Stefano Brizzolara

Virginia Tech (Virginia Polytechnic Institute and State University) | VT · Department of Aerospace and Ocean Engineering

Accurate predictions of ship maneuvering in waves are an increasingly important topic. The International Maritime Organization (IMO) has implemented standards to carry out motion prediction, aiming to ensure safer navigation and improved propulsive efficiency of ships in waterways. More emphasis has been placed on these standards with the enactment...

In this investigation, a comprehensive study was conducted on a U-shaped sloshing tank, based on reversing the classical treatment of such devices as motion stabilizers and using them instead to improve the performance of wave energy converters. The modeling encompasses a comparative analysis between a linear model and Computational Fluid Dynamics...

The paper presents a series of simulation results obtained with an integrated time-domain seakeeping and maneuvering dynamic model for the self-propelled ONR Thumblehome vessel in waves. A four degrees of freedom (surge/sway/yaw/roll) lumped-parameter model for maneuvering in calm water is first developed and verified against results obtained from...

Planar motion mechanism tests have been widely used in the virtual form for ocean craft, especially for underwater vehicles. These tests involve a predetermined sinusoidal trajectory for the AUV. While there are general guidelines for the choice of amplitude and frequency for such trajectories in existing literature, there are minimal to none for s...

The use of unconventional design has become a norm for mission-specific underwater autonomous craft. Geometrical characteristics and drag optimized shapes of single-hulled underwater vehicles are known since 1970s and a few significant improvements have been possible since then. These are mostly related to the efficiency of a wake adapted propeller...

An in-depth investigation into the effects of sweep on the aerodynamic and aeroacoustic performance of a rotor is carried out in this study. Dynamically similar swept and unswept rotor designs were tested and compared at the Virginia Tech Open Jet Wind tunnel for varying rotational rates and inflow speeds. It was observed that introducing sweep did...

This thesis studies the motion of an autonomous underwater vehicle towing another autonomous underwater vehicle which is a large as it is. The towed vehicle cannot be assumed to be just a mass attached to the towing vehicle. There is an interaction between the two vehicle. The towed vehicle places a force on the towed vehicle and the towed vehicle...

We provide theory and results obtained from the application of a 6-degree of freedom lumped parameter maneuvering model (LPMM) able to predict the maneuvering motions of underwater vehicles navigating at shallow depth below free surface waves. The parameters of the maneuvering model are identified using a combination of steady and unsteady captive...

This study is aimed at using fully viscous RANSE simulations in StarCCM+ with the use of the SST k-ω-γ transitional model to determine the effective wake of the propeller behind an axi-symmetric AUV hull. This low drag hull design, named the DIVE 2020E, was optimized for its cruise speed to facilitate laminar flow up to a favorable axial position b...

Recent efforts at Virginia Tech have produced a 6-degree of freedom (6DOF) lumped parameter maneuvering model (LPM) that is able to accurately predict the deeply submerged maneuvering motions for a variety of underwater vehicles, including the VT 690 AUV. This model consists of 50 non-negligible hydrodynamic derivatives that are estimated through a...

Motivated by the needs of long-endurance autonomous underwater vehicles, we seek to better understand trade-offs associated with control systems that seek to reduce energy consumption. In this paper we demonstrate a technique for controller design for an autonomous underwater vehicle (AUV). We examine the well-known design requirements, such as ref...

OpenFOAM's volume-of-fluid, free-surface capturing solver, interFoam, is used in a myriad of naval architecture applications ranging from seakeeping and stability analysis to vessel performance and even the development of energy-based hydrodynamic maneuvering models for use in control design [1,2]. A recent study by Lambert et. al. at Virginia Tech...

Results are presented of a benchmark study organised by the ISSC-ITTC Joint Committee on global linear wave loads on a container ship with forward speed. The aim of the study is the assessment of the uncertainty in linear transfer functions due to different seakeeping codes and consequences on long-term extreme vertical wave bending moments. Seven...

