Characteristic Analysis of Water Lubricated Plain Journal Bearing under Transient Load

Transient load has a huge impact on the life and stability of water-lubricated bearings. In this paper work, CFD software is used to analyse the dynamic characteristic of water lubricated bearings under different transient loads of 500N, 1000N, 2000N and 3000N. The water film pressure contour distribution at different transient time was given. The time-varying relationships between the different transient loads with bearing forces, the journal displacement, the maximum value of water film pressure as well as the minimum value of water film thickness are obtained. The results show that with the increase of transient load, the effective bearing area of dynamic water pressure film decreases, and the maximum pressure increases. The bearing forces, the journal displacement, the maximum value of water film pressure as well as the minimum value of water film thickness will increase fast.

A Computationally Efficient, Mass Conserving Generalized Short Bearing Formulation for Dynamically-Loaded Journal Bearings

This paper describes a computationally efficient, finite element implementation of a generalized short bearing (GSB) formulation to account for mass conservation in cavitated bearing regions. The method is applied to a set of examples representing partial and full journal bearings under transient loads and kinematics. Bearing performance trends are captured well by the GSB formulation when compared with results obtained from complete two-dimensional formulations and from experiments. The computational speed of the GSB formulation is approximately 40 to 200 times faster than the complete formulation for the examples provided in the paper.

A Medium Voltage AC and DC Distributed Power Generation Testbed Deploying Transient Loads

Microgrids have been studied considerably over the last decade. They are being uniquely designed and controlled in a variety of applications to supply countless different loads, many of which may operate in a transient manner. Given their isolated nature, ships are often treated as microgrids allowing much of the same theory to apply. Historically, both electric grids and ships have relied upon fossil fuel powered motors to spin generators that source the electric power they need. Microgrids can deploy a host of different distributed generation sources that are interconnected and controlled in real time to improve overall grid reliability and redundancy. The use of medium-voltage-direct-current (MVDC) power distribution is one possible solution to minimize power loss in the conductors and to reduce the power conversion requirement when high voltage loads are present. The non-continuous operation of loads may introduce harmonics into the power system that severely impact power quality. Avoiding this is critical and more must be understood for successful mitigation. Model development and validation is critical for successfully deploying new architectures and control strategies. To study the reliable operation and control of such a power system, as well as to validate the models being developed, the Pulsed Power and Energy Laboratory (PPEL) at the University of Texas at Arlington (UTA) has designed and installed a testbed that can be used to study a small microgrid deploying transient loads. The testbed, operating at power levels higher than 300 kW, utilizes distributed AC and DC power sources and loads operating at the 480 VAC, 4160 VAC, 1 kVDC, 6 kVDC, and 12 kVDC, respectively. The testbed is being virtually extended utilizing a hardware in the loop (HIL) simulator. This paper will discuss the design of the testbed, the test plan methodology, and the results collected so far.

Improvement of Small Wind Turbine Control in the Transition Region

Wind energy conversion systems are very challenging from the control system viewpoint. The control difficulties are even more challenging when wind turbines are able to operate at variable speed and variable pitch. The contribution of this work is focused on designing a combined controller that significantly alleviates the wind transient loads in the power tracking and power regulation modes as well as in the transition zone. In a previous work, the authors studied the applicability of different multivariable decoupling methodologies. The methodologies were tested in simulation and verified experimentally in a lab-scale wind turbine. It was demonstrated that multivariable control strategies achieve a good closed-loop response within the transition region, where the interaction level is greater. Nevertheless, although such controllers showed an acceptable performance in the power tracking (region II) and power regulation (region IV) zones, appreciable improvement was possible. To this end, the new proposed methodology employs a multivariable gain-scheduling controller with a static decoupling network for the transition region and monovariable controllers for the power tracking and power regulation regions. To make the transition between regions smoother, a gain scheduling block is incorporated into the multivariable controller. The proposed controller is experimentally compared with a standard switched controller in the lab-scale wind turbine. The experiments carried out suggest that the combination of the proposed multivariable strategy for the transition region to mitigate wind transient loads combined with two monovariable controllers, one dedicated to region II and other to region IV, provide better results than traditional switched control strategies.

A new cumulative damage model for time-dependent reliability analysis of deteriorating structures

Performance and reliability of structures will deteriorate with the effects of loads, environment, and interior factors of materials. In this article, a novel cumulative damage model is developed for time-dependent reliability analysis of deteriorating structures. The deterioration is a combination of three stochastic processes: the gradual deterioration posed by aging effects, the sudden deterioration caused by transient loads, and the additional deterioration introduced by sustained loads. The aging effect is modeled as a gamma process, while the transient load is described by a Poisson process. The sustained load is modeled by a stationary binomial process and a Poisson square wave process, respectively. The load threshold for three different scenarios are all considered and applied to not only the transient loads but also the sustained loads. The time-dependent reliability of deteriorating structures is then evaluated based on this model via semi-analytical methods or numerical simulation methods. Three numerical examples and an example involving a natural gas pipeline are used to validate the effectiveness of the proposed model for computing the time-dependent reliability.