This paper discusses similar-scale mechanical models of a thrips wing using microelectromechanical systems (MEMS) piezoresistive cantilevers to quantitatively evaluate bristled wing characteristics. Each cantilever had combs with varying widths and neighboring gaps that were adjusted so that a constant surface area was maintained. The cantilever body was 1,324 × 256 × 5 μm3 in size. An aerodynamic drag force from the airflow applied to the cantilever surface was measured using the fractional resistance change of the piezoresistor due to the cantilever's deformation. The aerodynamic characteristics of each model were evaluated in a wind tunnel with airflow velocities between 1.2 and 5.6 m/s. The experimental results suggest that at a lower comb-width-based Reynolds number that was approximately equal to that of a bristled wing of a thrips, the comb areas of the cantilever act as an airflow suppression due to boundary layer effects, which results in an increased aerodynamic force.
Evaluation of the thoracic injury due to blunt impacts during the contact and collision sports activity is very crucial for the development and validation of the chest protectors for the athletes and safety balls of the sports such as cricket, baseball, lacrosse and the golf. In order to evaluate the thoracic injury due to solid sports ball impacts, a series of nonlinear transient dynamic, finite element simulations were carried out by impacting the FE model surrogate of the thorax “MTHOTA” (Mechanical THOrax for Trauma Assessment) with a baseball (both soft-core and synthetic) and a cricket ball at impact speed of 10 - 45 m/s, with an increment of 5 m/s. Only for the impact speed for which measured VCmax was 1 m/s, further simulations were carried out by introducing the ball spin (1000 - 8000 rpm, with an increment of 1000 rpm). Soft-core baseball, synthetic baseball and cricket ball impacts have caused VCmax = 1.0 m/s (25% probability for AIS3+ injuries) at impact speeds of 30.7 m/s, 27.9 m/s and 23.2 m/s respectively. For the normal impacts, spin (about impact direction and two directions perpendicular to the impact direction) of the ball has got no impact on the blunt thoracic trauma. At usual pitching speeds, soft-core baseball didn’t offer any safety and performance point of view, it was found to be as bad as synthetic baseball. Deflection response of the MTHOTA and the solid sports ball - MTHOTA energy interactions have yielded VCmax ∝ [(TEmax)1748, (Time rate of KEmax)0.9489, (Deformation velocitymax)2.3227, and (Impact velocitybaseball)2.548]. Similarly, Stored Energy Criterion and Energy Storing Rate Criterion (Wang, 1989) have yielded the relations Peak stored energy ∝ (Peak deflection MTHOTA)1.253 and Rate of peak stored energy ∝ (Peak deflection MTHOTA × Rate of peak deflection MTHOTA)0.5554.
The present paper presents the numerical results of a finite-element analysis of the role of a linear buckling phenomena in the etiology of idiopathic scoliosis. In a previous study, we assumed that idiopathic scoliosis is a buckling phenomenon induced by the growth of vertebral bodies, and we used the finite-element method with a spine model to demonstrate the results of linear buckling. However, a program based on the theory of nonlinear buckling did not produce clear buckling modes that were similar to the observed clinical modes. In this study, we return to the starting point and use rather simple models to confirm the existence of a buckling phenomenon that has various geometrical properties. We assumed that the growth of the vertebral bodies can be modeled by the generation of a non-elastic bulk strain. We use the finite-element method to analyze linear buckling modes caused by the growth deformation, and we confirm the existence of the buckling phenomena and clarify the range of the geometrical parameters in which this buckling occurs. By a comparison of different models, we investigate the influence of the region of the buckling phenomena on the physiological curvature of the spine and the intervertebral articulation. Our results support Dickson's hypothesis that a flattening or reversal of normal thoracic kyphosis at the apex of the curvature of the spine causes the buckling phenomenon.
To investigate roughness effect in spine implant, a contact model is offered in this paper. The contact surfaces are modeled macroscopically as semi-spherical containing micro-scale roughness. A minimum mean surface separation between two rough surfaces is defined and related to contact force. This is accomplished through a statistical account of elastic and plastic micro contact at the surface roughness scale and the subsequent integration of micron level events to obtain macro level expectation of force as a function of mean surface separation. Contact force - minimum separation relation facilitates the derivation of hysteretic energy loss during a load-unload event. It is found that the surface high plasticity index yields more energy per cycle. Using the force-minimum surface separation in a dynamic interaction of the implant, approximate leads to the prediction of contact natural frequencies and damping ratio of the implant. These characteristics along with energy loss in implant affect implant's performance and durability.
