Ebook: Technology and Science for the Ships of the Future

On behalf of the Scientific Committee, I am glad to introduce the proceedings of NAV 2022.

They contain contributions by Italian and European Universities and Research Centres, as well as from Industries and the Italian Navy, covering the most updated subjects in the field of naval, commercial and pleasure crafts.

The papers have been presented in a three-day conference organised by ATENA and held in Genova and La Spezia on 15 to 17 June 2022. After a delay of one year due to the COVID Pandemic it was an excellent return to the tradition of NAV conferences, reaching this year the 20th edition. As known, these events have been organised itinerantly in Italy since as far back as 1980.

The contributions have been selected and reviewed by experts in the relevant fields and are now collected here for your convenience.

Please enjoy the reading!

Enrico Rizzuto

Chairman of the Scientific Committee of NAV 2022

In recent years, green shipping becomes one of the fundamental challenges for the marine industry: the limits imposed on ship emissions by IMO (International Maritime Organization) are increasingly stringent, especially in terms of SOx (sulfur oxides). The installation on board of scrubbers has proved to be a helpful solution to SOx abetment, in particular for the ships already in navigation: it allows to respect the limits imposed by the IMO even with the use of HFOs (Heavy Fuel Oils), so without the need to carry out a complete refitting of the propulsion system. However, such systems, usually installed in the funnels, have large dimensions. The integration between components is the best method to optimize the spaces, facilitating the installation of the scrubbers on board. The present work investigates a combined CFD-FEM (Computational Fluid Dynamics-Finite Element Method) methodology to evaluate the acoustic performances of a model-scale scrubber. Some papers in the literature consider the acoustic properties of SCRs (Selective Catalytic Reduction systems) for marine applications, while a thorough study on scrubbers’ performances is missing. Independent CFD or FEM calculations may evaluate the acoustic properties of the scrubber. However, the combined methodology reduces the computational burden by about 90% compared to the CFD modelling. Moreover, it gives the advantage of considering the influence of flow on acoustic properties, which is impossible for a fully FEM approach

The harvesting of wind energy and its transformation into a thrust force for the ship propulsion is the basics of Wind-Assisted Ship Propulsion (WASP). The concept has been gaining in popularity in the last years due to the expected benefits in emission reduction. To exploit the benefits, a proper integration between the conventional diesel engine-screw propeller propulsion plant and the WASP is mandatory. This paper aims to study the integration of the Flettner rotor technology with a conventional ship propulsion plant with controllable pitch propellers. The method allows to evaluate the engine-propeller working points and, eventually the total ship propulsive power, considering the influence of the rotor and the wind conditions. The total ship power is modelled on the amount of power required to spin the rotor, providing a way to compare hybrid propulsive solutions in terms of fuel consumption and CO2 emissions. A 3000 ton Ro-Ro/Pax ferry has been selected as a case study. Results on the parametric analysis of rotor dimensions and wind conditions are presented. Assuming fixed wind conditions, the effect of the rotor at different ship speeds is shown.

In the field of green shipping the reduction of acoustic noise partially transmitted into water and the need of guarantee high comfort levels are important aspects in the view to agree with the UN 2030 Agenda in respect to life below water and good health and well-being. Both these aspects imply actions to increase absorption and dissipation of vibrational energy radiated towards the hull. To accomplish this effect, viscoelastic materials (VEM) characterized by high levels of damping are commonly used on board ships. In the last times, new strict requirements led to the development of Isocyanate free VEM, so the necessity of a provisional method to investigate in an efficient way new VEM is required. Experimental tests are essential in order to obtain performance indicators (non-standard procedure) or material physical characteristics (Oberst’s beam test, ASTM E756 – 05). The implementation of the usual experimental setup could result rather complicated and it needs a high degree of accuracy, so in the last times finite element methods (FEM) has been increasingly used. Knowing VEM physics parameters allows numerical simulation in both the provisional and the optimization phase to be accurate and reliable. In this paper, an experimental-numerical method is proposed, with the aim of overtake the issues linked to the small-scale traditional cantilever beam test and paving the way to the selection of the most appropriate shape of the specimen. The innovation proposed through this method lies in the evaluation of the VEM complex modulus based on a reverse engineering approach, in which the loss factor estimation, contrarily from the traditional methods, is free from peak sharpness dependence. The proposed procedure is validated by comparison with the traditional method.

