Floating Storage And Regasification Unit Research Articles

Performance Analysis of a Renewable‐Powered Multi‐Gas Floating Storage and Regasification Facility for Ammonia Vessels With Reconversion to Hydrogen

ABSTRACTNatural gas and renewable energy carriers play critical roles in the energy supply chain due to rising energy consumption demands and a significant shift toward cleaner energy. However, the requirement to liquefy and regasify liquefied natural gas (LNG) and renewable energy carriers for transportation makes the entire process expensive and challenging. Hence, a floating storage and regasification unit (FSRU) plant provides a solution to the aforementioned problems with the additional benefit of being more affordable, time‐efficient, and having less land footprint requirement than the conventional onshore facility. The proposed integrated FSRU in this study, is powered by renewable energy, including solar and ocean thermal energy. The subsystems of integrated FSRU consist of parabolic dish collectors (PDC), Rankine cycle, organic Rankine cycle (ORC), multi‐stage flashing (MSF) desalination unit, decomposition, reliquefication, and regasification plants, which provide valuable commodities such as freshwater, electricity, hydrogen, and heating. It can also cater to standard multi‐gas harboring vessels for storage and regasification of sustainable energy carriers. The study assesses the performance of the proposed system thermodynamically by analyzing mass, energy, entropy, and exergy balance equations using the engineering equation solver (EES) software. Furthermore, parametric studies were conducted to understand the interlinkage among various variables. The analytical results show that the proposed system is able to produce 1.82 MW of electricity, 2056 kg/day of fresh water, and 338.3 kg/day of hydrogen, achieving an overall system energy efficiency of 32.7% and exergy efficiency of 79.3%. This approach aims to foster energy diversification, enhance energy security, and support the transition toward sustainable energy systems, as well as further the advancement of maritime transport systems.

Risk assessment of emergency operations of floating storage and regasification unit

As the receiving terminal of liquefied natural gas (LNG), the efficient emergency response of the floating storage and regasification unit (FSRU) is crucial to ensure the safety of LNG transportation at sea. However, few existing literature study the risk issues of FSRUs during emergency operations. In order to improve the emergency response capability of FSRU, this study proposes an innovative assessment method to identify hazards, quantify and rank the risks associated with emergency response and disposal operations of FSRU accidents. Firstly, a comprehensive index hierarchy system applicable to human, equipment, environment, and management aspects of emergency response and disposal operations of FSRU accident is established through an extensive literature review, analysis of accident reports, and expert judgments. Secondly, based on the concept of Intuitionistic Fuzzy Numbers, the Intuitionistic Fuzzy Hybrid Weighted Euclidean Distance (IFHWED) operator is used to enhance the conventional FMEA approach. This method considers the varying levels of expert confidence and integrates subjective and objective weights of risk influential factors (RIFs), and the efficacy is validated through sensitivity analysis. Finally, a comprehensive evaluation model employing the Analytic Hierarchy Process (AHP) and fuzzy comprehensive evaluation algorithms is used to aggregate the risk values of RIFs. The findings of this study offer decision-makers insights into risks during emergency operation, provide valuable guiding strategies for FSRU accident management, and improve the capability for emergencies at sea.

Aligning stars: making LNG imports happen in Australia

We present the inputs and results of a discounted cash flow model which details the requirements for an import terminal to eventualise. The key requirement is high certainty cash flows from foundation users. This can be made possible through capacity booking which can be potentially underwritten by governments to ensure security of supply during peak winter months. The out-chartering of the floating storage and regasification unit (FSRU) to serve as a liquefied natural gas (LNG) carrier during the peak northern winter will provide an additional revenue source. We also analyse the legacy supply decline and various price setting mechanisms for the southern states which will soon turn net importers. We will describe the status of the four projects in the pipeline and identify milestones. We conclude that an import terminal provides an alternative proposition in the southern states considering the highly seasonal demand profile, the decline of Gippsland Basin production, and the relative inflexibility of coal seam gas. Further, FSRUs can be redeployed to other regions, which reduces stranded asset risk from pipeline expansions, given Australia’s net zero targets.

