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1دورية أكاديمية
المؤلفون: Zhong, Shenghui, Xu, Shijie, Zhang, Fan, Peng, Zhijun, Chen, Longfei, Bai, Xue Song
المصدر: Proceedings of the Combustion Institute; 39(2), pp 2513-2522 (2023) ; ISSN: 1540-7489
مصطلحات موضوعية: Energy Engineering, Cool flame wave propagation, Engine combustion network, Eulerian stochastic field, Spray combustion, Two-stage ignition
الوصف: Cool flame has an important impact on the performance and emission of advanced low-temperature combustion (LTC) internal combustion engines (ICEs) in which the liquid fuel is injected earlier at a lower ambient temperature (Tam) than that in the conventional diesel combustion engines. However, the cool flame characteristics of spray combustion under ICEs conditions are not fully understood, e.g., the effect of cool flame on the spray ignition and flame stabilization is not well studied. In this paper, the so-called cool flame wave propagation (CFWP) in the Engine Combustion Networks Spray A flames at three ambient temperatures Tam (800 K, 900 K and 1000 K) is analyzed using the data from large eddy simulation with an improved Eulerian based transported probability density function sub-grid combustion model. A good agreement between the LES results and experimental data is obtained for the spray liquid penetration length, vapor fuel penetration length, mean pressure rise profile, and flame liftoff length. It is shown that CFWP in the spray ignition process promotes the ignition of the fuel-rich and cold reactant mixture, leading to the most reactive mixture shifting toward fuel-richer locations due to the spatial stratification of temperature and concentration, and turbulent mixing. As a result, the high temperature ignition (HTI) can be shortened compared to the ignition in the homogeneous mixture. At Tam = 800 K, the HTI kernels are consistently formed following the CFWP propagating toward the spray head region. However, as Tam increases, the spatial correlation between HTI kernels and CFWP fronts is weakened. On the other hand, the turbulent mixing (quantified using local scalar dissipation rate) contributes more to the formation of HTI kernels at higher Tam. The present results indicate that CFWP is more profound at lower Tam in the spray ignition process. Finally, it is found that cool flame propagates mainly into pre-reacted fuel-rich mixture in an ignition wave propagation mode from the spray upstream ...
العلاقة: https://lup.lub.lu.se/record/29dd9370-ba7f-4707-9187-a2ab7f4e2404Test; http://dx.doi.org/10.1016/j.proci.2022.08.056Test; scopus:85140830216
الإتاحة: https://doi.org/10.1016/j.proci.2022.08.056Test
https://lup.lub.lu.se/record/29dd9370-ba7f-4707-9187-a2ab7f4e2404Test -
2كتاب
المؤلفون: Haneda, Katsuyuki, Rudd, Richard, Vitucci, Enrico, He, Danping, Kyösti, Pekka, Tufvesson, Fredrik, Salous, Sana, Miao, Yang, Joseph, Wout, Tanghe, Emmeric
مصطلحات موضوعية: Communication Systems, Dense multipath models, Enhanced COST2100 channel model, Full-wave radio propagation models, Geometry-based stochastic channel models, ITU-R path loss models, Multipath clustering algorithms, Multipath estimation algorithms, Propagation environments, Ray-based models of wave propagation, Site-specific channel models
الوصف: This chapter provides overview of fundamental definitions, tools and new methods towards improved channel modeling reported in the Co-operation in Science and Technology (COST)-Inclusive Radio Communications (IRACON) Action for future wireless communications and networks. The overview first covers definitions of propagation environments as they determine most relevant propagation mechanisms to consider and model, and furthermore, guide approach to channel modeling methods. This chapter then introduces new insights into popular approaches of channel modeling, i.e., site-specific and geometry-based stochastic channel modeling, where the latter particularly features canonical and standardized channel modeling approaches taken by the 3rd Generation Partnership Project (3GPP), COST, and International Telecommunication Union (ITU) communities. Finally, this chapter shed lights on new modeling approaches to small-scale radio propagation behaviors, covering plane wave propagation paths and distributed diffuse scattering.
