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The wave induced motions and vertical bending moments induced by extreme seas on a Cruise Ship is investigated numerically and experimentally. Six sea states and extreme wave sequences, which could trigger modulation instability and induce high nonlinear ship responses, were chosen. The ship responses are simulated in the time domain with a body nonlinear seakeeping code based on strip theory. Two levels of complexity are used and compared: (a) the first assumes that the body nonlinear effects in the vertical responses are dominated by the hydrostatic and Froude-Krylov components, therefore the related forces are nonlinear, while radiation and diffraction is kept linear (partially body nonlinear method); (b) the second considers all forces as body nonlinear and they are updated at each time instant during the simulation depending on the hull wetted surface (fully body nonlinear method). The paper presents comparisons of direct time domain simulations with experimental records, as well as probability distribution of maxima. The fully body nonlinear code compares very well with the experiments in extreme wave conditions.

This paper investigates the experimental and numerical vertical bending moments induced by abnormal waves on two ships, namely, a bulk carrier and a Roll-on/Roll-off. The experimental data was obtained by seakeeping tests with scaled models in head waves at two Froude numbers. The wave traces were predefined and corresponding to wave records measured during storms in the North Sea. These wave records are particularly interesting because each of them includes one abnormal wave. The ship models, which are similar in length but different in their geometry, were tested in the same predefined wave conditions. The objective is to investigate the hull geometry influence on vertical bending moment under extreme sea conditions. Some conclusions are made by comparing directly the measured responses from the two models. The experimental data is also used as benchmark to validate the predictions by a partially nonlinear time domain seakeeping numerical model. The numerical model is then used to generalize the comparative analysis between the two ships.

The vertical response of an Ultra Large Containership in high seas is analysed by means of numerical methods, which are compared with experiments. The experiment was conducted in a wave tank on a free running model with aluminium back bone and the flexible response of the ship is measured. The ship was tested in regular waves of moderate amplitude to analyse springing, and in severe irregular seas for whipping response. It was found that the flexibility of the model increases the largest sagging peak by up to 32%. The hydroelastic response of the ship is numerically calculated using a body nonlinear time domain method based on strip theory. A practical engineering method is followed for calculating the dependency of the hydrodynamic forces on the geometrical nonlinearity of the wetted hull. The time domain code is coupled with a Finite Element Model and the ship hull is modelled as a non-uniform Timoshenko beam. The ship responses in moderate seas are very well calculated by the numerical method. Even though vertical motions in very high seas are slightly overestimated by the numerical results, the numerical vertical bending moments are reasonably in good agreement with the experimental results.

A body-nonlinear time domain code based on strip theory is used to calculate the vertical ship responses of a containership in extreme sea conditions. The numerical method calculates the radiation forces based on Cummins formulation. A practical engineering approach is followed for calculation of the radiation/diffraction forces for instantaneous wetted surface of the hull. The Froude–Krylov and hydro static forces are also calculated for instantaneous wetted surface area of the hull. The numerical method calculates the vertical responses of a container ship in abnormal waves embedded in a real deterministic sea and the results are compared with the model test data. Results obtained from the numerical code that uses body-nonlinear hydrodynamic and hydrostatic forces are compared with results from another code that uses linear radiation/diffraction force and body-nonlinear Froude–Krylov and hydrostatic force. Time series of the vertical ship motion, vertical bending moment at the midship, and the relative motion at the bow are calculated and compared. Additionally, short term distribution of peaks of the vertical motion and bending moment, and the largest vertical bending moment peaks are analyzed. It is observed that the body nonlinear radiation/diffraction forces significantly improve prediction of the ship responses in extreme waves.

The aim of this paper is to critically assess the methods used for the evaluation of wave-induced loads on ships examining analytical, numerical and experimental approaches. The paper will focus on conventional ocean going vessels and loads originating from steady state and transient excitations, namely slamming, sloshing and green water, for the latter, and including extreme or rogue waves, as well as the more occasional loads following damage. The advantages and disadvantages of the relatively simpler potential flow ap-proaches against the more time consuming CFD methods will be discussed with reference to accuracy, modelling nonlinear effects, ease of modelling and coupling, suitability for long term response evaluation and suitability for incorporation within design and operational decision making. The paper will also asses the uncertainties involved in predicting wave-induced loads and the probabilistic approaches used for the evaluation of long term response and fatigue analysis. The current design practice will be reviewed and the role of numerical prediction methods within the classification framework and goal based design approach will be discussed. Finally the suitability of current developments in prediction methods to meet the needs of the industry and future challenges will be discussed focusing on hybrid approaches, systems approach and data fusion.

A body nonlinear time domain method based on strip theory with a weakly nonlinear formulation for the free surface condition is proposed and used to analyze the vertical responses of a cruise ship in random seas. The term ‘body nonlinearity’ implies the dependence of the hydrodynamic forces on the instantaneous wetted surface area of the ship hull. The radiation forces are calculated by means of Cummins formulation and are calculated for the wetted hull under the incident wave profile. A practical engineering approach is followed for the estimation of the body nonlinear radiation and diffraction forces. The hydrostatic forces are calculated for the wetted hull under the incident wave profile. The free surface condition is represented using a weakly nonlinear formulation and the incident irregular waves have nonlinearities up to second order. The wave pressure is calculated from the first- and second-order wave potentials using the Bernoulli equation and is integrated over the exact wetted surface to calculate the Froude-Krylov forces. The numerical results are compared with the experimental results measured in a wave tank. The comparative study is carried out by analyzing the statistics of the waves and through probability of exceedance of the wave peaks.

