Experimental Investigation Into SWATH Ship Motions and Loadings

The main objectives of this thesis are firstly to present experimental data of SWATH (Small Waterplane Area Twin-Hull) ship motions and dynamic loadings, and secondly to compare the experimental data with the existing numerical modellings for validation purposes. The experiments were conducted by employing a model of tandem strut per hull configuration (SWATH1) . The basic idea of using this configuration is as the SWATH ship is a relatively new concept of advanced marine vehicle, and as there can be a wide range of configurations, experimental data on any particular configuration, such as the SWATH1 model, is very limited. The first and second chapters of this thesis will overview the basic concept of SWATH ships development and the theoretical background of SWATH ship motions. SWATH1 model motions in three different sea heading, namely beam, quartering and head seas are investigated. The experimental results are then presented together with the theoretical predictions based on two-dimensional strip theory and three-dimensional sink-source technique. The agreement amongst the three sources is then discussed. The usefulness of the experimental data from the previous work in improving SWATHL computer program is briefly described. Further experiments are set up to investigate the dynamic loads on the SWATH1 model in regular beam and quartering seas. The investigations are focused on the bending moment on the cross structure and vertical forces on the struts. The data generated is important for a study of SWATH structures. From a practical point of view, the motion and structural loading characteristics of a SWATH ship in regular seas are meaningful if the data generated can be used for predicting the motions and loadings in random seas. The only reliable method to accomplish this task is the application of spectral analysis. This is outlined in chapter seven, including evaluation by making use of SWATH seakeeping criteria. Recommendations for future experiments on SWATH model motions and loadings are outlined in the conclusions

Analisis Integritas Struktur Kaki Jack-up yang Mengalami Retak dengan Pendekatan Ultimate Strength; Studi Kasus Jack-up Maleo MOPU (Mobile Offshore Production Unit)

Jack-up adalah suatu struktur bangunan lepas pantai yang terdiri dari lambung (hull), kaki (legs), dan suatu sistem jacking sehingga memungkinkan untuk dipindahkan dari satu lokasi ke lokasi yang lain. Pada penelitian ini akan dilakukan studi kasus struktur Maleo MOPU (Mobile Offshore Production Unit) yang dioperasikan oleh SANTOS (Madura) Pty.Ltd. yang beroperasi di Selat Madura blok Maleo dengan kedalaman perairan di lokasi ini adalah 57 m terhadap MSL (Mean Sea Level). Studi kasus ini dilakukan karena ditemukan indikator retak lelah/damage pada sambungan antara kaki jack-up dan mudmat. Analisis ultimate strength akan dilakukan untuk mengetahui integritas struktur terhadap beban maksimal . Variasi dead load, live load dan environmental load menjadi tahapan penting dalam analisa ini untuk mengetahui tingkat integritas struktur. Dengan pengaruh variasi beban (dead load dan live load) terhadap struktur untuk tiap-tiap kasus didapatkan nilai unity check (UC) yang dari semua kasus dikategorikan aman karena tidak ada nilai UC yang melebihi 1,3 (API RP 2A WSD). Dari semua analisis yang dilakukan dead load lebih berpengaruh dibandingkan dengan live load. Dari analisis pushover yang telah dilakukan pada jack-up Maleo MOPU yang dimitigasi dengan menambahkan brace dan menambahkan ketebalan dihasilkan nilai Reserve Strength Ratio (RSR) terkecil pada arah pembebanan 2700 dengan nilai 6,5 pada Brace Clamp case dan terbesar dengan nilai 18,3 pada X-Bracing case. Nilai RSR tersebut masih memenuhi syarat yang telah ditetapkan API RP 2A berupa nilai RSR minimal untuk platform berpenghuni adalah 1,6.

