grain (2)

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2008 Napa Ltd NAPA User Meeting 2008

Workshop No. 1

Grain Stability Calculations

Jukka Mttnen and Jan Mattsson, Napa Ltd

2 Grain Stability Calculations

Jukka Mttnen and Jan Mattsson

NAPA User Meeting 2008 2008 Napa Ltd

Table of contents 1. Introduction..............................................................................................................................3 2. Basics of the grain rule ..............................................................................................................3

2.1 Grain shift moment................................................................................................................3 2.2 Load types............................................................................................................................4 2.3 Initial voids...........................................................................................................................6 2.4 Grain load after shifting .........................................................................................................6

3. Grain calculations with NAPA......................................................................................................7 3.1 Creating the rooms for the arrangement .................................................................................7 3.2 Create the grain cargo space..................................................................................................7

3.2.1 Defining the hatch.............................................................................................................9 3.2.2 Defining girders...............................................................................................................11 3.2.3 Grain feeding holes .........................................................................................................12 3.2.4 Tween decks...................................................................................................................12 3.2.5 Multiple hatches into the same grain cargo space...............................................................12

3.3 Check the hold geometry .....................................................................................................12 3.4 Check the load....................................................................................................................14 3.5 Calculate the actual grain heeling moment tables...................................................................14 3.6 Create allowable grain heeling moment tables .......................................................................15 3.7 Create loading conditions and check that they do pass the criteria ..........................................17

4. Manager applications for Grain Stability.....................................................................................19 4.1 GS Manager (MGR*GS)........................................................................................................19 4.2 LR SCM Manager (LR_SCM) .................................................................................................20

5. Relationship between CR, LD and GS tasks................................................................................21 6. Relationship between the numbers ...........................................................................................22

6.1 LIST in the grain task ..........................................................................................................22 6.2 Volumes, weights, centre of gravity, vertical grain shift, etc ....................................................22

7. Changes between Release 2007.2 and 2008.1 ...........................................................................23 7.1 Changes that may affect calculation results or backwards compatibility....................................24

7.1.1 Grain shift moments in LD................................................................................................24 7.1.2 Void depth calculations ....................................................................................................24 7.1.3 Feeding distance and upper stool tanks.............................................................................24 7.1.4 Voids under stools ...........................................................................................................24 7.1.5 Void depths in fore and aft hatch configurations ................................................................25 7.1.6 Hatch coaming height......................................................................................................25 7.1.7 Control of alternative calculation methods .........................................................................25 7.1.8 Grain feeding holes compatible with tween decks and multiple hatches................................25 7.1.9 DESCRIBE command (DES) ..............................................................................................25 7.1.10 Assigning variables ..........................................................................................................25

7.2 New features ......................................................................................................................26 7.2.1 Permissible heeling moments list limited with intact criteria.................................................26 7.2.2 New alternative layout for permissible heeling moments list ................................................26 7.2.3 New plotting options........................................................................................................26 7.2.4 Functionality supporting macros .......................................................................................26 7.2.5 Miscellaneous..................................................................................................................26

8. Acknowledgements .................................................................................................................26




1. Introduction The International Grain Code specifies how to determine the grain shift moment, and it sets the stability criteria for ships carrying grain in bulk. The purpose of the Grain Stability subsystem in NAPA is to:

calculate grain shift moments calculate the allowable grain heeling moments determine whether a loading condition complies with the grain stability criteria create the tables needed for the loading manual

2. Basics of the grain rule

2.1 Grain shift moment

In most holds, grain cargo cannot be loaded so that it perfectly fills up the compartment and no empty spaces exist; there are usually some voids under the deck after loading. The cargo also settles during the voyage, so that even if the cargo filled up the hold perfectly before the voyage, there may be voids during the voyage.

Figure 1 The cargo shifts when the ship heels

When the ship heels enough, the cargo will slide towards the lower side, and the center of gravity of the cargo will not be in the same place anymore. When the ship comes upright again, the load will not level itself as a liquid would and the center of gravity is still off the original one.