Industry 4.0 has favoured the expansion of many technologies where application boundaries are very diffuse. Although some technologies may have very specific applications, there are others much more open. The Shipbuilding Industry is quite traditional, however there are many advantages if the Industry 4.0 technologies could be applied from the beginning of the ship design to autonomous shipping. CAD/CAM tools are used to manage many data that must be considered in advance for the further stages of the ship lifecycle.

Augmented Reality, Virtual Reality and Mixed Reality are closely related to the Digital Twin and interlaced with Big Data, which are generated by CAD tools and all surrounding solutions, which applies some cloud/edge/fog computing to these data in a merged technology between finite-state machines and Artificial Intelligence cognitive processes. To perform all these integrations in an agile manner requires a network which support different connections to add specific devices, i.e. Internet of the Things, which can access to the data, creating and modifying them, in a different layer which affects to the basic information layer created by the CAD/PLM tools in the shipyard and later on being used by the autonomous ships. This network should be secure, but also open to allow distributed work, which must be tracked such that all design or process modifications are recorded an open, transparent, trusted and non-modifiable working method for all stakeholders, like shipyard, engineering offices, classification society and ship owner.

This paper briefly summarizes how Industry 4.0 technologies may be applied to the shipbuilding, whether through direct integration or in connected periphery applications, and its application to autonomous ships.

In the last years, the leisure vessels market had a very positive trend and, every year, more and more ships will be present in our waters. This is giving a push to the demand and needs of increased security, in the protection against theft, and safety, in the protection against losing the mooring while anchored with the risk of having accidents against rocks or other vessels. The ARGOS Solution is offering the capabilities and performance to answer those needs with easy plug-in installation of a device in the boat.

The ARGOS Solution is under development in the frame of the ARGOS (Anti-theft Robust Galileo-based Operational System) project co-funded by the EU Agency for the Space Programme (EUSPA) within its Fundamental Elements funding programme. The ARGOS Solution, leveraging the services provided by Galileo and thanks to its scalable and modular architecture, provides timely alerts in case of theft or risk of losing the mooring of the anchor point. It also provides high robustness against environmental conditions, e.g. multipath, shadowing of the GNSS signals, etc…, and external factors that can be unintentional (e.g. interference sources) or intentional (e.g. jamming or spoofing attacks in order to support a theft attempt).

These differentiating capabilities are based on the new features of Galileo, the European GNSS system, specifically the Open Service Navigation Message Authentication (OSNMA) that will increase the robustness against certain types of spoofing attacks, and the I/NAV Message improvement that will increase the performance of the GNSS signal processing in harsh environments (e.g. ports, natural harbours, etc…). These capabilities are integrated in the solution and improved with an advanced Navigation Engine in the ARGOS device by fusing the GNSS information with data from other on-board sensors (e.g. Inertial Measurement Unit) in order to provide timely alerts with high performance detection of risky conditions.

The International Maritime Organization has formally approved as recommended guidelines the methods and procedures of the Second Generation Intact Stability Criteria (SGISC). These criteria introduce the concept of dynamic stability assessment of ships, defining the failure modes that might occur to a ship that navigates in harsh sea conditions. This paper focuses on the failure mode surf-riding/broaching-to in stern-quartering seas, with the objective of analyzing the characteristics and the potential of SGISC risk assessment in the ship design. The risk-evaluation criteria of surf-riding and broaching were followed through Level 1 and Direct assessment of SGISC. Two different hull designs were considered, a Fast Displacement Ship and a high-speed V-bottom, hard chine hull. Time domain simulations were performed using a time domain potential flow boundary element method. A detailed definition of broaching was used to detect the event occurrence in irregular waves, and the results were compared with failure mode definition of SGISC concerning the roll and lateral acceleration safe limits exceedance. The SGISC were also employed in the attempt to evaluate the different failure mode risk assessment due to different stern appendages configurations of the two hull designs with respect to broaching and surf-riding.

One year later the finalization of Second Generation Intact Stability criteria (SGISc), there is still the need to validate the robustness and consistency of these criteria as indicated by IMO. Not compliance with a stability criterion cannot be always fixed acting only on the vessel design; also operative considerations are needed in order to reduce the risk level during the navigation. After an introduction to SGISc and rule framework for passenger ships, an application will be carried out. A Ro-Ro pax ferry has been selected as subject of this investigation. Vulnerability levels (i.e. Level 1 and Level 2) are applied in order to assess the compliance of a modern representative Ro-Ro ferry. Moreover, a study about how the environmental conditions may affect the results is undertaken considering different scenario, such as the geographical area or the maximum encountered wave height.

