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A raised crossing (RC), as an alternate to the current form of level crossings to minimise risks of wheel-rail contact failure under frontal collision of trains onto stuck trucks, has been recently formulated by the authors (Engineering Failure Analysis, 80 (2017) 403–415) to mitigate the severity of accidents at road-rail crossings. The aim of the present paper is to assess the effectiveness of the profile of the RC to minimise the risk of speeding through and minimise the peak vertical acceleration of the passing road vehicle below the threshold level for discomfort and safety of its occupants. For this purpose, a simplified two-dimensional multibody dynamic simulation modelling method has been formulated and validated using a detailed three-dimensional industry standard model. The validated model has then been used to optimise the geometric profile of the RC by minimising the peak vertical accelerations of the occupants below the safety threshold of 0.7 g. It is shown that the optimised profile of the RC increases the peak acceleration with the increase in speed of travel of the road vehicles whilst the LC does the opposite. This finding confirms that the RC has the potential to reduce the risk of speeding, which is vital to the safety of the train and road vehicles at rail – road crossings.

In this paper, a composite planing hull response is tested in a numerical environment, using real material properties obtained from hull excerpts in lab. Extreme loads are simulated in a numerical quasi static situation using register rules recommendations for pressure and vertical acceleration values. The results are compared with the experimental values recorded using full scale hull and trials in real conditions on the river, for different speed values comprised between 4 and 12 m/s

The paper analyzes the effects of vibrations on allowable vibration exposure time in intercity bus users for the criterion of reduced comfort according to the ISO 2631/1985 standard. The analysis was carried out using a validated spatial oscillatory model of 65 degrees of freedom (DOF) built in the ADAMS/View module of the MSC.ADAMS package. Simulation results revealed that passengers on the bus front and rear overhang have very short allowed exposure time. In order to extend the exposure time, by using Design of Experiments (DOE) analysis, new oscillatory parameters for passengers' seats are proposed. With new oscillatory parameters, the exposure time is significantly extended for the assistant driver and passengers on the front and rear bus overhang. For the passenger on the last row seat, power spectral density of weighted vertical acceleration is of lower intensities even at frequencies above 4 Hz. Relevance to industry: Bus users (passengers and drivers) are exposed to harmful effects of vibrations. Vibrations influence comfort, work ability, and if increasingly intense can affect human health. Allowable vibration exposure time referring to oscillatory comfort has a particular importance for intercity bus' passengers when traveling longer distances. Vibration time could be extended by proper selection of seat oscillatory parameters. Results of such an analysis can significantly help bus manufacturers and designers in order to improve ride comfort for bus' passengers.

Explosion from an anti-tank landmine under a military vehicle, known as underbody blast (UBB), may cause severe injury or even death for the occupants inside the vehicle. Severity and patterns of lower extremity, pelvis and lumbar spine injuries subjected to UBB have been found highly related to loading conditions, i.e. the vertical acceleration pulse. A computational human model has been developed and successfully simulated the tibia fracture under UBB in the previous study. In the present study, it was further improved by building a detailed lumbar spine and pelvis model with high biofidelity. The newly developed pelvis and lumbar spine were validated against component level test data in the literature. Then, the whole body model was validated with the published cadaver sled test data. Using the validated whole body model, parametric studies were conducted by adjusting the peak acceleration and time duration of pulses produced in the UBB to investigate the effect of waveform on the injury response. The critical values of these two parameters for pelvis and lumbar spine fracture were determined, and the relationship between injury pattern and loading conditions was established.

