<p> The tire air cavity mode is known to be a significant source of vehicle structure-borne road noise near 200 Hz. A porous lining placed on the inner surface of a tire is an effective countermeasure to attenuate that resonance. The two noticeable effects of such a lining are the reduction in frequency and the attenuation of the air cavity mode. In this thesis, through both theoretical and numerical analysis, the mechanism of the effects of a porous lining was studied. A two-dimensional duct-shaped theoretical model and a torus-shaped numerical model were built to investigate the lined tire in conjunction with the Johnson-Champoux-Allard model describing the viscous and thermal dissipative effects of the porous material. Design parameters of the porous lining were varied to study their impact and optimal ranges of the design parameters were identified. Finally, in an experimental analysis, the sound attenuation and the frequency drop were observed in measurements of force, acceleration, and sound pressure. In conclusion, it was demonstrated that the suggested theoretical and numerical models successfully predict the effects of porous linings and that the frequency reduction results from the decreased sound speed within the tire owing to the presence of the liner. </p>

No description available.

[pt] A óptica de espaço livre (FSO), inicialmente estudada na década de 60, está atraindo atenção no contexto dos sistemas 5G+, que exige tecnologias de back-hauling sem fio com taxas de dados extremamente altas em distâncias de poucos quilômetros. A atual falta de um modelo global de perda de percurso para FSO motiva o estudo do comportamento do enlace óptico sob diferentes condições atmosféricas. Esta tese trata do desenvolvimento de modelos para prever a atenuação devido a neblina e chuva para projetar enlaces FSO em tecnologias 5G e além. Estudamos os bancos de dados de medições de superfície disponíveis em todo o mundo como referência para analisar as respostas do FSO considerando os dados disponíveis de longo prazo e descobrimos que o maior impacto na visibilidade em todo o mundo é causado por neblina, neve e chuva. Assim, selecionamos neblina e chuva como o foco deste estudo. Vários modelos de perda de percurso, baseados na visibilidade, são avaliados através de uma abordagem analítica. Propomos modelos de limite inferior e superior para estimar a atenuação específica devido ao nevoeiro considerando incertezas quanto à sensibilidade da atenuação específica, gama, em função da visibilidade em 1.550 micrômetros e o melhor ajuste aos resultados do modelo microfísico. Com relação à atenuação causada pela chuva, estudamos modelos disponíveis na literatura para enlaces de micro-ondas e os modificamos para aplicação em enlaces FSO. Quando os efeitos de espalhamento múltiplo são considerados, foi encontrada uma redução significativa na atenuação da chuva. Construímos a partir dos modelos, um método para combinar estatisticamente a atenuação em enlaces FSO causada por diferentes condições climáticas. O desempenho dos enlaces ópticos é avaliado em termos do máximo comprimento do enlace em relação à disponibilidade sob quatro condições climáticas: (i) somente chuva, (ii) somente neblina, (iii) chuva e neblina, e (iv) e todas as condições. Finalmente, eventos experimentais para os enlaces FSO e mmWave implementados no campus Leonardo do Politecnico di Milano são classificados e analisados dependendo do efeito atmosférico estudado: chuva estratiforme, chuva convectiva, chuva leve, vento, neblina pesada, neve e outros. / [en] Free-space optics (FSO), initially studied in the 60s, is attracting attention in the frame of 5G+ systems, which demands wireless back-hauling technologies with extremely high data rates over distances up to a few kilometers. The current lack of a global path loss model for FSO motivates studying the optical link s behavior under different atmospheric conditions. This thesis deals with the development of models for predicting the attenuation due to fog and rain for designing FSO links in 5G and beyond technologies. We study extensive surface measurement databases worldwide as a benchmark for analyzing FSO responses considering available long-term data. We find that the highest impact on visibility worldwide is caused by fog, snow, and rain. Thus, we select fog and rain as the focus of this study. Several path loss models based on visibility are assessed. We propose lower and upper-bound models to estimate the specific attenuation, gamma, due to fog which considers uncertainties as the sensitivity of gamma to the visibility at 1.550 µm and a micro-physical model of fog. Regarding attenuation caused by rain, we study models available in the literature for microwave links and modify them for application to FSO. When the multiple scattering effects are considered, a significant reduction in the rain attenuation has been found. From the findings, we build a method to statistically combine the attenuation effects on FSO caused by different weather conditions. The performance of FSO links is assessed in terms of the maximum link range against availability under four weather conditions: (i) rain only, (ii) fog only, (iii) rain and fog, and (iv) all conditions. Finally, experimental events for FSO and mmWave links implemented at Leonardo Campus of Politecnico di Milano are classified and analyzed depending on the studied atmospheric effects: stratiform rain, convective rain, light rain, wind, heavy fog, snow, and others.

