Application of Probabilistic and Nonprobabilistic Hybrid Reliability Analysis Based on Dynamic Substructural Extremum Response Surface Decoupling Method for a Blisk of the Aeroengine

For the nondeterministic factors of an aeroengine blisk, including both factors with sufficient and insufficient statistical data, based on the dynamic substructural method of determinate analysis, the extremum response surface method of probabilistic analysis, and the interval method of nonprobabilistic analysis, a methodology called the probabilistic and nonprobabilistic hybrid reliability analysis based on dynamic substructural extremum response surface decoupling method (P-NP-HRA-DS-ERSDM) is proposed. The model includes random variables and interval variables to determine the interval failure probability and the interval reliability index. The extremum response surface function and its flow chart of mixed reliability analysis are given. The interval analysis is embedded in the most likely failure point in the iterative process. The probabilistic analysis and nonprobabilistic analysis are investigated alternately. Tuned and mistuned blisks are studied in a complicated environment, and the results are compared with the Monte Carlo method (MCM) and the multilevel nested algorithm (MLNA) to verify that the hybrid model can better handle reliability problems concurrently containing random variables and interval variables; meanwhile, it manifests that the computational efficiency of this method is superior and more reasonable for analysing and designing a mistuned blisk. Therefore, this methodology has very important practical significance

On the natural frequency and vibration mode of composite beam with non-uniform cross-section

In this paper, the vibratory properties and expression of natural modes of laminated composite beam with variable cross-section ratios of elastic modulus and density along the axis of the beam have been investigated via theoretical analysis. Based on the generalized Hamilton principle, the longitudinal and transverse vibration equations have been deduced by the means of variational method. Then, the natural frequencies of longitudinal and transverse vibration modes have been obtained using the method of power series, which agree well with finite element simulations. The first-order natural frequencies of longitudinal and transverse of composite beams are plotted as a function of the elastic modulus or densities difference of two components. With distinct material characteristics, the effect of shape factor on the first and second order lateral modes of composite beam is also revealed. In addition, the study shows that the boundary conditions impose a strong effect on the shape factor. The method presented in this paper is not only suitable for the laminated composite beam with variable cross-section, but will also be applicable to more general cases of composite beams of complex geometry and component in vibration mechanics. This controllable vibration performance achieved in this paper may shed some light on and stimulate new architectural design of composite engineering structures

A novel method to determine droop coefficients of DC voltage control for VSC-MTDC system

For droop control in voltage source converter based multi-terminal HVDC systems, the determination of droop coefficients is a key issue, which directly affects both power distribution and DC control performances. This paper proposes a novel design of droop coefficients considering the requirements of power distribution, DC voltage control and system stability. Considering the power margins of different converters, the ratio relationship among droop coefficients is established. Converters with larger power margins take bigger portion of power mismatch to avoid overload problem. Furthermore, the integral square error of converters DC voltage is adopted as the DC voltage control performance index, and optimization of droop coefficients to achieve coordinated DC voltage control of steady-state deviation and transient variation, is derived. Finally, the constraint of droop coefficients is established to guarantee the DC system stability after power disturbance. Case studies are conducted on the Nordic 32 system with an embedded 4-terminal DC grid to demonstrate the feasibility and effectiveness of the proposed droop control scheme

Ruminant-specific multiple duplication events of PRDM9 before speciation

The PR domains of human PRDM7 and PRDM9 are aligned with the corresponding sequences of each lineage. (PDF 96 kb

A novel travelling‐wave direction criterion for hybrid multi‐terminal HVDC system

Fast and accurate fault direction criteria are crucial for efficient protection in hybrid multi‐terminal HVDC transmission systems. The current variation method is commonly used to identify fault direction, but it is affected by fault resistance and distributed capacitance. This paper proposes a new direction criterion based on the backward fault travelling wave, which has stronger resistance to interference from transition resistance and operates at a faster speed than other methods. Additionally, this paper provides the time‐domain expression of the travelling wave after multiple reflections between the fault point and the converter station port, enabling the calculation of the threshold setting for the criterion. The new direction criterion is tested in PSCAD/EMTDC, and simulation results demonstrate that it can accurately identify fault direction and has a strong ability to withstand transition resistance

Protection for DC Distribution System with Distributed Generator

DC distribution system has advantages of high power quality, large transmission capacity, high reliability, simple structure, economy and low energy consumption, and so forth. It has been a key part of smart grid nowadays. However, the development of DC distribution system is constrained by the lack of operational experience in DC system, the small interrupting capacity of DC circuit breaker (CB), and the lack of protection schemes for system itself. In this paper, protection for DC distribution system with distributed generator (DG) is fully investigated and verified. Firstly, the electromagnetic transient model of DC distribution system with DG is presented. Simulation based on the electromagnetic transient model is carried out. Both the step response and the steady-state performance verify the accuracy of the model. Then the fault characteristic mechanism is analyzed, and the protection principles and scheme are investigated in detail, including voltage mutation principle as protection starting component, differential current protection principle for DC bus, and two-section current protection for distribution lines. Finally, transient responses with protection scheme are analyzed during faults. The results present that the protection principles and scheme are feasible for DC distribution system with DG

A multi-terminal current differential protection setting method for fully weak-infeed distribution networks based on restricted enumeration method

With the high penetration connection of inverterinterfaced distributed generators and the increasing application of large-capacity energy routers, fully weak-infeed distribution networks consisting entirely of power-electronized weak-infeed power sources are set to become one of the fundamental forms of future distribution networks. For fully weak-infeed distribution networks, multi-terminal current differential protection is considered an optional or even preferred line protection scheme. In this paper, a multi-terminal current differential protection setting method for fully weak-infeed distribution networks is proposed based on the restricted enumeration method. To address the impact of data synchronization errors and measurement errors of multi-terminal current on differential current, the problem of determining the maximum differential current superimposed with the multi-terminal current phasor errors is transformed into a high-dimensional non-convex optimization problem. The distribution law of the global optimal solution in the non-convex constraint space is deeply studied and analyzed, and a restricted enumeration method is proposed that can quickly solve the protection setting value, thereby solving the problem of multi-terminal current differential protection setting. The accuracy and rapidity of the proposed method are verified by comparing the calculation accuracy and time consumption of the restricted enumeration method and the exhaustive search. It is shown that the proposed multi-terminal differential protection setting method exhibits sufficient reliability and sensitivity in fully weak-infeed distribution networks, as verified through simulation analysis using a fully weak-infeed distribution network model built in PSCAD/EMTDC