Current Issue : January - March Volume : 2015 Issue Number : 1 Articles : 5 Articles
This paper concerns themechanism for harvesting energy fromhuman bodymotion.Thevibration signal fromhuman bodymotion\nduring walking and jogging was first measured using 3-axes vibration recorder placed at various places on the human body. The\nmeasured signal was then processed using Fourier series to investigate its frequency content. A mechanism was proposed to harvest\nthe energy from the low frequency-low amplitude human motion. This mechanism consists of the combined nonlinear hardening\nand softening mechanism which was aimed at widening the bandwidth as well as amplifying the low human motion frequency.\nThis was realized by using a translation-to-rotary mechanism which converts the translation motion of the human motion into the\nrotational motion.The nonlinearity in the system was realized by introducing a winding spring stiffness and the magnetic stiffness.\nQuasi-static and dynamic measurement were conducted to investigate the performance of the mechanism. The results show that,\nwith the right degree of nonlinearity, the two modes can be combined together to produce a wide flat response. For the frequency\namplification, the mechanism manages to increase the frequency by around 8 times in terms of rotational speed....
With the continuous development of mechanical automation, the structural health monitoring techniques are increasingly high\nrequirements for damage detection. So structural health monitoring (SHM) has been playing a significant role in terms of damage\nprognostics.Themain contribution pursued in this investigation is to establish a detection system based on ultrasonic excitation and\nfiber Bragg grating sensing, which combines the advantages of the ultrasonic detection and fiber Bragg grating (FBG). Differencing\nfrom most common approaches, a new way of damage detection is based on fiber Bragg grating (FBG), which can easily realize\ndistributed detection. The basic characteristics of fiber Bragg grating sensing system are analyzed, and the positioning algorithm\nof structural damage is derived in theory. On these bases, the detection system was used to analyze damage localization in the\naluminum alloy plate of a hole with diameters of 6 mm. Experiments have been carried out to demonstrate that the sensing system\nwas feasible and that the estimation method of the location algorithm was easy to implement....
The aim of this study is to measure and quantify perceived intensity of discomfort due to vibration in a vehicle in situ considering\ncomplete vehicle dynamic behaviour. The shaker table based discomfort curves or the road test results may not accurately and\nuniversally indicate the true level of human discomfort in a vehicle. A new experimental method, using a seated human in a car on\nthe four-post rig simulator, is proposed to quantify discomfort. The intensity of perception to vibration decreased with decreasing\ninput and increasing frequency; the rate of change is different from the published literature; the difference is large for angular\nmodes of inputs. Vehicle dynamic response is used to inform and analyse the results. The repeatability of the method and the fact\nthat they are in situ measurements may eventually help reduce reliance on the road tests. Furthermore, discomfort curves obtained,\nsubsequently, can be used in predictive models....
A unified analytical approach is applied to investigate the vibrational behavior of grid-stiffened cylindrical shells with different\nboundary conditions. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell\nin order to obtain the equivalent stiffness parameters of the whole panel. Theoretical formulation is established based on Sanders�\nthin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives\nare legitimized using Stoke�s transformation. A 3D finite element model is also built using ABAQUS software which takes into\nconsideration the exact geometric configuration of the stiffeners and the shell.The achievements fromthe two types of analyses are\ncompared with each other and good agreement has been obtained. The Influences of variations in shell geometrical parameters,\nboundary condition, and changes in the cross stiffeners angle on the natural frequencies are studied. The results obtained are\nnovel and can be used as a benchmark for further studies. The simplicity and the capability of the present method are also\ndiscussed....
Introduction of holes into plate-like structures is commonly found as one of the practical noise control measures to reduce sound\nradiation. However, perforation also reduces the panel stiffness and hence increases its vibration. The discussion on this effect is\nlacking and hence this paper discusses the dynamics of a perforated panel from the results obtained from Finite Element (FE)\nmodel. Different hole geometries and arrangement are simulated to investigate their effect on the plate mobility. In general, it is\nfound that increasing the perforation ratio increases the plate mobility. For a fixed perforation ratio, the mobility increases at high\nfrequency (above 1 kHz) for a smaller hole density in the plate.The plate with holes concentrated at the middle shows the largest\nincrease of vibration around the plate centre compared to those uniformly distributed or away fromthe middle and concentrated at\nthe plate edges. This is because as the hole separation becomes smaller, the reduction of the global stiffness around the mid area of\nthe plate becomes greater. This also corresponds to the finding here that the mobility is greater at the vicinity of the hole. Different\nconditions of the plate edges are found to give consistent trend of the effect of perforation....
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