العلاقة: https://lup.lub.lu.se/record/bd2c5bfb-3119-406a-8094-6e29deeb7859Test; http://dx.doi.org/10.1016/B978-0-12-820581-5.00008-0Test; scopus:85127688176
الإتاحة: https://doi.org/10.1016/B978-0-12-820581-5.00008-0Test
https://lup.lub.lu.se/record/bd2c5bfb-3119-406a-8094-6e29deeb7859Test -
3دورية أكاديمية
المؤلفون: Gustafson, Carl, Haneda, Katsuyuki, Wyne, Shurjeel, Tufvesson, Fredrik
المصدر: IEEE Transactions on Antennas and Propagation; 62(3), pp 1445-1455 (2014) ; ISSN: 0018-926X
مصطلحات موضوعية: Electrical Engineering, Electronic Engineering, Information Engineering, Millimeter wave propagation, channel modeling, 60 GHz WLAN, IEEE 802.11ad, IEEE 802.15.3c
الوصف: Efficient and realistic mm-wave channel models are of vital importance for the development of novel mm-wave wireless technologies. Though many of the current 60 GHz channel models are based on the useful concept of multi-path clusters, only a limited number of 60 GHz channel measurements have been reported in the literature for this purpose. Therefore, there is still a need for further measurement based analyses of multi-path clustering in the 60 GHz band. This paper presents clustering results for a double-directional 60 GHz MIMO channel model. Based on these results, we derive a model which is validated with measured data. Statistical cluster parameters are evaluated and compared with existing channel models. It is shown that the cluster angular characteristics are closely related to the room geometry and environment, making it infeasible to model the delay and angular domains independently. We also show that when using ray tracing to model the channel, it is insufficient to only consider walls, ceiling, floor and tables; finer structures such as ceiling lamps, chairs and bookshelves need to be taken into account as well.
وصف الملف: application/pdf
العلاقة: https://lup.lub.lu.se/record/4276705Test; http://dx.doi.org/10.1109/TAP.2013.2295836Test; https://portal.research.lu.se/files/3607678/4276756.pdfTest; wos:000332731700048; scopus:84896346712
الإتاحة: https://doi.org/10.1109/TAP.2013.2295836Test
https://lup.lub.lu.se/record/4276705Test
https://portal.research.lu.se/files/3607678/4276756.pdfTest -
4كتاب
المؤلفون: Andersen, Lars V., Peplow, Andrew T., Persson, Peter
المساهمون: Papadrakakis, Manolis, Fragiadakis, Michalis
المصدر: COMPDYN Proceedings; 2, pp 3422-3447 (2019) ; ISSN: 2623-3347
مصطلحات موضوعية: Geotechnical Engineering, Insertion Loss, Layered Half-Space, Soil, Wave Impedance, Wave Propagation
الوصف: Pile driving and other activities in the built environment cause ground vibration at low frequencies. This may result in annoyance to people as well as damage to civil structures. It is known that masses added on the ground surface can have an impact on the vibration levels in the surrounding environment. Hence, employing a semi-analytical model for rigid blocks on the surface of a layered ground, this paper investigates whether circular arrays of such blocks can be used as a means of vibration mitigation. The frequency range 0–80 Hz is considered, since this is relevant to whole-body vibrations of humans as well as the fundamental modes of resonance in building elements, e.g., floors and walls. Two different soil profiles are analysed: a soft dry sand layer over a till half-space and a soft wet clay layer over a lime half-space. Further, three configurations of the block arrays are taken into consideration, and for the first soil profile also the height of the blocks is varied to test its influence on the insertion loss in a zone 20–40 m away from the source. The aim is to quantify the overall insertion loss that can be expected using the proposed methodology. Further, the variation in insertion loss caused by changes in the block array configuration is examined.
العلاقة: https://lup.lub.lu.se/record/86d19b57-b7ec-4251-a5e4-8d3d2b8b5093Test; scopus:85079062646
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5كتاب
المساهمون: Papadrakakis, Manolis, Fragiadakis, Michalis
المصدر: COMPDYN Proceedings; 3, pp 4548-4556 (2019) ; ISSN: 2623-3347
مصطلحات موضوعية: Construction Management, Axisymmetric, Dynamic stiffness matrix, Elastic wave propagation
الوصف: In the context of range-independent solid media, we propose a well-conditioned dynamic stiffness matrix for an elastic layer sitting over an elastic half-space. This formulation overcomes the well-known problem of numerical ill-conditioning when solving the system of equations for deep-layered strata. The methodology involves the exact solutions of transformed ordinary differential equations in the wavenumber domain, namely a projection method based on the transformed equations with respect to the depth coordinate. By re-arranging the transformed equations, the solutions remain numerically well-conditioned for all layer depths. The inverse transforms are achieved with a numerical quadrature method and the results presented include actual displacement fields in the near-field of the load in plane-strain and three-dimensional axisymmetric cases. Verification against finite element method (FEM) calculations demonstrates the performance and complexity of the two approaches.
