Walvis Bay LNG FSRU. Concept Study Report REV August XARIS Namibia

Transcription

1 Walvis Bay LNG FSRU Concept Study Report REV August 2014 XARIS Namibia

2 Walvis Bay LNG FSRU Concept Study Report S RP-PP-001-R1.docx 18 August 2014 REV. TYPE DATE EXECUTED CHECK APPROVED CLIENT DESCRIPTION / COMMENTS 01 D DAS AAM Approved TYPE OF ISSUE: (A) Draft (B) To bid or proposal (C) For Approval (D) Approved (E) Void XARIS Namibia Prestedge Retief Dresner Wijnberg (Pty) Ltd 5 th Floor, Safmarine Quay, Clock Tower Precinct, Victoria & Alfred Waterfront Cape Town, South Africa PO Box 50023, Waterfront 8002 T: Cape Town, South Africa Santiago, Chile Perth, Australia Seattle, USA

3 Copyright Disclaimer This Document, including all design and information therein, is Confidential Intellectual Property of PRDW and/or Xaris. Copyright and all other rights are reserved by PRDW and/or Xaris. This Document may only be used for its intended purpose. XARIS Namibia Prestedge Retief Dresner Wijnberg (Pty) Ltd 5 th Floor, Safmarine Quay, Clock Tower Precinct, Victoria & Alfred Waterfront Cape Town, South Africa PO Box 50023, Waterfront 8002 T: Cape Town, South Africa Santiago, Chile Perth, Australia Seattle, USA

4 CONTENTS Page N 1. INTRODUCTION Background Scope of Work 1 2. FUNCTIONAL REQUIREMENTS Battery Limits Berth Availability and Throughput Considerations Limiting Operational Conditions Survival Conditions for FSRU at Berth Ship Manoeuvring Operations Cargo Operations Navigational Criteria Design Vessel Stopping Distance Turning Areas Channel Geometry Berth Geometry LNG Safety Requirements 5 3. CONCEPT LAYOUT DEVELOPMENT Concept Layouts Marine Infrastructure Berthing Structure Pipeline Support Layout Evaluation and Preferred Layout ENVIRONMENTAL CONDITIONS Introduction Water Levels Wind Description of Available Data Operational Wind Climate Extreme Wind Speeds Waves Description of the Wave Model Operational Wave Climate Model Setup Model Results Effect of Proposed FSRU Berth on Proposed Tanker Berths Extreme Wave Heights 21

5 Model Setup Model Results Geology VESSEL NAVIGATION SIMULATION Introduction Description of the Simulator Simulation Environment (2D Model) Simulator Programme Simulation of Environmental Conditions Simulator Ship Model Tug Simulation Evaluation Criteria Simulation Runs Simulation Run Analysis Berthing Manoeuvres Sailing Manoeuvres Tug Power Evaluation CAPITAL COST ESTIMATE Introduction Allowance for P&G Allowance for Design Risk Allowance for Site and Engineering Capital Cost Estimate CONCLUSIONS WAY FORWARD REFERENCES 35 TABLES Page N Table 2-1: Design vessel characteristics 3 Table 2-2: Semi-protected channel depth requirements 4 Table 2-3: Berth depth requirements 5 Table 4-1: Tidal characteristics of the port of Walvis Bay (SANHO, 2013) 12 Table 4-2: Extreme value analysis of wind speed at Pelican Point Lighthouse. See Figure 4-1 for location of data. 15 Table 4-3: Extreme value analysis of wind speed at modelled wave height at the proposed FSRU berth. See Figure 4-5 for location of data. 23 Table 5-1: Summary of simulated environmental conditions 27 Table 5-2: Characteristics of the simulator ship model 27 Table 5-3: Simulator tug characteristics 28 Table 5-4: Simulation runs completed 29

6 FIGURES Page N Figure 3-1: Planned tanker berths of the Walvis Bay SADC port (PRDW, 2014) 6 Figure 3-2: FSRU layout 1-200m channel offset. Incorporated with planned tanker berths. 7 Figure 3-3: FSRU layout 2-300m channel offset. Incorporated with planned tanker berths. 7 Figure 3-4: FSRU layout 3-200m channel offset. Incorporated with existing Walvis Bay port entrance channel. 8 Figure 3-5: Typical LNG berthing structure 9 Figure 3-6: Light trestle example, San Vicente Bay LPG, Chile (Panoramio, 2014). 9 Figure 3-7: Preferred FSRU layout - 200m channel offset. Incorporated with planned tanker berths. 11 Figure 4-1: Locations of wind data used in this study. 12 Figure 4-2: Wind roses of mean wind speed for measurements at Pelican Point Lighthouse and NCEP hindcast node located at 14 E, 23 S. See Figure 4-1 for location of data. 14 Figure 4-3: Wind speed exceedances at Pelican Point Lighthouse. See Figure 4-1 for location of data. 14 Figure 4-4: Extreme value analysis of 1 min average wind speed at Pelican Point Lighthouse. See Figure 4-1 for location of data. 15 Figure 4-5: Model bathymetry, mesh and model output locations. 17 Figure 4-6: Example of spectral wave model output with wave boundary conditions Hm0 = 4.2 m, Tp = 13 s, Mean Wave Direction = Figure 4-7: Wave height roses at the proposed FSRU berth, entrance channel, and start of entrance channel. See Figure 4-5 for location of data. 19 Figure 4-8: Wave period roses at the proposed FSRU berth, entrance channel, and start of entrance channel. See Figure 4-5 for location of data. 19 Figure 4-9: Occurrence of Hm0 and Tp combinations at the proposed FSRU berth. See Figure 4-5 for location of data. 20 Figure 4-10: Comparison of wave height exceedance at the proposed FSRU berth, entrance channel, and start of entrance channel. See Figure 4-5 for location of data. 20 Figure 4-11: Wave roses at the proposed Tanker berth 1, with and without the proposed FSRU berth. See Figure 4-5 for location of data. 21 Figure 4-12: Comparison of wave height exceedance at the proposed Tanker berth 1, with and without the proposed FSRU berth. See Figure 4-5 for location of data. 21 Figure 4-13: Extreme value analysis of modelled wave height at the proposed FSRU berth. See Figure 4-5 for location of data. 22 Figure 4-14: Scatter plot of Hm0 vs Tp at the proposed FSRU berth. 23 Figure 5-1: Six-degrees of freedom of movement 25 Figure 5-2: Simulation environment layout 26 Figure 5-3: Simulation run A01 30 Figure 5-4: Simulation run A04 31 Figure 6-1: Estimated capital cost for three scenarios all using trestle pipe support 33 Figure 6-2: Estimated capital cost for three scenarios all using subsea pipeline for pipe support 33

