Soft Matter and Complex Systems Seminar
sala 1.40, ul. Pasteura 5
2026-11-06 (09:30) 
Daria Żyła-Jabłońska (WMEiL PW)
Towards perfect cloaking: combining cloaks to conceal defects in water waveguide systems
We present a novel technique for rendering objects invisible to incident surface water waves in a parallel-wall water waveguide over a broad frequency range. As a case study, we consider a vertical, surface-piercing, impermeable circular cylinder placed on the centreline of a waveguide of width L, with cylinder diameter D=0.6L. In the reference configuration, the cylinder is placed in an unmodified parallel-wall waveguide and acts as a scattering defect.
In the first cloaking approach, the waveguide walls in the immediate vicinity of the cylinder are locally deformed. This wall shaping substantially reduces wave reflection, yielding a reflection coefficient at least 20 times lower than in the reference parallel waveguide. Experimental results confirm the efficiency of the approach, showing that the backscattered energy is reduced by a factor of 100–5000 within the considered frequency range.
The approach is then extended by combining local wall deformations with variable bathymetry around the cylinder. Two hybrid configurations are investigated, using either smooth or stepped axisymmetric bathymetry. An iterative surrogate-based optimisation procedure simultaneously adjusts the wall geometry and bottom profile to minimise the total scattered field, defined from the transmitted and reflected wave coefficients relative to the reference configuration. The optimised hybrid designs reduce the total scattered energy by at least a factor of 25 for kL< 5.652, demonstrating that combined wall and bathymetry shaping outperforms wall-only cloaking and provides an effective route toward broadband reduction of wave scattering by surface-piercing structures.
In the first cloaking approach, the waveguide walls in the immediate vicinity of the cylinder are locally deformed. This wall shaping substantially reduces wave reflection, yielding a reflection coefficient at least 20 times lower than in the reference parallel waveguide. Experimental results confirm the efficiency of the approach, showing that the backscattered energy is reduced by a factor of 100–5000 within the considered frequency range.
The approach is then extended by combining local wall deformations with variable bathymetry around the cylinder. Two hybrid configurations are investigated, using either smooth or stepped axisymmetric bathymetry. An iterative surrogate-based optimisation procedure simultaneously adjusts the wall geometry and bottom profile to minimise the total scattered field, defined from the transmitted and reflected wave coefficients relative to the reference configuration. The optimised hybrid designs reduce the total scattered energy by at least a factor of 25 for kL< 5.652, demonstrating that combined wall and bathymetry shaping outperforms wall-only cloaking and provides an effective route toward broadband reduction of wave scattering by surface-piercing structures.