Using the Effect of Compression Stress in Fatigue Analysis of the Roller Bearing for Bimodal Stress Histories

A new approach based on the direct spectral method for fatigue analysis of elements subjected to bimodal stress histories, including high compression effects, is proposed. A correction factor, taking into account the influence of the mean compressive stresses, is used in the proposed method. Equivalent amplitude is estimated, based on criteria proposed by Smith, Watson, and Tooper, and by Bergmann and Seeger. The method is presented with example of a thrust roller bearing. Two cases in which the rollers were subjected to constant force 206 N (where constant amplitude stresses occurred in the rollers) and cyclic force (where bimodal stresses with variable amplitudes occurred in the rollers) are studied. It is observed that multiaxial fatigue criteria (Crossland, Papadopoulos) do not include the influence of bimodal stresses and should not be used for such loading conditions. The proposed method includes both kinds of stress waveforms in the fatigue analysis and can be applied for the accurate identification of stress components and the determination of fatigue life. The damage rate calculated by the proposed approach for rollers subjected to a cyclic force (equivalent load equal to 151 N) was 0.86, which is in good agreement with the recommendations provided in the literature. The obtained accuracy of the proposed method is above 95%.

A Perturbation-Based Methodology to Estimate the Equivalent Inertia of an Area Monitored by PMUs

This paper proposes a novel methodology to estimate equivalent inertia of an area, observed from its boundary buses where Phasor Measurement Units (PMUs) are assumed to be installed. The areas are divided according to the measurement points, and the methodology proposed can obtain the equivalent dynamic response of the area dependent of or independent of coherency of the generators inside, which is the first contribution of this paper. The methodology is divided in three parts: estimating the frequency response, estimating the power imbalance and estimating inertia through the solution of the swing equation by Least-Squares Method (LSM). The estimation of the power imbalance is the second contribution of this paper, enabling the study of areas that contain perturbations and attending the limitation of methods of the literature that rely on assumptions of slow mechanical power. It can be further divided in three steps: accounting the total power injected, estimating an equivalent load behavior and estimating an equivalent mechanical power. The quality of results is proved with test systems of different sizes, simulating different types of perturbations.

Collaborative Optimization Method of Power and Efficiency for LCC-S Wireless Power Transmission System

Dynamic wireless charging enables moving equipment such as electric vehicles, robots to be charged in motion, and thus is a research hotspot. The applications in practice, however, suffer from mutual inductance fluctuation due to unavoidable environmental disturbances. In addition, the load also changes during operation, which makes the problem more complicated. This paper analyzes the impacts of equivalent load and mutual inductances variation over the system by LCC-S topology modeling utilizing two-port theory. The optimal load expression is derived. Moreover, a double-sided control strategy enabling optimal efficiency and power adjustment is proposed. Voltage conducting angles on the inverter and rectifier are introduced. The simulation and experimental results verify the proposed method.

Rigid–flexible coupling dynamics analysis with joint clearance for a 5-DOF hybrid polishing robot

SUMMARY Considering the polishing requirements for high-precision aspherical optical mirrors, a hybrid polishing robot composed of a serial–parallel manipulator and a dual rotor grinding system is proposed. Firstly, based on the kinematics of serial components, the equivalent load model for the parallel manipulator is established. Then, the elastodynamic model of kinematic branched-chains of the parallel manipulator is established by using the spatial beam element, and the rigid–flexible coupling dynamic model of the polishing robot is obtained with Kineto-elasto dynamics theory. Further, considering the dynamic properties of the joint clearance, the rigid–flexible coupling dynamic model with the joint clearance for the polishing robot is established. Finally, the equivalent load distribution of the parallel manipulator is analyzed, and the effect of the branched-chain elasticity and joint clearance on the motion error of the polishing robot is studied. This article provides a theoretical basis for improving the motion accuracy and dynamic performance of the hybrid polishing robot.