7 ANNEXURES ANNEXURE A DESIGN BASIS ANNEXURE B FUTURE WALVIS BAY TANKER BERTH LAYOUT ANNEXURE C LNG FSRU PREFERRED LAYOUT ANNEXURE D VESSEL NAVIGATION SIMULATION DETAILS

8 XARIS Walvis Bay LNG FSRU Concept Study Report 1. INTRODUCTION 1.1 Background Prestedge Retief Dresner Wijnberg (Pty) Ltd (PRDW) has been appointed by Xaris to develop a concept layout, supported by a vessel navigation study, for a LNG offloading facility at Walvis Bay. Xaris have specified that LNG carriers will offload their product into a Floating Storage and Regasification Unit (FSRU) which will regasify the LNG and pump it onshore, where it will be used to fuel a 250 MW gas fired power plant. This report provides a broad description of the study. It includes the critical assumptions and logic used to define the preferred layout. In addition the results of the wave modelling and vessel navigation simulation, performed on the preferred layout, are included. An approved Design Basis report detailing initial assumptions preceded this report. The Design Basis is included in Annexure A. Section 2 of this report contains key assumptions and specifications with regards to the functional requirements of the facility. The layout selection is included in Section 3. The environmental conditions, including wave transformation modelling details, are presented in Section 4. The vessel navigation simulation, capital cost estimates and conclusions follow in Sections 5, 6 and 7 respectively. 1.2 Scope of Work The scope of work for this project, as defined in the proposal, is broken down below: Prepare a design basis capturing the functional requirements of the FSRU mooring and berthing facilities (civil infrastructure). The required Topsides and Trestle Gas Pipeline Engineering and Procurement will be provided by Excelerate. Develop a general arrangement layout of the FSRU mooring and berthing facilities (civil infrastructure), integrated with the Namport oil terminal and future Walvis Bay Southern African Development Community (SADC) Port. Desktop ship simulation (navigation) study to confirm the new layout accommodating FSRU and LNG carriers. Rough order of magnitude capital cost estimate for the FSRU marine infrastructure (berth, access trestle, dredging). Report compilation. XARIS Concept Study Report Page 1 of 36

9 2. FUNCTIONAL REQUIREMENTS 2.1 Battery Limits This study only considers the marine facilities. This includes the marine structures and consideration of the gas pipeline from the berth to the coastline. 2.2 Berth Availability and Throughput Considerations The required berth availability is dependent on the required throughput, throughput frequency and storage volume of the LNG facility. In the case where the LNG is used as feedstock for a power plant there is very little scope to allow a plant shutdown due to a lack of LNG. It is assumed the facility will service a power plant with finite tank volume; hence the following berth availability requirements have been made: The marine facilities will be designed to a maximum berth unavailability of 5 consecutive days In order to ensure that berth unavailability does not exceed 5 consecutive days, at a concept design level, it is assumed that the annual berth availability should be 98.6%, in lieu of storm duration data. The anticipated throughput at the facility has been defined, by Xaris, as m 3 /yr, with vessel calls every 60 days. 2.3 Limiting Operational Conditions Survival Conditions for FSRU at Berth For survivability of a FSRU at the berth the limiting significant wave height (Hs) is 2.5 m (Ramirez, 2014). A moored vessel, 1 minute averaged, wind speed (Vw,1min) limit of 25 m/s, acting transverse, to the quay may not be exceeded (PIANC, 2014) Ship Manoeuvring Operations The limiting wave height conditions for ship manoeuvring operations will be based on the support vessel (tugs) operational limits. This requires that the significant wave height does not exceed a value of 1.5 m to 2.0 m (PIANC, 2012). Operation of the pilot boat is limited to a significant wave height of 2.5 m. Limiting wind conditions during berthing and unberthing operations are 10.0 m/s (transverse to quay) and 17.0 m/s (longitudinal to quay) respectively (wind speeds are Vw,1min) (PIANC, 2014) Cargo Operations Limiting wind conditions during cargo transfer operations are 16.0 m/s (transverse to quay) and 22.0 m/s (longitudinal to quay) (wind speeds are Vw,1min) (PIANC, 2014). LNG transfer between a LNG carrier and FSRU are deemed unsafe in conditions exceeding a Hs of 2 m and a peak wave period (Tp) of 8 s (Ramirez, 2014). 2.4 Navigational Criteria Design Vessel The LNG berthing and offloading facilities should cater for a m 3 capacity FSRU and a m 3 LNG tanker. The navigation criteria will be based on the larger of the two vessels, the FSRU. The main dimensions of the LNG tanker and FSRU are specified in Table 2-1. XARIS Concept Study Report Page 2 of 36

