چكيده به لاتين
This thesis involves the design, modeling, and analysis of results for three novel, practical broadband configurations with a base spherical canonical geometry, composed of multi-morphic piezo-viscoelastic smart materials, for underwater acoustic cloaking based on a three-dimensional elasto-acoustic interaction approach. In the first problem, the hybrid control of vibro-acoustics of a smart sandwich spherical shell submerged in water and filled with air is theoretically modeled, examined, and analyzed using semi-active or fully active smart materials for both thin-walled and thick-walled cases. The mentioned sandwich configuration includes layers of bimorph piezoelectric (PZT) actuator shells arranged in series and parallel polarization, connected to a semi-active electro-rheological fluid (ERF) core layer. Two separate coupled elasto-acoustic formulations have been systematically developed. The first model is based on the variational principle of structural mechanics and the Kirchhoff-Love thin shell theory, utilizing the standard sliding mode control (SMC) approach to activate the sound scattering cancelation capability of the hybrid structure. The second model is based on the theory of three-dimensional piezo-elasticity and the classical state-space transfer matrix approach, combined with an active damping control (ADC) strategy. Extensive numerical simulations show that the optimal performance of broadband scattering cancelation can be effectively achieved with an active/semi-active smart hybrid bimorph piezo-sandwich cloaking spherical shell operating in a parallel polarization state. Furthermore, in order to quantify the overall performance efficiency of the cloaking, the error percentage (Err %) of the total external acoustic pressure field relative to the incident acoustic pressure field is calculated in the critical frequency ranges resulting from structural resonances. The obtained results demonstrate the effective cloaking performance of the thick wall smart hybrid shell (25%) in the medium to high frequency regions (Err < 1.5%), while this performance is somewhat reduced (Err < 8%) in a narrow low frequency band, primarily due to elasto-dynamic coupling resonances. On the other hand, the obtained results demonstrate the effective cloaking performance of the thin wall smart hybrid shell (7%) mainly in the low frequency range (Err < 1.5%), while this exceptional performance gradually decreases somewhat (Err < 6.5%) with increasing wave frequency. In the second issue, an active/semi-active hybrid spherical shell configuration composed of homogeneous alternating piezoelectric and smart viscoelastic layers (PZT/SVE) is proposed, which has the capability to effectively cloak a macroscopic three-dimensional underwater object from broadband acoustic incident waves. The proposed smart hybrid structure consists of a finite sequence of fully active PZT multi-morph layers connected in parallel, which act in conjunction with intermediate layers of semi-active SVE materials within the framework of a Multi-Input-Multi-Output Active Damping Controller (MIMO-ADC) optimized based on a Particle Swarm Optimization (PSO) algorithm. The elasto-acoustic modeling of the problem has been conducted using the spatial state space method based on the classical three-dimensional piezo-elasticity theory combined with wave equations for the internal and external acoustic fields. The acoustic cloaking performance of the proposed configuration has been evaluated for four different categories of SVE intermediate layer materials with adjustable rheological properties (i.e. field-dependent), including Magnetorheological Elastomer (MRE), Shape Memory Polymer (SMP), Electrorheological Fluid (ERF), and Magnetorheological Shear Thickening Polishing Fluid (MRSTPF). The obtained results indicate a significant decrease in the range of the Far-field backscattering form function amplitude |f_∞ (θ=π,k_ex R_(ex ) )|), as well as a reduction in the percentage of cloaking errors in the external acoustic field (%Err), by employing a sufficient number of multi-morph layers of PZT/SVE smart materials. Additionally, the use of a middle layer based on MRSTPF material in the acoustic cloaking configuration, even in a completely passive state, can serve as a suitable alternative to the SVE smart layer in the low-frequency range without consuming any effective external energy. Furthermore, since achieving three-dimensional, omnidirectional, broadband, near-perfect cloaking in the proposed configurations of the second problem requires a relatively high number of active/semi-active smart layers (N_max=31), the hybrid active/semi-active spherical shell configuration of the third problem employs an alternating arrangement of non-homogeneous piezoelectric-viscoelastic layers with an optimized structure (PZT/OSVE) to minimize the total number of broadband near-perfect cloaking configuration layers and also to reducing computational and experimental implementation costs. In this regard, it was observed that by using the optimized seven-layer non-homogeneous configuration, the maximum cloaking error percentage (%Err) could be reduced across the entire frequency range from eight percent to below one percent (achieving near-complete concealment). On the other hand, the results obtained indicate that achieving near-perfect broadband concealment (%Err < 1) in the homogeneous configuration requires a minimum of 31 hybrid active/semi-active smart layers, whereas the optimized non-homogeneous configuration needs only 7 hybrid active/semi-active smart layers. Additionally, the analysis of the sensitivity of cloaking performance to the arrangement of smart viscoelastic materials in the Cloaking body shows that using magnetorheological elastomer (MRE) and conventional passive viscoelastic (VE) materials in the inner layers, along with shape memory polymer (SMP) in the outer layers of the optimized configuration, creates a more favorable environment for achieving near-perfect, three-dimensional, omnidirectional broadband cloaking. The results of the proposed study can be considered an important step toward the practical development and experimental implementation of high-performance acoustic cloaking tools, aimed at achieving nearly complete omnidirectional broadband cloaking for three-dimensional underwater objects of various shapes, without relying on exotic metamaterials.
