This study conducted a series of tests on a shock mitigating seat designed for high speed craft using various input excitations to better understand the relationship between various seat and operational conditions, and the response of the seat. A seat model of the test seat is used for a parametric study of various spring, damping and operational configurations. A seat shake rig is implemented to simulate motions of multiple high-speed craft as well as various defined inputs. At each test input the occupant weight and suspension preload is varied and the response is analyzed to find changes in acceleration, which is representative of the changes in force and displacement. By representing the seat as a based-excitation two-degree-of-freedom system, we develop the equations of motion and model them in Simulink to analyze the effects of various spring rates and damping coefficients. Based on the results it is found that an increase in occupant mass results in a decrease in observed acceleration. Increasing suspension preload is found to be detrimental to the mitigating abilities of the seat, changing the dynamics to those similar of a rigid-mounted seat. An analysis of the defined inputs resulted in confirming various seat characteristics. The analysis of the Simulink model revealed that increasing the spring rate results in an increase in acceleration. An increase in damping coefficient resulted in an increase in acceleration and ride harshness. / Master of Science

The straight line calm water performance of stepped planing hulls has been studied experimentally, by prediction method, and numerically. A model test was conducted to provide a systematic understanding of the effects that displacement and step location have on the performance of a stepped planing hull. Ten different step configurations were tested at three different displacements and over a range of four different speeds in calm water. Seven of these configurations were tested at two different Longitudinal Center of Gravity (LCG) locations. Of all the configurations tested, the stepped hull configurations showed reduced resistance compared to the unstepped hull. The configurations with the largest step height aft showed the least amount of resistance over the speed range tested. Increasing displacement and shifting LCG had similar effects on craft performance for both stepped and unstepped hulls. The current stepped hull prediction method was expanded to include a three dimension wave profile and the ability for the stagnation line to cross the step. Using previous model test data and existing two dimension wave profile equations, a single equation was developed to predict the three dimension wave profile aft of a step. Formulations were added to Savitsky's planing prediction method to include very high speed craft and chines dry conditions. Lastly, two simulations were performed using two computational fluid dynamics numerical tools, OpenFOAM, and NFA. The results of these simulations were compared to the experimental test results to assess each code's relative strengths and weaknesses for use in detail design of stepped planing craft. / Ph. D.

Slamming loads are the critical structural design load for high-speed craft. In addition to damaging the hull structure, payload, and injuring personnel, slamming events can also significantly limit operating envelopes and decrease performance. To better characterize slamming events and the factors affecting their severity, a parametric study will be carried out in the Virginia Tech Hydroelasticity Lab. This thesis provides the groundwork for this longitudinal project through meticulous analysis of irregular wave tow tank experiments. Through the modification of machine learning techniques and taking inspiration from facial recognition algorithms, key parameters were identified to form an experimental matrix which captures intricacies of the complex interdependent relation of variables in the slamming problem. The independent effects of parameters to be evaluated include hull flexural rigidity, LCG location, heave and surge velocity, and impact trim, angular velocity and acceleration. In preparation for this parametric study, an innovative experimental setup was designed to simulate the impact of a deep-vee planing hull into waves, through a controlled motion slam into calm water. To provide a baseline to compare data from future controlled motion experiments to, a model drop experiment was completed to characterize the relationships of impact velocity and trim to slamming event severity. During this experiment, the position, acceleration, strain, and pressure were measured. These measurements illustrated a decrease in peak acceleration, pressure, and strain magnitude with an increase in impact trim. Additionally, as trim was increased a delay in the time of peak magnitude for all measurements was observed. These results are attributed to the change in buoyancy with the change in impact angle. At non-zero angles of trim, a pitching moment was generated by the misalignment of the longitudinal center of buoyancy and center of gravity. This moment caused racking in the setup which was observed in the acceleration time histories immediately after impact. This finding furthers the need to investigate the angular velocity and acceleration of the model at impact, through the proposed series of experiments, as they are crucial naturally occurring motions inherent to slamming events. / Master of Science / Slamming loads are the critical structural design load for high-speed craft. Slamming events occur when a boat or ship impacts the water. This impact causes high peak pressures and accelerations. In addition to damaging the hull structure, payload, and injuring personnel, slamming events can also significantly limit operating envelopes and decrease performance. To better characterize slamming events and the factors affecting their severity, a parametric study will be carried out in the Virginia Tech Hydroelasticity Lab. This thesis provides the groundwork for this longitudinal project through meticulous analysis of irregular wave tow tank experiments, which mimic actual conditions in a sea way. Through the modification of machine learning techniques and taking inspiration from facial recognition algorithms, key parameters were identified to form an experimental matrix which captures intricacies of the complex interdependent relation of variables in the slamming problem. The independent effects of parameters to be evaluated include hull structural stiffness, location of the longitudinal center of gravity, vertical and forward velocity at impact, and impact angle, angular velocity and angular acceleration. In preparation for this parametric study, an innovative experimental setup was designed to simulate the impact of a generic high-speed boat into waves, through prescribing a motion path to the boat as it slams into calm water. To provide a baseline to compare data from future controlled motion experiments to, a precursor experiment dropping a boat into calm water was completed to characterize the relationships of impact velocity and trim to slamming event severity. During this experiment, the position, acceleration, strain, and pressure were measured. These measurements illustrated a decrease in peak acceleration, pressure, and strain magnitude with an increase in impact trim. Additionally, as trim was increased a delay in the time of peak magnitude for all measurements was observed. These results are attributed to the change in buoyancy with the change in impact angle. At non-zero angles of trim, a pitching moment was generated by the misalignment of the longitudinal center of buoyancy and center of gravity. This moment caused racking in the setup which was observed in the acceleration time histories immediately after impact. This finding furthers the need to investigate the angular velocity and acceleration of the model at impact, through the proposed series of experiments, as they are crucial naturally occurring motions inherent to slamming events.