A number of seventeen models of Ferry in scale 1: 28.750 of 10250 ton displacement have been built at the Italian Model Basin, to be tested in the Emilio Castagneto towing tank at INM in Rome. The results of the tests have been collected in this report, delivered and presented in easy and useful form.

The maritime transport is guilty for about 2.5% of global greenhouse gases emission, since 940 million tonnes of CO₂ are emitted around every year. Moreover, even though now the 96% of ships can be recycled, current recycling practices cause negative environmental impacts. Indeed, researches carried out on ‘ships graveyard’ showed a concentration of petroleum hydrocarbons 16,793% higher than at the control. Epoxy Fibres Reinforced Composites (FRCs) are sustainable candidates in this field. In fact, having the FRCs structures a light weight, fuel-efficient ships can be built. The global epoxy composites market size was valued at USD 25.32 billion in 2019 and is expected to expand at a compound annual growth rate (CAGR) of 6.2% from 2020 to 2027. In this sense, in the next few years, the market is expected to rapidly replace conventional materials with epoxy composites in several fields, including the marine one. However, concerns about their non-recyclability are rising more and more. In this study, by following a twofold “design for recycling” and “design from recycling” approach the chemical recycling process for thermoset polymer composites developed by Connora Technologies (California, USA) was considered as solution to overcome this issue. Moreover, the adoption of natural fibres, i.e. flax, and bio-based epoxy resin was used as environmentally-friendly solution to even avoid the use of petroleum based raw materials. To follow the first approach, i.e. “design for recycling”, Flax FRCs with bio-epoxy matrices were first produced via hand lay-up with vacuum bagging. Next, they were chemically treated to obtain a recycled thermoplastic (rTP). Then moving on the “design from recycling” approach, a reuse strategy was developed by exploiting the Electrospinning technique and producing electrospun fibers suitable for the interlaminar toughening of composite laminates.

5xxx (Al-Mg) and 6xxx (Al-Mg-Si) series alloys are most commonly used in the marine sector as they can guarantee both a good mechanical behaviour and good resistance to corrosion in the marine constructions. In fact, sea water contains high amounts of chlorides that can cause, after short exposure times, the failure of entire metal structures. Since in a boat there is the coexistence of different materials, it is inevitable that some of them must be welded together. Welds between dissimilar materials often require the use of non-traditional techniques, such as the process of Friction Stir Welding (FSW) and explosion welding. In this work, the resistance to corrosion of FSW joints (AA5083/AA6082) and trimetallic explosion welded joints (AA5083/AA1050/structural steel) combining galvanic coupling and immersion tests with microstructural characterization of corroded regions. In particular the focus of the work is on the corrosion behaviour of thermo-mechanically and nugget zones in FSW joints and on the AA1050/steel interface in the trimetallic joints obtained by explosion welding.

Defense budget are shrinking and human resources are becoming more critical, while operational needs of Warships increase and change in the life cycle to face new threats.

To achieve the best balance between operational availability (Ao) and costs all along the life cycle, the sustainability requires a correct initial definition of the support followed by its continuous optimization, guaranteed by constant monitoring and analysis of the data coming back from the field, by a review of the reliability parameters, maintenance plan and spare parts list.

The ITN (Italian Navy) started a change management initiative from beginning of 2000’ through an optimization process by analysing the return from the field data during the TGS FREMM contract, which has lasted for more than 10 years. This process consist of:

∙ An initial definition of the support: configuration management, obsolescence monitoring, maintenance plans and definition of stocks, optimized with OPUS10 tools, whose models are created starting from the logistic databases provided by the private industry;

∙ The evaluation and analysis of return from the field data: measure of the reached availability, KPIs (Key Performance Indicator) evaluation and reliability calculation, trough assessment software tools (Weibull) and recalculation software (Calypso);

∙ The optimization of support: in terms of operational availability and costs, in compliance with the operational requirements.

After the FREMM experience, ITN is taking over all the activities performed so far by the private companies, for current and future shipbuilding programs (LSS, PPA and LHD).

