The velocity required in IEC 61373 for long-life random vibration testing of Category-3 rolling stock equipment in the vertical direction is 2.7821 m/s, but the maximum velocity of existing ...electrodynamic shakers falls in the range of 2–2.5 m/s. In this study, an electrodynamic shaker with a velocity satisfying the requirements for vibration testing of Category-3 rolling stock equipment was developed. First, mechanical and equivalent circuit models of an electrodynamic shaker were developed. On this basis, reducing the impedance of the armature coil was identified as the best option for increasing the velocity of the shaker. However, owing to the impact of the back electromotive force of the armature coil, a decrease in the input impedance of the armature coil at low frequencies leads to an increase in its input impedance at high frequencies. To reduce the input impedance at high frequencies, a shading coil was incorporated into the circuit. The shading coil-incorporated new design was modeled using equivalent circuits and simulated numerically. The results showed that the improvement measures—incorporating a shading coil, increasing the cross-sectional area, and reducing the number of turns of the armature coil—effectively reduced the input impedance of the armature coil, thereby increasing the armature coil current and the velocity of the shaker. Finally, a shaker with a maximum velocity of 3.2 m/s was fabricated based on the new design and was validated to satisfy the high-velocity requirement for the long-life vibration test of Category-3 equipment in the vertical direction as specified in IEC 61373.
As ECS President, I recently had the privilege of representing the Society at the Perkin Medal award ceremony in Philadelphia. The event was particularly gratifying since the 2004 recipient of this ...prestigious award was Dr. Gordon E. Moore. Dr. Moore co-founded both Fairchild Semiconductor and Intel.
Trunk shaking is the most common mechanical harvesting system for harvesting pistachio. Harvesting machine operators often subjectively decide how to set the shaking parameters such as frequency and ...duration and this requires experience. The main objectives of this study were to evaluate the effect of tree morphology and shaking parameters such as trunk size and shaking pattern on the energy distribution through the branches and to optimise the shaking intensity of individual pistachio trees based on a tree-specific feedback loop. Wireless 3D accelerometer sensors were built and used to measure vibration transmission through the tree canopy at different locations and to monitor the energy transmission between the machine shaker head and the tree trunk. Thirty trees were selected for this study and were divided into three groups based on the trunk circumference size. To study the effect of a shaking pattern on the vibration transmission through the tree, four shaking patterns were selected and tested. Shaking duration was measured and it showed an average of 30% longer time compared to the shaking pattern duration. The effect of all four shaking patterns was analysed using continuous wavelet transform. The responses of trees were analysed and the optimum shaking intensity for each tree was determined. A model was developed to estimate the optimum shaking intensity for pistachio trees based on their trunk size. The model showed that 37, 57, and 65% are the optimum shaking intensity percentages for small, medium, and large trees, respectively.
•Mechanical harvesting systems for pistachio trees were studied.•Vibration transmission through the pistachio tree canopy was measured and analysed.•Wavelet analysis was used to find proper shaking intensity for each tree.•A model for optimum shaking intensity based on trunk size was developed.
Drilling engineers and derrick men, from the largest integrated oil companies, like Shell and Exxon, to the smaller drilling and service companies, like Mustang, need the information in this book out ...on the rig and in the office. Much of this material has, until now, only been available to the engineer through word of mouth, tradition, or in an internal company manual. The ASME Shale Shaker Committee set out to put this information in an accessible form for engineers all over the world to use, in the field, classroom, or industry short course. Besides shale shakers and other drilling rig equipment, the book's scope includes many other aspects of drilling solids control, including chapters on drilling fluids, cut-point curves, mud cleaners, and many others.
•A test rig for the identification of force coefficients on gas bearing is proposed.•Stiffness and damping coefficients of Herringbone Grooved Journal Bearings are measured.•The Narrwo Groove Theory ...slighlty overestimates the stiffness and damping coefficients.•Stiffness and Damping coefficients are found to be linear against excitation amplitude.
The Narrow Groove Theory (NGT) is commonly used to simulate and design grooved gas bearing. However, measurements of dynamic force coefficients of Herringbone Grooved Journal Bearings (HGJBs) is missing, hence the validation historic NGT has never been performed, despite its importance. A test rig was built in order to identify stiffness and damping coefficients of HGJBs of a rotor perturbed by piezo-electric shakers. Results indicate that the NGT captures the qualitative behavior of HGJB well but tends to overestimate the stiffness and damping coefficients by 23 and 29% respectively. Gravity led to a eccentricity ratio in excess of 15% without significant effect. The direct damping coefficient was found to be mildly non-linear with the excitation amplitude.