Clustering is one of unsupervised learning algorithm to group similar objects into the same cluster and the objects in the same cluster are more similar to each other than those in the other clusters. Forecasting is making prediction based on the past data and efficient artificial intelligence models to predict data developing tendency, which can help to make appropriate decisions ahead. The datasets used in this thesis are the signal attenuation time series data from the microwave networks. Microwave networks are communication systems to transmit information between two fixed locations on the earth. They can support increasing capacity demands of mobile networks and play an important role in next generation wireless communication technology. But inherent vulnerability to random fluctuation such as rainfall will cause significant network performance degradation. In this thesis, K-means, Fuzzy c-means and 2-state Hidden Markov Model are used to develop one step and two step rain attenuation data clustering models. The forecasting models are designed based on k-nearest neighbor method and implemented with linear regression to predict the real-time rain attenuation in order to help microwave transport networks mitigate rain impact, make proper decisions ahead of time and improve the general performance. / Clustering is een van de unsupervised learning algorithmen om groep soortgelijke objecten in dezelfde cluster en de objecten in dezelfde cluster zijn meer vergelijkbaar met elkaar dan die in de andere clusters. Prognoser är att göra förutspårningar baserade på övergående data och effektiva artificiella intelligensmodeller för att förutspå datautveckling, som kan hjälpa till att fatta lämpliga beslut. Dataseten som används i denna avhandling är signaldämpningstidsseriedata från mikrovågsnätverket. Mikrovågsnät är kommunikationssystem för att överföra information mellan två fasta platser på jorden. De kan stödja ökade kapacitetsbehov i mobilnät och spela en viktig roll i nästa generationens trådlösa kommunikationsteknik. Men inneboende sårbarhet för slumpmässig fluktuering som nedbörd kommer att orsaka betydande nätverksförstöring. I den här avhandlingen används K-medel, Fuzzy c-medel och 2-state Hidden Markov Model för att utveckla ett steg och tvåstegs regen dämpning dataklyvningsmodeller. Prognosmodellerna är utformade utifrån k-närmaste granne-metoden och implementeras med linjär regression för att förutsäga realtidsdämpning för att hjälpa mikrovågstransportnät att mildra regnpåverkan, göra rätt beslut före tid och förbättra den allmänna prestandan.

Wireless transmission is an everyday part of movie production and a tool many people use in their work. Work, on a movie production, is fast, intense, and varies in geographical location almost on a daily basis (sometimes several locations in a day). Despite this, the stream, the transmission, must hold so the crew can work. This thesis explores the different impacts materials have on the transmission (using the Boxx Atom System as a test object). The materials were everyday occurrences such as walls (wood and stone), doors (steel, wood), windows (glass), and humans (the crew). The tests were done in the office of Video Assist Sweden in Stockholm, testing both quality and calculating the link margin. The results gave room for improvement but were interesting and sometimes surprising. Glass is best for a smooth transmission. Wooden doors and human beings’ impact were basically the same and stone and steel had the largest impact. In this thesis, we attempt to explain the results and draw conclusions from them and our own experiences in the field. / Trådlös överföring är en vardaglig del av en filmproduktion och ett verktyg som många använder i sitt arbete. Arbetet med en filmproduktion är snabbt, intensivt och varierar mellan olika platser nästan dagligen (ibland flera platser på en dag). Trots detta måste video transmissionen fungera så att hela teamet kan arbeta effektivt. Detta examensarbete undersöker de olika effekterna material har på transmissionen (med hjälp av Boxx Atom System som testobjekt). Materialen var vardagliga händelser som väggar (trä och sten), dörrar (stål, trä), fönster (glas) och människor (besättningen). Testerna gjordes på Video Assist Swedens kontor i Stockholm, där man testade både kvalitet och beräknade länk-marginalen. Resultaten gav utrymme för förbättringar men var intressanta och ibland överraskande. Glas är bäst för en smidig överföring. Träs och människors påverkan var i princip densamma och sten och stål hade störst påverkan. I detta examensarbete försöker vi förklara resultaten och dra slutsatser från dem och våra egna erfarenheter inom området.

