Experimental investigation of the aquatic propulsion caused by localised flexural wave propagation in immersed wedges and plates

This paper describes the results of the experimental verification of the idea of wave-like aquatic propulsion of autonomous and man-inhabited vessels first published about 10 years ago by one of the present authors (V.V.K.). The idea is based on employing the unique type of localised flexural elastic waves propagating along edges of wedge-like structures immersed in water (wedge elastic waves). Such wedge-like structures supporting localised elastic waves can be attached like fish fins to a body of a small ship or a submarine and used for their propulsion. The proposed principle of employing localised flexural waves as a source of aquatic propulsion has been biologically inspired by the specific swimming mode used in nature by stingrays. To verify the idea experimentally, the first working prototype of a small catamaran using the above-mentioned wave-like propulsion via the attached rubber keel has been build and tested in Loughborough University. The tests have been carried out in two phases, in a water tank and then in open water. The test results have shown that the catamaran was propelled very efficiently and could achieve the speed of 36 cm/s, i.e., about one vehicle length per second, thus demonstrating that the idea of wave-like propulsion of small man-inhabited craft is viable. The reported proof of the viability of this idea may open new opportunities for marine craft propulsion, which can have far reaching implications.     

New general guidance method in constrained optimal control,part 2: Application to space shuttle guidance

The application and the performance of the neighboring optimal feedback scheme presented in Part 1 of this paper is demonstrated for the heating-constrained cross-range maximization problem of a space-shuttle-orbiter-type vehicle. This problem contains five state variables, two control variables, and a state variable inequality constraint of order zero.This research was supported in part by the Deutsche Forschungsgemeinschaft under the Schwerpunktprogramm Anwendungsbezogene Optimierung und Steuerung.The authors wish to express their sincere and grateful appreciation to Professor Roland Bulirsch who encouraged this work.     

Brillouin light scattering from a biopolymer gel: hypersonic sound waves in gelatin

Rayleigh-Brillouin light scattering experiments were performed on gelatin gels in order to obtain the (hypersonic) sound velocity and sound attenuation as a function of gelatin concentration. The results show that in the high frequency regime there is a strong coupling in the gel between the dynamics of the network and that of the fluid. The network sound velocity varies with ^1/2. Sound attenuation increases with increasing gelatin concentration.     

在线质谱仪在车内VOCs现场快速监测中的应用

挥发性有机物(VOCs)影响车内空气质量和驾乘者的身心健康。自主研发的在线挥发性有机物质谱仪(SPI-MS 2000),实现了有机物分子的单光子电离,产生无碎片的分子离子,可实现秒级响应,仪器的质量分辨率优于800 FWHM,质量精度优于0.02 amu,对甲苯的测定限优于3μg/m^3,且在3~8000μg/m^3范围内有良好的线性关系。将该仪器应用于某客车车内空气的在线检测:在5 s内检测到20多种微克~毫克每立方米量级的有机物。该仪器在车内VOCs现场快速监测方面有广泛的应用前景。     

Radiometric observations of the 752.033-GHz rotational absorption line of H2O from a laboratory jet

The intensity and lineshape of the Doppler-broadened 752.033-GHz (2₁₁ 2₀₂) rotational transition of H₂O has been studied passively using a high-resolution two-stage heterodyne radiometer with single-sideband system noise temperature of 45,000 K. The purpose of the experiments was to demonstrate the observability at submillimeter wavelengths of a high-altitude rocket plume simulated by a laboratory H₂O jet in a vacuum chamber. First-stage mixing was accomplished by means of a GaAs Schottky diode with first local-oscillator power supplied by a CO₂-laser pumped formic-acid laser (761.61 GHz), generating and X-band IF signal. Second localoscillator power was provided by a tunable C-band source. One-MHz resolution capability was obtained by means of a 3-GHz waveguide cavity filter with only 9-dB insertion loss. In the H₂O jet experiments, the center frequency of the line was determined to within 1 MHz of the previously reported value. A rotational temperature 75 K, a linewidth 5 MHz, and a Doppler shift 3 MHz (from a 45-degree rotation of the flow direction) were measured with the line-of-sight intersecting the jet axis at a distance downstream of 30 nozzle diameters. These absorption data were ogtained against continuum background radiation sources at temperatures of 1175 and 300 K.     