The authors will go through the process set, tested for FREMM program, will show results after more than 10 years of experience, and will cover all the activities Italian Navy is taking care by itself for new programs, mentioning as well ITN investments and available tools.

The shifting of the neutral axis in the cross section of ship structures is an important result of progressive collapse analyses. The main purpose of the present study is to apply a Deep Neural Network (DNN) method to linear systems and estimate in a relatively short time span the shift of the neutral axis for intact and damaged ships. First, the initial source data related to the intact condition and to several symmetric damaged grounding scenarios of five different vessels (Double Hull Oil Tanker, Single Hull Tanker, 1350TEU Container Vessel, 3500TEU Container Vessel, Bulk Carrier) have been determined with a self-developed code based on the well-established Smith method. With the application of the DNN, the shift of the neutral axis has been predicted for a set of completely new damage scenarios of a ship cross section, demonstrating that the deep neural network approach can estimate the neutral axis performance. The successful prediction obtained within this paper will lead to the DNN’s application for computing the ultimate strength capacity.

THALASSA is a large research project, developed in the field of the naval structures. It aimed at studying innovative solutions of significant impact in increasing environmental sustainability through a weight reduction, a careful production planning and a circular approach to the entire life cycle of the parts, from design to the disposal/recycle/reuse. The project is led by NAVTEC Technological District and it is composed of a large team counting more than 300 researchers of several centres among which the CNR institutes, the Universities of Messina, Palermo, Catania, Roma “La Sapienza”, and Udine. Innovative solutions for industrial processes of greatest interest for some major national shipbuilding operators such as Azimut Benetti and Fincantieri or for shipowner such as Caronte&Tourits have been investigated, and players such as ATRIA have been assisted in the formulation of innovative coatings. The presence of NAVTEC District has allowed to concentrate the field of action on themes of strong industrial interest and at the same time to widen the research action on a number of different topics with a view on the entire product life cycle. The district allowed to network skills, laboratories and resources that individually would not have led to carry out activities on such a high number of variables, in terms of materials and joint types. Several issues have been addressed, by identifying solutions thanks to skills of the industrial players, such as: joining technologies (i.e. etching / texturing laser, clinching, self piercing riveting, co-curing, bonding, friction stir welding); eco and bio-sustainable composite reinforced by natural (i.e. vegetable or mineral) and hybrid fibres; degree of recoverability of traditional or bio-resins; corrosion of conventional metal structures and processes for increasing the useful life; and innovative coatings that are combined with the functional protection needs of the structures.

A numerical model of a dual-chamber Oscillating Water Columns (OWC) Wave Energy Converter (WEC) is built through the DualSPHysics software. This code is based on the Smoothed Particle Hydrodynamics (SPH) model, a Lagrangian meshless method where particles represent the flow, interact with structures, and exhibit large deformation with moving boundaries. A one phase approach – only water - is chosen in order to limit the computing time, as it increases with the total number of particles. The power take-off (PTO) of the system is modeled by the force applied by a vertical linear spring link on a floating plate inside the chamber. The force formula and coefficients are described, discussed, and tuned for various wave states to optimize the model. Validations against experimental data available from previous tests in wave flumes are performed. The floating plate heave of the numerical model is compared with the experimental free surface elevation. The result analyses establish the benefits and limits of DualSPHysics to model a fixed dual-chamber OWC WEC.

The “Autonomous Ship” is the new technological paradigm which is driving the trend for increasing ship automation. In this context, Fincantieri Nextech launched in 2019 the MARIN (Monitoraggio Ambientale Remoto Integrato Navale, Naval Integrated Remote Environment Monitoring system) R&D project, sponsored by Regione Puglia within the framework of “Contratti di Programma”. The objective of MARIN project is to set-up and test at sea a technological demonstrator of the enabling technologies for autonomous navigation. The paper presents a technological overview of the research project and its achievement, including the preliminary results of the 2021 sea tests.