10 Table 2-1: Design vessel characteristics Parameter LNG tanker FSRU Cargo Capacity (m 3 ) Length oa (m) Length pp (m) Beam (m) Loaded Draft (m) Depth to Main Deck (m) Stopping Distance In protected waters, a stopping distance of 5 times the maximum design vessel length will be used (Thoresen, 2010). The stopping distance, in protected water, shall be measured from the end of the protected manoeuvring area. Stopping distances less than this will be based on the assumption that the berth will only be accessed when the significant wave height is less than 1.5 m (i.e. where there is tug assistance available). This requires a manoeuvre with the use of tugs providing directional control and reducing the headway of the arriving vessel Turning Areas The minimum diameter of a turning circle where the vessel turns solely by engine and rudder movements should be approximately 4 times the length of the vessel. Under very favourable manoeuvring conditions this could be reduced to 3 times the length of the vessel and should tugs be employed this can be further reduced to 2 times the length of the vessel. Should the vessel be equipped with a bow and/or stern thruster, the diameter can be further reduced to 1.8 times the vessel length Channel Geometry The channel geometry including dredge depths and channel dimensions required for the design vessel will be based on the guidelines and recommendations from PIANC (2014). The channel width required is 230 m, based on 5 times the beam of the design vessel. The semi-protected channel depth requirements for the proposed layouts are shown in Table 2-2 below. A channel depth of 15.6 m CD is required for the channel, however the future tanker berths require a channel depth of 16.5 m CD. Typically access channels are navigated by a leading light indicating the centre of the channel and buoys demarcating the extents. Widening the tanker berth channel and only deepening the wider section of the channel to the required 15.6 m CD would create a dangerous navigational passage for the tanker vessels. Thus, for layout 1 and 2, the channel depth has been set at 16.5 m CD. XARIS Concept Study Report Page 3 of 36

11 Table 2-2: Semi-protected channel depth requirements Zone Depth Related Factors Semi-Protected Channel Design Draft Tidal Allowance 0.00 Nominal Depth Zone (Vesselrelated Factors) Vertical Vessel Motions: Wave Response Motions (PIANC 2014, p ) 1.07 Dynamic List 0.40 Squat (PIANC 2014, p. 194) 0.40 Out of Trim Allowance 0.00 Net under keel Clearance 0.50 Nominal Depth (Advertised depth) Maintenance Zone (Seabedrelated Factors) Allowance for Sounding Accuracy 0.10 Allowance for Siltation 0.30 Allowance for Dredging Accuracy 0.00 Scour Protection Clearance 0.00 Total Channel Depth Requirement Berth Geometry The minimum length of the berth pocket should be 1.25 times the overall length of the maximum design vessel (Thoresen, 2010). This corresponds to a berth pocket length of approximately 370 m. The width of a berth pocket should be at least 1.25 times the beam of the largest vessel to use the berth, corresponding to a width of 60 m. A berth depth of -15 m CD is required for the offloading berth based on the guidelines and recommendations from PIANC (2014). The same depth is required for the manoeuvring area. The berth depth requirements are shown below in Table 2-3. XARIS Concept Study Report Page 4 of 36

12 Table 2-3: Berth depth requirements Zone Depth Related Factors Berth depth Design Draft Tidal Allowance 0.00 Nominal Depth Zone (Vesselrelated Factors) Vertical Vessel Motions: Wave Response Motions (PIANC 2014, p ) 0.35 Dynamic List 0.38 Squat (PIANC 2014, p. 194) 0.02 Out of Trim Allowance 0.50 Net under keel Clearance 0.50 Nominal Depth (Advertised depth) Maintenance Zone (Seabedrelated Factors) Allowance for Sounding Accuracy 0.10 Allowance for Siltation 0.30 Allowance for Dredging Accuracy 0.00 Scour Protection Clearance (piled structure) 0.00 Total Channel Depth Requirement LNG Safety Requirements The LNG safety requirements were based on Sandia National Laboratories (2004), SIGTTO (1997) and Thoresen (2010). The following, planning level, safety zones were discussed and agreed on with the project stakeholders. 200 m safety radius offset from other vessels in transit. 500 m safety radius between LNG vessels and other marine infrastructure. XARIS Concept Study Report Page 5 of 36

13 3. CONCEPT LAYOUT DEVELOPMENT 3.1 Concept Layouts Three alternative layouts were produced for the facility. Two layouts, similar in concept but differing with regards to safety zone dimensions, were initially defined. Both layouts use the planned channel for the future tanker berths, of the Walvis Bay SADC port, to offset capital costs. Subsequently a third layout was created, in order to provide an alternative to using the tanker berth channel, in the event that the tanker berth project was delayed or cancelled. The third layout is situated on the east side of the existing Walvis Bay port channel. At the time of writing the tanker berth project was in the process of being awarded as an Engineering, Procurement and Construction (EPC) contract. The tanker berth layout is shown in Figure 3-1 below, the full extents are included in Annexure B. The three conceptual LNG FSRU layouts are shown further below in Figure 3-2 to Figure 3-4. Figure 3-1: Planned tanker berths of the Walvis Bay SADC port (PRDW, 2014) XARIS Concept Study Report Page 6 of 36

14 Figure 3-2: FSRU layout 1-200m channel offset. Incorporated with planned tanker berths. Figure 3-3: FSRU layout 2-300m channel offset. Incorporated with planned tanker berths. XARIS Concept Study Report Page 7 of 36

15 Figure 3-4: FSRU layout 3-200m channel offset. Incorporated with existing Walvis Bay port entrance channel. The layouts may be labelled and summarized as follows: FSRU layout 1-200m channel offset. Incorporated with planned tanker berths. FSRU layout 2-300m channel offset. Incorporated with planned tanker berths. FSRU layout 3-200m channel offset. Incorporated with existing Walvis Bay port entrance channel. 3.2 Marine Infrastructure Berthing Structure It is proposed that piled dolphin structures are used for the berth and mooring facility. This matches the structure type planned for the future tanker berths and is feasible with regards to the geology at the site (described in Sub-section 4.1). A photo of a typical example is shown below in Figure 3-5. XARIS Concept Study Report Page 8 of 36

