Local and convected rates of change

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SUMMARY

The discussion focuses on the local and convected rates of change in hydrodynamics, specifically analyzing the equation \(\frac{D\psi}{Dt} = \frac{\partial\psi}{\partial{t}} + (\underline{u} \cdot \nabla)\psi\). The participant understands the derivation but seeks clarity on why the total derivative \(\frac{D\psi}{Dt}\) does not equal the partial derivative \(\frac{\partial\psi}{\partial{t}}\). The capital 'D' in the total derivative indicates the material derivative, which accounts for both local and convective changes in the variable \(\psi\).

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  • Understanding of hydrodynamics principles
  • Familiarity with vector calculus, particularly gradient operations
  • Knowledge of derivatives, specifically total and partial derivatives
  • Basic grasp of fluid dynamics concepts
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Homework Statement


This is less of a help me answer something question more a help me understand this question.

I was reading though my hydrodynamics notes and there was a derivation that ended up with the follow equation
\frac{D\psi}{Dt} = \frac{\partial\psi}{\partial{t}} + (\underline{u}.grad)\psi
now i completely understood the derivation, what I don't understand is the result why doesn't \frac{D\psi}{Dt} = \frac{\partial\psi}{\partial{t}}? Also what do the capital D even mean?

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