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The aim of this paper is to describe significant potential risks that were identified in a typical waste-heat recovery unit (WHRU) used in a natural gas processing unit and to recommend some improvements and best practices in order to minimize those potential hazards that might lead to operational incidents, particularly during the commissioning phase. A case study of a WHRU operating in a gas processing is taken as example and where a heating coil circulating a thermal fluid recovers the waste heat from the exhaust gas of a gas turbine that serves for power generation in the processing of raw natural gas. The potential risks identified are the possibility of coking formation in the circulating thermal fluid, the surge of high backpressure in the exhaust gas from the turbine and, finally, the possibility of corrosion in the dampers and heating coil.
The paper provides valuable guidelines and best practices to prevent operational problems during the startup and operation of the WHRU from gas turbines. The recommendations are intended to minimize the risks by improving the sealing airflow to the main damper with the proper dimension of the piping network and by avoiding stagnant flow of the thermal fluid. Additional recommendations include monitoring constantly the exhaust gas backpressure to prevent the pressure surge, as well as the installation of mechanical devices that can prevent the full closure of the two dampers simultaneously. Finally, the selection of the recommended construction materials can minimize the potential risks of corrosion.
Piping systems under multi-phase flow are subjected to unbalanced forces during plant operation and they experience vibration. Usually, the piping vibrations can be minimized by either modifying piping configuration/supports or alteration of operational modes. This paper presents an engineering study of a challenging piping vibration problem, which was resolved by an inventive and cost optimizing solution, as there are limitations in modification of existing pipe support/configuration. The inventive resolution reduced implementation cost to the Company without impacting the operations.
A comprehensive study was conducted to identify the root cause of piping vibration in rich amine piping system (36" pipe) from heat exchanger to amine regenerator, a tall column. The vibration screening and likelihood-of-failure calculations were carried out based on Energy Institute's guidelines and observed that the piping system is in concern/problem zones.
The process study including review of hydraulics, verification of line size and control valve design was performed to identify the root cause of piping vibration. The piping stress analysis (static/dynamic) was carried out with actual operating conditions, which is under multiphase flow with varying density/forces.
The process study revealed that the flow velocity and momentum are within process design requirements. However the flow in the piping system is multi-phase type, which generates unbalanced forces due to slug loads at each elbow of the piping system.
Based on piping stress analysis results, it was identified that the natural frequency of piping systems is variable as the whole weight of the vertical piping system is resting on spring type supports, which in turn, are supported from vertical vessel cleats. These supports are provided to take care of relative displacements between vessel and vertical piping systems. Piping configuration cannot be modified considering large bore piping and requirement of huge structural supports. The existing supports also cannot be modified as they are connected to pressure vessel and will impact its design.
In this scenario of multiple limitations, the indispensable flow induced vibrations of piping can only be minimized by damping the effect of flow-induced excitation with dampers. The dampers have elastic-viscous material in its main restraining body which can absorb the piping vibrations. The damper vendor performed the stress analysis, considering the effect of the damper in the whole piping system, and ensured the integrity of piping system.
The challenge of maintaining existing spring supports and achieving required damping of piping vibration was successfully accomplished. Considering large sized piping and requirement of major structural supports in case of modifications, proposed solutions could be treated as cost effective and innovative. Though it was not possible to eliminate the root cause, this alternate innovative solution helped to not only to minimize vibration, but also optimize implementation/shutdown costs. Vibration damper in piping systems is unique to piping installations.
Leng, Dingxin (Ocean University of China) | Xu, Kai (Ocean University of China) | Liu, Guijie (Ocean University of China) | Xie, Yingchun (Ocean University of China) | Tian, Xiaojie (Ocean University of China)
The present paper focus on the effectiveness performance of a MRE damper for vibration control of offshore platform under seismic loadings. MRE materials are fabricated, and a MRE damper in mixing coupling mode is designed. Testing and dynamic modeling of the proposed MRE damper is conducted. Finite element mode of offshore platform with MRE damper is established. The results demonstrated that, by applying proposed MRE damper, the dynamic responses (displacement, acceleration and local stress) of offshore platform under seismic loadings are greatly reduced, which presents MRE damper is an effective semi-active vibration control devices for offshore platform.
