基于TMS320F2812的船舶电网短路电流自动录波软件设计与实现

针对船舶直流幅压电网短路故障电流上升率高、幅值大的特点,对一种结合电流上升率和电流幅值的短路故障判据算法进行了研究,提出了一种基于TMS320F2812 DSP处理器平台的短路电流自动录波软件设计方案,对录波软件的工程实现方法、工作流程和通信协议设计等作了重点说明,利用脉冲功率发生器测试电路对录波软件的效能进行了测试.研究结果表明,该录波软件能够实现短路故障电流自动检测及短路全过程电流波形自动记录且实时性强,能为船舶电网事故后分析提供重要的数据.     

Pressure effects on flow boiling instabilities in parallel microchannels

The effects of pressure on flow boiling instabilities in microchannels were experimentally studied. Experiments were conducted using water in 223 μm hydraulic diameter microchannels with mass fluxes ranging from 86 to 520 kg/m² s and pressures ranging from 50 to 205 kPa. Onset of flow oscillation, critical heat flux (CHF) conditions, local transient temperature measurements along with flow boiling visualization were obtained and studied. System pressure was found to significantly affect flow instabilities. For high pressure, it was observed that boiling instabilities were significantly delayed and CHF was extended to high mass qualities. Local temperature measurements also revealed lower magnitudes and higher frequencies of oscillations at high system pressures.     

A Review of two-phase flow dynamic instabilities in tube boiling systems

The earliest research in the field of two-phase flow was conducted by Lorentz (1909). The studies on the analysis of two-phase flow instabilities by Ledinegg (1938) created considerable interest concerning the phenomenon of thermally induced flow instability in two-phase flow systems. The objective of this review is to sum up the experimental and theoretical work carried out by various investigators over a period of several years, demonstrating and explaining three main instability modes of two-phase flow dynamic instabilities, namely, density-wave type, pressure-drop type and thermal oscillations, encountered in various boiling flow channel systems. The typical experimental investigations of these instabilities in tube boiling systems are indicated and the most popular models to predict the two-phase flow dynamic instabilities, namely the homogenous flow model and the drift-flux models are clarified with the solution examples and the validation of the model results with experimental findings are also provided.     

Numerical simulation of nucleate boiling on a horizontal surface at high heat fluxes

Nucleate boiling at high heat fluxes has been studied numerically by solving the equations governing conservation of mass, momentum and energy in the liquid and vapor phases. The interface is captured by using the level set method based on a sharp-interface representation. The evaporative heat flux from the liquid microlayer is incorporated in the analysis. The effects of wall superheat, number density of nucleation sites and waiting period on the bubble dynamics and heat transfer in nucleate boiling are investigated. The heat fluxes obtained from the present numerical simulations are compared with the experimental data reported in the literature.     

Evolution of cure,mechanical properties,and residual stress during electron beam curing of a polymer composite

Evolution of cure, mechanical properties, and residual stress during E-beam (Electron Beam) processing was studied to evaluate the influence of process parameters – dose and dose per pass – using an epoxy reinforced with IM7 carbon fibers. The composite prepreg was also cured thermally to various cure levels and compared with the E-beam cured composite. Cure evolution changed substantially with irradiation condition; lower dose/pass and wider scanning width of the beam (for the same dose/pass) resulted in rapid curing. For a given degree of cure, the longitudinal (E₁₁) and transverse (E₂₂) moduli of the E-beam cured composite varied with dose/pass and were less than that of the thermally cured composite. Transverse strength and failure strain of the composite cured at 20 kGy/pass were higher than that of composites cured thermally and at other dose/pass conditions. E-beam curing resulted in lower residual stresses than thermal curing and lower dose per pass resulted in lower cure-induced residual stress than higher dose/pass.     

A comprehensive study of externally venting flames—Part I: Experimental plume characteristics for through-draft and no-through-draft ventilation conditions and repeatability

Externally venting flames have been examined during a series of eight full-scale flashover tests. Furniture was used in a burn room larger than a standard one. The purpose of the work has been to investigate the likelihood of external fire spread from a burn room window with standard glass when the external facade is non-combustible. The effects on externally venting flames of internal ventilation conditions and wind have been studied in detail. Secondary fires and glass breakage have been examined. Repeatable experimental data and reliable information on externally venting flames have been generated for numerical model validation and performance-based design code development. In Part I of this two-part paper, the emphasis is on the repeatability of the experimental data on externally venting flames. A new averaging method introduced previously has been used for this purpose. In Part II, extensive comparisons are given with available experimental data and empirical approximations from the literature. Surface fits to the experimental data are also presented for communication purposes.     