Skin, external surface, coating… Those are words strictly linked to the concept of appearance, which means to be watched, to show, and sometimes to seem: a comparison between being and appearing. From a design point of view, the surface coating is, mainly, an esthetical choice. Nevertheless, sometimes that element has been due to other reasons. During the First World War, painting warships with the dazzle technique allowed them to “hide” from the enemy: the shapes and colours applied to hulls allowed them to appear in different sizes or positions compared to the actual real one. In that case, the skin assumed a vital defensive role. Even if most yachts today do not shine with peculiar external surfaces – if we closed our eyes we could imagine hulls in neutral colours, generally in one or two tones – skin however is a project element with significant potential. Ivana Porfiri commissioned Jeff Koons, acclaimed contemporary artist, to finish the external coat of the Guilty. The skin highlights shapes and formal choices of hull and superstructure, and also takes forward the link between art and yacht design, explicit by the display of art in the interiors. Another example of designed skin is LAP-1 by Francesco Paszkowski Design. Here the external coating was designed with camouflage with shades of blue, a symbolic colour for the Baglietto shipyard, responsible for building the yacht. Finally, browsing the most significant projects, the paper aims to analyse the design and use of external coatings of yachts. The skin project in a nautical context is today mainly linked to aesthetic reasons. Nevertheless, also thanks to the use of new materials, innovative painting, and covering techniques, new possibilities for skin design are envisaged. External coating, colours, textures and hull finishing could meet different and new needs in the energy and environmental field.

The shipping industry is under increasing pressure to comply with new demanding requirements for exhaust gas emissions. Alternative fuels as well as new technologies need to be developed to meet these goals and reduce Green-House Gases (GHG). This paper investigates ammonia as an alternative fuel for the cruise ship market. A focus is given on the regulatory framework (e.g. EU, IMO and Classification Societies) that at present defines requirements for gaseous emissions and design principles of the fuel containment as well as supply systems. Ammonia allows for effective reduction of CO₂ but is potentially toxic for human life and the environment. Due to the innovative nature of ammonia as a fuel, the regulatory approach is based mainly on alternative design instead of prescriptive rules. A case – study, with Internal Combustion Engine ICE (Dual-Fuel) and Propulsion Electric Motors (PEM) as selected standard propulsion system, has been carried out to investigate the impacts of ammonia as fuel on a large passenger ship. The purpose is to evaluate the variation of navigation autonomy, arrangement and weights/stability, considering also specific storage and handling requirements.

The present paper discusses a practical case study of a hydrodynamic assessment for a double-ended ferry designed to operate in the Venice’s lagoon. The main objective of this study was to compare two propulsive configurations, with 2 or with 4 azimuthing thrusters, both in terms of powering and manoeuvrability performances. Additional design requirements were: good ship handling, even in case of one propulsor failure, and a limited drift angle. The results of this overall hydrodynamic assessment gave important indications on the performance of the ship and helped the definition of the optimal ship design.

The paper conceives a flexible new generation naval ship Destroyer (DDX, Destroyer, Experimental) with a primary focus on low environmental footprint, high efficiency, and reliability. The ship implements an innovative propulsion power generation and storage system based on a CODOGOL (COmbined Diesel Or Gas Or eLectric) architecture and a Battery Energy Storage System (BESS). The proposed modular solution is also suitable for retrofitting applications and represents an innovation in the state of the art of hybrid propulsion systems for big, front-line naval ships. The shipboard BESS is used as a backup power source to ensure minimum generator operation (MGO) mode reliability requirements. The benefits of the proposed solution are discussed in detail, highlighting a reduction of the operating costs and fuel consumption, as well as low pollutant emissions and Life Cycle Costs. Eventually, dynamical simulation is used to assess the effectiveness of the proposed solution in critical conditions.

Reducing the human environmental impact is one of the most critical issues nowadays: in this perspective, the progressive decommissioning of fossil fuels is a significant priority to guarantee a sustainable future for the next generations. This paper proposes a zero-emission ferry for inland waterways and short-sea navigation, focusing on realistic solutions to provide the best trade-off between operational performance and environmental sustainability. In particular, the object of this study is the refitting of a double-ended ferry working in the Lago Maggiore, one of the largest Italian lakes. Systems suitable for the purpose have been selected and integrated onboard to maximize efficiency, implementing full-electric propulsion with electric motors, a Li-ion battery storage system, and photo-voltaic panels. The benefits and drawbacks of the considered technologies have been evaluated to select the most promising design solution, focusing on both onboard and on-shore impact in terms of compatibility with the existing infrastructures and considering life-cycle sustainability.

