Front seat passengers’ experience of ride comfort and NVH in modern cars

Due to the refinements in combustion-engine and electric cars, ride comfort has become a prominent attribute when it comes to developing cars in the future. A variety of factors, such as seat, seatbelt, sound and vibration, have been shown to influence perceived overall ride comfort in passenger cars. Numerous studies have investigated human responses to sound and vibration. However, few studies have investigated passengers’ experiences of sound and vibration in real passenger cars, in different real-world driving scenarios. The purpose of this licentiate thesis is to identify human experiences of sound and vibration in modern passenger cars. An approach has been developed to investigate how sound and vibration influence overall perceived ride comfort in combustion-engine cars (CVs) and electric cars (EVs). The first research question relates to the definition of ride comfort, from the passenger’s perspective, and the methodology used to specify the factors that influence overall ride comfort. The second research question deals with specifying how ride comfort is influenced by sound and vibration.The research includes literature reviews of human responses to sound and vibration and a user study using a mixed-method research approach that focused on subjective judgements and objective measurements of overall ride comfort. The literature reviews found that several laboratory studies have covered the level and frequency ranges of interest for vibration and sound found in passenger cars. Other studies have employed realistic ride postures with populations of various ages, gender and anthropometric measures to investigate the influence of vibration on ride comfort. Studies of sound in passenger car have explored approaches to identify sound sources, assess sound quality and design product sound. The overall conclusion from the literature reviews was that there is a lack of studies that consider all the different parameters influencing the overall ride comfort experience of automotive vehicle passengers. Also, further studies are specifically needed to investigate the influence of sound and vibration on passengers’ experience of overall ride comfort. The user study comprised eight typical driving scenarios (initial comfort, start/stop, acceleration and deceleration, constant speed, speed bumps, long bumps and cornering, bridge joints and rough roads) with ten participants in a CV and an EV. The overall results indicated that the two cars were similar in terms of the prominent effects of ingress, room for the body, seat adjustment and seat support on initial comfort, but varied in terms of dynamic discomfort. Induced body movements dominated dynamic discomfort in the CV, while annoying sound dominated in the EV. Sound annoyance in the CV was primarily triggered by tyre noise at lower speeds and wind noise at higher speeds. In the EV it was the high-frequency tonal sound from electrical components that produced the most annoyance. In both cars, vibration discomfort was linked most strongly to induced body movement. Sound annoyance was judged lower when passengers perceived pronounced induced body movement or when participants experienced vibrations coherent to the sound. Nevertheless, the overall influence of sound accumulated over time, making it difficult for passengers to relax. In contrast, the instantaneous judgement of vibration discomfort was not affected noticeably by the simultaneous sound.The main conclusion of this licentiate thesis is that from the passenger’s perspective, ride comfort encompasses static comfort and dynamic discomfort. Static comfort is associated with ingress, room for the body, seat support and seat adjustment. While dynamic discomfort is attributed to the annoying sound, induced body movement, as well as discordance between sound and vibration. The influence of sound and vibration on perceived ride comfort varies depending on the type of driving scenario (e.g., road profile and speed) and on the type of cars (e.g., CV or EV). Moreover, dynamic discomfort could be controlled by controlling sound and vibration

Modelling fluorescence quenching in systems with restricted diffusion: applications to oligonucleotides and polypeptides