Inertial measurement units (IMUs) have been extensively used to detect gait events. Various methods have been proposed for detecting initial contact (IC) and toe-off (TO) using IMUs affixed at various anatomical locations. However, the accuracy of such methods has yet to be compared. This study evaluated the accuracy of three common methods used for detecting gait events during jogging and running: (1) S-method, in which IC is identified as the instant of peak foot-resultant acceleration and TO is identified when the acceleration exceeds a threshold of 2g in the region of interest; (2) M-method, in which IC and TO are defined as the minimum before the positive peak shank vertical acceleration and the minimum in the region of interest, respectively; and (3) L-method, in which IC is indicated by the instant of peak pelvis anteroposterior acceleration and TO is identified by the maximum in the region of interest. The performance of the IMU-based methods in detecting IC and TO and estimating stance time (ST) were tested on 11 participants at jogging and running speeds against a reference provided by a force-platform method. The S-method was the most accurate for IC detection (overall mean absolute difference (MAD): 4.7 ± 4.1 ms). The M-method was the most accurate for TO detection (overall MAD: 7.0 ± 3.5 ms). A combination of M- and S-methods, called the MS-method, was the most accurate for ST estimation (overall MAD: 9.0 ± 3.9 ms). Thus, the MS-method is recommended for ST estimation; however, this method requires four IMUs for bilateral estimation.

In this paper, vertical motion (heave, roll, and pitch) state estimation and control simulation are performed by using the LQG approach. Cummins’ equation is used to represent the mathematical model of 3DOF ship motions. A passenger ship in irregular bow quartering waves at the Froude number of 0.45 is considered during the simulations. Two pairs of foils which are located on the bow side of the passenger ship are used as actuators. First, the results of the uncontrolled simulation case are presented to show the reliability of the mathematical model. Then, all states are estimated by measuring only velocity signals based on LQE design. Finally, the LQG approach is applied to mitigate the vertical motions and accelerations by taking feedbacks from only easy-measurable velocity signals. LQG results are compared with LQR results as well. Results showed that the implemented LQG approach reduced the bow motions and accelerations up to approximately 40%.

Slab arching is one of the most common damages of the slab track system in Chinese high-speed railway, which causes the instability of the track structure, changes the wheel-rail dynamic characteristics, and even affects the safety. Therefore, to prevent the occurrence of the above problems, the first important step is to detect the slab arching in advance. There have been some detection methods for slab arching, but it is difficult to detect the arching under different degrees, especially for the arching in the early stage. Aiming at the current situation, this paper proposed an arching detection method based on the dynamic responses of the car body. Integrated the analytical mode decomposition and continuous wavelet transform, the arching-induced characteristics in the car body vertical acceleration data, calculated by the vehicle-track finite element model, were found. After that, the measured data from different inspection areas were used for arching detection based on the discovered characteristics. The results showed that the amplitude of the component of the wavelength from 4 m to 6 m of the car body vertical acceleration could be used for slab arching detection. The method has good adaptability to different arching degrees. In practice, the proposed method can be used to detect slab arching, thus guide scientific maintenance.

In the last 30 years, there has been a great development of seismic isolation systems. The most used are elastomeric type devices and frictional pendulum bearings. Although different, both types generate horizontal seismic isolation, but not vertical. This study presents a nonlinear three-dimensional seismic isolation system called vertical rocking isolation (VRI) system, based on devices called ISO3D. Unlike conventional seismic isolators, the ISO3D device is vertically flexible and laterally stiff. Although the proposed system can be applied to any type of structure, it is particularly attractive as a seismic protection system of special structures, such as fluid storage tanks supported on legs, power transformers and sensitive equipment with vertical acceleration. In this research an application to legged wine storage tanks is presented. Two models were studied: a 3 m 3 tank with 4 legs, and a 30 m 3 tank with 6 legs. The fluid-structure interaction was considered using a quasi-static approach, where the fluid behaves as a mass attached to the tank walls. Time-history analyses results show average reductions of axial loads and shear loads on the legs of 57% and 61%, respectively. Finally, a fragility analysis indicates that the PGA required to reach 50% of probability of failure increases by an average of 153% by using the VRI system.

