We present a numerical study of the packing of uniform spheres under three-dimensional vibration using the discrete element method (DEM), focusing on the effects of vibration condition (amplitude and frequency) and inter-particle frictions (sliding and rolling frictions). The results are analysed in terms of packing density, coordination number (CN), radial distribution function (RDF) and pore structure. It is shown that increasing either the vibration amplitude or frequency causes packing density to increase initially to a maximum and then decrease. Both vibration frequency and amplitude should be considered to characterize the effect of vibration process on packing structure. The sliding and rolling frictions between particles can decrease packing density since they dissipate energy, although the effect of rolling friction is less significant. In line with the change of packing density, microstructural properties such as CN, RDF and pore distribution also change: a looser packing often corresponds to smaller CN, less peaked RDF and larger but more widely distributed pores. 相似文献
Owing to the elasticity and plasticity of the skeleton, joints and muscles, the musculoskeletal system is capable of absorbing and damping mechanical vibration without damage as long as the vibration level is within tolerable limits. However, technical developments have led to the exposure of many people to intolerable variation levels with destructive changes as a result.
These injuries to the musculoskeletal system continue to be the subject of research interest. Initially, the joints and joint complaints attracted the greatest attention. Vibration damping takes place mainly in the joints. The incidence of destructive joint changes has been examined in comprehensive clinical, epidemiological and radiographic studies, mainly concentrating on the joints of the hand and arm. The response of muscles to vibration is often expressed in the form of a tonic vibration reflex (TVR) which arises as a result of stimulation of the muscle spindles and therefore resembles the classic tonic stretch reflex. There is increased muscular activation for stabilisation of the joint positions, especially during whole-body vibration. Studies have also disclosed how vibration affects body equilibrium and equilibrium control and how vibration can elicit muscle pain, cramps and reduced muscular strength. 相似文献
Excessive floor vibration due to walking is an important serviceability condition to be considered in building design. This paper presents several case studies of problem floors. The case studies include complaints about office, classroom, and retail spaces where vibration levels were found disturbing. In each of these cases, the cause of the vibration was due to people walking around the space. These case studies are presented to reinforce the existence of this problem, to describe nonstructural factors that affect the behavior of floors, and to provide new data to the design and research communities. 相似文献
The transport and dosage of granular materials are an important part of Process Engineering. Thereby, the food, chemical, pharmaceutical and coating industries set high demands on the transport and dosage performances of the used plants. In this context, Ultrasound Process Technology in the past years has developed itself into an attractive alternative compared to presently used classical technologies.
This paper describes the application of ultrasonic progressive waves in a powder-feeding device. The use of a specific pipe material with appropriate damping characteristics allows to generate a progressive wave using a single piezoelectric actuator. Small objects can be carried along the surface of a pipe by the elliptic motion at the surface, which is the result of a flexural progressive wave. The operational principle is the same as in travelling wave ultrasonic motors.
It was experimentally confirmed that the device can be used for feeding and supplying small amounts of powder. The powder-fed performance, however, strongly depends on environmental conditions, so that a control of the system is required. Construction and characteristics of a trial device are shown. 相似文献