16 Figure 3-5: Typical LNG berthing structure Pipeline Support Both a light trestle structure and subsea pipeline were considered as solutions for supporting the LNG gas line/s to the coastline. Initial cost estimates showed the subsea pipeline to have a lower capital cost. However the subsea pipeline does not allow for easy inspection of the pipelines and access to the berths will need to be via a work boat. In a layout workshop including representatives from Xaris, Excelerate and Namport it was decided that the trestle option was best, hence the preferred layout makes use of a trestle rather that the subsea pipeline. In addition Elzevir Gelderbloem, the Walvis Bay Port Engineer, stated during the layout workshop that the future tanker berth trestle has capacity to support the LNG gas line. Thus for layout 1 & 2, a potential capital cost benefit exists as a large portion of the pipeline will be supported on the planned trestle. Provision has been made for a light trestle structure which will support the LNG pipeline and allow for light vehicle (personnel transit only) access to the berth. The trestle consists of a steel truss with piled supports at 20m centres. Photos of a typical example used at San Vicente Bay LPG, in Chile are shown below in Figure 3-6. Figure 3-6: Light trestle example, San Vicente Bay LPG, Chile (Panoramio, 2014). XARIS Concept Study Report Page 9 of 36

17 3.3 Layout Evaluation and Preferred Layout Two meetings were held with Xaris to discuss the layout alternatives. The first meeting, the layout workshop, (held as a teleconference) had representatives from Xaris, Excelerate, Namport and PRDW. Layouts 1 and 2 were discussed. It was agreed that the 300 m channel offset shown in layout 2 seemed overly conservative even at a planning level of study. Hence Layout 1 was selected as the preferred option. Additionally the use of a light trestle combined with use of the planned tanker trestle was agreed to, as opposed to a subsea pipeline. A second meeting was held between PRDW and Xaris in Johannesburg. The third layout, making use of the existing dredge channel, was presented as an option in case the future tanker berths study was differed or cancelled. The alternative layout was noted however it was deemed unlikely that the tanker project will not proceed. Hence the preferred layout remains layout 1. Subsequently the layout has been refined with regards to the navigation area and trestle alignment, the refined, preferred layout is shown below. A larger extent of the layout is attached in Annexure C. XARIS Concept Study Report Page 10 of 36

18 Figure 3-7: Preferred FSRU layout - 200m channel offset. Incorporated with planned tanker berths. XARIS Concept Study Report Page 11 of 36

19 4. ENVIRONMENTAL CONDITIONS 4.1 Introduction This section presents the environmental conditions at the site. The site conditions were considered in all elements of the design and were specifically used for defining the vessel simulation tests described in Section Water Levels The published tidal levels for the Port of Walvis Bay are shown in Table 4-1. The levels are referenced to Chart Datum (CD), which is defined as m below land levelling datum (LLD). Table 4-1: Tidal characteristics of the port of Walvis Bay (SANHO, 2013) Description Level (m CD) Highest Astronomical Tide (HAT) 1.97 Mean High Water Springs (MHWS) 1.69 Mean High Water Neaps (MHWN) 1.29 Mean Level (ML) 0.98 Mean Low Water Neaps (MLWN) 0.67 Mean Low Water Springs (MLWS) 0.27 Lowest Astronomical Tide (LAT) Wind Description of Available Data Wind data from two sources have been used as part of this study, namely land-based wind measurements at Pelican Point Lighthouse and offshore hindcast wind data. The locations of these two datasets are shown in Figure 4-1. Figure 4-1: Locations of wind data used in this study. XARIS Concept Study Report Page 12 of 36

20 The wind measurements at Pelican Point Lighthouse contain mean wind speed and direction at 10 min intervals, spanning the period October 2001 to August The measurements comprise only 8.6 years of valid data, once missing data has been taken into account. The wind data is measured at an elevation of 33 m above the surface, therefore the raw wind speed data was corrected to the standard reference level of 10 m, according to the following relationship (USACE, 2008): U 10 = U 33 ( ) 7 As highlighted in a recent study using the measured wind data at Pelican Point Lighthouse (PRDW, 2013), the dominant measured wind direction shifts by about 130 for all measurements after approximately April This shift is undoubtedly due to erroneous measurements, therefore the measured wind directions over this period were corrected by applying a constant correction factor of 130 to realign the dominant direction with that of the measurements before April This was preferred over discarding these data, as a long record of measured winds is an important input in terms of the quantification of extreme wind speeds and wave heights for this study. The hindcast wind data has been obtained from the National Centers for Environmental Prediction (NCEP) database (NCEP, 2012). The data provides uninterrupted estimates of mean wind speed and direction at the standard reference level of 10 m elevation, at 3 hourly intervals for the 31 year period of 1979 to Operational Wind Climate Figure 4-2 compares the wind rose at Pelican Point Lighthouse with that of the NCEP hindcast node located at 14 E, 23 S. The data indicates that the measured wind speeds at Pelican Point Lighthouse are on average weaker than those in the hindcast data. The dominant wind direction also shows a rotation of about 15 to the west. The Pelican Point Lighthouse data indicates a significantly higher percentage of westerly and northwesterly wind directions than observed in the offshore hindcast data. The higher prevalence of the northwesterly wind component is considered to be important in terms of wave generation, as the site is particularly exposed to waves from the north-west, while being sheltered from waves from the south-west. XARIS Concept Study Report Page 13 of 36

