Ship Survivability Research Articles

Computational analysis of submerged submarine bow hull dynamics subjected to torpedo blunt impact and warhead detonation events

In the maritime sector, ensuring the survivability of ships and submarines against diverse threats such as torpedo impacts, Underwater Explosion (UNDEX) events, and environmental factors is paramount. Comprehensive analysis of hull dynamics under various impact scenarios is essential. Numerical simulations of these impacts utilize different material models, ship grounding tests, impact modes, UNDEX simulations, and failure mechanisms. In the current study, the blunt impact of a torpedo on the submarine bow and the surface detonation effects of the torpedo warhead (at different distances from the hull) on the submarine bow structure were analyzed within an underwater enclosure. The torpedo design was based on the MK-48, with Ti6Al4V alloy used for the torpedo hull and HY-80 steel for the submarine hull. The impact simulations were conducted using ANSYS Explicit Dynamics® computational software. For the blunt impact scenario, a torpedo speed of 55 knots (102 km/h) was used. For the UNDEX studies, the warhead at the front end of the torpedo was modeled using PBX-9501 (a commonly used high explosive in warheads). The novelty of the current work was the employment of a water enclosure in the model to simulate the underwater impacts. The analysis focused on hull deformation, equivalent plastic and elastic strains, equivalent stress and damage profiles for the different impact scenarios. To effectively capture fluid–structure interactions, the study also examined pressure variations within the Eulerian domain. Among the scenarios analyzed, the near-field detonation of the warhead emerged as the most destructive, resulting in severe structural damage to the bow hull. In contrast, the blunt impact of the torpedo induced moderate plastic deformation, while the far-field detonation resulted in minimal damage.

Input saturated [formula omitted] optimal control to mitigate DTMB 5415 combatant roll motion using anti roll gyro stabilizer

Despite technological advances, rolling motion is the most critical motion for the stability and survivability of ships. This study examines the possibility of using Anti Roll Gyrostabilizer System (ARGS) as a control actuation system to mitigate the roll motion of the DTMB 5415. In the scope of conceptual study, state space model of the DTMB 5415 Combatant Warship has been obtained. Then, ARGS dynamics have been integrated into the roll motion dynamics. Parameters of the DTMB 5415 and actuator are identified from the literature. Comparing experimental and numerical studies in the literature have also expanded the damping term parameters in the equation of roll motion. However, a Monte Carlo analysis is carried out to define the preliminary parameters of ARGS. An actuator-saturated Linear Matrix Inequality (LMI) Full State-Feedback H∞ Optimal Controller is tested for this design iteration. The results are also contrasted with the requirements that military ships must meet. Ship roll amplitudes have significantly decreased (over 95% for various sea conditions) and have complied with STANAG 4154 standards. The 1 radian Precession Angle limit has not been overshot. Continuous and discrete-time control rules are implemented, thus demonstrating the applicability of this actuation and control method are shown.

러-우 전쟁사례 분석을 통한 드론 대테러 함정 생존성 설계 및시험평가 발전방안

Since the positive viability field remains the way it was in the 2010s, the ship test evaluation in the viability field is being applied to withstand the attack on an extremely limited kind of weapon system even the latest ship. In response, this paper analyzed and considered maritime warfare on anti-drone for counter-terrorism during the Russia-Ukraine War, which is an example of the latest war paradigm shift, and diagnosed the status of test evaluation in the field of Naval ship survivability to derive realistic development measures such as reflecting threat development trends, strengthening attack and damage control evaluation, confirming ship viability limits, and realizing test evaluation plans.

Study on Cable Tension Characteristics of Shore-Based Constant Tension Mooring Systems Under the Coupling Effect of Wind, Wave, and Current

Abstract This paper proposes a shore-based constant tension mooring system, which improves the cable tension distribution by adjusting the length of the cable to maintain the constant tension of the cable between the ship and the mooring pile in order to solve the problem of poor safety and reliability of the traditional mooring system in the mooring process. First, based on the three-dimensional potential flow theory, this paper uses the hydrodynamic software AQWA to numerically simulate the dynamic response of the traditional mooring system under the coupling of wind, wave, and current in different sea states. Subsequently, a shore-based constant tension mooring system using the principle of volume-varying hydraulic control was studied. On the basis of a comprehensive analysis of the working principle of the constant tension hydraulic control mooring system, a mathematical model of the main working circuit is established. The system was numerically simulated by relying on matlab/Simulink simulation software. Finally, by comparing with traditional mooring systems, the results show that the maximum cable tension of the shore-based constant tension mooring system is significantly reduced so that the tension is controlled within a fixed range, and the safety factor of the mooring cable is significantly improved, thus reducing the risk of mooring system failure and improving the ship's survivability.

