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The Prelude Floating Liquefied Natural Gas (FLNG) platform is designed to offload liquefied natural and petroleum gas products to carrier vessels moored in a Side-by-Side (SBS) configuration. Prior to the mooring operation, the carrier vessel is escorted and held alongside the FLNG with the assistance of tugs connected to her bow and stern to ensure sufficient control over the vessel in this critical phase. In order to better understand the impact of environmental conditions, to determine the optimum length, strength, material and configuration of the towline stretcher, and to estimate the maximum operable environments, coupled multi-body simulations have been performed in time domain. The numerical model, which considered both the LNG carrier and the forward tug, was calibrated using full-scale measurements of tug motions and tow line tension recorded during a real approach and berthing manoeuvre at Prelude FLNG. The measured environment effects were generated numerically and the model parameters were adjusted to reproduce the recorded behavior as accurately as possible. Since actions of the tug master are difficult to model numerically and only the statistical environment parameters are known, a simplified approach has been adopted for modelling the tug propulsion and steering using a combination of static forces, stiffness and linear and quadratic damping for relevant horizontal degrees of freedom. The calibrated numerical model was first subjected to several sensitivity assessments of the modelling level (single- or multi-body, inclusion of second-order wave loads, inclusion of forward speed). Then sensitivity studies were performed to help address operational requirements related to the wave height and direction, and the stretcher length and strength. The conclusions have been taken into consideration for the selection of the tow line configurations for future operations. Finally, the calibrated coupled LNG carrier and tug model was used to derive Prelude-specific tug operability criteria that may be used for decision-making based on weather forecasts, prior to the SBS offloading operations. A large matrix of swell and wind driven waves was simulated over a range of wave heights, periods, directions and static towing forces to allow a criterion to be developed based on a stochastic extreme tow line tension. Such criterion considers relevant wave parameters while remaining simplified enough for easy use in operations. This paper describes the assumptions and process to numerically model the towing configuration and calibrate the different coefficients, discusses the results obtained for the various sensitivities, and explains the operability criteria. Important conclusions and lessons learnt are also shared.

In anticipation of increased use of hydrogen as a means of decarbonizing future power generation used widely in combined heat and power plants, studies are underway to understand how hydrogen impacts operability and emissions from existing low emission gas turbines. In the current study, a full-scale annular combustor is used to study how added hydrogen to methane (as a proxy for natural gas) impacts lean blow-off limits. Of particular interest is understanding if hydrogen can be used strategically to extend low emissions operation at lower load. This would facilitate use of gas turbines to offset intermittent renewable power which is becoming increasing integrated into microgrid environments where combined heat and power system are prevalent. A combined experimental and numerical approach is taken. Tests were carried out at Southwest Research Institute using a full-scale annular combustor test rig at elevated temperatures and atmospheric pressure. The individual fuel injectors used were piloted injectors based on natural gas injectors used in practice. Various blends of hydrogen and methane were tested for different scaled load conditions and different pilot to main fuel splits. Besides identifying the overall equivalence ratio at blow-off, measurements also included temperature uniformity at the exit plane and imaging of the reaction. To complement and extend the study a chemical reactor network approach was also applied. The reactor network was initially validated on a prior study involving use of a piloted model combustor. The reactor network was applied to the current configuration and further tuned to align with the measured data. The agreement between the reactor network blow-off and measured blow-off was reasonable. The validated reactor network was then used in combination with a statistically designed simulation matrix to derive a design tool. The tool is then used to estimate other performance features including CO emissions near LBO and the impacts of ambient humidity and the presence of higher hydrocarbons typically found in natural gas. The design tool quantifies the extent to which hydrogen content and pilot percentage can extended part load operability for the full annular combustor system.

This paper aims to assess the gas turbine operability and overall hybrid electric propulsion system performance for a parallel configuration applied to a 150 passenger single-aisle aircraft. Two arrangements are considered: one where the low pressure shaft is boosted and one where the high pressure shaft is boosted. For identifying limits in the hybridization strategy steady state and transient operation are considered and the hybridization effect on compressor operability is determined. Having established the electric power on-take limits with respect to gas turbine operation the systems performance at aircraft level is quantified for the relevant cases. Different power management strategies are applied for the two arrangements and for different power degrees of hybridization. The results indicate that despite the fact that pollutant emission and fuel consumption may improved for hybrid propulsion, this comes at the cost of reduced payload and operability margins. Boosting the low pressure shaft may give the highest engine performance benefits but with a significant weight penalty, while the low pressure compressor system operability is negatively affected. On the other hand boosting the high pressure shaft provides lower engine performance benefits but with smaller weight penalty and with less operability concerns.

The article describes general approaches to creating an intelligent system for monitoring and diagnosing the operability of energy supply facilities. The general concept of the adaptive-predictive analysis system and the construction of an artificial neural network for its use in the predictive module for predicting the type and time of failure occurrence is given. The basic principles of training a neural network for recognizing various types of failures are also given. Critical remarks of the concept of creating a digital twin of such a complex object for modeling as energy-generating equipment are given.

Inlet distortion can significantly impact turbofan operability. In the present contribution, the focus is on vortex ingestion, which is a type of distortion that has received less attention in the literature for high-bypass-ratio fans of civil engines than inlet separation or boundary layer ingestion. Due to the unsteady and non-axisymmetric nature of the inflow, full annulus computations are performed, using an unsteady RANS approach with a sliding mesh interface between the rotor and the stator. The goal is to provide a detailed analysis and understanding of the mechanisms responsible for operability loss when a vortex is ingested by the fan. To that end, a simplified model of vortex is derived from previous simulations in crosswind conditions including the presence of the ground plane. The study test case is a turbofan demonstrator representative of modern turbofans. Simulations are run with and without vortex at several operating points until rotating stall is observed. The global results show that the vortex ingestion induces a stall margin loss of up to 8%. Modal analysis indicates a stall pattern with 10 cells rotating at somewhere between 52 and 67% of the shaft speed. A comparison of the two configurations shows that the stall inception mechanism is similar with and without distortion. In particular, examining the incidence at the fan blade, a similar critical angle is observed for the two configurations, which is leveraged to establish a stall criterion valid for vortex ingestion cases.

For the operability evaluation of an offshore unit, it is usual to adopt specific working limiting criteria dealing with ship motions and accelerations. These criteria given by operators reflect the ability of the vessel (or crew) to accomplish a precise target in an operative scenario with different meteorological conditions. However, an offshore vessel needs also to keep a determined position and heading during working operations. That means designers or operators have to consider criteria associated both with seakeeping and station keeping to evaluate the effective operability of the vessel. Traditionally, early design stage operability analyses do not combine seakeeping and station keeping predictions, which are referring to different working environments. Here, an innovative procedure allows to evaluate the joint operability of an offshore unit, adopting scatter diagrams for local environmental conditions. The method has been applied on a Pipe-Laying vessel, assessing the global operability for different areas of commercial interest.

This paper describes the development phases of a damping system for combustion instability reduction in an annular type combustor for heavy-duty gas turbine applications. As reported by the authors in a previous paper, the full scale annular test rig allowed for an extensive characterization of the combustor with realistic acoustic boundaries at engine-relevant conditions. Emissions and operability assessment over a wide range of load conditions was performed, allowing the evaluation of the response of the system near the thermo-acoustic instability onset. The instability is quantified by its acoustic growth rate. This quantity is a crucial input in the design process of dampers. A methodology has been used to extract these growth rates form measured pulsation data. Experimentally determined growth rates have been evaluated for different fuel flow rate split between the main and the pilot injections, providing input to dampers preliminary design. Given current combustor architecture constraints, a first attempt configuration has been proposed and performances evaluated in the full annular rig. Dampers have been equipped with dynamic sensors and thermocouples with the purpose of measuring the growth rate abatement and the consequent NOx emissions reduction. A dedicated numerical toolbox, in-house developed by GE Power, has been used for both dampers preliminary design and growth rate reduction evaluation. Fine tuning of dampers elements as well as design assumptions adjustments required additional experimental evaluations and design iterations. Encouraged by the successful test in the concept phase, an optimized design for engine implementation was defined, that featured a significant increased damper volume, involving combustor parts re-design. The optimized configuration was finally tested in full annular rig and results demonstrated an important enhancement of operability while maintaining NOx emissions below the target levels.

