联轴器不对中状态对船舶轴系动力学特性影响的试验

针对某船舶高速轴系不对中状态对轴系振动的影响,建立涡轮转子-传动轴-太阳轮转子试验模型,通过调整轴承支座的标高来模拟平行不对中和转角不对中量,进行多次升降速试验获得靠近轴承处的转子的振动位移。研究表明:不同的联轴器不对中状态对轴系的临界转速没有影响;在工作转速4 200 r/min时,不同联轴器对中状态下轴系各测点基频振动幅值变化很小,靠近套齿联轴器的太阳轮右侧轴承处转子2倍频振动明显大于左侧轴承处的振动;整体抬高太阳轮轴系标高对2倍频振动的影响较小;太阳轮左侧轴承支座标高降低时各轴承处2倍频振动幅值均有一定程度的增大;降低涡轮驱动端轴承支座的标高,轴系2倍频振动幅值整体增大;各对中状态下所有测点振动幅值的计算值与试验测量值的平均偏差小于20%,不同的对中状态对涡轮机转子的振动影响均小于对太阳轮转子的影响。     

A model of the thermal transient state of a wall of a room during the heating by a heating system

After turning on a room heating system (e.g. central heating) a thermal transient phenomenon takes place on the wall–room system, until it reaches a final thermal equilibrium state. The temperature profiles on the wall cross‐section, starting from an initial profile, corresponding to the initial thermal equilibrium state, come gradually through successive intermediate temperature profiles, to a final temperature profile corresponding to the final thermal equilibrium state. These intermediate, nonlinear and time‐dependent temperature profiles characterize the wall thermal transient state and describe the dynamic thermal behaviour of the wall–room system. The mass of the air in the room is negligible, compared to the mass of the surrounding walls, so the dynamic behaviour of the room–wall system is imposed by the corresponding thermal dynamic behaviour of the walls. The influence of this thermal transient state is important for the room heating behaviour because it acts as a thermal flywheel attenuating and smoothing the room temperature variations. In the present work, using the integral method, analytical expressions yielding the temperature profiles, and the duration of the transient state as a function of thermal and structural characteristics have been developed. Conclusions were drawn on the dynamic thermal behaviour of the room–wall system. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical Simulation of the Flow over a Model of the Cavities on a Butterfly Wing

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某电厂凝汽器冷端真空偏低现象的研究与解决

以某电厂凝汽器冷端真空偏低的现象为研究原型，通过计算分析，找出了该现象的原因，并给出了解决的一般方法，建立了具有一定通用性的计算模型。     

Comparison of the thermal effects of the transport of a short-pulse laser and a multi-pulse laser through a participating medium

Temporal signals resulting from the boundaries of a participating medium subjected to a short-pulse laser source are investigated. Cases of both a single as well as a pulse-train consisting of multiple pulses are considered. Temporal variation of the incident laser pulse can be a step or a Gaussian function of time. Temporal evolutions of transmittance and reflectance signals, and incident radiation at various locations in the planar medium are studied for a wide range of the values of the extinction coefficient. The problem is analyzed using both the finite volume method and the discrete ordinates method. In all cases, results of both the methods are compared. An excellent agreement has been found.     

Effect of a wavy interface on the natural convection of a nanofluid in a cavity with a partially layered porous medium using the ISPH method

The effect of a wavy nanofluid/porous-medium interface on the natural convection of a Cu–water nanofluid in a differentially heated non-Darcy porous cavity was investigated using the ISPH method. Wall boundary conditions were applied by improved scheme using the analytical kernel renormalization function and its gradient based on the quintic kernel function. The effect of the Rayleigh number and the Darcy number on the heat transfer of Cu–water nanofluid with a various solid volume fraction were studied. Results showed that higher amplitude, height, and the undulation number of the sinusoidal interface between the nanofluid and porous medium layer lead to a decrease in the average Nusselt number.     