Study on structural damage mechanisms and defence of rectangular closed-section simplified hull girders with thinner plates under near-field underwater explosions

Understanding the damage mechanisms of typical ship structures under fatal underwater explosion loads is crucial for developing effective defensive measures. To provide references for enhancing the survivability of ships, this paper conducts analyses of the damage mechanisms of simplified hull girders (SHGs) using a combination of experimental and simulation methods, and proposes targeted structural improvements. Initially, two types of thin-walled rectangular closed-section SHGs are subjected to near-field underwater explosion experiments. Corresponding simulation models are established, and the validity of the computational results is verified. The progressive damage processes of SHGs in hogging and sagging are examined from a structural perspective. Furthermore, the thin-walled plate deformation transfer processes are analyzed. Finally, based on the analyzed damage mechanisms, targeted defensive structures for overall damage are designed. The study results show that enhancing the anti-deformation capability of the upper and lower edges of the side plates can effectively improve the overall bending resistance of the SHG.

A dynamic simulation tool for ship's response during damage-generated compartment flooding

Survivability of ships in damaged condition is an issue of paramount importance. Therefore, the regulatory framework is constantly updated, in response to the societal aversion towards accidents with severe impact on human life and on the environment. The introduction of the probabilistic damage stability framework was a major step towards the rationalization of the procedure for the assessment of survivability of ships in damaged condition. Subsequent revisions of SOLAS 2009 included the increase of the safety standard via the new formulations for the R-Index and for the calculation of the probability of survival (s-factor), which however is still performed by a hydrostatic approach. Flooding simulation tools can be used for an in-depth investigation of the transient response of a damaged ship, aiming to identify conditions that could jeopardize her survivability during the initial phases of flooding, or to assist in the improvement of the s-factor formulation. In this work, a newly developed flooding simulation tool, employing the Smoothed Particles Hydrodynamics (SPH) method coupled with a ship motions solver, is presented. The developed methodology predicts the dynamic response of the ship during the flooding process, primarily focusing on the initial stages, when particularly violent flow phenomena may be observed.

Application of structural methods to assess the reliability of ship’s mechanical systems

At present, reliability indicators are of great importance at the design stages, during operation and in cases of extending the technical life. This is one of the reasons for choosing the research topic on the application of structural methods for evaluating the reliability of ship mechanical systems. The operational stage of the life cycle of ship’s mechanical systems is considered in the paper. Durability criteria such as service life, operating time, frequency of repairs are chosen as reliability indicators. In turn, work on the repair, maintenance or replacement of ship’s mechanical systems elements is carried out in accordance with the assigned regulations or in the case of an unforeseen failure. The comparison of event models of changes in the operating conditions of ship’s mechanical systems is carried out. To estimate the remaining resource in the form of graphs, events are shown by service life and operating hours, distributed by years. In order to improve the existing methods for assessing reliability, a set of elements of the average values of the residual resource and residual output is considered. The approach proposed by the authors for assessing both element by element and the entire ship mechanical system as a whole allows us to consider the residual resource from the moment of monitoring its technical condition to the transition to the limit state, to plan technical measures and prevent possible malfunctions. Three different time slices models corresponding to planned repairs and maintenance of systems, replacement of system elements and unforeseen accidents are considered in the study. The difference in the amplitudes of the calculated indicators of the ship’s mechanical systems reliability has shown that the closer the options between the maximum and minimum values are to the average, the more accurately the statistical indicators characterize this pattern. However, amplitude deviations can be used to apply fault risk assessment. This line of research seems to be important for ships in the Arctic navigation area, which are characterized by increased requirements for ship survivability.

The effect of the operational environment on the survivability of passenger ships

The in-force probabilistic framework for passenger ship survivability assessment covers collision hazards. The framework primarily pertains to a static approach. Nonetheless, more complex dynamic analyses usually employ the same damage definitions, adding besides the breach characteristics, the environmental condition selection or, more precisely, the irregular wave environment necessary to simulate the damage scenarios. The traditional dynamic approaches to survivability consider only the significant wave height sampled from statistical formulations, with the wave period deriving from a constant steepness assumption. However, wave height and period influence ship dynamics in waves differently, especially concerning survivability after damage. Therefore, aiming at a direct assessment of ship survivability and the probability of loss of lives determination in realistic operational scenarios, it is essential to properly study the influence of combined variations of wave height and periods and their occurrence. The present study proposes a methodology for dynamic simulations in site-specific conditions derived from the Global Wave Statistics. The study documents the process in two critical collision damages for a reference passenger ship, using wave height and period combinations typical of the main sea areas of interest for passenger ships and performing a sensitivity analysis on the simulations needed to evaluate survivability. This enhanced analysis allows identifying the limiting environmental conditions for the critical damage cases, including the effect of heading variations, determining the ship’s survivability to specific damage in an operational area.