The primary aim of the thesis was to investigate aluminum as building material for high speed craft, study the hull structure design processes of aluminum high speed craft and develop a parametric model to reduce the modeling time during nite element analysis. An additional aim of the thesis was to study the degree of validity of the idealizations and the assumptions of the semi-empirical design methods by using the parametric model. For the aluminum survey, a large amount of scientic papers and books related to the application of aluminum in shipbuilding industry were re-viewed while for the investigation of hull structure design, several designs of similar craft as well as all the classication rules for high speed craft were examined. The parametric model was developed on Abaqus nite ele-ment analysis software with the help of Python programming language. The study of the idealizations and the assumptions of the semi-empirical design methods was performed on a model derived by the parametric model with scanltings determined by the high speed craft classication rules of ABS. The review on aluminum showed that only specic alloys can be applied on marine applications. It also showed that the eect of reduced mechanical properties due to welding could be decreased by introducing new welding and manufacturing techniques. The study regarding the hull structure de-sign processes indicated that high speed craft are still designed according to semi-empirical classication rules but it also showed that there is ten- dency of transiting on direct calculation methods. The developed paramet-ric model does decrease the modeling time since it is capable of modeling numerous structural arrangements. The analysis related to the idealizations and the assumptions of the semi-empirical design methods revealed that the structural hierarchy idealization and the method of dening boundary by handbook type formulas are applicable for the particular structure while the interaction eect among the structural members is only possible to be studied by detailed modeling techniques.

Vibration is a part of human life. People use vibrations in many useful ways but eventually human exposure to vibration has become an impediment to human life. Health problems due to exposure to vibration and shock are common among the crew operating high speed craft (HSC). Whole body vibration and repeated shocks have been identified as one of the major causes for health effects among HSC crew. Whole body vibration can affect health, comfort and performance depending on the magnitude, waveform and time of exposure. Therefore it is prudent the significance of consideration of human exposure to vibration and shock when deciding the operational envelope of an offshore HSC. This report addresses this question in two correlated parts where it identifies the interrelationship between the human exposure to vibration and shock and the operational envelope of HSC. The first part consists of a state of the art review on methods and measures for evaluation of workplaces exposed to vibrations containing multiple shocks and select a suitable method to be used in the second part. The second part is a case study of a Swedish Coast Guard HSC, KBV 476, which describes crew exposure to shock and vibration using the method selected from the state of the art review, and discusses the results in relation to the risks involved with the crew in the perspective of short and long term exposure. Nature of the vibration exposure and the corresponding risk involved is then discussed with respect to the operational envelope of the craft.