Conceptual design of floating storage and regasification unit (FSRU) for Eastern Part Indonesia

Liquefied Natural Gas (LNG) can be used as an alternative fuel with environmentally friendly solutions. In general, the domestic distribution of natural gas in LNG is more cost-effective than transporting gas through underwater pipelines considering Indonesia as archipelagic country. According to Indonesia’s Minister of Energy and Mineral Resources Regulation Number 13 of 2020, the government supports converting 52 power plants to LNG. However, the current challenge in the LNG industry is the lack of supporting facilities. Storage and regasification facilities are among the infrastructure that requires optimization. Floating Storage and Regasification Unit (FSRU) are viable options for energy distribution that offer opportunities and competitiveness compared to onshore terminals. Small and medium-scale FSRU can serve as an alternative solution due to their relatively fast, flexible, and affordable development process. Therefore, this research will develop a small-medium FSRU design with a capacity of 60 MW − 70 MW in Eastern Indonesia. FSRU design should consist of four segments including location considerations and environmental conditions, powerplants gas requirements, LNG storage tank sizing and LNG regasification process. Calculations for various supporting FSRU components, seakeeping analysis, loading-offloading processes, 3D modelling and the integration of solar panels were discussed. The results obtained include the principal dimension, technical aspects of FSRU design, and the technology for LNG regasification processes used.

A Novel Approach for Assessing the Performance of Offshore Ground Improvement in Floating Storage and Regasification Unit (FSRU) Terminal Construction

A floating storage and regasification unit (FSRU) terminal has been planned to be constructed in Saros Bay (Türkiye). This study presents the ground improvement method using jet grouting to prevent the liquefaction of marine sediments in the project area. An approach for performance assessment of jet column construction is also discussed. The study site has a liquefiable ground level with a thickness changing between 2 m and 8 m. Jet grout columns with an 80 cm diameter were constructed under the sea level, which varied between 4 m and 18 m for ground improvement. The main issue is controlling the quality and performance of these jet columns. Therefore, a practical quality control procedure containing observational, mechanical, and geophysical methods for offshore grouting operations was proposed. The factor of safety values against liquefaction varied between 0.04 and 0.29 for natural conditions, while the minimum factor of safety after jet column constructions was obtained as 1.01. The results of the numerical analyses showed that the constructed terminal has sufficient performance against liquefaction. Consequently, the results of these methods have demonstrated that the jet grout applications performed by following this procedure are a suitable and effective improvement method for offshore soils.

Numerical analysis of local flow heat transfer of supercritical LNG across the pseudophase transition in different airfoil channels

As the core equipment of floating storage and regasification unit (FRSU), the function of liquefied natural gas(LNG)vaporizer is to heat the LNG from -162 °C to normal temperature under supercritical pressure, which is a pseudophase transition process. This paper numerically investigates the local flow and heat transfer of supercritical LNG during the pseudophase transition process of three airfoil channels with different structures and shapes under transcritical temperature condition. The secondary flow generated by the shape and structure of the airfoil has an important influence on the local flow heat transfer performance. Especially in the liquid-like region, the three airfoil fins not only generate mixed disturbance of the velocity vector in the y-direction, but also generate secondary vortices in the z-direction, which can more effectively interfere with the boundary layer and enhance the heat transfer performance. As the temperature increases, the density and the viscosity of the supercritical LNG in the pseudo-critical and gas-like regions decrease, the vortexes formed in the three airfoil fins appear above or below the tail of the airfoil. The research shows that under the selected conditions, Fin-2 has the best hydraulic performance, especially in the gas-like region, and its f-factor can be lower than 0.02. Because Fin-2 changes the curvature of the leading edge and minimizes the impact surface, it is conducive to the rapid discharge of local fluid, thus reducing the flow resistance and generating secondary flow at the tail of the airfoil. Fin-3 has the best heat transfer performance, and its j-factor is 5–10% higher than that of other airfoil fins. This is the tail shape of the airfoil is concave, and the secondary vortices are located in the concave area, which disturbance the boundary layer and improve the heat transfer process.