Figure 2 The center of gravity moves sideways and vertically

The center of gravity will also move vertically. Depending on the geometry this movement is up or down. In a section of the grain cargo space, the moment is

oCSection AdCGYGRM arg= where dCGY is the transverse movement of the grain cargo, and Acargo is the area of the cargo in the section. This areal moment will be integrated over the length of the cargo hold to get the volumetric grain shift moment GRMV. The volumetric moment is multiplied by the density to obtain the grain shift moment GRM.

rhoGRMVGRM = The actual grain shift moment for the loading condition is the sum of the grain shift moment for each hold. This is complicated by the fact that we do not know exactly how the cargo will behave when loading and shifting. Therefore, the international grain code makes some assumptions on which the calculations are based. There are also some pragmatic corrections made in the rule in cases where it has been difficult to quantify the effect of the grain shift on the stability. 2.2 Load types

The grain rule separates four different ways you can load grain:

Filled, untrimmed load: you fill the hold from the hatch and leave it just as it is. In the hatch, you trim the load, i.e. level the surface as much as possible. Filled means you fill it to the maximum extent possible, in normal circumstances up to the edge of the hatch coaming. The rule assumes that the load will flow from the hatch end beams and the side girders at an angle of thirty degrees.




Figure 3 Untrimmed grain load forward of the hatch

Filled and trimmed load: fill the compartment to the maximum extent possible and level all the

surfaces.

Figure 4 Filled and trimmed load; the cargo is packed into the hold as well as possible

Figure 5 Filled and trimmed load; the rule makes assumptions about how well the cargo can be loaded and how it will settle during the voyage causing assumed voids which are used for calculation of the grain shift moment

Partial load: load the compartment with a certain amount of grain. Partial loads must always be

trimmed, i.e. the surface of the cargo must be level.

Figure 6 Partial load, always trimmed




Filled, with untrimmed ends: this is a hybrid between the filled and trimmed load and the untrimmed

one and is allowed in specially suitable compartments', as defined in A.2.7. An example of a specially suitable compartment is a hold with topside tanks sloped more than 30 degrees, and where the hatch sides coincide with the topside tank.

2.3 Initial voids

For the purpose of calculating the adverse heeling moment due to a shift of cargo surface in ships carrying bulk grain it shall be assumed that: In filled compartments, which have been trimmed in accordance with A 10.2, a void exists under all boundary surfaces having an inclination to the horizontal less than 30 degrees, and the void is parallel to the boundary surface having an average depth calculated according to the formula Note that these assumed voids are used only for calculating the grain shift moment; they are not used for calculating the weight of the cargo. The formula for calculating the depth of the assumed voids takes into account the distance from the hatch to the boundary of the compartment and the depth of any beams and girders.

Figure 7 The void depth is affected by the distance from the hatch end beam or side girder to the boundary of the compartment, and the highest girder/beam between the hatch and the void

In partial loading conditions, there will be similar voids underneath any horizontal surfaces, in case the grain reaches up to them. 2.4 Grain load after shifting

In order to calculate the grain shifting moment, the grain code makes assumptions about how the cargo will settle after shifting. Instead of calculating how the cargo is moving, the assumptions are made regarding how the voids will move. First, the initial voids are established. Then the shifting angle is determined, based on the type of the load, 15 degrees for filled and trimmed, 25 degrees for untrimmed and partial loads. Using the shifting angle, the maximum void that can be formed against each girder is determined. If the grain is shifting to the port side, the calculation starts from the void far left (seen from aft). If the area of the initial void is less than that of the max shifted void that can be formed against the girder, the height of the shifted void is adjusted so that the area is the same as the initial void.

GolamHighlight




If the initial area is greater than the max void, the excess area will be transferred to the next void to the right. Then the process is repeated for this void, but instead of using the initial area of the void, we will use the initial area plus any area that was transferred from the previous void. Finally, we will have determined the area and the centre of gravity of each void after shifting, and we can get the center of gravity of the cargo in this section.