Machine Learning and Case-Based Reasoning for Real-Time Onboard Prediction of the Survivability of Ships

The subject of damaged stability has greatly profited from the development of new tools and techniques in recent history. Specifically, the increased computational power and the probabilistic approach have transformed the subject, increasing accuracy and fidelity, hence allowing for a universal application and the inclusion of the most probable scenarios. Currently, all ships are evaluated for their stability and are expected to survive the dangers they will most likely face. However, further advancements in simulations have made it possible to further increase the fidelity and accuracy of simulated casualties. Multiple time domain and, to a lesser extent, Computational Fluid dynamics (CFD) solutions have been suggested as the next “evolutionary” step for damage stability. However, while those techniques are demonstrably more accurate, the computational power to utilize them for the task of probabilistic evaluation is not there yet. In this paper, the authors present a novel approach that aims to serve as a stopgap measure for introducing the time domain simulations in the existing framework. Specifically, the methodology presented serves the purpose of a fast decision support tool which is able to provide information regarding the ongoing casualty utilizing prior knowledge gained from simulations. This work was needed and developed for the purposes of the EU-funded project SafePASS.

Research on the progressive sagging damage and plastic hinge line mechanism of basic simplified hull girder subjected to near-field underwater explosion bubble

Near-field underwater explosion bubbles are a major threat to the survivability of ships and may lead to severe and destructive accidents. Therefore, in this study, the damage mechanism of a basic simplified hull girder(SHG) under a near-field underwater explosion load is analysed using the Coupled Eulerian–Lagrangian (CEL) method. First, the calculation accuracy of the established finite element model is verified. Then, the damage development process of SHGs to near-field underwater explosions is investigated from the perspective of progressive sagging damage and plastic hinge lines. In addition, theoretical derivations are carried out based on the constructed plastic hinge line mode. Finally, some laws on the simulation data are discussed in terms of the plastic absorption energy and bending moment. The results show that a stable crease mode will appear in the midship when the SHGs are sagging damage under the near-field underwater explosion bubble load. These creases are necessary conditions for sagging damage, which are mainly W-shaped in this study. The analytical solutions of the W-shape size agree well with the simulation results.

On Boundary Conditions for Damage Openings in RoPax-Ship Survivability Computations

The survivability of a damaged RoPax ship in the case of a flooding accident can be critical, as these ships have a tendency for a rapid capsize. Various simulation tools are presently in use to study the behavior of damaged RoPax and cruise ships. Recent benchmark tests show that the numerical tools for this purpose are very useful, but their accuracy and reliability still leave something to be desired. In many numerical simulation codes for ship survivability, the water inflow and outflow through a damage opening are modeled with Bernoulli equation, which describes steady flow in an inertial frame of reference. This equation takes neither the floodwater inertia in the opening into account nor does it regard the effect of ship motions on the flow in the opening. Thus, there are some approximations involved in the use of the Bernoulli equation for this purpose. Some alternative formulations are possible. This study sheds light on the question of how relevant is it to use the more complicated formulations instead of the very simple and robust Bernoulli model in the numerical simulation of damaged ships in the sea.

Automated topology design to improve the susceptibility of naval ships using geometric deep learning

AbstractThe survivability of a naval ship is defined as its ability to evade or withstand a hostile environment while performing a given mission. Stealth technology, which reduces the probability of detection by enemy detection equipment using a highly advanced detection system, is one of the most important technologies to improve the survivability of naval ships. Moreover, radar cross-section (RCS) reduction is a very important factor in stealth technology because a small RCS, which is the main parameter determining susceptibility, improves the ability of ships to evade enemy detection equipment. In this study, an automated topology design for reducing susceptibility was developed by combining geometric deep learning and topology optimization. A convolutional neural network model was used as the geometric deep-learning model, and the triangular meshes of the naval ship models and equipment models were used as datasets. To compensate for the lack of training data, randomly generated meshes were additionally used as datasets. To express the feature data of the mesh as a matrix, points at equal intervals were projected orthogonally and the distance between the plane and point was set as a matrix value. The label data were defined as the highest RCS values excluding the cardinal points. After realizing the topology design for reducing susceptibility using the developed system, verification was performed through RCS analysis of the original model and the topology-designed model.

