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A method for the reconstruction of nonlinear ocean surfaces is presented and applied to regular waves. From random samples of surface elevation, the method reconstructs the nonlinear features of the observed waves by means of the High-Order Spectral approach. The reconstructed surface is then propagated to provide a prediction at a later time. The agreement of the reconstructed and predicted surfaces with the reference one is quantified for a wide range of wave steepness. In each case, the accuracy of the surface elevation and surface velocity potential is evaluated for the first-, second- and third-orders of nonlinearity, while the reference surface corresponds to a fourth-order solution. This way, the improvement of the solution pertaining to each order of nonlinearity can be easily identified. The results show that the grid-based method is able to correctly reconstruct highly nonlinear regular waves, providing an accurate initial solution for the surface propagation. Due to the effect of the nonlinear dispersion, it is further shown that the third order of nonlinearity is necessary to obtain an accurate reconstruction/prediction of steep waves.

Günther F. Clauss is one of the most influential and distinguished international experts in the field of ocean engineering. With 50 years of activities in the field, often in collaboration with national and international colleagues, he has contributed significantly to the visibility and progress of ocean engineering as a research discipline. In his scientific contributions, he has repeatedly established new ideas and set standards. His research contributions include the design, installation and decommissioning of offshore structures, the analysis of loads and motions on floating structures and ships, the development of SAR and oil spill response systems and deep-sea technology. Across all areas, from fundamental to application driven research, one topic always stood out — the investigation, simulation and experimental modelling of natural waves aiming at a comprehensive deterministic analysis of offshore structures and ships in natural sea states and extreme waves. From linear superposition of regular waves to the generation of highly nonlinear wave phenomena, from wave-structure interaction to marine oil spill response technologies this paper attempts the almost impossible task: to deliver an overview over 50 years of research by highlighting selected topics, telling the story of Günther F. Clauss who has conquered the inner space.

Climate change provides for a stronger wave climate and the open water area in this region will increase. The increase in open water area allows for an increase in higher energy surface waves than previously. In addition, human activities are much more complex in this zone, called Marginal Ice Zone, compared to the open ocean, so that there is an increased research interest in the physical processes of wave-ice interaction and the resulting statements on the influence on maritime technology. This work deals with the development of an efficient simulation environment for the 2D wave-ice interaction on the finite platform LS-DYNA. The numerical model based on the coupled ICFD and implicit structural solvers of LS-DYNA. The motion behavior and the mechanical behavior of the ice floe due to the interaction with different waves are investigated. The stronger wave climate in the Marginal Ice Zone intensifies, making the waves more energetic and increasing the wave steepness. The results of the simulation clearly show that larger wave steepnesses have a large influence on the mechanical stress in the ice floe and the deflection increases. These mechanical stresses lead in the critical cases to a fracture of the ice floe into several smaller ice floes. Consideration of the ratio of ice floe length to wave length showed that the smaller the ratio, the larger the heave and surge movements of the ice floe induced by the waves.

This paper explores the applicability of machine learning techniques for the generation of tailored wave sequences. For this purpose, a fully convolutional neural network was implemented for relating the target wave sequence at the target location in time domain to the respective wave sequence at the wave board. The synthetic training and validation data were acquired by applying the high-order spectral (HOS) method. The HOS method is a very accurate method for modeling non-linear wave propagation and its numerical efficiency allows the generation of large synthetic data sets. The training data featured wave groups of short duration based on JONSWAP spectra. The sea state parameters wave steepness, wave period and enhancement factor were systematically varied. At the end of the training process, the trained models were able to predict the wave sequences at the wave board based on the time series of the target wave defined for a specific target location in the wave tank. The accuracy of the trained models were evaluated by means of unseen validation data. In addition, the predictive accuracy of the trained models was compared with the classical linear transformation approach.

The interaction of waves and ice is of significant relevance for engineers, oceanographers and climate scientists. In-situ measurements are costly and bear uncertainties due to unknown boundary conditions. Therefore, physical laboratory experiments in ice tanks are an important alternative to validate theories or investigate particular effects of interest. Ice tanks use model ice which has down-scaled sea ice properties. This model ice in ice tanks holds disadvantages due to its low stiffness and non-linear behavior which is not in scale to sea ice, but is of particular relevance in wave-ice interactions. With decreasing stiffness steeper waves are required to reach critical stresses for ice breaking, while the non-linear, respectively non-elastic, deformation behavior is associated with high wave damping. Both are scale effects and do not allow the direct transfer of model scale test results to scenarios with sea ice. Therefore, the alternative modeling approach of Model Ice of Virtual Equivalent Thickness (MIVET) is introduced. Its performance is tested in physical experiments and compared to conventional model ice. The results show that the excessive damping of conventional model ice can be reduced successfully, while the scaling of the wave induced ice break-up still requires research and testing. In conclusion, the results obtained are considered a proof of concept of MIVET for wave-ice interaction problems.

