Intact Stability Research Articles

Design, local structural stress, and global dynamic response analysis of a steel semi-submersible hull for a 10-MW floating wind turbine

Platforms for floating wind turbines cannot be designed using conventional procedures like other offshore constructions. The design of floating wind turbine platforms must consider the significant nonlinearity of the fully coupled aero-hydro-servo-elastic dynamics, which necessitates a time-domain load transfer for structural stress analysis. This article presents and verifies an effective yet practical design method for floating wind turbine platforms, which can provide reasonable internal stress for design checks. A robust design process is proposed. Following the proposed method and procedure of a 10-MW wind turbine, a steel semi-submersible platform is developed with the criterion for the steel platform’s design checks, intact stability analysis, natural period analysis, and buckling analysis executed. A tangible concept is established, along with fully coupled numerical models of the 10-MW wind turbines supported on the steel structure. The dynamic behavior of the steel platform is evaluated by accessing and comparing the dynamic performances of the concrete- and steel-support wind turbine numerical models. The key findings and conclusions from the steel platform’s design and numerical study are summarized below. In addition, future design and analysis ideas are proposed, expanding the engineering practice and research on floating wind turbine platforms.

Toward the analysis of functional proteoforms using mass spectrometry-based stability proteomics.

Functional proteomics aims to elucidate biological functions, mechanisms, and pathways of proteins and proteoforms at the molecular level to examine complex cellular systems and disease states. A series of stability proteomics methods have been developed to examine protein functionality by measuring the resistance of a protein to chemical or thermal denaturation or proteolysis. These methods can be applied to measure the thermal stability of thousands of proteins in complex biological samples such as cell lysate, intact cells, tissues, and other biological fluids to measure proteome stability. Stability proteomics methods have been popularly applied to observe stability shifts upon ligand binding for drug target identification. More recently, these methods have been applied to characterize the effect of structural changes in proteins such as those caused by post-translational modifications (PTMs) and mutations, which can affect protein structures or interactions and diversify protein functions. Here, we discussed the current application of a suite of stability proteomics methods, including thermal proteome profiling (TPP), stability of proteomics from rates of oxidation (SPROX), and limited proteolysis (LiP) methods, to observe PTM-induced structural changes on protein stability. We also discuss future perspectives highlighting the integration of top-down mass spectrometry and stability proteomics methods to characterize intact proteoform stability and understand the function of variable protein modifications.

Weight Assessment of Marine Diesel Main and Auxiliary Engines

During the conceptual and preliminary ship design stages, designers must ensure that the selected principal dimensions and parameters are good enough to deliver a stable ship (statically and dynamically), besides deadweight and speed. To support this, the initial intact stability of the proposed ship must be calculated, and for that, the lightship weight and its detailed breakdown are necessary to be known. After hull (steel) weight, machinery weight, mainly marine diesel propulsion and power generation machinery, plays a vital role in the lightship weight estimate of a ship directly. It also affects the deadweight, displacement, draft, and trim, which finally influence stability. The correct estimation of respective weights improves calculating a ship’s initial stability, typically designed and built. Hence, it would be advantageous for the ship designer to convince the shipowner. Weight control is not easy, especially since its consequences in terms of deadweight and stability could be disastrous. It should start right at the beginning and control throughout the design and construction phases. Marine diesel main engines (MEs) and auxiliary engines (AEs) of various power output (generators output for AEs), engine speed, and cylinder number of different engine manufacturers are collected. These are analyzed and presented in tabular and graphical forms to demonstrate the possible relationship between propulsion engine weight and power generation engine weight, and their respective power, speed, and power–speed ratio. In this article, the authors have attempted to investigate the appraisal behavior of ME weight and AE weight regarding engine power, generator power, engine speed, and power–speed ratio (independent variables). Further attempts have been made to identify those independent variables that influence the weight of the propulsion engine and power generation engine (dependent variables) and their interrelationships. A mathematical model has thus been developed and proposed, as a guiding tool, for the designer to estimate the weight of main and AEs more accurately during the conceptual and preliminary design stages.

