Vibration Limits Research Articles

Limiting Effects of Construction Vibrations on Sensitive Equipment

Approaches are discussed for addressing concerns regarding the effects of construction-related vibrations on sensitive instrumentation and activities. The availability of related vibration criteria is noted, the limitations of available criteria are explored, and difficulties in meeting some of the vibration limits are indicated. Approaches to enabling construction to proceed with minimal interference with sensitive equipment and procedures are described.

Studies on the full vibrational energies and dissociation limits of some electronic states of Kr2+ and Xe2+ diatomic molecular ions

In addition to the algebraic method (AM) (Sun et al 2002 J. Mol. Spectrosc.215 93) that was proposed to generate accurate full vibrational energies for a stable diatomic electronic state that has regular (Morse-like) potentials, a parameter-free formula is suggested in this work in order to study the high-lying vibrational spectra and dissociation limits of four electronic states of Kr2+ and Xe2+ diatomic ions. Those reliable AM energies EυAM of high-lying vibrational states and dissociation limits DLAM for each electronic state that we have predicted in this study were probably difficult to obtain experimentally or theoretically before.

THE STUDY ON VIBRATIONS WHICH IS CAUSED BY THE ROAD TRAFFIC ACTIVITIES ALONG SEVERAL MAIN STREETS IN JAKARTA

The vibrations which is caused by road traffic activities have been monitored along several main streets in Jakarta, i.e Jalan MH. Thamrin, Jalan Merdeka Barat (around Taman Monas) and Hayam Wuruk Street (Gajah Mada Plaza and Glodok). Where in the near future, the Indonesian Government has planed to construct a new large scale project so called Mass Rapid Transport (MRT) along these roads. The purpose of this works was to study the existing vibrations radiated by the road traffic activities impacting to the buildings adjacent to the road. Furthermore, these vibrations data can also be used as supporting data in the realization of MRT project. From observation results showed that the amount of traffic volume along MH. Thamrin Street, Merdeka Barat Street and Hayam Wuruk Street, happened in the afternoon time, i.e. from 14.00 p.m. to 17.00 p.m. Where in this range time the large vehicles such as busses or trucks were frequently passing on these roads, and they generated the maximum vibration levels on the surface of ground with the levels of 0.315 mm/sec up to 0.332 mm/sec, and these maximum vibrations occurred at the frequency of 4 Hz. Refer to BAPEDAL Standard, the limit of buildings vibration at frequency 4 Hz must be less than 2 mm/s. Thus, the measured vibration levels were very low compared to the standard, therefore it would not damage to the structures of buildings adjacent to the road.

Damage to surface structures due to blast vibration

This paper describes effect of blast produced ground vibration on damage potential to residential structures to determine safe levels of ground vibration for the residential structures and other buildings in mining areas. Impacts of 341 blasts detonated at two mines were monitored at the test structures and 1871 blast vibrations signatures were recorded on or near the test structures. Cosmetic cracks in a native brick-mud-cement house were detected at peak particle velocities (PPV) between 51.6 and 56.3 mm/s. The reinforced concrete and cement mortar (RCC) structure experienced cosmetic cracks at PPVs of 68.6–71.3 mm/s at the first floor, whereas at second floor it was detected at PPV levels of 71.2–72.2 mm/s. Minor damage in brick-mud-cement house was recorded at PPV levels of 81.0–89.7 mm/s. The RCC structure at first and second floors experienced minor damage at PPV levels of 104 and 98.3–118 mm/s, respectively. The brick-mud-cement house experienced major damage at PPV level of 99.6–113.0 mm/s, while major damage was recorded in RCC structure on first floor at PPV of 122 mm/s, the second floor at PPV levels of 128.9–161 mm/s. Recommended threshold limits of vibrations for the different type of structures is based on these measurements and observations.