Figure 8 Shifted voids and void transfers used for determining the shape of the cargo surface after shifting

3. Grain calculations with NAPA The normal working order when carrying out grain calculations using NAPA:

1. Create the rooms and add them to the arrangement. 2. Define the grain cargo spaces, i.e. add structures, hatch definitions, etc. 3. Check that the hold geometry is what you expected using plots. 4. Check that the cargo surface behaves like you expect when loading grain, using plots. 5. Create actual grain heeling moment tables for each hold, the partial loads and the filled

loads. 6. Check that openings and deck edge curve are defined. 7. Create permissible heeling moment tables for the ship at different floating positions and

KGs. 8. Create loading conditions, and check that they comply with the grain stability criteria.

3.1 Creating the rooms for the arrangement

Create the geometry as close to the real cargo space as possible, including corrugated bulkheads and hatches. Add the rooms to the arrangement table. If there are corrugated bulkheads, make sure that the first LIMITS command in the room definition contains the corrugated surfaces. 3.2 Create the grain cargo space

The grain cargo space object is like a room, with some extra information about the structures that affect grain shifts. The grain cargo space is defined in the GS task.




There are two optional ways to create the grain cargo space: the Hatch Included approach and the Stripped room approach. The important thing is to select one approach and use that; do NOT mix the two approaches, it may lead to incorrect results. The hatch included approach

1. Define a grain cargo space with the same name as the room in the arrangement.

2. If there are corrugated bulkheads,

replace them using the Reference Planes command RP.

3. Tell GS that you are using the Hatch

Included approach by issuing the HI command.

4. Continue by defining hatches, girders,

decks, etc.

The stripped room approach

1. Create another room which is like the one in the arrangement, but remove the hatch coaming down to the deck, and replace any corrugated bulkheads with planes.

2. Create a grain cargo space with the

same name as the room in the arrangement. This grain cargo space should refer to the stripped room you created in step 1.

3. Continue by defining hatches, girders

decks, etc.

Figure 9 The room as it is defined in the arrangement, with corrugated bulkheads

Figure 10 The stripped room, the hatch has been removed, and the corrugated bulkheads have been replaced by planes




Example of the stripped room approach Original compartment in the arrangement: ROOM C13 'HOLD 3' LIM CBHD111, #147, D4GS, D4, DB, D1TEST,




When defining the hatch, the user should be familiar with the meaning of:

Max load height (ZL): o The maximum height up to which you can load grain in the hold. o Often this is the same as the coaming height, but, for example, with deep girders in the

hatch cover extending below the coming height the maximum load height will be lower. o If no max load height is given, it will be assumed to be the coaming height.

Coaming height (ZCOAM):

o You cannot load any higher than the coaming height, or the grain will flow over the coaming.

o The volume of the hold is calculated up to the coaming height. o If the coaming height is not given, the program will try to figure it out from the geometry.

Hatch cover height (ZC or HC):

o The height of the inner surface of the hatch cover.

Figure 11 The heights and the parameters in the hatch command that are used to set them

Where the deck is flat or otherwise well-defined, these measures can be given from the deck. Sheer, camber and raised decks will make it complicated to define the heights from the deck; therefore, the measurements from the baseline are often preferable. The way the maximum load height, the cover height and the coaming height affect the void in the hatch is explained in the figures below.




The room you add to the arrangement should be defined up to the inner surface of the hatch cover. The reason is that there are other calculations in NAPA that expect them to be modelled this way. If you define the hatch by referring to a room, that room should also reach up to the inside of the hatch cover. The reason is that when the load shifts, it will move into any open voids in the hatch cover. It is only the initial load that cannot be higher than the upper edge of the hatch coaming. 3.2.2 Defining girders

Deck girders and hatch cover girders are defined with the GIRDER command (see !expl GIRDER). In the hold definition shown below, there is one hatch cover girder at the centre line with one meter depth and two deck girders continuous with the hatch side girders. GCS C14 GIRDER (0 1) H HATCH (61.265 81.155 -7.68 7.68) HC=2.2 HBA=0.685 HBF=0.685 ZGL=15.96, ZGR=15.96 ZL=18.18 ZCOA=18.18 GIRDER (7.68 0.685), (-7.68 0.685) HI