The paper presents a numerical and experimental study of the wave induced motions of a Floating Production Storage and Offloading system for production of LNG (FLNG) and a shuttle tanker floating side by side in head seas. The objective is to investigate the side-by-side moored system first order (linear) wave frequency and second order low frequency responses. The focus is on the wave induced responses which might limit the system operability, namely, the relative motions and the loads on the mooring lines. A second objective is to validate a frequency domain numerical method for calculating second order responses to irregular wave excitations through comparisons with experimental data obtained in an offshore wave basin. A Green׳s function panel method is used for the hydrodynamic calculations. The second order calculations are performed with an approximate method where the second order velocity potential is calculated without considering the forcing function on the free surface boundary condition. The irregular seas calculations are performed in the frequency domain. It is shown that the second order low frequency loads cannot be neglected when calculating the tension on the side by side mooring system.

A strip theory based partially nonlinear time domain code is extended to include body nonlinearity in the calculation of radiation and diffraction forces, which expresses the dependence of hydrodynamic forces on the time changing underwater hull shape. The body nonlinear Froude–Krylov and hydrostatic forces are combined with the body nonlinear radiation and diffraction forces. The radiation forces are represented in terms of impulse response functions, infinite frequency added mass and radiation restoring coefficients. Additionally, a semi-empirical technique is employed to include the surge mode to overcome one of the strip theory two-dimensional simplifications. The method is used to calculate the wave induced vertical motions and bending moments on a modern Cruise Ship. Results from the time domain code in regular waves with different steepnesses, with and without nonlinear radiation and diffraction forces, are calculated and compared. Similarly, the analysis is carried out for design regular waves and is compared with model test experimental data obtained in a seakeeping tank.

The paper presents a numerical and experimental study of multi-body systems composed of two floating structures floating side-by-side in head seas. This type of arrangement is being investigated for the operation of liquefied natural gas (LNG) transfer from a floating production platform to a shuttle tanker in an offshore environment. The floating structures are moored amongst themselves and floating in close proximity. The objective is to investigate the first order relative motions of side-by-side moored floating structures and the loads on the mooring lines and fenders, and to validate the existing numerical method by comparing to experimental results. Two case studies are analyzed. The first consists of two similar tankers moored together in intermediate water depth (80 m). The second configuration considers a floating production storage and offloading system for production of LNG (FLNG), with a side moored shuttle tanker. The experimental work was carried out in two offshore wave basins with scaled models subjected to irregular operational seastates. The measured responses include the motions of the two floating structures and the loads in the mooring lines connecting them. A Green's function panel method is used for the hydrodynamic calculations.

This paper investigates the experimental and numerical vertical motion responses of a bulk carrier and a Roll-on/Roll-off ship in extreme seas. The experimental data were obtained from seakeeping tests with scaled models in head waves at two Froude numbers. The wave traces were predefined, corresponding to wave records measured during storms in the North Sea. These wave records are particularly interesting because each of them include one abnormal wave. The ship models, which are similar in length but different in their geometry, were tested in the same predefined wave conditions to investigate the influence of the hull geometry on the extreme vertical ship responses. Conclusions are derived by comparing directly the measured responses from the two models. Experimental data are also used as benchmark to validate the predictions by a partially nonlinear time domain seakeeping numerical model. The numerical model code is then used to generalize the comparative analysis between the two ships.

The paper investigates the effects of the surge hydrodynamic forces and surge mode of motion on the vertical responses of a container ship and a chemical tanker in waves. A partially body nonlinear time domain code based on strip theory is modified to include the surge mode. The Froude–Krylov and hydrostatic forces are calculated for the exact wetted surface area of the hull for each time instant. Certain practical engineering techniques are used to overcome the 2D limitations imposed by strip theory in order to include the surge. Surge hydrodynamic coefficients are calculated using conformal mapping technique and surge Froude–Krylov forces are calculated for instantaneous wetted surface. Surge radiation forces are calculated based on Cummins formulation. The analysis is done for the S175 container ship and a chemical tanker in head seas for a range of wave steepness and Froude numbers. The effect of surge on the transfer functions and the peaks values of the vertical motions and vertical bending moment are analyzed. The numerical results are compared with the experimental results. It is observed that longitudinal forces reduce the vertical bending moment about the transverse axis at deck level for the wave frequencies of interest.

A time domain code based on strip theory is applied to calculate the probability distributions of relative motions and bending moments of a cruise ship in a set of extreme seas. The code includes two levels of complexity. The simpler one combines linear radiation and diffraction forces with nonlinear Froude–Krylov forces, hydrostatic forces, and shipping of green water on the bow. Cummins formulation is used to represent the radiation forces. The second approach is a generalization of the first one and, although the formulation is based on the linear assumption (of the radiation forces), the effects of body nonlinearity are considered by a simplified method: the memory functions, infinite frequency added masses, and the radiation restoring coefficients are assessed at each time instant as function of the instantaneous wetted surface. A similar procedure is used to calculate the diffraction forces. The code is used to analyze the responses of a cruise ship in a set of extreme sea conditions. The short-term nonlinear responses are represented by empirical probability distributions, obtained from the nonlinear time domain simulations, and the quality of the predictions is assessed by comparing with model tests experimental data. Finally, the long-term value of the bending moment is calculated from the short-term distribution of the nonlinear loads in a few extreme sea states selected based on coefficient of contribution method, and the results are compared with the International Association of Classification Societies (IACS) rule bending moment.

