Electro-Hydraulic Control Systems for Subsea Applications

Communication underwater is severely limited when compared to communications in air because water is essentially opaque to electromagnetic radiation except in the visible band. Even in the visible band, light penetrates only a few hundred meters in the clearest waters and much less in waters made turbid by suspended sediment or high concentrations of marine life. Consequently, acoustic techniques have been developed for underwater communication systems and now represent a relatively mature and robust technology. Acoustic systems are capable of long range communication, but offer limited data rates and significant latency (due to the speed of sound in water). We are developing an optical communication system that complements and integrates with existing acoustic systems resulting in an underwater communications capability offering high data rates and low latency when within optical range combined with long range and robustness of acoustics when outside of optical range. Amongst a wide array of applications, this combination of capabilities will make it possible to operate self-powered ROVs from support vessels or platforms without requiring a physical connection to the ROV. Such a capability will help simplify operations and potentially reduce costs through the use of less capable surface vessels. New deployment strategies may offer game-changing opportunities within all areas of undersea activities. For example, rapid event response will be enhanced and repair and maintenance of the emerging ocean observatory infrastructure will become more cost effective. Such through-water communications will likewise enable exchange of large data files from fixed sensors using AUVs (or ROVs) as data mules, shuttling real-time video from untethered vehicles for inspection, identification, and other related operations. Interconnectivity for dense arrays of underwater sensors without the need for expensive and difficult to install undersea cables is also possible. An unmanned battery operated vehicle, dedicated to a subsea node, that can be wirelessly operated though a combination of acoustic and optical communications, will be an important asset for both scientific exploration and commercial applications. We have demonstrated robust multi-point, low power omnidirectional optical communications over ranges of 100 meters at data rates up to 10 mega bits per second using a few tens of Watts of battery power with small, inexpensive transmitters and receivers. During the next few years, we will be exploring applications of this new technology directly in support of ongoing science and engineering programs. High-speed underwater optical communication is an enabling technology that has many potential applications in a range of environments from the deep sea to coastal waters. This development effort will enhance infrastructure for scientific research and commercial use by providing technology to efficiently communicate between surface vessels, underwater vehicles and seafloor infrastructure.

This paper will describe the work done by KOP in the use of open standard systems to provide the control system backbone for the retrieval of large amounts of data from subsea control systems. The use of the OPC and TCP/IP standards allows the easy connection of almost any application to the subsea control system. Introduction The current generations of subsea control systems tend to be closed systems. These systems are constrained by the difficulties of connecting in other systems such as downhole systems or platform control systems. Vital areas of the system are implemented using proprietary protocols and methods that are poorly defined and entirely non-standard within the subsea community. This means that during the implementation of a system, integration of various manufacturers' equipment leads to a large number of well identified problems. It also leads to problems when additional functionality needs to be added to a system following its commissioning. It is becoming clear that, in future, there will need to be an increase in the amount of data that is retrieved from a subsea control system. The arrival of intelligent wells and the need for more information from reservoirs will have a large affect on the facilities that will need to be provided by any control and monitoring system. In the design and building of any new control and monitoring systems, open architecture standards are vital to enable inter-connectivity between the subsea equipment and other systems. Open systems can be considered to be fundamental standards and technologies used in the general computing market. These open standards define how different systems interconnect and how the data should be transferred between systems. The standards have been used for many years within the automation and control industries but less so within a subsea control and monitoring system environment. Theory and Definitions The use of interface standards will allow applications to connect to the subsea control system with ease and data to be passed around the wider system and to other applications in a much more efficient way. When the use of fibre optic technology or faster copper communications (increasing the speed of the line), exception based data retrieval (increasing the efficiency of the line) and the overall modularization of the system (increasing the flexibility of the system) are combined with the open standards, a control and monitoring system that can respond to future needs is produced. The ideas that have driven this work are to implement technology that has been used successfully in other areas and to apply this to the subsea field. The technologies that are used should advance the connectivity and flexibility of the system such that benefits can be seen in the time to configure a user system, the simplification of the interfaces to other systems and the extension of functionality beyond that of current systems. This work has principally investigated 2 open standard technologies.TCP/IP (The Transmission Control Protocol / Internet Protocol) is the protocol suite that drives the Internet.

