SOW MP-NSC-230111 Rev(-). NSC Reduction Gear Oil Sump CFD Analysis (002).pdf

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Statement of Work: MP-NSC-230111 NSC Reduction Gear Oil Sump CFD Analysis

Rev (-): 11Jan23

1 INTRODUCTION

1.1 Background. The USCG National Security Cutters (NSC) (WMSL-750/760) are combined diesel and gas turbine powered vessels; 2 Diesel Engines (DE) and 1 Gas Turbine (GT) turning two shafts and propellers. Each shaft is capable of operating under power from: either diesel(s); gas turbine and diesel(s); or gas turbine alone. Two Main Reduction Gears (MRG) and a Cross Combining Gear (CCG) distribute power as needed. Each gear has its own oil sump with oil circulated using gear and/or electric motor driven pumps. Exxon/Mobil Nuto H100 oil distributed from the gear sumps is use for control oil, gear/bearing lubrication, and the diesel engine fluid couplings. Air entrainment in the gear oil is believed to affect operation of gear components including oil pumps and seal ring bushings.

1.3 Objective. Develop a Computational Fluid Dynamics (CFD) model of the NSC Reduction Gear Oil Sump system and perform CFD analyses under varying environmental and operational conditions to determine sources of oil aeration and the flow conditions at the oil pump’s suction and discharge into the sump.

2 REFERENCES

2.1 Responsible Charge Definition; NSPE Position Statement No. 10-1778.

2.2 ANSI/NISO Z39.18 Scientific and Technical Reports - Preparation, Presentation, and Preservation.

2.3 ASTM-D3427-19 Standard Test Method for Air Release Properties of Hydrocarbon Based Oils.

3 DEFINITIONS

For this SOW:

3.1.1 Pump(s) shall mean each gear’s oil and control oil pump(s).

3.1.2 Oil shall mean the oil used for control oil, gear lubrication, and the diesel engine fluid couplings.

3.1.3 Sump shall mean each gear’s oil sump: 2x MRG and 1xCCG.

3.1.4 Oil system sump(s) shall mean the complete oil system from the sump oil return discharge pipes to the oil pump(s) discharge pipes. The sump is used to maintain oil availability and to promote oil de-aeration.

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3.1.5 Oil distribution system shall mean the complete oil lubrication, fluid coupling, and control oil supply and distribution system from uptake into the pump suction pipes, to machinery component oil distribution, and return to the sump oil return pipes. The distribution system is used to supply oil to, and return oil from the bearing, gears, clutches, and fluid coupling, etc.

4 GENERAL REQUIREMENTS

4.1 All work shall be performed by or under the direct control and personal supervision of a Professional Engineer (PE) currently licensed and in good standing in one of the United States of America. The PE shall be in Responsible Charge of the work and shall Sign and Seal the Final Report [8.2]. A PE in Responsible Charge is actively engaged in the engineering process, from conception to completion.

Engineering decisions must be personally made by the PE or by others over which the PE provides supervisory direction and control authority. Reviewing drawings or documents after preparation without involvement in the design and development process does not satisfy the definition of Responsible Charge [2.1].

4.1.1 The PE in Responsible Charge of the work shall demonstrate to the Government’s satisfaction before beginning work that:

4.1.1.1 They are currently licensed and in good standing as a PE in one of the United States of America.

4.1.1.2 Will be in Responsible Charge of the work.

4.1.1.3 They have the depth and breadth of experience necessary to be in Responsible

Charge of the work as demonstrated by:

4.1.1.3.1 A Ph.D. in Mechanical Engineering, preferably in fluid mechanics, from an ABET accredited school.

4.1.1.3.2 A minimum of 10 years’ experience using the CFD software proposed for the analysis.

4.2 The analyst performing the CFD shall:

4.2.1 Have received a Ph.D. or M.S. in Mechanical Engineering, preferably in fluid mechanics, from an ABET accredited school.

4.2.2 Have a minimum of 5 years’ experience using the CFD software proposed for the analysis.

4.3 CFD analysis and modeling shall be performed using the latest version of a commercially available, or validated open source, RANS CFD (Reynolds- Averaged Navier Stokes Computational Fluid Dynamics) program.