The paper presents realistic horizontal wave drift force coefficients and low frequency damping coefficients for the Exwave semi-submersible under severe seastates. The analysis includes conditions with collinear waves and current. Model test data is used to identify the difference frequency wave exciting force coefficients based on a second order signal analysis technique. First, the slowly varying excitation is estimated from the relationship between the incoming wave and the low frequency motion using a linear oscillator. Then, the full quadratic transfer function (QTF) of the difference frequency wave exciting forces is defined from the relationship between the incoming waves and the second order force response. The process identifies also the linear low frequency damping. The paper presents results from cases selected from the EXWAVE JIP test matrix. The empirical wave drift coefficients are compared to potential flow predictions and to coefficients from a semi-empirical formula. The results show that the potential flow predictions largely underestimate the wave drift forces, especially at the low frequency range where severe seastates have most of the energy.

Blindness makes life rather difficult for people who suffer from this health problem, but the use of technology can help in some day-to-day tasks. In this context, the present work focuses the development of a photo-to-speech application for the blind. The project is called Camera Reading for Blind People, and its ultimate purpose is the development of a mobile application that allows a blind user to “read” text (a sheet of paper, a signal, etc.). To achieve that, a set of frameworks of Optical Character Recognition (OCR) and Text to Speech Synthesis (TTS) are integrated, which enables the user, using a smartphone, to take a picture and hear the text that exists in the picture.

The paper presents an analysis of the mooring system effects on the dynamics of an arbitrary floating wave energy converter (WEC) and on the efficiency of the device. The mooring system dynamics are calculated by a finite differences method, which accounts for the lines’ physical characteristics such as mass and stiffness, as well as for the hydrodynamic inertial and damping characteristics. A method is proposed and applied to consider the inertial, damping and stiffness effects of the mooring system on the WEC’s linear dynamics. An identification method is used to determine the linear mooring system coefficients from pre-calculated nonlinear time domain forces of the mooring system on the floater (the importance of nonlinear effects is assessed as well). Finally the mooring system dynamics is represented by additional inertial, damping and stiffness matrices which are added to the ones of the WEC. The influence of the mooring system on the WEC dynamics and efficiency is assessed in terms of wave induced motions and absorbed power. Results are presented for the transfer functions, statistics in selected stationary sea states and the expected annual absorbed energy. A wave scatter diagram representative of the Portuguese Pilot Zone is used for the annual predictions.

Most of the wave energy converters under development are planned for operation in shallow to intermediate water depths, typically 30 m to 70 m. However, the limited water depth reduces the wave energy resource as compared to offshore deep water. This paper presents an analysis of the water depth effects on the wave energy resource and on the energy absorbed by a floating device. The analysis is based on a procedure to modify the wave spectrum as the water depth reduces, namely the TMA method Bouws et al., 1985 . J. Geophys. Res. 90 (C1), 975–986. The method is based on the hypothesis that the similarity principle for the saturation range of shallow-water spectrum is not restricted to the equilibrium range, but is valid across the entire spectrum. A point absorber-type wave energy converter is modelled and the wave climatology of Figueira da Foz (Portugal) is used as a case study. Significant reduction has been identified for both the wave energy resource and wave energy converted as the water depth decreases. The presented methodology can be used for preliminary cost benefit analysis and decision making regarding the best water depth for installation of specific wave energy converters.

The paper presents an analysis of the radiation forces on a ship advancing with forced heave and pitch motions. This analysis is based on experimental data obtained with model tests and on numerical simulations with two codes, one based on 3D time domain Greens function method and the other is a 2D linear strip theory method. The case study consists of a hull shape from a Fast Ferry and several speeds are investigated between 0 and 40 knot. The objective is to quantify the forward speed effects on the radiation forces and to verify the skill of the conventional strip theory and of a time domain panel methods in dealing with large forward speeds.The consequences of applying simplifications on the linear boundary conditions of the common seakeeping codes are investigated. It is concluded that forward speed has a large effect on the radiation forces, especially on the coupling terms, and thus it is important to consider the full linear interactions between the steady and unsteady flows in the numerical calculations as the speed of the ship increases and the time domain panel code is able to represent these effects.

The EXWAVE Joint Industry Project (JIP) was initiated with the aim of improving methods and standard industry practice in design prediction of nonlinear wave loadings on Mobile Offshore Drilling Units (MODUs) induced by severe and steep seastates. The focus is on slowly varying wave excitation, including wave-current interaction effects. The present paper describes the technical background which led to the EXWAVE JIP, the project objectives, the planned work program and initial results. An important part of the work program consists on performing model tests with representative floating structures. Two floating structures have been selected for investigation, namely a semi-submersible drilling rig and a floating production storage and offloading vessel (FPSO). Comparisons between experimental results and standard numerical calculations are presented for the semi-submersible. Computational fluid dynamics (CFD) is applied for detailed analysis and interpretation of complex physical phenomena.

This paper investigates the vertical motions and bending moments of a FPSO platform in regular waves and also in several design storms with a duration of three hours which correspond to the 100 years return period of the North Sea. An experimental program was carried out with a scaled model in a seakeeping tank. The experimental data is systematically compared with numerical results from a nonlinear time domain strip method in order to assess the capability of the method to estimate extreme vertical responses. The analysis of discrepancies between measurements and predictions indicates how the numerical model can be improved. The experimental results are also compared in terms of maximum responses induced by the design storms and induced by an abnormal wave. The objective is to conclude about the relevance of abnormal waves with regard to extreme bending moments. Finally the maximum bending moments, measured and calculated for the North Sea climate, are compared with the rule minimum requirements.

