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Stone-skipping is a common yet complex motion that involves rigid-body dynamics and fluid–structure interaction (FSI). While many computational fluid dynamics methods are used to simulate the interaction between a stone and fluid, little research has been done to consider the stone, fluid, and fluid boundary as a whole in a simulation. This study, focuses on the attitude motion and free-surface deformation of stone-skipping over shallow water to investigate how the boundary effect of FSI impacts ricochet behaviors. Initially, we establish an iteration framework for the stone-skipping FSI issue based on a weakly compressible smoothed particle hydrodynamics (SPH) method with a Riemann solver. We conduct particle-independence verification and simulate several cases under varying water heights. Additionally, we analyze and compare ricochets in deep and shallow cases with different incident angles and initial pitch angles. The numerical results demonstrate that in shallow flow scenarios, the "comma-shaped" high-pressure area is compressed by the stone and the fluid boundary, leading to a more moderate variation in pitch angle. Stone-skipping in shallow water typically covers a shorter distance and reaches a lower height compared to deep water cases. Changes in the incident angle show that shallow water hinders successful skipping. Futhermore, different initial pitch angles reveal that water height directly impact the stone's trajectory in both horizontal and vertical directions. These highlight the connection between motion patterns and parameters, offering a reliable numerical prediction for the stone-skipping problem using the Riemann SPH method. [ABSTRACT FROM AUTHOR]

To maintain the robustness of crashworthiness performance in energy absorbing structures, high specific energy absorption (SEA) and crush force efficiency (CFE) need to be maintained across a wide range of load angles. In this paper, concave design was proposed to address this issue. Finite element analysis was utilised to identify the main load-bearing elements for axial and shear loading. Furthermore, the design concepts were classified into surface variation and cross-section variation. Pattern design, which is a representative design of surface variation, can enhance crashworthiness performance by reducing the initial crushing load and maximising the development of a travelling hinge. However, there is a drawback that designing the cross-section to maximise the development of the travelling hinge leads to an increase in the dihedral angle, resulting in a decrease in the CFE. This paper proposed the concave design, that ensures excellent robustness of crashworthiness performance and minimised the trade-off between SEA and CFE performance under combined shear-compression loading. The design induces local crushing due to geometric imperfections, which reduces the peak load while maintaining the high load-bearing capacity, thereby increasing SEA. Furthermore, the surface of the energy absorbing structure is an important load-bearing component that supports shear loads, and the concave design induces progressive crushing modes for any load angle, thereby maximising the deformation of the surface and improving SEA. The structural characteristics of the concave design were validated through quasi-static loading tests. [ABSTRACT FROM AUTHOR]

Reducing structural shocks propagated as elastic waves in thin plate-like structures is of paramount importance in diverse engineering applications. In this study, a shock reduction method using elastic patches that deflect bending waves through wave refraction, while maintaining the structural stiffness and strength is presented. Elastic patches with gradual thickness variation were designed and thoroughly investigated both numerically and experimentally. Two types of triangular elastic patches, flat and pyramid-shaped, were utilized to refract and attenuate transient bending waves at different incident angles. All results from ray tracing, finite element analysis, and experiments consistently demonstrated the effective reduction of passing waves in areas behind the attached patches. Moreover, the influence of gradual thickness variation was thoroughly discussed. The proposed method provides a practical approach to mitigate transient shock responses in specific target areas across various structural applications without compromising structural stiffness and strength. [ABSTRACT FROM AUTHOR]

An experimental investigation of the effect of random vibration on the melting behavior of a phase change material (PCM) and the thermal performance of a PCM-based heat sink is presented. While random vibration from 2 to 16 g rms for the frequency range from 15 to 2000 Hz was applied to a rectangular enclosure, which contains paraffin wax and the heat sink, a constant heat flux was imposed on the heat sink to melt the PCM. The experimental results showed that the random vibration has no effect on the melting behavior early in the melting process during which conduction is the primary mode of heat transfer. However, the random vibration significantly affected the melting behavior later in the process during which natural convection is the primary mode of heat transfer. The random vibration augmented heat transfer in the molten PCM and increased the Nusselt number, 1.56 times greater under the vibration of 16 g rms than without vibration. The augmented heat transfer accelerated PCM melting and delayed the rise in temperature of the heat sink. The time for the temperature of the heat sink to rise to a threshold increased as the intensity of random vibration increased, 5.9 times longer under the vibration of 16 g rms than without vibration. [ABSTRACT FROM AUTHOR]

The crease line formed in an origami-shaped crash box (OSCB) acts as a geometric imperfection and mode inducer. Such geometric imperfections make it possible to protect occupants by lowering the peak force in the event of a collision. The OSCB also shows desirable performance as a crashworthy structure by inducing a collapsing mode with excellent energy absorption. There are many studies on crash boxes with origami patterns applied, but few studies on performance optimisation. This article describes the structural optimisation of an OSCB to maximise the specific energy absorption (SEA) by setting the corner length c and module length l as design variables. Numerical and experimental investigations of the crashworthiness performance were conducted by comparing the optimised OSCB to a circular crash box (CCB), which is known to have the best SEA among straight tubes. The numerical and experimental results were in good agreement, with the optimised OSCB collapsing into the diamond mode. The results of the numerical comparison showed that the SEA and the crush force efficiency (CFE) of the optimised OSCB were increased by 5.94% and 115.58%, respectively. However, in a quasi-static axial crushing experiment, the SEA of the optimised OSCB was 10% lower than that of the CCB, and the CFE was increased by 88.5%. The optimised OSCB in this study displayed an improvement in the SEA compared to the reference OSCB, as well as a reduction in the difference from the CCB, indicating high maintenance performance of the CFE. [ABSTRACT FROM AUTHOR]

In this paper, a novel concept of the adaptive vibration isolator is presented. The proposed adaptive isolator is based on the thin-walled Yoshimura-patterned tube, which is able to reconfigure its shape to tune the stiffness. Multiple numbers of reconfigurable modules compose the proposed vibration isolator; thus, the force transmissibility of the isolator can be adjusted by systematic reconfiguration of the modules to show the best performance for the subjected vibration environment. The paper presents the analytical and experimental analysis of the force transmissibility of the proposed adaptive vibration isolator. The dynamic equation of the motion for the isolator system is established, and the force transmissibility is analyzed for the various configuration that a single design can have. The prototype of the proposed adaptive isolator is manufactured with an embedded actuation mechanism for reconfiguration. The performance of the isolator is experimentally confirmed through the vibration test of the fabricated prototype. Both the results of the analytical and the experimental investigation well demonstrate the adaptive characteristics of the proposed isolator concept. [ABSTRACT FROM AUTHOR]