Numerical Analysis of Local and Global Hydroelastic Response of Wetdeck Slamming Events on Multihull Vessels

Catamarans operating in a large sea state encounter slamming events on the wetdeck that may lead to structural failure. Wetdeck slamming is a non-linear process which involves complex free-surface topology, high-velocity water jets, and breaking waves interacting with the bow and deck-hull geometry. The slamming process generates large pressures and loads that are time dependent and concentrated in space. The structure responds in a coupled manner to the complex fluid loading. Common approaches to design for the limiting slamming loads include analytical models or segmented model tests. Analytical slamming models assume a linear free-surface, prescribed velocities, and simplified geometries. These simplified assumptions make it difficult to apply to realistic cases. Experimental model tests capture slamming loads by using segmented models attached to a backspline. It is difficult to scale results to full-scale and to recreate model scale conditions that lead to the limiting load cases. A high-fidelity fluid-structure interaction solver is used to study a simplified impact problem and slamming on a catamaran. The canonical problem is a flat plate impacting a curved water surface. A detailed analysis is conducted on the simple flat plate showing the influence of boundary conditions, structural non-linearities, and the relative impact velocities. A new adaptive inertial under-relaxation scheme is developed for solving the artificial added mass instabilities due to the segregated coupling of the CFD and FEA models. Catamaran slamming simulations compare the influence of global loads on the local wetdeck structure. The full field data provided by the numerical solver is used visualization of flat wetdeck slamming loads. Careful evaluation of existing impact models are presented and recommendations for reduced order modeling of maximum stress during wetdeck slamming are provided.PHDNaval Architecture & Marine EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147495/1/grahmatt_1.pd

Global hydroelastic model for springing and whipping based on a free-surface CFD code (OpenFOAM)

The theoretical background and a numerical solution procedure for a time domain hydroelastic code are presented in this paper. The code combines a VOF-based free surface flow solver with a flexible body motion solver where the body linear elastic deformation is described by a modal superposition of dry mode shapes expressed in a local floating frame of reference. These mode shapes can be obtained from any finite element code. The floating frame undergoes a pseudo rigid-body motion which allows for a large rigid body translation and rotation and fully preserves the coupling with the local structural deformation. The formulation relies on the ability of the flow solver to provide the total fluid action on the body including e.g. the viscous forces, hydrostatic and hydrodynamic forces, slamming forces and the fluid damping. A numerical simulation of a flexible barge is provided and compared to experiments to show that the VOF-based flow solver has this ability and the code has the potential to predict the global hydroelastic responses accurately

Σύγχρονος σχεδιασμός της μεταλλικής κατασκευής πλοίων bulk carrier

174 σ.Στο πρώτο κεφάλαιο της διπλωματικής με τίτλο «σύγχρονος σχεδιασμός της μεταλλικής κατασκευής πλοίων bulk carrier», γίνεται προσπάθεια να εξοικειωθεί ο αναγνώστης με την έννοια της σχεδίασης της μεταλλικής του bulk carrier. Το δεύτερο κεφάλαιο αποτυπώνει τις βασικές αρχές που ακολουθούνται στο σχεδιασμό της μεταλλικής κατασκευής των χώρων φορτίου, ξεκινώντας από την περιγραφή της διαδικασίας, που είναι υποσύνολο της σπειροειδούς διαδικασίας κατά τη μελέτη του πλοίου.Το τρίτο κεφάλαιο είναι αφιερωμένο στον προσδιορισμό των φορτίων που επηρεάζουν την κατασκευή του πλοίου. Στο τέταρτο κεφάλαιο της διπλωματικής, γίνεται η παρουσίαση των υπολογισμών, σύμφωνα με τους κανονισμούς του Αμερικανικού Νηογνώμονα (ABS), για τη διαστασιολόγηση των στοιχείων που απαρτίζουν τη μεταλλική κατασκευή του bulk carrier, στην περιοχή της μέσης τομής. Το πέμπτο κεφάλαιο ασχολείται με την ανάλυση της αντοχής του πλοίου. Το έκτο κεφάλαιο επικεντρώνει στο συνολικό σχεδιασμό της μεταλλικής κατασκευής στην περιοχή των αμπαριών, όπως αυτή επηρεάζεται από τα λειτουργικά χαρακτηριστικά και τις ανάγκες που παρουσιάζονται κατά την επιχειρησιακή λειτουργία του πλοίου. Τέλος, στο έβδομο κεφάλαιο παρουσιάζονται όλα τα εναλλακτικά σχέδια της μορφής της μεταλλικής κατασκευής των bulk carrier που έχουν προταθεί τα περασμένα χρόνια, ενώ καταγράφονται και οι κυριότερες περιοχές καινοτομιών που μελετώνται και είναι υπό εξέταση η εφαρμογή τους στη λειτουργία του πλοίου.In the first chapter of this thesis an effort is being made to familiarize the reader on the concept of the bulk carrier design. The second chapter outlines the design principles followed in the structural design of the cargo spaces of a bulk carrier, starting from the structural design process, that is part of the design spiral. The third chapter mentions the determination of loads affecting the hull structure. In the fourth chapter, the calculations for the structural components in the midship section area of a bulk carrier are presented, whereas the fifth chapter of this study copes with the strength analysis of the hull structure. The sixth chapter copes with the overall design of the hold area in a bulk carrier, seen from an operational point of view. Finally, the seventh chapter outlines the main alternative designs that have been implemented last decades in bulk carrier structural design, whereas the major areas of concern for the design of the future are also listed.Σπανολιός Παντελεήμω

