces, distributed loads, point moments, springs, plots, CSV/JSON results, and deformation GIFs. Use when asked to analyze a simple beam, cantilever, fixed-fixed beam, overhang, support reactions, shear/moment/deflection plots, or a small educational beam mechanics movie/artifact.
license	3-clause BSD license
metadata	{"version":"0.2.0","skill-author":"Markus J. Buehler, Massachusetts Institute of Technology (MIT), Laboratory for Atomistic and Molecular Mechanics (LAMM)"}

Beam Mechanics

Run a simple dimensionless beam mechanics calculation. This skill is intentionally low freedom: always run the bundled script instead of writing a new solver or a custom input schema.

The model is a 1D Euler-Bernoulli beam with vertical displacement w and rotation theta at each node. Inputs are dimensionless. Sign convention: positive vertical force/displacement is upward, negative is downward. Prefer the positive-down helper flags when the user says a load acts downward.

Do not use units. Do not write YAML. Do not write JSON input files unless the user explicitly asks for a separate record. Translate the user's text directly into command-line flags.

Required Workflow

1. Create or use the requested output directory, usually skill_output_<timestamp>_beam-mechanics.
2. Select a preset or translate the user's boundary conditions and loads into flags.
3. Run scripts/simple_beam_lab.py.
4. Verify artifacts with find <output_dir> -maxdepth 2 -type f -print. If files are missing, fix the command and rerun.
5. Read <output_dir>/manifest.json and <output_dir>/summary.json.
6. Final answer must list exact artifact paths and report reactions, maximum absolute deflection, maximum absolute moment, maximum absolute shear, and vertical equilibrium residual from summary.json and reactions.json.

Default Command

From the session root where the skill is mounted as skills/beam-mechanics:

python3 skills/beam-mechanics/scripts/simple_beam_lab.py \
  --out skill_output_<timestamp>_beam-mechanics \
  --title "Simple Beam Mechanics" \
  --preset simply-supported \
  --length 10 \
  --point-down 5,1 \
  --quiet

Verify:

find skill_output_<timestamp>_beam-mechanics -maxdepth 2 -type f -print

Boundary Conditions

Use --preset for common setups:

• simply-supported: left pin, right roller.
• cantilever: left fixed, right free.
• fixed-fixed: both ends fixed.
• overhang: left pin, internal roller at 0.7 * length, right end free.
• custom: use --left, --right, --support, and --spring.

Support flags:

--left fixed
--right roller
--support 6,pin
--support 8,fixed
--spring 5,20

Support types are pin, roller, fixed, clamped, and free. For this simple 1D beam, pin and roller both constrain vertical displacement only. fixed and clamped constrain vertical displacement and rotation.

The script automatically inserts mesh nodes at support, load, moment, UDL end, and spring positions, so locations such as x=3.25 are valid.

Loads

Prefer these positive-down helpers:

--point-down X,MAGNITUDE
--udl-down START,END,MAGNITUDE
--moment-clockwise X,MAGNITUDE

Signed alternatives are available:

--point X,VALUE
--udl START,END,VALUE
--moment X,VALUE

Use negative signed vertical values for downward loads.

Repeat load and support flags for multiple loads/supports.

Text-To-Flag Translation

Use these examples to convert user language into flags.

Simply supported beam:

--preset simply-supported

Cantilever fixed on the left, free on the right:

--preset cantilever

Custom left pin and right roller:

--preset custom --left pin --right roller

Fixed support at x=3:

--support 3,fixed

Roller support at 70 percent of a length-10 beam:

--support 7,roller

Vertical spring at midspan with stiffness 20 on a length-10 beam:

--spring 5,20

Downward point load of magnitude 1 at midspan of a length-10 beam:

--point-down 5,1

Two downward point loads:

--point-down 4,1 --point-down 9,0.6

Downward uniform load of magnitude 0.2 across the middle 20 percent of a length-10 beam:

--udl-down 4,6,0.2

Downward uniform load across the full length:

--udl-down 0,10,0.2

Clockwise point moment of magnitude 0.5 at x=6:

--moment-clockwise 6,0.5

Outputs

The script writes:

• manifest.json: file map and summary.
• summary.json: key values and equilibrium check.
• reactions.json: support reactions.
• field_data.csv: sampled x,w,theta,moment,shear.
• structure.png: supports and loads.
• deformed_shape.png: scaled deformation.
• deflection.png: deflection curve.
• moment.png: bending moment curve.
• shear.png: shear curve.
• dashboard.png: combined figure.
• deformation.gif: deformation movie when GIF support is available.
• frames/frame_*.png: movie frames when GIF support is available.
• README.md: short run explanation.

Do not claim success unless find lists these files or manifest.json exists and names them.

If deformation.gif is missing because GIF writing is unavailable, report the frames/ directory when it exists and still report the static plots, CSV, JSON, and README.

Runtime Guidance

Use default --elements 80 --frames 32 --fps 12 for final artifacts. Add --quick only for smoke tests or timeout recovery. Do not present --quick outputs as final high-quality artifacts unless the user asked for a fast test.

Copyable Recipes

Simply supported beam, center point load:

python3 skills/beam-mechanics/scripts/simple_beam_lab.py \
  --out skill_output_<timestamp>_beam-mechanics \
  --title "Simply Supported Center Load" \
  --preset simply-supported \
  --length 10 \
  --point-down 5,1 \
  --quiet

Cantilever, tip load plus uniform load:

python3 skills/beam-mechanics/scripts/simple_beam_lab.py \
  --out skill_output_<timestamp>_beam-mechanics \
  --title "Cantilever With Tip Load And UDL" \
  --preset cantilever \
  --length 8 \
  --point-down 8,1 \
  --udl-down 0,8,0.2 \
  --quiet

Fixed-fixed beam with a uniform load:

python3 skills/beam-mechanics/scripts/simple_beam_lab.py \
  --out skill_output_<timestamp>_beam-mechanics \
  --title "Fixed Fixed Uniform Load" \
  --preset fixed-fixed \
  --length 10 \
  --udl-down 0,10,0.3 \
  --quiet

Custom beam with an internal spring and two point loads:

python3 skills/beam-mechanics/scripts/simple_beam_lab.py \
  --out skill_output_<timestamp>_beam-mechanics \
  --title "Beam With Internal Spring" \
  --preset custom \
  --length 12 \
  --left pin \
  --right roller \
  --spring 6,20 \
  --point-down 4,1 \
  --point-down 9,0.6 \
  --quiet

Overhanging beam with an end load:

python3 skills/beam-mechanics/scripts/simple_beam_lab.py \
  --out skill_output_<timestamp>_beam-mechanics \
  --title "Overhanging Beam End Load" \
  --preset overhang \
  --length 10 \
  --point-down 10,1 \
  --udl-down 0,10,0.1 \
  --quiet

For fast tests, add --quick. For final visible artifacts, omit --quick.