Presented in this paper is a model-based approach for leakage detection and identification in subsea blowout preventer (BOP) hydraulic control system. A physics-based model is implemented to quantify the overall leak rate of BOP control fluid from surface hydraulic power unit (HPU) to subsea BOP operator. The model input is the measured pressure at the surface main accumulator stack, and the model parameters are accumulator stack characteristics including precharge pressure and total fluid volume. To isolate the leak path in the BOP control system, a model-based leak indicator is derived for each of the control pod main rail pressure regulators. The performance and robustness of the proposed approach is investigated by conducting a what-if analysis using a virtual BOP model built in a simulation environment. The fluid leak monitoring algorithm is applied to field data collected from several deepwater drilling rigs. The results show that the proposed methodology is able to detect and monitor control fluid leak within the BOP control system.

The primary objective of protective deployment systems is to safely deploy, position, and land subsea equipment while preserving personnel safety and protecting investments. There are several protective design concepts available to meet today's deepwater operating needs. Future considerations are being examined to meet the demands of new challenges. This paper primarily addresses the deployment and recovery of work class remotely operated vehicle (ROV) systems and designs that can be applied to a wide variety of applications including the installation of subsea equipment. Introduction As subsea field development expands to include a wider range of applications in increasingly harsh environments, surface deployment systems continuously evolve to overcome the demanding design requirements. Deployment system configurations range from stationary to overboarding with installations being permanently built-in, modular with semipermanent components, or entirely mobile. Protective deployment systems are used extensively in the launch and recovery of ROV's. Other applications include tools, trees, connectors, pipeline jumpers, wirelines, manifolds, umbilical termination assemblies, workover equipment, and other subsea hardware. By incorporating protective methodology in current designs for deploying subsea equipment, financial liability is reduced by minimizing the risk of equipment damage while increasing the window of environmental limits. The end results are protective deployment systems used for a wider range of applications with improved performance, less down time, and most importantly, fewer accidents. There are several variables in the offshore environment that present challenges. These variables impose limitations on the system's overall capabilities and performance. Variables with the largest impact are environmental conditions in which the installation will be operating. Mechanical designs and operational procedures provide the best solutions to the challenges of the ocean environment. These methods incorporate ways to safely control deployed loads due to varying sea states, high winds, high currents, and increasing water depths. Dynamic loads induced by the vessel's motion are another design challenge. Dynamic loads become proportionally more significant on installations using smaller vessels such as multi-service vessels. By using protective deployment systems, smaller vessels can provide more costeffective operations by reducing or eliminating the need for larger, more expensive surface vessels. Protective deployment systems find applications on various types of vessels, including ships, semi-submersibles, barges, spar platforms, and TLPs, each of which has its own set of requirements. Their configurations are limited by a vessel's deck load capacity, the amount of space available for an installation, and the dynamic motions for a particular sea state. Advantages on larger vessels allow deployment operations to move to the less congested perimeter locations and free up prime operations area, which is especially important on drilling units. Maintaining personnel safety when operating in harsh environments is the most critical factor considered for these systems. Designs must be constructed to protect life and equipment, and procedures for operation must be properly outlined to foresee/prevent any unsafe operating conditions.

In this paper, we propose a novel polar code construction scheme, suitable for the underwater acoustic (UWA) multi-user communication system using orthogonal frequency division multiplexing (OFDM). We use the polar codes because the code rate of a polar code can be arbitrarily designed. Moreover, the polar codes can also be used to create a nested code structure, divided into several subsets (codebook). We exploit this feature of the polar codes and place the information bits in the codebook to avoid superimposition of all the users. This helps to eliminate the influence of the power allocation coefficient and make full use of the power of the transducer at the transmitted node. Furthermore, the proposed scheme maximizes the utilization efficiency of the OFDM subcarrier resource for each user by avoiding null pilot tones that are usually required for channel equalization in the traditional schemes. The proposed scheme also does not depend on the channel state information (CSI) as prior information as each user can decode their own data independently by using their own codebook without successive interference cancellation (SIC). The simulation and tank experiment results demonstrate that the proposed scheme can significantly guarantee the reliability of all the users, and reduces the complexity of the receiver, thus making it most suitable for the downlink UWA multi-user communication systems.

Widely available speakers and microphones in electronic devices motivate the use of generic audio hardware to establish acoustic communication links. Acoustic communication with generic hardware requires software modems for data modulation and demodulation. The resulting acoustic communications system paves the way for cheap and easily deployable underwater acoustic sensor networks through the use of audio hardware built in to the sensor modules. In this paper, we explore the potential of the acoustic communication system for both aerial and underwater environments. Our experiments profile both media with generic microphones and speakers. An initial test of the channel's underwater data communication capability has revealed that the channel can transfer data at 12bps and 24bps, with respective error rates of 10% and 20%, up to a distance of 10m.