裂纹轴刚度影响因素的研究

以两端简支的单盘偏置裂纹转子为研究对象,详细分析和讨论了支承跨度、裂纹位置和深度、转盘位置等因素对裂纹轴刚度系数的影响。研究结果表明：裂纹对转轴刚度的影响与支承跨度、裂纹深度、裂纹位置及转盘位置等诸多因素有关,很难通过统一的解析表达式来描述裂纹对转轴刚度的影响。     

Hydrothermal Behavior of a Ferrofluid in a Corrugated Channel in the Presence of a Magnetic Field

In this paper, results of applying a non‐uniform magnetic field on a dilute ferrofluid (water and 3% vol. Fe₃O₄) flow in a corrugated channel under a constant heat flux boundary condition have been reported. The thermal behavior of the flow is investigated numerically using a two‐phase mixture model and control volume technique. It is concluded that using a magnetic field with a negative gradient on a nanofluid flow in corrugated channels can be proposed as a suitable method to achieve higher heat transfer performance and augment the heat transfer coefficient and also reduces the wall temperature. This method can lead to the design of more compact heat exchangers. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 43(1): 80–92, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21060     

From a hard place to a rock: Questioning the energy security of a coal-based economy

We thank Brathwaite et al. for starting a very useful debate about what role, if any, coal should play in future energy transitions. Expanding upon their piece, we question that a coal-based economy, in which energy production for both electricity and transport comes from coal, can meet the energy security needs of the United States and other countries.     

Predicting the capacity of a heat exchanger by a thermal network method

In this paper a thermal network method using the effective specific heat model of a refrigerant with phase change is proposed for predicting the capacity of a plate‐fin and tube‐type heat exchanger. The effective specific heat model can attain an accurate result of a condenser's heat exchanging capacity when it has a small number of elements. By comparing calculated results with those of an experiment, it is found that the error in the condenser's calculated capacity is less than 1% when the range of subcool temperature is from 15 to 22 K at the outlet of refrigerant flow. © 2002 Scripta Technica, Heat Trans Asian Res, 31(2): 128–140, 2002; DOI 10.1002/htj.10021     

Analysis of a model for the operation of a vanadium redox battery

Although the vanadium redox battery (VRB) has recently attracted considerable interest as an energy storage technology, it has a relatively poor energy-to-volume ratio and a system complexity compared with other technologies; however, modelling can assist in optimizing cell and stack design. This paper analyzes a 2D time-dependent single-phase isothermal model for the operation of a single cell in a VRB. Unlike in all previous work, asymptotic methods are used to determine the characteristic current density scale in terms of operating conditions and cell component properties. Also, the analysis reveals that the fluid mechanics decouples from the electrochemistry, at leading order; an asymptotically reduced model is then proposed which preserves the original geometrical resolution. This approach is recommended for accurate and computationally efficient VRB stack models, as has been achieved for polymer electrolyte fuel cells; this will be a prerequisite for the use of modelling in stack design and thence large-scale commercialization of the VRB. Finite-element methods are used to compute results for the 1D steady state high-stoichiometry limit; although an idealized case, it is recommended for the in-situ experimental acquisition of VRB electrokinetic data that can then be used for the model when applied under more general operating conditions.     

复合角双射流气膜冷却的研究

采用数值模拟方法,研究了不同吹风比下孔排间距对复合角双射流气膜冷却特性的影响。结果表明,较小的孔排间距形成的反肾形涡为上下结构且不对称,冷却效果提高有限;而较大的孔排间距有利于形成左右对称的反肾形涡,能够在下游形成大面积的展向冷气覆盖,同时射流更好地贴附于壁面,大大提高了冷却效率;并将该结构应用到某重型燃气轮机静叶上,取得了良好的冷却效果。     

Investigations of the energetic and thermal characteristics of a module based on a Fresnel lens and a hetero-photo-converter in the AlGaAs-GaAs system

The energetic and thermal characteristics of a photobattery module based on a Fresnel lens and a hetero-photo-converter (HPC) in the AlGaAs-GaAs system are investigated. One has been shown experimentally an influence of volumetric irregularities regarding resistance of heterostructures formed up in active areas due to the diffusion of Zn atoms on p-n-junction boundaries under liquid-phase epitaxy on the photoconverter loading characteristics at low illumination levels. A substantial influence of the spread resistance on the HPC optimal parameters at elevated illuminations has been shown. For the regime chosen, the temperature of the cells reaches up to 80°C, and, at that temperature, it has no influence on the contacts’ properties and the space factor of the converter’s voltage-current characteristics (VCC). The module generates power up to 650 mW without forced cooling and allows combining it with a solar-heat collector.     