This study presents a comparison of the hydrodynamic responses generated by a boundary element method with linear free-surface boundary conditions and a volume of fluid RANSE CFD method with nonlinear surface capturing for a shallowly submerged prolate spheroid travelling with constant forward velocity. Observing the effects of free-surface proximi...

Implementation of the SSG/LRR-ω-γ model is carried out in the current study to predict transition to turbulence. The framework uses a Reynolds stress transport model, SSG/LRR-ω, as the base turbulence formulation and is coupled with Menter's γ transition model. To extend its applicability to different transition mechanisms, the production terms in...

Computational scientists frequently publish papers discussing various sources of uncertainty in numerical methods for computational fluid dynamics. The frequently discussed sources of uncertainty are round off error, discretization error, iterative error, and mathematical model uncertainty (i.e. uncertainty in turbulence modeling). While all of the...

In this study the impact of sweep angle on stepped hull resistance, running attitude, and dynamic stability is investigated for a range of planing speeds from ventilation inception (𝐹𝛻≈2) to high planing speeds (𝐹𝛻≈7) using RANS CFD. Potential performance benefits of the step are isolated for three speeds and two displacements using fixed trim simu...

In this paper we present an approach for representing the relationship between hydrodynamic modeling uncertainties of an autonomous underwater vehicle (AUV) and the vehicle's maneuvering performance uncertainty using Gaussian processes (GPs). A non-linear lumped-parameters model is linearized to find hydrodynamic coefficients which significantly im...

A study about the effect of different configurations of stationary and movable appendages on the dynamic stability of an autonomous underwater vehicle (AUV) is presented. A new stability index that can be used to assess dynamic stability in the vertical plane is derived. It improves upon the vertical plane stability index by accurately accounting f...

A method to derive a nonlinear model of the vertical plane hydrodynamic forces and moments on a planing hull using forced motion Unsteady RANSE CFD simulations and nonlinear system identification is investigated. The use of forced motion simulations on the fully three-dimensional hull form allows three-dimensional effects to be included in the nonl...

Advances in nonlinear modeling techniques have created opportunities for more robust modeling of planing hull dynamics than previous techniques relying on linear assumptions. These techniques rely on the imposition of complex, coupled forced motions on a hull. RANSE CFD provides a distinct advantage over experimentation when imposing complicated fo...

The novel second-order closure transition model, SSG/LRR-omega-gamma, is modified to include cross-flow transition effects in the current study. The original model framework uses the SSG/LRR-omega fully turbulence model coupled with the one-equation gamma transition model. A local helicity based approach is adopted into the original framework to ac...

This paper describes the computation of parameters for a Lagrangian mechanical system model of a submerged vessel moving near an otherwise calm free surface using a medium-fidelity potential flow code. The software uses the boundary element method to solve for the flow potential on the body and the free surface. The model, a system of integro-diffe...

In this study, hydrodynamic forces on a submerged vessel maneuvering near a free surface are determined using a reformulated Lagrangian nonlinear maneuvering and seakeeping model derived using Lagrangian mechanics under ideal flow assumptions. A Lagrangian mechanics maneuvering model is first reformulated to simplify the computation of parameters;...

The study investigates the influence of the propeller diameter and longitudinal position on the overall propulsion efficiency of axial-symmetric underwater vehicles, by means of high-fidelity viscous flow simulations.

This paper details the design, working principles, and testing of a novel position control mechanism for marine operations or inspection in extreme, hostile, or high-speed turbulent environments where unprecedented speed and agility are necessary. The omnidirectional mechanism consists of a set of counter-rotating blades operating at frequencies hi...

This paper introduces a method to improve maneu-vering models for AUVs that experience relatively tight turningradii (on the order of 2-3 vehicle lengths). By augmenting theoriginal virtual planar motion mechanism (VPMM) datasets usedin coefficient regression with high-angled steady-state CFD tow-tank data, maneuvering coefficients are adjusted to...