Hydro-structural studies on swath type vessels

This thesis presents a study on SWATH type vessels which is directed towards the collection and use for structural design of experimental data related to motions and primary dynamic loads of such vessels. This data will be of use in the validation of a mathematical model for motion and wave load predictions recently developed at the Department. Further, experimental data on slamming will also be acquired to lay a foundation for the future development of a reliable analytical model. Design loads pertinent to SWATHs comprising the extreme primary loads, lifetime cyclic loads and local panel pressures are then built upon the former findings to be of use in structural designs, especially in the determination of initial scantlings and fatigue characterisation. Examples are given throughout on the evaluation of hypothetical SWATHs operating in the North Atlantic. The underlying theoretical formulation of SWATH ship motions is presented together with a description of a newly developed motion prediction theory. This is followed by a clarification of the procedures for conducting seakeeping tests on SWATH models. Validation of the analytical motion model by the measured data of single and tandem strut SWATH models is then presented. Subsequently, practical applications of implementing motion predictions to the assessment of SWATH operatiblity in real seaways are described. Theoretical background of SWATH primary wave loads is briefly outlined. The enhancement of the motion program MARCHS to tackle the primary load on SWATHs is described. The development of experimental data on SWATH loadings by way of seakeeping techniques is presented. Correlation of this experimental data and the theoretical assessment is made to demonstrate the validity of the mathematical model so developed. Lifetime cyclic and extreme loads required in the fatigue and ultimate strength designs, respectively, are developed by applying long- and short-term wave statistics

Ensemble Kalman Filter with a Square Root Scheme (EnKF-SR) for Trajectory Estimation of AUV SEGOROGENI ITS

Results of a study on the development of navigation system and guidance for A UV are presented in this paper. The study was carried to evaluate the behavior of A UV SEGOROGENI ITS, designed with a characteristic length of 980 mm, cross-section diameter of i80 mm, for operation in a 3.0 m water depth, at a maximum forward speed of 1.94 knots. The most common problem in the development of AUVs is the limitation in the mathematical model and the restriction on the degree of freedom in simulation. in this study a model of linear system was implemented, derived from a non-linear system that is linearized utilizing the Jacobian matrix. The linear system is then implemented as a platform to estimate the trajecto1y. in this respect the estimation is carried out by adopting the method of Ensemble Kalman Filter Square Root (EnKFSR). The EnKF-SR method basically is developedfrom EnKF at the stage of correction algorithm. The implementation of EnKF-SR on the linear model comprises of three simulations, each of which generates 100, 200 and 300 ensembles. The best simulation exhibited the error behveen the real tracking and the simulation in translation mode was in the order of 0. 009 m/s, whereas in the rotation mode was some 0. 00 I radls. These fact indicates the accuracy of higher than 9 5% has been achieved. Copyright© 2015 Praise Worthy Prize S.r.l

Fatigue Life Analysis of Mooring System: The Effect of Asymmetry Mooring System Configuration on Single Point Mooring

This journal explains the fatigue life analysis of anchor chain in the stand-alone single point mooring by comparing the 4x1 asymmetric and symmetrical mooring system configurations to determine whether the effect of the asymmetrical mooring system configuration on the fatigue life of the anchor chain is related to the length of the mooring lines, the pretensions of the mooring lines, and the angle of spread. The analysis was reviewed on the condition of ULS and FLS environmental loading based on API RP 2 SK code using Orcaflex with 3 hours of time- domain simulation. In the ULS condition, the symmetrical configuration can withstand environmental loads better in the direction of 0o and 180o with the generated maximum tension and maximum offset value smaller than the result from asymmetrical configuration. While the asymmetrical configuration can withstand environmental loads better in the direction of 90o and 270o with the generated maximum tension and maximum offset value smaller than the result from symmetrical configuration. In the FLS condition, the asymmetrical configuration has a longer minimum fatigue life and design life of anchor chain than the symmetrical configuration. This happens because of the spread angle of the mooring line, the length of the mooring line, and the pretension of the mooring lin

Ensemble Kalman Filter with a Square Root Scheme (EnKF-SR) for Trajectory Estimation of AUV SEGOROGENI ITS