Model ice testing is the state of the art validation and testing method for ships and structures interacting with ice. Its initial design objective was the prediction of resistance forces of ice breaking ships by using Froude and Cauchy similitude to account to the most significant force ratios. In the ice breaking process the forces due to downward bending are considered most significant and therewith much emphasis was spent on the correct scaling of the bending strength or flexural strength of the model ice. Recent research on the mechanical behavior of model ice shows a significantly higher compliance in downward bending than targeted when following the applied scaling laws. This can lead to scale effects in the resistance force also when testing ice breaking ships. The too compliant ice facilitates an additional ride-up of the ship onto the ice and the vertical motions manifest as additional resistance contribution. The low compliance of model ice also imposes uncertainties on wave-ice interaction tests, which gain increasing significance due to the climatic changes in Polar regions. The modeling of ice break-up due to waves, with the current standard model ice, requires much steeper waves than in full scale as the ice surface needs to experience a much higher deflection to reach the critical failure stress. A similar issue arises for vertical structures exposed to drifting ice. In full-scale a pile-up of ice around the structure is observed and in the contact area so called high-pressure zones may form. Such effects cannot be modeled with classic model ice as it easily bends downwards and produces a failure pattern and failure process very different from full-scale as well as high-pressure zones do not form which is due to the string property gradient in model ice. The mentioned three scenarios are considered being highly relevant in marine research and for the marine industry and therefore this paper introduces two new model ice types with which those scenarios can be modeled. The ‘model ice of virtual equivalent thickness’ uses a different modeling approach to reach a scaled stiffness for improved modeling of waves in ice and ships’ resistance in thicker ice. The ‘wave model ice’ is modeled by using waves in the formation process and can resemble high-pressure-zones acting on a vertical structure. Both methods are considered as an extension to the existing standard model ice for dedicated scenarios by scaling or putting emphasis on different ice properties by altering the production process. The presented approach also emphasizes case-based-scaling, which means that the scaling or the model ice type needs is defined by the modeled scenario as the standard model ice is obviously not fully capable to reflect all properties of sea ice in scale.

Ocean waves penetrate hundreds of kilometres into the ice-covered ocean. Waves fracture the level ice into small floes, herd floes, introduce warm water and overwash the floes, accelerating ice melt and causing collisions, which concurrently erodes the floes and influences the large-scale deformation. Concomitantly, interactions between waves and the sea ice cause wave energy to reduce with distance travelled into the ice cover, attenuating wave driven effects. Here a pilot experiment in the ice tank at Aalto University (Finland) is presented to discuss how the properties of irregular small amplitude (linear) waves change as they propagate through continuous model sea ice. Irregular waves with a JONSWAP spectral shape were mechanically generated with a very low initial wave steepness to avoid ice break up and maintain a consistent continuous ice cover throughout the experiments. Observations show an exponential attenuation of wave energy with distance. High frequency components attenuated more rapidly than the low frequency counterparts, in agreement with a frequency-cubed power-law. The more effective attenuation in the high frequency range induced a substantial downshift of the spectral peak, stretching the dominant wave component as it propagates in ice.

In view of deterministic ocean wave prediction, we introduce and investigate a new method to reconstruct ocean surfaces based on randomly distributed wave measurements. Instead of looking for the optimal parameters of a wave model through the minimization of a cost function, our approach directly solves the free surface dynamics — coupled with an interpolation operator — for the quantities of interest (i.e., surface elevation and velocity potential) at grid points that are used to compute the relevant operators. This method allows a high flexibility in terms of desired accuracy and ensures the physical consistency of the solution. Using the linear wave theory and unidirectional wave fields, we validate the applicability of the proposed method. In particular, we show that our grid-based method is able to reach similar accuracy than the wave-model parameterization method at a reasonable cost.

This paper was removed at the author’s request on October 22, 2021. Copyright © 2021 by ASME

The data of simultaneous measurements of the surface displacement produced by propagating planar waves in experimental flume and of the dynamic pressure fields beneath the waves are compared with the theoretical predictions based on different approximations for modulated potential gravity waves. The performance of different theories to reconstruct the pressure field from the known surface displacement time series (the direct problem) is investigated. A new two-component theory for weakly modulated weakly nonlinear waves is proposed, which exhibits the best capability among the considered. Peculiarities of the vertical modes of the nonlinear pressure harmonics are discussed. The work was supported by the RFBR projects 19-55-15005 and 20-05-00162 (AK).

