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Presentation on ABS Advanced Analysis

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The Ship-Safe System by ABS Engineering utilizes advanced diagnostics and real-time monitoring to significantly enhance maritime safety and operational reliability. This comprehensive system ensures optimal vessel performance and safety through continuous assessment and early detection of potential issues.

ABS Engineering has introduced its innovative Ship-Safe System, a cutting-edge solution designed to enhance maritime safety and operational efficiency. This system integrates advanced sensor technology, real-time data analytics, and robust predictive algorithms to monitor vessel integrity and environmental conditions continuously. By providing critical insights and early warning alerts, the Ship-Safe System helps in preventing accidents and minimizing downtime.

Typical Presentation

The following has been taken from typical presentations on ABS experience and capability on advanced analysis for LNGC’s given by the Advanced ABS Engineering Analysis for LNGCABS Engineering and Focus Group members to the ABS clients and potential customers. Of course, depending of the source, the style of the slides will be different.

Presentation

In general the first figures of the presentation show the summary of the presentation that, in general contains all the aspects relative to the refined analysis that may be performed by ABS.

Safehull (safe-ship) Principles and Evolution

Figure 1 summarizes the history of SAFEHULL. SAFEHULL project started on 1990 as a revolutionary approach for the assessment of the scantlings of the ships. As anticipated in Module 5 and Part 1 of this Module, the introduction of SAFEHULL was ending the semi-empirical way to calculate the scantlings by simple formulae based on simple beam theory calibrated on basis of the experience on existing ships replacing it by a more sophisticated computer analysis, which takes into account the actual loads imposed by the sea on ship structures, and then adding, to the simple determination of the scantlings, a preliminary simplified fatigue analysis of the most critical areas.

Moreover, SAFEHULL is designer-friendly, once the geometrical data of the ship have been input, it permit one to find the best arrangement to optimize the distribution of the steel. Once the principles of SAFEHULL were settled, it was necessary to calibrate the program to the various types of ships. SAFEHULL for LNGC’s was introduced on 2001. It is to be noted that SAFEHULL is applicable to membrane LNG carriers.

Scheme - Safe-ship History
Fig. 1 History Safehull for Ships

SAFEHULL consists of two phases. The Phase “A” can be run on any PC and supplies the complete preliminary scantlings of the ships, based on the actual loads imposed by the environment and various loading cases. Basic scantlings of the ship may be assessed based on the Phase “A” results.

Scheme - Safe-ship System
Fig. 2 Safehull System

Phase “A” is followed by a more refined analysis, indicated as phase “B“. This is a sophisticated, three dimensional, Finite Element Analysis, which is used to confirm the results of phase “A“, to highlight possible high stressed spots, which would not be highlighted by carrying out the only phase “A“, to further optimize the structure having a more precise evidence of the behavior of the various structures in all the conditions that the ship might encounter during her life. In general the three dimensional model used for Phase B includes a portion of three holds of ship only. For a typical 4 tanks LNG carrier the typical model includes hold N. 4, 3 and 2.

SAFEHULL for LNGC’s has been tailored for membrane ships taking into account the loading patterns, the pressures deriving from the accelerations stated by the The Origins of the IGC CodeIGC Code, and the sloshing loads, supplies the required Hull Girder Section Modulus and assess the structures against Yielding, buckling and fatigue.

Part of SAFEHULL approach is the SAFEHULL monitoring approach described under Module 5.

The above is summarized in Figures 3 and 4.

Safe-ship Approach
Fig. 3 The Safehull Approach
Safe-ship Load Tips
Fig. 4 Safehull Load Considerations

SAFEHULL Phase “A”

Figure 5 is relative to Phase “A“. It shows a typical midship section of a membrane type LNGC drawn by SAFEHULL. In this slides the scantlings determined by SAFEHULL are not indicated.

Scheme - Membrane Type LNGC
Fig. 5 LNGC Membrane Type Components

SAFEHULL Phase “B”

Figure 6 is relative to the SAFEHULL Phase “B” and shows a typical three-dimensional model for the analysis relative to the cargo area.

