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1.7: Good Engineering Graphical Practice

  • Page ID
    21145
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    • Always label both axes, and always include the units of physical quantities.
    • Always write an explanatory one-line title. Such a short title cannot explain everything about the graph, but any title you use will almost certainly help the reader to understand the graph.
    • It is usually good practice to add grids to a graph. Grids help the reader to perceive values correctly. For example, the grids on Figure 1.6.1 show clearly that the peak velocity response is just above 7 m/s at a little after 5 s.
    • The commands in the script file that specify the densities of computed points are, first, t1=0:0.05:td while the pulse acts and, second, t2=td:0.1:25 following the pulse. For example, the first line directs MATLAB to compute the response at 0.05 s intervals; then plot(…,t1,v1,'k',…) directs MATLAB to plot small points for those instants, and to connect each two adjacent points with a straight line. If you use high point densities, then the overall plotted line will capture all important features of the response (extreme values, for example), and will appear to be a smooth curve. Indeed, the overall line should look like a smooth curve, because it represents a continuous physical response; neither the response itself nor its low-order derivatives should be discontinuous. On the other hand, if you use low point densities, then you might miss important features of the response, and the overall line will be unnaturally piecewise linear, with kinks (slope discontinuities). To visualize an extreme example of low point density, suppose that for the mass-damper system you were to compute and plot the velocity response at 4 s intervals; the velocity graph in Figure 1.6.1 would consist only of straight lines connecting the computed points at 0, 4, 8, 12, 16, and 20 seconds, which would badly represent the actual response. So always specify high point density on graphs of continuous physical response. You might not know initially what point density you should use, especially if you are analyzing an unfamiliar system. But try some plausible point density. If your plotted response curve appears unnaturally kinky, then increase the point density appropriately and run the M-file again. It will cost you nothing more than the little time required to edit and re-run the M-file (or any other graphing computer program).

    This page titled 1.7: Good Engineering Graphical Practice is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by William L. Hallauer Jr. (Virginia Tech Libraries' Open Education Initiative) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.