[pt] Os cabos ópticos submarinos estão distribuídos por boa parte dos oceanos ao redor do globo terrestre. Esses cabos começaram a ser instalados com maior intensidade na década de 90, apesar de o primeiro cabo submarino óptico ter sido instalado em 1982 nas ilhas Canárias. Atualmente a importância dos cabos ópticos submarinos é de grande relevância para as comunicações mundiais e vem crescendo muito ao longo do tempo com a demanda por serviços de internet, liderada hoje pelas grandes empresas de tecnologia e de exploração de mídia social, tais como Google, Amazon, Meta, etc. Hoje cerca de 99 por cento de todo o tráfego da comunicação mundial da internet passa pelos cabos submarinos. Os custos para implantação desses cabos são muito altos e, portanto, prover alternativas para a ampliação da sua duração para um período maior do que a sua expectativa de vida útil representa um ganho considerável para todos. Considera-se atualmente pelos fabricantes e organismos de padronização internacional, como o ITU-T (União Internacional de Telecomunicações), uma expectativa média de vida útil de 25 anos. Esta expectativa de vida útil dada para os cabos ópticos foi a principal motivação para o desenvolvimento dessa pesquisa, cujos objetivos visam apresentar evidências que indiquem que a tendência de vida útil dos cabos ópticos submarinos pode superar os 25 anos previstos, e dessa forma contribuir para o atendimento da crescente demanda por transmissão de dados no mundo impulsionada pelos serviços de Internet. A metodologia adotada foi coletar dados de medições com o OTDR em cabos ópticos submarinos ao longo de 24 anos e avaliar a degradação sofrida pelo coeficiente de atenuação em dB/km ao longo do tempo das fibras ópticas dos cabos em operação, e comparar com a degradação sofrida pelos cabos sobressalentes, e avaliar também a degradação das perdas nas emendas submarinas e a sua correlação com a profundidade de instalação no mesmo período. As análises foram realizadas através da avaliação das curvas em arquivos na extensão .Sor obtidas com as medições realizadas pelo OTDR. Os resultados obtidos demostraram que os cabos ópticos em operação sofreram degradações compatíveis com os valores esperados e dados pelo ITU-T, mas também mostraram através da análise de curvas de tendência, que a degradação tem um comportamento logarítmico, e a projeção da curva de tendência para os próximos anos indicou que esses cabos poderão continuar em operação por muito mais anos do que os 25 anos, dados como limite anterior. Foi observado também que a penalidade de potência dada pela perda nas emendas é muito superior a degradação somente nas fibras ópticas, que existe uma correlação positiva entre a profundidade das caixas de emenda e a degradação na emenda e que os cabos sobressalentes degradam muito mais que os cabos em operação. / [en] Submarine optical cables are distributed over most of the oceans around the globe.These cables were installed with greater intensity in the 1990s, despite the fact that the firstoptical submarine cable was installed in 1982 in the Canary Islands. Currently, theimportance of submarine optical cables is very relevant for world communications and hasbeen growing a lot over time with the demand for internet services, led today by largetechnology and social media companies such as Google, Amazon, Meta, etc. Today around 99 percent of all world internet communication goes through undersea cables. The costs forimplanting these cables are very high and, therefore, to provide alternatives for optimizingtheir use by extending their duration for a period longer than their expected useful life,given by international standardization bodies, such as the ITU-T (InternationalTelecommunications Union), and by the manufacturers, which currently is 25 years, is ahuge gain for everyone. The life expectancy given for optical cables was the mainmotivation for the development of this research, whose objectives aim to present evidencethat indicates that the useful life trend of submarine optical cables can reach much morethan the 25 years predicted and in this way contribute to meeting the growing demand fordata transmission in the world, driven by Internet services. The adopted methodology wasto collect measurement data with the OTDR in submarine optical cables over 24 years andto evaluate the degradation suffered by the attenuation coefficient in dB/Km over time ofthe optical fibers of the cables in operation and to compare with the degradation sufferedby the spare cables, and also evaluate the degradation of the losses in the underwater splicesand its correlation with the depth of installation in the same period. The analyzes werecarried out by evaluating the .Sor curves obtained with the measurements performed by theOTDR. The conclusions showed that the optical cables in operation suffered degradationscompatible with the expected values and given by the ITU-T, but also showed through theanalysis of trend curves, that the degradation has a logarithmic behavior, and the projectionof the trend curve for the coming years indicated that these cables could continue to operatefor many more years than the 25 years given as the previous limit. It was also observed thatthe power penalty given by the loss in the splices is much higher than the degradation inthe optical fibers alone, that there is a positive correlation between the depth of the spliceboxes and the degradation in the splice, and that the spare cables degrade much more thanthe cables in operation.

