Patent Grant
8643509
The field of the disclosure relates generally to the effects of sloshing within a tank of fluid on a ship, and more particularly, to methods and systems for providing sloshing alerts and advisories.
Sloshing describes the phenomenon of a liquid inside a tank where the liquid is excited by the motion of the vehicle carrying the tank. For example, on large liquid natural gas (LNG) carriers, sloshing of the LNG due to ship motion in a seaway can lead to extremely high loads on the cargo tank walls, resulting in extensive damage to the tank structure or insulation material. The cargo tank is particularly susceptible to damage when it is partially filled, and further susceptible to damage when the natural period of the liquid in the tank is in resonance with (near or equal to) roll or pitch motion periods of the ship.
Sloshing is stochastic, meaning that impacts cannot be predicted with certainty and the magnitudes of such impacts can vary widely. There are several factors influencing the severity of a sloshing response, including tank design configuration and local details such as chamfered topsides fabricated within the individual tanks, the fill level of the tanks, as well as excitation motion characteristics, including period, magnitude and duration. Factors influencing vessel motion include the loading condition of the vessel (i.e. the metacentric height (GM) and draft of the ship), inertia properties of the vessel about its axis of rotation, free surface effects (i.e. partially filled tanks effectively reduce GM), damping from ship appendages, as well as ship speed and heading relative to incoming waves.
As mentioned above, some LNG tanks are configured with a chamfered topside and hopper bottoms to reduce the chance of resonance while the tank is more than 95% full during a loaded passage, or less than 5% fill during the ballast leg. Loading and unloading operations usually take place at terminals or docks in protected water with good weather. As the LNG sector expands, larger tank sizes in larger vessels are built with new trades, which may entail the vessel operating with partially filled tanks and conducting cargo operations in more exposed waters. The increases in size and the need for partial fill loads also result in changes to tank natural periods. Certain of these periods are in range with roll and pitch periods of such ships. Coupled with increased severity of sea states on some trade routes, the risk of cargo and ship damage has significantly increased, especially when liquid sloshing occurs due to resonance with ship motions.
As an example, damage has occurred to several membrane tank LNG carriers due to sloshing of the LNG cargo. Lower filling levels in these LNG carriers can actually produce higher sloshing loads. Further, the study of sloshing is complex as many aspects are not easily addressed by calculations and testing. Computational fluid dynamic determinations are not fully reliable as they do not consider entrapped bubbles. As a result of recent sloshing damage incidents, regulations directed to lower filling heights for membrane ships have been reduced twice over a relatively short period. However, these reductions in cargo greatly restrict the flexibility LNG transporters have in dispensing partial loads at multiple sites. As a result, LNG transporters are currently restricted to travelling only with practically full or practically empty loads.
In one aspect, a method for providing an alert when the motion of a ship indicates a potential of sloshing damage from liquid cargo being transported by the ship is provided. The method includes calculating, with a processing device, a natural period for the tanks holding the liquid cargo based on received user inputs relating to a configuration of the tanks and a fill percentage of the tanks, receiving, at the processing device, data describing the actual motion of the ship with respect to three orthogonal axes, determining, with the processing device, a proximity of the natural period of the tanks to a period defined by the actual motion of the ship, and providing an alert to a user if the proximity in periods is within a threshold value.
In another aspect, a sloshing alert and advisory system for a ship operable to transport a liquid cargo is provided. The system includes a processing device, a user interface communicatively coupled to the processing device, a memory communicatively coupled to the processing device, the memory including data defining a natural period of liquid cargo within the ship, and a ship motion sensor communicatively coupled to the processing device and operable to provide data describing the motion of the ship with respect to three orthogonal axes. The processing device is programmed to provide an alert via the user interface when actual ship motions are approaching conditions that can lead to excessive sloshing of the liquid cargo, based on the natural period of the liquid cargo.
In still another aspect, a non-transitory computer-readable medium for providing an alert when the motion of a ship indicates a potential of sloshing damage from liquid cargo being transported by the ship is provided. The non-transitory computer-readable medium includes computer-executable instructions embodied thereon, wherein when executed by at least one processor, the computer-executable instructions cause the at least one processor to 1) determine, based on data related to the configuration of the tanks containing the liquid cargo and a fill percentage for each of the tanks, a natural period of the liquid cargo within the tanks, 2) determine an actual motion of the ship with respect to three orthogonal axes based on data received from a ship motion sensor, and 3) provide an alert via a user interface communicatively coupled to at least one processor when actual ship motions are approaching conditions that can lead to excessive sloshing of the liquid cargo, based on the determined natural period of the liquid cargo.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.