This paper describes the flow and vibrations measured in a 1.5-stage transonic research compressor tested at the Notre Dame Turbomachinery Laboratory. The compressor is a sub-scale version of a large-scale industrial gas turbine. The experiment measured the compressor performance and investigated the operability issues of stall and flow-induced blade vibrations due to buffet and flutter. The buffet was investigated at full-speed with fully-closed inlet guide vanes; the full-speed, no-load condition of gas turbines used for power generation. The flutter was investigated at part-speed conditions with partially closed guide vanes; the part-power condition where stall flutter typically occurs for aero-engines. At both of these conditions the blades operate with high incidence and moderate velocity, which can result in flow-induced vibrations. Aero-elastic simulations were performed to predict the flutter boundary. The flutter analysis predicted positive aerodynamic damping near the operating line, and a decrease in aerodynamic damping as the stall boundary was approached. No flutter was observed in the stable operating range of the compressor. The experimental campaign used blade tip timing to measure the vibrations and unsteady pressure transducers above the compressor blade. These two types of data were correlated to better understand the drivers of vibration. The paper describes the behavior of the aerodynamic drivers of buffet and flutter and the resulting vibration.

To address the uncertainty in both the monitoring and the forecasting of the environmental conditions for offshore operations, DNV recommends the use of Alpha factors. These factors are defined for the environmental conditions in North Sea and the Norwegian Seas. Since no localised Alpha factors are available for regions outside of North Sea, these factors are conservatively applied everywhere in the world. In a region with benign weather characteristics such as the Mediterranean, this could be overly conservative for the selection of operational weather windows. A deterministic weather forecast is sufficient to assess weather risk for short term operations; nonetheless, uncertainties of longer term predicted weather should still need to be addressed. Shore float-in of umbilicals and cables requires a number of sequential activities with associated durations that build up to a total timeframe. This timeframe is beyond what can be accurately assessed using only deterministic weather forecasts. The operational activities are also very sensitive to tidal, current & sea-state variation; particularly associated with the use of personnel in the water like divers and waders for the removal of floats and the use of small crafts for control of the of the product alignment. The use of Ensemble Forecast which utilises probabilistic approach compared to the deterministic approach, addresses the uncertainty of long term weather forecasting and remove artificially added conservatism such as the Alpha factor. This forecast is derived from multiple simulations, each with minor variations of initial conditions and slightly modified weather models. Ensemble Forecast has been applied in offshore operation planning and execution in a project offshore Egypt in Mediterranean; particularly for a shore float-in of a main umbilical. It was used to define the main operational window, the start of the operation and weather risk beyond deterministic weather forecast. The use of the Ensemble Forecast for selection of overall weather window has been shown to optimise operability, reduce the risk of product being damaged, provide added confidence in the offshore operational safety for the personnel involved while minimising waiting on weather. The strategy of defining storm riding configuration for umbilical could enhanced overall operability. When the operational restrictions relating to limiting activities are anticipated to be surpassed but remains still within the storm riding sea-state, these activities could be safely halted and product held in place in stand-by mode until the weather conditions improved without affecting its integrity or overloading installation equipment.

The application of machine learning to aerospace problems faces a particular challenge. For successful learning a large amount of good quality training data is required, typically tens of thousands of cases. However, due to the time and cost of experimental aerospace testing, this data is scarce. This paper shows that successful learning is possible with two novel techniques: The first technique is rapid testing. Over the last five years the Whittle Laboratory has developed a capability where rebuild and test times of a compressor stage now take 15 minutes instead of weeks. The second technique is to base machine learning on physical parameters, derived from engineering wisdom developed in industry over many decades. The method is applied to the important industry problem of predicting the effect of blade damage on compressor operability. The current approach has high uncertainty, it is based on human judgement and correlation of a handful of experimental test cases. It is shown using 100 training cases and 25 test cases that the new method is able to predict the operability of damaged compressor stages with an accuracy of 2% in a 95% confidence interval; far better than is possible by even the most experienced compressor designers. Use of the method is also shown to generate new physical understanding, previously unknown by any of the experts involved in this work. Using this method in the future offers an exciting opportunity to generate understanding of previously intractable problems in aerospace.

Digitization of networked engineered systems is a technology that is increasingly being adopted to respond to changes in the market. Hence, the need for design methods to design a system adaptable to dynamic changes in the market. It is evident through a critical review of literature that current approaches for designing of networked engineering systems are neither agile nor rapidly configurable, and, at design time, usually do not have flexibility in selection and determination of the values of design parameters to lower the overall cost during the execution of networked engineering systems and simultaneously ensure that the product quality is acceptable. Accordingly, in this paper, a method, Design for Dynamic Management, for the realization of networked engineering systems is proposed. The key features of this method, in the context of Design for Dynamic Management, are adaptability and operability in the design of systems. The efficacy of the method is illustrated on a 2-D panel stamping process. Our focus is on the method rather than the results per se.

Instances of gas accumulation in the subject systems have occurred since the beginning of commercial nuclear power plant operation. NRC Generic Letter 2008-01, “requests that each licensee evaluate its ECCS, DHR system, and Containment Spray system licensing basis, design, testing and corrective actions to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems, and that appropriate action is taken when conditions adverse to quality are identified.” All of the three NPPs have accomplished this evaluation and propose some corrective measures like revision of the operation procedures, installing the venting valves etc. Taipower also committed AEC to establish the acceptable quantity of the gas accumulation and continue to follow the development of gas transport methodologies in the industry. According to the NRC NRR Action Plan TAC.NO. ME3939 GAS MANAGEMENT (March 2011), other safety related systems, in additional to the systems covered by GL 2008-01, also have the gas accumulation issue and therefore must be concerned. This project will develop the numerical evaluation process with two phase flow software to simulate the gas accumulation and the transportation phenomena for the GL 2008-01 systems and validate the results by experimental analysis.

The use of pure biodiesel for compression ignition engines during the winter poses a challenge due to gelling and plugging of engine filters and fuel lines. The most common method to prevent this issue is blending with petroleum diesel and many engine manufacturers limit the biodiesel in blends to 20% or less for warrantee purposes; as low as 5% may be set for winter months. In a previous work, the authors proposed a novel fuel tank design that could potentially solve this problem and presented a numerical validation of the concept of using phase change materials (PCM) to enable cold weather operability of 100% biodiesel by maintaining its temperature above a cloud point of 5 degrees Celsius for over 3 days at an ambient temperature of −25 degrees Celsius and initial temperature of 20 degrees Celsius. In this research, an experimental analysis is performed using a scaled model of the fuel tank with canola oil as a test fluid in the tank. The tank is subjected to an ambient temperature of −20 degrees Celsius in an icing tunnel facility with air velocity at 10 m/s. The results show that the time above cloud point was increased from 18.6 hours to 22.5 and 33 hours respectively when 4 and 12 PCM tubes were inserted in the tank containing 33 litres of canola oil. A simple numerical model was formulated to predict the transient temperature of the oil and comparison with experimental results showed excellent agreement.

