Dynamic combustion characteristics of a rectangular scramjet combustor with single-side expansion were studied experimentally and numerically. Experiments were implemented with an isolator entrance Mach number of 3.46, and an air stagnation temperature of 1430 K. Ethylene was utilized to fuel the combustor over an equivalence ratio range of 0.20 < φ < 0.63. Results indicated that the combustion modes varied from different equivalence ratios. For an intermediate φ = 0.375, an intermittent dynamic combustion occurred. During the dynamic process, the flame sometimes stabilized in the jet wake of the top cavity, and at other time it oscillated between dual parallel cavities. The pseudo-shock train traveled periodically along the length of the combustor, and the penetration depths of the two injectors exchanged. Quantitative analysis illustrated that the average frequency of unsteady combustion was approximately 200 Hz. The reason for the occurrence of the self-sustained dynamic process was related to the interactions between the shock-induced separated region and heat release.

Transparent and flexible force sensor provides potential applications in a lot of area such as human wearable sensor, robotic sensor and underwater equipment. Here the work presents a zigzag patterned hydrogel-based force sensor. Slow-gelling alginate hydrogel, self-designed microextrusion 3D printer and polydimethylsiloxane (PDMS) were adapted for the sensor fabrication. A slow-gelling hydrogel printing ink was prepared and printed onto the treated PDMS layer with a computer-aided designed zigzag pattern. The line width and resistance of the printed hydrogel were precisely controlled by the self-designed microextrusion 3D printer. To stabilise the water content, a sandwich structure was adopted and two PDMS cover layers were fabricated to seal the hydrogel sensor. Theoretical analysis was performed and it is shown that the change rate of resistance was linear related to the force, and this analysis was proved by experiment. Experiments also show that the sensor was flexible and transparent. The zigzag patterned hydrogel also and the PDMS layers provided stable water content and recording.

The determination of fracture properties of hydrogels is of great importance while the hydrogel is used as medical scaffold or soft robotic. The simulations of the mechanical properties were used to reduce the experiment cost and improve efficiency. Here, the work presents a novel method to simulate the fracture behaviour of hydrogels based on discrete element method. Different with continuous methods, the hydrogel was characterised by number of particles. The viscoelastic model and bonding model within the particle model were applied to simulate the microscopic structure of hydrogels. By changing the critical parameters in the model, hydrogels with different mechanical properties were also simulated. Puncture compression test and uniaxial tensile test based on the model were performed. The fracture morphology, stress and strain during the tests were simulated. The results show that the model provides a novel and effective tool to simulate the fracture process of hydrogels.

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