The double-stepped design of lifting surfaces, planing in water, has been seen to benefit the calm-water performance by distributing forces over the washed area. The unsteady motion of such surfaces in waves, however, is not well understood. It is not clear how steps can influence the response of a planing vessel operating in waves. In the presented research, this problem is analyzed by developing a model, which is established using a 2D + t framework. Meanwhile, a CFD set-up is also designed to numerically replicate the motion of double-stepped planing hulls subjected to gravity waves. It is demonstrated the results of both models agree. Performing mathematical simulations, it is demonstrated that a double stepped design can decrease the heave and pitch responses of the vessel in the resonance zone. More importantly, mathematical data confirms that wave-induced motions of a vessel are highly sensitive to the heights of steps. A vessel with a shorter front step has smaller vertical responses, especially over the resonance zone, while it may have larger vertical acceleration at high-speeds. This is caused by the larger washed area of the middle surface, which can increase damping forces, while it allows larger wave forces to impact the vessel.

Biodynamic responses of the seated human body are usually measured and modelled assuming a single point of vibration excitation. With vertical vibration excitation, this study investigated how forces are distributed over the body-seat interface. Vertical and fore-and-aft forces were measured beneath the ischial tuberosities, middle thighs, and front thighs of 14 subjects sitting on a rigid flat seat in three postures with different thigh contact while exposed to random vertical vibration at three magnitudes. Measures of apparent mass were calculated from transfer functions between the vertical acceleration of the seat and the vertical or fore-and-aft forces measured at the three locations, and the sum of these forces. When sitting normally or sitting with a high footrest, vertical forces at the ischial tuberosities dominated the vertical apparent mass. With feet unsupported to give increased thigh contact, vertical forces at the front thighs were dominant around 8Hz. Around 3-7Hz, fore-and-aft forces at the middle thighs dominated the fore-and-aft cross-axis apparent mass. Around 8-10Hz, fore-and-aft forces were dominant at the ischial tuberosities with feet supported but at the front thighs with feet unsupported. All apparent masses were nonlinear: as the vibration magnitude increased the resonance frequencies decreased. With feet unsupported, the nonlinearity in the apparent mass was greater at the front thighs than at the ischial tuberosities. It is concluded that when the thighs are supported on a seat it is not appropriate to assume the body has a single point of vibration excitation.

The exact and simplified generalized analytical models for the sloped rolling-type seismic isolator in which two V-shaped surfaces in contact with cylindrical rollers are designed with arbitrary sloping angles are proposed. Numerical predictions are compared with horizontal seismic simulation test results to demonstrate the accuracy and practicability of the proposed simplified model. Furthermore, the influences arising from two simplification assumptions on the horizontal acceleration prediction are numerically examined. The results indicate that the effect of vertical acceleration excitation plays a more crucial role in prediction accuracy and conservative design compared to that of higher order terms of sloping angles.

Grha Sabha Pramana is an auditorium located at the front area of Universitas Gadjah Mada. In 1998, an excessive vibration was experienced by occupants while the building was being used for pop music concert. The excessive vibration was caused by rhythmic motion of the audience prompted by beat of music. Vertical excessive vibration occurred on the 2nd floor, having a long-span of prestressed concrete floor system with spans of 28.8 m and 21.6 m in EW and NS direction respectively. Additional column support at mid span as one of retrofit methods is not acceptable since the prestressed beams were designed to resist the positive moment only. The selected retrofit method is to add a fluid viscous damper (FVD). A group of fifty people is elaborated to do a full scale experimental tests inducing the floor system. The experimental test results are used to verify the numerical models which developed by using SAP2000 program. Furthermore, the model was used to simulate a dynamic response of one thousand and two hundred people exciting the floor system to represent the real concert situation. The study illustrates that the additional damper improves the vibration serviceability of the floor system. The study also indicates that the use of additional damper can reduce the response of vertical acceleration. Such in experimental test, the peak acceleration of the floor system without and with damper are 0.0159 g and 0.00157 g respectively. The additional damper also increases the damping ratio of the floor system from 4.58% to 14.51%.