العلاقة: https://lup.lub.lu.se/record/62963076-e8e7-4f45-89a1-030880d4d87bTest; http://dx.doi.org/10.7712/120119.7248.18695Test; scopus:85079090991
الإتاحة: https://doi.org/10.7712/120119.7248.18695Test
https://lup.lub.lu.se/record/62963076-e8e7-4f45-89a1-030880d4d87bTest -
6دورية أكاديمية
المصدر: Geophysical Journal International; 213(1), pp 169-180 (2018) ; ISSN: 0956-540X
مصطلحات موضوعية: Geophysics, Computational seismology, Numerical modelling, Wave propagation
الوصف: We derive an expression for the error introduced by the second-order accurate temporal finitedifference (FD) operator, as present in the FD, pseudospectral and spectral element methods for seismic wave modeling applied to time-invariant media. The 'time-dispersion' error speeds up the signal as a function of frequency and time step only. Time dispersion is thus independent of the propagation path, medium or spatial modeling error.We derive two transforms to either add or remove time dispersion from synthetic seismograms after a simulation. The transforms are compared to previous related work and demonstrated on wave modeling in acoustic as well as elastic media. In addition, an application to imaging is shown. The transforms enable accurate computation of synthetic seismograms at reduced cost, benefitting modeling applications in both exploration and global seismology. The Author(s) 2017. Published by Oxford University Press. All rights reserved.
العلاقة: https://lup.lub.lu.se/record/8ede7c96-d18d-414a-a369-a24f40df1ce6Test; http://dx.doi.org/10.1093/gji/ggx563Test; scopus:85041805864
الإتاحة: https://doi.org/10.1093/gji/ggx563Test
https://lup.lub.lu.se/record/8ede7c96-d18d-414a-a369-a24f40df1ce6Test -
7دورية أكاديمية
المصدر: IEEE Wireless Communications Letters; 6(1), pp 82-85 (2017) ; ISSN: 2162-2337
مصطلحات موضوعية: Communication Systems, censored data, channel characterization and modeling, Cross-polarization ratio (XPR), maximum likelihood estimation, millimeter-wave propagation measurements, radio propagation
الوصف: In wireless channel measurements, the relatively weak cross-polarized multipath components (MPCs) are typically severely affected by the measurement noise level. As shown in this letter, the typical cross-polarization ratio (XPR) model parameter estimation, which ignores the existence of censored samples, may lead to significant errors. We demonstrate how to achieve accurate parameter estimates with a maximum likelihood estimator that properly takes into account both the measured XPRs and the censored samples. Also, a new XPR model is presented in which the average XPR is modeled as a function of the MPC excess loss. The new model is shown to be insensitive to the channel measurement noise level. A practical example with measured data in an indoor environment at 60 GHz demonstrates the utility of the approach.
العلاقة: https://lup.lub.lu.se/record/fdff31c3-5e59-4470-8d7c-f984a60493e6Test; http://dx.doi.org/10.1109/LWC.2016.2633355Test; scopus:85013413515; wos:000395868700021
الإتاحة: https://doi.org/10.1109/LWC.2016.2633355Test
https://lup.lub.lu.se/record/fdff31c3-5e59-4470-8d7c-f984a60493e6Test -
8دورية أكاديمية
المؤلفون: Persson, P., Persson, K., Sandberg, G.
المصدر: Engineering Structures; 115, pp 18-27 (2016) ; ISSN: 0141-0296
مصطلحات موضوعية: Construction Management, Finite element method, Fluid-structure interaction, Green-field measurements, Soil dynamics, Vibration reduction, Wave barrier, Wave propagation
الوصف: Reduction in traffic-induced ground vibrations by the use of barriers is investigated. The traffic load characteristics were measured for motorway traffic. The effects of parameters on various types of barriers were examined by the use of a finite element model that was calibrated to green-field measurements. The model involved a layered soil and bedrock. The depth of a trench and the elastic modulus of a solid back-fill material were found to be the most important parameters to consider. In investigation of the effects of infiltration of water into an open trench, a coupled finite element formulation of the water and the soil was applied. Infiltration of water was found to decrease the achieved reduction. At long distances from the vibration source, of around 500 m and longer, amplification in vibration level can be seen when a trench has been installed. It was also found, at long distances, that the motion of the ground surface follows the motion of the bedrock.