The Efficacy of Mechanical Vibration Analgesia for Relief of Heel Stick Pain in Neonates

Hospitalized infants are often exposed to many painful procedures as a result of their illness or disease process. Untreated or poorly treated pain can have deleterious effects on normal nociceptive pain development as well as future development of pain pathways. Mechanical vibration has been found to be efficacious in adult and pediatric populations for the relief of mild-to-moderate acute and chronic pain. However, little is known about the efficacy of this intervention in the neonatal population. The purpose of this study was to test the hypothesis that mechanical vibration would be efficacious in the relief of pain associated with heel sticks in neonates. Heel sticks are one of the most common painful procedures during neonatal hospitalization. A random-sequencing crossover design was used with infants acting as their own controls. Newborn infants of 35 weeks' gestation or greater (N = 20) met the inclusion criteria for the study. Pain during heel stick was measured with the Neonatal Infant Pain Scale. The Neonatal Infant Pain Scale is a nonintrusive tool with extensive evidence of its reliability and validity in the neonatal population, when used by trained observers. Mechanical vibration produced an analgesic effect for infants who had previously experienced painful heel sticks that approached statistical significance. The apparent limitations of mechanical vibration as analgesia may be due to the concurrent use of sucrose and pacifier, the effects of order (ie, habituation), or type II error. Because vibration produced the predicted positive effect in some circumstances, further investigation in larger samples within a randomized clinical trial is warranted.

Distributed Downhole Measurements Describe Salt Drilling While Underreaming

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 124121, ’Salt Drilling While Underreaming Behaviors Illuminated by Distributed Downhole Measurements,’ by B.J. Kull, SPE, and R.G. Duff, SPE, Chevron, and A.J. Clarke, SPE, D.G. Perez, and S.M.Stuart, SPE, NOV, originally prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October. The paper has not been peer reviewed. Many developments in the deepwater Gulf of Mexico (GOM) target reservoirs below salt sections. Because well plans increasingly call for drilling through long salt sections, a common strategy in the GOM is to drill while simultaneously opening the hole with an underreaming tool. This configuration presents unique dynamic behaviors to the drilling system. Understanding the drilling system is important to reduce vibrations. Identification of drillstring dynamic behavior is critical. Introduction Deepwater GOM wells often require drilling through the salt canopy (Fig. 1). In some plays, subsalt targets equate to the majority of the well being placed in salt. Similarly, subsalt targets mean the wells may be very deep and therefore benefit from a large hole size to provide adequate clearances for deepening casing strings. Casing running in salt presents the added challenge of salt creep, often requiring oversized holes. A successful method to address the challenges of drilling deep wells through salt is simultaneously underreaming while drilling. The use of logging-while-drilling (LWD) and rotary-steering tools introduces constraints to underreamer placement and overall bottomhole-assembly (BHA) design. Distributed measurement in drilling assemblies is an established method of investigation for the operator; however, this study is the first of its kind known for the deepwater GOM. Many directional-measurement schemes use measurements at several locations. Distributed vibration measurement often is achievable in a BHA using multiple LWD tools with vibration-logging capability. Vibration measurement complements avoidance of destructive vibration modes by supplying symptomatic information about the downhole dynamic conditions. When vibrations are high, anecdotal evidence is used to diagnose a dynamic condition. On the basis of that diagnosis, mitigation of the phenomenon may be attempted. The operator currently is developing several fields that require drilling long salt sections. To optimize drilling and reduce overall development costs per well, understanding dynamic events and vibration limitations is a priority. The salt sections do not require much formation-evaluation data from LWD, so drill rates and tool-memory issues are not always a limiting factor in these sections. Similarly, the lack of permeability in salt reduces the need for controlled-drilling-rate operations because of equivalent circulating density (ECD). Underreaming presents unique challenges in all formations.

Robust optimization of the rate of penetration of a drill-string using a stochastic nonlinear dynamical model

This work proposes a strategy for the robust optimization of the nonlinear dynamics of a drill-string, which is a structure that rotates and digs into the rock to search for oil. The nonparametric probabilistic approach is employed to model the uncertainties of the structure as well as the uncertainties of the bit-rock interaction model. This paper is particularly concerned with the robust optimization of the rate of penetration of the column, i.e., we aim to maximize the mathematical expectation of the mean rate of penetration, respecting the integrity of the system. The variables of the optimization problem are the rotational speed at the top and the initial reaction force at the bit; they are considered deterministic. The goal is to find the set of variables that maximizes the expected mean rate of penetration, respecting, vibration limits, stress limit and fatigue limit of the dynamical system.