To mitigate the differential settlement of the soft soil foundation and to reduce the maintenance work of the embedded tram track, an innovative pile-plank-supported tram track configuration is proposed and utilized in Shanghai Tram Line T1/T2. Since this is the first application of this new structure in tram track projects, the dynamic properties and service performance of this structure are still not clear. In this work, an in-situ test on the dynamic performance of the pile-plank-supported ballastless tram track is carried out. The contact forces between the independently rotating wheelset of a five-module 100% low-floor tram and the channel rail of tram track are measured and investigated as well as the vertical acceleration of the plank. The measured wheel-rail contact forces are employed as a loading condition for a track-subgrade coupling model. The influence of multi-factors (i.e. dynamic loading, thermal conditions and subgrade settlement) on the tram track damage is investigated. The results indicate that the long-term service performance of the pile-plank-supported tram track is stable under the dynamic tram loads.

While it is well known that the gap between twin-box decks is a key design variable that impacts the onset flutter velocity of a bridge, further research is required to ascertain how modifications in several bridge design variables affect other aeroelastic responses. This paper utilizes aero-structural optimization techniques for the design of long-span bridges with short gap twin-box decks considering simultaneously structural, flutter and buffeting constraints. The optimization helps to reduce the material volume of the structure while maintaining all the performance and safety requirements below the imposed thresholds. It has been found that the geometry of the individual box cross-section is an important feature for the control of the buffeting response, particularly the vertical acceleration. On the other hand, flutter and torsional buffeting constraints require designs with larger gap distance and alternative box geometries, leading to a trade-off between conflicting design demands. Hence, depending on the expected wind load conditions and the specific requirements of a particular project, an optimum aero-structural bridge design with a particular deck shape can be identified. The framework presented in this study is an effective tool to achieve sustainable and safe bridge designs that seeks a most efficient balance between all the design constraints.

Train sudden deceleration (braking) that causes sliding in wheels could impact the design of rail components, supports, bearings, and bridge substructure. Despite the availability of research on the vehicle–bridge interaction (VBI) analysis of vehicles with constant velocity, few studies have investigated the effect of vehicle longitudinal acceleration on VBI and more research is required. In this study, the effect of vehicle horizontal acceleration is incorporated into an available numerical procedure developed for VBI analysis of vehicles with constant velocity, and a modified numerical element is proposed. The effect of acceleration is considered as external loads acting on each part of the vehicle masses. Using suitable transformation matrices and defining a new parameter called acceleration parameter, the vertical contact forces are reformulated. Subsequently, a new formulation for a VBI element containing the effect of vehicle acceleration is obtained. VBI elements are those bridge elements in contact with wheels of moving vehicle. Numerical results are presented to evaluate the importance of the proposed VBI element, and to investigate the vehicle and the bridge responses. Considerable effect was observed on vehicle vertical contact forces, vehicle vertical acceleration, and somewhat on midspan deflection. Minor effect was observed on bridge midspan acceleration, for which the effect of vehicle initial velocity is prominent, not the vehicle acceleration.

High-speed vessels require good resistance and seakeeping performance for safe operations in rough seas. The resistance and seakeeping performance of high-speed vessels varies significantly depending on their hull forms. In this study, three planing hulls that have almost the same displacement and principal dimension are designed and the hydrodynamic characteristics of those hulls are estimated by high-speed model tests. All model ships are deep-V type planing hulls. The bows of no.2 and no.3 model ships are designed to be advantageous for wave-piercing in rough water. No. 2 and no. 3 model ships have concave and straight forebody cross-sections, respectively. And length-to-beam ratios of no.2 and no.3 models are larger than that of no.1 model. In calm water tests, running attitude and resistance of model ships are measured at various speeds. And motion tests in regular waves are performed to measure the heave and pitch motion responses of the model ships. The required power of no.1 (VPS) model is smallest, but its vertical motion amplitudes in waves are the largest. No.2 (VWC) model shows the smallest motion amplitudes in waves, but needs the greatest power at high speed. The resistance and seakeeping performance of no.3 (VWS) model ship are the middle of three model ships, respectively. And in regular waves, no.1 model ship experiences ‘fly over’ phenomena around its resonant frequency. Vertical accelerations at specific locations such as F.P., center of gravity of model ships are measured at their resonant frequency. It is necessary to measure accelerations by accelerometers or other devices in model tests for the accurate prediction of vertical accelerations in real ships.