العلاقة: https://lup.lub.lu.se/record/ab5c00bb-246d-4e45-97b7-322214b56d0eTest; http://dx.doi.org/10.1016/j.engstruct.2016.02.025Test; scopus:84959345026; wos:000373649300002
الإتاحة: https://doi.org/10.1016/j.engstruct.2016.02.025Test
https://lup.lub.lu.se/record/ab5c00bb-246d-4e45-97b7-322214b56d0eTest -
9دورية أكاديمية
المؤلفون: Persson, Peter, Persson, Kent, Sandberg, G.
المصدر: Engineering Structures; 124, pp 361-375 (2016) ; ISSN: 0141-0296
مصطلحات موضوعية: Building Technologies, Finite element method, Soil dynamics, Soil improvement, Soil stabilisation, Vibration measurements, Vibration reduction measure, Wave propagation
الوصف: Vibration disturbances in buildings may stem from ambient sources, such as motorway traffic, or from internal sources such as people walking inside the building. Vibrations can exceed requirements for sensitive equipment or cause annoyance to humans and therefore the vibrations may need to be reduced. Vibrations from both external and internal sources can be reduced by modifying the properties of concrete slabs and of the soil underneath. Soil can be improved by being mixed with a binder material in order to increase its stiffness. In this study, parametric finite element analyses were conducted on the achieved vibration reduction on a slab on soil from improving the properties of a concrete slab on soil or of the soil underneath. The size, elastic modulus, and depth of the stabilised soil were found to markedly affect the level of reduction obtained. The soil stabilisation at a vibration-sensitive facility was used as an example case, where the developed finite element model was calibrated to green-field measurements carried out on-site. Frequency spectra of both road traffic loads and internal pedestrian loads were considered in the model. The calibrated finite element model predicted reductions of almost 60% for the road traffic and 80% for the pedestrian load.
العلاقة: https://lup.lub.lu.se/record/7da9ef2a-83a9-48a6-82ef-cca6b118234eTest; http://dx.doi.org/10.1016/j.engstruct.2016.06.020Test; scopus:84976622277; wos:000382793900026
الإتاحة: https://doi.org/10.1016/j.engstruct.2016.06.020Test
https://lup.lub.lu.se/record/7da9ef2a-83a9-48a6-82ef-cca6b118234eTest -
10رسالة جامعية
المؤلفون: Malmborg, Jens
مصطلحات موضوعية: Vehicle Engineering, Train-induced vibrations, ground vibration, wave propagation, soil dynamics, finite element method, soil stiffening, critical velocity
الوصف: The population is growing, and an increasing proportion of the population lives in urban areas. As a consequence, human exposure to noise and vibrations is increasing; two major sources being railway and road traffic. Larger and denser cities lead to a higher amount of traffic close to where people work and live. Land close to railways and heavily trafficked roads, previously left unexploited, are now being used for dwellings and offices. Vibrations are often accompanied by noise, to which long-term exposure is known to have serious health effects. Furthermore, some buildings such as hospitals and research facilities contain instruments that are highly sensitive to vibrations, and require proper vibration isolation to ensure safe operation. To address the problems of noise and vibrations, their generation and propagation need to be understood. The vibrations next to a railway track are caused by the forces exerted on the track by the passing train. These forces are the sum of a quasi-static part due to the deadweight of the train, and a dynamic part. The dynamic part is caused by various phenomena resulting in time-dependent train–track interaction forces. The vibrations generated at the track propagate through the underlying and surrounding soil as elastic waves of various types. The mechanical properties of the soil strongly influence the wave propagation and the resulting vibrations registered by a receiver at some distance from the track. For a building structure next to the track, the vibrations inside the building furthermore depend on the mechanical and geometrical properties of the building’s structural elements.In the thesis, numerical models and modeling strategies for predicting ground-borne vibrations from railway tracks have been developed. Various techniques to calculate the wave propagation in the soil have been implemented and used for studying different phenomena, such as the vibrations at the soil surface and in a building next to the track, caused by a train running over an uneven rail. ...
العلاقة: https://lup.lub.lu.se/record/8d8e04e1-b3ca-4c90-abf7-a38a99566a63Test; urn:isbn:978-91-8039-373-7; urn:isbn:978-91-8039-374-4
