Junyong Liu

Damage and Plastic Deformation Modeling of Beishan Granite Under Compressive Stress Conditions

Based on experimental investigations, we propose a coupled elastoplastic damage model to simulate the mechanical behavior of granite under compressive stress conditions. The granite is taken from the Beishan area, a preferable region for China’s high-level radioactive waste repository. Using a 3D acoustic emission monitoring system in mechanical tests, we focus on the cracking process and its influence on the macroscopic mechanical behavior of the granite samples. It is verified that the crack propagation coupled with fractional sliding along the cracks is the principal mechanism controlling the failure process and nonlinear mechanical behavior of granite under compressive stress conditions. Based on this understanding, the coupled elastoplastic damage model is formulated in the framework of the thermodynamics theory. In the model, the coupling between damage and plastic deformation is simulated by introducing the independent damage variable in the plastic yield surface. As a preliminary validation of the model, a series of numerical simulations are performed for compressive tests conducted under different confining pressures. Comparisons between the numerical and simulated results show that the proposed model can reproduce the main features of the mechanical behavior of Beishan granite, particularly the damage evolution under compressive stress conditions.

Reconfiguration of Distribution Network with Dispersed Generators Based on Improved Forward-Backward Sweep Method

This paper presented an improved forward-backward sweep method and applied the hybrid particle swarm algorithm to solving the distribution network reconfiguration (DNR) with the distribution of power generation units through network simplification. This method can improve the convergence ability and global optimization ability of the traditional PSO. Solution procedure applied the decimal code to simplify encoding process, and proposed an improved forward-backward sweep method using the node-layer incident matrix to calculate the power flow. Finally a typical example of 33 bus system was simulated. The results showed that the method can adapt to the dynamic power flow solution of power and doubled the speed of the flow calculation. Moreover, the introduction of the DG can decrease network loss and enhance the node voltage.

Notice of Retraction Power System Reliability Assessment Considering the Effect of Freezing Weather

The influence of the weather on power system reliability is increasing. At present, the majority of studies are only about the state weather, few studies of its relevance. This paper mainly studies the relevance between the freezing weather and the system reliability. Considering the effect of topography and ice cover increase, it is developed that time-section wind load model considering the impact of icing, and time-section ice load model considering the topography and then the integrated model. Because a transmission line may traverse several levels of freezing weather conditions, it is used that the sectional simulating and re-integrating to work out the failure rate about time. In RBTS6, assuming the lines traverse different topography and level of freezing weather conditions, it is calculated each lines short-term failure rate.

Dominant Frequency Characteristics of Acoustic Emissions in White Marble During Direct Tensile Tests

Acoustic emission (AE) is defined as elastic waves associated with a rapid release of localized stress energy that is propagated within a material. It has been proven to be a useful tool for studying rock fractures (e.g., Lavrov 2003; Prikry et al. 2003; Tham et al. 2005; Amann et al. 2011; Shukla et al. 2013; Liu et al. 2015; Moradian et al. 2016; Zhang et al. 2016). Parametric and waveform data are two basic forms of recordable AE data. In the past few decades, parameter analysis has been widely used to observe progressive damage processes resulting from AE, as well as to evaluate the degree of damage (e.g., Butt 1999; Baddari et al. 2011; Xie et al. 2011; Zhao et al. 2013; Zhang et al. 2015). However, a single complicated AE waveform still might conceal important information, or may even present misleading information, since it is discriminated by only a few parameters (Behnia et al. 2014). Thus, it may be difficult to adequately discriminate the characteristics of AE waveforms using such parameter-based approaches. In waveform-based approaches, spectral analysis methods are often used for signal waveforms analyses. Because frequency content in an AE is determined by the wave source, studying the dominant frequency characteristics provides significant controls on investigations of microscopic fractures. Some of the pioneering work that investigated the dominant frequency characteristics of rocks was performed based on spectral analysis (e.g., Chugh et al. 1968; Armstrong 1969). Later, numerous relevant studies were conducted that evaluated the dominant frequency characteristics of AE waveforms (e.g., Stephens and Pollock 1971; Fleischmann et al. 1975; Woodward 1976; Kranz 1979; Sondergeld et al. 1980; Read et al. 1995; Xu et al. 2010). Owing to both hardware and software restrictions, it was impossible to realize continuous sampling, digitization and storage of a large quantity of AE waveforms within a short time. Previous studies did not contain statistical analyses and mainly focused on the change of dominant frequency characteristics since few waveforms could be recorded. With the development of high-performance computational processors and a new generation of sensors, the acquisition of multichannel raw waveforms has become possible (Behnia et al. 2014) and benefits the statistical analysis of the dominant frequency characteristics of AE waveforms. However, some latest studies about the dominant frequency of AE waveforms (Lu et al. 2013; Reiweger et al. 2015) still did not involve the statistical analysis. Ohnaka and Mogi (1981, 1982) expounded on the importance of statistical analysis for investigating the dominant frequency characteristics of AE waveforms. Moreover, statistical characteristics of dominant frequency of AE waveforms may be beneficial to understand the microscopic failure mechanism of rock. & L. Zheng zhenglu@scu.edu.cn