Analisa Pengaruh Peletakan Panel Surya di Atas Deck House Kapal Ikan 30 GT Terhadap Keselamatan Operasional Penangkapan Ikan

The purpose of this study is to analyze the effect of laying solar panels on the deckhouse of small fishing vessels 30 GT. The additional load above which causes weight gain and will affect the ship's center of gravity is became the first effect of Fishing vessel stability. The second effect is on how the fishing vessel performs when there is a solar panel on the vessel. The data were collected by measuring the stability according to A.N Kyrylo’s method with standard checks according to the IMO (International Marine Organization). Code on Intact stability calculated the ship motion by using the STRIP method and measuring the wave characteristics using the JONSWAP method with the help of Maxsurf software. The results of this research show that the installment of solar panels above the deckhouse does not really affect the stability, where the results were agreed to the IMO standard criteria. Moreover, the success of the fishing operation will be more visible if the vessels operated on waves under 2 meters due to the more stable movement according to its seakeeping performance .

Extrapolation of ship capsize probability over significant wave height: Foundation on wave groups theory

The paper lays formal foundation for the “extrapolation over significant wave height” technique which has recently been incorporated into the Second Generation Intact Stability Criteria of the International Maritime Organization (IMO) for assessing the dynamic stability of ships in waves. The technique aims at estimating efficiently a ship's tendency to capsize in relatively mild sea conditions through parsimonious simulations of ship motion. To address the rarity of capsizes in such conditions, extrapolation is employed for the probability value obtained from severer sea states differing only in their significant wave heights. In its current version, the approach extrapolates as if capsize was caused solely by exceptionally large wave encounters, thus ignoring phenomena such as resonance or wave grouping. Herein, the concept is revisited from the perspective of the “critical wave groups” method which is demonstrated as a general framework enabling rigorous “extrapolation over significant wave height” formulations. In this setting, two new extrapolation models are developed from basic principles as improvements to the one suggested by the IMO. The first model accounts for the joint effect of wave heights and periods, while the second additionally integrates the temporal dependence between consecutive wave heights into the extrapolation scheme. The accuracy of the theoretical predictions as well as their sensitivity to the amount of available data are evaluated for the case of beam-sea rolling assuming two different spectrum types as possible characterizations of the prevailing wave conditions. Justification about the extrapolation capabilities of the derived models is provided in view of the advances in extreme wave stochastics accommodated by the theory of Quasi-Determinism.

Investigating the Capsizing Incident of the RoPax OCD Vessel Utilizing the RAO Approach in Wave Conditions

RoPax is the most famous ship in the world that simultaneously carries multipurpose such as passengers, cargo, and vehicles in bulk. Cargo ships experience the most accidents, but RoPax ships contribute the most casualties worldwide. RoPax OCD is practical and economical for the short-medium route but vulnerable in intact dynamic stability that causes capsize. The paper analyses the data of RoPax Opened Car Deck (OCD) accidents in range time (2003-2021) in Indonesia water that is reviewed by the Response Amplitude Operator (RAO). Internal ship data is obtained from Indonesia’s National Transportation Safety Committee (NTSC), and external data on wave characteristics are obtained from Global Ocean Waves Reanalysis Waves of Copernicus Marine Service. From RAO analysis of eight capsizing cases of RoPax OCD show that 62.5% occur in sub-critical (effect of low stability moment), 25% occur in supercritical (a result of small weight inertia moment), and 12.5% occur in critical (a consequence of small damping moment). The conclusion is that stability problems are the leading cause of the capsizing of RoPax, so existing ships must improve their stability or be diverted to operation areas with suitable wave characteristics.

