# What tense to use in thesis when describing complex simulation models?

I've researched the "rules" regarding use of tenses in scientific writing. However, I'm still not sure how to describe the simulations I've done during my thesis.

Just a simple example:

1: An example model was developed to simulate the behavior during compression.

Here I'm describing something I did in the past, similar to an experiment, hence I'm using the past tense.

Then I'll describe what happens during the simulation, or how specific properties of the simulation model were set.

2: The piston geometry is imported as a .stl-mesh. By moving the mesh in direction of the negative z-axis, the particles in the cylinder are compressed until...

I'm not sure about the tenses used in example 2. I could have also written:

3: The piston geometry was imported as a .stl-mesh. By moving the mesh in direction of the negative z-axis, the particles in the cylinder were compressed until...

I can't decide whether example 2 or 3 is the better choice.

• Use past passive. – Solar Mike Apr 7 '18 at 16:38
• You've gotten some good answers. I'll just add: present tense is probably good to describe an algorithm or method, past tense good to describe your procedure or actions. – aparente001 Apr 8 '18 at 3:14

I would say the present tense is appropriate if you are giving a description of how the model works in general. The model itself is timeless; it will keep working the same way now and forever.

The past tense puts the emphasis on what you did in your specific project; it reads like a report. You did it this way; someone else in the future might do something else.

• Thank you. I've decided to use past tense as I'm describing my procedure for my specific case. – matejmarti Apr 8 '18 at 9:52
• For some more specifics, You might say X is the piston mass, or the model produces cyclic dynamics for parameter values a, b, and c (present tense for inherent properties or descriptions of the model). But you would say "we performed a sensitivity analysis" or "we varied parameter Y from 1 to 10 test how general the observed dynamics were" (passed tense for procedures) – WetlabStudent Apr 8 '18 at 9:59

Closely tied to @Nate Eldredge's answer, one way to resolve this could be to see what you want to emphasize- the results from the simulation (maybe for a general engineering journal) or the simulation itself (maybe for a computational journal).

In the first case, use past tense, because you ran the simulation in a particular way to get those results, and others should do the same for reproducibility. In the second case, use present tense, because you are highlighting what the simulation does, and it is up to others to think what results they can use it for.

• I've marked @Nate Eldredge's answer as the correct one, but yours also helped solving the problem. Thank you. – matejmarti Apr 8 '18 at 9:54

What I do is use the past tense when talking in general like in an introduction or abstract, and the present when talking about the actual development of the model. I don’t think there is a general rule.