On the study of the temperature distribution within a human eye subjected to a laser source

A mathematical model to predict the temperature distribution within the human eye when subjected to a laser source was presented. The model was developed by employing the Pennes bioheat transfer equation. The intraocular temperature distributions were calculated using the Finite Volume method. Evaluation of the model predictions showed good agreement between model and experimental data up to 5%. The model was employed to study the impact of several phenomena such as the ageing of the human eye, change in thermal conductivity of the lens and laser power-off periods on its temperature distribution when subjected to a laser source.     

多层管排入口结构对旋风分离器性能影响分析

为改善旋风分离器的性能,利用ANSYS软件对传统型分离器与新型分离器(在分离器入口装配多层管排结构)进行了对比模拟。结果显示:多层管排结构对分离器入口部分气体质量流量、颗粒相分布、分离器压降、分级效率(50%分割粒径)均有影响,当入口速度为10 m/s时从入口内侧通过的颗粒数相比于传统分离器减小了8.4%,而大部分颗粒被气体携带从入口的中部、外部进入分离器,这部分颗粒进入分离器后很容易被捕捉;虽然压力损失相比于传统型分离器升高5%,但50%切割粒径从2.6μm减小到2.1μm,大大改善了分离器对细小颗粒的捕捉能力。     

Universal solutions for the streamwise variation of the temperature of a moving sheet in the presence of a moving fluid

A method has been developed for determining the streamwise variation of the temperature of a moving sheet in the presence of a co-flowing fluid. The solution does not depend on any material property of the sheet, its velocity, or its thickness. The solution is also independent of the properties of the fluid aside from the Prandtl number. Furthermore, the actual velocities of the sheet and the fluid need not be specified, but only their ratio is required. In the development of the method, a large knowledge base was first created by solving the differential equations for mass, momentum, and energy. The tabulated knowledge base served as input to a purely algebraic procedure whose end result is the streamwise variation of the sheet temperature. The procedure is iterative but requires no more than a least-squares curve-fitting capability. The iterative procedure is robust in that the converged result is independent of the initial iterant. It is also self correcting in the presence of an inadvertent error. Another method for determining the streamwise temperature variation, the relative-velocity model, was also investigated, and its accuracy assessed.     

Turbulent flow in a channel occupied by a porous layer considering the stress jump at the interface

For hybrid media, involving both a porous structure and a clear flow region, difficulties arise due to the proper mathematical treatment given at the interface. The literature proposes a jump condition in which shear stresses on both sides of the interface are not of the same value. This paper presents numerical solutions for such hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in turbulent regime. One unique set of transport equations is applied to both regions. Effects of Reynolds number, porosity, permeability and jump coefficient on mean and turbulence fields are investigated. Results indicate that depending on the value of the stress jump parameters, a substantially different structure for the turbulent field is obtained.     

Exploring the impacts of a carbon tax on the Chinese economy using a CGE model with a detailed disaggregation of energy sectors

This paper applies a computable general equilibrium model to investigate the impacts of a carbon tax on China's economy and carbon emissions based on China's 2010 Input–Output Table. To obtain robust simulation results, we further disaggregate the energy sectors into eight departments according to energy use characteristics. The empirical results indicate that a moderate carbon tax would significantly reduce carbon emissions and fossil fuel energy consumption and slightly reduce the pace of economic growth. However, a large carbon tax has a significantly negative impact on China's economy and social welfare. Moreover, a large carbon tax would entail marked price changes in China. Of the fossil fuels in use, reducing coal consumption would have the greatest impact on reducing carbon emissions, and the ad valorem duty rate for coal would be the highest after levying a carbon tax because it has the highest carbon emission coefficient. Therefore, China should strive to promote clean coal technology, which may be crucial to reducing carbon emissions. Moreover, levying a carbon tax would improve the use of clean energy, which would be an effective means of reducing carbon emissions. Therefore, the Chinese government should formulate the regulations for and pass a carbon tax as early as possible to achieve its carbon emission abatement target and further contribute to mitigating climate change.