Experimental Determination of Parameters of Nonlinear Electrical Load

The paper deals with issues of modeling nonlinear electrical loads of various types, such an uncontrolled rectifier, thyristor rectifier, thyristor power regulator and mixed equivalent nonlinear load. For these load types, existing analytical expressions were identified to determine the magnitudes of harmonic currents, and waveforms of currents were obtained during measurements in laboratory conditions with variable parameters of the grid impedance and load. The obtained results were compared, and it was found that the error in determining the magnitudes of harmonic currents can reach 60% for an individual load and 54% for an equivalent load. A more accurate method for determining the parameters of nonlinear electrical load is also proposed, which is based on the application of shunt harmonic filters. In laboratory conditions, it was found that when using the developed method, the error did not exceed 10% for an individual load and 14% for an equivalent load.

Parabolic tendons in prestressed concrete - how accurate are equivalent loads?

The mechanical effects of a parabolic tendon can be modeled replacing the tendon by external loads applied to the concrete. The intensity of these loads depends on the prestressing force P and curvature of the tendons. These two factors are also interrelated because the losses of prestress vary with the curvature. The structural analysis can be simplified by approximating that the line load against the tendon, able to maintain the initial parabolic form of the tendon and called equivalent load, is constant, perpendicular to the centroidal axis of the beam and equal to P/R where R is the radius of curvature of the parabola at its vertex. This approximation is one of the key issues in the textbooks but normally not properly justified. In this paper, the mathematical background for the approximation is formulated. Some typical tendon layouts are analyzed to evaluate the approximation error. The error proved to be insignificant for simple beams. For cantilever and continuous beams more accurate methods in the final design are recommended.

Damage Equivalent Load Synthesis and Stochastic Extrapolation for Fatigue Life Validation

Present verification of the fatigue life margins on wind turbine structures utilizes damage equivalent load (DEL) computations over limited time duration. In this article, a procedure to determine long term fatigue damage and remaining life is presented as a combination of stochastic extrapolation of the 10-minute DEL to determine its probability of exceedance and through computationally fast synthesis of DELs using level-crossings of a Gaussian process. Both the synthesis of DELs and long-term stochastic extrapolation are validated using measured loads from a wind farm. The extrapolation for the blade root flap and tower base fore-aft damage equivalent moment is presented using a three-parameter Weibull distribution, whereby the long term damage equivalent load levels are forecast for both simulated and measured values. The damage equivalent load magnitude at a selected target probability of exceedance provides an indicator of the integrity of the structure for the next year. The extrapolated damage equivalent load over a year is validated using measured multi-year damage equivalent loads from a turbine in the Lillgrund wind farm, which is subject to wakes. The simulation of damage equivalent loads using the method of level crossings of a Gaussian process is shown to be able to reconstruct the damage equivalent load for both blade root and tower base moments. The prediction of the tower base fore-aft DEL is demonstrated to be feasible when using the Vanmarcke correction for very-narrow band processes. The combined method of fast damage equivalent load computations and stochastic extrapolation to the next year, allows a quick and accurate forecasting of structural integrity of operational wind turbines.

Topology Optimization and Design for Additive Manufactured Supporting Structure of Vehicle Rudder

The object investigated in this work is a design method for the supporting structure of vehicle rudders, which are the crucial components in flight control system. As a practical application of topology optimization for additive manufacture, the design process was presented in this article. To obtain the optimal material distribution, topology optimization based on SIMP method was applied, with compliance minimization as the optimization objective. A numerical optimization model was built and calculated in Inspire, and the result in an equivalent load scheme of 30 percent point load and 70 percent uniform pressure was adopted to be the initial geometry for the subsequent design. Concentrating on realizing the optimized geometry, this design took a series of technical constrains for additive manufacture and mass requirements into consideration. Notably, the FEM simulation for the supporting structure is necessary, which consist of stress analysis and mode analysis. And the technical feasibility was verified in its practical manufacturing process. Finally, by the experiment about dynamic characteristic, it is verified that the lightweight rudder designed in this work can satisfy all the requirements for flight control.