Anomalous dissipation, anomalous work, and energy balance for smooth solutions of the Navier-Stokes equations

TL;DR

This paper investigates the energy balance in smooth solutions of the Navier-Stokes equations, revealing how anomalous dissipation and anomalous work by external forces can cause violations of energy conservation, with explicit examples and sharp conditions.

Contribution

It introduces the concept of anomalous work, analyzes its interplay with anomalous dissipation, and constructs solutions demonstrating these phenomena, clarifying conditions for energy balance in Navier-Stokes solutions.

Findings

Existence of solutions with anomalous dissipation and zero anomalous work.

Anomalous work can occur independently of anomalous dissipation.

Sharp conditions on solution regularity for energy balance are established.

Abstract

In this paper, we study the energy balance for a class of solutions of the Navier-Stokes equations with external forces in dimensions three and above. The solution and force are smooth on $(0,T)$ and the total dissipation and work of the force are both finite. We show that a possible failure of the energy balance stems from two effects. The first is the \emph{anomalous dissipation} of the solution, which has been studied in many contexts. The second is what we call the \emph{anomalous work} done by the force, a phenomenon that has not been analyzed before. There are numerous examples of solutions exhibiting \emph{anomalous work}, for which even a continuous energy profile does not rule out the anomalous dissipation, but only implies the balance of the strengths of these two effects, which we confirm in explicit constructions. More importantly, we show that there exist solutions exhibiting \emph{anomalous dissipation} with zero \emph{anomalous work}. Hence the violation of the energy balance results from the nonlinearity of the solution instead of artifacts of the force. Such examples exist in the class $u \in L_t^{3 } B^{\frac{1}{3} -}_{3,\infty}$ and $f \in L_t^{2-} H^{-1}$, which implies the sharpness of many existing conditions on the energy balance.