  This paper proposes and validates two new particle regularization techniques
for the Smoothed Particle Hydrodynamics (SPH) numerical method to improve its
stability and accuracy for free surface flow simulations. We introduce a
general form of the Dynamic pair-wise Particle Collision (DPC) regularization
technique that we recently proposed in the context of the Moving Particle
Semi-implicit (MPS) method in [1]. The DPC coupled with the standard Particle
Shifting (PS) technique has given rise to a hybrid approach that we propose to
alleviate particle clustering issues in the free-surface and splashed regions.
We validate the proposed techniques to four benchmark cases: (i) the
oscillating droplet, (ii) the two-dimensional water dam-break, (iii) the
two-dimensional water sloshing, and (iv) the three-dimensional water dam break
against a rigid obstacle. We evaluate their impacts on the stability, accuracy
and the conservation properties of the test cases. The qualitative and
quantitative analysis of the results shows that despite its simplicity, the DPC
technique is more effective in reducing the spatial disorder and capturing the
impact events compared with the standard and the newly improved hybrid PS
methods. Although the hybrid PS technique improves particle distribution at the
free surface, it still suffers from the inconsistent implementation of the PS
equation which unphysically increases the fluid volume and violates the
conservation of potential energy in the long-term simulations. Overall, the
conservative DPC algorithm proves to be a simple and efficient alternative
regularization technique for simulating such highly dynamic free-surface flows.