Risk informed floating storage and re-gasification unit (FSRU) location selection for local natural gas supply

In the present energy market due to high demand of liquefied natural gas (LNG) and the limited availability of land-based LNG import terminals, the use of offshore LNG terminals is destined to increase. Such terminals are referred to as LNG floating storage and re-gasification units (FSRUs). An FSRU terminal is a cost-effective and a time-efficient solution to quickly open up supply to onshore users with minimal environmental impact. This work focuses on the selection from a safety point of view of a possible location for an offshore or nearshore FSRU, given alternative candidate locations. For decision making, the maritime and process safety aspects of the LNG resupply operation have to be considered. This involves the approach of an LNG Carrier (LNGC) to resupply the FSRU. The whole resupply process is divided into three consecutive parts, beginning with the LNGC navigating in the inbound channel, going through its berthing operation, and ending with transfer of the LNG. The safety of the third part, the LNG transfer to the FSRU, could be evaluated by means of a quantitative risk assessment. For the maritime operations this was not possible and evaluation had to rely on expert elicitation. To create a comparison basis of navigating, turning and berthing hazards with the risks of the LNG transfer process, a novel safety utility value (SUV) was defined existing of five ranges. Hazard attributes of navigating and of turning and berthing of the maritime operations were identified/confirmed by simulator runs, their importance was ranked, as well as their safe operating ranges determined with the aid of queries to a large group of experts. Importance ranking was based on pairwise comparison judgment, responses aggregated by means of fuzzy number fits, processed in square matrices. Expert elicitation yielded safety attribute values (SAVs) for the five SUV ranges which were statistically treated. QRA provided potential loss of life (PLL) values, which also were converted into SUV ranges. Based on the importance ranking of the three parts and the SUVs, final results were obtained.

Modelling and Simulation Hydrodynamics Processes in Liquefied Natural Gas Transportation Systems

Global natural gas resources are growing and are increasingly geographically diverse. A Floating Storage and Regasification Unit (FSRU) is one of the most commonly used vessel types in the global ship fleet due to the possibility of storage, reloading to another ship, and regasifying it for re-injection into the natural gas grid. It is important to control system parameters for reliable technological processes such as tank hydrostatic pressure, vapor pressure, LNG density, LNG temperature, and phase changes between liquid and gas states. Additionally, pressure monitoring is important to control during transit in port and bunkering to prevent the pressure in the tanks from exceeding the tank design pressure. In this research study, a comprehensive hydrodynamic model for an LNG storage tank in a real-life regasification terminal (Floating Storage and Regasification Unit, LNG Terminal of Klaipeda City, Lithuania), operating in transportation mode to the regasification unit, was created. For this research, LNG is investigated as a compressible liquid and the speed of sound in LNG is evaluated. A complex mathematical model of the system allows the analysis of high-speed hydrodynamic and dynamic processes at cryogenic temperature (110 K) and evaluates the geometric parameters (tank geometry, electric motors and pumps, pipe geometric parameters, and roughness of internal surfaces) and the characteristics of pumps and electric motors. The complex mathematical model of the system was implemented using Fortran programing language and MATLAB R28a. It determined the parameters (pressure, velocity, liquid level of LNG in the tanks, electric motor angular velocity, torques, hydraulic energy losses, etc.) of the system during its start-up mode (until 5 s). It was found that hydraulic energy losses in all pipes contain 1.7% of the whole system power (the total power of the electric motors is 3132 kW). In case of increasing energy costs, this model could be used to control energy losses during the operation of the FSRU in various technological modes.

An assessment of mooring systems' forces of ships berthed at dolphins

In the current practice of structural design for berth structures, the mooring forces (tension in lines and compression in fenders) are typically determined through simplified linear static analyses, and then magnified by dynamic amplification coefficients. It is known, however, that the mooring's stiffness presents nonlinearities (both physical and geometrical) that may at times become relevant, raising the issue of whether linear analyses are really adequate. Also, the environmental loads induce oscillatory behavior whose peak values may not always be satisfactorily estimated through dynamic amplification coefficients, which are far from being well defined in the technical literature. This work presents an investigation on the forces developed on mooring systems of vessels berthed at dolphins, and the consequences of the current design practice's simplifications. Different hierarchical models are defined (linear static, nonlinear static and linear dynamic in the frequency domain) for a case study of a Floating Storage and Regasification Unit (FSRU) permanently berthed at dolphins at the Barcarena's Liquefied Natural Gas (LNG) terminal in Pará, Brazil. The vessel's displacements and their peak values are determined through stochastic and statistical theories. The corresponding forces on the mooring system are computed and the dynamic amplification coefficients therefrom obtained. A thorough discussion on the results is provided. The methodology presented may be a useful tool to ascertain the dynamic amplification coefficients required in the simplified methodologies from the international standards.