This article is part of a series of papers on the attempts to reconstruct and understand an early-17th-century Portuguese Indiaman based on the archaeological remains of the presumed Nossa Senhora dos Martires, a Portuguese nau that sank at the mouth of the Tagus River, Portugal, in September 1606. With the help of 3-D computer software, the authors try to understand how the interior space of this ship was used and occupied, and propose a plausible size, weight, and configuration for the cargo storage, which will be tested in terms of the fully loaded ship’s intact stability. The result is intended as a theoretical model of a ca. 1600 Portuguese nau. Only further archaeological probing will tell whether it is an accurate model or not.

This paper presents a procedure to calculate the design pressure distributions on the hull of a wave energy converter (WEC). Design pressures are the maximum pressure values that the device is expected to experience during its operational life time. The procedure is applied to the prototype under development by Martifer Energy (FLOW—Future Life in Ocean Waves). A boundary integral method is used to solve the hydrodynamic problem. The hydrodynamic pressures are combined with the hydrostatic ones and the internal pressures of the large ballast tanks. The first step consists of validating the numerical results of motions by comparison with measured experimental data obtained with a scaled model of the WEC. The numerical model is tuned by adjusting the damping of the device rotational motions and the equivalent damping and stiffness of the power take-off system. The pressure distributions are calculated for all irregular sea states representative of the Portuguese Pilot Zone where the prototype will be installed and a long term distribution method is used to calculate the expected maximum pressures on the hull corresponding to the 100-year return period.

The time domain method is further extended here in order to calculate the hydroelastic response of an ultra large containership in regular waves. Based on strip theory, the hydrodynamic and the hydrostatic forces are calculated for the instantaneous wetted surface area. Slamming forces are calculated using a Von Karman approach in which the water pile up during slamming is neglected. Timoshenko beam which takes into account the shear deformation and rotary inertia is used to model the structural dynamic characteristics of the hull. The beam is discretized using the finite element method and the ship vibration is solved using the modal analysis. The method is used to calculate the vertical bending moment acting on an ultra large containership in large amplitude regular waves. The results are compared with the experimental results measured in wave tank.Copyright © 2015 by ASME

Short term probability distribution of the vertical bending moment acting on a cruise vessel in extreme seas is calculated using a body nonlinear time domain method based on strip theory. The hydrodynamic forces are calculated for the exact wetted surface area under the incident wave profile. The incident potential satisfies the weakly nonlinear free surface condition based on the Stokes expansion. The disturbance potential satisfies the linear free surface and body boundary conditions. Certain practical engineering techniques are employed for the calculation of the body nonlinear forces. The statistics and the probability of distribution of the numerical vertical bending moment are compared with the experimental results measured in the wave tank.

Summary Discovered in 1993 at the mouth of the Tagus River, the SJB2 shipwreck—or ‘Pepper Wreck’—was tentatively identified as the Portuguese Indiaman Nossa Senhora dos Martires , lost on its return voyage from Cochin, India, on 14 September 1606. Following archaeological excavation and a tentative reconstruction of the ship’s hull and rigging, the next step is the study of its structural strength and sailing characteristics using the tools of modern naval architecture. This paper presents a methodology for investigating the sailing and structural characteristics of the ‘Pepper Wreck’, combining archaeological, iconographic and contemporary written sources with modern naval architectural calculations. © 2005 The Authors

The paper presents an analysis of structural design wave loads on an FPSO. The vertical bending moment at midship induced by rogue waves are compared with rule values. The loads induced by deterministic rogue waves were both measured in a seakeeping tank and calculated by an advanced time domain method. Two procedures are used to calculate the expected extreme vertical bending moment during the operational lifetime of the ship. The first one relies on a standard linear long term prediction method, which results from the summation of short term distribution of maxima weighted by their probability of occurrence. The short term stationary seastates are represented by energy spectra and the ship responses by linear transfer functions. The second one is a generalization of the former and it accounts for the nonlinearity of the vertical bending moment, by using nonlinear transfer functions of the bending moment sagging peaks which depend of the wave height.

The paper presents a comparison between experimental data and numerical results of the hydrodynamic coefficients and also of the wave induced motions and loads on a fast monohull model. The model with 4.52 m length was constructed in Fibre Reinforced Plastic (FRP), and made up of 4 segments connected by a backbone in order to measure sectional loads. The objective of the investigation was to assess the capability of a nonlinear time domain strip method to represent the nonlinear and also the forward speed effects on a displacement high speed vessel advancing in large amplitude waves. With this objective in mind the experimental program included forced oscillation tests in heaving and pitching, for a range of periods, three different amplitudes and several speeds of advance. In head regular waves comprehensive ranges of wave periods, wave steepness and speeds, were tested in order to measure heave, pitch and loads in three cross sections. The numerical method assumes that the radiation and diffraction hydrodynamic forces are linear and the nonlinear contributions arise from the hydrostatics and Froude–Krilov forces and the effects of green water on deck. The assumption of linearity of the radiation forces is validated by comparing calculated hydrodynamic coefficients with experimental data for three different amplitudes of the forced oscillations. Both global coefficients and sectional coefficients are compared. The motions and loads in waves are compared in terms of first and higher harmonic amplitudes and also in terms of sagging and hogging peaks.