The Cargo Area Model
Fig. 6 3D Global Coarse Mesh Model

Figures 7 and 8 show the same model after several running of the program for different loading conditions. The deformations of the hull are magnified to give emphasis to the behavior of the structures and the distribution of the stresses along the various structures is given through color codes in order to give an immediate perception of the high stressed areas.

Von Mises Stress Deformation
Fig. 7 VonMises Stress with Deformation
for Safehull Standard Loading Condition (L.C 1 to 4)
VonMises Stress Deformation
Fig. 8 Von Mises Stress with Deformation
for Safehull Standard Loading Condition (L. C 5 to 8)

Figures 9, 10 and 11 clearly show the model used for a Phase “B” analysis of a LNG carrier.

3D Coarse Mesh
Fig. 9 3D Coarse Mesh FEA
3D Fine Mesh
Fig. 10 3D Fine Mesh Model
Yielding Analysis
Fig. 11 Model Yielding Analysis

Figures 11 through 20 are relative to the zooming process to analyze the high stressed areas and to assess their fatigue life. The areas, which are indicated subject to high stress in the global coarse model, are examined in detail with fine mesh applying the loads and the stress obtained by in the global model.

Fatigue Analysis
Fig. 12 Model for Fatigue Analysis
Midship Zone Model
Fig. 13 3D Fine Mesh Model of Midship Zone
Hopper Knuckle Zone
Fig. 14 Fine Mesh Model of Hopper Knuckle Zone
Inner Skin & Inner Deck Knuckle Zone
Fig. 15 Fine Mesh Model of Inner Skin & Inner Deck Knuckle Zone
Transverse Bulkhead Zone
Fig. 16 Fine Mesh Model of Transverse Bulkhead Zone
No. 2 Stringer Zone
Fig. 17 Fine Mesh Model of No. 2 Stringer Zone
Lower Hopper Corner
Fig. 18 Lower Hopper Corner at Mid-Hold
Hopper Corner Upper Knuckle
Fig. 19 Hopper Corner Upper Knuckle at Mid-Hold
 Cofferdam BHD
Fig. 20 Cofferdam BHD Vertical Connections

Figure 21 indicates common causes of failure of structural details.

Causes of Failure
Fig. 21 Common Causes of Failure of Structural Details

Dynamic Loading Approach (DLA)

Dynamic Loading Analysis (DLA) is a sophisticated structural analysis to be carried out upon specific request of the Owner/Yard. From a certain point of view it may be considering as further step after SAFEHULL Phase “B” towards the accurate representation of the ship behavior. Figure 22 indicates the main steps of the approach.

Dynamic Load Approach
Fig. 22 Main Steps of the Approach

The approach starts from the definition of the actual statistical sea conditions in the routes the ship is likely to navigate during her life. This permits to arrange the model of the ship on a wave equivalent to the worst sea status (from the point of view of the ship’s strength) and to load the structures with the external static loads, the dynamic loads deriving from the movement of the ship and the internal loads due to the cargo, and its movement, if any (for instance slack holds). By imposing these loads on the structures designed in accordance with SAFEHULL, it is possible to determine the actual deflections, stresses, and to assess LNGC Fatigue Assessment and Heating Systemthe fatigue of the ship with a very high approximation. Figure 23 shows the complete model used for DLA.

 Model for DLA
Fig. 23 Global Finite Element Analysis

Figure 24 shows the ship model on the selected wave model.

Wave Profile
Fig. 24 Ship Model on the Wave Model

Figure 25 shows the distribution of the wave pressures on the ship.

Shell Pressure Distribution
Fig. 25 The Wave Pressures on the Ship

Finally figure 26 shows the deflections and the stresses of the hull.