Effect of rolling motion with large radius on flow and heat transfer characteristics of supercritical methane in a mini channel

• Rolling results in the violent fluctuation of flow and heat transfer in supercritical methane. • Additional force along the flow direction is the key to affect the flow and heat transfer. • Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. • Rolling produces greater fluctuation in the near-wall area than that in the inner center area. The offshore floating storage and regasification unit (FSRU) is developing rapidly as a new type of storage and gasification system for liquefied natural gas (LNG), and the heat transfer and system stability of offshore LNG vaporizers are greatly affected by ocean rolling. To reveal the regular pattern and mechanism of supercritical methane heat transfer performance under ocean motion, this research numerically studied the flow and heat transfer characteristics of supercritical methane in a 1 × 1 × 100 mm mini channel under the additional inertial force by large radius rolling. Based on the non-inertial coordinate system, the normal inertial acceleration, radial inertial acceleration and Coriolis inertial acceleration were considered. Moreover, Nusselt number, degree of fluctuation and friction factor were investigated. The ranges of Reynolds number and Nusselt numbers are 15,000 to 45,000 and 35 to 130 respectively. The results show that the Nusselt number and friction factor violently fluctuate under rolling motion, and the fluctuation period is similar to the rolling period. Besides, the fluctuation degree of Nusselt number is greater than that of friction factor, and the largest fluctuation degree of Nusselt number is 27.9%. The effect of the fluctuation increases with the decrease of the rolling period and the increase of the rolling amplitude. Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. In addition, the degree of fluctuation is reduced with the increase of fluid temperature and mass flux. For the effect of rolling, the additional force in the mainstream direction plays a leading role. Besides, the influence of radial force is greater than that of normal force for horizontal flow condition.

Quantitative risk assessment of fire & explosion for regasification process of an LNG-FSRU

As global energy consumption is continuously on the rise, there is an increasing interest in the design of floating liquefied natural gas (LNG) regasification facilities in order to prepare for additional energy demand. In this study, following a process simulation to find operational conditions, a quantitative risk assessment (QRA) was performed for a regasification process of an LNG floating storage and regasification unit (FSRU). The regasification process was designed and simulated considering the required gas processing capability to obtain the thermodynamic states and operation conditions. A QRA was performed with combinations of frequencies and consequences of fire and explosion. The leak frequencies, representative hole sizes, and ignition probabilities for four hole size categories were estimated. Consequence simulation was conducted to assess risk results. The probabilistic safety distance for the flame length was estimated. The final risk consequences were obtained as number of fatalities per year by applying lethality values. The individual risk was found to be in as low as reasonably practicable (ALARP) ron compared to acceptance criteria. An f-N curve for fatality showed that the group risk is also in ALARP ron. The method and results presented in this study will help design LNG-FSRUs and other LNG facilities.

Prediction of dynamic responses of FSRU-LNGC side-by-side mooring system

Floating Storage and Regasification Unit (FSRU) becomes one of the most popular equipment in the industry for providing clean energy because of its technical, economic and environmental features. The interaction between the FSRU and Liquified Natural Gas Carrier (LNGC) under the combined loads from wind, wave and current is quite complex to model. In this paper, a configuration for the offloading operation of the FSRU-LNGC side-by-side mooring system is proposed to predict the motion responses, forces on the cables and fenders of the multi-floating mooring system. The damping lid method is adopted to improve the overestimated hydrodynamic coefficients calculated from conventional potential flow theory in the frequency domain. The dynamic response of the side-by-side mooring system including six degrees of freedom motion, relative motions, cable tensions and fender forces are provided and analyzed. The numerical results are validated using the experimental data. The proposed coupled analysis model and the numerical analysis can properly predict the dynamic response of the multi-floating mooring. The sensitivity analysis of pretension of the connecting cables on the dynamic responses of the two vessels are provided. Moreover, the non-dimensional damping parameters can be acted as a good reference to the dynamic response analysis of similar multi-floating mooring systems.

