Influence of Restrainer Piers on the Seismic Performance of Long Bridges with Equal-Height Piers

Pounding may occur between the main girders under the action of strong earthquakes, so as between main girders and abutments. This causes excessive longitudinal displacement of the main girder and unseating damage to bridges. Because long bridges in mountainous areas with high intensity are easy to unseat, the authors studied the influence of restrainer piers, expansion joint spacings (EJSs), and the span on the seismic performance of long bridges. The ABAQUS finite element software was used to simulate a bridge dynamic analysis model considering the elastoplasticity of the pounding effect of the pier and the beam. By inputting El-Centro, Northbridge, and Taft seismic waves, the time-history analysis of the seismic response of long bridges was carried out. The results indicated that a reasonable number of restrainer piers, an appropriate EJS, and a span could effectively reduce the maximum relative displacement of pier-beams. This behavior will improve the seismic performance of bridge structures. Moreover, for a 24-span equal-height beam bridge, the optimum seismic effect was obtained when 3 restrainer piers, an EJS of 70 mm, and a 50 m span were used.

Vibration isolation characteristics and control strategy of parallel air spring system for transportation under abnormal road and eccentric load conditions

The precision equipment bears the vibration excited by the road roughness during transportation, and faces the risk of damage arising from the vibration. The parallel air spring vibration isolation system (PAVS) has an excellent vibration isolation performance, so has a good application prospect in the precision equipment transportation. But under the conditions of abnormal road and eccentric load, PAVS bears great vibration excitation, and the resulting large deformation of air spring makes the air spring stiffness nonlinear, so to obtain an excellent vibration isolation performance faces a great challenge. Aiming at this problem, based on the measured parameters, the nonlinear dynamics model of PAVS is proposed. Then, the influence of air spring under large deformation on the vibration isolation characteristics is discussed. Finally, under the condition of eccentricity of precision equipment, the vibration isolation characteristics of PAVS with equal height control strategy is investigated. The results show that PAVS with the equal height control strategy has good vibration isolation characteristics. So for the transportation of large precision equipment, PAVS is a potentially useful method.

A Study on Plume Dispersion Characteristics of Two Discrete Plume Stacks for Negative Temperature Gradient Conditions

The dispersion of air pollutants emitted from industries has been studied ever since the dawn of industrialisation. The present work focuses on investigating the effect of negative atmospheric temperature gradient and the plume stack orientation of two individual equal-height stacks on the vertical rise and dispersion of the plume. The study carried out upon three-stack layout configurations namely inline, 45° and non-inline, separated by an inter-stack distance of 12 times the exit chimney diameter (12 D) and 22 times the exit chimney diameter (22 D) in each case over the two temperature gradients of −0.2 K/100 m and −0.5 K/100 m. The turbulence is modelled using realisable k-ε model, a model used in the FLUENT flow solver. In the case of the inline configuration, the upwind plume shields its downwind counterpart, which in turn allows for higher plume rise at a given temperature gradient. The plume oscillates more in the case of inline than 45° and non-inline cases. Also, for a temperature gradient of −0.5 K/100 m, the plumes oscillate violently in the vertical direction, mainly because, with the initial rise of the plume, cold air from higher altitudes moves down and forms a layer of lower temperature closer to the ground. The present study is important to highlight the plume dispersion characteristics under negative temperature gradient conditions.

FEATURES OF USING A GROUND LASER PROFILER TO ASSESS THE QUALITY OF SOIL CULTIVATION ON AGRICULTURAL SLOPE LANDSCAPES

The authors analyze an extensive set of data for measuring the daily surface profi le of the cultivated soil to assess its agrotechnical parameters. The research was carried out on a small agricultural catchment area of the Orininsky rural settlement, which is located in the Morgaushy district of the Chuvash Republic. Three agricultural fi elds were selected, ranging from 25 ha to 53 ha. The studied areas were cultivated in various ways: plowing with harrowing, disking the soil and winter plowing. The profi les of the studied elementary sections were measured using a developed ground-based circular laser profi lometer. Data on the state of the profi le were used to determine the main agrotechnical parameters - clumping, cloddiness, surface slope, and deviation of the travel trajectory of a machine and tractor unit from the line of equal height. A software tool for processing and analyzing data received from sensors has been developed. The results established that the deviation of the projection of the greatest elevation line changes (measured by the slope) from the travel trajectory of a unit with an angle of 62, a slope of 6.5, and in a quantitative size distribution soil aggregates of 1…4 inches in diameter prevail. The weighted average diameter of the clods was 3.99 cm. The research results have determined the use of recommend methods for stating the agrotechnical parameters of the daylight surface to evaluate the cultivated soil in accordance with agrotechnical requirements.

A model-based analysis of the mechanical cost of walking on uneven terrain

Human walking on uneven terrain is energetically more expensive than on flat, even ground. This is in part due to increases in, and redistribution of positive work among lower limb joints. To improve understanding of the mechanical adaptations, we performed analytical and computational analyses of simple mechanical models walking over uneven terrain comprised of alternating up and down steps of equal height. We simulated dynamic walking models using trailing leg push-off and/or hip torque to power gait, and quantified the compensatory work costs vs. terrain height. We also examined the effect of swing leg dynamics by including and excluding them from the model. We found that greater work, increasing approximately quadratically with uneven terrain height variations, was necessary to maintain a prescribed average forward speed. Greatest economy was achieved by modulating precisely-timed push-offs for each step height. Least economy was achieved with hip power, which did not require as precise timing. This compares well with observations of humans on uneven terrain, showing similar near-normal push-off but with more variable step timing, and considerably more hip work. These analyses suggest how mechanical work and timing could be adjusted to compensate for real world environments.

A predictor–corrector scheme for solving nonlinear fractional differential equations with uniform and nonuniform meshes

In this paper, we develop two algorithms for solving linear and nonlinear fractional differential equations involving Caputo derivative. For designing new predictor–corrector (PC) schemes, we select the mesh points based on the two equal-height and equal-area distribution. Furthermore, the error bounds of PC schemes with uniform and equidistributing meshes are obtained. Finally, examples are constructed for illustrating the obtained PC schemes with uniform and equidistributing meshes. A comparative study is also presented.