Damaged warship stability tests based on ANEP-77 : A case study for F-110

Resumen Pruebas de estabilidad en buques de guerra averiados con base en ANEP-77: Estudio de caso para F-110 Date Received: December 1st 2016 Fecha de recepción: Diciembre 1 de 2016 Date Accepted: December 22nd 2016 Fecha de aceptación: Diciembre 22 de 2016 Damaged warship stability tests based on ANEP-77: A case study for F-110 1 Royal Navy of Spain. Madrid, Spain Universidad Politécnica de Madrid. Madrid, Spain. Email: josemaria.riola@upm.es 2 SENER. Tres Cantos, Spain Universidad Politécnica de Madrid. Madrid, Spain. Email: rodrigo.perez.fernadez@upm.es 3 ISDEFE. Madrid, Spain Universidad Politécnica de Madrid. Madrid, Spain. Email: brodriguez@isdefe.es Ship Science & Technology Vol. 10 n.° 20 (19-30) January 2017 Cartagena (Colombia) 20 Th e future F-110 frigate class is under fi nal design defi nition phase and has further developed and matured the design baseline established at the end of the feasibility phase. Th e ship’s general arrangement, propulsion machinery and key systems had been fi nalized, with only minor details still outstanding. In the latest interaction, the F-110 design has a length of 145m, a beam of 18,6m, a draught of 5,5m and a displacement of up to 6.000Ton. Maximum speed is greater than 26kt, CODELAG propulsion machinery with a cruising speed of 17kt and a 4.100 nautical miles range at 15kn. Model tests will validate the hydrodynamic and sea keeping properties of the preliminary design selected for the frigate. Th e Spanish Navy’s requirements for the fi rst-of-class will be available in the 2023-24 timeframe. It is logical to think, since the sea is common for every ship, that merchant and warships are susceptible to the same type of accidents (groundings, collisions, fi res, loss of stability...) and encounter the same adverse weather conditions (seafaring, fog...). On the other hand, due to the purpose for which they have been projected, warships have to deal with additional threats like hostile actions of diff erent nature and intensity, representing all a potential risk to their stability and buoyancy. In the United Nations Convention on the Law of the Sea (UNCLO), article twenty-nine defi nes a warship as “a ship belonging to the armed forces of a State bearing the external marks distinguishing such ships of its nationality, under the command of an offi cer duly commissioned by the government of the State and whose name appears in the appropriate service list or its equivalent, and manned by a crew which is under regular armed forces discipline.” Th e International Convention for the Safety of Life at Sea (SOLAS), in its rule three “Chapter I – General Provisions”, states that its rules do not apply to warships and ships that transport troops. So, warships are exempt from most of the laws of the merchant ships (Fig. 2), and as such, both the international and national levels have directed the safety of naval surface ships independent of statutory organizations. But there are exceptions to this; vessels can be classifi ed and certifi ed by Classifi cation Societies (SC) or fl ag authorities and there are some aspects of the statutory legislation that warships have to consider. Th us, development of rules for warships or Naval Ship Rules by various SC is the most important contribution to work in this area. Admitting that there is no equivalent of the International Maritime Organization (IMO) for warships, the only recognized navy specifi cations, Stability DDS-079-1 (Fig. 3), the North Atlantic Treaty Organization (NATO) established a decade ago some teams of specialists in the Naval Ship Classifi cation Association (NSCA) and a partnership for classifi cation of warships. Th ese teams of specialists have been entrusted with the preparation of the Naval Ship Code (NSC) and a benchmark of international standards for ships. Th is promotes greater transparency and consistency in safety standards for warships. Th is code aims to fi ll the gap by providing the framework for armed forces security that has Introduction Fig. 1. Virtual picture F-110 Frigate class (MDEF, 2016) and ANEP-77 Edition Riola, Pérez, Rodríguez Ship Science & Technology Vol. 10 n.° 20 (19-30) January 2017 Cartagena (Colombia) 21 achieved acceptable levels of safety and will be the link between IMO, the Classifi cation Societies and Navies. Th e development of this code provides a cost-eff ective framework for a naval surface ship safety management system based on and benchmarked against IMO resolutions. Th e specialists’ teams established a goal-based approach to the development of the code, developing each chapter in turn. Th e Naval Authority Knowledge Management Offi ce (NAKMO) website contains the latest version and its corresponding guide, and NATO adopts the publication as an Allied Naval Engineering Publication ANEP-77. Th e current version (F) was published on August 2014. From 2009 to 2014, the evolution of some aspects of the ANEP-77 Ed. F in comparison to its 2009 edition is substantial, with a major restructuring to the Table of

Th e future F-110 frigate class is under fi nal design defi nition phase and has further developed and matured the design baseline established at the end of the feasibility phase.Th e ship's general arrangement, propulsion machinery and key systems had been fi nalized, with only minor details still outstanding.In the latest interaction, the F-110 design has a length of 145m, a beam of 18,6m, a draught of 5,5m and a displacement of up to 6.000Ton.Maximum speed is greater than 26kt, CODELAG propulsion machinery with a cruising speed of 17kt and a 4.100 nautical miles range at 15kn.Model tests will validate the hydrodynamic and sea keeping properties of the preliminary design selected for the frigate.Th e Spanish Navy's requirements for the fi rst-of-class will be available in the 2023-24 timeframe.
