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The development of fibrous actuators with diverse actuation modes is expected to accelerate progress in active textiles, robotics, wearable electronics, and haptics. Despite the advances in responsive polymer-based actuating fibers, the available actuation modes are limited by the exclusive reliance of current technologies on thermotropic contraction along the fiber axis. To address this gap, the present study describes a reversible and spontaneous thermotropic elongation (~30%) in liquid crystal elastomer fibers produced via ultraviolet-assisted melt spinning. This elongation arises from the orthogonal alignment of smectogenic mesogens relative to the fiber axis, which contrasts the parallel alignment typically observed in nematic liquid crystal elastomer fibers and is achieved through mesophase control during extrusion. The fibers exhibiting thermotropic elongation enable active textiles increase pore size in response to temperature increase. The integration of contracting and elongating fibers within a single textile enables spatially distinct actuation, paving the way for innovations in smart clothing and fiber/textile actuators. 

Flight vehicles that operate in the supersonic regime can be subject to adverse fluid–structure interactions due to their lightweight design. The presence of geometric obstructions such as control surfaces or fins can induce shocks that can interact with the boundary layer, leading to flow separation. This work investigates experimentally the interaction between a compliant panel in a Mach 2 flow under a compression ramp-induced shock-wave/boundary-layer interaction (SBLI). Thin brass panels of different thickness are investigated in a wind tunnel. Tests are performed both with and without a 20◦ compression ramp installed. This direct comparison allows characterization of the effect of the SBLI on the system dynamics. High-speed stereoscopic digital image correlation (DIC) and fast-response pressure sensitive paint (PSP) are used to obtain simultaneous measurements of full field deformation and surface pressure of the panels. The panel vibration is dominated by the first bending mode. Despite the forcing of the separation shock foot, the presence of the SBLI does not significantly modify the operational deflection shape, frequency, and amplitude of the dominant vibration mode, beyond what is observed for the no-SBLI case. On the other hand, analysis of the shock foot motion shows that the shock primarily oscillates at the first natural frequency of the panel. This leads to the conclusion that the shock foot oscillation is driven by the panel vibration in a one-way coupling mechanism. The SBLI does modify the higher modes, which is likely due to localized forcing by the separation shock foot. Full-field surface pressure predictions are made using first order piston theory. Results show that the fluid–structure interaction is dominated by the large region of attached flow upstream of the shock foot. 

This work investigates surface pressure unsteadiness on a compliant panel under a shockwave/boundary-layer interaction (SBLI) induced by a 2D compression ramp with an angle of 20o in a Mach 2 wind tunnel. High-speed digital image correlation (DIC) and fast-response pressure-sensitive paint (PSP) measurements are used to measure the panel displacement and panel and ramp-face surface pressure fluctuations at 5kHz and 20kHz, respectively. The data reduction technique of POD (proper orthogonal decomposition) was employed both for pressure and displacement fields. POD mode distribution for the pressure fields reveals that the first six modes have 60% of the total energy and exhibit low-frequency content for both rigid and compliant panels. The vibration of the compliant panel was seen to alter the energy distribution of the high energy modes as compared to the rigid panel case. The cross-correlations between the displacement and pressure modes were made using the time coefficients. This analysis shows significant correlations were present among the lower modes. The highest correlation was between displacement mode 1 and the pressure mode 4, which stemmed from the upstream of the intermittent region. The analysis was also made for the surrogate shock foot and reattachment lines. The correlation shows that panel vibration lowers the correlation between the shock foot and reattachment line when compared with the rigid panel case. 

A thin compliant panel was tested in a Mach 2 wind tunnel. The panel was mounted flush with the tunnel floor and was of dimensions L=121.9 mm (chord), W=63.5 mm (span) and h=0.254 mm (thickness). A 20 degree compression ramp was placed 5 mm downstream of the model, which induced a shock/boundary layer interaction with fully separated flow over parts of the panel. Full-field deformation was measured using Digital Image Correlation and the surface pressure field was obtained from fast-response pressure-sensitive paint. Analysis of the shock foot motion was performed using a curve-fitting method. Comparison of the shock motion between a rigid and compliant panel case showed no difference in the size of the intermittent region but found that the shock motion over the compliant panel is affected by the panel vibration. Proper Orthogonal Decomposition revealed that the surface pressure is dominated by low-frequency unsteady shock motion, in both cases (rigid and compliant panel). The sixth POD mode clearly shows the streamwise shock foot motion oscillates at the first panel vibration frequency. The surface pressure field upstream of the shock foot is dominated by piston-theory aerodynamics and thus correlated to the slope of the compliant panel. The Sparse Identification of Nonlinear Dynamic Systems algorithm was employed to find low-order representations of the system dynamics. Linear stiffness matrices could be consistently recovered. The measurement noise however prevented extraction of additional relations, such as linear damping matrices or forcing terms from the surface pressure.