While the size of new built semi-submersibles is steadily increasing, their mooring systems are not experiencing a similar change. Most of the sixth-generation drilling units rely heavily on thruster assisted mooring to increase their operability in harsh environments and shallow waters. Frequency domain programs are commonly used to calculate mooring line tensions in the design analyses. This analysis technique assumes linearity in both the mooring system and the thruster assist controller. The study presented in this paper examines the validity of these assumptions by comparing frequency and time domain analyses in two state-of-the-art analysis programs. The linear thruster assist controller in frequency domain analyses is benchmarked against the Kalman filter-based controller in time domain simulations and against a real thruster assist controller coupled with the time domain software.Copyright © 2018 by ASME

This paper presents an efficient methodology for multi-objective design optimization of drilling riser in ultra-deep water considering maximum operability window and minimum weight of drilling riser system. As exploration activity moves to ultra-deep waters, the associated drilling cost increases, putting pressure on the operators to expand the drilling operability and reduce costs. Drilling systems are an integral part of oil and gas exploration particularly in deep waters. The drilling riser design requires a time-consuming design loops and scenarios analyzed with different FEM models, such as connected mode, drift-off, hang-off, recoil analysis, emergency disconnection, etc. The main purposes of this work is to improve the safety and cost-effective for drilling riser design by employing multi-objective optimization based on metamodel. The Radial Basis Function (RBF) metamodel is constructed by the design of experiment sampling and is utilized to solve the problem of time-consuming analyses. In the optimization module, multi-objective optimization by a non-dominated sorting genetic algorithm II is performed. Thereby, RBF optimum solutions forming a Pareto set are obtained and compared with accuracy analysis to determine their validity. The optimization results indicate that the proposed optimization strategy is valid and provide an efficient optimization design method for drilling riser in ultra-deep water.

All modern drillships are equipped with moonpools, through which drilling and other subsea operations are performed. The operability of the vessel, is the percentage of time that the vessel can perform a specific operation in a specific location not limited by environmental conditions. Specific operations such as lowering a BOP or X-tree through the splash zone, have strict operability criteria and often a drillship is waiting on weather to perform these operations. In this paper, the underwater shape of the moonpool of a drillship is varied and the operability of the vessel is calculated and compared to the original shape. Ten moonpool configurations are used for the study. The GustoMSC “Galene” moonpool shape is used which is comprised of an upper and a lower chamber. The lower chamber or cutout step dimensions such as length, breadth and height are the variables for this study. An analytical method originally proposed by Newman [1] and extended by Chalkias and Krijger [2] is used in this optimization study. The method is comprised of a potential flow radiation/diffraction solver, where the moonpool modes are accounted as additional separate generalized modes. In this way each mode can be damped separately. In order to calculate the damping factors for the moonpool modes used in the potential flow solver, free decay CFD calculations are performed and a P-Q analysis is applied on the resulting time-traces. Additional regular wave CFD calculations are performed for method validation purposes. The efficiency and ease of the proposed method is demonstrated by calculating the responses and operability of multiple shape variations in the frequency domain.

This paper describes the development phases of an annular type combustor for heavy-duty gas turbine applications. High cycle efficiency and low emissions are required over a wide range of load conditions, with the consequence of reducing margin to thermo-acoustic instability onset and lean blow-out. In addition, in lean premixed combustors, the increased fuel air mixing times required to keep emissions low, may lead to undesired ignition or flashback into the fuel burner ducts. All these aspects are matter of this work and focus is on fuel burner design modifications which allowed dry emissions reduction while maintaining a sufficiently wide safe operation window. A synergic effort has been put in place, involving experimental campaigns and CFD simulations, with the purpose of assessing design changes initially and doing screening. In the meanwhile, numerical practices have taken benefits form the experience growth. Results of past work on similar components has been leveraged too. Test campaign involved different scale facilities, from single burner through full annular combustor up to full scale prototype engine. The progressive reduction of viable option for combustor components design changes, due to high impact of such modifications during the gas turbine late development phases, forced designers to concentrate efforts onto fuel burner optimization, looking for efficient ways to implement modifications and assess their effectiveness of combustion system performances. Emissions trends, blow-out and flashback margin for several burner designs are reported. Numerical analysis results are also shown, which revealed to be well aligned with the experimental outcomes, allowing burner optimized solution to be identified. Finally, characterization with respect to fuel gas composition is shown as well as sensitivity to different operating conditions.

Driven by global warming, a relentless march towards increased fuel efficiency has resulted in increased firing temperature for HA-class engines without an increase in baseload emissions. Moreover, emissions compliance for CO, NOx, and unburned hydrocarbons are desired over increased range in gas turbine load. In addition, exceptional gas turbine operational flexibility is desired to address potential intermittency due to the penetration of renewables in the electrical grid. Staged/sequential combustion is a state of the technology to provide operational flexibility and reduced emissions in power generation gas turbines. GE Power’s 7HA-class gas turbine combustion system combines GE’s proven DLN-2.6+ combustion technology, that has run reliably for over 1.3 million fired hours across more than eighty 9FA.03, 9F.05 & 7FA gas turbine engines, with an axially fuel staged system (AFS). Axially staging combustion to two zones allows for increased firing temperature at baseload (while maintaining the same NOx level) by operating the later/second stage hotter than the first/primary stage. During low load operation as the gas turbine firing temperature is reduced, percentage fuel split in the staged fuel system can either be reduced significantly or turned off and thereby keeping the overall combustion system into emissions compliance over a wider range of firing temperatures. This paper presents both the development testing of the staged combustion in the FA and HA class gas turbine combustion system rigs at GE Power’s Gas Turbine Technology Laboratory and the validation testing of staged combustion system for the 7HA.01 engine completed during Spring 2016 at GE Power’s engine test facility in Greenville, SC. The paper also discusses the significant simplification of operational principle and flexibility of startup, loading and baseload operation of the 7HA combustion system. Discussion of engine test results will show how axial fuel staging was utilized to demonstrate emissions compliance ( NOx (15% O2) < 25 ppm; CO < 9 ppm), operation from 14% load to 100% load with low combustion dynamics and also to enable wide wobbe capability, which is a normalized measure of fuel flexibility.

Inlet swirl distortion has become a major area of concern in the gas turbine engine community. Gas turbine engines are increasingly installed with more complicated and tortuous inlet systems, like those found on embedded installations on Unmanned Aerial Vehicles (UAVs) and Auxiliary Power Units (APU). These inlet systems can produce complex swirl distortion in addition to total pressure distortion. The effect of swirl distortion on engine or compressor performance and operability must be evaluated. The gas turbine community is developing methodologies to measure and characterize swirl distortion. There is a strong need to develop a database containing the impact of a range of swirl distortion and total pressure distortion on compressor operability. In one aircraft installation of an APU, the compressor experienced a wide range of combined total pressure and swirl distortion levels as a result of the APU inlet geometry. In this unique installation, the inlet system includes a check valve at the entrance of the inlet plenum through which all the airflow to the APU compressor passes. During APU operation, the check valve flaps are pushed open by the force of the airflow entering the plenum. The orientation of the check valve with respect to the compressor centerline introduces a varying amount of combined total pressure and swirl distortion. Consequently, it was necessary to test and map the compressor for a range of check valve positions in order to find an orientation with the lowest surge margin loss. The check valve comprises of two “D” shaped flaps hinged at the diameter of a circular flow entrance to the plenum. The plenum forms a “U’ shaped volume which allows the flow to turn 90 degrees from the check valve into the compressor annulus. A series of compressor tests was conducted where the check valve was rotated on its base such that the check valve had various clocking orientations with respect to the compressor axis. The check valve orientation was varied by lining the flap hinge line parallel to the compressor centerline (defined as zero degrees) then rotating the check valve in 30 degree increments from this reference all the way up to 150 degrees. Compressor speed lines were mapped at each check valve orientation and the surge margin loss/gain from a nominal undistorted surge line was determined. Fully 3D CFD analyses of each of these check valve orientations were run. The CFD models included the full valve and plenum geometry up to the compressor annulus. From the CFD analysis, the ARP1420 (Reference 1) total pressure distortion descriptors and the AIR5686 (Reference 2) swirl distortion descriptors were calculated on the annular plane at the compressor eye. Using these total pressure and swirl distortion descriptors determined for each check valve orientation along with the surge margin change available from the test data, a correlation of operability behavior was successfully obtained. This paper discusses the lessons learned and a recommended methodology todetermine an operability correlation for combined total pressure and high swirl distortion inlet systems.