It is logical to think, since the sea is common for every ship, that merchant and warships are susceptible to the same type of accidents (groundings, collisions, fi res, loss of stability…) and encounter the same adverse weather conditions (seafaring, fog…).On the other hand, due to the purpose for which they have been projected, warships have to deal with additional threats like hostile actions of diff erent nature and intensity, representing all a potential risk to their stability and buoyancy.
In the United Nations Convention on the Law of the Sea (UNCLO), article twenty-nine defi nes a warship as "a ship belonging to the armed forces of a State bearing the external marks distinguishing such ships of its nationality, under the command of an offi cer duly commissioned by the government of the State and whose name appears in the appropriate service list or its equivalent, and manned by a crew which is under regular armed forces discipline."Th e International Convention for the Safety of Life at Sea (SOLAS), in its rule three "Chapter I -General Provisions", states that its rules do not apply to warships and ships that transport troops.So, warships are exempt from most of the laws of the merchant ships (Fig. 2), and as such, both the international and national levels have directed the safety of naval surface ships independent of statutory organizations.But there are exceptions to this; vessels can be classifi ed and certifi ed by Classifi cation Societies (SC) or fl ag authorities and there are some aspects of the statutory legislation that warships have to consider.Th us, development of rules for warships or Naval Ship Rules by various SC is the most important contribution to work in this area.
Admitting that there is no equivalent of the International Maritime Organization (IMO) for warships, the only recognized navy specifi cations, Stability DDS-079-1 (Fig. 3), the North Atlantic Treaty Organization (NATO) established a decade ago some teams of specialists in the Naval Ship Classifi cation Association (NSCA) and a partnership for classifi cation of warships.Th ese teams of specialists have been entrusted with the preparation of the Naval Ship Code (NSC) and a benchmark of international standards for ships.Th is promotes greater transparency and consistency in safety standards for warships.Th is code aims to fi ll the gap by providing the framework for armed forces security that has Introduction From 2009 to 2014, the evolution of some aspects of the ANEP-77 Ed.F in comparison to its 2009 edition is substantial, with a major restructuring to the Table of Contents.Chapter 3 of the ANEP-77 is titled "Buoyancy, Stability and Controllability" and has goals to provide an adequate reserve of buoyancy (NSA, 2012) in all foreseeable intact and damaged conditions, an adequate stability to avoid capsizing, permit embarked persons to carry out their duties and protect the embarked persons and essential safety functions in the event of foreseeable accidents and emergencies.Th erefore, the primary goal of this chapter has been set to provide the ship with the ability to remain afl oat in an upright orientation in all operating conditions including loading, heavy weather and applied "foreseeable" disturbances including cases of damage causing loss of watertight integrity.Also, this chapter and the corresponding explanation guide with its solutions presents the performance requirements  and the verification methods about intact and damage stability (Pérez and Riola, 2011b).