21 Figure 4-2: Wind roses of mean wind speed for measurements at Pelican Point Lighthouse and NCEP hindcast node located at 14 E, 23 S. See Figure 4-1 for location of data. Limiting operational wind speeds for this study have been defined in terms of the 1 min average wind speed (PIANC, 2014), rather than the mean wind speed (conventionally defined as the 30 min or 1 hour wind speed). Mean wind speeds have been converted to theoretical 1 min average wind speeds through the relationship (USACE, 2008): U 1min = U 30min /0.814 Figure 4-3 presents wind speed exceedances based on wind speed measurements at Pelican Point Lighthouse, in terms of both the measured mean wind speed as well as the theoretical 1 min average wind speed. Figure 4-3: Wind speed exceedances at Pelican Point Lighthouse. See Figure 4-1 for location of data Extreme Wind Speeds Extreme value analyses (EVA s) on wind speed have been carried out using the MIKE by DHI EVA (Extreme Value Analysis) toolbox (DHI, 2012a). Figure 4-4 presents the results of the extreme value analysis of the theoretical 1-min average wind speed at the Pelican Point Lighthouse. Table 4-2 presents a summary of the results of EVA s carried out on both the measured mean wind speed and theoretical 1 min average wind speed at Pelican Point Lighthouse. XARIS Concept Study Report Page 14 of 36

22 Figure 4-4: Extreme value analysis of 1 min average wind speed at Pelican Point Lighthouse. See Figure 4-1 for location of data. Table 4-2: Extreme value analysis of wind speed at Pelican Point Lighthouse. See Figure 4-1 for location of data. Return period Measured mean U 10 (m/s) Theoretical 1 min average U 10 (m/s) (years) Lower 95% confidence limit Best estimate Upper 95% confidence limit Lower 95% confidence limit Best estimate Upper 95% confidence limit It must be borne in mind that the presented EVA s have been based on 8.6 years of valid wind speed measurements. There is therefore inherent uncertainty in estimates of wind speed in the order of the 100 year return period. Due to this unavoidable uncertainty, it is suggested that the upper 95% confidence limit be used to define extreme wind speeds for this study. A 1-min average wind speed of 25 m/s, defined as the survivability limit of a moored vessel at the FSRU berth (Sub-section 2.3.1), is therefore estimated to have a return period of approximately 10 years. 4.4 Waves Description of the Wave Model The operational and extreme wave climate at the site has been estimated through the application of a spectral wave model. The MIKE 21 Spectral Waves (SW) Flexible Mesh model was used for this purpose. The XARIS Concept Study Report Page 15 of 36

23 application of the model is described in the User Manual (DHI, 2012b), while full details of the physical processes being simulated and the numerical solution techniques are described in the Scientific Documentation (DHI, 2012c). The model simulates the growth, decay and transformation of wind-generated waves and swells in offshore and coastal areas using unstructured meshes. For this application MIKE 21 SW included the following physical phenomena: Wave growth by action of wind Non-linear wave-wave interaction Dissipation due to white-capping Dissipation due to bottom friction Dissipation due to depth-induced wave breaking Refraction and shoaling due to depth variations Operational Wave Climate Model Setup One of the required wave model outputs for the present study is the effect of the proposed FSRU berth on the operational wave climate at the proposed tanker berths (Section ). The operational wave climate at the proposed tanker berths has already been defined in a previous study (PRDW, 2013). The present model setup was therefore kept identical to the previous model setup (PRDW, 2013), changing only the modelled layout, to include the additional dredging requirements necessitated by the proposed FSRU berth. Bathymetry data was sourced from MIKE C-MAP electronic hydrographic charts (DHI, 2014d). The computational mesh is comprised of a combination of rectangular and triangular elements, with the resolution ranging from approximately 5 km offshore to approximately 30 m in the areas of interest. Figure 4-5 shows the extent of the model domain, the model bathymetry, mesh and the model output locations for which data have been presented in this report. XARIS Concept Study Report Page 16 of 36

24 Figure 4-5: Model bathymetry, mesh and model output locations. The model has been run in fully spectral instationary mode, thus allowing for wave transformation from deep water into Walvis Bay, as well as additional wave generation within the model domain due to wind. Fully spectral boundary conditions for the operational wave model were obtained from a hindcast wave model developed for the previous tanker berth study (PRDW, 2013). The measured time-series of wind speed and direction at Pelican Point Lighthouse were applied over the model domain, accounting for wind-wave generation in the model. The operational wave climate at the site has been determined by modelling the environmental conditions over the year 2006, generating model output at 1 hourly intervals. The year 2006 was chosen as it is the only calendar year for which there is a complete record of wind measurements at the Pelican Point Lighthouse, as well as the fact that the year 2006 has been shown to be representative in terms of offshore wave and wind conditions (PRDW, 2013) Model Results Figure 4-6 presents an example of the output of the spectral wave model for wave boundary conditions Hm0 = 4.2 m, Tp = 13 s, Mean Wave Direction = 200. As was highlighted in the aforementioned wave refraction study (PRDW, 2013), the effect of the proposed dredge channel on wave refraction is significant, with refraction on the side of the channel creating a wave guide. This leads to significantly higher wave heights on the western side of the proposed channel than on the eastern side, and causes a variation in wave direction from one side of the entrance channel to the other. XARIS Concept Study Report Page 17 of 36

25 Figure 4-6: Example of spectral wave model output with wave boundary conditions H m0 = 4.2 m, T p = 13 s, Mean Wave Direction = 200. Figure 4-7 and Figure 4-8 present wave height and wave period roses at the various model output locations defined in Figure 4-5. Figure 4-9 presents and occurrence table of the modelled combinations of wave height and wave period at the proposed FSRU berth, while height exceedances at the various model output locations are provided in Figure These results have informed the vessel navigation study discussed in Section 5. XARIS Concept Study Report Page 18 of 36