Results of a study on the development of navigation system and guidance for A UV are presented in this paper. The study was carried to evaluate the behavior of A UV SEGOROGENI ITS, designed with a characteristic length of 980 mm, cross-section diameter of i80 mm, for operation in a 3.0 m water depth, at a maximum forward speed of 1.94 knots. The most common problem in the development of AUVs is the limitation in the mathematical model and the restriction on the degree of freedom in simulation. in this study a model of linear system was implemented, derived from a non-linear system that is linearized utilizing the Jacobian matrix. The linear system is then implemented as a platform to estimate the trajecto1y. in this respect the estimation is carried out by adopting the method of Ensemble Kalman Filter Square Root (EnKFSR). The EnKF-SR method basically is developedfrom EnKF at the stage of correction algorithm. The implementation of EnKF-SR on the linear model comprises of three simulations, each of which generates 100, 200 and 300 ensembles. The best simulation exhibited the error behveen the real tracking and the simulation in translation mode was in the order of 0. 009 m/s, whereas in the rotation mode was some 0. 00 I radls. These fact indicates the accuracy of higher than 9 5% has been achieved. Copyright© 2015 Praise Worthy Prize S.r.l

The Study of Tandem Offloading Performance and Operability on The Cylindrical Hull FPSO Sevan Stabilized Platform with Variation in Mooring System Configuration

This study has been carried out to evaluate the dynamic behavior of the Cylindrical FPSO Sevan Stabilized Platform (SSP) and the LNG Carrier (LNGC) during the process of tandem offloading. The study includes hydrodynamics modellings, computations, and simulations of both cases SSP and LNGC operated individually and in combination for offloading operations. The SSP is moored with two variations of mooring, namely taut and catenary. Environmental loads are waves with the incorporated winds and currents propagating 90o, 210o, and 330o relative to the SSP headings. Excitation of random waves up to Hs = 4.50 m instigates the relatively low SSP motions in standalone condition. In offloading condition, when LNGC is connected, the SSP motion could magnify as much as 2.0 up to 5.0 times higher than that in standalone condition, but still considered in an acceptable level. The motion quality of LNGC in offloading operation is comparable with the SSP. For various random wave headings with Hs = 4.50 m during offloading operation may generate maximum tensions between 1,600 kN up to 2,600 kN in the casse of catenary mooring, and between 4,700 kN up to 7,000 kN in the case of taut mooring. Even then, this largest tension preserves a safety factor of 2.05 which is well above the limit of 1.67 as required by the governing standards. Finally, the study conclude an operability of as much as 90% could be achieved on SSP and LNGC offloading operation in the Masela Block of the Abadi Gas Field

Analysis of Pipe Lay Barge Hafar Neptune Capability in Pipelaying Operation at Offshore North West Java Oil and Gas Field

When pipelaying activity is carried out, the most influential factor is the significant wave height. In this final project, the maximum significant wave height allowed for the PLB during the pipelaying process was analyzed with the variation of pipe diameters, which are 8 inches, 10 inches, and 12 inches; variations in the direction of coming waves namely 0o, 45o, 90o, 135o, and 180o; and stinger angle variations. First, static analysis was performed using OFFPIPE software Then, Pipe Lay Barge (PLB) Hafar Neptune modelled with MOSES software and validated with ABS MODU codes. The output was RAO from the Hafar Neptune PLB. Next, dynamic analysis was performed with OFFPIPE software, where the input is static analysis, RAO of Pipe Lay Barge Hafar Neptune, and JONSWAP wave spectrum formulation. The result of the analysis was the significant wave height that could hit the PLB when pipelaying is 3 meters for all pipe diameter variations. For variations in the direction of the wave data, the maximum Hs were 3 meters for 0 ° and 180 °, 2.5 meters for 45 °, 1.5 meters for 90 ° and 135 °

Local Stress Analysis in the Chain Link of Mooring Line That Had Diameter Degradation

Mooring systems are used to moored ships at a particular area. One of its type is SPM by using a buoy. The system generally uses chains used to tie buoys to the seabed. However, chains that are used continuously can experience degradation in the diameter of the chain connection. The degradation experienced by the connections between the chains will certainly affect the local ( von Mises stress).  According to ABS rules, the amount of local stress or von Mises stress that occurs on an object must not exceed 90% of the yield strength of the material. Therefore, it is necessary to do a local stress analysis to determine the extent of degradation of the diameter of the chain connection so that the local stress value does not exceed that allowed. The largest mooring tension value that occurs in the mooring system is 1838,252 kN. The results show that if the chain connection is subject to a tension of 1838,252 kN, the diameter degradation that occurs in the chain connection must not exceed 15% of the initial diameter so that the local or von Mises stress does not exceed 369 MPa (90% of the yield strength of the material 410 MPa)