The paper presents the results of an experimental investigation of added masses and damping coefficients of a model of a fast monohull. A model of 4.5 m length between perpendiculars was constructed of fiber glass reinforced plastic (FRP) with four segments connected by a backbone. The backbone was instrumented with load cells at the positions of the cuts. This configuration, combined with load cells measuring the force exerted by the forced motion actuators, made it possible to obtain the hydrodynamic coefficients for each of the four hull segments. The investigation focused on the vertical motions. Thus, the experimental program included forced harmonic heave and pitch motions in calm water (no incident waves). Subtracting inertial and restoring forces from total measured forces, one obtained the hydrodynamic component, which then resulted in the hydrodynamic coefficients. The effects of steady forward speed on the radiation forces were investigated by conducting model tests at four forward speeds. Finally, nonlinear effects were assessed by conducting model tests for three amplitudes of forced heave and forced pitch motions.

An assessment is made of the maximum wave induced bending moment expected to occur during the operational lifetime of a fast monohull, based on long term distribution calculations of the non-linear vertical bending moment at mid-ship. The ship is assumed to operate in the Northern North Sea, with an operational life of 25 years. A succession of short-term stationary ship responses represented by Rayleigh distributions of peaks results in the long-term distribution of the structural loads. Non-linear pseudo transfer functions are used in the procedure to calculate the variances of the short-term responses. The amplitudes of these transfer functions are calculated by a non-linear time domain seakeeping program. The results are compared with rules minimum required values and also with results from simpler calculation procedures such as adopting design sea states.

A nonlinear time-domain procedure is presented which is used to calculate the vertical responses of a container ship advancing in head waves. The method assumes linear radiation forces represented by time convolution of memory functions, infinite frequency added masses, and radiation restoring coefficients. The nonlinear hydrostatic restoring and Froude–Krilov forces are computed exactly over the instantaneous wetted surface of the ship's hull. Forces due to green water on deck are calculated using the momentum method. Nonlinear effects are identified on different vertical ship responses, namely on the heave and pitch motions, the vertical accelerations, and the vertical bending moment. These non-linear effects are expressed by the variation of the transfer function with the wave amplitude, the higher-order harmonics of the time signals, the offset of the time series, and the asymmetry of the peaks. The numerical results and the quantified nonlinear effects are compared with experimental results showing an ability to reproduce the main nonlinear effects.

The paper analyzes the effect of 2nd order waves on the vertical ship responses in extreme seas. The numerical simulations are carried out using a body nonlinear time domain code based on strip theory. The radiation, diffraction, Froude-krylov and hydrostatic forces are calculated for the exact wetted surface area of the ship for each time step. A practical engineering approach is followed to calculate the body nonlinear radiation and diffraction forces. First order Froude Krylov pressures are replaced with a second order model for the present study. The 2nd order Froude-Krylov pressures are integrated upto the exact wetted surface area for each time instant. The ship responses in regular waves with varying steepness are analyzed. Finally, the vertical ship responses are compared with the responses in design waves measured in the wave tank.

This paper discusses the numerical analysis of an ultra large containership model in severe head seas. A body nonlinear time domain code based on the strip theory is used for the calculation of the rigid body response of the vessel. The radiation, diffraction, Froude-krylov and hydrostatic forces are calculated for the exact wetted surface area of the ship at each time step. A practical engineering approach is followed to calculate the body nonlinear radiation and diffraction forces. The numerical vertical bending moment is compared with the experimental results. The experiment was conducted on a flexible model in both regular and irregular waves. The model comprised six segments that were joined with an aluminum backbone of variable stiffness characteristics in order to replicate the hydroelastic behavior of the real ship. The model was tested for two ship speeds, 15 and 22 knots. For the first three harmonic values of the vertical bending moment, a good agreement between the numerical and the experimental results are found. However, higher harmonics significantly contributed to the total experimental vertical bending moment, in regular waves with 8m wave height and a ship speed of 15 knots. Similarly, the value of the fourth harmonic was 32% of the first harmonic values when the ship encountered a 5m regular wave with 22 knots speed. On comparison of the rigid body response in irregular seas, the hydroelastic loads resulted in 49% increase in the maximum value of the vertical bending moment.

The evaluation of structural responses is key element in the design of ships and offshore structures. Fundamental to this is the determination of the design loads to support the Rule requirements and for application in direct calculations. To date, the current design philosophy for the prediction of motions and wave-induced loads has been driven by empirical or first-principles calculation procedures based on well-proven applications such as ship motion prediction programs. In recent years, the software, engineering and computer technology available to predict the design loads imposed on ships and offshore structures has improved dramatically. Notwithstanding, with the stepwise increase in the size and structural complexity of ships and floating offshore installations and the advances in the framework of Rules and Standards it has become necessary to utilise the latest technologies to assess the design loads on new designs. Along the lines of the recommendations from the International Ship and Offshore Structures Committee (ISSC) I.2 on Loads this paper reviews some of the recent advances in the assessment of loads for ships and offshore structures with the aim to draw the overall technological landscape available for further understanding, validation and implementation by the academic and industrial communities. Particular emphasis is attributed on methodologies applicable for the prediction of environmental and operational loads from waves, wind, current, ice, slamming, sloshing and operational factors. Consideration is also given to deterministic and statistical load predictions based on model experiments, full-scale measurements and theoretical methods. © 2013 Elsevier Ltd.