26 Figure 4-7: Wave height roses at the proposed FSRU berth, entrance channel, and start of entrance channel. See Figure 4-5 for location of data. Figure 4-8: Wave period roses at the proposed FSRU berth, entrance channel, and start of entrance channel. See Figure 4-5 for location of data. XARIS Concept Study Report Page 19 of 36

27 Figure 4-9: Occurrence of H m0 and T p combinations at the proposed FSRU berth. See Figure 4-5 for location of data. Figure 4-10: Comparison of wave height exceedance at the proposed FSRU berth, entrance channel, and start of entrance channel. See Figure 4-5 for location of data Effect of Proposed FSRU Berth on Proposed Tanker Berths A required output of the wave model for this study was to quantify the effect of the proposed FSRU berth on the wave climate at the proposed tanker berths. This was carried out by simulating environmental conditions for the year 2006 as described above, both with and without the additional dredging requirements of the FSRU berth. The wave rose and wave height exceedance curves shown in Figure 4-11 and Figure 4-12 indicate that the inclusion of the proposed FSRU berth has a negligible effect on the wave climate at the proposed tanker berths. XARIS Concept Study Report Page 20 of 36

28 Figure 4-11: Wave roses at the proposed Tanker berth 1, with and without the proposed FSRU berth. See Figure 4-5 for location of data. Figure 4-12: Comparison of wave height exceedance at the proposed Tanker berth 1, with and without the proposed FSRU berth. See Figure 4-5 for location of data Extreme Wave Heights Model Setup While Pelican Point provides shelter to the site from the dominant swells from the south-west, the site is particularly exposed to smaller waves propagating from the north-west. The increased prevalence of northwesterly wind directions in the Pelican Point wind measurements when compared with the offshore NCEP hindcast data (Figure 4-2) implies that the inclusion of realistic wind speeds and directions in the modelling of waves at the site is important. Only 8.6 years of wind measurements are however available (accounting for missing data), and the raw time-series could not be used as a direct input into the model, due to the presence of missing data. For this reason, the missing data in the Pelican Point measurements were filled XARIS Concept Study Report Page 21 of 36

29 with offshore hindcast data, extending the record to 11.8 years. This was seen as the best use of the available wind data, being preferable to using the raw offshore hindcast wind data as direct input to the model. Subsequent to the development of the operational wave model described above, PRDW developed offshore fully spectral wave data for the boundary of the wave model (14 E, 23 S), derived from spectral partition data obtained from NCEP (NCEP, 2012). It is thought that this fully spectral data is an improvement on the fully spectral data developed for the operational wave model (PRDW, 2013), and has thus been used as the model boundary condition in determining extreme wave heights at the site. The model was run over the full 11.8 years for which environmental data are available, generating output at 1 hour intervals over the duration of the simulation Model Results Extreme value analyses (EVA s) on modelled wave height were carried out using the MIKE by DHI EVA (Extreme Value Analysis) toolbox (DHI, 2012a). Figure 4-13 presents the results of the extreme value analysis of the modelled wave height at the proposed FSRU berth, while Table 4-3 presents a summary of these results. Figure 4-13: Extreme value analysis of modelled wave height at the proposed FSRU berth. See Figure 4-5 for location of data. XARIS Concept Study Report Page 22 of 36

30 Table 4-3: Extreme value analysis of wind speed at modelled wave height at the proposed FSRU berth. See Figure 4-5 for location of data. Return period H m0 (m) (years) Lower 95% confidence limit Best estimate Upper 95% confidence limit It must be borne in mind that the presented EVA s have been based on 11.8 years of modelled environmental conditions. There is therefore inherent uncertainty in estimates of wave height in the order of the 100 year return period. Due to this unavoidable uncertainty, it is suggested that the upper 95% confidence limit be used to define extreme wave heights for this study. A wave height (Hm0) of 2.5 m, defined as the survivability limit for a moored vessel at the FSRU berth (PRDW, 2014), is therefore estimated to have a return period of significantly greater than 100 years. A wave height (Hm0) of 1.5 m, defined as the operational limit for a moored vessel at the FSRU berth (PRDW, 2014), is estimated to have a return period of approximately 40 years. Figure 4-14 provides a scatter plot of the modelled relationship between Hm0 and Tp over the full duration of the 11.8 year simulation at the proposed FSRU berth. While the data indicates two distinct populations (sea and swell), the highest waves are due to swells, with Tp s between ranging between 14 s and 18 s. This highlights the range of periods which would be expected to be associated with the extreme wave heights presented above. Figure 4-14: Scatter plot of H m0 vs T p at the proposed FSRU berth. 4.5 Geology The area underlying the site recently formed part of a geotechnical investigation for the future tanker berths and access channel of the Walvis Bay SADC port. The field work consisted of onshore and offshore boreholes XARIS Concept Study Report Page 23 of 36