The prediction of planing hull motions and accelerations in a seaway is of paramount importance to the design of high-speed craft to ensure comfort and, in extreme cases, the survivability of passengers and crew. The traditional approaches to predicting the motions and accelerations of a displacement vessel generally are not applicable, because the...

The structure of the boundary layer developed on ship propeller blades is significantly influenced by the Reynolds number. The propeller flow regime will determine the radial distribution of vorticity and shear stress within the boundary layer and ultimately, the hydrodynamic loading exerted by the moving fluid particles on the blades. Therefore, w...

This paper presents the main results of an investigation regarding the effectiveness of reducing the wave resistance of a system of sea vehicles by varying the lateral and longitudinal offsets of each ship. A high-order free-surface Rankine-source boundary element method was used to conduct simulations on a series of seven adapted medium-sized auto...

In this study, four approaches are investigated to predict the motions and structural loads on a containership in waves. The Flockstra (1974) containership model is used as the benchmark for this study as extensive experimental data is available to compare to the predictions. The hydrodynamic loads and motions are predicted using strip theory, a ze...

This paper describes the concept design and preliminary dynamic analysis of a pitching wave energy converter (WEC) device, based on a pitching resonant floater, a pitch resonance tuning tank system and Wells turbines in regular head waves. The device has a bow/stern symmetry, which gives an advantage of the U-tank been strongly coupled with the flo...

This study compares the effect of non-linear free-surface boundary conditions for a high-order non-linear free-surface Rankine-source boundary element method on wave disturbance and hydrodynamic forces acting on an underwater vehicle travelling near a calm free-surface. In particular, simulations for a steady nonaxisymmetric prolate spheroid using...

This study presents a multi-fidelity framework that enables the construction of surrogate models capable of capturing complex correlations between design variables and quantities of interest. Resistance in calm water is investigated for a SWATH hull in a multidimensional design space using a new method to derive high-quality response surfaces throu...

"Shape Optimization of Engineering Systems for Superior Hydrodynamic Performance" For further reading, please follow the link to the Special Issue Website at: https://www.mdpi.com/journal/jmse/special_issues/zara_shape_optimization_engineering_syst ems_Superior_hydrodynamic_performance

The study investigates the influence of the propeller diameter and longitudinal position on the overall propulsion efficiency of axial-symmetric underwater vehicles, by means of high-fidelity viscous flow simulations. Firstly, we augment the classical problem of choosing the optimum propeller diameter, including the variable longitudinal clearance...

The free surface turbulent flow around a vertical surface-piercing strut advancing in calm water has been studied by using an open-source Smoothed Particle Hydrodynamics (SPH) solver DualSPHysics. The strut has a symmetric NACA 0024 foil section and it advances with uniform rectilinear motion, at Froude number 0.55. The combination of high relative...

Hull and strake geometries on a craft typically influence effective rudder angle during turning maneuvers. In this paper, we propose a simple yet accurate model for effective rudder angle that can be used in lumped-parameter maneuvering simulations. The model defines the effective angle as a function of the local inflow angle through a linear coeff...

This paper details the design and simulation of a novel position control mechanism for marine operations or inspection in extreme, hostile, or high-speed turbulent environments where unprecedented speed and agility are necessary. The omnidirectional mechanism consists of a set of counter-rotating blades operating at frequencies high enough to dampe...

The propeller of an Autonomous Underwater Vehicle (AUV) operates at low Reynolds number in laminar to turbulent transition region. The performance of these propellers can be calculated accurately using RANSE solver with γ − Reθ transition model. In this study, the global and local hydrodynamic characteristics of open and ducted propeller are invest...

The estimation of wave breaking and run-up on sloped beaches is a relevant issue in different coastal engineering applications. The present study stresses on the capabilities of a Smoothed Particle Hydrodynamics (SPH) solver, with optimal numerical and physical parameters, to accurately simulate the complex flow field in the surf zone and run-up re...