Animal acoustic communication systems can be built upon co-opted structures that become specialized for sound production or morphological novelties. The ghost crab, Ocypode quadrata, evolved a novel stridulation apparatus on the claws that is used during agonistic interactions, but they also produce a rasping sound without their claw apparatus. We investigated the nature of these sounds and show that O. quadrata adopted a unique and redundant mode of sound production by co-opting the gastric mill (grinding teeth of the foregut). Acoustic characteristics of the sound are consistent with stridulation and are produced by both male and female crabs during aggressive interactions. Laser Doppler vibrometry localized the source of maximum vibration to the gastric region and fluoroscopy showed movement of the gastric mill that coincided with stridulation. The lateral teeth of the gastric mill possess a series of comb-like structures that rub against the median tooth to produce stridulation with dominant frequencies below 2 kHz. This previously undescribed gastric stridulation can be modulated and provide a means of assessment during aggressive interactions, similar to the use of the claw stridulation apparatus. This functional redundancy of stridulation in crabs offers unique insights into the mechanisms of evolution of acoustic communication systems.

Underwater acoustic communications are required for controlling and networking a variety of underwater or sea surface objects. Due to the unique characteristics of the underwater acoustic channel, e.g., complicated multipath propagation, selective frequency fading, extreme Doppler effect and heavy ambient noise, FH-MFSK techniques play a vital role in robust underwater acoustic communication, especially in shallow water. However, based on detecting the frequency of the receiving signals, the demodulation scheme for FH-MFSK may be sensitive to the frequency shifting caused by underwater Doppler shifts. This paper focuses on how to design the frequency demodulation scheme and to improve the performance of underwater FH-MFSK acoustic communication system. By using an original Double-Line Interpolation algorithm with Hanning window, we propose a demodulation scheme to enhance the tolerance of the Doppler shift and improve the detection rate. Simulations and demodulation performance were tested. Experimental results show a promising future for FH-MFSK demodulation in underwater acoustic communication system.

Standard bolted flanges are the most commonly used and cost effective method for connecting pipelines both on shore and offshore in conventional water depth. This paper will address the advantages bolted flanges can offer in deep water pipelines where expansion of pipes may be a critical issue. A field proven system, which can be used to remotely connect bolted flanges subsea, will be presented. Lessons learned from the remote connection of over 100 flanges in deep water operations in West Africa will be presented. This has included disconnection and reconnection operations, as well as the remote tie-in of deep water flowlines in both horizontal and vertical orientations. Other applications for bolted flanges, such as the repair of deep water pipelines, will be discussed together with ways in which several pipeline operators can benefit simultaneously from the advantages offered by flanges. Introduction The past 15 years has seen a fundamental change in subsea construction technology, from being a diver dominated activity to the remote systems used for the construction of today's deep water field developments. The need to work in water depths beyond the capability of divers has driven this change to remote technology leading to the development of reliable Remotely Operated Vehicles (ROV) and a collectionof tools capable of performing a wide range of tasks. The remote connection of flowlines and pipelines in particular has been the subject of significant development activity over this period, resulting in the development of a number of proprietyconnectors and connection systems /1/. The majority of these connection systems are based upon mechanical connectors, which have been developed specifically for the remote connection of pipelines; many based upon connectors used for drilling applications. Consequently the connectors andresulting tie-in spools can be relatively large and complex (Figure 1). Figure 1 : Tie-In Spool with Remote Mechanical Connectors (available in full paper) For pipeline connections installed by divers the use of standard bolted flanges became and still are the connector of choice both from a reliability and an economic point of view. As a result, back in 1996, the challenge of enabling the use of bolted flanges for deep water pipeline connections was taken up by the Acergy engineering team. The resulting connection and alignment system known as MATIS (Modular Advanced Tie-In System) was first used on a deep water project in 2000 for the flowline and riser connections at the Girassol development offshore Angola /2/. Since then over 100 flangeshave been successfully connected in deep water. The use of standard bolted flanges for the connection of deep water pipelines may provide some significant advantages over the mechanical connectors more commonly used in deep water today, these include :-Bolted flanges are field proven and have been extensively used in subsea applications throughout the offshore industry for high pressure gas/oil pipeline for many yearsFlange material and design can be easily customized to fit the fluid and flow characteristics (CRA, HP/HT, etc.)Bolted flanges offer the most tolerant connection with regards to stress in the system and long term reliability. In addition they are least subject to damage in case of future disconnection and reconnection.