The description of different advantageous embodiments is presented herein for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different advantageous embodiments may provide different advantages as compared to other advantageous embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
Liquid sloshing is a phenomenon in a LNG tank caused by the motion of the ship 10 in a seaway. When the ship encounters sea states with sufficient wave energy, the liquid is excited by ship motions. Even with relatively moderate ship motions, the transfer of energy may lead to liquid motions inside the tank, especially when the period of ship motion is close to the natural period of the liquid within the tanks. The resulting wave action of liquids within these tanks can cause severe damage to the cargo containment system if the wave actions (the sloshing) are left unchecked.
More specifically and again referring to
Given the background provided by
More particularly and as further described below, SAAS 100 incorporates predictive and real-time motion analysis onboard the ship that can be used by the ship operator to reduce ship motions that may lead to sloshing damage. In embodiments, the ship instrumentation may include real-time motion sensors, accelerometers, and data recorders so that SAAS motion and sloshing modeling algorithms running within SAAS 100 can be improved and modified over time to match actual ship behavior. Additionally, alerts can be provided both in planning and execution phases in real-time, for example, when actual ship motions are approaching conditions that can lead to sloshing damage. Specifically, SAAS 100 provides users with advisories on how to change the conditions, including, but not limited to, ship heading, speed, route, draft and trim, and schedule so that sloshing is minimized. Further, SAAS 100 provides users anticipated results that would result from such changes.
Referring specifically to
Specifically, computer 102 receives and/or generates a time and date, position, speed, and heading using the data received from such systems 122. Computer 102 further receives data from motion sensors 124 on the ship. Specifically, pitch, roll, yaw, and acceleration data may be received by the computer 102. Optionally, computer 102 may also receive vibration, and/or fluid level data from one or more sensors 126 within or external to the tanks.
Computer 102 is programmed with a sea keeping model 130 for the ship that includes data relating to the design of the hull of the ship and data relating to ship motion theory for the specific ship. Further, computer 102 is programmed with tank related data 132 for each tank on the ship. Particularly, computer 102 is programmed with the natural period for each tank, based on the fill level and tank configuration, for example using one or both of linear wave theory and model test data.
Computer 102 provides certain outputs 106 including sea keeping guidance 140, alerts 142, event storage 144, and an analysis of modeling accuracy 146. In one embodiment, which is further described below, sea keeping guidance 140 takes the form of a polar chart display providing advisory information to a crew, including at least one of a suggested heading, speed, route, draft and trim, and schedule, which, according to sea conditions (as determined through weather and ocean forecasts, observations input by the user, environmental sensor data, sensor data, climatological averages, or other means), should result in reduced sloshing resonances. Alerts 142 include audio and/or visual warnings and any other alarms necessary to alert a ship's crew as to a current sloshing condition. While event storage 144 is classified as one of the outputs 106, it generally refers to a memory associated with computer 102 that provides storage of certain recorded events, for one or more of event playback and post-voyage analysis. Computer 102 also provides an analysis 146 of the modeling accuracy.
In summary, SAAS 100 advises the ship operator on headings, speeds, and other factors to minimize potential sloshing risks while underway. The advisories are based in part on forecasted weather, ocean conditions, and predicted ship motions resulting therefrom. The program running within computer 102 takes into consideration various inputs, including ship speed, heading, tank design, and the vessel's response amplitude operators for a range of fill heights, loading conditions, and more. Motion sensing hardware and software is used to acquire data that indicate situations conducive to excessive sloshing, which include calculation and prediction of resonant motions.
In one embodiment, a real-time ship motion measurement algorithm is utilized to indicate if a safe operating limit has been exceeded, in which case an alert will be issued. The algorithm includes predictive and real-time motion analysis onboard the ship that can be used by the ship operator to reduce motions that may lead to sloshing damage. To that end, SAAS 100 also provides advisories on how to change the conditions, such as heading, speed, route, etc., so that sloshing may be minimized.