Gas turbines are widely used power generation equipment and very important for its efficiency and flexible operability. With the increasing demand of low carbon or less greenhouse gas emission from gas turbine, usage of clean fuel (i.e. hydrogen) is highly recommended. Adaptation with various type of fuels without any operability issues are the primary focus of interest while design and development of a low NOx gas turbine combustion system. Due to chemical and physical property variation of different fuel, a common combustion system design is complex and require extensive testing. The present paper is focused on fuel flexibility of an industrial prototype burner, designed and manufactured by Siemens Industrial Turbomachinery AB, Sweden. In this work, a baseline case (Methane fuel) is compared with different custom fuel blends (mixture of methane with natural gas and hydrogen). The primary and secondary combustion characteristics were modified when hydrogen blended fuels were introduced. The Lean Blowout limit was extended for the primary and secondary flames. The secondary flame macro structure was captured using Planar Laser Induced Fluorescence and natural luminosity imaging; whereas primary flame location was characterized by the thermocouple readings. Operational stability map and emission (NOx and CO) capability of the burner was determined from the experiment. Numerical calculation using ANSYS FLUENT was performed to simulate the combustion process and compare the results with experiment. The experimental and simulation effort provided information about the flame macrostructure and operability (lean operability limit was extended by 100 K) of the new technology burner when the combustion system was exposed to different type of fuels.

In order to properly design the mooring and offloading equipment, and assess the availability of Floating Liquefied Natural Gas (FLNG) units during the engineering phase, TechnipFMC has paid a particular attention to the operability prediction of LNG offloading operations. For the FLNG projects currently under construction, the chosen offloading solution is the Marine Loading Arms (MLA) technology with the LNG carrier (LNGC) moored in side-by-side (SBS) configuration. In this paper, an improved methodology using Monte Carlo simulations is proposed to create a representative sample of a typical hindcast for North West Australia, assuming the case of a 147,000 m3 LNGC moored side-by-side to a TechnipFMC in-house design FLNG. It is shown that the random sampling is very well suited for large number of dimensions implied by the driving parameters (e.g. significant height, peak period, relative heading) of multiple wave partitions. In a second step, different multidimensional scattered data interpolation techniques are evaluated in order to further improve the accuracy. Since this would not be practical in time-domain and because the objective for this study is to compare the sampling and interpolation techniques to a benchmark on the whole hindcast, the vessels’ motions and SBS offloading operability are calculated in frequency-domain. The conclusions could also be applied to time-domain simulations. The paper also presents the sensitivity studies to the different interpolation methods and their key parameters and discusses the suitability of the proposed solutions.

Drilling riser system provides a short-term connection between subsea oil well and drilling vessel or platform. The analysis of different operability envelopes are required for drilling riser analysis, for example, connected drilling, connected non-drilling and hang-off analysis. The operability envelope analysis could provide operators statistical information for riser operational management. The current practice to calculate the drilling operability envelope is to use deterministic approach. However, deterministic approach could not take the randomness from environmental loadings and structures into consideration. Structural reliability method is an analysis tool to quantify probability of failure of components or systems accounting for uncertainties in environmental conditions and system parameters. It is particularly useful in cases where limited experience exists or a risk-based evaluation of design is required. It is gaining increasing popularity in the offshore and marine industry to predict failure probability. In this paper, structural reliability analysis is adopted to analyze the offshore drilling riser deployment. The uncertainties are mainly from wave and current loadings. The significant wave height HS is modeled by a Weibull probability density function, the zero-crossing wave period TZ conditional on HS is modeled by a lognormal distribution, and the surface current speed is modeled as Weibull distribution. Multiple simulations are performed by software Flexcom [1] and efficient structural reliability methods are adopted to get the failure probabilities. The deployment operability will be calculated based on structural reliability methods and the results will be compared with those calculated based on deterministic approach.

Potential flow frequency domain calculations have been performed to predict the natural frequencies and water motions for several moonpools. The moonpool free surface has been replaced by a damping lid in WAMIT without changing the kinematic free surface condition. Instead, the free surface modes of motion have been modeled as generalized modes. In this way, different damping values per mode can be applied. Damping values have been calculated based on CFD free decay tests and validated with model tests. Two vessels were chosen for this study with different moonpool dimensions and shapes. The first is a construction vessel with a small rectangular moonpool, whereas the second is a drillship featuring a large moonpool optimized for transit. Free decay CFD calculations have been performed for both vessels, while CFD regular wave calculations have been performed for the construction vessel and model tests were performed for the drillship. Using the aforementioned methodology, a motion reduction device is designed and presented in this paper. The aim of this device is to reduce the motions experienced in the moonpool during vessel operations in a sea state and thus to increase the operability of the vessel with respect to moonpool motion limitations. The increased vessel operability with the new device is shown by a wave scatter analysis. In order to calculate the workability limit curves, suitable limits have been chosen for the free surface elevation and the water vertical velocity in the moonpool.

Marine subsea operations are performed by highly specialized ships, referred to as Inspection, Maintenance, and Repair (IMR) and Offshore Construction Vessels (OCV). Although the ships and their on-board equipment are designed to operate in harsh environmental conditions, the current practice often is to terminate operations when a rigid and conservative weather limitation is reached, often specified in terms of the significant wave height as the exclusive criterion. Such general limitations do not account for vessel specific motion behavior. Since the offshore industry is aiming for all-year-round safe subsea operations, there is a strong interest amongst ship designers, owners and operators to establish vessel and task specific criteria. The project Vessel Performance within the Norwegian Centre for Research-based Innovation on Marine Operations (SFI MOVE), is developing response-based procedures, that are leading to case-specific operational ranges. This approach enables the full exploitation of vessel performance capabilities for safe and efficient offshore operations. Two methods with different complexity levels are proposed. Firstly, on the higher level, detailed operability analysis for a fleet and sea area of interest are performed by means of numerical tools. This level can be used to obtain detailed results for existing ships, but the procedure can also be applied as guidance in the design stage. Secondly, on the lower level, generic diagrams can be used to estimate and compare the operational performance of different vessels based on fact sheet parameters. This is especially relevant for decision making processes where a detailed study cannot be performed.

This study describes one of the technical solutions for Small Scale FLNG (SSFLNG)[1] development specifically designed to monetize Associated Gas (AG) of producing oil fields located within convenient distance of an existing LNG Plant or Port with LNG storage facility. Limited production capacity combined with short range small scale LNG carriers (SSLNGC), provide a cost effective means for LNG production. Ship to ship off-loading operation by loading arm has been considered in AG SSFLNG. Produced LNG is to be off-loaded from the SSFLNG to side-by-side moored SSLNGC. Relative motion and dynamic load acting on loading arm system in side-by-side mooring arrangement is one of key factors to estimate the offloading operability of the AG SSFLNG. In this paper, a numerical two-body motion analysis for the side-by-side moored SSFLNG in frequency- and time-domain is carried out. Also, the basic engineering work is carried out for the marine loading arms (MLA). Since the MLA reacts approximately as a linear system, it is calculated by a full spectral RAO analysis for each of the worst load cases issued from the spectral ranking. All loads and stresses inside the MLA are verified in accordance with EN1474-1[2] for the situations identified in the previous step. A high level fatigue analysis focused on the cryogenic swivel joints is carried out. Based on the numerical calculation for relative motion in side-by-side moored FLNG, we have been performed structural assessment for MLA in several environment conditions. The structural integrity of both MLA and the LNGC manifold are validated during offloading for Offshore West Africa.