Numerical investigation on thermal-hydraulic performance of a printed circuit LNG vaporizer

As a new type of micro-channel heat exchanger, printed circuit heat exchanger (PCHE) is widely applied to floating storage and regasification unit (FSRU) as LNG vaporizer for high efficiency and compactness. In this paper, a three-dimensional numerical model of counter-flow printed circuit LNG vaporizer is established, applying supercritical LNG and propane as cold source and heat source respectively. The flow and heat transfer characteristics in semicircular channels, and the effects of channel bending angle on them are studied. The results indicate that the channel bending causes the accelerating core of cold and hot fluids close to the inner wall of the corner, thinning or even destructing the boundary layer, which is conducive to convective heat transfer, although causes greater flow resistance. The larger the channel bending angle, the better the heat transfer and the greater the pressure drop. The criterion ζ=Nu/Nu0/f/f0 is used to evaluate the thermal-hydraulic performance of the printed circuit LNG vaporizer, and it shows that the channel bending angle 15° offers the best comprehensive performance.

Comparative analysis of natural gas imports by pipelines and FSRU terminals

Natural gas is one of the most sought-after trade commodities in the energy market, mainly due to exploitation of cleaner and sustainable energy sources. The most common transportation method for natural gas imports is either through designated pipelines in its gaseous state or carried in its liquefied state as Liquefied Natural Gas (LNG) by specialized tankers. The analysis and comparison of natural gas import by pipelines and FSRU (Floating Storage and Regasification Unit) terminals is presented in this paper. Pipeline import is currently the cheapest and most feasible option, but it requires significant infrastructural investments, which can affect imports in countries where production is far from the delivery, so alternatively vessels and import terminals are necessary to ensure natural gas imports and energy supply stability. This paper analyses the technology and current market outlook of both natural gas import methods.

Weathering/Ageing of Liquefied Natural Gas Cargoes During Marine Transport and Processing on Floating Storage Units and FSRU

The phenomenon of liquefied natural gas (LNG) cargo weathering is considered in terms of the conditions influencing boil-off gas (BOG) rates during the offshore movements and handling of LNG on marine LNG carriers (LNGC), floating storage and regasification unit (FSRU), and floating storage units (FSU). The range of compositions (grades) of commercially traded LNG is significantly broader than the range of compositional changes caused by typical storage times for offshore LNG cargoes. The different nitrogen and natural gas–liquid concentrations of LNG cargoes (i.e., ethane and heavier C2+ components) significantly influence the impacts of weathering and ultimately determine whether the LNG delivered to customers is within sales specifications or not. The BOG from LNG in storage is richer in methane and nitrogen; if nitrogen is present in the LNG, otherwise just richer in methane, than the LNG from which it is derived. This leads to the LNG becoming richer in the C2+ components as ageing progresses. LNG weathering is shown not to play a significant role in the rollover phenomenon of LNG moved and stored offshore, because nitrogen contents are low (typically < 1.0%) and auto-stratification is rarely an issue. LNG stored for long periods on FSU (greater than 8 weeks, or so) experiences significant weathering effects, but most LNG processed by FSRU (and most FSU) has a residence time of less than 30 days or so, in which case weathering has only minor operational impacts. Weathering rates and LNG compositional changes on FSRU for different LNG grades are provided.

An approach to estimating the boil-off rate of LNG in type C independent tank for floating storage and regasification unit under different filling ratio

The alternative terminal Floating Storage and Regasification Unit (FSRU) for gas storage and vaporization is rapidly expanding all over the world. FSRU with great storage capacity and long storage time is faced with the continually evaporation of liquefied natural gas (LNG), which result in the decrease of filling ratio. In order to improving the efficiency of electricity generation and utilization of the Boil-off Gas (BOG), accurate and efficient method to estimate the BOR under different filling ratio is in demand. An equivalent conductive model with the combination of adjacent fluid layer and flowing BOG is proposed in this paper to handle the complex convection from the multiphase simulation. Testified by experimental measurement, the highest relative error for BOR estimation is less than 4%, and also the heat transferred by evaporation can be estimated accurately under different filling ratio. With the valid temperature distribution got from this model, the initial condition of transient simulation under specific filling ratio can be given rapidly for further study. Furthermore, the comparison between numerical results and experimental measurement also reveals that the majority of heat is transferred from bulkhead during evaporation under lower filling ratio. Finally, the proposed approach is successfully applied for a case of 30,000 m3 FSRU, and proved to be a valid option to calculate BOR in the engineering field.