For exploration and production of oil and gas, the offshore structure industry has been flourishing since early 1940s (Mao, Zhong, Zhang and Chu,2015). One of the most typical offshore platforms are fixed steel jacket platforms located in water depth from a few meters to more than 300 meters (Ou, Long, Li and Xiao,2007). Offshore platforms should suffer in ocean environment, such as the dynamic loadings including ocean wind, wave, current, earthquake and ice (in high latitude region) (Raheem,2016). Among these ocean environmental loadings, in active fault zone, seismic loading is one of the greatest factors to the fatigue damage of offshore platforms and has a significant role on the operation safety of the offshore platforms (Wu, Shi, Wang, Guan, Ou,2010; Park, Koo, Kawano,2011). To ensure safety, serviceability and make people comfortable on the platform, it should be indispensable to reduce the overall responses (e.g. displacement, velocity and acceleration) of offshore platforms subjected to the seismic loadings.
In last decades, a series of studies have been conducted on vibration control of jacket offshore platforms under earthquake loadings. Jin, Li, Sun, Zhou, Guan (2007) conducted an experimental and numerical study on tuned liquid dampers for controlling earthquake responses of offshore platform; it was found that the ratio of the fundamental sloshing frequency of liquid to the natural frequency of platform was the key factor to control earthquake responses. However, the problem of tuned liquid dampers for vibration control of offshore platform is that the damping ratio is limited. That is, tuned liquid dampers may be very suitable for structures with low damping; however, for offshore platform, the damping ratio reach as high as 4%-5%, the practical control effectiveness of tuned liquid dampers could be much lower than that in the research work. Wu, Shi, Wang, Guan, Ou (2010) utilized rubber bearings and MR damper to reduce the vibration of offshore platform caused by earthquake; Kalman filter was used to estimate the system state and the dynamic responses of structures. The results showed that earthquake-induced vibrations can be effectively by the passive and semi-active damping systems. Wu, Zhao, Zheng, Wa (2016) studied high response performance of a tuned-mass damper for vibration suppression of offshore platform under earthquake loads; and the tuned-mass damper control scheme was compared with tuned-liquid damper and active mass damper control scheme.
Hodge, Caitlin Worden (Industrial Doctoral Centre for Offshore Renewable Energy (IDCORE) & Zyba) | Bateman, Will (Industrial Doctoral Centre for Offshore Renewable Energy (IDCORE) & Zyba) | Yuan, Zhiming (University of Exeter) | Thies, Philipp R. (University of Strathclyde) | Bruce, Tom (University of Edinburgh)
The mechanical motion of a wave energy converter (WEC) is converted by the power take-off (PTO) system into electricity, but these two systems are not independent, as they have been treated in WEC modelling. Treating them as such leads to inaccuracies in prediction of power output and reliability, and can erode confidence in numerical modelling tools. This paper presents a methodology for the two-way coupling of high fidelity modelling of WEC hydrodynamics with a more accurate representation of the PTO and investigates the impact of using simplified PTO models. Simplified models represent the full PTO with a single parameter which is in itself difficult to choose and may require a number of iterations. These different methods were used to assess the behaviour of the CCell WEC in a regular wave, with the calculations for mean power varying considerably in different wave conditions and the range of motion consistently under predicted by the simpler models. The coupled model increased the computational requirement for the simulation, however it provided the developer a better understanding of the impact on and utilisation of different hydraulic components.