A semi-analytical method is proposed in this study to estimate tube wall temperature versus time for Waste Heat Recovery Units (WHRU) and fired heaters in a typical LNG plant. The results are used to estimate Safety Time to avoid failure of tubes. Safety time estimation is crucial for control loop design of equipment in the operating plant. Two case studies are presented based on real control loop design data for an LNG plant. The results show that for both case studies, process safety time for control loop is less than the tubes safety time. Therefore the control system is capable of safely stopping the equipment from operation without tube failure or degrading of the process fluid. The proposed semi-analytical method is capable of calculating the Safety Time for WHRUs and fired heaters in an economical way while the method offers a reasonable accuracy due to its analytical nature. The proposed method can be used in Fundamental Engineering and Evaluation Designs (FEEDs), Hazard and Operability studies (HAZOPs) and Hazard Identification (HAZID) studies for LNG plants and power plants.

With the introduction of the EPA Tier 4 NOx emission limits for rail diesel engines this year, engine developers are forced to implement more advanced emission control technologies such as selective catalytic reduction (SCR) or cooled external exhaust gas recirculation (EGR). The integration and control of these systems for ensuring optimum performance throughout the operating range brings about new challenges on top of the well-known requirement for unconstrained operability in a very wide range of conditions. As a consequence, engines and their subsystems have to be designed for maximum flexibility. The turbocharging system in particular needs to be capable of dealing with extreme ambient conditions associated with high altitudes, hot summers, severe winters, tunnel operation, etc. This flexibility must be achieved without compromising reliability and while ensuring continuous in-use compliance with the emissions standards throughout the life of the installation. At the same time, engine performance should be maintained at the highest level possible. This study demonstrates that all of these targets can be met by combining two-stage turbocharging and EGR with suitable control elements. Two-stage turbocharging, which has become increasingly popular in other industry sectors due to its potential for improving the bsfc / NOx emissions trade-off when used in combination with correspondingly optimized valve actuation (Miller timing), is starting to be adopted also for rail applications. A variety of EGR concepts was proposed or put into practice over the past few years, and the most important or promising of these have been taken into consideration for this study. Extensive simulations of the resulting engine and turbocharging systems have been performed using ABB’s in-house simulation platform, based on a generic engine model that can be considered representative of the rail sector. It is shown that integration of EGR, two-stage turbocharging and appropriate control elements is highly attractive as it offers outstanding operational flexibility and very high fuel efficiency without any compromise in terms of reliability. The selection and specification of control elements and turbocharging system components depends on the EGR concept applied. As is shown below, this can be tailored to the application to ensure optimum performance and flexibility. In view of these obvious benefits, we are very confident that such integrated EGR / two-stage turbocharging systems will be adopted more widely on railway engines.

Environmental and economic factors have driven the advancements in fluid power technologies over the last two decades. Gradual development has been made over time on the state-of-the-art fluid power technology; however, there has been no major advancement leading to radical improvement on systems’ efficiencies. Displacement-controlled (DC) actuation has been under investigation by the authors’ group since its conception in 1998 as a highly efficient alternative to its valve controlled counterpart, demonstrating fuel economy improvements of up to 40% and the possibility for engine downsizing of up to 50% for an excavator truck-loading cycle. Through the installation of a variable displacement hydraulic pump/motor per actuator, DC actuation entirely eliminates the losses due to resistive control and allows for the recuperation of energy from overriding loads. The one-pump-per-actuator requirement however represents the technology’s largest obstacle due to the increased machine production costs. For this reason the authors’ group proposed the idea of pump switching wherein a reduced number of hydraulic units is connected to the actuators in a multi-actuator machine through a distributing manifold. The idea relies on proper design of the distributing manifold and enabling controls to realize machine operability. Work by the authors’ group has demonstrated that the pump-switching idea is feasible on the actuator level, achieving seaming-less switching transitions while retaining the basic fuel savings demonstrated for DC actuation. This paper presents the first formal attempt to create a supervisory controller for a DC multi-actuator machine with pump switching. The controller is based on priority levels geared towards the maximization of the number of available actuator combinations. Implementation on a DC hydraulic hybrid excavator prototype show the feasibility of the control approach as well as the limitations and further improvements.Copyright © 2015 by ASME

In recent years many studies were performed with the aim of reducing losses and to optimize the oil flow management in complex machines like excavators. One of the most promising ideas is to implement multiple hydraulic power sources but this requires a flexible pump switch system, in fact depending on flow request and machine mode one or more pumps can be switched to serve each actuator. To put into practice these studies it is necessary to in-depth design the distribution system, through which hydrostatic transmissions are applied to the different loads. The system presented couples more actuators to every single pumps and offers also cross connections, in order to increase systems flexibility in flow management. The paper presents a new component to realize the pump switch management, applying the matrix concept to the hydraulic flow connections. The matrix for oil flow management is a new hydraulic component, flexible, safe and scalable, that can be coupled to other similar, offering a real matrix of lines and columns. From the working principle point of view, each line is connected to a pump and each column is connected to a load, only a section can be opened for each pump, but more connections can be opened for an actuator, offering a flexible flow management. The component is a rotating distributor with a safety spool, that can connect P and T port of one pump to the A and B port of each actuator, moving the safety spool only when the rotary distributor is coupled with the desired actuator. Both closed center and open center configurations are possible, as well as regenerative systems can be implemented. The solution is presented with focus on the mechanical design and on the working principle, offering an optimal solution to the switching system, that free the distribution system design from the constraint of a predefined coupling of pumps with actuators. Since the component is in its early stage of development, the paper will focus mainly on design concept and architectural alternatives and potential benefits of the implementation of the concept on state of art architectures from the functional capability point of view. Some argument will be given then on the topic of Functional Safety disclosing some of the operability and safety potentials of the system. Further important design aspects such as Internal Leakage, Axial and Radial Forces on Spools, Dynamic Response will be addressed in later publications, as well as system simulation of working cycles and Testing of Prototype has to be obviously undertaken in the future.

Solid oxide fuel cell (SOFC)/ gas turbine (GT) hybrid systems possess the capacity for unprecedented performances, such as electric efficiencies nearly twice that of conventional heat engines at variable scale power ratings inclusive of distributed generation. Additionally, these hybrids can have excellent operational flexibility with turndowns possibly as great as 85%. There are, however, developmental needs such as turbomachinery characterization and re-design. A leading example is that of greater propensity to have occurrences of stall-surge given the significantly different operating environment in contrast to conventional heat engines. Additionally, dynamic variation in power generation has to be done with significant a priori insight to avoid thermomechanical threats to cell stack and turbomachinery. State-of-the-art approaches involving hardware-in-the-loop simulation and, ultimately, additive manufacturing are being pursued to enable such characterization and re-design considerations given variable and dynamic operability requirements. Compressor performance in hybrid systems has been characterized at the United States National Energy Technology Laboratory (NETL), inclusive of a capability of feed forward hardware-in-the-loop simulation of hybrid systems under dynamic conditions and a capability of replacing turbine and compressor components at a relatively low cost. This paper highlights some of the simulation results, and the net result is an approach that addresses hybrid system developmental needs for accommodating generation transients.