Wave characteristics change significantly when the waves propagate in a solid ice field. The damping of the incident waves due to the presence of the ice sheet has a significant impact on the modification of wave propagation and dispersion. In this study the interaction of waves with solid ice are investigated by means of model tests. The objective of the study is to measure wave and ice characteristics and analyze the data regarding wave damping and the change of wave parameters in model ice. The experiments were performed in the ice tank of the Hamburg ship model basin (HSVA) with a set of regular waves with varying wave number and steepness. The surface elevation of the waves is recorded by acoustic and motion capturing measurement devices. By comparing the measurements of the incident open water waves with the waves in ice, the change in terms of wave amplitude and dispersion due to the presence of ice is analyzed. It is shown that once the waves travels through the ice the angular frequency remains unchanged while the wave amplitude exponentially decays, with an increasing decay coefficient at smaller wave length. Furthermore, the dispersion relation in ice, represented by the measured angular frequency and wave number, is consistent with the theoretical dispersion relation.

This paper investigates the question of the existence of nonlinear wave–ice interaction with the focus on nonlinear wave propagation and dispersion of waves. The scope of this investigation is to provide a better understanding of ice and wave conditions required to observe nonlinear wave effects under level ice. Direct numerical simulations of nonlinear waves in solid ice are performed within the weakly nonlinear Schrödinger equation (NLSE) framework, using the theoretical findings from Liu and Mollo-Christensen’s 1988 paper. Systematic variations of wave and ice parameters address the impact of the mechanical ice properties and ice thickness on traveling waves of certain wave lengths. The impacts of parameter characteristics on nonlinear focusing and wave dynamics, as well as possible constraints regarding physical consistency, are discussed. It is presented that nonlinear focusing in level ice occurs theoretically. Hereby, distinctive areas of validity with respect to nonlinear wave focusing are identified within the parameter study, which strongly depends on the material properties of the level ice. The results obtained in the parameter study are subsequently used to investigate wave focusing under level ice. Therefore, an exact solution of the NLSE, the Peregrine breather, is utilized. The analytical solution for level ice is compared to the open water solution and accompanied by direct numerical simulations. These investigations show that nonlinear wave focusing can be predicted under level ice for certain parameters. In addition, the agreement of the direct simulations and the analytic solution verifies the numerical approach for nonlinear waves in solid ice.

Soliton and breather solutions of the nonlinear Schr\"odinger equation (NLSE) are known to model localized structures in nonlinear dispersive media such as on the water surface. One of the conditions for an accurate propagation of such exact solutions is the proper generation of the exact initial phase-shift profile in the carrier wave, as defined by the NLSE envelope at a specific time or location. Here, we show experimentally the significance of such initial exact phase excitation during the hydrodynamic propagation of localized envelope solitons and breathers, which modulate a plane wave of constant amplitude (finite background). Using the example of stationary black solitons in intermediate water depth and pulsating Peregrine breathers in deep-water, we show how these localized envelopes disintegrate while they evolve over a long propagation distance when the initial phase shift is zero. By setting the envelope phases to zero, the dark solitons will disintegrate into two gray-type solitons and dispersive elements. In the case of the doubly-localized Peregrine breather the maximal amplification is considerably retarded; however locally, the shape of the maximal focused wave measured together with the respective signature phase-shift are almost identical to the exact analytical Peregrine characterization at its maximal compression location. The experiments, conducted in two large-scaled shallow-water as well as deep-water wave facilities, are in very good agreement with NLSE simulations for all cases., Comment: (14 pages, 12 figures)

A highly efficient numerical procedure for the computer based prediction of nonlinear deep water ocean surface waves is presented. To reconstruct consistent initial conditions from measured surface elevation data, the approach employs a combination of a high order spectral method with Krylov subspace techniques. Aiming at prediction horizons of a few minutes, the method allows real-time prediction of sea states for domains of several square kilometres. Taking the nonlinearity of the wave evolution equations into account leads to a substantial increase in accuracy of the prediction at only moderate additional cost.