Approximation techniques for the coefficients that parameterize the hydrodynamic forces acting on a maneuvering underwater vehicle are presented and discussed. While captive tests yield the highest fidelity coefficients, they also incur significant costs that are prohibitive in early vehicle design phases. We present a method, requiring only a vehi...

Growing interest in marine autonomous systems such as underwater gliders and autonomous underwater vehicles (AUVs) has led to the increase of research on hydrofoil performance at low Reynolds numbers, bringing forward the issue of simulating laminar to turbulent transition using computational fluid dynamics (CFD). Most conventional turbulence closu...

A hydroelastic study of a deformable catamaran is presented. Two-way coupling has been implemented between a RANS (Reynolds Averaged Navier-Stokes) multiphase finite volume flow solver and a finite element method for a highly flexible hull structure. The presented cases consider the hull is advancing at a constant speed in head waves. Different lev...

Efficient design of wave energy converters based on floating body motion heavily depends on the capacity of the designer to accurately predict the device’s dynamics, which ultimately leads to the power extraction. We present a (quasi-nonlinear) time-domain hydromechanical dynamic model to simulate a particular type of pitch-resonant WEC which uses...

The effectiveness of a Metamodel-Embedded Evolution Framework for model parameter identification of a Smoothed Particles Hydrodynamic (SPH) solver, called DualSPHysics, is demonstrated when applied to the generation and propagation of progressive ocean waves. DualSPHysics is an open-source code that provides GP-GPU acceleration, allowing for highly...

We present an effective multi-fidelity framework for shape optimization of super-cavitating hydrofoils using viscous solvers. We employ state-of-the-art machine learning tools such as multi-fidelity Gaussian process regression and Bayesian optimization to synthesize data obtained from multi-resolution simulations, and efficiently identify optimal c...

The hybrid hydrofoil/SWATH (Small Waterplane Area Twin Hull) designed and patented by Stefano Brizzolara, is a novel vehicle that is optimized to operate in both a high-speed foilborne mode and a displacement mode. The deployable hydrofoils on the vehicle take on a unique four surface piercing anhedral foil configuration. This foilborne design had...

The proposed study aims at the understanding of the seakeeping responses of three multi-hull vessel configurations, namely catamarans, Small Waterplane Area Twin Hulls (SWATHs) and trimarans. Performance prediction has been obtained by using a first order 3D Boundary Element Method (BEM) based on a distribution of Rankine sources. Empirical models...

The paper presents a framework for set-based design under uncertainty and demonstrates its viability through designing a super-cavitating hydrofoil of an ultra-high speed vessel. The framework achieves designs that safely meet requirements as quantified precisely by superquantile measures of risk (s-risk) and reduces the complexity of design under...

Near field flow characteristics around catamarans close to resonant conditions involve violent viscous flow such as energetic vortex shedding and steep wave making. This paper presents a systematic and comprehensive numerical investigation of these phenomena at various oscillating frequencies and separation distances of twin sections. The numerical...

A new viscous lifting-line method for three-dimensional supercavitating hydrofoils is presented. The method is designed to allow for the strong nonlinear hydrodynamic characteristic of two-dimensional supercavitating sections. These nonlinearities, manifesting as sudden variation of the sectional lift-curve slope, are included in the numerical mode...

The correct prediction of seakeeping performance of fast multi hull ships is a key feature to design new high performance vessels. Focusing on lateral motions, and particularly on roll response, effects of viscosity must be included in the analysis when using methods based on ideal fluid hypothesis. A study on lateral motion response of multi hull...

Small Waterplane Area Twin Hulls (SWATHs) are known to have superior seakeeping performance but higher resistance compared to equivalent catamarans or mono-hulls. A way to improve their resistance characteristics is to use unconventional hull forms parametrically defined and optimized by CFD methods. This study builds on previous SWATH optimization...

