Vibration energy harvester for variable speed rotor applications using passively self-tuned beams

A vibration energy harvester is proposed for rotating systems based on transverse vibrations of an assembly of thin beams and electromagnetic interaction of a carried magnet with a coil of wire. The harvester is designed in a way such that centrifugal forces are utilized to tune the system’s natural frequency to the expected frequency of torsional vibrations. In fact, a novel combination of a tuning mass positioned at the beam’s support and an applied preload are introduced to establish a tuning mechanism that is capable of maintaining resonance along a wide frequency range. The device’s tuning can cover relatively high rotor speeds, overcoming previous limitations on the size and the physics of tuning via axial loads. Moreover, exact expressions of the beams’ mode shapes are taken into account to improve the accuracy of the proposed tuning mechanism. Numerical simulations of the device’s response are carried out for case studies corresponding to different frequency orders. It is shown that the system can maintain a flat power output across a wide range of operating speeds, effectively leading to purely broadband energy harvesting

Vibration energy harvester for variable speed rotor applications using passively self-tuned beams

A vibration energy harvester is proposed for rotating systems based on transverse vibrations of an assembly of thin beams and electromagnetic interaction of a carried magnet with a coil of wire. The harvester is designed in a way such that centrifugal forces are utilized to tune the system’s natural frequency to the expected frequency of torsional vibrations. In fact, a novel combination of a tuning mass positioned at the beam’s support and an applied preload are introduced to establish a tuning mechanism that is capable of maintaining resonance along a wide frequency range. The device’s tuning can cover relatively high rotor speeds, overcoming previous limitations on the size and the physics of tuning via axial loads. Moreover, exact expressions of the beams’ mode shapes are taken into account to improve the accuracy of the proposed tuning mechanism. Numerical simulations of the device’s response are carried out for case studies corresponding to different frequency orders. It is shown that the system can maintain a flat power output across a wide range of operating speeds, effectively leading to purely broadband energy harvesting

Impact of supply problems of preservative-free glaucoma medications on patients and hospital staff

PURPOSE: Glaucoma is a chronic ocular disease, which is usually managed with long-term daily medical therapy, in the form of eye drops. Patients who are intolerant to preservatives in topical medicines require preservative-free versions. From early 2011 patients attending Moorfields Eye Hospital, London, UK, started to report recurring problems with the supply of the following preservative-free glaucoma medications: Timolol 0.25% (Timoptol 0.25%, MSD UK); Dorzolamide (Trusopt, MSD UK); Dorzolamide and Timolol 0.5% (Cosopt, MSD UK). This study investigates the impact of the supply problems of these medications at Moorfields Eye Hospital from a patient, administrative and clinical perspective. METHODS: Information was sought by interviewing both patients and hospital staff, and by a retrospective case note review between April 2010 and May 2013. RESULTS: Many hospital roles, both administrative and clinical, were involved in attempting to resolve the impact of the supply problems. All staff reported a considerable increase in their workload. At the peak of the problem, the glaucoma secretaries received about 150 enquiries per week. A review of 83 sets of patient notes, retrieved from a random sample of 125 patients, showed that 22% encountered a supply problem. Of these, more than one-third attended Moorfields Eye Hospital Accident & Emergency (A&E) for repeat supplies and 89% eventually had their medication changed. In telephone interviews with 39 of a random sample of 50 patients (a subset of the 83 notes retrieved), 59% of the interviewees reported a supply problem. Of these, one-third attended Moorfields Eye Hospital A&E for repeat supplies and half eventually required an alternative medication. Some patients reported going to considerable lengths to obtain ongoing supplies in the community. CONCLUSIONS: This study shows that medication supply problems can have a major impact on patients and hospital services. Supply problems occur across many fields of medicine and with increasing frequency. The findings of this study highlight the importance of early communication of impending shortages between manufacturers and the Department of Health, as recommended in the best practice guidelines. In order to minimise the impact of medicine shortages on patients, clinicians and administrative staff, hospitals need immediate notification of potential supply problems and clear updates on supply resolution. In addition, hospitals should consider nominating an individual as a contact point for patient enquiries regarding medicine supply problems

The relationship between unwarranted variation in optometric referrals and time since qualification

Purpose: To investigate variation in optometric referral decision-making and the influence of experience and continuing education and training (CET). Methods: To gain insight into unwarranted variation in referral activity in the UK: (1) triage data were audited to investigate source of referral, provisional diagnosis, and outcome; (2) an online system was developed to present two sets of ten vignettes, designed to avoid prompting answers. Participating optometrists completed ten pre-CET vignettes, recording their tests and management decisions. The main group of participants chose whatever CET they wished over a six-month period and then completed another ten post-CET vignettes. A second group of newly-qualified optometrists completed the vignettes before and after a CET course intervention, followed by a third group of pre-registered optometrists with an intervention of six-months experience of their pre-registration year. Results: The audit identified 1951 optometric referrals and 158 optometrists (211 referrals were from GP practices), with 122 of the 158 optometrists making fewer than ten referrals. Two newly-qualified optometrists generated 12.5% of the total referrals in the audit (N = 2162). Many suspect glaucoma referrals were based on a single suspect measurement resulting in a high discharge rate after community review, as did referrals for certain fundus-related appearances for which no treatment was indicated. The intervention of gaining CET points appeared to have no significant impact (p = 0.37) on referral decision-making, although this part of the study was underpowered. Self-selection bias was confirmed in the main group. When the main group and newly-qualified practitioners were compared, the number of referrals was negatively associated with time since qualification (p = 0.005). When all twenty referral decisions were compared, all optometrists referring more than ten vignette patients came from a group of newly-qualified practitioners up to two years post qualification. Pre-registered optometrists generally referred more appropriately than newly-qualified. Upon qualification, there was a significant increase in the number of sight tests undertaken per day (p = <0.0005). Conclusions: Gaining CET points alone is unlikely to significantly improve referral decision-making. Mentoring and targeted CET for the newly-qualified up to two years post-qualification should be considered. Ophthalmology replies to the referring newly-qualified optometrist are vital for moderating future referrals and developing clinical confidence