4.3.1.1 Grid convergence simulations shall be used to demonstrate that a sufficiently resolved set of simulations are being performed.

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4.4 At a minimum the CFD shall be used to:

4.4.1 Calculate the percent aeration of the oil. The CFD shall be run until the percent aeration at the source (flow entering the sump) equals the aeration at the sink (downstream of oil pump) within 5%. The intent is to allow the oil aeration to stabilize at the systems aeration dissipation capacity.

4.4.2 Calculate oil flow conditions (pressure, velocity, flow direction, swirl, vortexing, etc.) at each operating pump’s suction inlet and pipe discharge into the oil sump.

Intent is to identify flow conditions that have potential to create air entrainment into the oil.

4.4.3 Identify flow conditions within the sump that have potential to create air entrainment into the oil.

4.4.4 Calculate the path and the (dwell) time required for oil to flow between each operating pump’s return pipe oil discharge into the sump and oil re-uptake into the pumps’ suction inlet. Intent is to characterize oil dwell times in the sump, extent of oil de-aeration possible, and possible sump modifications to increase the oil path length and dwell times.

4.4.5 For each gear’s oil sump calculate the oil capacity necessary to de-aerate the oil using:

4.4.5.1 Each sump’s oil volume.

4.4.5.2 The combined flow for all operating oil pumps within the gear’s sump.

4.4.5.3 The average dwell time of all operating pumps as determined in 4.4.4.

4.4.5.4 Oil de-aeration time for each operating temperature using the deaeration time as determine in 5.1.2.

4.4.6 Calculate the Net Positive Suction Head Available (NPSHA) immediately upstream of each pump’s suction flange. Intent is to identify flow conditions that produce less than 200% of the pump Net Positive Suction Head Required (NPSHR) at the pump suction inlet.

4.5 Sump Oil properties representative of Exxon/Mobil Nuto H100 as informed by 5.1 testing shall be used for the CFD.

4.6 All assumptions, oil and material properties, boundary conditions, loads, constraints, and methods must be clearly stated, provided to, and agreed upon with the Government prior to running the CFD.

4.7 The NSC MRG is a complex system operating under varying environmental and operating condition.

4.7.1 Environmentally the sump it is subject to + 8o roll and + 3o pitch producing varying levels of submergence at the oil pumps’ suction and discharge.

4.7.2 Sump oil levels vary due to oil consumption and fill, producing varying levels of submergence at the oil pumps suction and discharge.

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4.7.3 The lubricating oil pumps are both electric and gear driven. The electric driven pumps are dual speed and are started/stopped with the MRG/CCG operating profile. Output of the gear driven pumps are dependent on the gear operating

RPM.

4.7.4 The MRGs and CCG are used in 4 normal operating modes to combine and distribute power from the diesel engines and gas turbine to the two propeller shafts. Details of the operating modes will be provided after an NDA is in place.

4.7.4.1 Cruising Mode.

4.7.4.2 Maneuvering Mode.

4.7.4.3 Gas Turbine Mode.

4.7.4.4 CODAG Mode.

5 TASK STATEMENTS

Perform the following task statements at a minimum:

5.1 TASK 5.1 – OIL TESTING

5.1.1 Determine the oil properties necessary to perform the CFD analysis through testing [4.5]. (AS REQUIRED).

5.1.2 Determine through ASTM D-3427 testing the time required to de-aerate the oil from 2%, 6%, 9%, 12%, and 15% volume aeration to 0.2% volume aeration.

Separate tests shall be performed at 50%, 75%, 100% and 125% of the anticipated oil operating temperature.

5.1.3 Provide a clearly stated and brief report to the Government documenting

TASK 5.1.

5.2 TASK 5.2 – GATHER NEEDED DATA

5.2.1 Obtain dimensional data for the current as-built oil system. A ship check to Pascagoula, MS; Charleston, SC; or Alameda, CA may be necessary.