31 and vibrocores. In-situ testing consisted of Standard Penetration Tests (SPT). Laboratory testing consisted of particle size distribution, Atterberg limits and Uniaxial Compressive Strength tests. An interpretive report detailing the findings of this investigation was compiled by WSP Environmental (WSP Environmental (Pty) Ltd, 2014). This report has been made available by Namport and has been used as the basis for this high level geological interpretation of the site. The upper part of the stratigraphy is made up of recent to late quaternary sediments. This is underlain by cemented coarse grained lithic sandstones and conglomerates which are said to form part an alluvial fan formed by an extinct river system. These sandstones and conglomerates unconformably overlie the bedrock horizon. The bedrock in this instance forms part of the Precambrian Damara Metamorphic Complex being intruded over time by granites, pegmatites and granodiorites. No boreholes have been drilled in the direct vicinity of the proposed LNG berth. So information is inferred from the boreholes drilled at the proposed tanker berths, which are approximately 1300 m to the south-east, as well as the vibrocores completed along the alignment of the proposed access channel. Four main layers have been identified and are listed below: Layer 1: Layer 2: Layer 3: Layer 4: Layer thickness ranging from 1 m 4 m consisting of very soft clayey silts, silty clays and diatomaceous oozes. Layer thickness ranging from 2 m 20 m medium dense to very dense fine grained sand. Layer thickness ranging from 4 m 32 m soft to medium hard rock consisting of lithic arenites and conglomerates. Weathered soft to hard bedrock consisting of granites, gneisses and migmatites. In summary, the anticipated geotechnical conditions at the nominated LNG berth site and access channel are relatively favourable. Dredging in Layers 1 and 2 may be undertaken using a trailer hopper suction dredger. A preliminary estimate of the dredge material composition is 68% sand and 32% silt. While Layers 2 and 3 provide suitable founding for the proposed piled berth structure. XARIS Concept Study Report Page 24 of 36

32 5. VESSEL NAVIGATION SIMULATION 5.1 Introduction A desktop ship manoeuvring simulation study was conducted in order to determine if there is an acceptable margin of safety for vessel navigation in the proposed layout. 5.2 Description of the Simulator The ship manoeuvring simulation study was carried out using SimFlex Navigator, a simulation software application developed by Force Technology. Force Technology is based in Denmark and is seen as a market leader in the provision of ship simulation software technology. SimFlex Navigator was operated on a Desktop Simulator at the offices of PRDW. The capability of advanced manoeuvring is due to the fact that the SimFlex simulator model includes a motion platform incorporating the six-degrees of freedom of movement of the vessel. This comprises surge, sway, yaw, heave, roll and pitch. The importance of the six-degrees of freedom of movement is that it ensures the simulation model reacts as expected to the predetermined environmental conditions. The six-degrees of freedom of vessel motion are illustrated in Figure 5-1. Figure 5-1: Six-degrees of freedom of movement Hydrodynamic effects such as ship-ship interaction, bank interaction and squat are incorporated in the model which is a fundamental requirement for simulation in restricted waterways. 5.3 Simulation Environment (2D Model) The proposed berth infrastructure and navigation layout design were modelled within a 2D simulation environment. The 2D model was constructed by PRDW and the environment consisted of the following layers: Land Sounding Depth Contour Navigation Mark XARIS Concept Study Report Page 25 of 36

33 Current Wave; Fender The simulation environment was made in-house using a software application known as SimFlex Area Engineer. SimFlex Area Engineer provides users with the capability to design the 2D and 3D environments to be used on the SimFlex Navigator ship simulator. The simulation environment combined the proposed berth layout, the surveyed bathymetry and the proposed navigation channel geometry as defined in the navigation layout. The simulation environment is illustrated in Figure 5-2. Figure 5-2: Simulation environment layout 5.4 Simulator Programme Two days of simulation runs were carried out at the PRDW offices from 31 July 2014 to 1 August A simulation test programme scheduled a possibility of completing 6 simulation runs and incorporated both berthing and sailing manoeuvres in the predetermined environmental conditions. The test results for the simulation runs are presented and analysed in Section 5.9. The simulation runs were carried out by John Burns, a PRDW simulation pilot and maritime specialist. 5.5 Simulation of Environmental Conditions The environmental conditions considered for the simulation study were categorised into operational and extreme event limitations based on the environmental conditions at the site (Refer to Section 4). The selected environmental conditions are presented in Table 5-1. The operational limitations would typically consider the berthing (and/or sailing) of the LNG carrier at the berth. The extreme event limitations would typically represent the limiting conditions when the FSRU will need to sail prior to an extreme event occurrence. This XARIS Concept Study Report Page 26 of 36

34 is in the case when the predicted environmental conditions are forecasted to exceed the survival conditions of the FSRU at the berth. For the purposes of this study, the operational limitations were considered for berthing manoeuvres while the extreme event limitations were considered for sailing manoeuvres. Table 5-1: Summary of simulated environmental conditions Environment Operational Limitations Extreme Event Limitations Condition Wind SSW x m/s SSW x m/s Current NE x 0.1 m/s NE x 0.1 m/s Waves - Berth (Direction/H s/t p) NW/0.7 m/10-12 s NW/1.5 m/10-12 s Waves - Channel (Direction/H s/t p) WNW/1.8 m/10-12 s WNW/2.9 m/10-12 s The wind conditions were simulated over the entire simulation environment area. No shielding of the wind from other structures was considered in the study. The wave conditions that were simulated included a northwesterly swell which was progressively reduced or increased as per the vessel s movement through the channel. 5.6 Simulator Ship Model The ship models used in the ship simulation study included a fully laden LNG carrier. The simulation runs were undertaken to verify that there were no navigational risks associated with the proposed navigation channel and manoeuvring area. The characteristics of the simulator ship model is shown in Table 5-2 below. Table 5-2: Characteristics of the simulator ship model Ship Model No Parameters ( m³) Vessel Type LNG Carrier Displacement (m 3 ) LOA(m) 315 L pp (m) 305 Beam (m) 50.0 Draft (m) 12.0 Block Coefficient 0.76 Main Thrust (kw) 2 x Bow Thruster (kw) - Rudders Twin Lateral Windage (m 2 ) The simulator ship model selected for the study is seen as representative of the manoeuvring characteristics of both the fully laden FSRU and LNG carrier design vessels considered in the study. A ballast condition was not considered as part of the study and should be considered in a more detailed analysis. XARIS Concept Study Report Page 27 of 36