No description available.

Necessary for effective ambulation, head stability affords optimal conditions for the perception of visual information during dynamic tasks. This maintenance of head-in-space equilibrium is achieved, in part, by the attenuation of the high frequency impact shock resulting from ground contact. While a great deal of experimentation has been done on the matter during steady state locomotion, little is known about how head stability or dynamic visual acuity is maintained during asymmetric walking. In this study, fifteen participants were instructed to walk on a split-belt treadmill for ten minutes while verbally reporting the orientation of a randomized Landolt-C optotype that was projected at heel strike. Participants were exposed to the baseline, adaptation, and washout conditions, as characterized by belt speed ratios of 1:1, 1:3, and 1:1, respectively. Step length asymmetry, shock attenuation, high (impact) and low (active) frequency head signal power, and dynamic visual acuity scores were averaged across the first and last fifty strides of each condition. Over the course of the first fifty strides, step length asymmetry was significantly greater during adaptation than during baseline (p d =2.442). Additionally, high frequency head signal power was significantly greater during adaptation than during baseline (p d =1.227), indicating a reduction in head stability. Shock attenuation was significantly lower during adaptation than during baseline (p d =-0.679), and a medium effect size suggests that dynamic visual acuity was lower during adaptation than during baseline as well (p =0.052; d =0.653). When comparing the baseline and adaptation conditions across the last fifty strides, however, many of these decrements were greatly reduced. The results of this study indicate that the locomotor asymmetry imposed by the split-belt treadmill during the early adaptation condition is responsible for moderate decrements to shock attenuation, head stability, and dynamic visual acuity. Moreover, the relative reduction in magnitude of these decrements across the last fifty strides underscores the adaptive nature of the locomotor and visuomotor systems.