함정 대공방어시스템의 효과도를 활용한 피격성 추정 가능성 연구

Recently, the increased use of anti-ship guided missiles, a weapon system that detects and attacks targets in naval engagement, has come to pose a major threat to the survivability of ships. In order to improve the survivability of ships in response to such anti-ship guided missiles, many studies of means to counteract them have been conducted in militarily advanced countries. The integrated survivability of a ship can be largely divided into susceptibility, vulnerability, and recoverability, and is expressed as the conditional probability, if the ship is hit, of damage and recovery. However, as research on susceptibility is a major military secret of each country, access to it is very limited and there are few publicly available data. Therefore, in this study, a possibility of estimating the susceptibility of ships using an anti-air defense system corresponding to anti-ship guided missiles was reviewed. To this, scenarios during engagement, weapon systems mounted to counter threats, and maximum detection/battle range according to the operational situation of the defense weapon system were defined. In addition, the effectiveness of the anti-air defense system and susceptibility was calculated based on the performance of the weapon system, the crew

Protection mechanism of underwater double-hull coated with UHMW-PE subjected to shaped charge

Shaped charge warhead which is widely utilized for underwater weapons has a severe threat to the survivability of naval ships. Therefore, it is of great significance to improve their anti-destructive capability. Three types of loads - shock wave (SW), shaped charge projectile (SCP) and bubble - are generated during the process of shaped charge associated with underwater explosion, which can cause different damage characteristics into double-hull structure. In this paper, these three loads characteristics and their combined damage into double-hull structure are analyzed. Besides, the protection of fiber metal laminates on this structure are discussed. Firstly, Coupled Eulerian-Lagrangian (CEL) is used to simulate the full physical process of double-hull subjected to shaped charge associated with underwater explosion. Secondly, the damage characteristics of double-hull are obtained under the combined damage of the shock wave, shaped charge projectile and bubble. After that, the steel plate/UHMW-PE laminate (Fiber Metal Laminate, FML) is designed according to the equal surface density theory. The blast and penetration resistance of ultra-high molecular weight polyethylene (UHMW-PE) material is analyzed and the optimized FML models are discussed. The results show that a small plastic deformation and hole of the outer and inner plates of the double-hull are generated by the shock wave and the shaped charge projectile, respectively. A large plastic deformation of the outer plate is caused by the subsequent bubble load, which is torn and pulled off. The hole size of plate coated with PE and the residual velocity of projectile reduced by 26.66% and 69.50% compared with those of the steel plate, respectively. Besides, for the coated cases the outer and inner plates is respectively not pulled off and penetrated by projectile. Additionally, it is worth noting that the bubble collapses and cannot cause the secondary damage into double-hull due to the protection of coated PE. It indicates that the PE has a great protection performance of the double-hull subjected to shock wave, bubble and projectile, which can provide a reference for the naval ships protection design.

CFD study of extreme ship responses using a designed wave trail

The need for fully physics-based nonlinear solvers such as URANS CFD solvers is imminent to evaluate extreme ship responses in a seaway. However, such computations are very time-consuming and practically impossible to search through all wave environments to evaluate the extreme ship responses and ship survivability, which are considered rare but influential events. One way to enhance the practicality of the nonlinear tools is to develop physics-informed mathematical methods, in which the wave trail can be designed statistically by the information provided by the limited number of nonlinear simulations. In this study, the extreme responses of KRISO Container Ship (KCS) are analyzed using wave trails designed by the conditioning technique based on one irregular wave simulation. An irregular wave simulation was conducted for the ship advancing at Fr = 0.26 in waves with JONSWAP spectra under Seas State 5. Three wave trails are designed to generate heave responses with a maximum amplitude of 0.08, 0.16, and 0.2 m (28%, 56%, and 70% of the ship draft) using Gaussian and non – Gaussian processes. CFD simulations with the designed wave trails revealed that the designed wave trails often result in the desired heave response. Additional simulations are also performed in calm water and regular waves for verification and validation purposes.

Process, methods and tools for ship damage stability and flooding risk assessment

Development of damage stability as a scientific subject, specifically in damage ship hydrodynamics and, generally, flooding risk assessment, has evolved primarily by inquisitive academics with support by people with vision and passion towards maritime safety enhancement from industry and Government, the latter in the wake of serious accidents. Notwithstanding this, the subject has seen remarkable development in a short period of time in terms of understanding process, and developing methods and tools for practical implementation of such developments. The stage has now been reached where large-scale EC and industry-funded projects are bringing all requisite knowledge and experience together towards implementation by end users with the view to institutionalizing such developments. The paper critically traces and presents key developments starting from basic concepts to a complete framework for performing numerical simulations of ship survivability in operational conditions in the seaway, leading to flooding risk assessment with application potential for new and existing ships with focus on the design phase but with operation potential in ship operation, the latter involving emergencies.

