Universiẗat, Diss., 2005--Heidelberg.

Syntactic foams-composite materials consisting of hollow particles embedded in a host matrix-have many applications for manufactured products, including weight reduction, thermal insulation, and noise reduction. In this thesis, a certain variety of syntactic foam is investigated with regards to reducing fluid borne noise in hydraulic systems. Such a foam maintains stiffness at low hydrostatic pressures and becomes compressible as pressure increases. With this compressibility, the foam is potentially useful as a liner for a reactive noise control device, much like compressed gas style devices currently in use; but the syntactic foam additionally adds significant damping to the system. In order to predict device performance, a linear multimodal model is developed of a hydraulic suppressor, constructed as an expansion chamber lined with a syntactic foam insert. Material models are developed for various compositions of the foam liners, based on an inverse analysis matching the model to experimental results. Two model simplifications are considered, and it is found that a simplified bulk modulus model gives sufficiently accurate results to make approximate predictions of suppressor performance. Several optimizations are performed to predict the optimal material composition for hydraulic excavator work cycles. To help compare the prototype suppressor against commercially available bladder style suppressors, a model is developed for the bladder style silencer and is validated experimentally. Overall, this work both demonstrates the current and potential utility of syntactic foam as a device lining material, and contributes new models to the hydraulics noise control community.

Numerical models will be developed for the prediction of silencer transmission loss under the operating conditions present in gas turbine exhausts. In these systems the large diameter ducts and high operating temperatures produce a challenging acoustic environment due to the unverified behaviour of fibrous materials at high temperatures and the existence of complex sound fields. To understand the behaviour of fibrous materials at high temperatures their bulk acoustic properties are measured using a modified impedance tube which can heat material samples up to a temperature of 500 C. It will be demonstrated that the high temperature material properties can be extrapolated from room temperature measurements given knowledge of the temperature dependant flow resistivity. Finite element numerical models using point collocation and mode matching techniques to predict the transmission loss of silencers are developed and successfully validated. Dissipative silencer designs with various cross-sectional designs are explored numerically and experimentally according to common industry standards. It is demonstrated that transmission loss may be optimised by the arrangement of the fibrous material across the cross-section. The accurate numerical models allow for effe cient silencers to be designed reducing silencer size and cost. A new hybrid silencer is presented combining dissipative and reactive elements with the aim of increasing the low frequency attenuation of large silencers while maintaining an effective broadband spectrum. Measurements and predictions show this innovative design to be successfull. Application of the hybrid silencer allows for more flexible noise control solutions when design is limited by low frequency noise.

Plasminogen activator inhibitor type 2 (PAI-2) is a serine protease inhibitor traditionally regarded as a regulator of fibrinolysis and extracellular matrix degradation. More recently, PAI-2 has been implicated in diverse processes such as keratinocyte differentiation, cell death and viral pathogenesis. Although PAI-2s limited pattern of expression in vivo generates significant interest in this molecule, little is known about the underlying mechanisms controlling its cell specific regulation. In this thesis, the function that the previously identified PAI-2 gene silencer (Antalis et al., 1996) plays in the regulation of PAI-2 gene expression was investigated. The PAI-2 upstream silencer element 1 (PAUSE-1) is located approximately 1800bp upstream of the PAI-2 transcription initiation site. By employing electrophoretic mobility shift assays and transient transfection assays with mutant PAUSE-1 sequences, the sequence that defines PAUSE-1 was identified as TCT N3 AGA N3 T4. This element was shown to bind a number of protein complexes of similar electrophoretic mobility from various cultured cell lines. Transient transfection assays with the cervical adenocarcinoma, HeLa S3 and the macrophage-like, U937 cell lines, showed that PAUSE-1 repressed transcription by approximately 2.5 fold when cloned into the SV40 promoter or the minimal PAI-2 promoter. Ultraviolet (UV)-crosslinking analyses determined that the PAUSE-1 binding protein (BP) was approximately 67kDa. Examination of several similar DNA promoter sequences, such as the human IFNb and insulin promoters, suggested that PAUSE-1 might be an example of a universal silencer with the consensus sequence TCT Nx AGA, where x=4. The PAUSE-1 sequence shows significant homology to the binding sequence of the transcriptional regulators Ski, Smad3 and Smad4. EMSAs incorporating anti-Ski, -Smad3 and -Smad4 antibodies suggested that each are members of the PAUSE-1 BP complex in HeLa S3 cells. The PAUSE-1 BP complex has been purified by employing DNA affinity chromatography using streptavidin labelled magnetic beads. Approximately nine PAUSE-1 associated proteins from HeLa S3 extracts were visualised. Amino-terminal protein sequencing identified the first eight amino acids of the PAUSE-1 BP as EIQQRAAQ. The PAUSE-1 BP fails to show significant sequence similarity to any known protein and therefore potentially represents a novel DNA binding protein.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2000. / Includes bibliographical references.

Automotive turbo compressors generate high frequency noise in the air intake system. This sound generation is of importance for the perceived sound quality of luxury cars and may need to be controlled by the use of silencers. The silencers usually contain resonators with slits, perforates and cavities. The purpose of the work reported is to develop acoustic models for these resonators where relevant effects such as the effect of realistic mean flow on losses and possibly 3D effects are considered. An experimental campaign has been undertaken where the two-port matrices and transmission loss of four sample resonators has been measured without flow and for two different mean flow speeds (M=0.05 & M=0.1) using two source location technique. Models for the four resonators have been developed using a 1D linear acoustic code (SIDLAB) and a FEM code (COMSOL Multi-physics). Different models, from the literature, for including the effect of mean flow on the acoustic losses at slits and perforates have been discussed. Correct modeling of acoustic losses for resonators with complicated geometry is important for the simulation and development of new and improved silencers, and the present work contributes to this understanding. The measured acoustic properties compared well with the simulated model for almost all the cases.