Probabilistic Assessment of Human Response to Footbridge Vibration

Modern pedestrian bridges are becoming increasingly slender due to more demanding aesthetic requirements and increased strength of structural materials. As a consequence, they might suffer from excessive vibration under pedestrian-induced dynamic loading and therefore have their vibration serviceability compromised. For a reliable assessment of acceptability of vibrations to bridge users, it is necessary to define subjective vibration limits for pedestrians – human vibration receivers who are moving across a vibrating surface, rather than being stationary. This paper aims to develop a methodology for defining vibration limits for walking humans. For this, substantial pedestrian traffic across a lively box girder footbridge was monitored. After interviewing 100 randomly chosen pedestrians about their subjective assessment of the vibration felt during the crossing significant variability in subjective rating of vibrations was observed. To account for this variability, the vibration limit for walking people was defined in a probabilistic sense. The limit defined allows for estimating the percentage of people who would complain about footbridge liveliness.

Blast Limits for Transmission Structures. I: Response Spectra Development

To develop a defense strategy to protect power transmission lines against blast-induced ground motions, an understanding of the dynamic responses of these structures must be first established. This paper presents the results from ground motion monitoring at two blast sites in southern United States. These studies are being conducted as part of a research effort to establish strong ground motion characteristics necessary for developing blast limits for power transmission systems. Ground movements caused by the surface mining blast and quarry blasting were recorded using geophones and wireless triaxial sensing units. The process of establishing the ground motion response spectra via analyzing actual ground motion measurements, including noise filtration and signal processing, is then described. These ground motion response spectra are the necessary inputs for spectrum analysis of structural responses that can be used to establish ground vibration limits.

Nonlinear dynamic analysis of the Three Gorge Project powerhouse excited by pressure fluctuation

This study established a 3D finite element model for 15# hydropower house of the Three Gorges Project (TGP) and performed a nonlinear dynamic analysis under pressure fluctuation. In this numerical model, the stiffness degradation in tension for concrete was considered on the basis of the continuum isotropic damage theory. Natural vibration frequencies of the damaged and undamaged structures were compared after static water pressure was applied. Then a study was further conducted on forced vibration of the powerhouse with pre-existing damages under pressure fluctuation that acts on the flow passage; displacement, velocity and acceleration of the important structural members were afterwards presented and checked. Numerical results show that tensile damages in concrete surrounding the spiral case only exert significant impact upon the dynamic characteristics of substructure but show little effect on the superstructure. Nevertheless vibrations of the powerhouse are still under the recommended vibration limits.

Strong ground movement induced by mining activities and its effect on power transmission structures

Surface mining activities may introduce damages to nearby infrastructure. Concerns are put forward by the power company about structural integrity of electric power transmission structures in areas where coal mining activities cause strong ground vibrations. Common practice in the power industry is to limit ground motion by specifying maximum Peak Particle Velocity. So far, there is a lack of industry-wide recognized guidelines on how ground vibration limits should be set for the transmission structures. In order to develop a defense strategy to protect power transmission lines against strong ground motions in mining areas, a systematic research work was conducted to establish strong ground vibration characteristics and to study impacts of ground excitations on transmission pole structures. Ground movements were recorded using geophones and wireless tri-axial sensing units. The process of generating ground motion response spectra via analyzing actual ground motion measurements is described in the paper. These spectra developed based on peak particle velocities were used as a basis for spectral analysis performed using validated Finite Element models to obtain structural displacements, reactions and stress states of the transmission pole structures in the mining sites. A quantitative ground motion limit was established by comparing structural responses with the corresponding design requirements.

Quantification of ground vibration differences from well-confined single-hole explosions with variable velocity of detonation

An explosion experiment was conducted in the Barre granite of central Vermont during July 2008 using five explosions and three different types of explosives with a wide range of velocities of detonation. Black powder, heavy ANFO, and Composition B were used to generate increasing amounts of borehole pressure and different types of rock damage. The velocity of detonation was found to affect the peak particle velocities (PPV). ANFO produced the largest PPV, while the Composition B PPVs were slightly lower. Black powder produced much lower PPV, likely due to it deflagrating rather than truly detonating. An equation was fit to the data for predicting the PPV from a confined blast in the Barre granite using two methods, including true vector summation. Vector summation provides a more accurate measure of particle velocity. We found the frequency of the PPV decreases with increasing distance from the blast, and therefore extra care must be taken for large blasts where lower frequency energy may exceed vibration limits at greater distances.