Risk Accident Analysis Due to the Effect of Wrong Loading on Ship Stability

In this study, the effect of laying and shifting load is considered as one of the main factors of ship safety. Ferry Ro-Ro that carry vehicles and passengers were chosen as the object of study with the assumption that the vehicles are not lashed. Safety measurement is carried out through static stability analysis with criteria limits IMO Intact Stability Code 2008 and PM44 2021 and dynamic stability with roll motion limitations due to beam sea to result quantitative risk assessment data. The wave height is taken from the waters of the Bali strait with a Beaufort scale conversion of BF1 to BF6. Because of the vehicle is not lashed, the vehicle is simulated to shift horizontally as far as 10% to stack onto the starboard, while the assumption of passenger movement is vertical and horizontal. The biggest heel angle due to the shifting load is 9 degrees when all loads are stacked on the starboard (G1). Analysis of the calculation of static stability shows that several conditions do not meet the criteria with the greatest Roll Amplitude value of 39.56 deg at BF6 4 m. In dynamic stability conditions through maxsurf motion, the safe wave height for Ferry Ro-Ro operation is up to BF4 1.14 m. The highest risk of ship capsizing occurs when operating on BF5 with wave heights above 2 m.

Intact stability operational measures: Criteria, standards and examples

Harmonised treatment of design and operation is very efficient to provide a required safety level. However, operation is usually not addressed by intact stability rules of IMO or classification societies. A substantial change was introduced in the second-generation intact stability criteria of IMO, which address both design requirements and ship-specific operational measures. Moreover, this is done using the same criteria, standards, and safety level, so that operational measures can be used as a loading condition-specific alternative to design assessment. This paper proposes several operational measures, discusses relevant criteria, and defines corresponding acceptance thresholds. Further, it is discussed whether operational measures can always be acceptable as an alternative to the design assessment, when operational measures should be prepared, and how cross-sea and ship propulsion and steering abilities can be addressed. Examples of the proposed operational measures are shown for five ships.

Evaluation by a Quantitative Index about Intact Stability Performance in Waves of a Set of Megayacht Units

Intact stability represents one of the most important topics when addressing ship safety, and it is ruled by the IMO Intact Stability code, evaluating ship stability in a calm water scenario. However, the interest in ship stability in waves has increased in recent years and this has led to the formulation of the second generation intact stability criteria (SGISc), finalized at IMO in 2020. In this research, an approach to quantitatively and comprehensively evaluate the ship stability performance in waves has been pursued. A methodology is developed with reference to the SGISc. The intact stability in waves index (ISWI) has been proposed, with the aim to become a complementary tool for designers and shipbuilders in the assessment of stability performance in waves. The ISWI represents a comprehensive stability index, able to capture the stability in waves performance of a vessel. The stability index has been verified on a set of megayacht units and its sensitivity to the wave characteristics has been tested, changing the environmental conditions. The outcomes point to a good agreement between the ISWI and the influence of environmental condition changes on the stability performance.

Application of Buoyancy Support System to Secure Residual Buoyancy of Damaged Ships

SOLAS (Safety of Life at Sea), which was first enacted in 1914 as a result of the Titanic disaster, presents mandatory requirements for ship safety, such as the adoption of watertight bulkheads. However, ship accidents continue to occur despite the development and application of numerous safety technologies. In the case of a marine accident, the risk of sinking or capsizing due to flooding can be reduced by subdividing the watertight area, but shipbuilding costs, the weight increase for light ships, and the intact stability of the vessel must be considered together. For this reason, in this study, a BSS (buoyancy support system) was designed in accordance with ISO 23121-1 and ISO 23121-2. The characteristics of watertight and non-watertight spaces were reviewed and the BSS was implemented for a small car ferry. By applying additional safety technologies while securing economic feasibility in terms of ship construction and operation, an alternative to reduce the loss of human lives, environmental damage, and property losses in the case of a ship accident was proposed.

