Water entry of compliant structures is a major area of interest within different fields of engineering. In the case of highly flexible panels, an application for this topic is on drag reduction due to shape reconfiguration of panels near the free surface to support further development of undulatory propulsors. Moreover, it has been an important concept in the study of the slamming of small high-speed craft with flexible bottom structures, such as those made of composites. In this work, this fluid-structure interaction problem is experimentally investigated in different stages. In Stage I, free-falling water entry experiments are conducted on wedges that have bottom panels with different flexural rigidities. Kinematics, hydrodynamics, spray root propagation, and structural response of the model are measured during the experiments. Results are interpreted to evaluate the effect of flexural rigidity on the slamming characteristics. The comparison between the rigid and flexible wedges shows that the evolution of the spray root on a flexible wedge is influenced due to fluid-structure interaction. In Stage II, a hybrid approach is proposed that incorporates spray root measurements with the existing analytical models in order to estimate the hydrodynamic loads in water entry of wedges with different boundary conditions. The validity of this approach is evaluated using a case study of a flexible wedge drop experiment. The results of this analysis show that the proposed approach can reasonably predict the wedge kinematics and hydrodynamic pressure due to impact. Future components of this study will further develop this tool to be used for highly-flexible structures, where it is not easy to install traditional pressure sensors. Stage III of this work is on analysis of a tow-tank test of a rigid composite planing-hull model performed at the U.S. Naval Academy. Experiments conducted in regular waves were examined in terms of their kinematics and pressure loads. The goal of this analysis is to begin planning of the towing-tank tests that will be conducted at the VT Advanced Towing Tank Facility. These future VT experiments will combine the flexible composite panel with the hull form and motions, which are analyzed in the tow-tank study to investigate the fluid-structure interaction in the slamming of a flexible-planing hull. In stage IV, The findings of experimental investigations on wedge water entry are utilized in a 2D+t method to predict the hydrodynamics and motions of a prismatic planing craft. In this approach, the hydrodynamic loading on each V-type section of the vessel is calculated employing wedge water entry experiments (Stage I) and existing theoretical models (Stage II). A modified strip theory, also known as 2D+t, is then implemented to use these data and solve for the hydrodynamics and motion of the high-speed craft in calm water. Results show a good agreement with that of Savitsky prediction method and existing towing tank measurements. / Doctor of Philosophy / Water entry of compliant structures is a major area of interest within different fields of engineering. One application is to study the motion of highly-flexible plates near the free surface. This is inspired by the manta rays that change the stiffness of their flapping fins during swimming in the ocean in order to have a more smooth motion. Another application is related to small high-speed craft that repeatedly become airborne and impact the water surface in waves. These individual impacts, called slamming, can adversely influence the maneuverability, cause failure to the structure or injure the crew on board. Thus, it is crucial to study and understand this phenomenon in order to mitigate its negative effects. The problem becomes more challenging when the vessel structure, such as those made of composites, can endure some deflections in order to dampen the slams. The interaction between this deflection and the water impact can deviate the slamming characteristics from the traditional theoretical predictions. Therefore, more investigation is needed to study this fluid-structure interaction. In this work, this problem is experimentally investigated in different stages. In Stage I, water entry of a wedge is analyzed, where the wedge represents a section of the high-speed craft. Different bottom panels, including a composite panel, are studied and results are compared in order to understand the effects of deflection of the panel on the slamming characteristics. In Stage II, a new approach is proposed to estimate the hydrodynamic loading in water entry of objects with arbitrary shapes. This approach is developed to estimate the slamming loads during the impact without using any sensors. In fact, the high-speed videos of the water contact around the object during the impact is used to predict the slamming characteristics on the model. This technique can be so useful for the water entry of the objects that have very thin panels, which restrict mounting the pressure sensors. In Stage III, an analysis is conducted on the tow-tank tests of a composite planing-hull model. In these experiments, a small model is tested in regular waves and slamming is examined in terms of the kinematics and pressure loads on the model. The future experiments in VT Advanced Towing Tank will combine the flexible composite panel with the hull form and motions, which are analyzed in the tow-tank study to evaluate the fluid-structure interaction in the slamming of a flexible-planing hull. In Stage IV, the findings of experimental investigations on wedge water entry are utilized to predict the hydrodynamics and motions of a high-speed craft. In this approach, the hydrodynamic loading on each V-type cross section of the vessel is estimated employing wedge water entry measurements (Stage I) and existing theoretical models (Stage II). The calculated hydrodynamic loading on the vessel sections are then used to solve for the hydrodynamics and motion of the entire vessel.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/113962 |
| Date | 03 September 2021 |
| Creators | Javaherian Hamedani, Mohammad Javad |
| Contributors | Aerospace and Ocean Engineering, Gilbert, Christine Marie, Seidel, Gary D., Brown, Alan J., Brizzolara, Stefano |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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