Case 1 Maximum filling level is equal to hatch coaming

OPEHATCH

HATCH

Top of Hatch Coaming = maximum filling height of grainAssumed void from settling of grain is

150mm

Total void depth is hatch cover depth plus

150mm

Case 2 Maximum filling level is below top of hatch coaming

OPEHATCH

HATCH

Top of Hatch Coaming Assumed void from

settling of grain is 150mm

Total void depth is hatch cover girder depth plus 150mm

Maximum filling height of grain =height of Hatch Cover Girders

Case 3 CLOSED HATCH COVER

CLOSEHATCH

HATCH

Top of Hatch Coaming Assumed void from settling of grain is

150mm

Total void depth = 150mm




3.2.3 Grain feeding holes

Feeding holes for the hatch end beams are defined with the command FH (see !expl FH). In the hold definition shown below, the command FH refers to a table in which the feeding holes for aft and fore beams are defined. GCS C14 HATCH (61.265 81.155 -7.68 7.68) HC=2.2 HBA=0.685 HBF=0.685 ZGL=15.96, ZGR=15.96 ZL=18.18 ZCOA=18.18

GIRDER (0 1) H FH FHD*C14_HEBF FHD*C14_HEBF GIRDER (7.68 0.685), (-7.68 0.685) D (1.798 18.18 1.6382) HI In the table FHD*C14_HEBF, there are three columns. DIST is the distance between holes, CLEAR is the clearance from the deck and DIA is the diameter of the holes. All holds are placed symmetrically with the centre line, so the distance of the first hole is to the centre line. DIST CLEAR DIA [m] [m] [m] ------------------------ 0.40 0.35 0.17 0.80 0.35 0.17 0.80 0.35 0.17 0.80 0.35 0.17 3.2.4 Tween decks

If the ship has a tween deck, define it by using the DECK command. Then add hatches and girders to the deck. Note that all hatches and girders apply to the previous deck defined. Any hatch and girder definitions prior to the DECK commands are assumed to be on the main deck. NAPA supports up to nine tween decks in grain calculations, but we have only tested it with 0-3 tween decks which we think should cover the majority of designs. 3.2.5 Multiple hatches into the same grain cargo space

There are ships with multiple hatches leading into the same cargo hold. Usually, these are forward and aft hatch arrangements. NAPA can handle these; you just have to do two separate hatch definitions for the same deck. Multiple hatches abreast of each other should not be attempted. 3.3 Check the hold geometry

The hold can be plotted in three projections. The X-projection is the most useful, since the calculations are done in these sections. Select the section by using the SECT command.




Figure 12 PLOT X, plot the section of the cargo hold

The Z-projection is useful for checking hatches and girder definitions. It can also be used to find out where the program has placed the calculation sections.

Figure 13 PLO Z TDS, Plot Z-projection, add Title (T), girder depths (D) and Scale (S)

The Y-projection is useful for checking the geometry of the hold and how the load behaves. Please note that the load may not be fully accurate; the calculation is done in the x-sections, and this plot is just connecting the points on the surface. PLOT Y the geometry of the hold PLOT YIL 0 F the initial load, at Y=0, filled and trimmed




Table 1 Plotting options for girders

PLOT G girder sections PLOT GD girder depths PLOD GID girder IDs PLO GC girder coordinates

3.4 Check the load

To be able to check that the voids are correctly formed, there are a number of PLOT commands for voids. The plots are also useful for identifying a void, in case you have to use a custom depth. PLOT V plots the initial voids PLOT VD marks the depth of the voids PLOT VID add void IDs to the drawing PLOT V15 plot the maximum voids formed with a 15 degree shifting angle PLOT V25 plot the maximum voids formed with a 25 degree shifting angle To check how the cargo surface will behave when loading there is the LOAD command. LOAD F / UT / UTE Load filled and trimmed / untrimmed load / untrimmed ends LOAD 14.3 Load partial load, up to Z=14.3m PLOT +IL Plot the load before shifting and the hold PLOT +SL Plot the load after shifting and the hold Handy shortcuts: AUTO PLOT +IL when the section is changed, or the loading is changed, the system will run the

