Sums of Forces and Moments - mkraska/meclib GitHub Wiki

Extraction of sums of forces and moments from MecLib images.

[fx,fy,m]: sum_xyM(obj,names,rp,lu) Returns the sums of forces fx, fy and moments m about reference point rp using length unit lu.

  • objects Input field with object list
  • names Input field with object names
  • rp coordinates of the reference point in grid units [x,y]
  • lu symbolic length unit

Currently the sum of forces in x and y direction and the sum of moments about a given reference point are handled. The reference point can be input by the "crosshair" object or given in the task description.

TBD: Let the user select the direction for summing up the forces. This could be done by two interactive "disp" objects, possibly with a helper point perpendicular to the direction, much like the "line" object used in constructing centers of rotation.

Question Variables

Make sure that fb_fbd.mac is included. It contains the relevant functions.

Feedback Variables

This is a typical use if the reference point is obtained from the position of object i_P, which could be a "crosshair"

obj: stackjson_parse(objects);
[fx,fy,m]: sum_xyM(obj,names,names[i_P],a);

PRT Node

Display of the sum of forces and moment (formative feedback).

<p>\( \displaystyle \Sigma F_x={@fx@}\) </p>
<p>\( \displaystyle \Sigma F_y={@fx@}\) </p>
<p>\( \displaystyle \Sigma M_0={@m@}\) </p>