政府奖励对报废汽车回收模式选择的作用机制研究——基于企业社会责任视角

随着我国报废汽车数量的增多,由其造成的交通隐患、环境污染和资源浪费已成为重要社会问题,而如何设计合理可行的回收模式成为解决问题的关键。以制造商主导为前提,提出了基于企业社会责任的报废汽车回收模型,构建了制造商回收、销售商回收和第三方回收模式下的回收流程和数学模型,通过实例对考虑和不考虑企业社会责任两种情况下的回收模型进行了分析,探讨了不同政府奖励下报废汽车回收模式的策略选择。通过研究发现:(1)不论是否考虑企业社会责任,随着政府奖励的增加,制造商最终都会选择由自己进行回收;(2)当考虑企业社会责任时,政府奖励和决策者经济责任偏好都会导致决策的改变,随着政府奖励和赋予经济责任权重的同步增加,制造商的决策由第三方企业回收模式或销售商回收模式变成了制造商回收模式,表明政府奖励和企业社会责任对报废汽车回收模式选择具有显著影响。     

A review of mobility metrics for next generation vehicle mobility models

In the United States, the NATO Reference Mobility Model (NRMM) has been used for evaluating military ground vehicle mobility and the Vehicle Cone Index (VCI) has been selected as a mobility metric. VCI represents the minimum soil strength required for a vehicle to consistently make a specific number of passes, usually one or fifty passes. In the United Kingdom, the Mean Maximum Pressure (MMP) has been adopted as a metric for assessing military vehicle cross-country mobility. MMP is the mean value of the maxima occurring under all the wheel stations of a vehicle. Both VCI and MMP are empirically based. This paper presents a review of the basis upon which VCI and MMP were developed, as well as their applications to evaluating vehicle mobility in practice. With the progress in terramechanics and in modelling and simulation techniques in recent years, there is a growing desire to develop physics-based mobility metrics for next generation vehicle mobility models. Based on the review, criteria for selecting physics-based mobility metrics are proposed. Following these criteria, metrics for characterizing military vehicle traction limits and traversability on a given operating area are recommended.     

A sharp‐interface immersed boundary framework for simulations of high‐speed inviscid compressible flows

A new finite‐volume flow solver based on the hybrid Cartesian immersed boundary (IB) framework is developed for the solution of high‐speed inviscid compressible flows. The IB method adopts a sharp‐interface approach, wherein the boundary conditions are enforced on the body geometry itself. A key component of the present solver is a novel reconstruction approach, in conjunction with inverse distance weighting, to compute the solutions in the vicinity of the solid‐fluid interface. We show that proposed reconstruction leads to second‐order spatial accuracy while also ensuring that the discrete conservation errors diminish linearly with grid refinement. Investigations of supersonic and hypersonic inviscid flows over different geometries are carried out for an extensive validation of the proposed flow solver. Studies on cylinder lift‐off and shape optimisation in supersonic flows further demonstrate the efficacy of the flow solver for computations with moving and shape‐changing geometries. These studies conclusively highlight the capability of the proposed IB methodology as a promising alternative for robust and accurate computations of compressible fluid flows on nonconformal Cartesian meshes.     

Biofuels–Renewable Energy Sources: A Review

Biodiesel is biodegradable and nontoxic, and it significantly reduces toxic and other emissions when burned as a fuel. The advantages of biodiesel as diesel fuel are its portability, ready availability, renewability, higher combustion efficiency, non-toxicity, higher flash point, and lower sulfur and aromatic content, higher cetane number, and higher biodegradability. The major disadvantages of biodiesel are its higher viscosity, lower energy content, higher cloud point and pour point, higher nitrogen oxide (NO_x) emissions, lower engine speed and power, injector coking, engine compatibility, high price, and greater engine wear. The technical disadvantages of biodiesel/fossil diesel blends include problems with fuel freezing in cold weather, reduced energy density, and degradation of fuel under storage for prolonged periods. The sources of biodiesel are vegetable oils and fats. The direct use of vegetable oils and/or oil blends is generally considered to be unsatisfactory and impractical for both direct injection and indirect type diesel engines because of their high viscosities and low volatilities injector coking and trumpet formation on the injectors, higher level of carbon deposits, oil ring sticking, and thickening and gelling of the engine lubricant oil, acid composition. Biodiesel is obtained by transesterifying triglycerides with methanol. A popular variation of the batch transesterification process which needs high alcohol/acid ratio (several separation problems and high corrosivity and toxicity) is the use of continuous stirred tank reactors in series. This continuous process is heterogeneous and is based on reactive distillation. The key factor is the selection of the right and effective solid catalyst which leads to reduction of energy consumption and investments at all.     

最小二乘B样条函数在火箭发动机数据处理中的应用

在固体火箭发动机地面试验数据处理中,通过应用最小二乘三次B样条函数拟合的方法,进行野值辨识和修复。文中阐述了实际应用中的步骤及应注意的几点问题。为避免常规的控制序列中含有野值而影响数据辨识的问题,提出差别选取控制点循环过滤的方法,实现精度更高的野值辨识。进而采用门限判别方法,实现野值的修复。通过实测数据处理的应用表明,该算法对单个和成片野值的辨识度都很高,适用于火箭发动机地面试验数据处理。