This study investigated propelling the attendant-propelled wheelchair on a level surface and up slopes, as well as pulling on the wheelchair while descending slopes, with varying resistive loads caused by the slopes and also by changing the weight of the system. The research questions in this study were: 1) How do attendants naturally adapt their walking speed and upper extremity posture when pushing/pulling an attendant-propelled wheelchair? 2) How did this vary with increased resistive loads? 3) What individual differences occurred between participants? When ascending, as the resistive loads increased the wheelchair speeds decreased. The Spearman's rank-order correlation for monotonicity showed was strong, negative correlation between horizontal pushing force and wheelchair speed, which was statistically significant. The maximum mechanical power used by the majority of participants when ascending was approximately 60W at the highest resistive load. The posture learning forward with pushing relatively lower from horizontal direction in ascending, kept joint moments in upper extremity low, up to 60N horizontal force. Over the 60N in horizontal force, the performed pushing force in horizontal direction still kept joint moments low. In descending, the wheelchair speed in most participants did not have clear monotonicity against the increase of the resistive load. Aligned the upper arm and forearm corresponding to the vector of pulling force reduced joint moment in shoulder and elbow. From these findings a model will be established, which can be used in future research to establish how hard different terrains are for wheelchair users and test improvements to the environment as well as the design of the wheelchair.
A new plantar foot sensation-testing instrument (PFS Tester) was developed for the practical screening of diabetic neuropathy and the prediction of fall risk for frail elderly people. Human plantar sensation may play an important role in many processes, including postural control, walking, and the clinical testing of diabetic peripheral neuropathy. The PFS Tester uses shear force on the skin as the mechanical stimulus, unlike any existing devices or tools for sensory examination, and it automatically provides the test site on the plantar foot with a pre-programmed sequence of stimuli. Although the PFS Tester uses two factors to distinguish stimulus intensity (a variable range and the speed of the shearing movement), measurements of the shear force on a material that simulates a human body showed that only a range of the probe movement affected the stimulus intensity. Also, the increment profiles of twenty-grade stimulus of the PFS Tester were similar to those of the Semmes-Weinstein (SW) monofilament, which is the most typical sensory exam tool. In addition, repetitive measurements of the force using the PFS Tester and the SW monofilament showed that the stimulus intensity of the PFS Tester had better reproducibility than that of the SW monofilament. To verify the validity of the sensory examination's results of the PFS Tester, sensory thresholds on three sites of the plantar foot in nineteen subjects with diabetes mellitus were measured using the SW monofilament test and the PFS Tester. The sensory thresholds obtained by the PFS Tester had a favorable correlation to those obtained by the SW monofilament test. The results of this study demonstrated that a PFS Tester could be used as a simple sensory examination machine with good reliability, simplified operation, and a high compatibility with the SW monofilament test.
A computational study of effects of vessel dynamics and compliance on coronary artery hemodynamics with / without stenosis is presented. The coronary artery hemodynamics with stenosis has been a main subject as one of the major cardiovascular diseases induced by atherosclerosis; most computational models assume that the vessel movement and deformation are negligible (Zeng, et al., 2003; Kim, et al., 2010). However, it is till unclear whether the hemodynamic characteristics owning to vessel dynamics and compliance is clinically significant or not particularly under pathological conditions. In this study, we aim at investigating the hemodynamic effects of the vessel dynamics and compliance in right coronary artery under healthy situation without stenosis as well as under diseased conditions with stenosis. We constructed a three-dimensional geometric model of the right coronary artery based on X-ray angiographic images, in which both vessel movement and deformation were taken into account. A specific volumetric flow rate was employed as a boundary condition imposed on inlet. Furthermore, we carried out an extensive study on the inlet waveform dependence and the effects of the vessel compliance on coronary hemodynamics. Our results demonstrate that the conventional assumption on ‘rigid’ artery models holds only in the cases of normal coronary arteries but fails for stenosed coronary arteries where the vessel dynamics and compliance do extend significant influence on distributions of the oscillatory shear indices (OSIs). Moreover, we find that the effects of vessel dynamics and compliance on coronary hemodynamics seem to be independent of both inlet boundary conditions and the vessel compliance.
July 27, 2015 There had been a system trouble (from July 26‚ 2015 15:25 to July 27‚ 2015 1:00 (GMT)). The service has been back to normal.
July 15, 2015 A new online journal "Mechanical Engineering Letters" has been launched by The Japan Society of Mechanical Engineers (JSME). This publication of such a letter journal is not only a new experience but also a tremendous challenge for the mechanical engineering society.
May 01, 2015 Please note the "spoofing mail" that pretends to be J-STAGE.