Fuel flexibility is a key feature for Dry Low NOx (DLN) combustors, which shall be capable of accepting a wider range of fuel compositions to meet more and more challenging requests from the Oil and Gas market segment (upstream and downstream applications). Non-methane hydrocarbons (C2+) are one of the main targets of GE Oil & Gas efforts to enlarge the fuel flexibility of DLN combustors, as they are often present in high concentration in fuel gas streams that customers would like their gas turbine to be fed with. The main concerns with such fuel gases in DLN combustor are: the risks of flashback, hardware overheating, increased combustion dynamics and NOx emission, ignition in unexpected locations (with potential damage of the combustor, operability issues and impact on durability). In order to assess the capability of the current Frame 5 DLN1 hardware design with high C2+ fuels, a single can full pressure test campaign was conducted on a full size DLN1 combustor at Sesta Combustion Lab (Italy). The combustion chamber was successfully tested in premix mode up to 50%v. of ethane content, observing safe and reliable operation with regard to the above mentioned risks. Special tests were carried out in both Premix and Lean-Lean operating modes, in order to verify the ability of the combustor to maintain a stable and harmless flame and assess the operability margins in the different operating conditions of the combustor. Tests demonstrated a good margin already with the current design. After optimizing the air flow path, the expected performances also in terms of NOx and CO emissions and combustion dynamics were achieved in the investigated ethane content range. These tests outcomes allowed a paramount enlargement of the Frame 5 DLN1 capability in terms of acceptable C2+ concentration in fuel gas.

The GE Rapid Response plant design is described and compared to conventional combined cycle plant design. Advantages of the Rapid Response improved operational flexibility are explained and compared to conventional combined cycle plants. Improvements include faster power delivery to the grid, more economical plant startup, more profitable plant startup and lower emissions during plant startup. The capability of a drum type HRSG for the Rapid Response cycling service is explored. Joint studies between GE and HRSG suppliers are highlighted supporting the adoption of drum type HRSGs for this cycling service. Necessary modifications to other plant equipment are explained. Quantitative comparisons of Rapid Response and conventional combined cycle plant operability are given for electrical energy production and emissions reduction. An advanced Selective Catalytic Reduction SCR control is shown providing improvements in combined cycle plant transient emissions control. Elements of the new control are explained. Argument is made to designate the new control as a second generation GEN II control compared to all other currently existing controls designated GEN I. A brief outline of the current state of Rapid Response plant deployment is provided.

NASA’s Environmentally Responsible Aviation (ERA) Program calls for investigation of the technology barriers associated with improved fuel efficiency for large gas turbine engines. Under ERA, the highly loaded core compressor technology program attempts to realize the fuel burn reduction goal by increasing overall pressure ratio of the compressor to increase thermal efficiency of the engine. Study engines with overall pressure ratio of 60 to 70 are now being investigated. This means that the high pressure compressor would have to almost double in pressure ratio while keeping a high level of efficiency. NASA and GE teamed to address this challenge by testing the first two stages of an advanced GE compressor designed to meet the requirements of a very high pressure ratio core compressor. Previous test experience of a compressor which included these front two stages indicated a performance deficit relative to design intent. Therefore, the current rig was designed to run in 1-stage and 2-stage configurations in two separate tests to assess whether the bow shock of the second rotor interacting with the upstream stage contributed to the unpredicted performance deficit, or if the culprit was due to interaction of rotor 1 and stator 1. Thus, the goal was to fully understand the stage 1 performance under isolated and multi-stage conditions, and additionally to provide a detailed aerodynamic data set for CFD validation. Full use was made of steady and unsteady measurement methods to understand fluid dynamics loss source mechanisms due to rotor shock interaction and endwall losses. This paper will present the description of the compressor test article and its measured performance and operability, for both the single stage and two stage configurations. We focus the paper on measurements at 97% corrected speed with design intent vane setting angles.

As part of the Great Horned Owl (GHO) program Southwest Research Institute© (SwRI©) has developed a small, lightweight gas-turbine generator to provide power for an electric or hybrid electric Unmanned Aerial Vehicle (UAV). This original design for a fuel-to-electricity component of a hybrid propulsion system was designed, built and tested at the SwRI facility in San Antonio, TX. The design is based on a patented SwRI gas-turbine configuration and went through five major design iterations leading to the final configuration. The design iterations of the gas generator were driven by aggressive targets for weight, size and performance that were part of program requirements. The design of the GHO machine evolved from the initial concept based on lessons learned from previous testing at SwRI and considerations to improve manufacturability and operability. Improvements to the design were also incorporated to meet performance goals and increase life of hot section parts. This machine is low-cost and simple to operate and in addition to the original design intent of fuel-to-electricity use in a hybrid propulsion system can be used as a technology demonstration platform. SwRI plans to use the GHO machine in projects such as instrumentation development, as a test bed for new technologies such as ceramic or additive manufactured parts and for use as a component in a hardware-in-the-loop system.

Engine inlet distortion complications have plagued the turbine engine development community for decades, and engineers have developed countless methods to identify and combat the harmful effects of inlet distortion. One such type of distortion that has gained much attention in recent years is known as inlet swirl, which results in a significant flow angularity at the face of the engine. This flow angularity can affect the pressure rise and flow capacity of the fan or compressor, and subsequently affect compressor and engine performance. Previous modeling and simulation efforts to predict the effect inlet swirl can have on fan and compressor performance have made great strides, yet still leave a lot to be desired. In particular, a one-dimensional parallel compressor model called DYNTECC (Dynamic Turbine Engine Compressor Code) has been used to analyze the effects of inlet swirl on fan and performance operability of the Honeywell F109 turbofan engine. However, when compared to experimental swirl data gathered at the United States Air Force Academy (USAFA), the model predictions were found to be inaccurate. This paper documents work done to compare the initial predictions generated by DYNTECC to the latest set of experimental swirl data, analyze the potential shortcomings of the initial model, and modify the existing model to more accurately reflect test data. Extensive work was completed to create a methodology that can calibrate the model to existing clean inlet fan map data. In addition, an in depth study of fan/compressor stalling criteria was conducted, and the model was modified to use an alternate stalling criteria that more accurately predicted the point of stall for various swirl inlet conditions. The prediction of the fan stall pressure ratio for all inlet swirl conditions tested is within 2% of the ground test stall point at the same referred fan speed and referred mass flow.

A state-of-the-art, rotary-disc atomizer driven by a permanent-magnet electric motor and supported by active magnetic bearings (AMB) was designed, fabricated, and tested as part of a spray-dryer system within a pharmaceutical-processing plant. The atomizing process imposed several challenges on the AMBs, including large, highly-dynamic rotor imbalances and large, quasi-periodic external radial impulses. Several design changes were systematically implemented to mitigate the effects of large rotor imbalances. A novel impulse detection and recovery system was introduced to alleviate the effects of external impulses. These changes, which have steadily improved the operability and reliability of the machine, are described here along with field test data.Copyright © 2015 by ASME

This paper introduces a multi-point design capability to discrete adjoint-based aerodynamic shape optimization for multi-stage turbomachines. The developed optimization framework allows to improve a compressor or turbine design not only for a certain operating point, but enables the inclusion of additional off-design operation points, therefore guaranteeing a robust design and annihilating the risk of improving the configuration for a specific design point while deteriorating the overall operability of the turbomachine. To keep the computational cost to a minimum, at every design cycle the flow and adjoint solutions are first calculated and stored for each operating point. This approach ensures that the subsequent finite-difference approximation of the residual sensitivity with respect to the design variables is obtained at a cost nearly independent of the number of investigated operating points. The objective function gradient is then assembled as a weighted sum of the sensitivities calculated for the different operating points. The developed multi-point optimization method is applied to a single-stage transonic compressor and both the back pressure and the rotor wheel speed are varied to investigate the use of adjoint-based design methods to efficiently explore robust turbomachinery designs.Copyright © 2015 by ASME