Can One Predict Changes from SN1 to SN2 Mechanisms?

The reactions of substituted benzhydryl bromides Ar(2)CHBr with primary and secondary amines in DMSO yield benzhydryl amines Ar(2)CHNRR', benzophenones Ar(2)C=O, and benzhydrols Ar(2)CHOH. Kinetic investigations at 20 degrees C revealed the rate law -d[Ar(2)CHBr]/dt = (k(1) + k(2)[HNRR'])[Ar(2)CHBr], where the amine independent term k(1) gave rise to the formation of Ar(2)C=O and Ar(2)CHOH and the amine-dependent term k(2)[HNRR'] was responsible for the formation of Ar(2)CHNRR'. Clear evidence for concomitant S(N)1 and S(N)2 processes was obtained. While the rate constants of the S(N)1 reactions correlate with Hammett's sigma(+) constants (rho = -3.22), the second-order rate constants k(2) for the S(N)2 reactions are not correlated with the electron releasing abilities of the substituents, indicating that the transition states of the S(N)2 reactions do not merge with the transition states of the S(N)1 reactions. The correlation equation log k(20 degrees C) = s(E + N), where nucleophiles are characterized by N and s and electrophiles are characterized by E (J. Am. Chem. Soc. 2001, 123, 9500-9512), was used to calculate the lifetimes of benzhydrylium ions in the presence of amines and DMSO. The change from S(N)1 to S(N)2 mechanism occurred close to the point where the calculated rate constant for the collapse of the benzhydrylium ions with the amines just reaches the vibrational limit; that is, the concerted S(N)2 mechanism was only followed when it was enforced by the lifetime of the intermediate. The nucleophile-specific parameters N and s needed for this analysis were determined by studying the kinetics of the reactions of a variety of amines with amino-substituted benzhydrylium tetrafluoroborates (Ar(2)CH(+)BF(4)(-)) of known electrophilicity E in DMSO. Analogously, the rates of the reactions of laser flash photolytically generated benzhydrylium ions Ar(2)CH(+) with DMSO in acetonitrile were employed to determine the nucleophile-specific parameters N and s of DMSO, and it is reported that DMSO is a significantly stronger O-nucleophile than water and ordinary alcohols.

Safety-design criteria of sliding systems for preventing friction-induced vibration

In order to acquire safety-design criteria for preventing friction-induced vibration, dimensionless analysis and numerical simulation have been conducted for a single-degree-of-freedom system with friction. The model includes the discontinuity between static and kinetic friction and the dependence of the kinetic friction coefficient on the relative velocity. Dimensionless description reduces the number of parameters from nine to five; four of the five dimensionless parameters control the occurrence limit of friction-induced vibration. We have derived the occurrence-limit equation on the basis on a previous study on stick–slip in the Coulomb friction model, and we have constructed the discriminant inequalities with the four parameters. They are sufficient conditions for preventing friction-induced vibration, i.e., not only stick–slip but also instability of steady sliding; they are expected to provide safety-design criteria of sliding systems with high usability and high accuracy.

Low-lying spectra and E2 transition rates in 160–170Er isotopes in the interaction boson model

Spectra and E2 transition rates for the 160–170Er isotopes are studied in the framework of the interaction boson model. A schematic Hamiltonian able to describe their spectra and B(E2) transition is used. It is found that the 160–170Er isotopes are in the transition from the vibrational limit to rotational limit.

Derivation of Vibration Parameters for Repulsive Magnets Type Vibration Limit Switch

In order to quantitatively design of repulsive magnets type vibration limit switch, we have derived the vibration parameters which are expressed in vibration equation from experimental results. The vibration parameters are spring coefficient and damping coefficient at switch-on state. The vibration parameters and the structure parameter of switch were related quantitatively as linear and polynomial equations.