WECs are designed to convert the energy from waves into a mechanical motion which is then converted into electrical power through the power take-off (PTO) system. Oscillating wave surge converters, such as the CCell device, Fig. 1, have generally evolved as buoyant bottom-hinged flap WECs, which pitch back and forth from sea to shore under the influence of the horizontal motion of waves (Cameron, L, 2010). This pitching motion is transformed into useful energy usually through a hydraulic piston, which draws on the robustness and high power density that hydraulic circuits offer. Similar systems have also commonly been used in heaving buoys (Cargo, C, 2012).
Numerical modelling has become a valuable toolbox for WEC developers as it allows rapid modifications to a WEC design, without the additional manufacture and testing costs, or scaling issues. It can build up a picture of the Mean Annual Energy Production (MAEP) and the load estimates on the device which can aid design decisions and inform the required O&M procedures. However, numerical simulations can be slow to compute without adequate computer power and some simplifications must be introduced for efficiency, especially regarding the modelling of the power take-off system and/or the hydrodynamics.
In case of conventional shallow-draft semisubmersibles, unacceptably large riser stroke was the restricting factor for dry-tree-riser-system development. Many developments to address this issue have focused on using larger draft and size with extra heave-damping plates, which results in a huge cost increase. The objective of this paper is to investigate an alternative solution by improving riser systems through the implementation of a magneto-rheological damper (MR Damper) so that it can be used with moderate-size/draft semisubmersibles. In this regard, both linear/viscous and MR-damper riser systems and connections are numerically modeled so that they can couple with hull-mooring time-domain simulations. The simulation results show that the moderate-size semisubmersible with MR damper system can be used with conventional dry-tree pneumatic tensioners by effectively reducing stroke-distance even in the most severe storm environments. Furthermore, the damping level of the MR damper can be controlled to best fit target cases by changing input electric currents. The reduction in stroke allows smaller topside deck spacing, which in turn leads to smaller deck and hull. As the penalty of reducing riser stroke by MR damper, the force on the riser system can significantly be increased.
Tuned liquid dampers (TLD) are passive vibration absorbers of lightly damped structures such as airport towers, chimneys, skyscrapers, long-span bridges, overhead power lines, tall buildings, masts and offshore platforms. TLDs dissipate the structural vibration energy with the help of sloshing waves, hydraulic jumps, wave breaking and wave run-up in the tank walls. In shallow water condition, the frequency and damping of TLD are amplitude dependent; a “hardening- spring type” nonlinear behavior of water sloshing is documented in many literatures. The present study has accounted this hardening behavior in the numerical model. In this paper, the empirical relation, between the jump frequency ratio of TLD and the non-dimensional amplitude of external excitation, proposed by Yu et al (1999) is used.
TLD is a liquid tank and acts as a passive vibration control-system for lightly damped structures subjected to dynamic loads. The idea of TLD is to dissipate the structure's vibrational energy in terms of enhanced liquid motion. It is usually placed on the top of a structure and is preferred due to its easy installation, maintenance and low-cost. The main phenomenon inside the TLD is sloshing which is liquid motion in a partially filled container subjected to dynamic loads. The liquid's oscillation frequency (Tank frequency) is tuned to the natural frequency of the structure so that sloshing should occur in resonance. TLD dissipates the structure's vibrational energy in terms of sloshing waves, hydraulic jumps, wave breaking, wave- impact on the walls and wave run-up in the tank walls. Based on the relative water depth, TLD can be classified into the deep water TLD where baffles and screens are needed to enhance the damping effects; and the shallow water TLD which dissipates energy mainly due to wave-breaking, hydraulic jump and slamming. All modes of sloshing can be modeled by a set of mass- spring-dashpot systems based on the following principals (Ibrahim, Pilipchuk and Ikeda, 2001):
Patil, Devendra (Smart Materials and Structures Laboratory, University of Houston) | Kalia, Akshay (OneSubsea, a Schlumberger Company) | Zhu, Junxiao (Smart Materials and Structures Laboratory, University of Houston) | Ho, Siu-Chun Michael (Smart Materials and Structures Laboratory, University of Houston) | Zhang, Peng (Smart Materials and Structures Laboratory, University of Houston) | Lara, Marcus (OneSubsea, a Schlumberger Company) | Song, Gangbing (Smart Materials and Structures Laboratory, University of Houston)
