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Fatigue Meters have been installed in eight topdressing and three non-agricultural aircraft. Total recording time to date is 3,600 h. The Meters record exceedings of eight vertical acceleration levels ranging from −0.5 to + 3.5g. Other records taken enable average weight and flight time to be determined for use in fatigue life calculations. Fatigue life of agricultural aircraft is largely dependent on piloting technique, and is shown to be very variable. Fatigue lives of a ‘typical’ agricultural aircraft calculated from the measured spectra range from 11,000 to 113,000 h. A load spectrum to be used for test purposes and life calculations is proposed. The most severe agricultural load spectrum recorded resulted in calculated fatigue lives of only 10 per cent of the minimum life expected for non-agricultural operations. A recording period of 100 h is suggested as sufficient to establish a long-term load spectrum for an agricultural aircraft/pilot combination with reasonable accuracy.

The vertical accelerations involved in crouching and returning to the erect position were computed from the measured forces applied by the subject's feet to a force plate. The subjects were simply instructed to squat, retrieve an object from the floor and return to the erect position in a normal manner. The average peak accelerations were found to range from 0.118 to 0.166 G. If an astronaut's acceleration pattern is the same under weightlessness, a restraint system or device capable of holding with a force equal to at least one third the astronaut's earth weight will be required to prevent his feet from leaving the floor when crouching and to prevent launching himself away from the floor when arising from a crouched position.

The problem of weather forecasting has been intimately related to the problem of the prediction of the pressure field and, therefore, to the mechanism of pressure change. For this reason meteorologists have sought an explanation of pressure change. However, despite the efforts of research workers during the past century it appears that there is not yet a completely satisfactory explanation of this phenomenon. In view of the uncertain state of knowledge it is the intention of the author to review briefly the more prominent theories of the pressure-change mechanism.

Ponència presentada al XI International Conference on Structural Dynamics (Eurodyn 2020), del 23 al 26 de novembre de 2020 In the present contribution the effect of the continuity of the ballasted track on the dynamic response of simply-supported railway bridges composed by structurally independent adjacent slabs at each span is addressed. Previous research works and experimental campaigns performed on simply-supported structures have shown that the presence of the ballast layer and other track components (rails, sleepers) may induce a dynamic coupling effect between the bridge spans or adjacent decks. In this study the influence of this effect on the train-induced vibrations is assessed. With this purpose a preliminary three-dimensional finite element (FE) model that includes the track components as a set of discrete mass, stiffness and damping elements has been implemented to numerically evaluate the influence of the continuity of the track components on the prediction of the bridge acceleration response under the passage of railway vehicles. The numerical model is calibrated with the load test results performed on a simply-supported railway bridge composed by several adjacent slabs. Finally the measured structural response of the bridge under train induced vibrations is compared with the numerical predictions. Preliminary conclusions regarding the importance of considering the continuity of the track components for the prediction and the assessment of the Serviceability Limit State of vertical acceleration in ballasted simply-supported railway bridges are presented.

Post-reconnaissance findings after recent earthquakes have shown that the effect of the vertical acceleration component of the ground motion can be more damaging than typically considered thus far, particularly in near-field regions where the ratio of vertical-to-horizontal ground accelerations may exceed considerably the 2/3 scaling factor used in design. Besides, the usual period range for the constant-acceleration region of vertical acceleration spectra often overlaps with the range of vertical vibration periods in reinforced concrete (RC) structures. These reasons explain the appearance of large dynamic axial forces, which can reduce the column shear strength due to tensile demands or alternatively promote direct compressive failures. Estimating the change in the member axial forces during nonlinear seismic response due to the vertical ground motion component is therefore of paramount significance and can only be simulated through dynamic analyses, for which a specific damping model needs to be assigned. Using a cantilever bridge pier with a top mass as an illustrative example, the present paper assesses the effects of the most commonly used damping models and damping values on the simulation of axial forces. Distributed plasticity beam elements with distinct formulations are employed, and a range of top masses is considered. The results show that, even for very low damping values, distinct damping models can have a very significant influence on the simulation of the seismically-induced axial forces, which increases considerably for larger values of the top mass.

The present study was designed to investigate the determination of vertical jumping height by means of force plate measurements. Four different sources of error influence this determination: the measurement of body mass, the determination of take off, the integration frequency, and the assessment of the initial conditions influencing the determination of the start of the movement. A theoretical model was utilized to simulate the vertical ground reaction forces in vertical jumping and to compare the outcome of analytical and numerical double integration of the vertical acceleration of the body centre of mass. A high integration frequency and an optimizing loop for body mass determination were found to be important and should be taken into account when determining jumping height parameters.