A time domain code based on strip theory is applied to calculate the probability distributions of relative motions and bending moments of a cruise ship in a set of extreme seas. The code includes two levels of complexity. The simpler one combines linear radiation and diffraction forces with nonlinear Froude-Krylov forces, hydrostatic forces and shipping of green water on the bow. Cummins formulation is used to represent the radiation forces. The second approach is a generalization of the first one and, although the formulation is based on the linear assumption (of the radiation forces), the effects of body nonlinearity are considered by a simplified method: the memory functions, infinite frequency added masses and the radiation restoring coefficients are assessed at each time instant as function of the instantaneous wetted surface. A similar procedure is used to calculate the diffraction forces. The code is used to analyze the responses of a cruise ship in a set of extreme sea conditions. The nonlinear radiation and diffraction effects on the responses are analyzed by comparing the “fully nonlinear” results with the numerical predictions assuming linear radiation and diffraction forces. The short term nonlinear responses are represented by empirical probability distributions, obtained from time domain simulations, and the quality of the predictions is assessed by comparing with model tests experimental data.

The present investigation focuses on the motions and global structural loads induced by abnormal waves on a bulk carrier. A nonlinear time domain method based on strip theory is used to predict the ship responses. The results are compared with experimental data obtained at the model scale. The time domain hydrodynamic forces are calculated by convolution of linear memory functions, while nonlinear contributions arise from Froude-Krylov forces, hydrostatic forces and shipping of green water. The time domain simulations are compared directly with experimental records from bulk carrier model tests with in head waves for two Froude numbers. Extreme wave conditions (such as the New Year Wave) previously measured at sea during real storms were replicated both at the seakeeping tank and by the numerical code. The comparison analyses show a good agreement between numerical and experimental with good accuracy.Copyright © 2013 by ASME

In the last years the identification and investigation of critical wave sequences regarding offshore structure responses became one of the main topics in the ocean engineering community. Thereby the area of interest covers the entire field of application spectra at sea — from efficient and economic offshore operations in moderate sea states to reliability as well as survival in extreme wave conditions. For most cases, the focus lies on limiting criteria for the design, such as maximum global loads, maximum relative motions between two or more vessels or maximum accelerations, at which the floating structure has to operate or to survive. These criteria are typically combined with a limiting characteristic sea state (Hs, Tp) or a rogue wave. For the investigation of offshore structures as well as the identification of critical wave sequences, different approaches are available — most of them are based on linear transfer functions as it is an efficient procedure for the fast holistic evaluation. But, for some cases the linear method approach implies uncertainties due to nonlinear response behavior, in particular in extreme wave conditions. This paper presents an approach to these challenges, a response based optimization tool for critical wave sequence detection. This tool, which has been successfully introduced for the evaluation of the applicability of a multi-body system based on the linear method approach, is adjusted to a nonlinear task — the vertical bending moment of a chemical tanker in extreme wave conditions. Therefore a nonlinear strip theory solver is introduced into the optimization routine to capture the nonlinear effects on the vertical bending moment due to steep waves acting on large bow flares. The goal of the procedure is to find a worst case wave sequence for a certain critical sea state. This includes intensive numerical investigation as well as model test validation.

The paper presents experimental results from model tests with a containership advancing in abnormal wave conditions and comparisons with numerical simulations. A nonlinear time domain method based on strip theory is used for the calculation of vertical ship responses induced by abnormal waves. This code combines the linear diffraction and radiation forces with dominant nonlinear forces associated with vertical response arising from Froude-Krylov forces, hydrostatic forces and shipping of green water. The time domain simulations are compared directly with experimental records from tests with a model of a container ship in deterministic waves for a range of Froude numbers. Extreme sea conditions were replicated by the reproduction of realistic abnormal waves like the New Year Wave and abnormal wave from North Alwyn. Head sea condition is considered and the comparisons include the wave elevation, the vertical motions of the ship and the vertical bending moment at midship.Copyright © 2011 by ASME

The paper presents an experimental investigation of the first order and second order wave exciting forces acting on a body of simple geometry subjected to long crested irregular waves. The body is axis-symmetric about the vertical axis, like a vertical cylinder with a rounded bottom, and it is restrained from moving. Second order spectral analysis is applied to obtain the linear spectra, coherence spectra and cross bi-spectra of both the incident wave elevation and of the horizontal and vertical wave exciting forces. Then the linear and quadratic transfer functions (QTF) of the exciting forces are obtained. The QTF obtained from the analysis of irregular wave measurements are compared with results from experiments in bi-chromatic waves and with numerical predictions from a second order potential flow code.Copyright © 2011 by ASME

Martifer Energia is developing a concept of a wave energy converter (WEC) to be used at near shore locations with water depths starting at around 40m. It is a floating device composed of two bodies connected by a one degree of freedom articulation. The energy is extracted at the articulation by a power takeoff system actuated by the relative motion between the bodies. One of the important components of many WECs is the mooring system, since usually the cost is large compared global cost of the device. In this case the WEC will be moored by a spread mooring that allows the device to weathervane with the environmental loads. The paper presents one design solution for the mooring system investigated during the development stage of the concept. It is composed of four hybrid lines, each one with a segment of nylon rope connected to the floating device and a part of chain that contacts with the sea bottom and ends at the anchor. The wave frequency hydrodynamics are first calculated with a frequency domain boundary element method. The nonlinear cable dynamics problem, which is coupled to the slow drift motions of the floater, is solved in the time domain by a finite difference method. The design considers the climatology of the future area of operation of the prototype. Since the loads on the lines depend on the characteristics of the lines themselves, the design solution is obtained iteratively. Appropriate safety factors are considered. The result is the number of mooring lines, their angular separation, length and diameter of each line component.Copyright © 2009 by ASME