Stability Requirements Evolution
This is the reason why this chapter is so important for the hydrodynamics model basin naval architects.To increase the safety of damaged ships, designers (Surko, 1994) focus more on damage mitigation than accident prevention.
The damage mitigation requires prediction of the damage stability (Sarchin and Goldberg, 1962), the structural integrity, and the motion analysis for damaged ships in waves.Furthermore, pertinent ANEP-77 damage scenarios are developed to the damage safety criteria.
There are some notorious variations in the drafting of Regulation 2 (Watertight Integrity) and 3 (Reserve of Buoyancy) deleting the prescriptions related to maneuverability contained in order to create the new Regulation 5 (Maneuverability).But, without any doubt, the most remarkable change happened in Regulation 4 (Reserve of Stability) where only minor general requirements about stability were specified in 2009 Ed. of NSC and now in Ed.F a variety of several goals for the study of intact stability were chosen to be included by the people responsible of the project.The specialists' teams established a goal-based approach to the development of the code, developing each chapter in turn.
The basic principle of a goal-based approach is that the goals should represent the top tiers of the framework, against which a ship is verified both at design and construction stages, and during ship operation.This enables the ANEP-77 to become prescriptive if appropriate for the subject, or remains at a high level with reference to other standards and their assurance processes.The goal-based approach also permits innovation by allowing alternative arrangements to be justified as complying with higher-level requirements.The increasing width of the triangle as the ANEP-77 descends through the tiers implies an increasing level of detail (Riola and Pérez, 2009).
In ANEP-77, the goal based standards approach is anchored in five tiers outlined as follows: • Tier 0 -Aim (philosophies and principles) • Tier 1 -Goal • Tier 2 -Functional areas • Tier 3 -Performance requirements • Tier 4 -Verification methods • Tier 5 -Justification Therefore, the goal-based approach provides a systematic framework for certification of a ship to meet the goals of ANEP-77.Performance requirements are defined based on the Concept of Operations (CONOPS) and verified using appropriate criteria.Although this approach contained in ANEP-77 provides for implementation of FSA approaches, it is not the same as an overarching design for safety approach in that ANEP-77 allows a Naval Administration to apply FSA in the Tier 4 verification of specific performance requirements associated with defined When a ship accident occurs because of several causes, both the hull and structures are damaged.
Th ese damages cause the ship to fl ood, which can lead to sinking, capsizing or breaking up.Th e damage conditions used to predict the expansion of and loss due to damage are composed of a combination of the ship dimensions, sea states, and damage confi gurations, such as the location and extent of a damage hole.Th e ship dimensions can be represented by the loading conditions and geometrical characteristics such as the hull, length, breadth, draft, KG, and compartment arrangement, and the environmental conditions refer to wind and wave conditions such as height, length and period, and of course, the angle of the wave heading that has to be taking into account also.
The damage categories (Table 2), in ANEP-77, are based on defined shapes: • Collision.To be used in the correct vertical orientation to describe the extent of collision damage from the bow of another ship, the apex representing the maximum penetration.• Raking/grounding.To be used in the appropriate horizontal orientation to describe the extent of raking or grounding damage, the apex representing the maximum penetration.• Cube.To be used to define the volume directly affected by fire and which may change in shape to fit the compartment.• Sphere.To be used for explosions.For explosions detonating against the exterior of the hull, half the sphere to be used.Grounding: it is not common to find a frigate sailing in swallow waters, considering the risks this represents, not so with littoral combat ships, amphibious ships or patrol boats.Grounding damage cases are described using the longitudinal location of the damage and the number of spaces affected.Using triangular prism shape specified on the ANEP-77 Code, the author can simulate which compartments of the ship have been affected by the accident.The damage extents are defined as the longitudinal damage length and width, which are determined by the ships speed, the thickness of the steel hull or structural details as transverse web spacing, and the underwater stone characteristics as height, hardness or toughness.