5.2.2 Obtain oil and control oil pump curves.

5.2.3 Obtain oil and control oil pump operating profiles.

5.2.4 Obtain other data as necessary.

5.3 TASK 5.3 – DEVELOP OPERATIONAL PROFILE

5.3.1 For each operating mode [4.7.4] determine the worst, median, and best sump operating conditions. The Government expects that:

5.3.1.1 Combined oil flow, gear RPM, and suction/discharge submergence shall be used to establish operating conditions.

5.3.1.2 Worst operating conditions will likely occur at minimum sump level, maximum pitch/roll, and maximum gear RPM.

5.3.1.3 Best operating conditions will likely occur at maximum sump level, no pitch/roll, and minimum gear RPM.

5.3.1.4 Median operating conditions will likely occur at median oil level, median pitch/roll, and median gear RPM.

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5.3.2 For each 5.3.1 operating mode condition identify:

5.3.2.1 Environmental and sump conditions; see [4.7].

5.3.2.2 Cutter operating condition; e.g., propulsion plant operating mode such as

Maneuvering Mode, number of shafts/gears operating, BHP and RPM each engine and GT, each propulsion shaft RPM.

5.3.2.3 Each oil pump’s: 1.) operating condition (On/off); 2.) Suction and discharge pipe submergence with respect to the sump oil level; 3.) Oil flow rate and pump

RPM.

5.3.2.4 Oil temperature, sump oil level, and inclination of sump oil surface with respect to ground

5.3.3 Provide a clearly stated and brief report documenting Tasks 5.3 to the Government for concurrence and approval prior to running the CFD.

5.4 TASK 5.4 – DEVEOP INITIAL CFD MODEL OF OIL SYSTEM SUMP

5.4.1 Develop a complete CFD model for each gear’s oil system sump [3.1.4], interconnecting the sump models as necessary to represent the installed condition. The purpose is to understand system operation and to uncover obvious faults before proceeding to more detailed CFD analysis.

5.4.2 The model shall be based on the current as-built configuration of the NSC Class and shall include at a minimum:

5.4.2.1 Oil tight boundaries.

5.4.2.2 Hull structure.

5.4.2.3 Piping, baffles, and physical elements within the sump.

5.4.2.4 Pump suction pipes shall be modeled from their sump oil uptake to downstream of each pump’s discharge flange. The piping downstream of the oil pump(‘s) discharge flange shall be modeled until a substantial change in pipe diameter has occurred. Suction piping shall incorporate high spots likely to trap air.

5.4.2.5 Oil return pipes shall be modeled upstream of the sump until a substantial change in pipe diameter has occurred.

5.4.3 Oil properties shall be representative of the oil used [4.5, 5.1.1] and consistent with operating temperature.

5.4.4 The CFD model shall be built to allow the sump oil surface/level to be adjusted for oil level and inclination conditions.

5.4.5 Determine an appropriate mesh size for the analysis and document the reason why the mesh size is suitable for this analysis. The model mesh size should be set to obtain a reasonable understanding of the system without requiring undo effort.

5.4.6 Provide a clearly stated and brief report documenting 4.6 and the CFD model development, detailing assumptions, material properties, boundary conditions, loads, and methods to the Government for concurrence and approval prior to running the CFD.

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5.5 TASK 0 – PERFORM INITIAL CFD ON OIL SYSTEM SUMP

5.5.1 Perform CFD analysis on the oil sump system developed in Task 5.4 and calculate/determine all items under 0.

5.5.2 CFD shall be performed at each 4.7.4 operating mode using the 5.3.1 Worst operating condition.

5.5.3 Provide a clearly stated and brief report of the findings to USCG after running the CFDs noting:

5.5.3.1 Areas where potential air entrainment into the oil have been observed.

5.5.3.2 Suggested system modifications for reducing air entrainment.

5.5.3.3 Report all 0 calculations.

5.5.3.4 Propose refinements to the model to enhance system understanding.

Refinements may include finer time scales, localized finer grid resolution, or other analysis as warranted. CFD model refinements or additional analyses shall be approved by the Government prior to beginning Task 5.6.