AbstractLow hydrocarobon prices have raised concerns over the viability of offshore field development and maintenance over next several years. These oil and gas prices have called for engineering efforts to innovate new technologies to reduce the operational costs and improve the life span of the subsea exploration and production (E&P) systems in inhospitable environments like deep water. Subsea pipeline and jumpers are among these subsea E&P systems and it is crucial for operators to have these systems function in smarter and more efficient way, to adapt the inhospitable environment while generating profits. Due to their geometry and location, these pipelines are typically susceptible to vibrations induced by multiple factors, such as flow-induced vibrations (FIV) and vortex-induced vibrations (VIV). FIV and VIV can cause excessive stress on pipeline joints, thus limiting the operational lifespan of pipelines, specifically jumpers and risers. Every year, oil and gas operators spend significant amounts of money analyzing the cause and effect of these vibrations on the fatigue life of jumpers and pipelines, and installing traditional vibration mitigation devices like strakes and shrouds that have proven to be only partially effective. In most situations, these devices fail to suppress the vibrations and force operators to choke the flow from the well for safety, resulting in lost revenue.This paper introduces the pounding tuned mass damper (PTMD) - a novel device developed in a joint collaboration between OneSubsea and the University of Houston to absorb and dissipate the undesired vibrations in subsea pipelines and jumpers. The PTMD is based on principles of both the tuned mass damper and the impact damper. The tuned mass in the PTMD absorbs the kinetic energy of the structure and dissipates the absorbed energy through collisions on viscoelastic material. During development, detailed numerical analysis and experimentation were performed to study the effectiveness of the PTMD on the jumper. In the experiment, a full size M-shaped jumper was tested in both air and shallow water conditions for VIV at NASA's Natural Buoyancy Laboratory (NBL). The experiment also examined the robustness of PTMD for different frequency VIVs. Experimental results showed that the PTMD effectively reduced the in-plane and out-plane vibration of the jumper up to 90%. The observed reduction in vibration amplitude can reduce fatigue damage to jumpers, thus enabling operators to optimize spending on vibration mitigation devices, minimize lost revenues, improve system lifespan and availability, and enhance operational flexibility. Reduction in stress also means improved reliability and reduction in costs associated with inspection, maintenance, and repair of subsea jumpers and pipelines. These long-term financial benefits and ability to be installed on existing and new jumpers (pipelines) makes the PTMD a desired solution for vibration suppression in deep water environments.
Patil, Devendra (University of Houston) | Kalia, Akshay (OneSubsea, a Schlumberger Company) | Ho, Siu-Chun Michael (University of Houston) | Zhang, Peng (University of Houston) | Lara, Marcus (OneSubsea, a Schlumberger Company) | Song, Gangbing (University of Houston)
This paper discusses the pounding tuned mass damper (PTMD) - a novel device developed in a joint collaboration between OneSubsea, a Schlumberger Company and the University of Houston to absorb and dissipate the undesired vibrations generated due to VIV and FIV in subsea pipeline and jumpers. The PTMD is based on principles of both the tuned mass damper (TMD) and the impact damper. The tuned mass in the PTMD absorbs the kinetic energy of the structure and dissipates the absorbed energy through collisions on viscoelastic material. During development, detailed numerical analysis and experimentation were performed to study the effectiveness of the PTMD on the jumper. In the experiment, a full size M-shaped jumper was tested in both air and shallow water conditions for VIV at NASA’s Natural Buoyancy Laboratory (NBL). The experiment also examined the robustness of PTMD for different frequency VIVs. Experimental results showed that the PTMD effectively reduced the in-plane and out-plane vibration of the jumper up to 90%. The observed reduction in vibration amplitude can reduce fatigue damage to jumpers, thus enabling oil and gas operators to optimize spending on vibration mitigation devices, minimize lost revenues, improve system lifespan and availability, and enhance operational flexibility. Reduction in stress of these pipelines also means improved reliability and reduction in costs associated with inspection, maintenance, and repair of subsea jumpers and pipelines. These long-term financial benefits and ability to be installed on existing and new jumpers (pipelines) makes the PTMD a desired solution for vibration suppression in deep water environments.