Collision
Weapons Damages: Fire and Explosions (cube and sphere cases): For naval ships, it is necessary to consider the damage of the attack caused by enemy weapons in addition to collision and grounding.At the moment, design rules for naval ships apply the criteria only to evaluate the adequate damage stability performance based on the righting arm curve but continuous research has focused on this area in recent years (Pérez and Riola, 2011a).Of course, it is impossible to predict the damage size, extension and location because it mainly depends on the success of the enemy weapon.As the ANEP-77 is to provide a level of safety appropriate to the role of the ship and benchmarked against statute while taking into account naval operations, it is necessary to define the degree of survivability in a way that can be taken into account in the development of the different chapters.As an example, the main  diff erence between the fi re safety approach from a naval and civilian shipping point of view is that SOLAS considers the risk of fi re based on the function of each compartment whereas for naval ships, hostile acts may result in fi re anywhere on the ship, both externally and internally.
able to gatherthe information sent from the free model moving on the waves emitting light diodes.
To maintain the same hydrostatic properties, a fi berglass model is built in a scale with the corresponding scale characteristics.It is required that the model is instrumented so that its roll, heave and pitch motions as well as its heel, sinkage and trim attitudes are monitored and recorded throughout the test.All the signifi cant appendages such as rudders and keels are fi tted and the inner damaged area compartmentation was made as realistic as possible.It is also important to ensure that the damaged compartments are modeled as accurately as practicably possible to ensure that the correct volume of fl oodwater is represented.In order to reproduce the damage stability tests in the dynamic lab, a rigid scale model, a wave spectrum and a data acquisition system are necessary.Th e model should be as large as possible, since details of damaged compartments are easier constructed in larger models and the scale eff ects are reduced.It is therefore recommended that the model length is not less than that corresponding to a 1:40 scale.Th e data acquisition system consists mainly in an optical tracking system Th e model, considering the damages assumed, must be as thin as practically possible to ensure that the amount of fl ood water and its center of gravity is adequately represented.It is recognized that it may not be possible for the model hull and the elements of primary and secondary subdivision considering the damage to be constructed with suffi cient detail and due to these constructional limitations it may not be possible to accurately calculate the assumed permeability of the space and the percentage of volume of the space, which may be occupied by seawater if the space is fl ooded.Typical values from the SOLAS are 0.95 for empty spaces, tanks, and living spaces, 0.85 for machinery spaces and 0.60 for spaces allocated to stores.
Th e vertical extent of the model can aff ect the results when tested dynamically, so it is required that the ship is modeled to at least three superstructure standard heights above the freeboard deck so that the large waves of the wave train do not break over the model.After measuring the damaged draughts it may be necessary to make adjustments to the permeability of the damaged compartment by either introducing intact volumes or by adding weights.Th is, to ensure that the model motion characteristics, the intact GM and the mass distribution are verifi ed.Th e transverse radius of gyration of the actual ship is not to be taken as being greater than 0.4B and the longitudinal radius of gyration is not to be taken as being more than 0.25L.Th e balance period will be defi ned as follows: Where K is the radius of inertia of the ship.It is normal to defi ne this ratio as a beam function: f values depend on the type, load case and general arrangement of the ship.
It is required that for every test run, the wave spectrum is recorded and documented.
Measurements for this recording are to be taken in the immediate vicinity of the model and also near the wave maker machine.Extensive research carried out for the purpose of developing appropriate criteria for new vessels has clearly shown that in addition to the GM and freeboard being important parameters in the survivability of ships, the area under the residual stability curve up to the angle of maximum GZ is also another major factor.Consequently, in choosing the worst ANEP-77, damage for compliance with the requirement of the worst damage is to be taken as that which gives the least area under the residual stability curve up to the angle of the maximum GZ (Fig. 12).
Frigate design scale model will be verifi ed in the following tests on the model basin: dynamic rolling, parametric excitation, resonant excitation, impact excitation, transient fl ooding, broaching, survivability test, etc.In order to defi ne the boundary conditions of each test, the specifi cations of ANEP-77 Environmental test conditions (refer Table 1) will be used, meeting the parameters of the three diff erent conditions specifi ed (Operational, Survival or Damage).Furthermore, the wave spectrum shall also be defi ned.Due to the severe characteristics, the survivability of warships model test in a basin must be tested with a Joint North Sea Wave Project (JONSWAP) wave spectrum.As an example, the transient fl ooding and survivability test has been chosen as the most representative, which will be explained in more detail in the next paragraphs.