Riders generally use reins as a means for communication with the horse. At present, the signalling pattern is poorly understood. The aim of this study was to illustrate and analyse the rein tension patterns in a number of rider/horse combinations across a variety of exercises in the canter gait. Our hypothesis was that some riders will follow the movement of the horse more closely than others. Data were collected from eight professional riders riding each three (in one case two) horses that were familiar to them in canter. Horses were instrumented with rein tension meters logged by inertial measurement unit technique (IMU). Inside and outside rein tension data were synchronised with the gait using the vertical acceleration IMU-signal at the poll. Stride-split data (0-100 percentages) were analysed using mixed models technique to elucidate the inside/outside and stride percentage interaction, taking into account the exercises performed. In general, tension was maximal just before the beginning of vertical stance, as defined by the maximal acceleration of the head, with the release closer to the suspension phase. The release was significantly more marked on the outside rein, but between riders and horses the pattern varied substantially. In total 26% of the variation was represented by riders and 21% by the horses. On average there were significant inside/outside rein differences, but at the same time in some horse/rider combinations these differences did not exist.

where (x, j;) are the span coordinates, t is time, El is the stiffness, Tc is the constant axial compressive load, K is the elastic foundation constant, c is the viscous damping constant, p is the span mass density, and A is the span's cross sectional area. If y0m is the absolute vertical acceleration at the midpoint of the mth mass segment located at distance zm, then the loading /(x, t) for the ith span is fi(x,t) = qm(t)fm(x) (2a) where ap «! + ! , . . .a2—1, a 2 = (l/d)(Mg~My0m)

MILLER, DORIS I. and CAROLYN F. MUNRO. Body segment contributions to height achieved during the flight of a springboard dive. Med. Sci. Sports Exerc., Vol. 16, No. 3, pp. 234–242, 1984. The way in which athletes achieve the necessary height to accomplish the rotational requirements of springboard dives was investigated by focusing upon the take-offs of dives from the forward and reverse groups. Films of eight women in the 3-m final of the 1982 Canadian championship and of five men practicing for the 1979 Fort Lauderdale Invitational Meet provided data for the analysis. The vertical acceleration of the diver's center of gravity was expressed relative to that of the metatarsals, which represented the point on the board directly beneath the feet. The divers were only able to accelerate upward relative to the metatarsals for approximately the first half of springboard depression. This period of positive relative acceleration was considered to be a key factor in effective deflection of the springboard. The lower extremities were responsible for about three-quarters of the diver's vertical acceleration during this period. Two-thirds of their contribution was attributed to their role in accelerating the large mass of the trunk upward. The upper extremities accounted for about 10% of the diver's vertical acceleration during the initial half of springboard depression. Their acceleration-time patterns clearly fell into three classifications depending upon whether their upward acceleration relative to the shoulders preceded, coincided with, or followed initial contact with the board for the take-off.

If all the oceans were filled with islands as close together as in certain parts of the Pacific and Indian oceans, perhaps the geodesists would be satisfied to measure the intensity of gravity at land stations only. There are, however, great ocean areas containing no islands, and the determination of gravity over these areas is a very difficult problem. At the present time the only method of determining the intensity of gravity with high precision is by the use of pendulums. But gravity pendulums cannot be used on an ordinary ship, not only because the motion of the ship displaces the pendulum on its support but also because the pendulum will measure both the acceleration of gravity and the vertical acceleration of the ship and the two effects cannot be separated. During the past twenty-five years several attempts have been made to design some type of apparatus that could be used at sea and give an accuracy comparable with that obtained on land with the pendulum apparatus. The net result has been perhaps two different types of sea apparatus which can be used with fair success. They do not, however, give the accuracy required for the scientific study of the isostatic condition of the earth's crust.

General problems of gravity measurement at sea are discussed. A treatment of the effects of vertical accelerations shows that gravity meter nonlinearities cause errors that ordinarily are proportional to the square of the vertical acceleration. In a treatment of horizontal accelerations, similarities and differences that exist between gimbal supported and stabilized platform gravity meters are pointed out. It is shown that optimization of the parameters of a stabilized reference can reduce gravity meter errors by two or more orders of magnitude at long periods. A method for correcting for inadequate period of a stabilized reference is given. The Schuler-tuned stabilized platform is briefly described. The theory of inherent type cross coupling and examples of imperfection type cross coupling are given. Theory and significant details of construction are given for the LaCoste and Romberg (L&R) gravity meter and stabilized platform. Tests on L&R air-Sea gravity meters made during the last decade are discussed. The largest error in earlier work is shown to have been due to vertical accelerations. A method of correcting for these errors is described. Tests indicate that presently attainable accuracy of L&R gravity meters is appreciably better than 1 mgal.