Integration of lightweight and sustainable solutions in marine structures design is essential to achieve weight reduction goals and improve structural response. A key step to assess the reliability of innovative structural solutions is represented by large-scale experimental investigation. The current paper deals with the analysis of a lightweight ship balcony overhang, which includes an aluminium honeycomb sandwich structure and bimetallic welded joints. The design of the ship balcony overhang was previously performed, as an illustrative example, with the aim of suggesting the replacement of common marine structures with more green and lightweight alternatives. In order to validate the design procedure and to assess the feasibility of the suggested solution, an experimental investigation on a large-scale structure was performed. The ship balcony overhang was tested under bending with a configuration representative of severe loading conditions for ships balconies. The experimental analysis allowed the evaluation of the structure’s strength, stiffness and failure modes, which are useful data to improve the design methodology of such structures and to calibrate numerical models. Comparison with similar structures reported in literature were performed in order to assess the benefits and drawbacks of the suggested lightweight structure.

The paper explores the accuracy of a low-cost CFD based approach to evaluate the propeller load variation experienced during manoeuvring conditions. The proposed procedure is based on the inclusion, in the ship hydrodynamic analyses by RANS, of the propeller effect through a body-force approach calibrated on BEM calculation to realize a computationally efficient method. Numerical results have been compared with the literature available experimental data performed on the well-known DTMB5415 benchmark test case, where the thrusts experienced by both of her propellers during dedicated Captive Model Tests were recorded. Both pure drift and pure yaw tests have been considered in the numerical campaign to cover the entire kinematic conditions involved during standard IMO manoeuvres. To prove the effectiveness of the method, also a severe turning circle condition is evaluated. The comparison shows the maturity of these numerical calculations, even if based on a simplified approach, to correctly evaluate the propeller unbalance, opening the way to the application of the proposed method to investigate the causes of load variations in manoeuvre conditions and directly in manoeuvre simulations.

In the last years, the idea of implementing greener and sustainable solutions merged with the basic principles of life cycle assessment concept has turned to be of paramount importance for the boatbuilding industry. In this framework, construction technologies based on wood such as strip-planking represent possible solutions, as they allow the use of a natural-grown material for attaining refined and solid structures. However, since these techniques imply wood bonding through conventional epoxy adhesives, the global eco-friendliness of the final product is lowered. As a consequence, the adoption of innovative bio-based adhesives is a promising solution to investigate. It is known that, generally, bonded joints in wooden hulls are weak spots of the structure, so the performances of the used adhesives should be duly assessed in order to guarantee an effective bonding. In the present research activity, the assessment of the performances of bonded joints manufactured with bio-adhesives is carried out through a FEM-based methodology, starting from the data present in both technical datasheets and literature for the materials used. In such a way, the most promising products can be preliminarily identified in order to deeply investigate their mechanical characteristics through experimental tests, so limiting expensive and time-consuming activities. The proposed methodology was validated through the comparison between the results coming from the FE analysis and the ones stemming from experimental tests. Moreover, the proposed methodology could be profitably used to analyse more complex geometries, such as real and large structures of wooden hulls.

Marine diesel engines are systems integrated into a complex ship’s propulsion plant and comprehensive diagnostic analysis of possible degradations and failures is very challenging. Nowadays, current software and hardware allow exploring innovative ways, although each methodology cannot be considered apart from an adequate onboard monitoring system. In this work, the effects of several typical degradations of a ship’s engine, affecting some parameters that can be monitored on board, have been supposed and analyzed in order to their detection at an early stage by processing some parameters that can be monitored on board. The main aim is to provide a tool able to trace the engine performance decay. The procedure is based on the simulation of the engine model performed with input data measured on board and on a comparison of the outcomes with the real data. The case study is a 12.000 kW (750 rpm) 4-stroke marine diesel engine, simulated in a Matlab/Simulink environment and validated through the manufacturer’s datasheet. At this stage of the research, to make up for the lack of experimental data recorded onboard, a more detailed engine simulator is used to generate onboard data, with some alterations of the operating conditions as, intercooler efficiency and loss of pressure, turbocharger fouling, and many others. The numerical diagnostic tool acts on the minimization of the mean square errors (optimization problem) between the measured and the numerically simulated engine variables (such as pressures, temperatures, etc…) by properly varying the model parameters. The state of the engine is evaluated by analyzing the offset between the parameters of the degraded model and those obtained through the identification procedure for the degraded case.