Full Ship-safe Analysis
Fig. 26 The Deflections and the Stresses of the Hull

Spectral Fatigue Analysis (SFA)

As the DLA, the Spectral Fatigue Analysis (SFA) is a more refined analysis of fatigue, which, when performed, makes the ship eligible to the SFA class notation. Figures 27 and 28 are self-explanatory and delineate the SFA procedure.

The SFA Procedure
Fig. 27 Spectral Fatigue Analysis
SFA Procedure
Fig. 28 Spectral Fatigue Analysis Procedure

Figure 28 defines the environmental and cargo loading conditions, while slides 29 and 30 indicate the typical wave grid data used for the evaluation versus the typical wave data grid used by ABS.

Environmental and Cargo Lading Conditions
Fig. 29 The Environmental and Cargo Loading Conditions
Wave Grid
Fig. 30 The Typical Grid for Evaluation

The difference between the criteria used for fatigue assessment with SAFEHULL and SFA analysis are indicated in Figure 31.

ABS Grid
Fig. 31 The Typical Grid using by ABS

Figures from 32 through 41 show the screening and zooming process for the assessment of the fatigue life of the selected details.

Ship-safe and SFA Difference
Fig. 32 SAFEHULL and SFA Analysis Difference
SFA-Fatigue Screening Process
Fig. 33 Assessment Process of the Details Fatigue Life
Fine Mesh Model
Fig. 34 Local Finite Element
SFA Fatigue Test
Fig. 35 SFA-Fatigue Screening
Corner Hopper Design
Fig. 36 Hopper Corner Structure
Corner trunk design
Fig. 37 The Trunk Corner Structure
Cross Connection BHD
Fig. 38 Transverse BHD Connection
Opened Dome
Fig. 39 Dome Opening
Potential Crack
Fig. 40 Connection of Inner Bottom and Longitudinal Girder
Bunker Corner
Fig. 41 Hopper Corner
Ship-safe Corner
Fig. 42 Carrier Corner

Figure 43 shows the calculation of the hot spot stresses.

Hot Spot Stress Calculation
Fig. 43 The Hot Spot Stresses Calculation

Figure 44 shows typical results of SFA.

SFA Results
Fig. 44 Typical SFA Results

Figure 45 shows how fatigue life is calibrated.

Worldwide Trading Routes
Fig. 45 Calibrated Fatigue Life

DLA/SFA for Moss-Rosenberg Ship

SAFEHULL is not available for Moss-Rosenberg ships. In order to analyze these ships it is necessary to use the DLA and SFA approach. The following slides refer to the Steel Fracture Modes & Hull Structural Analysis of LNGDLA and SFA analysis carried out by ABS on the project of a 145 000 m3 Moss-Rosenberg LNGC.

Figures 46 through 50 show some details of the model mesh used for the analysis.

Model Mesh Details
Fig. 46 DLA for Moss-Rosenberg Ship
Model Mesh Details
Fig. 47 DLA for Moss-Rosenberg Ship (2)
Model Mesh Details
Fig. 48 DLA for Moss-Rosenberg Ship (3)
Model Mesh Details
Fig. 49 DLA for Moss-Rosenberg Ship (4)
Model Mesh Details
Fig. 50 DLA for Moss- Rosenberg Ship (5)

Figures 51 through 53 show the ship model on the selected wave model as well as the ship behavior in rough sea.

Wave Model Ship-safe
Fig. 51 Ship Model on the Wave Model
Rough Sea Ship Behavior
Fig. 52 Ship Behavior in Rough Sea
 Boat Behavior
Fig. 53 Vessel Behavior in the Storm

Figures 54 and 55 show the pressure distribution on the sides of the model and the calculated hull girder bending moments.

Pressure Distribution Model
Fig. 54 Model Pressure Distribution
Flexion Moment
Fig. 55 Vertical Bending Moment of the Beambody

Next 8 figures (56-63) show examples of deflection and stress distribution of the whole hull and some selected parts in various loading conditions.