By using multi-body dynamics simulation software SIMPACK, the paper completed full vehicle modeling of bus air suspension. In four typical working conditions, body vertical acceleration, suspension working space and dynamic tire load were selected as performance indexes to analyze the matching of suspension damping and air spring. On the basis of comparison of simulation data, a suitable damping was selected for a good matching with air spring in corresponding condition and the performance of the suspension system was improved.

The feasibility of a preview control is examined for tracked vehicle’s suspension systems to improve the performance of tracked vehicle systems. Numerical results are compared with LQ, robust H∞, reference model tracking and hybrid preview control methods. The ride quality analysis is performed based on the vertical acceleration at the driver’s position. On the simulations, it is proven that the hybrid preview controller is the most efficient and practical method.

In this paper a Human–Vehicle–Road (HVR) model, comprising a quarter-car and a biomechanical representation of the driver, is employed for the analysis. Differential equations are provided to describe the motions of various masses under the influence of a harmonic road excitation. These equations are, subsequently, solved to obtain a closed form mathematical expression for the steady-state vertical acceleration measurable at the vehicle–human interface. The solution makes it possible to find optimal parameters for the vehicle suspension system with respect to a specified ride comfort level. The quantitative definition given in the ISO 2631 standard for the ride comfort level is adopted in this paper for the optimization procedure. Numerical examples, based on actually measured road profiles, are presented to prove the validity of the proposed approach and its suitability for the problem at hand.

A novel accelerometer based on a strain-chirped optical fiber Bragg grating (FBG) is proposed. The FBG is glued in a slanted direction onto the lateral side of a right-angled triangle cantilever beam with a mass bonded on its free end. Vertical acceleration applied to the cantilever beam leads to a uniform bending along the beam length. As a result, the FBG is chirped and its reflection bandwidth changes linearly with the applied acceleration. A high sensitivity of 0.679 nm/g has been achieved in the experiment. This sensor is temperature insensitive, owning to the temperature-independence nature of reflection bandwidth of the FBG.

WOS: 000253598100027, In this paper, constraints on the transfer functions from the road disturbance to the vertical acceleration, the suspension travel, and the tire deflection are derived for a quarter-car active suspension system using the vertical acceleration and/or the suspension travel measurements for feedback. The derived constraints complement the similar constraints in the literature. By using the factorization approach to feedback stability, it is shown that tire damping couples the motions of the sprung and unsprung masses; and eliminates a constraint at the wheel-hop frequency. The influence of tire damping on the design of an active suspension system for a quarter-car model by a mixture of the LQG methodology and the interpolation approach is also illustrated

A human-centered measure of floor slipperiness could be useful as an adjunct to conventional tribologic measures. This paper reports on the development and evaluation of a measure of slip distance based on variables derived from the signal of a heel-mounted accelerometer. Twenty-one participants walked on a laboratory runway under several surface slipperiness conditions at three walking speeds during a protocol designed to produce a wide range of slip distances at heel strike. Analysis of variance showed significant effects of slip distance (no-slip, micro-slip and slide), walking speed (1.52, 1.78 and 2.13 m/s) and their interactions on peak forward acceleration, peak vertical acceleration and deceleration time of the heel following heel strike in 704 trials. Regression analysis of slip distance and deceleration time showed the strongest relationship with R2=0.511. Large individual variation in the strength of this relationship was observed. The heel-mounted accelerometer may have utility as an adjunct measure in the evaluation of floor slipperiness, particularly for field applications where direct measurement may not be feasible.