Nowadays, metamaterials have found their places in different branches of wave physics ranging from electromagnetics to acoustic waves. Acoustic metamaterials are sub-wavelength structures in which their effective acoustic properties are dominated by their structural shape rather than their constitutive materials. In recent years, acoustic metamaterials have gained increasing interest due to numerous promising applications such as sub-wavelength imaging, perfect absorption, acoustic cloaking, etc. The focus of the work herein is to leverage acoustic metamaterial/metasurface structures to manipulate the acoustic wavefront to pave the road for future applications of the metamaterials. In the first part of the work, the metamaterial structure is introduced, which can be leveraged for better manipulation of the transmitted wave by modulating both phase and amplitude. Initially, a general bound on the transmission phase/amplitude space for the case of arbitrary metasurface has been presented and subsequently, the necessary condition for the complete modulation of the transmitted wave is investigated. Next, a horn-like space coiling metamaterial is introduced, which satisfied the aforementioned condition and enabled us to simultaneously modulate both the phase and amplitude of the transmitted wave. Furthermore, our initial efforts toward designing a metamaterial capable of real-time phase modulation with relatively constant amplitude will be discussed. In the second part of this work, a novel metamaterial-based methodology is presented for the design of the air-permeable acoustic silencer. In this work, the concept of the bilayer-transverse metamaterial is introduced, and its functionality for silencing the acoustic wave is demonstrated. Furthermore, it is shown that the methodology presented herein essentially does not limit the ratio of the open area, and ultra-open metamaterial silencers may be designed. Eventually, based on the presented methodology, the ultra-open metamaterial featuring nearly 60% open area is designed, and silencing capacity of about 94% at the targeted frequency is experimentally realized. In the last part of this work, the behavior of a locally resonant class of acoustic metamaterial in the non-Rayleigh regime has been explored. Elaborately, it is demonstrated that in the case of spherical inclusion in a matrix material, large variation in the effective acoustic impedance emerges near the inclusion’s Eigenmode. Eventually, the potential application of this novel phenomenon in the non-destructive evaluation (NDE) and ultrasound imaging is discussed. / 2020-08-09T00:00:00Z

Scania is known as a front-runner in the development of power trains for heavy vehicles, marine, and general industrial applications. As the regulations on emissions for combustion engine vehicles are getting tougher with increasing awareness on sustainable solutions and reducing environmental impact, the goal at Scania is to develop combustion engines to achieve low-pollutant emissions whilst achieving higher efficiency. Consequently, the exhaust after-treatment systems must continuously evolve to meet changing legislative requirements and customer demands.  To achieve this goal in this competitive market, Scania must adapt to these changes within a short period of time. The purpose of this thesis is to explore and improve the existing development process for the exhaust after-treatment system particularly for Large silencer platform by introducing design automation intended for computational fluid dynamics simulations. The objective was to introduce a method to reduce development time and allow designers to generate CFD models as effectively as possible. Two new methods were developed and proposed to create geometries intended for CFD simulation. The first method focuses on the extraction and splitting of internal volume/fluid region and these models will be utilized in the simulation solvers to perform CFD simulation. The second method was to standardize the naming of extracted surfaces specific to CFD simulation since every surface is treated differently in the simulation solvers. A simple user-friendly graphical user interface was created for easy operation and faster adaptability. Finally, the developed methods were evaluated and it was shown that it has the potential to save a significant amount of time during the pre-processing of the development phase and thus allow the engineers to focus on other value-adding and important task.

With the need for stealth in defense applications steadily increasing, noise reduction continues to play an important role in the world of aeronautics. With the ever increasing number of small UAV flight vehicle designs and their stringent weight requirements, acoustic solutions become progressively more complex. This thesis investigates the use of refractory foam, a new class of porous material, for designing effective silencers for small IC engines. The solution must be lightweight, compact, conformable, and capable of handling the rigors of flight. Throughout the course of this research, many silencer designs were fabricated to take advantage of refractory foam technology. These silencer designs were then tested against existing designs using both anechoic and outdoor testing techniques. These results proved refractory foam to be a superior broadband noise absorber that can survive harsh flight environment. Silencer designs using this material showed overall improvements in the areas of noise reduction, weight, size, and backpressure, compared to commercial designs. The final silencer design boasted an Aweighted overall sound pressure level that was 12.1 dBA lower than the reference case. This result was accomplished using nearly half the volume required by other designs to attain similar results. / Master of Science

Lined silencers of various configurations are used to attenuate the noise from building HVAC equipment, gas turbines, and other machinery. First-mode analytical solutions are presented for sound attenuation along rectangular lined ducts, parallel-baffle silencers, and circular lined ducts. The sound absorptive lining is treated using a bulk property model. The analytical solutions entail solving a nonlinear characteristic equation in the transverse direction after the rigid-wall boundary condition is applied. The solution is compared to the boundary element solution and a local impedance analytical solution for several test cases.