PLOT + IL command again. AUTO PLOT +SL is also useful. AUTO FILL RED when auto plot draws the load, the load will be filled with red color AUTO FILL OFF turn off the automatic filling AUTO PLOT OFF stop plotting automatically SEC N next section SEC P previous section 3.5 Calculate the actual grain heeling moment tables

After the necessary definitions have been done, the grain heeling moment tables can be created by using the LIST command. Without any arguments, it will produce the table for partial loads. The heights are controlled by the Depth or Ullage commands (D, ULL).




GS?>lis D GVOL GVOLR GMY GRMV DCGY m m3 m3 m4 m4 m ------------------------------------------------- 0.000 0.0 0.0 0.0 0.0 0.00 2.000 800.0 800.0 4506.3 4506.3 5.63 20.000 7893.6 7893.6 1816.8 1816.8 0.23 22.000 8078.6 8078.6 840.1 840.1 0.10 GS?>lis f D GVOL GVOLR GMY GRMV DCGY m m3 m3 m4 m4 m ------------------------------------------------- 22.000 8078.6 8078.6 764.2 764.2 0.09 A frequently asked question is why the grain moment (GRMV) is different for the partial filling at Z=22m and the filled and trimmed condition. The reason is that the filled and trimmed condition is calculated using 15 degrees shifting angle while the partial load is calculated with 25 degrees. In order for a load to be filled, it must be specified as F, UT or UTE. All the other loads are partial, although the amount loaded is enough to fill it. GS?>lis ute D GVOL GVOLR GMY GRMV DCGY m m3 m3 m4 m4 m ------------------------------------------------- 22.000 7682.2 7682.2 2622.5 2622.5 0.34 GS?>lis ut D GVOL GVOLR GMY GRMV DCGY m m3 m3 m4 m4 m ------------------------------------------------- 22.000 7523.3 7523.3 3524.6 3524.6 0.47 GS?> 3.6 Create allowable grain heeling moment tables

Traditionally, the grain heeling moment tables have been created in the GCR?> task. Starting from release 2008.1, they can also be created in the CR_I?> task. The benefit of doing it in the intact criteria task is that you can limit the list output with other intact criteria. For the loading manual, you usually need a list of permissible heeling moments, where the combinations of KG & displacement combinations that are not allowed because some non grain criteria fails. Previously, values in the allowable heeling moment list had to be taken out by hand, or by using a macro, but now we can do the following:




TASK?>CR CR_I?>T 10 11 12 CR_I?>ZCG 10 11 12 CR_I?>RCR AREA30, AREA40, AREA3040, GZ0.2, MAXGZ25, GM0.15 CR_I?>LIST AHM -------------------------------------------- T DISP GRM GRM GRM ZCG=10 ZCG=11 ZCG=12 m t tm tm tm -------------------------------------------- 10.000 43889.4 23788.2 14080.5 - 11.000 48623.4 25584.6 14829.8 - 12.000 53452.0 28605.0 - - -------------------------------------------- CR_I?>RCR CR_I?>LIST AHM -------------------------------------------- T DISP GRM GRM GRM ZCG=10 ZCG=11 ZCG=12 m t tm tm tm -------------------------------------------- 10.000 43889.4 23788.2 14080.5 - 11.000 48623.4 25584.6 14829.8 - 12.000 53452.0 28605.0 8579.8 - -------------------------------------------- With a LIST CRT we can see what criteria is limiting the table at draught 12m, KG 11m. Loading condition: T=12 m; TR=0 m --------------------------------------------------------------- RCR TEXT REQ ATTV UNIT STAT --------------------------------------------------------------- AREA30 Area under GZ curve . 0.055 0.181 mrad OK AREA40 Area under GZ curve . 0.090 0.252 mrad OK AREA3040 Area under GZ curve . 0.030 0.072 mrad OK GZ0.2 Max GZ > 0.2 0.200 0.504 m OK MAXGZ25 Max. GZ at an angle . 25.000 24.090 deg NOT MET GM0.15 GM > 0.15 m 0.150 1.278 m OK --------------------------------------------------------------- CR_I?>