Impact-induced vibration in vehicular driveline systems: theoretical and experimental investigations

The paper investigates the conditions leading to the emergence and persistence of an acute metallic noise in light-truck drivelines. Sudden demands in torque in the presence of lash zones give rise to this phenomenon, which is onomatopoeically referred to as clonk. The study of clonk requires combined rigid multi-body dynamics and flexible body oscillations. The results show high-frequency contributions in the driveline vibrational response of certain structural modes of the driveshaft pieces, which are induced by remote impact of meshing transmission teeth through backlash. The numerically predicted spectrum of vibration shows good correlation with experimental measurements of radiated noise from a dynamic drivetrain rig

Gear transmission rattle: assessment of meshing forces under hydrodynamic lubrication

The dynamic behavior of gear transmissions poses several challenges from the standpoint of design and requires the availability of more advanced models capable of simulating a wide range of operating conditions. In this paper, several formulations to represent efforts related to the lubricant in gear transmissions subjected to reduced torque levels has been assessed. Under these conditions, the lubrication regime is hydrodynamic and the dynamic behavior of the meshing contacts can happen in different scenarios depending on both the lubricant properties and operating conditions. Such problems are cumbersome in gear transmissions in which acoustic performance is a determining design factor, such as in car applications. In this regard, gear rattle is one of the subjects of concern by powertrain designers. In spite of several authors have approached this phenomena, the most recent interest is focused on the role played by the lubricant. The variety of fundamentals and aims of the developed models in this respect requires a better understanding of the effect taken into account by the different formulations in the accurate modeling of hydrodynamic lubrication in gears subjected to low torques. This is the reason why, in this work, several alternatives currently available in the literature to address the formulation of efforts in hydrodynamic regime was collected and presented. Such formulations were implemented in a transmission model previously developed by the authors which was used to simulate different operating conditions in order to assess the results obtained with each one of the considered formulations.This work has been supported by project DPI2013-44860 funded by the Spanish Ministry of Science and Technology and project PRX14/00451 funded by the Spanish Ministry of Education, Culture and Sports and COST Action TU 1105

An investigation on impact-induced oscillations and noise in lubricated conjunctions

Energy efficiency and Noise, Vibration and Harshness (NVH) have been in the centre of attention for automotive manufacturers during the last decades. Energy losses occur in different forms, such as friction, impacts and noise. Physical understanding of the mechanisms that lead to aggressive dynamics and noise generation is a key in order to design more efficient systems with better NVH performance. In the current study, impact energy is calculated at the lubricated piston-liner conjunctions combining dynamics and tribology. The vibration power at the engine block surface is converted into sound pressure level (SPL) at any desired location analytically. Then, a technique is presented to reduce the severity of impact dynamics by controlling piston's secondary motion, comprising vibration absorbers with nonlinear characteristics. The piston secondary motion dynamics are studied and the absorber effectiveness on vibration reduction is discussed

Dynamic and tribological study of a planetary gearbox with local nonlinearities

A planetary gearbox model comprising five spur gears (sun, ring and three planets) and the carrier has been developed and analysed. The influence of gear teeth backlash and friction during mixed regime of lubrication has been taken into consideration. Greenwood and Tripp model is employed, while viscous friction is calculated analytically using the functions of Evans and Johnson. A combined tribodynamics modeling approach has been implemented and modal analysis is performed in order to predict the coupled mechanism of tribological and dynamic behavior, subjected to backlash and excited at the gear meshing frequency. The software used for the simulations is ADAMS MSc (Student Edition), where the model variables (concerning gear geometry and forcing functions) have been added in a parametric way. The results showed that small variations of the dynamic transmission error affect notably the viscous friction through changing the contact load between the engaged teeth pairs. Also, higher values of the Stribeck oil parameter due to higher film thickness or lower surface roughness in the mixed lubrication regime lead to reduction of the boundary friction, whereas a reduction of the total generated friction occurs when increasing the angular velocity of the input gear body (due to higher film thickness and smaller asperity interactions). The above lead to reduced power loss of the mechanism. Finally, a characterization of the system dynamics is presented using the calculated eigenvalues and eigenmodes of the corresponding linearized system. Potential interactions with the gear meshing frequency of the system are also examined