In this paper we describe the architecture and the performances of a hybrid modular acquisition and control system prototype for environmental monitoring and geophysics. The system, an improvement of a VME-UDP/IP based system we developed for interferometric detectors of gravitational waves, is based on a dual-channel 18-bit low noise ADC, a 16-bit DAC module at 1MHz, and a 20-bit slower ADC necessary for the acquisition of an external calibration signal. The module can be configured as stand-alone or mounted on a motherboard as mezzanine in parallel with other modules. Both the modules and the motherboard can send/receive the configuration and the acquired/correction data for control through a standard EPP parallel port to a standard PC, where the real-time computation is performed. Experimental tests have demonstrated that the distributed control systems implemented with this architecture exihibit a delay time of less than 25 μs on a single channel, that is a sustained sampling frequency of more than 40kHz. The system is now under extensive test in two different experiments: the remote control and data acquisition of a set of seismometers, velocimeters and accelerometers to simulate a geophysics networks of sensors and the remote control of the end mirrors of a suspended Michelson interferometer through electrostatic actuators for interferometric detectors of gravitational waves.

The threat of riser gas in deepwater drilling operations is real. Studies show that gas kicks unintentionally entrained in oil-based mud in deepwater are unlikely to break out of solution until they are above the subsea blowout preventers (BOPs). The rig diverter is conventionally used to vent riser gas with minimal control and considerable risk and environmental impact involved. Reactive riser gas systems provide a riser gas handling (RGH) joint that is composed of a retrofitted annular BOP and a flow spool with hoses installed on top of the rig marine riser. A proactive, alternative approach to riser gas handling, called riser gas risk mitigation, is proposed by using managed pressure drilling (MPD) equipment. MPD involves the use of a rotating control device (RCD) to create a closed and pressurisable drilling system where flow out of the well is diverted to an automated MPD choke manifold with a high-resolution mass flow meter that increases the sensitivity and reaction time of the system to kicks, losses and other unwanted drilling events. Experiments and field deployments have shown that the deepwater MPD system can detect a gas influx before it dissolves in oil-based mud, allowing for management of the same using conventional well control methods. Since the MPD system has already closed the well in, automatic diversion and control of gas in the riser is also possible, if required. This paper presents experience gained from deepwater MPD operations in the Asia-Pacific to illustrate this, and possible deployment options in Australia are discussed.

Underwater control applications, such as control of Autonomous Underwater Vehicles (AUV)s, have recently gained significant interest, and there is a growing demand for high-speed wireless communication between AUVs and base station. Acoustic communication provides low data rates and high propagation delays, both of which are not suitable for employing high control gains for the navigation of AUVs. On the other hand, Radio Frequency (RF) communication provides high data rate, but it is constrained by high attenuation due to high conductivity and permittivity of water resulting in a short working range. In this work, we propose an underwater networked control system with acoustic and RF hybrid communication, where an acoustic link is employed for long range communication and RF link is applied in close range. Our performance results indicate that the acoustic and RF hybrid communication system takes up to 38.5% less time to dock, up to 91% smaller steady state error and spends up to 39% lower communication energy as compared to the acoustic only system at the expense of up to 22.35% higher motive energy.

With the evolution of modern technology wireless sensor nodes are finding a lot of applications in day to day life starting from smart home system to military surveillance. The primary building block of a wireless sensor network is a spatially distributed set of autonomous sensor nodes or motes. In order to design a wireless sensor network it is necessary to understand the structure and working of a sensor node. The sensor nodes can be considered as tiny battery powered computers that consists of a computing subsystem, communication subsystem, sensor subsystem, power subsystem. In this paper we review the features of these subsystems so that it is easy for the application developer to quickly understand and select the type of component for building customized sensor node platform. In this paper we have studied the features of different microprocessors and transceivers properties used in sensor nodes. We also study the classifications of sensors based on applications, the relevant sensor parameters, and different storage devices with their properties. This paper can be a ready reference to beginners interested in this field. One more major problem of wireless sensor network application that should be addressed is the limited lifetime of sensor nodes due to energy constraints. We also review how energy harvesting can increase the lifetime of a wireless sensor network and the possible methods that can be implemented for energy harvesting.

In order to conduct in-orbit servicing using space robots, we propose and develop a function distributed reconfigurable arm system for robot satellites. The arm can make a rearrangement between its upper 3DOF part and lower 2DOF part. This reconfigurability makes it possible to perform various in-orbit services by changing its configuration. Technical issues of reconfiguration are including end-effector mechanism, communications subsystem and power subsystem. For extemal sensors to obtain relative position and attitude information between satellites in order to perform reconfiguration autonomously, we examine CCD camera and PSD. Outline of the arm system and a fundamental reconfiguration experiment are shown in the paper.

Reliability analysis of subsea blowout preventer control systems subjected to multiple error shocks