As described above, the ship is instrumented with real-time sensors for motion, vibrations, and/or fluid level, and data recorders such that SAAS motion modeling can be improved and modified over time to match actual ship behavior, and so that alerts can be given both in planning and execution phases in real-time, for example, when actual ship motions are approaching conditions that can lead to sloshing damage.
Turning now to
Processor unit 304 serves to execute instructions for software that may be loaded into memory 306. Processor unit 304 may be a set of one or more processors or may be a multi-processor core, depending on the particular implementation. Further, processor unit 304 may be implemented using one or more heterogeneous processor systems in which a main processor is present with secondary processors on a single chip. As another illustrative example, processor unit 304 may be a symmetric multi-processor system containing multiple processors of the same type.
Memory 306 and persistent storage 308 are examples of storage devices. A storage device is any piece of hardware that is capable of storing information either on a temporary basis and/or a permanent basis. Memory 306, in these examples, may be, for example, without limitation, a random access memory or any other suitable volatile or non-volatile storage device. Persistent storage 308 may take various forms depending on the particular implementation. For example, without limitation, persistent storage 308 may contain one or more components or devices. For example, persistent storage 308 may be a hard drive, a flash memory, a rewritable optical disk, a rewritable magnetic tape, or some combination of the above. The media used by persistent storage 308 also may be removable. For example, without limitation, a removable hard drive may be used for persistent storage 308.
Communications unit 310, in these examples, provides for communications with other data processing systems or devices. In these examples, communications unit 310 is a network interface card. Communications unit 310 may provide communications through the use of either or both physical and wireless communication links.
Input/output unit 312 allows for input and output of data with other devices that may be connected to data processing system 300. For example, without limitation, input/output unit 312 may provide a connection for user input through a keyboard and mouse. Further, input/output unit 312 may send output to a printer. Display 314 provides a mechanism to display information to a user.
Instructions for the operating system and applications or programs are located on persistent storage 308. These instructions may be loaded into memory 306 for execution by processor unit 304. The processes of the different embodiments may be performed by processor unit 304 using computer implemented instructions, which may be located in a memory, such as memory 306. These instructions are referred to as program code, computer usable program code, or computer readable program code that may be read and executed by a processor in processor unit 304. The program code in the different embodiments may be embodied on different physical or tangible computer readable media, such as memory 306 or persistent storage 308.
Program code 316 is located in a functional form on computer readable media 318 that is selectively removable and may be loaded onto or transferred to data processing system 300 for execution by processor unit 304. Program code 316 and computer readable media 318 form computer program product 320 in these examples. In one example, computer readable media 318 may be in a tangible form, such as, for example, an optical or magnetic disc that is inserted or placed into a drive or other device that is part of persistent storage 308 for transfer onto a storage device, such as a hard drive that is part of persistent storage 308. In a tangible form, computer readable media 318 also may take the form of a persistent storage, such as a hard drive, a thumb drive, or a flash memory that is connected to data processing system 300. The tangible form of computer readable media 318 is also referred to as computer recordable storage media. In some instances, computer readable media 318 may not be removable.
Alternatively, program code 316 may be transferred to data processing system 300 from computer readable media 318 through a communications link to communications unit 310 and/or through a connection to input/output unit 312. The communications link and/or the connection may be physical or wireless in the illustrative examples. The computer readable media also may take the form of non-tangible media, such as communications links or wireless transmissions containing the program code.
In some illustrative embodiments, program code 316 may be downloaded over a network to persistent storage 308 from another device or data processing system for use within data processing system 300. For instance, program code stored in a computer readable storage medium in a server data processing system may be downloaded over a network from the server to data processing system 300. The data processing system providing program code 316 may be a server computer, a client computer, or some other device capable of storing and transmitting program code 316.
The different components illustrated for data processing system 300 are not meant to provide architectural limitations to the manner in which different embodiments may be implemented. The different illustrative embodiments may be implemented in a data processing system including components in addition to or in place of those illustrated for data processing system 300. Other components shown in
As one example, a storage device in data processing system 300 is any hardware apparatus that may store data. Memory 306, persistent storage 308 and computer readable media 318 are examples of storage devices in a tangible form.
In another example, a bus system may be used to implement communications fabric 302 and may be comprised of one or more buses, such as a system bus or an input/output bus. Of course, the bus system may be implemented using any suitable type of architecture that provides for a transfer of data between different components or devices attached to the bus system. Additionally, a communications unit may include one or more devices used to transmit and receive data, such as a modem or a network adapter. Further, a memory may be, for example, without limitation, memory 306 or a cache such as that found in an interface and memory controller hub that may be present in communications fabric 302.