The definition of wave induced structural loads for the design of ship structures nowadays is in most cases still based on empirical formulas from classification societies. However, as computers become faster and cheaper, there is a tendency to apply procedures based on direct calculations to define the design wave loads. These procedures rely on models of the hydrodynamics, which are derived from physical and mathematical considerations, together with a proper characterization of the stochastic properties of waves and of ship responses. There are several advantages from using these more advanced methods: eventually the design wave loads will be more accurate and tailored for the specific ship characteristics, novel ship concepts can be assessed while empirical formulas are, in principle, valid for existing ships only, and, besides global structural loads determined by integration along the hull and applied on a resisting transverse section, it is possible to obtain consistent pressures along the hull for finite element calculations, thus including the effects of these pressures on local structural elements. Several procedures have been proposed to calculate the maximum expected wave loads during the ship lifetime, accounting for the stochastic nature of the waves. However, apparently, conditions associated with the encounter of the ship with abnormal waves are not taken into account as the probabilistic models describing the waves do not seem to consider the abnormal waves. An abnormal wave is defined when its height divided by the significant wave height of the sea state is larger than 2. There are some reports from accidents that stated that the accidents resulted from the encounter of the vessels with waves that were much larger than those expected from the existing sea state. It is also believed by some authors that such abnormal waves were responsible for the mysterious vanishing of some ships. For this reason Faulkner and Buckley 1 suggested that the methods to determine the design loads should be revised to account for the effects of the abnormal waves on the ship structure. Existing calculation procedures do not consider abnormal wave conditions.

Moored ship behavior inside harbors and, therefore, the operational and security conditions at a port terminal does not have a straightforward relationship with local environmental conditions. Due to the diversity and complexity of the phenomena involved it is important to use a methodology that combines physical model tests with numerical simulations, taking advantage of potential synergies. Results of prototype measurements are also a key element to making the validation and calibration of both physical and numerical models possible. This paper focuses on studying the behavior of moored tankers using combined methodology. Aspects related with the inclusion in the numerical models of shallow water effects, non-linear characteristics of mooring lines and fenders, the influence of harbor boundaries and viscous damping are analyzed and discussed. The role of physical modeling as a tool to address/quantify some of the conditions and to provide data for the calibration of numerical models is presented, as well as the methodology defined for the study of the operational conditions at an existing berth. This methodology includes the development of a computer vision system to measure ship motion at the port terminal (prototype). Actual operational conditions at the berth are also described in the paper.Copyright © 2008 by ASME

The paper studies the hydrodynamic interactions between two bodies in close proximity oscillating on the free surface due to incident harmonic waves, inspired in the problem of offloading from a LNG floating platform to a tanker. It deals with a modified Wigley hull and a rectangular barge arranged side by side. The numerical results include hydrodynamic coefficients, exciting forces, absolute motions, and drift forces, and they are compared with published experimental data followed by further analysis of the effects of free surface elevation between the two bodies. The calculations are carried out with the WAMIT® code, which is based on a panel method, or boundary integral method.Copyright © 2008 by ASME

Wave drift forces acting on floating wave energy converters (WEC) are often the most important loading component for the design of the mooring system. On one hand these forces may be, at least, one order of magnitude larger than wind and current forces, and on the other hand the floating structure and mooring system may respond dynamically to the slowly varying wave drift forces. The paper presents an analysis of the wave drift forces on an articulated floating wave energy converter. Particular attention is given to the effects of the wave energy extraction on the time history of the horizontal drift forces. The hydrodynamic calculations are carried out by a frequency domain Green function panel method, resulting on the transfer function of the WEC motions as well as the transfer function of the mean drift forces. The power takeoff system is represented by a simple linear model where the extracted power is related to the relative velocity in the articulation and the damper of the PTO. With the transfer function of the mean drift forces, the variance spectrum of these same forces is calculated for stationary irregular seastates, and finally time histories of the drift forces are produced for typical operational conditions.Copyright © 2008 by ASME

The paper presents a systematic study of the structural loads induced by abnormal waves on a FPSO. This work is a follow-up of a previous investigation that explored the possibility of using freak, abnormal or episodic waves as additional wave load conditions to be considered in the design of ships and offshore platforms. In the previous work, a procedure was developed and implemented to adopt deterministic time series of wave elevation, which may include abnormal waves, as reference design conditions to calculate the wave induced structural loads on ships. An application example was presented for a FPSO subjected to the well known New Year Wave trace that was measured during a severe storm in Central North Sea. In the present paper, the same procedure is applied to obtain the wave induced structural loads on a FPSO, but a systematic investigation is carried out by using a large set of wave traces. These wave traces have been measured at different occasions in the North Sea, additionally at one location in the Central Gulf of Mexico, and they all include episodic freak waves. In this way it is possible to assess the influence of realistic rogue wave characteristics on the wave induced structural loads. Finally, and based on the platform responses to all wave traces, some statistics are produced, regarding the platform responses and structural loads induced by rogue waves.Copyright © 2005 by ASME

The increasing numbers of reported rogue waves with extreme crest and wave heights and unusual group pattern with the consequence of severe damages raise the question if such exceptional events have to be considered routinely for the design of ships and offshore structures. For the investigation of the effects of rogue wave impacts time domain simulation methods are required in addition to traditional frequency domain methods which may not be sufficient to consider these extreme events. In this paper the vertical bending moments at the midship section of an FPSO are investigated using state of the art numerical simulation tools in combination with experiments. For the seakeeping tests the extremely high New Year Wave (registered in the North Sea) is generated in the wave tank, and motions and structural forces are analyzed at model scale. For validation the results are evaluated deterministically and compared to numerical simulations. The time domain calculation allows to artificially change local wave characteristics. The steepness of the selected rogue wave is varied and the influence on wave induced loads is studied. A comparison with standard procedures of seakeeping analysis and classification rules closes the paper.Copyright © 2004 by ASME