激光纹理化调控材料表面疏水性能研究进展

超疏水表面由于具有减阻、抗污、防水等独特性能,广泛应用于日常生活、军事、工业等场景,材料表面的微纳结构及化学成分对其超疏水性能有着重要影响。激光纹理化技术由于具有加工分辨率高、加工方式灵活、可加工材料多等优势,可用于制备疏水性能精确可控的表面微纳结构,在制造超疏水表面方面有着广阔的应用前景。首先,介绍了激光纹理化的作用机理,综述了常用的激光纹理化方式,如激光直接写入法、激光干涉图案化法及激光诱导周期性结构法等,并介绍了激光参数对微纳结构的影响。根据表面微纳结构的形貌、周期及尺寸特点对激光纹理化制备的表面分层微纳结构进行了总结归纳,包括覆盖随机纳米结构或激光诱导周期性结构的微沟槽、微网格、微柱及微峰,重点介绍了分层微纳结构的制备方式及微纳结构对疏水性的影响。总结了提高分层微纳结构表面疏水性的后处理方式,包括环境老化、表面化学改性及热处理等,并介绍了后处理方式调控疏水性的作用机理。最后,对采用激光纹理化技术制备超疏水表面的应用前景进行了展望。     

顶部侧开缝的倾斜通道热流场及开口中性面研究

为了掌握通道在上壁面不同宽度的开缝条件下,不同倾斜角度的通道内热流场特性及两端开口处中性面高度的变化规律,对一200 cm长的通道内一靠近低端开口一侧火源产生的热流场进行了实验与基于Vreman亚格子模型的大涡模拟研究.通过实验值与数值模拟结果的对比,验证了构建的数学模型对于上壁面有侧开缝的倾斜通道内热流场模拟的有效性;确定了通道上壁面的开缝对于通道内热流场的温度分层特性、通道两端开口处U速度以及中性面高度随着通道倾角变化的规律影响不大;对于一定的通道倾斜角度,随着通道上壁面侧开缝宽度增大,火源两端温度分布的对称性增强,通道上壁面附近的温度降低,通道内的高温区域向下壁面的偏移幅度减弱,通道两端开口处靠近上壁面附近的空气流速逐渐降低,两端开口处中性面高度升高;上壁面有开缝的通道两端开口处中性面的高度曲线随着通道倾斜角度的增大有一个交叉,交叉发生在通道倾斜角度小于5°时.     

The dynamic characteristics of silicone rubber isolator

The dynamic stiffness and the specific damping energy, as well as the vibration response characteristics of a silicone rubber isolator were researched. The results of the vibration test showed that the silicone rubber isolator was excellent in the performance of vibration control. The dynamic stiffness and the damping characteristics were non-linear. From the comparison between experimental results and simulation analysis, the displacement transmissibility characteristics of the isolator were obtained. As a result, the dynamic characteristics of the isolator could be accurately described by the quadratic type non-linear terms at small amplitude.     

结构声耦合对膨胀腔水消声器声学性能的影响

水消声器可以有效降低管路系统水噪声,为更加准确的预测水消声器传递损失,利用结构声耦合数值模型分析消声器内部声场,研究不同部位结构声耦合效应对充水膨胀腔消声器声学性能的影响规律.计算厚径比为1的充水膨胀腔消声器传递损失,并与刚性条件下的数值结果及理论结果进行比较,以验证方法的正确性;对比二维轴对称模型与整体计算模型的计算结果,验证基于二维轴对称模型分析的可行性.数值研究表明:本方法可以有效的预测水消声器传递损失;随着水消声器腔壁厚度的减小,弹性结构与流体的耦合程度增加,结构声耦合效应对水消声器的声学性能影响增加;周向腔壁的结构声耦合效应会造成膨胀腔消声器的传递损失曲线向低频方向移动;端部腔壁的结构声耦合效应会使消声器传递损失曲线出现反共振峰、共振峰,这与膨胀腔端板结构的固有模态相关;膨胀腔壁的结构声耦合作用使腔内声压在较低频段内出现三维高次波,增加消声量;管路结构声耦合效应对水消声器声学性能的影响不大.