Engine models are widely used to simulate the engine behavior at steady state and transient operating conditions over the full flight envelope. Within the engine development process such simulations are used to support component design, evaluate engine performance, operability and test data, as well as to develop and optimize the engine controls. Recent developments have raised interest in the modeling of start-up processes of turbofan engines in order to support the definition of sufficient engine control laws. This implies that simulations are started at a condition where the engine shafts are static and temperatures and pressures are equal to ambient. During start-up the engine can only be operated transiently through the sub-sub-idle region (near zero speed) using a starter torque. The activity presented here was targeted to support the development of industrial-standard high-fidelity turbofan engine models capable of simulating start-up, shutdown or windmilling operation. Within the three previously mentioned cases starting from an engine-off condition, ground start from zero-speed is the most challenging in terms of physical and numerical modeling. For this reason, this paper concentrates on that case only. Zero mass flow and speed at the beginning of the simulation impose a set of special problems that do not exist in standard simulations: the modeling of a static engine-off condition, the modeling of static friction, and the modeling of reverse flows. The requirement to support an existing industrial model development process also made it necessary to apply the same quality of physical modeling to start-up simulations as would be the case for above-idle engine simulations. The physical effects present during engine start are discussed and modeling solutions are presented. Finally, results of a dry crank simulation are presented and discussed, illustrating that the expected effects are present and that the simulation is capable of predicting the correct trends.

The High Performance Computing Modernization Program (HPCMP) is developing high-fidelity simulation tools through the Computational Research and Engineering Acquisition Tools and Environments (CREATE™) program. CREATE-AV is the component of the CREATE program focused on air vehicles. Kestrel is the simulation product for fixed-wing aircraft in the CREATE-AV program. To investigate engine/inlet system performance and operability issues, the Kestrel product includes the capability to model propulsion components in aircraft simulations through the Firebolt propulsion component. Firebolt Capability 1 accounts for propulsion system effects by integrating a 0-D engine model directly into the computational fluid dynamics (CFD) process. Firebolt Capability 2 extends the capability by enabling the user to couple full-annulus 3-D rotating turbomachinery into the aircraft CFD simulation. This paper gives an overview of the Kestrel product including the Firebolt propulsion capability. In addition, this paper will demonstrate Firebolt Capability 1 and 2 by applying a 0-D TF34-GE-100A engine model and a TF34 3-D full annulus rotating turbomachinery fan in an A-10 aircraft CFD simulation. Finally, the inlet performance for the nacelles with both the 0-D engine model and full-annulus turbomachinery fan will be compared to subscale wind tunnel inlet test data.Copyright © 2015 by ASME

As the industry continues to push the boundaries of offshore exploration into deeper water depths and harsher environments there is an increased need to ensure the integrity of both the drilling riser and wellhead in the event of loss of station-keeping in dynamically positioned (DP) rigs. In order to determine vessel limiting operating/alert offsets it is necessary to carry out a vessel drift-off analysis which predicts the vessel drift-off speed and direction in the event of a DP failure. This analysis is typically performed for a limited combination of environmental conditions (usually collinear wind, wave and current) and will generally assume a vessel position that is directly above the wellhead. Whilst the results of the standard drift-off analysis, and associated drift-off plots, are useful in determining expected drift-off speed and feasibility of the emergency disconnect sequence (EDS), the outputs are of little operational use to the rig personnel in determining allowable operational/alert offsets for day to day operations. As the vessel is rarely located directly above the wellhead and environmental conditions can vary significantly in both direction and magnitude over the drilling campaign a more comprehensive analysis methodology and set of load cases is required in order to develop useful inputs to the well specific operating guidelines (WSOG). The current standard industry approach is to generate drilling riser operability envelopes independently of drift-off curves and thus recommended operating offsets do not account for drift-off speed, reaction times or EDS times. This can lead to a potential lack of conservatism in WSOG. In order to avoid this lack of conservatism in calculation of operating offsets a coupled steady-state/transient response analysis approach is required to ensure that a DP failure event at limiting operational offset does not lead to damage to the wellhead or riser system. A new revised methodology for the calculation of allowable operating windows and associated alert offsets is presented in this paper. This new methodology couples both the steady state operating limits of the vessel and the transient system response during a drift-off, due to DP failure, in order to present a comprehensive go/no-go operability chart of allowable offset vs. environment for use as input to the WSOG.

Flexible products are becoming ever longer and larger to cope with the technical demands of deepwater fields and tie-backs. The implication of this being that product reels are becoming larger, heavier and more complex to manage during installation and recovery operations. This paper explores the current limits of reel-based installation equipment evaluating the implications of the increased deck footprint, the necessity for modularity from an equipment repositioning and handling perspective and the limitations placed on vessel selection and vessel stability during installation. The safety, engineering, operability and commercial factors associated with each area of development are analysed to produce a complete snapshot of where the current industry limits lie and how far we can push the envelope for this method of installation. Specific equipment focus is placed on reel-drive systems which are the industry standard and under-roller systems which, although represent a more dated technology, are still accepted in certain regions for flex lay operations.

A new riser anti-recoil control design is presented in this research paper using the novel riser hybrid tensioning system by combining a fast acting electrically powered riser tensioning system with existing conventional hydro-pneumatic tensioners. This work is the further development of a control system for the previous work presented in the framework proposal of riser hybrid tensioning system. This innovation that we bring forward here is all designed to increase operating envelope of the vessel. A system model integrating both electrical and hydro-pneumatic tensioners and the riser string is built for anti-recoil control purpose. The main goal of this control design is a safer and more predictable position control of the riser string. A LQG control design technique is applied here. A feedback controller with Kalman estimator of the system state space variables is designed and implemented. The Matlab simulation helped to demonstrate the concept feasibility of this anti-recoil control strategy and to further verify that a more robust and accurate control performance could be achieved by this riser hybrid tensioning system. This control technique increases the testability of the riser anti-recoil system; reduce potential damage and increase operator’s confidence. The new proposed data logging system improves the detectability of the anti-recoil system. And the position control, when the riser string “soft hang-off” on the tensioners, opens the possibility to extend the operability to other applications.

The concept of gas pipelines sectionalized by block valves in Brazil has focused on safety rather than operability, and so all such valves are automatically controlled. However, operational history has indicated that undesired actuation of automatically controlled blocking valves is among the major risks of supply failure. Thus, a statistical study was carried out to identify the chief causes for undesired closures and opportunities for improvements. One of the most important causes is the lack of standardization of equipment and procedures within the pipeline network. The lack of standardization usually results in higher costs and complexity of operation and maintenance. With the purpose of overcoming such drawbacks, it was required to establish a program for process optimization, in order to obtain well-adjusted maintenance and operational procedures throughout the life cycle of the equipment and facilities. A maintenance strategy for the automatic block valves is an important point to achieve the objectives defined in this program, such as an increase in operational reliability, minimizing the risks of gas-supply failure and the reduction of operational costs. Although the project is still in progress, it is already possible to observe some positive outcomes related to operational reliability, showing a significant reduction in the number of operational occurrences of automatic block valves in 2013.