As mentioned above, the above described SAAS 100 incorporating computer 102 is operable for mitigating the risks associated with unabated sloshing of liquid within the hold of a ship. Particularly, and as described below, SAAS 100 operates to warn the ship operator, in real time, when dangerous levels of sloshing may be imminent or occurring. As described with respect to the following figures, SAAS 100 also displays alternative ship speeds and/or headings believed to be useful in reducing sloshing and thereby reducing the risk of damage to the ship and/or liquid cargo.
In one embodiment, SAAS 100 includes a personal computer that receives inputs from a ship motion sensor, for example, via a USB interconnection. In embodiments, the ship motion sensor is a unit that contains roll and pitch inclinometers, yaw rate gyros, and multi-axis accelerometers. In one specific embodiment, the motion sensor is placed proximate the centerline of the ship, with the fore-and-aft axis parallel to the center line.
In a real-time mode, the SAAS 100 continuously (i.e., at 4 Hz) monitors the vessel motion, computes the ship's roll and pitch periods, and plots them onto a strip chart (either on paper or on a computer display). The cargo tank natural periods (which are calculated for the user-specified fill level) are indicated on the same strip chart. When an amplitude and number of consecutive ship motion periods meet certain thresholds, the SAAS 100 indicates a sloshing warning or sloshing alarm (alert 142) visually and/or audibly.
When operated in a predictive mode, SAAS 100 indicates the possibility of tank sloshing in forecast or user-specified weather conditions. In the predictive mode, SAAS 100 utilizes an algorithm to predict vessel motion amplitudes and periods under various sea conditions, headings and speeds utilizing proven ship motion theory. Advice on heading and speed changes to mitigate the risk of structural damage due to sloshing are depicted, in one embodiment, through the use of a polar diagram indicating the relative risks of tank resonance with ship motions. In an embodiment, a user of the SAAS 100 can specify the thresholds (e.g., Safe Operating Limits) to tailor the SAAS 100 for the intended passage and cargo conditions. The Safe Operating Limits can also be used as routing constraints to optimize the route for minimum fuel consumption and on-time arrival.
Starting the SAAS program within computer 102 results in a motion recorder display screen 400, such as shown in
Still referring to screen 400, on the top left is a real-time roll angle gauge 420 which provides the roll angle in degrees. Below the roll angle gauge 420 is a roll cycle indicator 422 that indicate the number of roll cycles 424 and their associated roll periods 426 that have been previously recorded. The time of recording can be referenced by a white horizontal line with Month/Date/Hour which is inserted into roll cycle indicator 422, for example, every fifteen minutes. Similarly, another set of displays are for the recorded pitch angle and associated periods. Specifically, a real-time pitch angle gauge 440 provides the pitch angle in degrees. Below the pitch angle gauge 440 is a pitch cycle indicator 442 that indicate the number of pitch cycles 444 and their associated pitch periods 446 that have been previously recorded. The time of recording can be referenced by a white horizontal line 448 with Month/Date/Hour which is inserted into pitch cycle indicator 442, for example, every fifteen minutes.
The histogram (cumulative number of cycles) of the roll and pitch periods is updated when each motion cycle is completed. Each individual roll or pitch cycle is shown on the respective indicator 422, 442 as a line above its corresponding period, which ranges, for example, from 3 to 28 seconds. The colors of the lines (i.e., green, yellow, red) indicate the amplitude (maximum angle) of the motion and correspond to normal, warning, and alarm levels. The thresholds for each level are configurable by the user as shown in
In one embodiment, an audible alarm may be disabled by selection of a “Disable Alarm” selection under the Configure menu as shown in
Referring once again to
Selection of the Configure button on display 400 causes SAAS 100 to display a drop down list of motion sensor channels to be configured as shown in
Referring once again to
The drop down list 800 allows the user to select a particular period to playback. In the illustrated embodiment, the time code format is YYYY-MM-DD HH:MM. Selection of the “X1” button causes the time histories to be displayed at the same speed as they were recorded in real-time. Clicking on the button again will double the current speed up to a maximum of X32 as the computer processor speed permits. Clicking on Play will start the replay. When playing, the button changes to a “Pause” button. Selection of Pause will stop the replay. As contemplated, the Playback function is to be used to investigate past events of sloshing and further refine the detection algorithms within SAAS 100.