A novel method for the probabilistic assessment of ship grounding damages and their impact on damage stability

Existing statistics for use in ship damage stability assessment are based on either accident investigation reports or empirical crew records. This is the reason why the databases used within the context of ship design for safety are either incomplete or miss critical information. This paper introduces a methodology for the probabilistic evaluation of passenger ship damage extents. The model accounts for the influence of crashworthiness in real operational conditions. Based on operational statistical records for ships before grounding, a Monte Carlo simulation is utilized to randomly generate a realistic profile that accounts for variable ship speed, conical rock geometry, rock position, and height in both deep and shallow waters. Subsequently, using the operational parameters as input, a six degrees of freedom fluid–structure interaction (FSI) model is used to combine the influence of ship dynamics, and structural mechanics on the probability distributions of hull breaches. Ship damage stability evaluation is carried out using NAPA software, which measures ship survivability via an attained subdivision index. Probabilistic results are compared against existing distributions of damage extents and demonstrate an increase in the mean distribution of damage length. The findings demonstrate the method's adequacy for improving passenger vessel safety in case of ship grounding. It is concluded that the method allows for low-fidelity optimization of the structural arrangement of the bottom of the ship, probabilistic evaluation of loads associated with ship crashworthiness, and the assessment of operational limitations during an evasive maneuver. It could therefore be used for the future development of ship damage stability standards or ad - hoc forensic investigations.

Exploring smart methodologies for critical flooding scenarios detection in the damage stability assessment of passenger ships

A more contemporary damaged stability assessment of a passenger ship can be addressed with a non-zonal approach, assessing multiple damage types and environmental conditions and employing dynamic analysis for ship survivability. This direct method necessitates the generation and simulation of many damage scenarios. However, the probabilistic models for damage characteristics describe many damages that are not critical for ship survivability. To restrict the number of damage scenarios, hence calculation time, designers currently apply empirical rules, such as critical damages are only above two compartments, considering that damage stability regulations currently in force to ensure survivability levels beyond this damage extent. However, a rigorous approach is lacking. The present work explores the use of more scientific methods as damage filters. The first method uses preliminary static calculations. The second uses the energy absorbed by the ship during an impact, and the third is suitable for a purely dynamic approach. The paper critically compares the three methodologies on two sample passenger ships for collision damages, showing their respective advantages and disadvantages.

The influence of damage breach sampling process on the direct assessment of ship survivability

The current damage stability regulatory framework for passenger and dry cargo ships allows addressing vessel survivability after flooding due to collisions with probabilistic requirements. This methodology also applies to other hazards responsible for the flooding of a ship such as bottom and side groundings. Traditionally, the application of Monte Carlo sampling of pertinent distributions allows for assessing ship survivability. Such a method introduces randomness in the process, leading to a dispersion of the attained survivability index within multiple sets of generated damages. The present work investigates sampling methods alternative to Monte Carlo, based on Latin Hypercube and Randomised Quasi-Monte Carlo processes. The sampling methods application for collisions, side and bottom groundings on a reference barge available in the literature for benchmark purposes shows that the Randomised Quasi-Monte Carlo method based on multidimensional Sobol sequences grants lower dispersion of the final survivability index data within samples of equivalent size. Finally, the application on a sample cruise ship of Monte Carlo and Randomised Quasi-Monte Carlo methods highlights the possibility to reduce the number of damage breaches necessary to evaluate the survivability index within an engineering confidence interval, thus improving accuracy and efficiency in the amplification of probabilistic damage stability methods by the industry.

Application of smoothed particle hydrodynamics method for simulating the flooding process of a damaged ship cabin in full-time domain

The flooding process of a damaged ship is very complicated and it closely relates to the ship survivability and life security. Therefore, it is very necessary to master the process of water flooding and its influencing factors. There are many approaches for the studies, such as the static one, the quasi-static one, and the full-time domain one, etc. In this paper, the Smoothed Particle Hydrodynamics (SPH) method combined with the strip theory is used to study the flooding process of a damaged ship cabin in full-time domain and three kinds of cabins are studied. The displacement, velocity, and rolling angle of the cabin during the process are compared and analyzed. Firstly, the flooding processes of damaged cabins with different opening positions, and opening sizes are simulated and the responses of the damaged cabins to the flooding hydrodynamics are obtained. Then, the effects of the barriers in the cabin on the flooding process are studied. Some reasonable suggestions are put forward to provide references for the anti-sinking design of ships.