Should I cite a concept I have already cited earlier? I am writing a proposal for my PhD and it is majorly based on numerical modelling. I have cited the original model that I will be using earlier, and I think it is very clear throughout the proposal which model I am talking about. Should I still cite it again when I mention it later even though I think the running theme throughout is of the specific model I want to use? For example here:


  The experimental data thus acquired will then be used to construct the deformation history for the fractured rock, which will then be used to parametrise the numerical models.


I cite the models a few sections earlier, but the models are discussed throughout the whole text.
This is hard to answer precisely without seeing your entire document.  In general, I'd say if it is very obvious what you are talking about, then you do not need to cite again.  The problem is that what is "obvious" to one person is not obvious to another.  Especially it can be hard for you to know if it is obvious or not because you are too close to it.  One suggest is to have a friend or other graduate student read the whole paper, and then ask them for an opinion.  Or, just err on the side of slightly more citations.