A Study on Intelligent Warning in Power System Dispatching

The connotation of intelligent warning is defined from five facets including category, screening, tracing and location of the cause, exhibition and information processing. The warning sets which are commonly used in power system real-time dispatching are classified component level, system level, single, serial, concurrent, combined, sensitivity and gradient warnings; meanwhile, these warnings are given definition, equation expression and illustration. Moreover, the application of intelligent warning is verified by rules, dates, modeling and deduction. Through the analysis of intelligent warning, the dispatchers will know the state of system and equipments distinctly, evaluate the power system security in general, and take control measures promptly, to guarantee the safety of system. Keywords-Intelligent warning; real-time dispatching; power system fault; warning sets

A distributed hierarchical structure optimization algorithm based poly-particle swarm for reconfiguration of distribution network

With the increased scale of distribution networks, the dimension for reconfiguration of distribution network got larger and larger. A distributed hierarchical structure poly-particle swarm optimization approach using the hierarchical structure concept of control theory was presented in this paper. In the first layer, each loop of distribution network was optimized separately as a subsystem, which could reduce the dimension. The best position found by each subsystem was regarded as the best position of single particle of the second layer. Then the global optimization was performed. Considering the features of distribution network, the principle of treatment for isolated island and loop circuit was presented, which could improve the probability of producing feasible solutions. The test of proposed method on two typical IEEE testing systems showed that the arithmetic performs better both on convergence rate and accuracy, and was adaptive for large-scale reconfiguration of distribution network.

Pareto Improvement of Large Customer Direct Power-Purchase by Use of Multi-Objective Optimization

Large customer direct power-purchase(DPP) rises gradually in China with the development of power market which should bring risks to all participant as little as possible to avoid excessive and unnecessary market fluctuation. This paper proposes a multi-objective optimization model using Pareto improvement from the view of supervision institution which takes charge of design, supervision and management of power market. Direct power-purchase volume proportion, floating ratio of time-of-use(TOU) transmission price and grid-supplied price are chosen as control variables to formulate the problem. The model presented in this paper has two objective of economy and environment consideration with some constraints including network loss, emission, price, market power, and so on and the model can optimize the control variables without benefit loss of any participant. The essential of the problem is to utilize price elasticity matrix of large customer to adjust profit distribution and to achieve the social integrated benefit optimization. Some power plants and large customers are supposed to form a scenario, which is used to validate the effect of method.

On Acoustic Emission and Post-peak Energy Evolution in Beishan Granite Under Cyclic Loading

Cyclic tests (loading–unloading) provide an effective way for a better understanding of damage and deformation characteristics in rocks. In general, elastic and plastic strain components can be distinguished during cyclic experiments (Elliott and Brown 1986). In addition, the influence of accumulated damage on rock strength can be studied by this method (Martin and Chandler 1994). Detectable acoustic emission (AE) signals are emitted when the specimen is loaded, and AE monitoring techniques have been used to provide a detailed view of fracture nucleation and growth (Lockner et al. 1991; Thompson et al. 2005, 2006; Cai et al. 2001, 2007; Cai and Kaiser 2005). Since the AE events are closely related to the damage or fracturing of the rock, rock degradation or damage can thus be measured (Falmagne et al. 1998). Furthermore, energy is dissipated during the whole failure process and can be quantified (Xie et al. 2009, 2011; Wasantha et al. 2014). In this study, cyclic tests were carried out on Beishan granite chosen as potential host rock for a high-level radioactive waste (HLW) repository in China (Wang 2010). AE recording system was utilized to monitor the fracturing process during the test. In addition, based on stress–strain curves, the energy evolution in the post-peak stage of Beishan granite was studied.

The Multi-objective Medium and Short-term Trade Planning correction for Environmental Protection and Demand Response

Traditional trading methods are based on the integrated optimization problems of economy and environmental protection, but do not consider the effects on demand-side. A revised model for medium and shortterm trade planning is presented in this paper. It firstly forecasts the industry electric quantity of peak, flat, valley monthly on the demand side using the parameter-modified grey model and consider the minimum of power purchase cost, environmental protection and the network loss to determine the generation Scheduling. With the fluctuation of electricity price, the price elasticity matrix computes the new industry electric quantity of peak, flat, valley monthly and gets the revision trade planning of the month. Then it gives the penalty cost, when the correction value reaches a certain level the electricity price will change with it, thus influence the trade planning by impact on the all-network power purchase cost. It can be used as an auxiliary decision-making for the trading center. Keywordsgrey model; price elasticity matrix; energy-saving dispatch; penalty cost; medium and short-term trading

Notice of Retraction A Matching Model of the Direct Power Transaction Based on the Bilateral Patterns

Traditional direct power transaction mostly based on the matching of bilateral quantity and prices of electricity. It is lack of effective means to optimize the electric transmission quality in the transaction. This paper considers the electric characteristic curves of the purchase and sales sides, and builds an auxiliary model for transaction which is based on bilateral patterns technical matching. The transaction schemes which are beneficial to power grid dispatching and reserve reduction are discussed in the direct power transaction market environment. Model uses multi-objective correlation analysis as the core, clustering process as the base and information entropy as the evaluation method to construct a combined algorithm, and provide the reference for making the direct power transaction schemes which are related to the electric patterns of participants. The data collected from a power grid company is used in this paper as an example of matching analysis. It verifies the validity of the model.