Parameter sensitivity of the excessive acceleration failure mode in second-generation intact stability

In this study, the parameter sensitivity of the level 1 and 2 assessments of the excessive acceleration failure mode in the International Maritime Organization second-generation intact stability was analyzed. Monte-Carlo simulations were conducted using the input parameter space, which was generated using a Gaussian distribution, and a variance-based sensitivity analysis was performed using the Monte-Carlo simulation results. The longitudinal and vertical positions of the check point, natural roll period, and roll decay coefficient were selected as input parameters for the level 1 assessment, whereas the roll damping coefficient and effective wave slope coefficient replaced the roll decay coefficient for the level 2 assessment. The results revealed that the highest total sensitivity index for the level 1 assessment was the natural roll period, which was 0.8, and the effective wave slope had a total sensitivity index of 0.5 for the level 2 assessment. This indicated that the uncertainty of the natural roll period was dominantly propagated to the resultant value of the level 1 assessment, while the effective wave slope coefficient was the most sensitive parameter in the level 2 assessment. The uncertainty in the input variable was found to cause the opposite decision if the resultant value was close to the criterion value under a given loading condition.

Initial Design of a Novel Barge-Type Floating Offshore Wind Turbine in Shallow Water

The studies on floating offshore wind turbines (FOWTs) have been increasing over recent decades due to the growing interest in offshore renewable energy. The present paper proposes a barge platform with four moonpools to support the Technical University of Denmark 10 MW wind turbine for a designed water depth of 60 m. A 4 × 2 mooring system with eight mooring lines is also proposed for the barge platform. The main dimensions of the barge platform are optimally selected with respect to its preliminary hydrodynamic properties and potential financial benefit. The proposed barge-type FOWT is then demonstrated to be aligned with the DNV standard requirements in terms of its intact and damage stability. Furthermore, coupled time-domain simulations are conducted for the proposed barge FOWT with mooring under the selected environmental and operational conditions by using Simo-Riflex-AeroDyn (SRA). Through decay test simulations, the natural periods of the barge-type FOWT are demonstrated to be within the DNV recommended ranges. The proposed mooring system is also benchmarked with the 3 × 3 mooring concept that was used for a 3 MW barge-type FOWT installed in Kitakyushu. The response magnitudes of the barge platform and mooring line tension are similar to both mooring systems, and thus the 4 × 2 mooring system is preferred due to its lower cost. In addition, the proposed barge platform is preliminarily demonstrated to be able to survive for the 50-year extreme environmental conditions under parked wind turbine status, as well as the normal environmental conditions under the operating status.

Further Study on One of the Numerical Methods for Pure Loss of Stability in Stern Quartering Waves

The International Maritime Organization (IMO) finalized the second-generation intact stability criteria in 2022. However, an accurate and practical numerical method for stability loss has yet to be established. Therefore, a 6 DOF numerical model is further improved based on the previous study. Firstly, the rolling motion is simulated using a seakeeping model instead of the previous maneuvering mathematical model. Secondly, the roll-restoring variation is calculated directly considering the instantaneous wet hull instead of the previous pre-calculated method. Thirdly, transferring frequency to time is used to obtain heave and pitch motions, further considering yaw angle and sway velocity. Fourthly, the dynamic forces for sway, roll, and yaw motions are calculated, further considering the effect of the speed variation. Fifthly, the 6 DOF motions are used to determine the instantaneous wet hull, and the FK force and the hydrostatic force are calculated by the body’s exact method. Finally, a new conclusion is obtained that the sway and yaw motions’ effect on the ship speed loss, the relative longitudinal wave profile by the speed loss, the rudder angles, and the accompanying rudder forces in the rolling direction are significant, and much more than their centrifugal force or coupled force in the rolling direction.

Level 1 vulnerability criterion for the dead ship condition: A practical methodology for embedding operational limitations

The framework of second generation intact stability criteria (MSC.1/Circ.1627) allows introducing so-called “operational limitations”, by specifying alternative environmental conditions based on the expected operation of the ship. Relevant calculation parameters of the criteria are correspondingly modified, according to standardized procedures specified by the Explanatory Notes. This is a significant novelty, and information is available for implementing operational limitations for most of the failure modes and levels of assessment. However, this is not the case for the level 1 vulnerability criterion for the dead ship condition. Therefore, the paper investigates the development of a rational simple procedure to contribute filling this gap. The devised approach provides a tool for determining a modified reference wind speed based on the environmental conditions representative of the considered operational limitations. Specifically, the modified wind speed is defined as the wind speed with a specified probability of exceedance. The reference probability of exceedance is determined considering the standard conditions and assumptions in the framework of MSC.1/Circ.1627. The modified reference wind speed can then be used to re-define all the calculation parameters of the criterion, according to the relevant theoretical background. Two example applications of the devised approach are also provided.