On Full Scale Slamming Testing of High-Speed Boats

This dissertation consists of four articles on the experimental investigation of slamming in high speed craft. The investigation utilizes data from the purpose-built 9 meter high-speed offshore research boat Numerette. The unique hybrid steel/composite construction and high-speed, high channel count instrumentation and data acquisition system have enabled collection of the wealth of experimental data that is analyzed in these articles. In the first article the role of hull bottom panel stiffness in slamming is investigated. Two panels of differing construction are mounted on starboard and port on the Numerette, which is run at relatively high speeds in the Atlantic Ocean. Displacements of the two different panels are compared. The structural response under slamming loading is then compared with the behavior under static loading. It is shown that the static stiffness relationship is not directly reflected in the experimental slamming data; rather the relative response falls somewhere between the case of a static loading and the dynamic response of a simple mass-spring system. In the second article, the structural response of bottom panels to slamming loads is investigated further. Experiments are described and results presented for modal and static analysis of the Numerette bottom panels in free air. Strain data is then presented from slamming experiments, investigating the influence of wave encounter conditions and vessel rigid body motions on response in the time and frequency domains.The third article presents an analysis technique that uses the wavelet transform to provide insight into the behavior of marine structures subjected to slamming loads. Pressure, strain, acceleration and displacement data for an isolated slamming event are presented in the time domain and in the frequency domain with Fourier transforms and wavelet transforms. Two periods of high acceleration are identified and using the wavelet transform are shown to be vibration at the dry and then wet eigenfrequencies. Mode shapes are identified during these two phases using data from an array of accelerometers. The optimal time-frequency resolution of the wavelet transform makes it a powerful tool in analyzing slamming data, revealing non-stationary behavior that the Fourier transform obscures. Identifying such behavior can be critical, in particular in hull structures with reduced stiffness where strong hydroelastic effects are expected.The final article presents the validation of a high fidelity CFD/FE FSI code using data from Numerette. The CFD code CFDShip-Iowa and finite element solver Ansys are used. Hydrodynamic simulations are performed at a range of Froude numbers and sea conditions. Good agreement is shown with experimental data in calm seas. A one-way fluid structure interaction study is performed and strains show a qualitative agreement between numerical and experimental data.These articles give insight to the designer of high speed craft by comparing the response of panels of varying, but relevant constructions to slamming loads. Additionally, the time-frequency analysis tool presented enables evaluation of structural response and identification of behavior that can be critical in slamming. Finally the collected data is used to validate a CFD/FE FSI code that could be used early in the design phase to optimize a structure and hull geometry under realistic conditions

Summary of Research 2000, Department of Mechanical Engineering

The views expressed in this report are those of the authors and do not reflect the official policy or position of the Department of Defense or U.S. Government.This report contains project summaries of the research projects in the Department of Mechanical Engineering. A list of recent publications is also included, which consists of conference presentations and publications, books, contributions to books, published journal papers, and technical reports. Thesis abstracts of students advised by faculty in the Department are also included

Interaction between Waves and Maritime Structures

This book is the result of a stimulating Special Issue of Water, focusing on the “Interaction between waves and Maritime Structures”. This broadly inclusive title allowed the gathering of articles on different topics of engineering concern, making the book appeal to both scientists and practical engineers. Original contributions on evergreen problems, such as wave overtopping at conventional and unconventional coastal structures, wave-induced pressures at vertical walls, hydraulic stability of rubble mound breakwaters and dynamics of crown-walls indeed represent the main core of the book; however, other intriguing research topics are also tackled, including the solution of the Navier–Stokes equations for biphase flows, the downscaling of large maritime structures in a physical lab, floating bodies mechanics and the numerical modeling of coastline evolution