The paper presents the results of an experimental investigation of the shipping of water on the bow of a containership. Model tests were carried out in head regular and irregular waves of large amplitude, and measurements were taken of: the absolute and relative motions, the structural loads, the height of water and the impact pressure on the deck, and the horizontal impact pressure and total force on the first line of containers on the bow.Copyright © 2003 by ASME

The paper presents a methodology to calculate the seakeeping performance of ships, which is given as an operability index, and discusses the sensitivity of the results to the use of different seakeeping criteria. The calculation of the operability index, which represents the percentage of time during which the ship is operational, depends on the wave climate of the ocean area where the ship operates, the dynamic response of the ship to the waves, and the ship mission. The relation between the ship operability and the mission characteristics is established through the seakeeping criteria. The calculation of operability indexes and the sensitivity analysis are carried out for a containership operating in the North Atlantique between Europe and the United states, and a fishing vessel operating near the Portuguese west coast. These are two ships with different mission profiles, which permits assessment of the sensitivity of the estimated operability index to different ship types.Copyright © 2002 by ASME

The seakeeping performance of fishing vessels is related to some critical values of motion related variables. The motions and accelerations of fishing vessels of different size and type are assessed using linear strip theory methods. Their response to irregular sea states is determined by the special approach and short- term and long-term predictions are made of their seakeeping performance in the coastal seas of Faro. Sines and Figueira da Foz in the Portuguese coast as well as for the seas offshore Portugal.

This paper presents the results of an experimental program carried out with a model of a FPSO (Floating Production, Storage and Offloading) unit moored and subjected to incoming waves. In regular waves, a wide range of wavelengths were tested and the effect of the wave amplitude was also investigated. In irregular waves the model was subjected to different sea states, including very severe significant wave heights. The measured responses include the six degrees of freedom absolute motions, relative motions, and the mooring forces. The experimental data of surge, heave, and pitch is compared with calculated results from a Green’s function panel method and a strip theory program. In general, the agreement between experimental and numerical data is very good. DOI: 10.1115/1.1951774

the design of the ship structures is mostly based onempirical design rules. However, as the computational resourcesbecome faster and cheaper, there is a growing tendency to applymore procedures based on direct calculations. These are based onhydrodynamic calculation of structural wave-induced loads to-gether with a proper stochastic characterization of the ocean wavesand of the induced ship responses. The ship structural strength willdepend on the expected extreme wave-induced hull-girder loadingduring its operational lifetime.In the case of linear hydrodynamic loads, the expected maxi-mum structural loads in irregular seaways can be calculated by lin-ear potential methods in the frequency domain and peak valueRayleigh distributions for Gaussian processes (e.g., Fukuda 1967,Guedes Soares & Moan 1991). However, it is known that at leastships with fine forms, or small block coefficients, respond nonlin-early to the waves. For these ships the vertical structural loads arehighly asymmetric with sagging peaks presenting larger magni-tudes than the hogging peaks. Thus, the conventional linearstochastic procedure cannot in principle be applied. Design nonlin-ear wave structural loads must be calculated by time domain non-linear codes together with appropriate extreme value distributions.Fully nonlinear methods are under development to solve thefully nonlinear three-dimensional boundary value problem, eitherassuming inviscid flow (Subramani & Beck 2000) or using Navier-Stokes Reynolds averaged solutions (Xing et al 2001). However,complete solutions have not yet been achieved. The numericalcomplexity and computational effort are enormous, and it is notforeseen that such methods will be used for practical applicationsin the medium-term future.The alternative is to apply partially nonlinear methods that in-corporate the assumed most relevant nonlinear contributions forthe ship responses. Several of these simplified nonlinear methodshave been proposed, which may be based on strip methods (Xia &Wang 1997, Fonseca & Guedes Soares 1998a) or panel methods(Lin et al 1996, Huang & Sclavounos 1998). However, these typesof procedures must be validated against experimental results.The International Ship and Offshore Structures Congress (ISSC)2000 Committee VI.1 on Extreme Loads (Jensen et al 2000) reportsthe recent developments on nonlinear seakeeping methods and

The Portuguese sailed yearly on the India Route during over two centuries, between the early XVI century and the XVIII century. Most ships employed in this route belonged to the Nau type and were among the largest and strongest ships of their time. Although extremely interesting, there is presently very little knowledge about the technical characteristics of these ships. The reason is that they were built in a pre-industrial era when technical design and documentation procedures almost did not exist. The method that is presently being applied by the authors to investigate the technical characteristics of these ancient ships combines the analysis of archaeological remains, the interpretation of contemporary texts on shipbuilding and modern Naval Architecture techniques. The paper starts by describing the ship wreck discovered recently at the mouth of the Tagus River, known as the Pepper Wreck, which was identified as the Portuguese ship Nossa Senhora dos Martires, lost in this place on its return voyage from Cochim, in India, on September 14, 1606. This is the first significant ship wreck of a Portuguese Nau comprehensively excavated and analyzed by Nautical Archeologists and in fact the resulting data made possible the study presented here. Based on the analysis of the archaeological remains and on contemporary texts, including Portuguese shipbuilding treatises, a reconstruction of the lines plan and rigging is proposed, as well as the lightweight and cargo distribution on board. The cargo spaces resulting from the reconstruction of the hull are evaluated using ancient tonnage measurement techniques and modern Naval Architecture techniques to evaluate the cargo capacity of the ship. The intact floatability and stability of the ship are also investigated and compared with a modern stability criterion appropriate for large sailing vessels.