Complements to Level 2 surf-riding/broaching vulnerability criterion regarding waterjet propelled ships and wave surge force correction

The Second Generation Intact Stability Criteria (SGISC) has officially entered the trial period for further validations and to collect feedback based on applications. This study focuses on the Level 2 surf-riding/broaching vulnerability criterion and proposes complements to the assessment procedures regarding two important issues. One is that the current procedure is only applicable to ships using propellers. However, waterjet propelled ships are common nowadays and they may be vulnerable to this stability failure mode as well. The other issue is that there lacks a both reliable and practical method for the wave surge force correction. The current procedure uses the Froude-Krylov (FK) component of the first order wave surge force as the input for the assessment, which significantly over-estimates the probability of surf-riding occurrence.Through the introduction of the thrust coefficient KT and the advance coefficient J for waterjet systems, the first issue is addressed by model the waterjet thrust based on the KT ∼ J relationship just as that of propellers. The validity of such treatment is first demonstrated through the actual data of a real pump, while the rationale behind the universality of such modelling is analyzed based on dimensional analysis. The second issue is addressed through the proposal of a practical method to estimate the wave surge force correction factor based on the ratio between the first order wave surge force and its FK component. Sample ship calculations are performed to demonstrate the reliability of the proposed method. Finally, the complete Level 2 surf-riding/broaching vulnerability assessment for a waterjet propelled ship is performed for demonstration. This study contributes to the improvement of SGISC, making it applicable to a wider range of ship types with higher accuracy.

Simplified operational guidance for second generation intact stability criteria

The SGISC have been developed to account for dangerous dynamic phenomena in waves. Five failure modes are defined, and a multi-layered structure, consisting of vulnerability criteria and Direct Stability Assessment, is adopted to check the ship vulnerability against each phenomenon. If the ship does not comply with one or more criteria, Operational Measures can be provided to reduce the likelihood of stability failures.The present paper provides an overview of Operational Measures and focuses on the application of the Simplified Operational Guidance (OG) for four different ships, each vulnerable to at least one of the failure modes. OG are derived according to IMO Interim Guidelines, by limiting ships’ operation in terms of sailing conditions. The original contribution of this work is the development and application of simple procedures to account for the effect of heading variations, leading to less conservative results in the evaluation of sailing conditions to be avoided.Results are presented in tabular form, reporting the critical speed for which the ship is vulnerable in defined headings, and in polar diagrams, identifying safe sailing conditions for given sea states.

Standard Wave Scatter Table Limitation for Evaluating SGISC Based on Hindcast Data Analysis

The operational measure (OM) of the Second-Generation Intact Stability Criteria (SGISC) is the initial step toward the design of a performance-based dynamic stability assessment of the ship by considering the vessel’s operation, loading condition and weather parameters. The SGISC recommends the standard wave scatter table (WST) for the environmental data, an indefinite requirement for a simplified assessment pathway, which provides the probability of wave occurrence. The existing standard WST was developed based on the North Atlantic Ocean. The study aims to identify the discrepancy in the probability of wave occurrence in the IMO-recommended WST when compared with developed hindcast WST for smaller regions of the North Atlantic Ocean for the application of the SGISC. This study is one of a kind and very significant, given that the assessment using the standard WST provided unrestricted operational ability to ship under the SGISC. The findings of this research provide insights into significant differences in the existing standard WST when compared graphically with hindcast data, especially across different seasons of the North Atlantic Ocean. A case study of OMs on the C11 class post-Panamax container ship for excessive acceleration is provided to better represent the study. In the case study, the operational limitation defined by the hindcast WST for individual sea areas and seasons is compared with the standard WST. This investigation shows that regional and seasonal operational limitations are required for season 4 operation beyond the standard WST safety estimation and that the operational limitation achieved with standard WST is not adequate. The findings suggest that the identified limitations significantly limit the use of a standard WST for unrestricted operational validation in the SGISC. The provided recommendation is very relevant in improving the safety assessment using vulnerability criteria, given that the hindcast data are reliable and available for the season and are also region-specific, and hence the accuracy of the ship stability can be improved while using the SGISC.

