Numerical visualization of drop and opening process for parachute-payload system adopting fluid–solid coupling simulation

In order to study the fluid–solid coupling dynamic characteristics of parachute-payload system during drop process and analyze the unsteady aerodynamic characteristics under finite mass opening conditions, an adaptive moving fluid mesh method is developed on the basis of the existing arbitrary Lagrangian–Eulerian (ALE) fluid–solid coupling method. The calculation results of open force and drop velocity on the C-9 parachute demonstrate the effectiveness of this method. On this basis, the effect of canopies with three different permeability on parachute-payload system motion characteristic including opening property, steady descent property and stability is studied. Comparative analysis is conducted for structures and characteristics of vortex with different canopy materials, and interference mechanism of unsteady flow for parachute-payload system in unsteady oscillation is revealed. The results show that the adaptive moving fluid mesh method can effectively eliminate restrictions of existing simulation methods for parachute-payload system and significantly reduce calculation time. For the lightweight parachute, permeability has significant effect on kinetic characteristic of parachute-payload system. Canopy with large permeability has small opening load and structural stress in opening stage. After opening, there are mainly small vortexes distributed evenly behind the canopy with good stability. However, canopy with small permeability has obvious breath behavior and oscillation in opening stage. The main vortexes periodically shed off after opening. With the change of permeability from small to large, Parachute-payload system eventually presents three steady descent modes: conical descent, gliding descent and stable vertical descent. Graphical abstract

Numerical simulation of water entry problems considering air effect using a multiphase Riemann-SPH model

The water entry is a classic fluid-structure interaction problem in ocean engineering. The prediction of impact loads on structure during the water entry is critical to some engineering applications. In this paper, a multiphase Riemann-SPH model is developed to investigate water entry problems. In this model, a special treatment, a cut-off value for the particle density, is arranged to avoid the occurrence of negative pressure. A remarkable advantage of the present multiphase SPH model is that the real speed of sound in air can be allowed when simulating water-air flows. In the present work, considering the air effect, several typical water entry problems are studied, and the evolution of multiphase interface, the motion characteristic of structure and complex fluid-structure interactions during the water entry are analyzed. Compared with the experimental data, the present multiphase SPH model can obtain satisfactory results, and it can be considered as a reliable tool in reproducing some fluid-structure interaction problems.

Creative Design of Legged Mobile Landers With Multi-Loop Chains Based on Truss-Mechanism Transformation Method

This paper proposes a novel family of the legged mobile lander (LML) with multi-loop chains to enable the stationary lander to walk, which is helpful to the Return and Base construction missions in the planetary exploration project. Generally, there are many issues that need to be focused, but one of the key issues is during the landing phase, for which the lander needs to be designed as a truss with ability to bear a large impact, while during the walking phase, the lander needs to be designed as a mechanism with flexible walking ability. To resolve this issue, a novel method for designing a mechanism based on a truss, which also can be called as the truss-mechanism transformation (TMT) method is developed. First, the detailed concept of the same topological arrangements (TAs) of a truss and a mechanism is proposed. Two singularity positions for the truss-mechanism transform are introduced. Second, following the concept, the procedure for designing a mechanism based on the TMT method is presented. Third, some basic knowledge for the creative design of the mechanism is introduced, including the intersection rules of motion characteristics, motion characteristic relationship of multi-loop mechanisms, and so on. Fourth, according to the procedure of the TMT method, numerous novel structures of LMLs with multi-loop chains are obtained. Finally, after the type qualitative evaluation, one typical LML is selected as an example to show its functions among stowed, walking, and orientation positions.

A Parametric Identification Method of Human Gait Differences and its Application in Rehabilitation

In order to understand the regularity of human motion, characteristic description is widely used in gait analysis. For completely expressing gait information and providing more concise indicators, parametric description is also particularly significant as a means of analysis. Therefore, in this paper, the mathematical models of gait curves based on the generalized extension-Bézier curve were investigated, of which the shape parameters were used as individual gait characteristics to distinguish whether the gait is normal or not and to assist in judging rehabilitation. To evaluate the models, angle data from three joints (hip, knee, and ankle) were recorded with motion capture system when participants (10 healthy males and 6 male patients with ankle fracture) were walking at comfortable velocity along a walkway. Then, the shape parameters of each subject were obtained by applying the mathematical models, and the parameter range of the normal group was further summarized. Through comparison, it could be found that most shape parameters of patients exceed the normal ranges in varying degrees, and are concentrated on specific parameters. The results can not only help to judge the recovery stages of patients but also figure out the corresponding abnormal postures, so as to provide guidance for rehabilitation training.

Not Just Going with the Flow: The Effects of Fluid Flow on Bacteria and Plankton

Microorganisms often live in habitats characterized by fluid flow, from lakes and oceans to soil and the human body. Bacteria and plankton experience a broad range of flows, from the chaotic motion characteristic of turbulence to smooth flows at boundaries and in confined environments. Flow creates forces and torques that affect the movement, behavior, and spatial distribution of microorganisms and shapes the chemical landscape on which they rely for nutrient acquisition and communication. Methodological advances and closer interactions between physicists and biologists have begun to reveal the importance of flow–microorganism interactions and the adaptations of microorganisms to flow. Here we review selected examples of such interactions from bacteria, phytoplankton, larvae, and zooplankton. We hope that this article will serve as a blueprint for a more in-depth consideration of the effects of flow in the biology of microorganisms and that this discussion will stimulate further multidisciplinary effort in understanding this important component of microorganism habitats.