A Critical Analysis of Finite-Element Modeling Procedures for Radial Bearing Stiffness Estimation

Different strategies are commonly employed by researchers in order to decrease the computational effort associated with the finite-element analysis of rolling-element bearings. The purpose of this work is to review and analyze the procedures and hypotheses that may be exploited to evaluate the nonlinear radial stiffness of these components. Techniques are utilized to develop a meshing procedure aimed at balancing the computational effort and the accuracy of the results, to define a robust approach to the problem. The geometry is reduced by taking advantage of the available symmetry planes, by removing unloaded rollers, and by substituting the shaft with an equivalent sinusoidal load. In addition, the element dimensions are adapted to the applied load depending on the size of the contact area as computed by means of the Hertz theory. The proposed methodology may be applied to all bearing types provided that symmetry conditions and contact area dimensions are properly assessed. The estimated stiffness is compared against analytical formulae retrieved from the literature. Influence of different element types, roller position, cage, and clearance on accuracy and computational time is discussed.

Bending fatigue of single-wall and double-wall corrugated paperboards under sinusoidal and random loads

The bending fatigue tests of single-wall and double-wall corrugated paperboards were conducted to obtain the εrms– N curves under sinusoidal and random loads in this paper. The εrms– N equation of corrugated paperboard can be described by modified Coffin–Manson model considering the effect of mean stress. Four independent fatigue parameters are obtained for single-wall and double-wall corrugated paperboards. The εrms– N curve under random load moves left and rotates clockwise compared with that under sinusoidal load. The fatigue life under random load is much less than that under sinusoidal load, and the fatigue design of corrugated box should be based on the fatigue result under random load. The stiffness degradation and energy dissipation of double-wall corrugated paperboard before approaching fatigue failure are very different from that of single-wall one. For double-wall corrugated paperboard, two turning points occur in the stiffness degradation, and fluctuation occurs in the energy dissipation. Different from metal materials, the bending fatigue failure of corrugated paperboard is a process of wrinkle forming, spreading, and folding. The results obtained have practical values for the design of vibration fatigue of corrugated box.

Experimental Validation of Metaheuristic and Conventional Modulation, and Hysteresis Control of the Dual Boost Nine-Level Inverter

In this article, various modulation strategies and hysteresis-band control of a recently introduced dual-boost nine-level inverter (DB9LI) are implemented. DB9LI is a switched capacitor based inverter capable of generating symmetrical nine output voltage levels by employing a single DC source. The topology generates a boosted bipolar voltage at the output side without applying end-side H-bridge (usually employed to generate negative levels), which contrasts with some of the switched-capacitor topologies. The capacitors employed have an inherent self-balancing feature. Additionally, due to lower individual and total standing voltages, switches of low voltage ratings are required. As a result, the cost of switches and the inverter reduces considerably. Metaheuristic-based selective harmonic elimination and mitigation (SHE and SHM) and various sine-triangular pulse width modulation techniques are implemented and compared on various parameters. Finally, a robust eight-band hysteresis control is designed and implemented, which helps to obtain sinusoidal load current with a unity power factor. The modulation strategies and the hysteresis control are validated on the MATLAB simulation environment and an experimental prototype.

Nonlinear Position Control Using Differential Flatness Concept with Load Torque Observer for Electro Hydraulic Actuators with Sinusoidal Load Torque

We propose a nonlinear position control using a differential flatness concept with a load torque observer to compensate for the sinusoidal load torque in electro-hydraulic actuators (EHAs) EHAs. In an EHA with a rotational joint, the load torque is a sinusoidal disturbance, whose magnitude can be estimated via a load torque observer. In the proposed load torque observer, the load torque can be estimated without requiring its maximum frequency to be known. The position controller tracks position and comprises an inner-loop load pressure controller and an outer-loop position controller. The former tracks the desired pressure via near input–output linearization. The desired pressure is developed using the differential flatness of the mechanical system in the EHA. The feedback plus feedforward outer-loop position controller is designed to track the desired position and to compensate for the load torque. The stability of the closed-loop system is mathematically proven using the input-to-state stability property.

Loss Counter in Power Double Winding Transformers Implementing the Method of Conditionally Constant Coefficients in Online Mode Using the Information Platform

The article describes the developed loss counter in power double-winding transformers of distribution net-works. The principle of operation of the proposed measuring unit of the loss counter is considered on the exam-ple of one channel for measuring current and voltage in accordance with the above functional scheme. The ap-pearance and main characteristics of the loss counter are given. The main characteristics of the developed loss counter are confirmed by the adjustment Protocol based on the results of measurements in the FBU «Rostov CSM» and are at the level of existing characteristics of electric energy quality analyzers. The data measured and calculated by the microcontroller of the loss counter, necessary for the implementation of the method of conditionally constant coefficients, are transmitted over the USB bus to a single-Board computer. Using the de-veloped software written in the high-level General-purpose programming language Python, the formation and sending of data to the information platform Yandex.Cloud. The approbation of the operation of the loss coun-ter on the developed physical model «power transformer-asymmetric and non-sinusoidal load» and operating substations is shown. Thus, the developed loss counter can be used to calculate losses from higher harmonic components in power transformers by the method of conditionally constant coefficients in the online mode us-ing the resources of the information platform Yandex.Cloud.