To meet the increasing energy demand of the world, the oil and gas industry has pushed hydrocarbon exploration to harsher environments like deep water. These environments present new set of challenges for the safe operation and maintenance of exploration and production (E&P) systems in the oil and gas industry.
Tsouroukdissian, A. Rodriguez (GE Renewable Energy) | Park, S. (University of Massachusetts) | Pourazarm, P. (University of Massachusetts) | Cava, W. La (University of Massachusetts) | Lackner, M. (University of Massachusetts) | Lee, S. (Glosten Associates) | Cross-Whiter, J. (Glosten Associates)
The intention of this paper is to present the results of a novel smart semi-active tuned mass damper (SA-TMD), which mitigates unwanted loads for both fixed-bottom and floating offshore wind systems. The paper will focus on the most challenging water depths for both fixed-bottom and floating systems. A close to 38m Monopile and 55m Tension Leg Platform (TLP) will be considered. A technical development and trade-off analysis will be presented comparing the new system with existing passive non-linear TMD (N-TMD) technology and semi-active. The SA-TMD works passively and activates itself with low power source under unwanted dynamic loading in less than 60msec. It is composed of both variable stiffness and damping elements coupled to a central pendulum mass. The analysis has been done numerically in both FAST (NREL) and Orcaflex (Orcina), and integrated in the Wind Turbine system employing CAD/CAE. The results of this work will pave the way for experimental testing to complete the technology qualification process. The load reductions under extreme and fatigue cases reach up significant levels at tower base, consequently reducing LCOE for fixed-bottom to floating wind solutions. The nacelle acceleration is reduced substantially under severe random wind and sea states, reducing the risks of failure of electromechanical components and blades at the rotor nacelle assembly. The SA-TMD system is a new technology that has not been applied previously in wind solutions. Structural damping devices aim to increase offshore wind turbine system robustness and reliability, which eases multiple substructures installations and global stability. The paper is part of the US Department of Energy grant # DE-EE0005494.
Lee, Dong Yeop (Korea Research Institute of Ships & Ocean Engineering (KRISO)) | Nam, Bo Woo (Korea Research Institute of Ships & Ocean Engineering (KRISO)) | Jung, Dong Ho (Korea Research Institute of Ships & Ocean Engineering (KRISO)) | Hong, Sa Young (Korea Research Institute of Ships & Ocean Engineering (KRISO)) | Kim, Hyeon-ju (Korea Research Institute of Ships & Ocean Engineering (KRISO))
In this study, the motion characteristics of Ocean Thermal Energy Conversion (OTEC) platforms are investigated by experimental and numerical methods. A series of model tests for octagon-shaped Sevan OTEC platforms were carried out in Ocean Engineering Basin of KRISO(68.8m×37m×4.5m, Experimental area: 56m×28m×3.2m). Two experimental models such as the OTEC platforms with and without damper were considered to check the performance of the designed damper. The motion performances of OTEC platforms are evaluated under regular and irregular wave conditions. It is found that the resonances of heave and pitch are shifted to the longer period due to the effect of damper. In addition, it is observed that the peak motion amplitude is significantly reduced. The motion responses of the OTEC platforms from experiments are compared with numerical results by using HOBEM(Higher-Order Boundary Element Method). The agreement between experiments and calculations is fairly good.