科创中国

Natural frequency characteristics of a thin-walled multiple layered cylindrical shell under lateral pressure are studied.The multiple layered cylindrical shell configuration is formed by three layers of isotropic material where the inner and outer layers are stainless steel and the middle layer is aluminum.The multiple layered shell equations with lateral pressure are established based on Love's shell theory.The governing equations of motion with lateral pressure are employed by using energy functional and applying the Ritz method.The boundary conditions represented by end conditions of the multiple layered cylindrical shell are simply supported-clamped(SS-C),free-clamped(F-C)and simply supported-free(SS-F).The influence of different lateral pressures,different thickness to radius ratios,different length to radius ratios and effect of the asymmetric boundary conditions on natural frequency characteristics are studied.It is shown that the lateral pressure has effect on the natural frequency of multiple layered cylindrical shell and causes the natural frequency to increase.The natural frequency of the developed multilayered cylindrical shell is validated by comparing with those in the literature.The proposed research provides an effective approach for vibration analysis shell structures subjected to lateral pressure with an energy method.

The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.

The existing research of the active suspension system(ASS) mainly focuses on the different evaluation indexes and control strategies. Among the different components, the nonlinear characteristics of practical systems and control are usually not considered for vehicle lateral dynamics. But the vehicle model has some shortages on tyre model with side-slip angle, road adhesion coefficient, vertical load and velocity. In this paper, the nonlinear dynamic model of lateral system is considered and also the adaptive neural network of tire is introduced. By nonlinear analysis methods, such as the bifurcation diagram and Lyapunov exponent, it has shown that the lateral dynamics exhibits complicated motions with the forward speed. Then, a fuzzy control method is applied to the lateral system aiming to convert chaos into periodic motion using the linear-state feedback of an available lateral force with changing tire load. Finally, the rapid control prototyping is built to conduct the real vehicle test. By comparison of time response diagram, phase portraits and Lyapunov exponents at different work conditions, the results on step input and S-shaped road indicate that the slip angle and yaw velocity of lateral dynamics enter into stable domain and the results of test are consistent to the simulation and verified the correctness of simulation. And the Lyapunov exponents of the closed-loop system are becoming from positive to negative. This research proposes a fuzzy control method which has sufficient suppress chaotic motions as an effective active suspension system.

Current researches show that mechanical deformation of seal ring face makes fluid film clearance decrease at high pressure side, thus a divergent clearance is formed and face wear occurs more seriously at the high pressure side than that on the low pressure side. However, there is still lack of published experimental works enough to prove the theoretical results. In this paper, a spiral groove dry gas seal at high pressures is experimentally investigated so as to prove the face wear happened at the high pressure side of seal faces due to the face mechanical deformation, and the wear behavior affected by seal ring structure is also studied. The experimental results show that face wear would occur at the high pressure side of seal faces due to the deformation, thus the leakage and face temperature increase, which all satisfies the theoretical predictions. When sealed pressure is not less than 5 MPa, the pressure can provide enough opening force to separate the seal faces. The seal ring sizes have obvious influence on face wear. Face wear, leakage and face temperature of a dry gas seal with the smaller cross sectional area of seal ring are less than that of a dry gas seal with bigger one, and the difference of leakage rate between these two sizes of seal face width is in the range of 24%–25%. Compared with the effect of seal ring sizes, the effect of secondary O-ring seal position on face deformation and face wear is less. The differences between these two types of dry gas seals with different secondary O-ring seal positions are less than 5.9% when the rotational speed varies from 0 to 600 r/min. By linking face wear and sealing performance changes to the shift in mechanical deformation of seal ring, this research presents an important experimental method to study face deformation of a dry gas seal at high pressures.

In the mixed-flow pump design,the shape of the flow passage can directly affect the flow capacity and the internal flow,thus influencing hydraulic performance,cavitation performance and operation stability of the mixed-flow pump.However,there is currently a lack of experimental research on the influence mechanism.Therefore,in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance,the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment.In this experiment,parameters,such as the head,the efficiency,and the shaft power,are measured,and the pressure fluctuation and the noise signal are also collected.The research results suggest that after processing the inlet flow passage,the head of the mixed-flow pump significantly goes down;the best efficiency of the mixed-flow pump drops by approximately 1.5%,the efficiency decreases more significantly under the large flow rate;the shaft power slightly increases under the large flow rate,slightly decreases under the small flow rate.In addition,the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump.At the same time,the noise dramatically increases.Overall speaking,the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance,thus suggesting a special attention to the optimization of flow passage.This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment,which will benefit the optimal design of the flow passage of the mixed-flow pump.

With the increasing noise pollution,low noise optimization of centrifugal pimps has become a hot topic.However,experimental study on this problem is unacceptable for industrial applications due to unsustainable cost.A hybrid method that couples computational fluid dynamics(CFD)with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects.Under Langthjem's assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps,the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software.The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency(BPF)noise,and the sound pressure level(SPL)reached peaks near the cutoff that corresponded with the pressure pulsation in this region.An experiment is performed to validate this prediction.Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model.The simulation results for the noise are analyzed and compared with the experimental results.The variation in the calculated noise with changes in the flow agreed well with the experimental results.When the flow rate was increased,the SPL first decreased and reached the minimum near the best efficient point(BEP);it then increased when the flow rate was further increased.The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps.The noise simulation method in current study has a good feasibility and suitability,which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.

蒸纱机作为纺织行业原料纱线的给湿定形装备,按照《固定式压力容器安全技术监察规程》对压力容器类别的划分,其一般应属于第Ⅰ类压力容器.对上述监察规程中关于压力容器的设计、制造、使用和监督管理等内容作了概述,结合蒸纱机装备发展现状总结了目前行业中存在的问题,并在此基础上对蒸纱机装备的进一步发展提出了建议.

南水北调中线天津干线采用全箱涵无压接有压自流输水方案,调节池是实现无压流和有压流平稳过渡的重要控制性建筑物.经多方案比选,斜坡式调节池结构安全稳定,水力条件好,实现了上下游流态的平稳衔接.

抽汽压损是一种不明显的热力损失,使蒸汽的作功能力下降、热经济性降低.假定抽汽口的压力不变,加热器端差不变,分析抽汽压损变化对热力系统的影响.根据抽汽压损的理论分析和热力系统汽水分布方程建立抽汽压损对回热系统抽汽系数影响的数学模型,并结合炯平衡原理和小扰动理论建立抽汽压损对炯损分布的影响的数学模型.以某电厂N1000-25/600/600机组热力系统为例,在TRL工况下,定量计算热力系统炯损变化情况.根据定量计算结果定性分析了抽汽压损对热力系统的影响.