Dizertačná práca rieši problematiku analýzy akustických vlastností pohonných jednotiek. V úvodnej časti je teoretický rozbor fyzikálnych princípov vibrácií a hluku a prehľad súčasného stavu riešenia problematiky v oblasti návrhu pohonných jednotiek. Vlastná časť práce popisuje konštrukčný návrh elektrodynamického budiča vibrácií, návrh hodnotenia výsledkov merania a taktiež spôsob spracovania výsledkov. Akustické vlastnosti sú hodnotené pomocou normálových rýchlostí kmitania povrchu. V závere práce sú prezentované ukážky využitia metódy v praktických príkladoch spojených s návrhom pohonnej jednotky. Celé riešenie predstavuje ucelený spôsob analýzy vhodný pre rýchle hodnotenie vplyvu konštrukčných úprav na akustické vlastnosti.

Cutting movement is still one of the main means to obtain the desired machined surface. As the most representative cutting method in subtractive manufacturing, milling is widely used in industrial production. However, the chatter induced by the dynamic interaction between machine tool and process not only reduces the accuracy of the machined workpiece, but also increases the tool wear and affects the rotary accuracy of the spindle. The stability lobe diagram can provide stable machining parameters for the technicians, and it is currently an effective way to avoid chatter. In fact, the dynamic interaction between the machine tool and process is very complicated, which involves the machine tool, milling tool, workpiece and fixture. The induced mechanism of chatter depends on different machining scenarios and is not entirely dependent on the vibration modes of milling tool. Therefore, it is important to obtain stable machining parameters and to know the dynamic surface location error distribution, which can ensure machining quality and improve machining efficiency. In this dissertation, two methods for constructing stability lobe diagram are first introduced, and then two machining scales, macro milling and micro milling, are studied. For the macro-milling scale, the dynamic response of the in-process workpiece with time-varying modal parameters during the material removal process is analyzed. The stability lobe diagrams for thin-walled workpiece and general workpiece with continuous radial immersion milling are established respectively. Besides, the cumulative surface location error distribution is also studied and verified for the general workpiece. For the micro-milling scale, the dynamics at the micro-milling tool point is obtained by means of the receptance coupling substructure analysis method. The stability lobe diagram and surface location error distribution are analyzed under different restricted/free tool overhang lengths. The relationship between measurement results and burrs is further explained by cutting experiments, and the difference between the two milling scales is compared in the end.

<p>When a design feature (such as material choice, internal bracing pattern, guitar body depth, and sound hole diameter) of an acoustic guitar changes, the effect of the change on the guitar’s sound is not well understood. As a result, luthiers approximate how to make guitars that have resonant frequencies of around 95-105 Hertz (Hz), the frequency range which sounds “good.” The researcher designed a reconfigurable fixture that simulated an acoustic guitar body with a variable body depth and sound hole diameter. The researcher used this testing fixture to examine the relationship between sound hole diameter, body depth, and resonant frequency. She conducted an experimental parameter sweep, measuring frequency response functions (FRFs) to collect data on the first, Helmholtz, and second resonant frequencies of the simulated acoustic guitar. The researcher pinpointed the general trends in the correlation between resonant frequency, body depth, and sound hole diameter using the frequency data from the FRF measurements. She determined that as sound hole diameter increased, the first, Helmholtz, and second resonant frequencies increased; and as body depth and body volume increased, the first and Helmholtz resonant frequencies decreased, while the second resonant frequency increased up until a body depth of approximately 4.50” inches. Exploring alternative design features and material choices contributes to improving urban infrastructure by encouraging luthiers to make instruments with sustainable materials (National Academy of Engineering, Grand Challenges – Restore and Improve Urban Infrastructure, 2023).</p>