轿车排气系统一维数值模型简化及模态实验验证

对排气组件进行简化,建立排气系统一维梁振动模型,并进行整车NVH(noise,vibration and harshness)性能的数值和实验模态分析.研究结果显示,排气组件简化合理,排气系统一维模型可以较准确地描述排气系统的动力学特性,模型可用于排气系统的优化及疲劳特性预测.     

城市空间特色的认知规律与调研分析

针对我国目前城市空间特色的衰退及对其简单化的认识问题，论述了城市空间特色的认知规律，强调应通过调研确定一个城市的空间特色，并结合南京实例、提出了调研分析方法。     

Development and validation of a coupled heat and mass transfer model for green roofs

This paper describes a dynamic model of transient heat and mass transfer across a green roof component. The thermal behavior of the green roof layers is modeled and coupled to the water balance in the substrate that is determined accounting for evapotranspiration. The water balance variations over time directly impact the physical properties of the substrate and the evapotranspiration intensity. This thermal and hydric model incorporates wind speed effects within the foliage through a new calculation of the resistance to heat and mass transfer within the leaf canopy. The developed model is validated with experimental data from a one-tenth-scale green roof located at the University of La Rochelle. A comparison between the numerical and the experimental results demonstrates the accuracy of the model for predicting the substrate temperature and water content variations. The heat and mass transfer mechanisms through green roofs are analyzed and explained using the modeled energy balances, and parametric studies of green roof behavior are presented. A surface temperature difference of up to 25 °C was found among green roofs with a dry growing medium or a saturated growing medium. Furthermore, the thermal inertia effects, which are usually simplified or neglected, are taken into account and shown to affect the temperature and flux results. This study highlights the importance of a coupled evapotranspiration process model for the accurate assessment of the passive cooling effect of green roofs.     

Experimental study of effect of hydrogen addition on combustion of low caloric value gas fuels

The effect of hydrogen on the premixed combustion of low calorific value gas in cylinder was carried out. The engine bench test system was built, and the effects of hydrogen on the pressure in cylinder, the characterization parameters of flame stability, flame shape, combustion cycle variation, flame surface structure and development were studied. The experimental results show that adding hydrogen to low calorific value gas fuels can increase laminar flame propagation rate, increase heat release rate, improve engine volumetric efficiency and reduce engine cycle variation. With the increase of hydrogen fraction, the maximum cylinder pressure of the engine rises, the corresponding crankshaft angle moves forward, and the flame development period and the rapid combustion period of the engine working cycle are reduced. The flame propagation rate of hydrogen blended low calorific value gas is larger, which enhances the strength of the vortex blob in cylinder to some extent. The increase of hydrogen fraction in mixture increases the flame propagation velocity, and enhances the effect of the combustion process on vortex intensity in cylinder, which increasing the effect of vortex blob on the flame surface structure. With the increase of hydrogen fraction, the vortices of the flow field in the cylinder increase, the time of which the flame surface reaches the same fold is in advance, and the flame development period is shortened.     

Aleatory Construction Based on Jamming: Stability Through Self-Confinement

The physical process of jamming could take architectural sustainability/recyclability to a whole new level. It involves achieving structural rigidity through the crowding of particles within a confined space, rather than by permanent bonding. Project Z-Form, a collaboration between a team of physicists from the JaegerLab at the University of Chicago – including PhD students Kieran Murphy and Leah Roth and professor Heinrich Jaeger – and artist Dan Peterman , sets out to develop a pourable material that not only self-supports but can also bear loads. Here they explain the project and the concepts behind it.     

Lerner aktivierende Lernformen für Bauingenieure – Beispiele für den Einsatz digitaler Medien in der universitären Lehre

Active learning for civil engineers – examples for the use of digital media at a university. The digitalization of teaching (at university) has been a much discussed topic for several years. There are many different approaches that also have a different impact on the daily work at the university. Additionally, an increasing emphasis on competence orientation of the degree programs is being demanded politically. At the chair for steel structures at TU Darmstadt, digital media are being used for several years and in different settings. The following article presents some variants. The basis of all these teaching concepts is the idea to activate more students during class. Thereby a better learning performance should be reached.     