The objectives of the present thesis are 1) to systematically develop a series of models and theoretical expressions for the diffusion-controlled reaction, which can be used to analyze the time-resolved fluorescence data in systems where the diffusion is restricted, and 2) to investigate the structural and dynamic properties of oligonucleotides and polypeptides by applying fluorescence-based methods and theoretical models. Firstly, the diffusion-controlled reaction in one- to three-dimensional systems was analyzed with the Smoluchowski approach. The analytical expressions containing diffusion coefficient in different systems were summarized for time-resolved fluorescence data fitting. Some of these expressions were drawn from literature sources and presented here in a unified form and new expressions have also been derived to fill some gaps found in the literature. This work is very useful not only for my own project but also for the global research framework in our group. ("Biomolecular and Supramolecular Kinetics in the Submicrosecond Time Range: The Fluorazophore Approach", W. M. Nau and X. Wang, ChemPhysChem, 2002, 3, 393-398 (Appendix II)). The diffusion-controlled intrachain fluorescence quenching was also analyzed. With the help of Prof. E. N. Bodunov, equilibrium conformational distributions of short polymer chains were simulated with Monte Carlo techniques. The kinetics of intramolecular end-toend collisions of short biopolymer chains that are labelled with a probe and a quencher at opposite ends was numerically simulated and the survival probability of the excited endattached probe, which reacts with the quencher at the other end upon contact, has been calculated. The results were compared with the experimental work on polypeptides carried out by other group members, suggesting that the reduced mobility of the ends of shorter chains was attributed to an increased steric hindrance, which results in an “internal friction” during intrachain motion. ("Fluorescence Quenching Kinetics in Short Polymer Chains: Dependence on Chain Length". X. Wang, E. N. Bodunov, and W. M. Nau Opt. Spectrosc. 2003, 95, 560-570 (Appendix IV)). Furthermore, two novel FRET energy donor/acceptor pairs with small critical radius, Trp/DBO and Nal/DBO, were employed to experimentally recover the end-to-end distance distribution and the intramolecular diffusion coefficient in Gly-Ser peptides. This work offered an independent approach to verify the theoretical analysis and compare it with the previous study based on collision-induced quenching systems. ("Application of FRET donor/acceptor pairs with small critical radius to recover the structural and dynamic properties in short flexible peptides", F. Huang, X. Wang, E. Haas, and W. M. Nau, 2004, in preparation (Appendix VII)). At the same time, some experimental projects were also carried out to investigate the structural and dynamic properties in DNA, RNA and 2′-O-methyl RNA single-stranded oligonucleotides. A phosphoramidite DBO derivative was synthesized, which can be directly applied in the automated solid-phase synthesis to obtain 5'-DBO-labeled oligonucleotides. The desirable properties of DBO, such as long lifetime, good solubility in water as well as efficient quenching by guanine upon direct contact, make it possible to extract the kinetics of molecular fluctuations from the intrachain fluorescence quenching. The end-to-end collision rates in short single-stranded oligodeoxyribonucleotides were successfully measured for the first time, which provided a strong support for the configurational diffusion model of hairpin formation. ("Kinetics of End-to-End Collision in Short Single-Stranded Nucleic Acids". X. Wang and W. M. Nau, J. Am. Chem. Soc. 2004, 126, 808-813 (Appendix VI)). The investigation on RNA and 2′-O-methyl RNA oligomers showed that the 2′ substitutions could result in different sugar puckering and fluctuational freedom in these analogues. Consequently, the conformational and dynamic properties of different oligonucleotides can be predicted, which will be useful for the research efforts in the area of antisense agents. Additionally, a kinetic hopping model for one- and two-directional charge migration in a one-dimensional system was developed and applied to the analysis of charge transfer processes in DNA strands. ("Kinetics of one- and two-directional charge hopping in onedimensional system: application to DNA". X. Wang and W. M. Nau, ChemPhysChem 2001, 2, 761-766 (Appendix I)) The mathematic methods obtained from these projects were also applied in the data analysis of cyclodextrin host-guest complexation and diffusion-controlled fluorescence quenching in biopolymer chains. ("A Joint Structural, Kinetic, and Thermodynamic Investigation of Substituent Effects on Host-Guest Complexation of Bicyclic Azoalkanes by β-Cyclodextrin", X. Zhang, G. Gramlich, X. Wang, and W. M. Nau, J. Am. Chem. Soc. 2002, 124, 254-263 (Appendix III) and "Exploiting Long-Lived Molecular Fluorescence" W. M. Nau, F. Huang, X. Wang, H. Bakirci, G. Gramlich, and C. Marquez, Chimia 2003, 57, 161- 167 (Appendix V))