This paper explores the applicability of envelope soliton solutions of the non-linear Schrodinger-type equation as an innovative design wave for wave–structure interaction investigations. The major benefits of envelope solitons are the potential to generate non-linear wave groups of certain frequency and (physically possible) wave steepness as well as the availability of an analytical solution. Furthermore, the fact that envelope solitons are characterized by a limiting frequency bandwidth enables the tailor-made generation of critical wave conditions for task-specific wave–structure investigations. For the evaluation of the applicability of envelope solitons, wave–structure investigations with a chemical tanker were performed in a set of envelope solitons at certain frequencies and wave steepness. The applicability of envelope solitons as design waves as well as their impact on the chemical tanker are compared to classical design wave concepts and tailored extreme wave events. For the extreme wave events, the Peregrine breather solution and a real world abnormal wave reproduction, the famous ‘New Year Wave’, were selected. The investigations comprised model tests as well as numerical simulations. Altogether, this paper shows that envelope solitons are excellent design waves for extreme response investigations suitable for model tests as well as numerical investigations.

This paper presents the transient wave packet (TWP) technique as an efficient method for wave–ice interaction experiments. TWPs are deterministic wave groups, where both the amplitude spectrum and the associated phases are tailor-made and manipulated, being well established for efficient wave–structure interaction experiments. One major benefit of TWPs is the possibility to determine the response amplitude operator (RAO) of a structure in a single test run compared to the classical approach by investigating regular waves of different wave lengths. Thus, applying TWPs for wave–ice interaction offers the determination of the RAO of the ice at specific locations. In this context, the determination of RAO means that the ice characteristics in terms of wave damping over a wide frequency range are obtained. Besides this, the wave dispersion of the underlying wave components of the TWP can be additionally investigated between the specific locations with the same single test run. For the purpose of this study, experiments in an ice tank, capable of generating tailored waves, were performed with a solid ice sheet. Besides the generation of one TWP, regular waves of different wave lengths were generated as a reference to validate the TWP results for specific wave periods. It is shown that the TWP technique is not only applicable for wave–ice interaction investigations, but is also an efficient alternative to investigations with regular waves.

The environment in cold regions undergoes significant changes that manifest in rising temperatures and melting ice caps. These processes allow access to new areas for shipping and the installation of structures. However, the occurring changes are not solely a reduction of ice, but also waves increasingly occur in cold regions contributing to ice break up in the Marginal Ice Zone (MIZ) and the transport of ice towards the open sea. Much work has been done to combine the single topic disciplines: wave-hydrodynamics, ice mechanics and structure mechanics to wave-structure (WSI) and ice-structure interaction (ISI). The changing environment in cold regions and the increased wave activity form a new combined discipline: wave-ice-structure interaction (WISI). This paper addresses existing knowledge gaps of the future loading scenario WISI that need to be addressed in engineering to ensure safety for future operations in Polar Regions. The knowledge gaps however, do not only refer to the discipline interfaces, i.e. challenges in combining them, but also to knowledge gaps within them. Wave statistics and the cross-effect between wave and ice are widely unknown which limits the definition of a design wave-scenario. Structures in such environments are exposed to subzero temperatures and neither their impact on properties nor on fatigue life is fully understood. While most phenomena of these two disciplines and their implementation into numerical models are established the ice mechanics appear as the weakest link. Ice is a complex material and not all aspects of its mechanical behaviour are understood and if – the implementation into (numerical) models has not been successful yet. Ice pieces that are energetically charged by waves and collide with structures at high velocities and for such high impact loads the governing ice mechanics are hardly covered by the state of the art or not at all.

This paper investigates the fundamental question of nonlinear wave-ice interaction under level ice focusing on nonlinear wave propagation and dispersion of waves. Therefore, numerical investigations are performed to verify theoretically if nonlinearity takes place under level ice and if this can lead to intense wave events far away from the ice edge in order to provide an explanation for observed real-world ice break-ups. Therefore, nonlinear wave-ice interaction as well as the impact of the ice characteristics on this interaction will be investigated. The direct numerical simulations of the nonlinear wave propagation under solid ice are performed within the Nonlinear Schrödinger Equation (NLSE) framework. The Peregrine breather solution is applied to represent exact solutions of the NLSE for a nonlinear wave group. The application of such a nonlinear wave group is predestined for the verification of occurring nonlinear wave-wave interaction below the ice sheet. For the definition of wave and ice parameters in the simulation setup, the results of the presented parameter study are used. The parameters are analyzed regarding relevant characteristics of nonlinear wave-ice interaction and wave propagation. By assuming constraints with respect to physical consistency, the parameter range for the NLSE simulations can be narrowed. The scope of this investigation is to provide a better understanding of the ice conditions required to observe nonlinear wave effects under level ice.