Warship naval architects admit that the naval ship survivability is one of the most attractive and important aspects in the preliminary phases of the naval project.Survivability is the enhanced ability of a ship to survive even in damaged conditions.Th erefore, for new designs, the applicable stability and buoyancy standards must be integrated with the operational requirements.As it mentioned before, righting arms after damage curves are used to determine the adequacy of the ship´s stability.
With the intention to get a good correlation between scale model and real ship, the following aspects shall be correctly defi ned: • Defi nition of the compartments of the ship.Ships are provided with watertight subdivision to halt the fl ooding of water after damage and (1) (2) Dynamic Phenomena Basin Test For ship motion simulation with sudden water ingress and waves, Cummins is the most appropriated to simulate the phenomenon: Weather conditions are important factors in a survival condition after damage.SICP is the Spanish acronym for Integrated Control Platform System.Th e main mission of the SICP is to provide up-to-date, reliable and well-structured information to SICP operators with the ultimate goal of reducing staff members dedicated to monitoring and controlling the platform, as well as to increase access to coherent and complete information on the status of the platform to the ship's command personnel.
Th anks to the design of the SICP, its operators are always fully aware of the state of the subsystems of the platform.All of these capabilities make the implementation and use of the SICP increase the on board safety of the ship.Th e SICP increases the predictive maintenance capacity by controlling and monitoring a large number of platform elements.Every parameter related with the stability tests made to the model shall be included in the SICP system in order to help in the controllability and maneuverability of the ship.
• Th e ANEP-77 has become the criterion of stability in damage that most closely resembles the standards of the navy in the 21st century, as it has been refl ected throughout the paper.
• We have proposed an extensive explanation of the ANEP-77 stability after the damage criteria.Th ere are many areas where military vessels could improve safety standards, although not necessarily to be regarded as less secure than the civil vessels.However, there are major diffi culties in implementing all the rules of the Classifi cation Societies in the naval fi eld, especially to establish a priority mission and capacity combat against security.It is remarkable to distinguish the importance of the new ANEP-77 rules about dynamic ship phenomena, especially in damage tests.
• For the eff ective application of the ANEP-77, it is necessary to clearly defi ne the extent of the damage that refl ects the potential damage caused by hostile acts, the damage location, degree of vulnerability, hull and superstructure protection, systems redundancy, materials, the post-damage ship capability and the philosophy for recovery from the damaged state.
• Hydrodynamics Studies on damage safety aim to make F-110 frigates safer on an ongoing basis, in particular, there are many outstanding descriptions, formulas, and technical procedures on this stability paper that shows factors that can be used to develop damage scenarios for collision, grounding, and attack accidents.Damage safety assessment is not only required in the design phase but can also be applied in the operation phase that should guarantee high rapid response and useful information to the decision makers in emergencies. •

Fig. 5 .
Fig. 5. Different damage shapes (ANEP-77, 2014) Th e future Frigates F-110 model tests can be carried out in the sea keeping basin of El Pardo Model Basin (CEHIPAR) close to Madrid.Th e basin has a sixty fl aps wave maker, a computerized carriage (CPMC) and the following dimensions: 150 meters long x 30 meters width x 5 meters depth.IMO survivability tests, European Commission researches and the Stockholm Agreement supplement were carried out over recent decades, have provided widely recognized and experienced personnel in the maritime security fi eld.

Table 2
. Summary table of damage categories (ANEP-77) Damaged warship stability tests based on ANEP-77: A case study for F-110 Ship Science & Technology -Vol. 10 -n.° 20 -(19-30) January 2017 -Cartagena (Colombia) The F-110 frigate class represents a critical program into the Spanish Navy strategic goals.Before initiating the execution phase, model basin test shall be carried out to improve the capabilities of the ship.As we are actually checking at CEHIPAR, dynamic stability tests are the most critical.Damage survivability tests are a fundamental database for the future frigate behavior in operations.The data obtained from the basin tests have an enormous value for future behavior of the SICP response for the comfort of the crew in normal sailing conditions and specially, during the fast response under emergency situations.