To further facilitate the investigation of past events and developing better algorithms to predict sloshing induced damage, SAAS 100 provides the capabilities to convert the binary records into comma delimited text files for export into spreadsheets by simply selecting the files with YYYYMMDDHH.xbw to export and save under user specified folders as shown in
To assist the user in deciding the best ship speed and heading to mitigate the risk of damage due to heavy weather as well as sloshing, SAAS 100 provides the capability of predicting vessel motion and period based on established ship motion theory. Clicking on the Seakeep button 412 on the menu bar 402 will cause the polar diagram display 1100 of
The polar diagram 1160 shows the incoming wind and wave directions as well as possible warning at each ship speed for 360 degrees of heading. The black dot 1162 is indicative of the present ship speed and course over ground, for example, from GPS input. Each concentric circle is 1 knot. The lower left panel 1180 shows the estimated natural periods of the liquid for roll and pitch at user defined fill levels for each tank. When the natural periods are within 1 second of the ship's roll or pitch motion period, resonance may occur. This is indicated by the color coded arc within polar diagram 1160. To indicate the severity of sloshing resonance, user can set warning and alert levels based on the predicted roll and pitch angles as described above. When sloshing is predicted, the ship's roll or pitch periods and affected tank periods turns into Green (possible), Yellow (warning) and Red (alert) color. One objective of the polar chart 1160 display is to provide guidance on ship speed and heading changes which will minimize the risk of sloshing, generally, directing the ship from red arcs toward green arcs. In conjunction with the real-time display of the measured roll and pitch angle/period, overall risk of sloshing induced structural damage will be reduced. Summarizing, polar diagram 1160 in one embodiment passively displays all the possible headings and speeds one could use to minimize sloshing providing all the information needed for a captain to choose one heading and speed to reduce sloshing.
In one embodiment, GPS and gyrocompass signal from the ship's navigation system are used to get ship's position, heading, and speed. In another embodiment, this data is collected from a stray AIS signal that is available on certain ships. External memory 1210 is used in one embodiment to get the data off the ship. With the data card 1212, such data can be uploaded over an available cell phone network when the ship is in port. Not illustrated in
Uploading of data is not required for the functioning of SAAS 100, but such uploading allows shoreside persons to monitor and analyze results, as well as providing valuable feedback so that the SAAS can be updated to give improved performance that is based on actual performance.
This written description uses examples to disclose various embodiments, which include the best mode, to enable any person skilled in the art to practice those embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2997973 | Hawthorne et al. | Aug 1961 | A |
| 3938258 | Zook | Feb 1976 | A |
| 4647928 | Casey et al. | Mar 1987 | A |
| 4651128 | Kolb | Mar 1987 | A |
| 5383359 | Challoner et al. | Jan 1995 | A |
| 5560161 | Lou | Oct 1996 | A |
| 6023221 | Michelotti | Feb 2000 | A |
| 6694225 | Aga et al. | Feb 2004 | B2 |
| 7546224 | Campbell | Jun 2009 | B2 |
| 7714712 | Emigh et al. | May 2010 | B2 |
| 8079321 | Balasubramanian | Dec 2011 | B2 |
| 20080217874 | Miskin | Sep 2008 | A1 |
| 20100256882 | Dreier et al. | Oct 2010 | A1 |
| 20110307128 | Igarashi et al. | Dec 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 07002169 | Jan 1995 | JP |
| Entry |
|---|
| Rathje et al.; “Concept and Implementation of an Innovative Shipboard Routing Assistance System”; presented at Royal Institution of Naval Architects (RINA) International Conference Design and Operation of Container Ships; Apr. 23-24, 2003). |
| Mikelis et al.; “Experimental and Numerical Simulation of Sloshing Behaviour in Liquid Cargo Tanks and its Effect on Ship Motions”; National Conference on Numerical Methods for Transient and Coupled Problems, Jul. 9-13, 1984 Venice, Italy, Report 0661-P, 1984, Delft University of Technology. |
| Hine, L.; New Software Aims to Reduce Risk of Sloshing; TradeWinds; Dec. 10, 2010; vol. 21, No. 49; 2 pages. |