The applicability of the High-Order Spectral Method (HOSM) as a very fast non-linear method for deterministic short-term wave prediction is discussed within this paper. The focus lies on the systematic experimental validation of the HOSM in order to identify and evaluate possible areas of application as well as limitations of use. For this purpose, irregular sea states with varying parameters such as wave steepness and underlying wave spectrum are addressed by numerical simulations and model tests in the controlled environment of a seakeeping basin. In addition, the influence of the propagation distance is discussed. For the evaluation of the accuracy of the HOSM prediction, the surface similarity parameter (SSP) is utilized, allowing a quantitative validation of the results. The results obtained are compared to linear wave prediction to discuss the pros and cons of a non-linear deterministic short-term wave prediction. In conclusion, this paper shows that the non-linear deterministic wave prediction based on HOSM leads to a substantial improvement of the prediction quality for moderate and steep irregular wave trains in terms of individual waves and prediction distance.

Human Capital Management setzt sich zum Ziel, den Wert des Humankapitals im Unternehmen festzustellen und durch geeignete Masnahmen zu steigern. Vor allem vor dem Hintergrund des demografischen Wandels und dem damit verbundenen Wettbewerb um die besten Spezialisten und Fuhrungskrafte gewinnt diese spezielle Sichtweise des Personalmanagements vermehrt an Bedeutung. Dieser Beitrag zeigt, wie IT-Systeme (sog. Personalinformationssysteme) Prozesse und Masnahmen des Human Capital Managements unterstutzen sowie effizienter und effektiver machen konnen. Hierzu werden drei exemplarische Einsatzgebiete von Personalinformationssystemen dargestellt: Erstens wird gezeigt, wie mobile Smartphone-Applikationen den Prozess der Kompetenzerfassung beschleunigen und durch den orts- und zeitunabhangigen Zugriff auf notwendige Funktionen die Validitat der Ergebnisse verbessern sowie Tablet-basierte Applikationen die Qualitat von Mitarbeitergesprachen erhohen konnen. Zweitens wird erlautert, wie unternehmensinterne soziale Netzwerke genutzt werden konnen, um das Humankapital des Unternehmens effektiver einzusetzen, indem bspw. das Auffinden von Experten oder das Finden von Kandidaten fur vakante Stellen erleichtert wird. Drittens wird aufgezeigt, inwiefern Entscheidungsunterstutzungssysteme dazu genutzt werden konnen, die Effizienz und Effektivitat des Nachfolgemanagements zu verbessern. Hierdurch werden sowohl eine passendere Auswahl von Nachfolgekandidaten ermoglicht als auch eine zielgerichtete Entwicklung der Mitarbeiter in Bezug auf zukunftig benotigte Kompetenzen angestrebt. Abschliesend werden weitere aktuelle Forschungsfelder, wie bspw. Smart HRM oder Mobile und Micro Learning kurz beschrieben.

The precise knowledge of loads and motions in extreme sea states is indispensable to ensure reliability as well as survival of ships and floating offshore structures. In the last decades, several accidents in severe weather with disastrous consequences have shown the need for further investigations. Thus, within the framework of the project “Handling Waves” funded by the European Union, ship responses and structural loads are systematically investigated. The investigations address the impact of freak waves on the total load considering three different types of ships. The focus lies on the determination of the influences of bow flare and freeboard height on the global loads. The study comprises systematic investigations in a tailored real world sea state with embedded freak wave accompanied by tests in high and steep regular waves. It is shown that large bow flares and freeboard heights contribute significantly to the vertical bending moment.

This paper discusses the potential of deterministic wave prediction as one basic module for decision support of offshore operations. Therefore, methods of different complexity&mdash, the linear wave solution, the non-linear Schr&ouml, dinger equation (NLSE) of two different orders and the high-order spectral method (HOSM)&mdash, are presented in terms of applicability and limitations of use. For this purpose, irregular sea states with varying parameters are addressed by numerical simulations as well as model tests in the controlled environment of a seakeeping basin. The irregular sea state investigations focuses on JONSWAP spectra with varying wave steepness and enhancement factor. In addition, the influence of the propagation distance as well as the forecast horizon is discussed. For the evaluation of the accuracy of the prediction, the surface similarity parameter is used, allowing an exact, quantitative validation of the results. Based on the results, the pros and cons of the different deterministic wave prediction methods are discussed. In conclusion, this paper shows that the classical NLSE is not applicable for deterministic wave prediction of arbitrary irregular sea states compared to the linear solution. However, the application of the exact linear dispersion operator within the linear dispersive part of the NLSE increased the accuracy of the prediction for small wave steepness significantly. In addition, it is shown that non-linear deterministic wave prediction based on second-order NLSE as well as HOSM leads to a substantial improvement of the prediction quality for moderate and steep irregular wave trains in terms of individual waves and prediction distance, with the HOSM providing a high accuracy over a wider range of applications.

