Galactic nuclei are extreme environments where stars are densely packed around a supermassive black hole (SMBH). Occasionally, dynamical interactions in the galactic center cause stars to interact violently at short distances with each other or with the SMBH, resulting in the formation of various nuclear transients. In this talk, I will discuss two types of nuclear transients, tidal disruption events  and high-velocity collisions between stars, based on detailed hydrodynamics simulations. In the first part of my talk, I will focus on tidal disruption events, one of the most dramatic nuclear transients involving the destruction of stars by the SMBH. The conventional view describes the events as single-flare X-ray events with luminosity decaying according to a specific power law. However, these events are in fact more diverse, including repeating partial TDEs-a plausible mechanism for periodically recurring nuclear flares-and extremely relativistic events, where the debris evolution is qualitatively different from that of ordinary TDEs. In the second part of my talk, I will discuss disruptive stellar collisions where collisions are so powerful that the two colliding stars can be destroyed, leaving behind an expanding ejecta. These collisions are another promising, though less highlighted, type of nuclear transients.