This paper aims to investigate the amount of energy which can be harvested by a cantilever beam type piezoelectric energy harvester from a bridge vibration. The sources of vibration are vehicles ...traversing the bridge. Two types of masses are considered as models for traversing vehicles: concentrated and distributed masses. The mass of the harvester is assumed negligible compared to that of the bridge. First, the problem of moving mass travelling with a constant speed over a beam is considered. The formulations for both concentrated and distributed masses are presented. The obtained results are then compared to the data available in the literature, in order to validate the model of a beam with a moving mass. Next, a mathematical model for the harvester is proposed, which is composed of an Euler–Bernoulli beam as a substrate, a tip mass, and a single piezoelectric patch whose electrodes are connected to a changeable resistance. To validate the model, the harvester is fabricated and tested on a shaker. The electroelastic frequency response functions of the system are measured by low-amplitude chirp excitation tests. The optimal resistive load at the resonance frequency, obtained from theory and experiments, are compared. Finally, the acceleration time histories for the beam at mid-span, where the harvester is located, are calculated for two mass types and used as base excitation signals to the harvester. These signals are replayed on an electromagnetic shaker to simulate the bridge vibrations on the fabricated harvester and the experimental results are compared with theoretical ones. Good agreement is observed.
•Piezoelectric energy harvesting from a bridge vibration is investigated.•Concentrated and distributed masses are considered as a passing vehicle models.•For concentrated mass, increase in voltage is proportional to the speed increment.•For distributed mass, the maximum voltage occurs at the exit step of the mass.•As the mass spread over the beam, the RMS of generated voltage output will reduce.
•Continuous contact between canopy tree and shaker is key for an effective harvesting.•Contact between shaker and canopy can be automated in real-time.•The tree resistance to shaking provides ...promising results in the contact control.•The distance between shaker and tree can be used for controlling the contact.•The low, middle and top zones of the tree have a different pattern of shaking.•The control system must be synchronized with the start point of shaking the tree.
Most crops destined for industrial transformation employ mechanical harvesters that have been developed satisfactorily by adapting the tree to the machine features. Not all fruit trees can be adapted, and this is the case in traditional olive orchards, where canopies are very irregular and a complex harvesting system is necessary to adapt to different tree geometries and sizes. Lateral canopy shakers have arisen as an alternative system, the use of which is spreading as they allow continuous integral harvesting of several crops such as citrus fruit or, more recently, the olive. Contact between the shaker and the canopy is a key harvesting factor that must be studied. Manually positioning several shaker heads at different heights to follow the tree contour during continuous harvesting is a tedious task for an operator and may decrease potential efficiency. However, automation of shaker contact with the canopy may increase harvester efficiency. Two automatic systems composed of several electronic devices were developed and incorporated into a harvester with several shaker heads. The first system controlled canopy contact based on measuring the distance between the shaker and the tree contour. The second system measured the variation of the shaker mechanism’s hydraulic pressure in order to adjust the position of each head relative to the canopy. Both systems were compared to manual control by studying removal efficiency, harvesting efficiency, debris production and percentage of shaking time within the control intervals. Results determined the suitability of automatic harvesting systems with an increase of 5.9% in removal efficiency based on the criterion of tree resistance to shaking, with no significant differences in tree damage and an increase in field capacity ha h-1 person-1. Laser LED may be a valid technology for measuring the distance to canopy in real time and gave satisfactory results but a decrease of 7.9% in removal efficiency compared to manual sighting. The bottom, middle and top of the tree present different patterns in the harvesting process, and as resistance mode adjusts control intervals to the different patterns, it may provide a closer fit to follow than distance mode. Further improvements are required to enhance harvesting efficiency by connecting automation between the removal system and the catch frame.
Electrodynamic shakers are widely used in experimental investigations of vibrated fluids and granular materials. However, they are plagued by undesirable internal resonances that can significantly ...impact the quality of vibration. In this work, we measure the performance of a typical shaker and characterize the influence that a payload has on its performance. We present the details of an improved vibration system based on a concept developed by Goldman (2002) 1 which consists of a typical electrodynamic shaker with an external linear air bearing to more effectively constrain the vibration to a single axis. The principal components and design criteria for such a system are discussed. Measurements characterizing the performance of the system demonstrate considerable improvement over the unmodified test shaker. In particular, the maximum inhomogeneity of the vertical vibration amplitude is reduced from approximately 10 percent to 0.1 percent; moreover, transverse vibrations were effectively eliminated.
AbstractThis paper presents a unique study on the dynamic identification of the tallest glue-laminated timber frame building in the world using forced vibration tests (FVTs) and long-term ambient ...vibration tests (AVTs). Because the amount of sway in service under wind has become the governing design criterion for tall timber buildings, this paper aims to provide useful information and evaluate available tools and methods for modal identification in tall glulam timber frame buildings. First, combined operational modal analysis schemes based on the variational mode decomposition with the stochastic subspace identification and the random decrement technique were adopted to identify the modal properties from nonstationary ambient data. Then, unique full-scale forced vibration tests were conducted using two different methods to excite the building: measured electrodynamic shakers excitation and unmeasured rhythmic human-induced excitation. Finally, a finite-element (FE) model of the tall glulam frame building was developed and frequency response function (FRF)–based model updating was conducted showing that the FE model was able to predict the modal behavior of the test building. The results show that natural frequencies identified from output-only techniques are in good agreement with the FVT results. Damping ratios obtained from both AVTs and FVTs exhibited amplitude-dependent behavior with a larger variation observed in the FVT results due to larger range of response amplitudes. These results have significant consequences for the design of tall timber buildings under serviceability-level loading, where damping plays an important role. The resulting damping ranges presented in this paper can serve as a useful guideline for practicing engineers in developing their prediction models of tall timber buildings under serviceability-level loading.
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