International audience; A series of laboratory experiments related to Kuznetsov-Ma breather solution have been performed in a seakeeping wave tank with different initial wave steepness and intermediate water depths. Analysis of the experimental results reveals that the maximum wave height in Kuznetsov-Ma breather solution is normally accompanied with a large crest amplitude, which can be largely reduced with the decreasing water depth due to the slower modulational process and the limited length of wave tank, regardless of the initial nonlinearity. The laboratory observations can be accurately simulated by the high-order spectral model (HOS) if the initial Benjamin-Feir index is not very large as a result of weak nonlinearity and/or decreased water depth. Numerical studies also indicate that in the evolutionary process the amplitude of carrier wave will decrease sharply and a peak frequency downshifting can be detected. If the evolutionary time scale is long enough, the spectrum will eventually evolve into a continuous one with the energy relocated in the lower wave frequency part. For Peregrine breather solution that is a particular case of Kuznetsov-Ma solution, it is found that in some cases a specific phase shift of the initial condition can lead to a longer distance for the wave group to travel to achieve the first maximum amplitude and a larger amplification factor than that predicted by the theoretical solution.

The investigation of dynamics of intense solitary wave groups of collinear surface waves is performed by means of numerical simulations of the Euler equations and laboratory experiments. The processes of solitary wave generation, reflection from a wall and collisions are considered. Steep solitary wave groups with characteristic steepness up to $kA_{cr} = 0.3$ (where $k$ is the dominant wavenumber, and $A_{cr}$ is the crest amplitude) are concerned. They approximately restore the structure after all the considered interactions. In the course of the interaction with the wall and collisions the maximum amplitude of the wave crests is shown to enhance up to 2.5 times. A standing-wave-like structure occurs in the vicinity of the wall, with certain locations of nodes and antinodes regardless the particular phase of the reflecting wave group. A strong asymmetry of the maximal wave groups due to an anomalous set-up is shown in situations of collisions of solitons with different frequencies of the carrier. In some situations of head-on collisions the amplitude of the highest wave is larger than in over-head collisions of the same solitons. The discovered effects in interactions of intense wave groups are important in the context of mechanisms and manifestations of oceanic rogue waves.

How safe is ‘safe’? During the design phase of floating structures, specifications such as range of application, warranty of economical efficiency and reliability are integral parts of the evaluation process. The key decision is the choice of environmental design conditions to be considered for operation and survival: this issue cannot be solved globally, i.e. different operating conditions (transit, operation, survival) and criteria (body motions, local and global loads) will lead to individual results. In this paper a procedure for the systematic identification of critical (design) wave sequences for offshore structures is presented—a response based identification tool for critical wave sequence detection. The basic principle of this procedure is characterized by tailoring of short wave sequences to obtain a certain maximum response. The fully automated procedure combines wave/structure interaction analysis programs with an optimization algorithm. The objective is to find a critical wave sequence with respect to the predefined maximum responses. By means of this procedure, the identification and evaluation of critical design conditions can be conducted more systematically, accurately and thus efficiently. To demonstrate the broad scope of this procedure, a typical example is presented. The results obtained are reviewed against classical design methods. The investigations comprise numerical calculations as well as model test validations.

We observe the dispersive breaking of cosine-type long waves [Phys. Rev. Lett. 15, 240 (1965)] in shallow water, characterizing the highly nonlinear ``multisoliton'' fission over variable conditions. We provide new insight into the interpretation of the results by analyzing the data in terms of the periodic inverse scattering transform for the Korteweg--de Vries equation. In a wide range of dispersion and nonlinearity, the data compare favorably with our analytical estimate, based on a rigorous WKB approach, of the number of emerging solitons. We are also able to observe experimentally the universal Fermi-Pasta-Ulam recurrence in the regime of moderately weak dispersion.