Damage assessment of basaltic rock mass due to repeated blasting in a railway tunnelling project – A case study

The demand for tunnelling and underground space creation is rapidly growing due to the requirement of civil infrastructure projects and urbanisation. Blasting remains the most inexpensive method of underground excavations in hard rock. Unfortunately, there are no specific safety guidelines available for the blasted tunnels with regards to the threshold limits of vibrations caused by repeated blasting activity in the close proximity. This paper presents the results of a comprehensive study conducted to find out the effect of repeated blast loading on the damage experienced by jointed basaltic rock mass during tunnelling works. Conducting of multiple rounds of blasts for various civil excavations in a railway tunnel imparted repeated loading on rock mass of sidewall and roof of the tunnel. The blast induced damage was assessed by using vibration attenuation equations of charge weight scaling law and measured by borehole extensometers and borehole camera. Ground vibrations of each blasting round were also monitored by triaxial geophones installed near the borehole extensometers. The peak particle velocity ( V max) observations and plastic deformations from borehole extensometers were used to develop a site specific damage model. The study reveals that repeated dynamic loading imparted on the exposed tunnel from subsequent blasts, in the vicinity, resulted in rock mass damage at lesser vibration levels than the critical peak particle velocity ( V cr). It was found that, the repeated blast loading resulted in the near-field damage due to high frequency waves and far-field damage due to low frequency waves. The far field damage, after 45–50 occurrences of blast loading, was up to 55% of the near-field damage in basaltic rock mass. The findings of the study clearly indicate that the phenomena of repeated blasting with respect to number of cycles of loading should be taken into consideration for proper assessment of blast induced damage in underground excavations.

Theoretical and experimental sensitivity analysis of extra insensitive input shapers applied to open loop control of flexible arm

In this paper, the motion input pre-shaping, applied to flexible manipulators for space applications, is analyzed in terms of sensitivity and robustness to parameters uncertainties. The special environment of space operations and the project specifications lead to the design of manipulators with light and flexible structures. In order to highlight the performances of these methods an open loop control technique is implemented. The control technique is verified by both numerical simulations and experiments. This paper presents the experimental set-up and the results of a series of experimental tests carried out on the space robot simulator assembly, called test-bed for microgravity simulation in robotic arm dynamics (TeMSRAD). The innovative task of the research is to determine experimentally the sensitivity curve for one-hump and two-hump extra-insensitive input shapers, for different vibration limits, by purposely introducing errors in the system model, in order to simulate typical operating conditions.

Case Study of MRI Installation in Existing Hospitals

Medical facilities frequently seek to add function and capacity to their imaging facilities. The addition of new MRI units into existing hospital spaces is quite common, however many manufacturers impose and stringent low‐frequency vibration limits which must be met before a unit can be delivered and installed. Vibration sources such as mechanical systems and external transit can degrade the achievable imaging resolution at levels undetectable by unaided humans. A case study is presented for one such project which required significant vibration controls to existing ventilation, water, and electrical systems to ensure acceptable vibration levels at an unlikely equipment installation.

Vibration effects in healthcare facilities

In the USA, the principal rating system for "green" buildings is named, "Leadership in Energy and Environmental Design" (LEED). There is now a proposed LEED rating system for healthcare facilities as described in a "pilot draft" document that was released for public comment in November 2007. This document, in turn, cites the 2006 AIA/AHA Draft Interim Sound and Vibration Design Guidelines. These AIA/AHA Guidelines focus on both the human perceptual effects of vibration as well as the control of structure-borne noise. This paper addresses another aspect of vibration in healthcare facilities - the effects of vibration upon sensitive diagnostic equipment installed on floors above grade. Such equipment may include magnetic resonance imagers, surgical microscopes, and computed tomography (CT) scanners, some of which do not have specific vibration limits provided by the manufacturer. The obvious need for attaining low-level building vibration may conflict with other design constraints imposed on modern healthcare facilities as architects and engineers strive for lightweight floor bays having widely-spaced support columns. This paper reviews the generic vibration design criteria found in the AIA/AHA Guidelines and discusses them in light of several case studies.