The natural frequency of valves is an important design requirement to ensure that valves do not go into resonance during operation and consequently fail structurally or fail to perform their design and safety related functions. Besides its impact on operability, valve resonance can initiate piping vibration that could damage pipes and their supports; which is undesirable. As important as equipment natural frequency is to valve operability, one would expect that testing should be the de facto method for confirming its value. Ideally, this should be the case, however, cost considerations limit the extent to which testing is used. On the other hand, testing does have some issues with respect to accuracy such as the effect of supporting structure flexibility resulting in a conservatively lower natural frequency measurement. In addition, the multiplicity of valves in nuclear power plants with different designs, sizes and safety classes limit the use of testing to establish valve natural frequencies except when required in the equipment specifications. Frequently, valve natural frequencies are determined by analysis either using finite element techniques (FEA) or by first principles of beam and mass models; the latter being more frequently used. This paper presents the studies performed to correlate valve natural frequency test results to the results derived from analytical techniques using Raleigh’s energy principle and from finite element analysis (FEA) methods. In a previous paper on valve natural frequency [1], Ezekoye et al. presented a model for estimating valve natural frequency by incorporating mass inertia of the valve structures with the more traditional methods that are based on a lumped mass model to determine displacements. In the process, the flexibility of the extended structure (otherwise referred to as the superstructure) and the valve body itself are considered. Using limited test data, Ezekoye et al. showed that there is merit in using their enhanced analysis model. Their correlation was promising. The finite element analysis, on the other hand, is a well-established technique for solving complex structural mechanics problems and should be expected to provide reasonable results comparable to actual valve tests provided the boundary conditions provide a reasonable representation of the actual valves tested. In this paper, ANSYS Version 12.1 was used to model valve natural frequencies. Additionally, a more extensive testing of valves for natural frequency was performed in this paper than was reported in Reference 1. The results of both the FEA and the Raleigh’s principle model as presented in Ezekoye et al. are compared against the test results. By comparing the three results, strengths and weaknesses of each method become apparent. The choice of whether or not one chooses to test or perform analysis depends on the valve specification requirement and the preference of the designer.Copyright © 2014 by ASME

This paper outlines pioneering work in the field of subsea compressor technology. The guiding design principles for the subsea motor-compressor of the authors’ company were operational safety, robustness, reliability, and remote operability. An early demonstrator was realized and tested in collaboration with the end-user upfront and consecutively improved gradually where indicated. This turned out to be beneficial in the phase of project execution since the early knowledge of application specific requirements resulted in an already elaborated overall design basis. The presented design also draws on extensive top side experience from sealed motor-compressors, where a portion of the process gas is taken directly from an intermediate stage of the compressor and fed back to the suction line after passing through, and thus cooling, the motor and the active magnetic bearings. This minimizes the number of interfaces and required sub-systems. Various simulations were performed to account for differences between subsea and topside environments. The focus of the work presented in this paper is on the effect of the high heat transfer resulting in an altered overall temperature situation. At the time of writing, the first units of the discussed subsea motor-compressor have successfully passed Factory Acceptance Testing (FAT) under atmospheric conditions. At the moment, they are being prepared for extended submerged testing with production gas at a test facility of the end-user.

Conceptual design of a hydrogen fueled dry low NOx combustor for heavy duty gas turbine is presented in this paper, including a complete experimental validation, with focus on both NOx emissions and operability. Effort was first provided in the identification of viable conceptual solutions: a technology screening has been carried out, balancing both innovation content and proven experience of each concept. A look to alternative solutions coming from literature has been given too. Three burner concepts have been selected, designed and procured to be tested into a reduced scale rig, arranged to mimic main features of a small size gas turbine combustor, in terms of combustion air inlet temperature, hot gases residence times and amount of cooling: atmospheric pressure operation was considered a proper approximation to actual operating conditions for a conceptual design phase. The three solutions have been first characterized in terms of emissions against equivalence ratio, pilot percentage and burner pressure drop. At the same time, safe operation margins to both flashback and combustion instabilities onset have been identified for both pure hydrogen and pure natural gas feeding options. Results, while recommending different development paths for each of the investigated concepts, clearly indicate the most mature among them, allowing authors to address specific operability detailed investigations on it: flashback and flame holding resistance tests were thus performed, demonstrating that such a solution is mature for a preliminary full scale arrangement design and experimental characterization.Copyright © 2014 by ASME

Arnold Engineering Development Complex (AEDC) is the most advanced and largest complex of flight simulation test facilities in the world. The center operates 43 aerodynamic and propulsion wind tunnels, rocket and turbine engine test cells, space environmental chambers, arc heaters, ballistic ranges and other specialized units. Over the years since these facilities have been operational, there have been a series of operational issues that have arisen involving compression system performance or the effect of compressor operability on facility performance or structural integrity. This paper presents three cases[1] where ground test facilities have experienced some form of compression system performance issue or a test article’s abnormal operation such as surge cycles effect on facility structural or operational capability. In each case, the analysis engineer trying to figure out what might be the cause or the effect of these abnormal operations on facility operation is hampered by the lack of proper instrumentation that would provide insight into the issue. In these types of situation, it has been shown that some form of numerical simulation can provide great insight into possible causes and even suggest solutions to the observed anomaly. This paper highlights where a specific numerical simulation based upon one-dimensional physics and its application to parallel compressor theory has been applied to the analysis of three aerospace facility compression system issues.

The utilization of the Northern Sea Route by commercial ships is an official fact. Since 2009 the number of international cargo vessels using the passage has been increasing, and a continuous raise in these numbers is expected if the route establishes itself as reliable. The route saves vessels approximately two weeks’ time in summer over a route via the Suez channel, but the increase brings concerns, regarding environmental impact, safety, and operability on the route. This paper investigates the current challenges of using LNG fueled ships for arctic transport routes. A panorama of the recent conditions and predictions for the arctic environment regarding ice concentration and seasonal route availability is presented. The current development of LNG as a commercial fuel is discussed based on this arctic panorama, approaching key topics such as infrastructure, economic viability, propulsion requirements, and environmental impact. Special attention is given to the performance of LNG propulsion systems under arctic conditions, focusing on powering and air emissions. We conclude the paper by proposing the implementation of a lifecycle model to predict economical and environmental performance indicators when simulating a fleet of LNG fueled ships operating under many possible future ice conditions scenarios.

The riser system selection and sizing is one of the most challenging design issues of the subsea world specifically for deepwater applications. Bundle riser towers have been used for few deep water developments since the late 1990s and have demonstrated their capacity to meet the operational constraints in terms of field layout congestion, flow assurance, mechanical design, fabrication and installation etc. From the pioneer application in the Gulf Of Mexico (Green Canyon 29 – 1988) to the 2nd generation systems in Western Africa (GIRASSOL to Rosa or CLOV), the design of Hybrid Riser Towers has evolved to improve mechanical robustness, installation efficiency and operability. This article reviews the past evolutions and gives an overall view of the performance achieved so far, mainly in West African sectors. The move of the offshore industry towards ultra-deep (WD > 1800m) and/or marginal fields may trigger some additional design evolutions which are highlighted in the article, with a focus on the water depth increase considering environmental conditions met on previous projects. The feasibility in harsher conditions is not addressed in this document. In addition, the challenges raised by the engineering of such deepwater Hybrid Riser Tower concepts are discussed: • Structural models of different scales shall be used to properly account for potential couplings between the global behavior of the whole tower with the local responses of each individual component; • Top and bottom assemblies as well as the rigid or flexible spools, the piping and connectors shall be introduced into the FE models to define correct boundary conditions to the HRT; • Slug or severe internal flows shall be considered for fatigue issues requiring complex models which combine CFD and structural calculations; • Risks of hydrodynamic instabilities shall be assessed like plunge and torsion galloping for non-cylindrical sections and VIV for bare peripherals; • A specific attention shall be paid to the fatigue budget spent from towing and Installation to the In-place configuration.