Real-time ship stability evaluation program through deterministic method based on second-generation intact stability

IMO suggests Second-Generation Intact Stability Criterion (SGISC), which consists of five failure modes, because of continuous accidents due to a lack of ship stability. In this study, Level 1 and Level 2 stability of SGISC were evaluated for three stability failure modes (Dead Ship Condition, Surf-riding, and Excessive Acceleration). Level 1 was calculated in the same way as the second-generation intact stability calculation method, and Level 2 was calculated in a deterministic manner by using a real-time maritime environment rather than a probabilistic approach for all maritime environments. Based on this, a program was developed to visualize dangerous and safe areas on a map. Using the developed program, it is expected that SGISC can be used not only in the design stage, but also in the operation stage of ships, such as route planning or selection of operating locations in the ocean.

A Vulnerability Criterion of Dynamic Instability for Ship Course-Keeping in Following Waves

_ A practical criterion which can be used for assessing the course-keeping capability of a ship in following waves, is proposed and evaluated. Presently, it accounts for regular waves and it accrued from an analytical estimation of the course instability region’s boundary by applying the method of harmonic balance. The calculation is performed with regard to the third-order yaw equation, derived from a classic sway-yaw-rudder model of ship maneuvering motions, with time-dependent coefficients at two places, which is like a Mathieu-type equation extended to third order. The proposed analytical criterion was evaluated thoroughly against simulations with regard to this sway-yaw model and it was found to be adequately accurate. A supplementary quasi-static yaw stability criterion (fitting to ship operation with frequency of encounter, with respect to the waves, close to zero) was also considered in order to determine which one yields more stringent requirements, for various operating conditions. The proposed criterion could be an extra vulnerability check for broaching-to, in the context of the Second Generation Intact Stability Criteria. Introduction The difficulties of steering of ships in following seas have received the attention of the research community since more than 70 years ago (Davidson 1948). A relevant direction of research refers to the avoidance of the broaching-to instability and, in particular, to the development of practical criteria that could ensure sufficient course-keeping capability for a ship encountering steep following waves. Some classic works on this topic, such as those of DuCane and Goodrich (1962), Wahab and Swaan (1964), and Motora et al. (1981), were focused on the quasi-static condition of a ship on the wave which could be practically realized if the ship was advancing with speed equal to the wave celerity (zero frequency of encounter). As implied, these works were essentially focused on the avoidance of a type of broaching-to instability that is preceded by the realization of surf-riding, a phenomenon where the ship is forced to move with the wave, usually riding a downslope.

Design and Dynamic Analysis of a Novel Large-Scale Barge-Type Floating Offshore Wind Turbine with Aquaculture Cage

In this study, a novel large-scale barge-type floating offshore wind turbine with an aquaculture cage (LSBT-FOWT-AC) in a water depth of 100 m is designed through fully coupled analysis using the SESAM tool to support the Technical University of Denmark (DTU) 10 MW wind turbine. The intact stability and natural period of motion of the newly designed LSBT-FOWT-AC are evaluated based on the DNV rules and standards. Then, the dynamic responses of the LSBT-FOWT-AC under various sea conditions are studied. The motion of the LSBT-FOWT-AC platform is considerably affected by waves, and its motion response is within a reasonable range even under the extreme sea conditions of the 100-year return period. By analyzing the results of the out-of-plane bending moment of root of blade 1 (RootMyc1), it can be seen that the rotor frequency (1P) has a visible influence on the wind turbine. Through the analysis of dynamic response statistics of the LSBT-FOWT-AC structure by the single variable method of environmental loads, it is found that wind force exerts the greatest impact on the dynamic response compared to the wave-excitation force and current drag force.