Repräsentative Vorkrümmungen e0 für das Biegeknicken – Ergänzende Untersuchungen

Equivalent geometrical initial bow imperfections e₀ for flexural buckling – additional investigations. According to Eurocode 3 Part 1‐1, a member subjected to an axial compression force may be verified by two different approaches: a verification by the equivalent member method or a cross sectional verification. Concerning the second possibility bending moments according to second order theory must be calculated, where initial bow imperfections e₀ must be taken into account, which should be taken normally from EN 1993‐1‐1, table 5.1. The values e₀ used up to now should be changed, because they are partly unsafe, this was shown earlier by intensive investigations [5]. The results of additional investigations are explained here concerning test results and analytical values for high strength steel S700. Furthermore comments are given to values e₀ calculated depending on the non‐dimensional slenderness λ .     

Beitrag zur aussteifenden Wirkung von Sandwichelementen

Diaphragm effect of sandwich panels. Full scale tests were carried out within the scope of [5] to investigate the diaphragm action of sandwich panels. Shear diaphragms were constructed to assess the load carrying action of the sandwich panels bracing the structure. The bearing behaviour of the various components contributing to the shear diaphragm effect was investigated in more detail on smaller experimental set ups. These small scale tests include investigations into the screw connections between the sandwich panels and the substructure, as well as a series of tests on the load transfer through the longitudinal joint between the individual panels. The most untapped potential for improvement of the bearing capacity has been found to be the influence of the longitudinal joint. An increased force transmission in the longitudinal joint leads to higher values of stiffness and maximum bearable load of the shear diaphragm. Various methods to improve the contribution of the joints were developed. Of these, the hook‐and‐loop tape joint reinforcement has been found to yield the best results. Therefore, this reinforcing method has also been investigated in full scale tests. The use of hook‐and‐loop tape in the longitudinal joint makes the panels acting as one big plate. The impact on the screw connection has been successfully reduced by improving the load transfer in the longitudinal joints.     

Measurement and calculations of long-lived radionuclide activity forming in the fast neutron field in some ITER construction steels

Measurement and calculations of long-lived gamma-emitting radionuclide activity forming in the fission reactor fast neutron field were done, for some ITER construction steels. The activation was conducted in fast neutron irradiation channel of the MARIA research fission reactor (Poland). The dimensions of steel samples were 10 mm × 10 mm × 1 mm and mass was approximately 0.8 g. The neutron flux density was measured by means of activation foil method and unfolding technique; fraction of neutrons above 1 keV was 95%. The activation lasted 242 h and cooling took 100 days; the mean neutron flux density was 2.9E12 n/(cm² s) (neutrons above 500 keV are 53% of total) whereas total fluency 2.53E18 cm⁻². The activity measurements were done by means of gamma-ray spectrometry. Activity calculations were done by means of FISPACT-II code using the activation libraries EAF-2010 and TENDL-2011 and experimentally determined neutron flux. Measured activity of long-lived gamma emitting radionuclides was, in average, about 6.3 MBq/g 100 days after activation; the dominant radionuclides were ⁵⁸Co and ⁵⁴Mn (about 81% and 14% of total activity respectively). The C/E ratio differs for particular radionuclides and is in the range 0.86–0.92 for ⁵¹Cr, 0.93–1.21 for ⁵⁴Mn, 0.77–0.98 for ⁵⁷Co, 0.91–1.21 for ⁵⁸Co, 1.17–1.27 for ⁵⁹Fe, and 1.75–2.44 for ⁶⁰Co.     

Efficient model selection for real-time adaptive cold start strategy of a fuel cell system on vehicular applications

The PEMFC maximum power is greatly influenced by subfreezing temperature and degradation phenomena. Therefore, a dependable model is required to estimate the power with respect to the variation of the operating conditions and state of health. Semi-empirical models are potent tools in this regard. Nonetheless, there is not much information about their cold environment reliability. This paper comprehensively compares the performance of some models (already tested in normal ambient temperature) in subfreezing condition to introduce the most reliable one for PEMFC cold start-up application. Firstly, seven models are compared regarding voltage losses and precision. Subsequently, the three most dependable ones are selected and experimentally compared at sub-zero temperature in terms of polarization curve estimation for three PEMFCs with different degradation levels. The results of this study indicate that the model introduced by Amphlett et al. has a superior performance compared to other ones regarding the characteristic's estimation in below-zero temperature.