The in-plane dynamic crushing behaviors and energy-absorbed characteristics of honeycombs with negative Poisson’s ratio (NPR) have been studied by means of explicit dynamic finite element analysis (DFEA) using ANSYS/LS-DYNA. First, the honeycomb models filled with different reentrant cells by the variation of micro-cell configuration parameters (cell-wall angle and shape ratio) are established. The respective influences of micro-structure and impact velocities on the deformation behaviors, the dynamic plateau stresses and the absorbed energy of reentrant honeycombs are explored in detail. It is shown that owing to the variation of cell micro-structure, reentrant honeycombs display different macro-/micro- deformation properties during the crushing. For the given impact velocity, the dynamic plateau stresses are related to the shape ratio by a power law and to the cell-wall angle by least-square curves. And they are also proportional to the square of impact velocities for a high impact velocity. Based on the finite element simulated results and one-dimensional shock wave theory, an empirical formula for auxetic honeycomb to predict the dynamic plateau stress is derived in terms of relative density and impact velocity.

The optimal ecological performance of a Newton's law generalized irreversible Carnot refrigerator with the losses of heat resistance, heat leakage and internal irreversibility is derived by taking an ecological optimization criterion as the objective, which consists of maximizing a function representing the best compromise between the exergy output rate and exergy loss rate (entropy production rate) of the refrigerator. Numerical examples are given to show the effects of heat leakage and internal irreversibility on the optimal performance of generalized irreversible refrigerators.

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Physical insights and characteristics of beam transformations based on multimode interference (MMI) in multimode waveguides are illuminated and analyzed. Our calculations show that, utilizing a short piece of cylindrical multimode waveguide, an input Gaussian beam can be readily transformed to frequently desired beams including top-hat, donut-shaped, taper-shaped, and Bessel-like beams in the Fresnel or the Fraunhofer diffraction range, or even in both ranges. This is a consequence of diffractive propagation of the field exiting the waveguide. The performance of the beam shaper based on MMI can be controlled via tailoring the dimensions of the multimode waveguide or changing the signal wavelength. This beam shaping technique is investigated experimentally using monolithic fiber devices consisting of a short piece of multimode fiber (approximately 10 mm long) and a single-mode signal delivery fiber.