Mittlerweile fuhren zahlreiche Softwareanbieter mobile Anwendungen fur das Personalmanagement in ihrem Produktportfolio. Auf Basis einer strukturierten Marktanalyse beinhaltet dieser Artikel einen Uberblick uber mobile Softwarelosungen zum Unterstutzen von HR-Prozessen. Des Weiteren wurden entsprechende Softwareanbieter hinsichtlich Rahmenbedingungen, Nutzen und Grenzen fur einen Einsatz dieser Losungen im Unternehmen interviewt. Die aus den Interviews gewonnen Erkenntnisse bieten zusammen mit dem erstellten Marktuberblick eine Informationsgrundlage fur Unternehmensvertreter bezuglich der Einsatzmoglichkeiten mobiler Anwendungen fur Prozesse des Personalmanagements.

Seit einigen Jahren etablieren sich Plattformen fur die Vergabe von Privatkrediten ohne Einbindung eines Kreditinstituts als Finanzintermediar. Auf diesen Peer-to-Peer(P2P)- Banking-Plattformen werden die Kreditfinanzierungen den aktiven Communitys uberlassen. Die Zusammenfuhrung von Kreditnachfragern und - anbietern kann durch Community-orientierte Funktionen, beispielsweise Freundeslisten und Awarenessfunktionen, unterstutzt werden. Der Beitrag charakterisiert ausgewahlte Plattformen im Hinblick auf die Verwendung von Social-Networking-Service(SNS)- Funktionalitaten. Es wird gezeigt, dass SNS-Funktionen unter Umstanden Nutzerinteraktivitat und Plattformakzeptanz steigern konnen und daraus wiederum mehr Kreditvolumen generiert werden kann.

In the past years the existence of freak waves has been affirmed by observations, registrations, and severe accidents. One of the famous real-world registrations is the so-called “New Year Wave” recorded in the North Sea at the Draupner jacket platform on January 1, 1995. Since there is only a single point registration available, it is not possible to draw conclusions on the spatial development in front of and behind the point of registration, which is indispensable for a complete understanding of this phenomenon. This paper presents the temporal and spatial development of the “New Year Wave” generated in a seakeeping basin. This extreme sea state is measured at different locations in the tank, in a range from 2163 m (full scale) ahead of to 1470 m behind the target position—520 registrations altogether. The focus lies on the detailed description of a possible evolution of the “New Year Wave” over a large area. The group velocity, wave propagation and energy flux of this wave group as well as the wave kinematics and dynamics are analysed. As a case study a Ro/Ro vessel has been investigated in the “New Year Wave”, with special emphasis on the vertical bending moment.

Befragungen zeigen, dass sich IT- und Human-Resource-(HR-)Verantwortliche durch eine Auslagerung von HR-Anwendungssystemen auf externe Software-as-a-Service-(SaaS-)Anbieter Einsparungen von Betriebs- und Wartungskosten sowie eine Steigerung der Systemflexibilitat versprechen. Bevor eine Entscheidung fur eine SaaS-Auslagerung getroffen wird, bedarf es einer Prufung der grundsatzlichen Eignung von HR-Anwen-dungssystemen. Dafur werden in diesem Artikel einerseits die SaaS-Eignungskriterien Datensensibilitat, Schnittstellenkomplexitat und strategische Relevanz fur diese Systeme operationali-siert. Andererseits werden die Eigenschaften von HR-Referenzsystemen mithilfe dieser Kriterien bestimmt, und es wird daraus eine idealtypische SaaS-Eignung abgeleitet. Die Untersuchung zeigt, dass sich Learning-Management- und Personalabrechnungssysteme sowie mit Einschrankungen Personalbedarfsplanungs-, Personalkostenplanungssowie Test- und Szenariosysteme fur SaaS eignen. Fur weitere HR-Anwendungssys-teme, beispielsweise Personaleinsatzplanungslo-sungen, trifft dies nicht zu. Die groβten Probleme bei einer Auslagerung solcher Systeme stellen dabei sensible, personenbezogene HR-Daten dar, die durch SaaS in heterogenen Fremdsystemlandschaften verarbeitet werden.

