Dynamic Load Variations Research Articles

Pavement Strain from Moving Dynamic 3D Load Distribution

This paper presents the formulation and the application of a continuum-based finite-layer approach to evaluate pavement strain response under actual traffic loading. The model incorporates important pavement response parameters such as the dynamic tire-pavement load variations and corresponding complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization. Results of a parametric study in which two typical thin and thick pavement sections were subjected to traffic loading moving at different speeds are included. As an important application of the proposed method, pavement strain responses generated by wide-base and dual tires have been presented. This study reveals that contradictory to the past studies, the impact of tire-pavement contact shear stress on tensile strain at the bottom of asphalt concrete is insignificant.

Calibration of Weigh-in-Motion Systems Through Dynamic Vehicle Simulation

Abstract This paper describes two methods for calibrating weigh-in-motion (WIM) systems with the aid of dynamic vehicle simulations. A modified version of the vehicle simulation model VESYM, named VESYMF, is used for predicting the dynamic axle load variation exerted by heavy vehicles at a WIM site. The first method uses test trucks performing controlled runs over a WIM system, while the second method relies on the consistent properties of the steering axle loads of traffic stream 5-axle tractor semi-trailer trucks such as the 3-S2. For the first method, test truck runs are performed at a number of replicate speeds and the WIM measurements of individual axles are plotted versus speed. For a given axle and speed, the variation in WIM measurements is equal to the precision of the WIM system. Combining this source of variation with the dynamics-induced variation calculated through VESYMF, gives the anticipated frequency distribution in WIM measurements for the pavement roughness at a site. This is used for estimating the probability of a particular WIM measurement, which in turn allows the calculation of the weighed average of the axle load WIM measurements obtained at different speeds. Calibration is effected by fitting a zero-intercept linear regression equation between the static and the average WIM axle load measurements. The second method is based on the consistent properties exhibited by the mean load of the steering axles of traffic-stream 3-S2 trucks. Its combined variance is calculated by adding the variance in static 3-S2 steering axle loads for traffic-stream vehicles to the other two components of variance described previously. This establishes a confidence interval for the mean of the WIM measurements of a number of 3-S2 steering axle loads. The feasibility of these two methods was demonstrated by field experimentation.

Effect of Vehicle-Pavement Interaction on Pavement Response

The structural response of flexible pavements is studied under different dynamic loads and pavement roughness conditions. The factors affecting dynamic load variability are investigated with regard to pavement-vehicle interaction. Furthermore, the study considers the viscoelastic nature of asphalt concrete and the nonlinearity and plasticity of granular and subgrade materials. The Florida COMPAS computer program was used to estimate the dynamic wheel force, and the ABAQUS three-dimensional finite-element program was used to determine the pavement response. The effects of vehicle and pavement characteristics such as vehicle type, vehicle speed, suspension type, level of roughness, pavement stiffness, and layer thickness were studied and statistically analyzed. The walking-beam suspension causes more dynamic load variation than the air-bag and leaf-spring suspension. The dynamic load coefficient for the walking-beam suspension is approximately twice the other suspensions. Vehicle speed is an important factor; the 20 km/hr speed resulted in permanent displacement approximately 10 times the permanent displacement produced by the 130 km/hr speed. The pavement response varies with distance due to roughness. Pavement stiffness and thickness had some effect on pavement response, but truck type and truck suspension type did not have a large effect.

Flexible transmission bandwidth management with effective channel reservation techniques for NGSO MSS networks

This paper describes efficient transmission bandwidth management based on flexible channel assignment and effective grade of service (GOS) control methods for nongeostationary orbit mobile satellite service (NGSO MSS) networks. Our basic approach for the flexible channel assignment is to use linear programming (FLEXCA-LP), and to apply the column generation technique for further reduction of the total bandwidth requirement. These methods efficiently assign channels, taking account of moving spot beam coverage and dynamic traffic load variation for large-scale networks. The GOS is investigated for the channel assignment by FLEXCA-LP to make the GOS of ongoing calls better than that of fresh calls as stipulated in ITU-T Recommendations. We propose a few effective means to improve the results of FLEXCA-LP by reducing the disruption possibility of ongoing calls. One is to add channels utilizing a hysteresis concept. The others are effective use of GOS control techniques for NGSO MSS networks. These techniques are evaluated by a simulation study to identify promising techniques. Under time-variant conditions, we show that a reliable channel assignment plan is generated first by FLEXCA-LP considering the traffic load of fresh calls only and then by GOS control techniques to improve handover failure and call disruption rates.

Discrete Adaptive Active Suspension for Hardware Implementation

SUMMARY This paper presents a discrete adaptive control approach for an active suspension. The study involves formulation of an active suspension as a digital controller problem involving the time delays. A nonlinear time varying (NTV), single input single output (SISO) suspension model is considered for the analysis. A discrete model reference adaptive control (DMRAC) approach with recursive least square (RLS) estimation is used to form the controller. The controller is designed to maintain the static equilibrium irrespective of dynamic load variations as a disturbance force on the model. Simulation results for deterministic and stochastic inputs are presented to substantiate the approach. Results indicate good performance of adaptive controller even for large dynamic variations of the model and has the potential for a successful hardware implementation.

Dynamic Load and Root Stress Analysis of Spur Gears

Dynamic loads on spur gears are calculated by using an analytical model based on torsional vibrations of gears, and dynamic load variations during a mesh cycle of a tooth are determined. Tooth profile modifications, profile and pitch errors are included in dynamic load calculations. Variable stiffnesses of gear teeth, which are required for dynamic load calculations, and tooth root stresses resulting from dynamic loads are found by using the finite element method. Calculated tooth root stresses are used in fatigue failure analysis.

Approximated dynamic analysis of single anchor leg storage system

This paper is concerned with the determination of dynamic load variations in the riser and yoke pivot components of an offshore vessel/mooring oil production and storage system. Forces on the yoke system arise from wave induced inertial and drag forces including current and motion due to vessel surge, heave and pitch. The analysis is carried out in the frequency domain and the results yield the limiting wave height for a specific design of SALS which will give rise to loss of tension in the riser. Also presented are the maximum horizontal and vertical components of load variation at the yoke pivoted connections with the vessel.

Dynamic Behavior of Planetary Gear : 6th Report, Influence of Meshing-Phase

The authors carried out experimental investigations about the dynamic load and the torque variation in two cases, in which the meshing-phases of each planet gear in a single-stage Stoeckicht planetary gear differ. The results are as follows : (i) The variation of dynamic load due to the errors per mesh in the case in which the meshing-phases of each planet gear are equal is smaller than that in the case in which they are different. But the torque variation of a higher-speed shaft in the case of the former is larger than that in the case of the latter, because the phases of the variation of dynamic load at three meshing points are equal. (ii) The modes of free vibration at the resonance frequency of ring gear change according to the meshing-phases of each planet gear.