5.5.3.5 The necessity and reasons for proceeding to Task 5.6.

5.6 TASK 5.6 – REFINE TASK 5.4 CFD MODEL (AS REQUIRED and APPROVED)

5.6.1 Refine the TASK 5.4 CFD model as approved under 5.5.3.4.

5.7 TASK 5.7 – PERFORM CFD ON TASK 5.6 CFD MODEL (AS REQUIRED and Approved)

5.7.1 Perform CFD analysis on the oil sump system developed in Task 5.6 above and calculate/determine all items under 0.

5.7.1.1 Initially the CFD shall be performed at each 4.7.4 operating mode using the

5.3.1 Worst operating condition.

5.7.1.2 If no sources of aeration are found, then additional CFD runs shall be performed sequentially to discover aeration sources:

5.7.1.2.1 5.3.1 Median operating condition shall be run for each 4.7.4 operating mode.

5.7.1.2.2 5.3.1 Best operating condition shall be run for each 4.7.4 operating mode.

5.7.1.2.3 At up to 5 other conditions as recommended by the analyst to enhance system understanding and as approved by the Government.

5.7.2 Provide a clearly stated and brief report of the findings to Government after running the CFD and before proceeding to Task 5.8 Reporting:

5.7.2.1 Areas where potential air entrainment into the oil have been observed.

5.7.2.2 Suggested system modifications for reducing air entrainment.

5.7.2.3 All 0 calculations.

5.7.2.4 If no significant sources of aeration are found then:

5.7.2.4.1 Discuss and make recommendations for areas of further study under separate SOW to enhance system understanding such as:

5.7.2.4.1.1 Incorporating the oil distribution system into the CFD model.

5.7.2.4.1.2 Sub-modeling of oil distribution components: e.g., fluid couplings, clutches, spray nozzles, oil pumps, gear teeth mesh.

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5.8 TASK 5.8 – REPORT and FINAL CFD MODEL

5.8.1 Provide a clearly stated Preliminary Report fully documenting Tasks 5.1 through

5.7. Submit to the Government for review and comment.

5.8.2 Provide a clearly stated Final Report fully documenting Tasks 5.1 through 5.7, incorporating Government comments on the Preliminary Report.

5.8.3 Provide electronic CFD models developed as part of the analysis to the Government with the Final Report.

5.8.4 Reports shall be in accordance with ANSI/NISO Z39.18 Scientific and Technical Reports - Preparation, Presentation, and Preservation.

5.8.5 Calculations shall be complete enough so a reviewer can follow through the work, step-by-step. The reports shall document the requirements, type of analyses performed, coordinate axis system, description of the CAD/CFD programs used, plots of the full CFD model, local details, boundary conditions, oil properties, and pump curves at a minimum.

5.8.6 Document why the mesh size is suitable for the analysis. Provide an accuracy assessment.

5.8.7 Document operating conditions where:

5.8.7.1 Oil aeration is possible to occur.

5.8.7.2 Insufficient NPSHA exists to meet pump NPSHR.

5.8.7.3 Insufficient sump oil dwell time exists to de-aerate the oil.

5.8.7.4 Other areas of concern.

5.8.8 Discuss the model, assumptions, boundary conditions, results of the analysis, including uncertainty and comparison to real world observed parameters, and identify recommended changes. Recommended changes shall include:

5.8.9 Means to increase dwell time within the sump.

5.8.10 Minimum and maximum oil sump usable heights.

5.8.11 The report shall document the following for the CFD at a minimum for each modeled condition:

5.8.11.1 A time-series-simulation animation sufficient in length to show the transit of a nominal particle of oil from one extreme end of the circuit to another.

5.8.11.2 Flow vectors and cut views showing flow patterns at each pump suction and discharge location.

5.8.11.3 Pressure distribution plots visualizing stagnation / backflow (low-pressure mixing areas) at each pump suction and discharge location.

