Hengliang Zhang

Online Fatigue-Monitoring Models with Consideration of Temperature Dependent Properties and Varying Heat Transfer Coefficients

Thermal stress failure caused by alternating operational loads is the one of important damage mechanisms in the nuclear power plants. To evaluate the thermal stress responses, the Green’s function approach has been generally used. In this paper, a method to consider varying heat transfer coefficients when using the Green’s function method is proposed by using artificial parameter method and superposition principle. Time dependent heat transfer coefficient has been treated by using a modified fluid temperature and a constant heat transfer coefficient. Three-dimensional temperature and stress analyses reflecting entire geometry and heat transfer properties are required to obtain accurate results. An efficient and accurate method is confirmed by comparing its result with corresponding 3D finite element analysis results for a reactor pressure vessel (RPV). From the results, it is found that the temperature dependent material properties and varying heat transfer coefficients can significantly affect the peak stresses and the proposed method can reduce computational efforts with satisfactory accuracy.

A Methodology for Online Fatigue Monitoring With Consideration of Temperature-Dependent Material Properties Using Artificial Parameter Method

Following the basis of the ASME codes, the major nuclear components are designed to successfully avoid the fatigue failure. However, such design is generally very conservative and it is necessary to accurately assess the fatigue life of the components for the optimal life. The assessment of fatigue damage accumulation due to the thermal transients is currently performed via online fatigue monitoring systems. The algorithms for online calculation of thermal stress are one of the main components of these systems and are often based on the Green function technique (GFT), in which machine parameters such as fluid temperatures, pressures, and flow rates are converted into metal temperature transients and thermal stresses. However, since the GFT is based upon the linear superposition principle, it cannot be directly used when the temperature-dependent material properties are considered. This paper presents a methodology to consider the temperature- dependent material properties using artificial parameter method. Two cases are presented to compare the results calculated from the proposed models with those calculated by finite element method (FEM). It is found that the temperature-dependent material properties have significant influence on the maximum peak stresses which can be accurately captured by the models proposed in this work.

Analytical method for steady temperature and thermal stresses of a FGM hollow cylinder with temperature-dependent material properties

This paper presents the analytical calculation models of steady temperature and thermal stresses in a functionally graded material (FGM) hollow cylinder with temperature-dependent properties. The constitutive material properties are assumed exponentially variable along thickness direction. An example has been given to check the influence of temperature dependent properties. Results show obviously that when the properties are temperature dependent, the stresses have distinct difference with those calculated with constant properties.

A Balance Method Without Trial Mass Based on Lag Phase

Mass unbalance is one of the most common faults found in steam turbine shafting. It was reported that about 70% of the total turbo-generator units newly put into commission needs high-speed dynamic balance in site. Because of longer shafting and relatively lower support stiffness, the vibration of multi-rotor bearing system, is much more sensitive to mass-unbalance. In most cases, trial masses and runs are required for the calculation of correction masses before balancing a turbo-generator rotor and such a procedure is time-consuming and expensive. Our experience shows that one balance for a turbo-generator rotor in China, by using traditional balance method, will take at least 3 to 5 runs, even 6 to 10 runs. That means 100∼500t oil will be consumed each time for balancing a turbo-generator unit with capacity of 200MW to 600MW. A balancing method without trial mass was proposed at the end of 1980’s. As it needs no trial runs if the magnitude and orientation of the rotor unbalance could be determined by calculating the amplitude-frequency and phase-frequency characteristics of various rotor sections, it has been adopted by highly skilled engineers. But the principle disadvantage of this method is that effective application requires a high degree of operator insight or knowledge of the support characteristics (i.e., requires data taken at previously balanced procedure, or from other units to determine the magnitude and location of the unbalance). This paper deduced empirical formula for dynamic balancing without trail mass at first. Then, based on the data of lag phase from the experience over 100 units, a balance method without trial mass was developed. Implementation of this method on a 1000MW turbo-generator rotor shows that it is an effective and economical procedure and the balancing risk is reduced.Copyright

On-Line Calculation Method of Exhaust Steam Humidity Based on BP Neural Network for Steam Turbine

For condensing turbine, steam exhaust point is in wet steam area. The exhaust steam humidity of steam turbine is difficult to get due to lacking of effective measuring method. Calculation of exhaust steam humidity has always been one of the key parts of the analysis of thermal power units. The main factors affecting exhaust steam humidity are turbine load and turbine exhaust pressure etc, and they are of non-linearity. This paper develops a calculation method to calculate exhaust steam humidity based on BP neural network. Taking a N1000-25/600/600 ultra-supercritical (USC) steam turbine as an example, the exhaust steam humidity is calculated and the results show that the method has a good accuracy to meet the needs of the engineering application.© 2013 ASME

Temperature and thermal stress analytical models of metal materials in heat treating

In this paper, the mathematical models have been established to describe temperature and stress distributions in an axis-symmetric metal specimen. The models can treat nonlinear problem caused by temperature dependent properties. An example has been given to compare the results calculated by the models with those calculated by finite element method (FEM). It is shown that the analytical models obtained have high accuracy.