Applied Mechanics and Materials Vols. 672-674

Abstract: A procedure for obtaining the load distribution in a four point contact wind turbine yaw bearing considering the effect of the structure’s elasticity is presented. The inhomogeneous stiffness of the supporting structures creates a variation in the results obtained with a rigid model. A finite element model substituting the rolling elements with nonlinear compression springs has been built to evaluate the effect of the supporting structure elasticity on the contact forces between the rolling elements and the raceways.

Abstract: This paper investigates a design and analysis of a novel energy harvester that uses magnetic levitation to produce an oscillator with a tunable resonance. The governing equation of the system which could be derived based on the Newton’s second law is reduced to the form of a Duffing’s equation. The system steady-state amplitude frequency response relationship is analyzed by harmonic balance and numerical simulation, respectively. In the weakly nonlinear system, the curve of amplitude frequency response using harmonic balance method accords with the curve using numerical simulation;and in the strongly nonlinear system, the curve using harmonic balance basically accords with the curve using numerical simulation as well.

Abstract: The ship power system is a complex system with time varying, nonlinear and strong coupling characters. The traditional PID controller is difficult to meet the requirements of the system.In this paper, a multiple models fuzzy PID controller is designed. Considering the different operating conditions of on-land ship power system, two excitation regulation model which respectively corresponds to a fuzzy PID controller are set up. Each time, based on the input operation condition tested, only one fuzzy PID Controller is chosen to improve the control precision. At the end, simulation results show that multiple model fuzzy PID controller is superior to the single fuzzy PID controller, which effectively improves the transient response of the system, the steady state accuracy and robustness, having good prospects for engineering applications.

Abstract: Currently shipping costs are increasing sharply due to the rising oil prices. In order to reduce shipping costs, most low-speed two-stroke diesel engines run at low speeds to reduce fuel oil consumption, and this measure might result turbocharger surge. For modern marine diesel engines, the exhaust gas turbochargers are becoming more and more important; their working conditions have a direct impact on the performance of diesel engines, consequently affecting the operation of the ship. Surge will fail a turbocharger to achieve the supercharging ratio, damage the turbocharger components and even lead to a damage accident of the whole turbocharger. Therefore, a good understanding of the reasons for marine diesel engine turbocharger surge will help to prevent and eliminate turbocharger surge in operation. This paper is to make an analysis on the special surge mechanism occurred to the turbocharger on MV "Crystal Star", and propose some appropriate supervisory and preventive measures against the problem.

Abstract: Based on the analyses of the current solenoid valve driving circuits in marine diesel, a new type of dual-power double-maintain injector driving circuit is designed for marine high-pressure common-rail diesel. The circuit uses BOOST high voltage (80V) and storage battery low voltage (24V) to make up of dual-power time-sharing driver, which achieves automatic PWM feedback modulation of the solenoid valve injection current from the hardware. Experiments were carried out on a certain type of injector, the results showed that: the driving circuit had fast response time, only 0.045ms from zero to 22A of the solenoid valve current was required; the peak value of driving current has a good consistency, parameters including peakvalue current altitude, lasting time, maintain current altitude and maintain current lasting time could be adjusted flexibly. Besides, the circuit could be flexibly configured without occupying MCU resources.

Abstract: The relative internal efficiency for steam turbine is one of the main economic indexes in evaluating the economic operation of steam turbine. It is usually obtained by thermal performance tests or online monitoring. In power plants, by means of measuring and calculating the relative internal efficiency for steam turbine, steam turbines’ thermal economy can be analyzed and diagnosed, and the safe operation and energy saving work can be directed. But there still exist some problems in measuring and calculating the relative internal efficiency for steam turbine at present. In this paper, the two defining methods of the relative internal efficiency are analyzed and compared. The connection of two kinds of relative internal efficiency and the same effect in evaluating the operation economy of steam turbines are indicated.Key words : Steam Turbine; Thermal Performance Test; Economic Index ;Relative Internal Efficiency

Abstract: The physicochemical characteristics of a new composite oxygenated fuel named oligomeric polyoxymethylene dimethyl ether and DMM10 (the blend of this fuel and conventional diesel oil with 10% in volume) were analyzed. The power performance, fuel economy, combustion characteristics and exhaust gas emission of a four strokes, direct injection, turbocharged and intercooled diesel engine fuelled with DMM10 and diesel fuel were analyzed and compared. The results show that in comparison to original diesel engine, when the engine fuelled with DMM10 blend fuel, the power performance remains unchanged; BSEC decrease slightly, smoke emission decreases obviously and its decrease rate is up to 72%.

Abstract: To obtain a performance model for the adjustable blades axial flow fan, the performance surface of fan was fitted using binary polynomial fitting method, and the coefficients matrix was solved with QR decomposition. By comparing the fitting results show that the fitting effect is good when the 5 order polynomial was used to fit the performance surface of the fan and the 6 order polynomial was used to fit the boundary of performance surface. The accuracy of the obtained model can meet the requirements of the engineering application and scientific research.

Abstract: A summary of Siemens T3000 system digital electro-hydraulic (DEH) self-startup control is proposed. On the foundation of analysis in turbine subgroup logic condition and step sequence, critical link and step sequence of turbine startup process is put forward, which is convenient for operator to master turbine startup characteristics quickly. Existing problems in DEH control logic are revealed and specific disposing measures are given. Application of the system in a 2×660 MW thermal power plant proves a secure and smooth operation of power units.

Abstract: Natural frequency in tube bundles is the basis of vibration analysis in the heat exchanger. The calculation methods of the natural frequency are summarized in four type of tube bundles: straight tube, U-bend tube, finned tube and tube-fin. The influence of structure, temperature and fluid on the natural frequency are analyzed. Some anti-vibration measures are also put forward. The research direction of vibration analysis in tube bundles of heat exchanger in the future has good prospects.