Using scantling codes such as DNV or ISO for designing high speed craft has been a routine for many constructors. However, the validity of these design methods are to be questioned, especially when dealing with modern material concepts and structural layouts, since they are based on data from ships designed in the 1960ies and 1970ies using semi-empirical methods containing substantial uncertainties and limitations. For direct assessment of loading conditions, modern methods such as CFD are appreciated. But they consume lots of time and resources in the design stage, which makes efficiency worse. A simulation approach making detailed assessment of loading conditions and structural behavior for high speed craft in waves has been developed at KTH Royal Institute of Technology in Sweden, with parts of the method still in need of further validation. In the here presented project an experimental setup has been developed for detailed validation of simulated local structural responses for high-speed craft in waves. The experimental setup consists of a model structure instrumented with strain gauges and pressure sensors that is integrated into a high speed craft model. Experimental data has been generated through experiments in regular and irregular waves in the towing tank at University of Naples “Federico II”. The model structure and generated data are concluded to be feasible for the intended validation.

The VT i-Ship Lab has been assigned the task of designing and building a Personal Hydrofoil Craft capable of carrying two people, featuring the distinctive capabilities of foiling and diving. This thesis examines the attributes of fully submerged hydrofoils and their prospective advancements. Diverse configurations of fully submerged hydrofoils are scrutinized, accompanied by an exploration of their respective stability characteristics. A comprehensive analysis is conducted on the design space trade-offs, incorporating potential flow-based methodologies such as the lifting line and vortex lattice methods, encompassing considerations for the free surface, structural computations, and propulsion optimization. In conjunction with the design study computational fluid dynamics is employed to verify the estimated values and to fine-tune the system allowing for a robust low-fidelity system that can quickly estimate the appropriate hydrofoil arrangement for the desired conditions. Various hydrofoil and craft configurations are explored discussing the trade-offs with a final design being chosen and a thorough mechanical design pursued. / Master of Science / The VT i-Ship Lab is conducting research on a watercraft known as a "Personal Hydrofoil Craft." This vehicle is designed to carry two people, glide on the water's surface, and dive underwater. Hydrofoil crafts use specialized underwater wings to reduce resistance and enhance efficiency. Our focus is on fully submerged hydrofoils, studying their stability and efficiency. We employ computer simulations and advanced methods to design and optimize these submerged hydrofoils. The goal is to enhance our understanding of their functionality and performance through real-life experiments. This research has the potential to improve watercraft technology, leading to more efficient and stable boats in the future. By exploring the science behind hydrofoil designs, we aim to contribute valuable insights to the field of water transportation.

Planing hull is one solution to break the speed barrier of conventional hull, but as the boat reaches a high speed, massive whisker spray will be developed and attached to the hull, which causes a notable resistance increase. A Swedish company Peterstep invented an innovative spray deflector that can deflect the spray backwards and harvest kinetic energy from the spray.In the 2019 spray deflector project, many tests were done in Davison Laboratory Towing Tank, and there is a trim angle difference between plated and non-plated hulls. To investigate possible reasons, more tests are implemented in this project. According to the test results, the reason is determined as the different roughness of the hull and bottom due to differences in materials. Also, the tape for sealing the seam between hull and bottom plate affects the sharpness of the hard chine, thereby hindering the flow separation.The model used in previous experiments is no longer suitable for the further investigation. The modular design caused the different running position of plated and non-plated hull. In addition, the hull is too slender for the wave test. Therefore, a new model is needed to satisfy the new objectives of experiments. In this paper, the detailed design is surrounded by design aims and restrictions, such as increase spray resistance and avoid porpoising.There are few researches on HSC free running model test. To investigate the performance of the spray deflector in the test environment more similar to reality, a free running model with propulsion and steering system is necessary. The preliminary design, component selection and testing plan are outlined in this paper. / Planande skrov är en lösning för att bryta hastighetsbarriären hos ett konventionellt skrov, men när båten når hög hastighet kommer omfattande whisker spray att utvecklas på skrovet, vilket orsakar en anmärkningsvärd ökning av motståndet. Ett svenskt företag Peterstep har utvecklat en innovativ sprutdeflektor som kan avleda sprayen bakåt och skörda kinetisk energi från sprayen.Under sprutdeflektorprojektet 2019 gjordes många tester i Davison Laboratorys släpränna och det noterades en oönskad trimvinkelskillnad mellan modeller där skrovet byggts i en del eller med ett steg som fyllts igen med en bottenplatta. För att undersöka möjliga skäl till detta implementeras nya tester i detta projekt. Enligt testresultaten bestäms orsaken som skrovets och bottenplattans olika jämnhet på grund av materialskillnader. Även tejpen för tätning av sömmen mellan skrov och bottenplatta påverkar skärpan i slaget och hindrar därmed flödets avlösning.Modellen som använts i tidigare experiment är inte lämplig för fortsatt utredningen. Den modulära designen orsakade olika gångläge beroende på hur skroven hade byggts upp. Dessutom är skrovet för smalt för vågproven. Det behövs därför en ny modell för att uppfylla målen med experimenten.I det här arbetet har designen ytterligare designmål och begränsningar, som att mäta sprutmotståndet och att undvika porpoising.Det finns få undersökningar om HSC-test med frigående modeller. För att undersöka sprutdeflektorers prestanda i testmiljö som liknar verkligheten är det nödvändigt med en frigående modell med eget framdrivnings- och styrsystem. Den preliminära designen, komponentvalet och testplanen beskrivs i detta dokument.