Objective assessment for the effect of hearing protectors, background noise levels, and backup alarm acoustic features on listeners' abilities to localize backup alarm signals in the horizontal dimension, as well as on their ability to detect backup alarm signals in the distance dimension, is lacking in the acoustics and safety literature. Accordingly, two research experiments were conducted for this dissertation. In the first experiment, the effect of seven hearing protectors, two background pink noise levels (60 dBA and 90 dBA), and two backup alarm signals (standard and spectrally-modified) on the ability of normal hearing listeners to localize backup alarm signals in the horizontal dimension was investigated. Results indicated that a diotic sound transmission earmuff significantly degraded localization accuracy as compared to all other hearing protectors and the open ear condition. In addition, no significant difference existed between the open ear condition and the other hearing protectors in localization accuracy in most of the conditions tested. However, the E-A-R/3M HiFiTM earplug was advantageous in localization performance since it provided a significantly higher percentage correct localization than the Moldex foam earplug, the diotic earmuff, and the dichotic earmuff in 90 dBA pink noise. As for main effects of the other independent variables, the 90 dBA pink noise significantly degraded localization performance as compared to the quiet condition of 60 dBA, and a spectrally-modified backup alarm significantly improved localization performance as compared to the standard (narrowband) backup alarm. Potential application of these results includes the revision of backup alarm standards. In addition, these results provide clear advice for safety professionals to avoid the application of diotic sound transmission earmuffs for workers if localizing backup alarms is important. In the first experiment, listeners' feeling of comfort for each hearing protector was assessed subjectively by using a comfort rating scale. In addition, a subjective assessment for listeners' confidence in their localization decisions was established. Results indicated no significant difference between the hearing protectors in terms of comfort. However, in terms of listeners' confidence in localization decisions, their confidence was significantly degraded when they were fitted with the diotic earmuff. By contrast, they showed significantly more confidence in their localization decisions when they were fitted with the E-A-R/3M HiFi™ earplug as compared to when they were fitted with the Moldex foam earplug, the E-A-R/3M Ultrafit™ earplug, and the Bilsom passive earmuff. In the second experiment, listeners' performance in detecting a stationary backup alarm signal, including both a standard (narrowband) and broadband (pulsed white noise) alarm, was determined while they were equipped with various passive and electronic hearing protection devices. Listeners' performance was quantified by detection distance, which was defined as the distance between the stationary backup alarm device and the position where the listener detected the backup alarm signal. The resultant data demonstrated that normal hearing listeners detected a standard (narrowband) backup alarm signal at significantly longer distances as compared to the broadband (Brigade™) backup alarm signal, thus indicating the earlier forewarning by the standard alarm. In addition, passive hearing protection devices characterized with high attenuation significantly reduced the detection distance. These results may be applied to assist safety professionals in selecting hearing protectors and backup alarm signals that provide on-foot workers with ample time to react to an approaching backing vehicle, thus improving their safety. / Ph. D.

Remediation of contaminated groundwater remains a high-priority national goal in the United States. Water is essential to life, and new sources of water are needed for an expanding population. Groundwater remediation remains a significant technical challenge despite decades of research into this field. New approaches are needed to address the most severely-polluted aquifers, and cost-effective solutions are required to meet remediation objectives that protect human health and the environment. Source reduction combined with Monitored Natural Attenuation (MNA) is a remediation strategy whereby the source of contamination is aggressively treated or removed and the residual groundwater plume depletes due to natural processes in the subsurface. The USEPA requires long-term performance monitoring of groundwater at MNA sites over the remediation timeframe, which often takes decades to complete. Presently, computational tools are lacking to adequately integrate source remediation with economic models. Furthermore, no framework has been developed to highlight the tradeoff between the degree of remediation versus the level of benefit within a cost structure. Using the Natural Attenuation Software (NAS) package developed at Virginia Tech, a set of formulae have been developed for calculating the TOR for petroleum-contaminated aquifers (specifically tracking benzene and MTBE) through statistical techniques. With the knowledge of source area residual saturation, groundwater velocity, and contaminant plume source length, the time to remediate a site contaminated with either benzene or MTBE can be determined across a range of regulatory maximum contaminant levels. After developing formulae for TOR, an integrated and interactive decision tool for framing the decision analysis component of the remediation problem was developed. While MNA can be a stand-alone groundwater remediation technology, significant benefits may be realized by layering a more traditional source zone remedial technique with MNA. Excavation and soil vapor extraction when applied to the front end of a remedial action plan can decrease the amount of time to remediation and while generally more expensive than an MNA-only approach, may accrue long-term economic advantages that would otherwise be foregone. The value of these research components can be realized within the engineering and science communities, as well as through government, business and industry, and communities where groundwater contamination and remediation are of issue. Together, these tools constitute the Sâ ªEâ ªEâ ªPâ ªAGE paradigm, founded upon the concept of sound science for an environmental engineering, effectual economics, and public policy agenda. The TOR formulation simplifies the inputs necessary to determine the number of years that an MNA strategy will require before project closure and thus reduces the specialized skills and training required to perform a numerical analysis that for one set of conditions could require many hours of simulation time. The economic decision tool, that utilizes a life cycle model to evaluate a set of feasible alternatives, highlights the tradeoffs between time and economics can be realized over the lifetime of the remedial project. / Ph. D.