For seakeeping model tests and the experimental investigation of offshore operations the water depth is a parameter which is difficult to adjust to a particular problem and scale. It poses a limit for the feasibility of model tests by governing the model scale—especially in small testing facilities. Therefore, it is often desirable to violate or ignore the condition “water depth” and to use larger models in order to carry out tests at higher Reynolds numbers. In this paper its influence is examined in order to clarify how it affects wave kinematics, wave forces, and wave–structure interaction, and where the deep water assumption holds. After a short recapitulation of the water wave theory, a freak wave sequence is presented that has been reproduced at two different wave tanks at scales 1:75 and 1:81 and two water depths. The wave kinematics are approximated with asymmetric high order Stokes waves. The comparison of the computational wave kinematics reveals that moderate water depths are of low importance for extreme waves with identical surface elevations but different water depths. In order to examine the effects regarding wave–structure interaction with regard to seakeeping investigations model tests are conducted at various water depths using the huge semi-submersible crane vessel Thialf. Here, the effect on heave and pitch motion is investigated. The model tests are accompanied by numerical calculations utilizing the panel code WAMIT. A comparison of the hydrodynamic coefficients in deep water with those in decreasing water depths is shown including coupling effects taking into account viscous damping which is determined in experiments. It is shown that for the given scale of 1:75 a water depth of 1 m is sufficient to model deep water conditions.

This paper addresses the Higher Order Spectral (HOS) method as very fast and accurate non-linear method for deterministic wave forecast. The focus of the paper lies on wave propagation, with the objective to draw conclusions on the applicability of the HOS method for deterministic wave forecast. Systematic numerical and experimental investigations are conducted. The investigations comprise exact solutions of the nonlinear Schrödinger equation (NLS) as special non-linear wave groups, which are used as initial conditions for the subsequent simulations. Different parameters such as relative water depth, wave steepness and propagation distance are varied to evaluate the applicability of the HOS method. The results obtained are validated by experiments as well as fully non-linear simulations. It is shown that the HOS method is capable for non-linear wave forecast due to high accuracy and fast calculation time at once.

During the design process of floating structures, different specifications have to be aligned such as the range of application, the warranty of economical efficiency as well as the reliability and are an inevitable integral part of the evaluation process during the design stage. The validation of the performance by means of model tests in terms of sea state behavior and the associated local and global structural loads are an important milestone within this process. Therefore it is necessary to determine an adequate test procedure which covers all essential areas of interest. Thereby one field of interest are limiting criteria of the design such as maximum local and global loads as well as maximum accelerations due to the impact of extraordinarily high waves, at which the floating structure has to survive. Different alternatives are available to conduct model tests in high, steep waves — transient wave packages, regular waves, irregular waves with random phases or more sophisticated deterministic tailored irregular wave sequences such as reproductions from numerical simulations and real-world measurements. This paper introduces a new approach for the systematic investigation of wave/structure interaction in high, steep waves. Exact solutions of the nonlinear Schrodinger equation — the so called breather solutions — are implemented for the generation of extraordinarily high waves. Three types of breather solutions are investigated in the seakeeping basin and to cover the full range of interest, each solution has been used to generate freak waves at certain frequencies. To evaluate the applicability of breather solutions for model tests two types of ships — a LNG Carrier and a Chemical Tanker — are investigated in the seakeeping basin. The ships are segmented and connected with strain gauges to detect the vertical wave bending moment. Furthermore, green water probes are installed on deck to evaluate the local impact on the bow of the freak waves. The obtained results are compared to investigations in regular waves with certain frequency and steepness as well as in real-world freak wave reproductions.

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 existence of freak waves is indisputable due to observations, registrations, and severe accidents. The occurrence of extreme waves, their characteristics and their impact on offshore structures is one of the main topics of the ocean engineering research community. Real sea measurements play a major role for the complete understanding of this phenomenon. In the majority of cases only single point registrations of real sea measurements are available which hinders to draw conclusions on the formation process and spatial development in front of and behind the respective registration points. One famous freak wave is the “New Year Wave”, recorded in the North Sea at the Draupner jacket platform on January 1st, 1995. This wave has been reproduced in a large wave tank and measured at different locations, in a range from 2163 m (full scale) ahead of to 1470 m behind the target position — 520 registrations altogether. Former investigations of the test results reveal freak waves occurring at three different positions in the wave tank and these extreme waves are developing mainly from a wave group. The possible physical mechanisms of the sudden occurrence of exceptionally high waves have already been identified — superposition of (nonlinear) component waves and/or modulation instability (wave-current interaction can be excluded in the wave tank). This paper presents experimental and numerical investigations on the formation process of extraordinarily high waves. The objective is to gain a deeper understanding on the formation process of freak waves in intermediate water depth such as at the location of the Draupner jacket platform where the “New Year Wave” occurred. The paper deals with the propagation of large amplitude breathers. It is shown that the mechanism of modulation instability also leads to extraordinarily high waves in limited water depth. Thereby different carrier wave length and steepnesses are systematically investigated to obtain conclusions on the influence of the water depth on the modulation instability and are accompanied by numerical simulations using a nonlinear potential solver.Copyright © 2011 by ASME