Preliminary Study on Characteristics of Motions of Side-by-side Moored Vessels during Waves in Port

Recently FSRU (Floating storage and regasification unit) system has been applied to not only offshore region but also ports and harbors region. The motions and mooring loads of a ship moored along jetty and side-by-side moored two ships are influenced by wave conditions such as wave height, period and its direction, and shallow water effect. In this study, we have conducted several physical model tests on ship behaviors for a single moored ship (Ship-to-jetty: STJ) and side-by-side two vessels where one ship is moored along dolphins (STJ+STS: Ship-to-ship: STS) during waves to obtain the property of ship motions and mooring loads. Also a numerical simulation system has been developed for the side-by-side moored two vessels to investigate the property of ship motions and mooring loads.

Quantitative risk analysis of loading and offloading liquefied natural gas (LNG) on a floating storage and regasification unit (FSRU)

Natural Gas is becoming an important energy source option and the capacity of the world to produce it is surging. Large reserves of natural gas exist worldwide, particularly in areas where the resources exceed the demand. Therefore, natural gas is liquefied for shipping; and its storage and regasification process usually occurs in onshore facilities. Recently, Liquefied Natural Gas (LNG) offshore terminals have been proposed as an attractive alternative solution. This paper presents a complete quantitative risk analysis (QRA) of undesired events that may occur during the loading and unloading of Liquefied Natural Gas (LNG) considering a typical LNG carrier and an offshore terminal similar to those operating in Brazil. Initially, a historical survey of accidents at LNG facilities, along with a detailed study of LNG carriers and LNG offshore terminals, is presented to support hazard identification. Once the potential hazardous events are categorized in some possible scenarios, a probabilistic potential hazard assessment is performed; moreover, the frequencies of occurrence of the undesired events are estimated. Afterwards, traditional consequence models are briefly discussed aiming to identify the weakness of each one that supports the specification of the model used in the consequence analysis of a specified case, which is evaluated by providing the data to estimate the total risk of the installation. The risk is evaluated in terms of social and individual risk. Lastly, possible control measures able to reduce the frequency of occurrence, or mitigate the impacts associated with the analyzed scenarios, are proposed and new risks levels are estimated by considering those control measures. The paper presents a complete QRA, presenting the tools and the models chosen to perform the analysis as well as some of the advantages and limitations regarding the use of these tools and models.

A methodology for risk analysis based on hybrid Bayesian networks: application to the regasification system of liquefied natural gas onboard a floating storage and regasification unit.

This article presents an iterative six-step risk analysis methodology based on hybrid Bayesian networks (BNs). In typical risk analysis, systems are usually modeled as discrete and Boolean variables with constant failure rates via fault trees. Nevertheless, in many cases, it is not possible to perform an efficient analysis using only discrete and Boolean variables. The approach put forward by the proposed methodology makes use of BNs and incorporates recent developments that facilitate the use of continuous variables whose values may have any probability distributions. Thus, this approach makes the methodology particularly useful in cases where the available data for quantification of hazardous events probabilities are scarce or nonexistent, there is dependence among events, or when nonbinary events are involved. The methodology is applied to the risk analysis of a regasification system of liquefied natural gas (LNG) on board an FSRU (floating, storage, and regasification unit). LNG is becoming an important energy source option and the world's capacity to produce LNG is surging. Large reserves of natural gas exist worldwide, particularly in areas where the resources exceed the demand. Thus, this natural gas is liquefied for shipping and the storage and regasification process usually occurs at onshore plants. However, a new option for LNG storage and regasification has been proposed: the FSRU. As very few FSRUs have been put into operation, relevant failure data on FSRU systems are scarce. The results show the usefulness of the proposed methodology for cases where the risk analysis must be performed under considerable uncertainty.

The Application and Trend of the FSRU for LNG Import in China

The liquefied natural gas (LNG) floating storage and regasification unit (FSRU) is a kind of LNG receiving terminal forms on the sea. Nowadays, it is the most widely used sea receiving terminal form in the engineering project as it has many advantages. In this paper, the characteristics of the FSRU were discussed based on comparing of the several LNG offshore receiving terminal. The application and trend of the FSRU in China was analyzed. It was found that FSRU is recommended for LNG import in East and South coast of China.