The effects of posture and vibration magnitude on the vertical apparent mass and the fore-and-aft cross-axis apparent mass of the standing human body during exposure to vertical vibration have been investigated. Twelve male subjects were exposed to random vertical vibration over the frequency range 2.0–20 Hz at three vibration magnitudes: 0.125, 0.25 and 0.5 m s?2 rms. Subjects stood in five different postures: upright, lordotic, anterior lean, knees bent and knees more bent. The vertical acceleration at the floor and the forces in the vertical and fore-and-aft directions at the floor were used to obtain the apparent mass and the cross-axis apparent mass. The resonance frequency of the apparent mass was significantly reduced with knees bent and knees more bent postures, but there were only minor effects on the resonance frequency by changing the position of the upper body. Considerable cross-axis apparent mass, up to about 30% of the static mass of subjects, was found. The cross-axis apparent mass was influenced by all postural changes used in the study. In all postures the resonance frequencies of the apparent mass and the cross-axis apparent mass tended to decrease with increasing vibration magnitude. This nonlinear characteristic tended to be less clear in some postures in which subjects increased muscle tension

In this study, the response of concrete rectangular liquid storage tanks subjected to vertical ground acceleration is investigated. The importance of the vertical component of ground acceleration on the overall seismic behaviour of liquid storage tanks is evaluated. The combination of added mass and sequential method is proposed in which the flexibility of the tank wall is considered in the dynamic analysis. The time history response of the tank wall associated with the hydrodynamic pressure distribution is presented. Results show that the time history responses of liquid storage tanks by considering the flexibility of the tank wall in the calculation of hydrodynamic pressures are different from those obtained using the rigid wall assumption. The horizontal response of the tank under the assumed rigid wall boundary condition is more significant than that when wall flexibility is considered. It is concluded that the response of the tank wall due to vertical ground acceleration should be considered in the design.

Adaptations in tiptoe rising were studied in unilateral idiopathic clubfoot (ICF) children, who underwent conservative treatment. The current study concerned 10 ICF children and 10 healthy children of the same range of ages (8–12 year). All ICF children were rated “good” or “very good” treatment results, but showed residual m. Triceps surae atrophy and mild foot alignment flaws. Tiptoe rising task was performed with subjects standing quietly with the feet on separate force platforms. Subjects were instructed to rise onto tiptoes as fast as possible and to maintain the tiptoe erect posture for a few seconds. Surface EMG of muscles Gastrocnemius, Tibialis anterior, Peroneus longus were recorded on both sides, simultaneously with vertical reaction forces (RZ) and centres of pressure (CP) displacements, during a series of 10–15 trials. Foot preferentiality was without influence on the EMG and biomechanical activities of the control group. Although not aware of a deficit in performance, ICF children show less vertical acceleration than healthy children. Timing and magnitude of muscular activities, and Cp and RZ variables of ICF children, evidenced alterations in both affected and sound side, when compared to healthy subjects. Alterations in the affected side activities were well explained by Triceps surae atrophy. Alterations in the sound side were considered as adaptations of central nervous system (CNS), preserving a global symmetry of the task. These results highlight the CNS capacity to adapt even for mild deficiencies. They stressed that it is mandatory to follow ICF children, even if they recovered a normal life.

The transmission of vibration to the occupant of a car seat has been studied using the multiple vibration inputs to the seat. Twelve input signals at the seat base (tri-axial vibration at the four corners) and six output signals (tri-axial vibration at the backrest and seat pan) were measured while driving. The results showed that vibration inputs to the seat varied between the four positions at the seat base. The two fore-aft input accelerations at the left-hand side of the seat base and the two fore-aft input accelerations at the right-hand side of the seat base were highly correlated with each other. There was also a high correlation between the two pairs of lateral acceleration inputs at the front and rear of the seat base. A computer program for studying seat vibration transmission via multi-input channels was developed to allow the calculation of seat transmissibility with up to 12 different inputs. The transmission of multi-axis seat base vibration to fore-aft seat backrest vibration was investigated using single-input, two-input, six-input and eight-input models. Results showed that the fore-aft vibration and the vertical vibration, but not lateral vibration, at the four corners of the seat base contributed to fore-aft vibration of the backrest. The primary peak of the fore-aft backrest transmissibility occurred around 4–5 Hz. The coherency was improved when using the multi-input models, although the characteristics of the transmissibility remained similar. The transmission of lateral vibration at the seat base to lateral vibration at the backrest was studied using single-input and two-input models. With single-input models, the transmission of lateral acceleration at the seat base to lateral acceleration at the backrest was amplified between 18 and 35 Hz, with a peak at 26 Hz. Coherency was greater at frequencies above 20 Hz than at lower frequencies. The coherency at low frequencies was increased with a two-input model. The transmission of vertical vibration to vertical vibration at the backrest was investigated using single-input, four-input and six-input models. The results showed that vertical acceleration at the four corners of the seat base was highly correlated with vertical acceleration at the backrest. The results are consistent with previous findings that a single-input model is not sufficient to study the transmission of vibration to the seat back in the horizontal directions, while for the transmission of vertical vibration a single-input model is probably sufficient, especially when low frequencies are of main concern.