A computational framework to design a new family of unconventional supercavitating (SC) hydrofoils with optimized hydrodynamic performance is developed. A low-order boundary element method is used to solve for the steady potential flow over the hydrofoil predicting its hydrodynamic characteristics, including the vapor-cavity interface. Shape variat...

A computational framework to design a new family of unconventional super cavitating (SC) hydrofoils with optimized hydrodynamic performance is developed. A low-order boundary element method is used to solve for the steady potential flow over the hydrofoil predicting its hydrodynamic characteristics, including the vapor-cavity interface. Shape varia...

The influence of vessel size on the performance of a second generation Autonomous Surface Vessel (ASV) in irregular head waves is investigated. The hull of the SWATH type ASV is optimized using a combination of high fidelity hydrodynamic numerical models to achieve minimal propulsion powering requirement as well as lower motions in waves compared t...

Hydrofoils have been traditionally used in marine systems for propulsion and stabilization purposes. During the twentieth century, planning craft started to be partially sustained by lift forces generated by immersed hydrofoils with the aim to decrease the hull wetted area, and hence the resistance. It is clear that hydrofoil design becomes a very...

A new numerical approach based on the Vortex Lattice Method (VLM) for the solution of the hydrodynamic performances of cambered hulls in steady planing is formulated and validated. Due to its fully 3D formulation, the method can be applied to both cambered and un-cambered dihedral planing surfaces of any shape without any further approximation. The...

Capitalizing on the experience and technology developments gained with underwater autonomous vehicles, the current research frontier in the field of autonomous marine vehicles has moved from under water to the sea surface, i. e., autonomous sea surface vehicles. Current and future perspectives of these types of autonomous vehicles are given in Sect...

Capitalizing on the experience and technology developments gained with underwater autonomous vehicles, the current research frontier in the field of autonomous marine vehicles has moved from under water to the sea surface, i. e., autonomous sea surface vehicles. Current and future perspectives of these types of autonomous vehicles are given in Sect...

Marine tunnel thruster includes a duct, within which at least a propeller is fitted that is operatively connected to a rotational drive system. The duct is composed of three sections, which include a first central section and two end sections. The first central section has a specific length and a specific diameter, while the two end sections have a...

We present a CFD characterization of a new type of super-cavitating hydrofoil section designed to have optimal performance both in super-cavitating conditions and in sub-cavitating conditions (including transitional regime). The basic concepts of the new profile family are first introduced. Lift, drag and cavity shapes at different cavitation numbe...

The hydrodynamic performance of unconventional SWATH and Semi-SWATH for high speed applications are analyzed and compared in this paper. Bare hull resistance in calm water is estimated by an inviscid boundary element method with viscous corrections and verified by a fully turbulent, multiphase unsteady RANSE solver. Motions response in head waves,...

The next generation of Autonomous Surface Vessels (ASV) will be optimized for optimum performance at sea. The design of an innovative unconventional SWATH-ASV family, patented by the author and under further investigation at the MIT innovative Ship design lab is described in its main features. The new unconventional design of the hull is the key to...

A Semi-Small Waterplane Area Twin Hull (Semi-SWATH) ferry is optimized by an automatic procedure with respect to seakeeping and resistance at different speeds. The numeric procedure is based on a fully parametric model of the unconventional hull form, a 3D linear Rankine sources panel method for the steady wave resistance and the seakeeping problem...

Hydrodynamic performance optimization of ship hulls by CFD methods is becoming popular in modern naval architecture. From local or partial parametric shape optimization, the current frontline of the research is to solve the global hull shape optimization by automatic computational procedures. Key of these procedures is in the parametric hull form m...

The hydrodynamic performance of unconventional SWATH and Semi-SWATH for high speed applications are analyzed and compared in this paper. Bare hull resistance in calm water is estimated by an inviscid boundary element method with viscous corrections and verified by a fully turbulent, multiphase unsteady RANSE solver. Motions response in head waves,...