35 5.7 Tug Simulation Vector tug models were used in the desktop simulation study. The tug power requirements i.e. bollard pull was calculated empirically based on the methods described in PIANC (2012). The characteristics and calculated bollard pull of the simulator tug models are shown in Table 5-3. Table 5-3: Simulator tug characteristics Characteristics TUG Length Overall (m) 25 Beam (m) 11.0 Draft (m) 3.3 Bollard Pull (t) 50 Tug power used in the simulation study considered the reduced tug efficiency that results from tugs operating in wave conditions greater than 1.5 m Hs (PIANC, 2012). Full tug power was made available for the manoeuvre once the vessel was within the protected areas, i.e. less than 1.5 m Hs. The tug positions used in the study considered centre lead forward (bow) and aft (stern) of the vessel. 5.8 Evaluation Criteria After each simulation run, comments were recorded based on: the track keeping ability, the general manoeuvring conditions, the layout, the aids to navigation and the comfort of the simulator pilot during vessel manoeuvres. This data assists in identifying potential areas of navigational risk and ensures that an adequate margin of safety is included in the design. Each simulation run was analysed qualitatively and quantitatively. The qualitative assessments were based on the pilot s comments after each simulation run on presentation of the replay of the run. The quantitative assessment was based on the measuring of the vessel s speed as well as the tug usage and the engine and rudder movements during each simulation run. 5.9 Simulation Runs A total of 6 simulation runs were completed during the course of the study. The results of the simulation runs are presented as Annexure D. The simulation runs in Annexure D illustrate the vessel s track, list the input parameters and include graphs presenting the following output data where applicable: Longitudinal ground speed (kn) Engine power (kw) Rudder angle (deg.) Tug Force (t) Table 5-4 provides a summary of the simulation runs completed. XARIS Concept Study Report Page 28 of 36

36 Simulation Run Table 5-4: Simulation runs completed Ship Type Condition Manoeuvre Environmental Condition A01 LNG Carrier Laden Berthing Extreme (wind - 12m/s) A02 LNG Carrier Laden Berthing Operational A03 LNG Carrier Laden Sailing Extreme A04 LNG Carrier Laden Sailing Extreme A05 LNG Carrier Laden Berthing Operational A06 LNG Carrier Laden Berthing Operational 5.10 Simulation Run Analysis The analysis of the berthing and sailing manoeuvres is provided below Berthing Manoeuvres The berthing manoeuvre of the FSRU will consist of transiting the access channel, turning in the turning circle adjacent to the berth and berthing port side alongside the jetty berth. The pilot should board the arriving vessel in the port approaches, a minimum of one nautical mile from the access channel. Once the pilot has been transferred to the arriving vessel, the vessel will manoeuvre towards the access channel at a speed of approximately 5 to 6 knots heading south-easterly on a course of 153 (t). The vessel s speed will be reducing continually but an attempt will be made to maintain steerage way of the vessel. The vessel s tracks can be seen to be unstable at this stage due to the decreasing headway and reduced steering efficiency. The tugs are connected to the arriving vessel prior to the vessel reaching the turning circle. Due to the nature of the commodity, a consideration should be given to meet the arriving vessel prior to entering the channel. The vessel will be reducing speed continuously until it reaches the turning circle. The vessel will engage the main engine astern in order to further reduce headway. Once the vessel is stopped in the centre of the turning circle it will proceed to turn in order to berth port side alongside (i.e. bow to sea). Once the vessel has completed its turn, it will approach the berth. As the vessel approaches the berth, at an angle of approximately 30 degrees and a speed of less than 1 knot, both tugs prepare to push the vessel in to the berth. The tugs should be controlled in order to manoeuvre the arriving vessel into the berth, parallel and with little or no longitudinal speed and minimal lateral speed. Once the vessel has made contact with the fenders and the mooring lines are fast (secured), the tugs can stop pushing-in and prepare to disconnect their tow lines. Once the tugs are released, the pilot will disembark the vessel and the berthing manoeuvre is complete. Simulation Run A01 provides an example of the berthing of the LNG carrier on to the jetty berth (Refer to Annexure D). Simulation Run A01 is illustrated below in Figure 5-3. The simulation results showed that the LNG carrier could be successfully berthed port side alongside in the extreme event limiting conditions (Refer to Table 5-1). The wind speed simulated was 12m/s. This manoeuvre was extremely challenging and required three tugs to push the vessel alongside against the SSW wind condition. Simulation runs A05 and A06 considered berthing manoeuvres in the operational limiting condition with wind speeds from 10 to 12m/s. This proved to be less challenging and provided successfully results (refer to Annexure D). XARIS Concept Study Report Page 29 of 36

37 Figure 5-3: Simulation run A Sailing Manoeuvres Simulation Run s A03 and A04 considered sailing manoeuvres of the FSRU from the jetty berth in the extreme event conditions. Both runs comprised of the vessel being lifted off the berth by the aid of tugs and being towed into the channel. The sailing manoeuvres showed that the vessel was easily lifted off the berth due to the assistance but was only course-stable once the vessel was able to achieve sufficient headway. The simulation runs showed that the vessel could be successfully sailed from the berth in the extreme event condition. However, it is essential that the vessel efficiently gather headway or it will be set across the channel. Simulation Run A04 (illustrated in Figure 5-4) shows the vessel tracks of the FSRU sailing from the berth in a south-westerly extreme wind condition with a wind speed of 17 m/s. XARIS Concept Study Report Page 30 of 36

38 Figure 5-4: Simulation run A Tug Power Evaluation Time series results are available for each simulation run (refer to Annexure D). A bollard pull of 50t each with a tug fleet of three tugs was calculated empirically based on the methods described in PIANC (2012). The time series results show that the vector tug models of 50t bollard pull was sufficient for the manoeuvring of the design vessels. XARIS Concept Study Report Page 31 of 36