5.8.11.4 5.8.11.2 and 5.8.11.3 shall be documented:

5.8.11.4.1 Horizontally at eight equally spaced increments between the sump bottom and the oil surface.

5.8.11.4.2 Vertically at every 45 degrees through the pipe axis.

6 PERIOD OF PERFORMANCE

Period of performance shall be 46 weeks after contract award.

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7 SCHEDULE AND DELIVERABLES

All documents are to be provided in Microsoft Word (*.docx) and PDF format.

7.1 Kickoff Meeting: Provide a detailed POAM (Plan of Action and Milestones) to complete the analysis: Name and version of CFD software; Name of the PE in Responsible Charge and demonstration that they have the breadth and depth of experience to perform the work [4.1]; Analysis milestone dates; Data required and the data source; Obstacles to completing the analysis on schedule.

7.2 Estimated schedule and deliverables are shown in Table 1.

Table 1: Schedule and Deliverables

SOW

Item

Task Weeks After

Contract Award

7.1 Kickoff Meeting 2

5.1 OIL TESTING 12

5.1.1 Oil Properties

(AS REQUIRED)

5.1.2 ASTM D-3427 Oil Testing 12

5.1.3 Reporting Deliverable 12

5.2 GATHER NEEDED DATA 10

Other than 5.2.1 ship check 6

5.2.1 Ship check 10

5.3 DEVELOP OPERATIONAL PROFILE 12

5.3.3 Reporting Deliverable 12

5.4

DEVEOP INITIAL CFD MODEL OF OIL SYSTEM

SUMP

4.6, 5.4.6 Reporting Deliverable 16

0 PERFORM INITIAL CFD ON OIL SYSTEM SUMP 22

5.5.3 Reporting Deliverable 22

5.6

REFINE TASK 4.4 CFD MODEL

(AS REQUIRED and Approved)

5.7

PERFORM CFD ON TASK 5.6 CFD MODEL

(AS REQUIRED and Approved)

5.7.2 Reporting Deliverable 34

5.8 REPORT and FINAL CFD MODEL

5.8.1 Preliminary Report for Review Deliverable 40

5.8.2 Final Report Deliverable 46

5.8.3 Electronic CFD models Deliverable 46

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8 QUALITY ASSURANCE

8.1 The Government will review the contents and format of the deliverables in their entirety prior to issuing approval.

8.2 The PE in Responsible Charge of the work [4.1] shall Sign and Seal the Final Report [5.8.2].

9 SECURITY CLEARANCE AND NON-DISCLOSURE AGREEMENTS

9.1 This work is not classified. No security clearance is required, but technical data is under STINFO (Scientific and Technical Information) Distribution Statement D.

9.2 The Contractor and all individuals working on the project are required to complete a DHS Non-Disclosure Agreement; form 11000-6. Contract will not be awarded until NDA forms are in place.

9.3 Additionally, the shipyard and the equipment manufacturers may require Non-Disclosure Agreements.

10 PLACE OF PERFORMANCE

10.1 Work shall be performed at the selected contractor’s normal place of work. As noted in 5.2.1 a ship check to a CG facility may be necessary.

11 CONTRACTING OFFICER’S REPRESENTATIVE

11.1 The Contracting Officer’s Representative (COR) and technical point of contact at the U.S. Coast Guard Surface Forces Logistics Center will be Mr. Albert Hewitt, SFLC-ESD-NAME-MAIN PROP, Phone: (410) 762-6801, e-mail: Albert.L.Hewitt@uscg.mil.

11.2 The Alternate Contracting Officer’s Representative (ACOR) at the U.S. Coast Guard Surface Forces Logistics Center will be Mr. Tim Curry, SFLC-ESD-NAME- MAIN PROP, Phone: (410) 762-6737, e-mail: Timothy.J.Curry@uscg.mil.

12 Notes

12.1 Rights in Data. The GOVERNMENT shall retain Usage Rights in all data, including software, developed as part of the effort regardless of form or medium.

Government furnished data are considered to be solely the property of the Government and shall not be released without the written consent of the Government. The Contractor shall retain Commercial Rights to all software developed under this task.

mailto:Albert.L.Hewitt@uscg.mil mailto:Timothy.J.Curry@uscg.mil