Shell Part
Fig. 56 Shell Part Condition
Inner Hull Part
Fig. 57 Inner Hull Part Condition
Cover
Fig. 58 Cover Condition
Skirt Position
Fig. 59 Skirt Condition
For_Part
Fig. 60 For_Part Condition
 Mid_Part
Fig. 61 Mid_Part Condition
Aft_Part
Fig. 62 Aft_Part Condition
 Bow_Part
Fig. 63 Bow_Part Condition

Finally, figures 64 and 65 show an example of the zooming process on the high stressed area at the connection between the deck covering and the deck.

High Stressed Area
Fig. 64 Tank Cover
Area of High Stress
Fig. 65 Cover of the Tank

DLA for SBP Ships

Figures 66 and 67 show the models for a SPB FPSO and for the concept design of a large SPB ship.

Stress Distribution
Fig. 66 FEA model for FPSO with SPB tank
Hold Part
Fig. 67 Model of Hull and Tank for LNGC

Sloshing

Sloshing, especially on membrane ships, is a major problem. The major classification Societies are strongly competing to offer to the analysis more and more realistic and reliable, as this is one of the point that will be considered to assign the classes of the new generation larger LNGC’s. ABS has the capability to perform very sophisticated and realistic analysis of sloshing. Figure 68 summarizes the reason for which partial load is requested and figure 69 the main concern of partial loading.

Shlosing in LNG Tanks
Fig. 68 LNG Tank Shlosing
The Partial Loading
Fig. 69 Drivers for partial Loads

Figures 70 and 71 describe the ABS approach and contribution to the sloshing problem.

Prevailing Practice
Fig. 70 Approach and Contribution of ABS
Sloshing Analysis of ABS
Fig. 71 ABS Sloshing Analysis

Figures 72 through 74 describe ABS technical approach and the conclusions at this date on the sloshing problem.

Critical Sloshing Domain
Fig. 72 Technical Approach and Conclusions of ABS
Critical Rocking Loads
Fig. 73 Critical Sloshing Loads
Experimental Verification
Fig. 74 Experimental Validation

Finally, figure 75 focuses characteristics and problems of high filling limits versus low filling limits.

HFL & LFL
Fig. 75 Difference between HFL & LFL

Pump Tower Strength Assessment

Figures 76 to 78 are relative to the verification of the strength of the pump tower against the loads imposed by sloshing and the thermal loads.

Pump Tower
Fig. 76 Strength Verification of the Pump Tower
Ship-safe Stress
Fig. 77 Stress due to Swinging Load
Thermal Stress
Fig. 78 Thermal Stress at low Filling

Insulation Strength Assessment

In general, insulation/membrane systems for today’s standard LNG carriers (up to about 145 0000 m3 capacity) are quite well established and the experience of these systems is satisfactory. However, there is the concern whether the strength of these systems is also suitable for the next generation of larger LNG carriers.

For this reason, the assessment of the strength of the insulation system of the largest ships against the static, dynamic and sloshing loads is today a very important issue.

Figure 79 lists the data to be taken into account to verify the strength of the insulation / membrane system of a LNG carrier.

Strength Insulation System
Fig. 79 The Strength of Insulation System

Figure 80 shows wet and dry drop test on NO.96 and MARK III insulation simple samples. Dry test measures the impact strength of the insulation system. Wet test gives the actual response of the hull structures to the cargo loads transmitted through the non-rigid insulation.

Dry Test
Fig. 80 Strength Tests

Figures 82, 83 and 84 show the actual stress dumping through the insulation.

Test Simulations
Fig. 81 Stress Relief through Insulation
Pressure & Damping
Fig. 82 Test Pressure & Stress Damping
Stress due Insulation
Fig. 83 Test Reaction Forces at Mastics

Figure 85 shows some self-explanatory conclusions.

Some Conclusions
Fig. 84 Self-Explanatory Conclusions

Figure 86 shows MARK III system failure mode.

MARK III Failure Mode
Fig. 85 MARK III System Failure Mode

Figure 87 shows how the safety factor is assessed.

Safety Factor
Fig. 86 ABS Sloshing Procedure

Footnotes
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