Ship's hull response under extreme bending loading

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Υπολογιστική Μηχανική

Experimental and numerical study of planing hulls in waves

Il lavoro presentato nella presente tesi e\u300 stato svolto nell\u2019ambito del progetto SOPHYA (Seakee- ping Of Planing Hull YAchts). Il progetto di ricerca e sviluppo e\u300 finalizzato all\u2019indagine delle prestazioni imbarcazioni plananti da diporto in termini di tenuta al mare, sicurezza e propul- sione in condizioni di mare medie. Questa indagine e\u300 stata condotta attraverso tre approcci complementari: esperimenti in scala modello, prove in mare e simulazioni numeriche. La tesi si concentra principalmente sulla tenuta al mare degli scafi plananti, in particolare, buona parte del lavoro e\u300 stata dedicata allo studio sperimentale e all\u2019analisi dei dati delle prove su modello e scala reale. I risultati sono stati utilizzati come dati di riferimento per le simulazioni CFD al fine di sviluppare un procedura affidabile per le simulazioni di scafi plananti su onda. E\u300 stato condotta un\u2019indagine sperimentale estensiva sullo studio del comportamento non linea- re di scafi plananti in onde regolari e l\u2019effetti dei parametri geometrici dello scafo, della velocita\u300 e della pendenza dell\u2019onda sulla risposta ultra armonica dei moti e delle accelerazioni. Ilcontributo principale dello studio e\u300 rappresentato dall\u2019ampia analisi della seconda e terza risposta armonica del moto e delle accelerazioni. I risultati rappresentano inoltre un notevole contributo ai dati della serie sistematica di Napoli e forniscono un riferimento dettagliato per futuri studi computazionali. Le prove di tenuta al mare al vero sono state pianificate ed eseguite, lo yacht e\u300 stato com- pletamente strumentato e una boa ondametrica e\u300 stata utilizzata per la misurazione direzionale dello stato del mare. E\u300 stato sviluppato un metodo innovativo di analisi integrata delle misure di moti a bordo e d\u2019onda al fine di migliorare la stima delle funzioni di trasferimento in scala reale ed e\u300 stato investigato l\u2019effetto dei modelli di distribuzione direzionale dell\u2019onda sul risultato. Le funzioni di trasferimento al vero ottenute con l\u2019analisi integrata proposta sono confrontabili con quelle in scala modello. Sono state eseguite simulazioni in acqua calma e di seakeeping di uno scafo planante utilizzando un codice open source basato su foam-extend. In seguito e\u300 stata sviluppata una procedura di pre- processing automatizzata che riduce drasticamente i tempi di pre-simulazione. Questa procedura genera una griglia raffinata ad-hoc per simulazioni di idrodinamica navale e prepara una cartella del caso da simulare pronta per l\u2019uso. La procedura utilizza strumenti di generazione griglie compresi in openFOAM ed altri svilupati appositamente. Le simulazioni di acqua calma hanno mostrato una una sottostima dell\u2019assetto in corsa e della resistenza alle alte velocita\u300, tuttavia le simulazioni di seakeeping mostrano risultati molto piu\u300 fedeli ai dati sperimentali in termini di funzioni di trasferimento. Sono inoltre stati implementati nuovi strumenti per le simulazioni che debbano riprodurre fedelmente le condizioni della vasca navale, come accelerometri virtuali e nuove condizioni cinematiche piu\u300 fedeli al reale fissaggio del braccio di rimorchio. I solutori e gli strumenti sviluppati sono stati in seguito utilizzati per studiare l\u2019effetto delle variazioni della forma dello scafo sulle prestazioni di tenuta del mare di otto diverse varianti. I risultati sperimentali dello scafo con le migliori prestazioni sono comparabili con quelli ottenuti dalle simulazioni.The work presented in this thesis has been carried out as part of the SOPHYA (Seakeeping Of Planing Hull YAchts) project. The research and development project is aimed at the investigation of the performances of planing pleasure-boats in terms of sea-kindliness, safety and powering in mild weather conditions. This investigation is pursued via three complementary approaches: model scale experiments,sea trials and Numerical simulations. This thesis is mainly focused on the study of planing hulls seakeeping, in particular, a large part of this work has been dedicated to experimental investigations and data analysis both in model and full scale. The results of towing tank tests have been then used as reference data for CFD simulations with the aim of to develop a reliable computational framework for seakeeping simulations of planing hulls. A novel experimental work has been carried out in order to investigate nonlinear behavior of planing hulls in regular waves and the effects of geometrical parameters, speed and wave steepness on higher harmonic response of hull motions and accelerations. An extensive analysis of the second and third harmonic response of motion and accelerations is presented, adding valuable results to the Naples Systematic Series data set and providing detailed benchmark data for future computational studies. Full scale calm water and seakeeping trials have been carefully planned and executed, the yacht has been fully instrumented and a wave buoy has been used for directional sea state mea- surement. An innovative integrated analysis method of on-board and wave measurements has been developed in order to improve full scale transfer functions estimation. The effect of wave directional distribution models on the estimated transfer functions has been investigated. The results show a remarkable agreement with model scale experimental results. Planing hull calm water and seakeeping simulations have been performed using open source CFD code. An open source fully automated pre-processing procedure has been developed to drastically reduce time-to simulations. The procedure generate a mesh refined ad-hoc for planing hullsimulations and a ready-to-run case folder using OpenFOAM built-in and custom tools. Calm water simulations showed an underestimation of the running trim angle and resistance at high speeds. Seakeeping simulations however showed much better agreement with experimental results in terms of motion transfer functions. New simulation tools have been implemented for the specific case of reproducing towing tank conditions, such as virtual accelerometers and new restraint capabilities that are more faithful of the real towing arm restraint conditions. The tested simulation framework has been used to investigate the effect of hull form variations on seakeeping performances of eight alternative hulls. Experimental results on the best performing hull alternative show comparable results with simulations