During the 1999 Chi-Chi earthquake, extensive slope failures were triggered by the earthquake in central Taiwan. Among those, a large-scale dip-slope slide in Tsao-Ling occurred, which involved the mass movement of 120 million cubic meters. Four catastrophic dip-slope rockslide events in history in Tsao-Ling are reported; furthermore, the stability analysis of the Tsao-Ling landslide caused by the Chi-Chi earthquake was conducted for the original and remaining slope. Results of pseudostatic analysis indicated that a reduction factor of 2/3 for both vertical and horizontal peak ground acceleration with 30% of material strength degradation were likely the case for inducing the Tsao-Ling landslide, and the effects of vertical acceleration were significant. Accordingly, it was concluded that ground motion and degradation of material strength were the major factors for the inducement of the Tsao-Ling landslide by the Chi-Chi earthquake.

The vibration isolation efficiency of seating has been evaluated in 100 work vehicles in 14 categories (cars, vans, lift trucks, lorries, tractors, buses, dumpers, excavators, helicopters, armoured vehicles, mobile cranes, grass rollers, mowers and milk floats). Seat isolation efficiency, expressed by the SEAT value, was determined for all seats (67 conventional seats and 33 suspension seats) from the vertical acceleration measured on the floors and on the seats of the vehicles. For most categories of vehicle, the average SEAT value was less than 100%, indicating that the average seat provided some attenuation of vibration. However, there were large variations in SEAT values between vehicles within categories. Two alternative vibration frequency weightings (Wb from BS 6841, 1987; Wk from ISO 2631, 1997) yielded SEAT values that differed by less than 6%. Overall, the SEAT values determined by two alternative methods (the ratio of r.m.s. values and the ratio of vibration dose values) differed by less than 4·5% when using weighting Wb, although larger differences may be expected in some situations. The median SEAT value for the suspension seats was 84·6%; the median SEAT value for the conventional seats was 86·9% (based on weighting Wb and the ratio of r.m.s. values). Predicted SEAT values were obtained assuming that each seat could be interchanged between vehicles without altering its transmissibility. The calculations suggest that 94% of the vehicles investigated might benefit from changing the current seat to a seat from one of the other vehicles investigated. Although the predictions are based on assumptions that will not always apply, it is concluded that the severity of whole-body vibration exposures in many work environments can be lessened by improvements to seating dynamics.

This paper describes a model which makes it possible to predict the transport velocity of a crushed rock material bed along an ordinary screen with a circular stroke. Transport velocity can be predicted with respect to the inclination, stroke and frequency of the screen. The model is based on physical laws. A particle leaves the screen surface when the negative vertical acceleration of the screen surface exceeds that of the particle. The particle can also slide along the screen surface. Monte Carlo simulation is used to estimate the influence of the other particles. Thus, random values are used to simulate the collisions between particles. The predicted transport velocity is equal to the average transport velocity from a few runs with the model. To verify the model, experiments were made: the transport velocity of a bed of crushed rock particles along a wire cloth was measured for different inclinations, strokes and frequencies. The predictions made with the model agreed well with the experimental results. A model which makes it possible to predict the size distribution of both the remaining and the passed material on a screen with several interacting screen planes has already been presented by the author. In addition, it is necessary to know the transport velocity of the material to be able to estimate the bed thickness and the capacity of the screening process.