In this paper we investigate the resistance and seakeeping effects of an inverted bow by comparing the motions of an existing combatant hull, the Oliver Hazard Perry class frigate (FFG-7), with a modified version of the same hull with an inverted bow. The bow of the FFG-7 was redesigned by developing a set of basic curves that define the parametric...

A watercraft device according to the invention includes a central body and two lateral hulls, each having a shape optimized to reduce resistance to the advance motion and connected to the central body through at least one connecting arm, causing the central body to be in raised position with respect to the lateral hulls. The connecting arms have a...

A new fully numerical approach to solve the hydrodynamic problem of both cambered and un- cambered dihedral steady planing surfaces is described. The core of the proposed numerical technique is founded on a three dimensional Non- linear Vortex Lattice Method with adequate boundary conditions to represent the flow around planing surfaces of generic...

A semi-SWATH (Small Waterplane Area Twin Hull) designed for littoral passenger transport serviceis optimized by a full automatic procedure with respect to seakeeping and resistance at different speeds. The computer assisted procedure is based on: a fully parametric model of the unconventional hull form, which guarantees ampleshape changes while ens...

Results from a systematic verification and validation of Smoothed Particles Hydrodynamic methods for the numerical simulation of periodic breaking water waves on constant sloped beaches are presented. Periodic waves are generated in deep water and then numerically followed during their propagation in constant bottom depth and their transformation u...

Results from a systematic verification and validation of Smoothed Particles Hydrodynamic methods for the numerical simulation of periodic breaking water waves on constant sloped beaches are presented. Periodic waves are generated in deep water and then numerically followed during their propagation in constant bottom depth and their transformation u...

Ship motion problem is approached exploiting the assumption of linearity and subdividing forces acting on the hull in different components; in this paper the focus is on the radiation problem. A fully viscous solver, based on the numerical solution of the Navier-Stokes equation through the finite volume technique, is used to calculate radiation for...

The paper is focused on some benefits gained by the integration of CFD results into the simulation process over time, in order to develop a whole numerical model representing the dynamics of a large merchant ship during towing/escorting operations in severe weather conditions. In particular, the shown application is referred to the simulation of a...

The accurate prediction of motion in waves of a marine vehicle is essential to assess the maximum sea state vs. operational requirements. This is particularly true for small crafts, such as Autonomous Surface Vessels (ASV). Two different numerical methods to predict motions of a SWATH-ASV are considered: an inviscid strip theory initially developed...

The importance of considering hub effects in the design, optimization and verification of marine propellers is discussed in the paper. Different design variants of optimum moderately loaded modern propellers are obtained by means of fully numerical lifting line/surface vortex lattice methods, with and without hub effect. Anti-symmetric vortex image...

We present a comparison of performance of an all-electric-ship (AES) simulator using two different approaches to control the induction machine in forward as well as in cash astern operations. The first approach uses a constant-slip control while the second uses direct-torque control. We also investigate the use of proper breaking resistors required...

In these last years a growing interest has been devoted to counter-rotating propellers especially for pod/stern drive applications for pleasure boats. In this context DINAV has been interested in the framework of an industrial R&D project to develop design/analysis computer codes for such kind of propulsors which is based on a modern lifting-line/l...

The behavior of the ship in waves should be a matter of hull optimization in order to maintain required levels of seaworthiness and operability in rough sea. Still nowadays the majority of ship motion prediction codes are based on the inviscid flow solvers; but in case of particular ship types, such as catamarans and SWATHs, the higher computationa...

Conference code: 104545, Cited By :1, Export Date: 20 August 2016, References: Andronov, A., Merkuryev, Y., Optimization of statistical sample sizes in simulation (2000) Journal of Statistical Planning and Inference, 85, pp. 93-102;

The main theoretical and numerical aspects of a design method for optimum contrar-rotating (CR) propellers for fast marine crafts are presented. We propose a reformulated version of a well-known design theory for contra-rotating propellers, by taking advantage of a new fully numerical algorithm for the calculation of the mutually induced velocities...