High-speed craft are in high demand in the maritime industry, for example, in maintenance operations for offshore structures, for search and rescue, for patrolling operations, or as leisure craft to deliver speed and excitement. Design and operation of high-speed craft are often governed by the hydrodynamic phenomena of slamming, which occur when the craft impact the wave surface. Slamming loads affect the high-speed craft system; the crew, the structure and various sub-systems and limit the operation. To meet the ever-increasing demands on safety, economy and reduced environmental impact, there is a need to develop more efficient high-speed craft. This progression is however limited by the prevailing semi-empirical design methods for high-speed planing craft structures. These methods provide only a basic description of the involved physics, and their validity has been questioned. This thesis contributes to improving the conditions for designing efficient highspeed craft by focusing on two key topics: evaluation and development of the prevailing design methods for high-speed craft structures, and development towards structural design based on first principles modeling of the slamming process. In particular a methodological framework that enables detailed studies of the slamming phenomena using numerical simulations and experimental measurements is synthesized and evaluated. The methodological framework involves modeling of the wave environment, the craft hydromechanics and structural mechanics, and statistical characterization of the response processes. The framework forms the foundation for an extensive evaluation and development of the prevailing semi-empirical design methods for high-speed planing craft. Through the work presented in this thesis the framework is also shown to be a viable approach in the introduction of simulation-based design methods based on first principles modeling of the involved physics. Summarizing, the presented methods and results provide important steppingstones towards designing more efficient high-speed planing craft. / <p>QC 20160907</p>

Experimental and numerical analysis of loads and responses for planing craft in waves is considered. Extensive experiments have been performed on a planing craft, in full-scale as well as in model scale. The test set-ups and significant results are reviewed. The required resolution in experiments on planing craft in waves, concerning sampling frequencies, filtering and pressure transducer areas, is investigated. The aspects of peak identification in transient signals, fitting of analytical cumulative distribution functions to sampled data, and statistical convergence are treated. A method for reconstruction of the momentary pressure distribution at hull-water impact, from measurements with a limited number of transducers, is presented. The method is evaluated to full-scale data, and is concluded to be applicable in detailed evaluation of the hydrodynamic load distribution in time-domain simulations. Another suggested area of application is in full-scale design evaluations, where it can improve the traceability, i.e. enable evaluation of the loads along with the responses with more confidence. The presented model experiment was designed to enable time-domain monitoring of the complete hydromechanic pressure distribution on planing craft in waves. The test set-up is evaluated by comparing vertical forces and pitching moments derived from acceleration measurements, with the corresponding forces derived with the pressure distribution reconstruction method. Clear correlation is found. An approach for direct calculations of loads, as well as motion and structure response, is presented. Hydrodynamic loads and motion responses are calculated with a non-linear time-domain strip method. Structure responses are calculated by applying momentary distributed pressure loads, formulated from hydrodynamic simulations, on a global finite element model with inertia relief. From the time series output, limiting conditions and extreme responses are determined by means of short term statistics. Promising results are demonstrated in applications, where extreme structure responses derived by the presented approach, are compared with responses to equivalent uniform rule based loads, and measured responses from the full-scale trials. It is concluded that the approach is a useful tool for further research, which could be developed into a rational design method.