In this paper a comparative study of two different control strategies is done: Gain scheduling with classic controllers (PD and second order filter) versus QFT. Both of them are used to decrease motion sickness in a high speed ferry produced by the vertical acceleration associated with heave and pitch motion.

The Hicom nutating mill is a high intensity compact grinding mill of novel design. It is an adaptation of the centrifugal mill concept, but unlike the centrifugal mill, it's grinding chamber geometry and motion can only be adequately described in three dimensions. This has prompted an investigation into the load behaviour characteristics of the Hicom mill. Measurements of the Hicom mill's load behaviour have been made using conductivity and force probes passing through the shell of the mill. The results have shown that the load behaviour is unique and that existing two-dimensional load behaviour models for centrifugal mills are inadequate to describe the Hicom mill's load behaviour. The uniqueness of the Hicom mill's load behaviour is believed to be as a result of the vertical acceleration component of the chamber wall and base acting on the load.

Highly localized solitary states, driven by means of the spatially uniform, vertical acceleration of a thin fluid layer, are observed to propagate along the 2D surface of a fluid in a highly dissipative regime. Unlike classical solitons, these states propagate at a single constant velocity for given fluid parameters and their existence is dependent on the highly dissipative character of the system. The properties of these states are discussed and examples of bound states and two-state interactions are presented.

Low-back pain arising from repetitive lifting of objects out of deep containers is a significant problem in many industries and results in a great deal of time lost from work. This study measured electromyographic (EMG) activity of the lumbar paraspinal cles, vertical acceleration of three different loads, and the reaction force of the supporting upper extremity to compare the assisted one-hand lift and the two-hand stoop lift techniques. The results of the study indicate thatmus the assisted one-hand lift requires significantly less EMG activity than the two-hand stoop method when lifting loads out of deep containers. The acceleration of the load was not significantly different for three different loads, but the force on the supporting upper extremity was significantly related to the weight of the load lifted. Results of this study seem to indicate that, under certain circumstances, the one-hand lift is a less stressful method of lifting than the two-hand stoop method.

Vertical vibration tests with a rigid mould as well as dynamic and cyclic simple shear tests were conducted on sand to investigate the characteristics and mechanism of densification. Vertical acceleration was applied to the sample in the vertical vibration tests, but the dynamic stress was very small relative to the confining stress. Dynamic and cyclic simple shear tests were conducted by using the same simple shear apparatus. Both dynamic shear stress and horizontal acceleration were given to the sample in the dynamic simple shear tests. Cyclic simple shear tests were conducted under two conditions to investigate the role of acceleration in the densification of sand by vibration. /TRRL/

An assessment was made of the upper body low frequency steady-state vibration in five normal male subjects during level walking in a straight line. Speed of progression ranged from 0.99 to 2.35 m/s. Through a stereophotogrammetric technique, a three-dimensional measurement of the linear displacement of the longitudinal axis of the trunk and head was done. The relevant accelerations were obtained by double differentiation and described both in the time and frequency domains. The data were compared with those available on the biodynamic properties of body tissues and on the subjective response of humans to externally generated whole-body vibration. The comparison yielded a consistent indication of the characteristics of the vibration stimulus to which the human body may be adapted. As walking speed approached its maximum, the vertical acceleration spectrum increased in magnitude and shifted critically close to frequencies at which body organs are known to undergo resonance. A coordinated movement of the trunk with respect to the pelvis helped to reduce to a minimum the value of the acceleration to which the head was submitted in the antero-posterior direction and to shift the relevant spectrum towards the lower frequencies.

This paper examines theoretically the errors introduced into wave measurement by using an accelerometer which sets itself into the “apparent vertical”, that is, perpendicular to the local water surface, instead of being stabilised to measure the true vertical acceleration. The spectrum of the error signal in terms of wave height rises steeply at low frequencies, and although the errors do not seriously affect the main wave components, bands of low swell may be obscured under certain conditions.