3.7 Create loading conditions and check that they do pass the criteria

Starting from Release 2008.1, you can use the Loading Conditions window to load grain.

Figure 14 Grain loading in the Loading Conditions window

Alternatively, you can load from the command line by using the LOAD command. @@ fill and trimmed LOAD grain F HOLD1 HOLD2 HOLD3 @@ filled with untrimmed ends LOAD grain UTE HOLD4 @@ filled untrimmed LOAD GRAIN UT HOLD5 @@ partial load LOAD GRAIN 120 HOLD6 With LIST GCR, you can check the status of the grain criteria while in the LD task. The values inside brackets are the required values. There is an exclamation mark where the requirement is not met.




LD?>list gcr Load case: LOADCASE Displacement: 41980.0 t Height of center of gravity: 10.20 m GM (corrected): 1.257 m (0.3) Correction for free surfaces: 0.000 m Grain shift moment: 3025.1 tm Max. allowed grain shift moment: 0.0 tm Heel resulting from grain shift: 3.2 degree ! (3.19) Residual area: 0.016 RAD*M ! (0.075) Max righting lever (after shift) 0.15 m Angle of max righting lever 13.2 degree Heeling arm due to grain shift: 0.07 m LD?> The contents of the loading condition can be listed with LIST PAR. By adding the quantity GRM in the LQ you will get the grain shift moment for any holds containing grain loads. LQ PAR NAME, LOAD, MASS, VREL(FILL), XM, YM, ZM, GRM LD?> LD?>lis par ------------------------------------------------------------------- NAME LOAD MASS FILL XM YM ZM GRM t % m m m tm ------------------------------------------------------------------- CONTENTS=Grain load (RHO=0.78) HOLD1 GRAIN 6396.0 100.0 10.00 0.00 10.27 605.0 HOLD2 GRAIN 6396.0 100.0 30.00 0.00 10.27 605.0 HOLD3 GRAIN 6396.0 100.0 50.00 0.00 10.27 605.0 HOLD4 GRAIN 6396.0 100.0 70.00 0.00 10.27 605.0 HOLD5 GRAIN 6396.0 100.0 90.00 0.00 10.27 605.0 ------------------------------------------------------------------- SUBTOTAL GRAIN 31980.0 50.00 0.00 10.27 3025.1 ------------------------------------------------------------------- NAME LOAD MASS FILL XM YM ZM GRM t % m m m tm ------------------------------------------------------------------- ------------------------------------------------------------------- TOTAL 31980.0 50.00 0.00 10.27 3025.1 LD?>

Frequently asked question: Im checking a loading condition with the CHECK load command in the GCR task, then I check the same floating position by using CHECK disp= trim= zcg= and the result is not the same. Why? Answer:

1. The loading condition may contain free surfaces which affects the GZ curve. Depending on the freesurface rule this may happen even if there are no liquid loads onboard.

2. The loading condition might have a small initial heel which affects the result. 3. The GZ curves used for the checks are not necessarily the same. Check load takes the GZ-curve

from the loading condition. The other form of check creates it based on the given hull object. If the given heel arguments in the tasks are different, the curves may not be the same.




4. Manager applications for Grain Stability In NAPA 2008.1 there are two Manager applications available for grain stability calculations. GS (Grain Stability) Manager is available with the license feature GS. LR SCM (Lloyds Register Statutory Computational Manager) requires also a license feature for the use. These Manager applications are used for carrying out the grain stability process with a graphical user interface. The benefits of using these compared to using the command window are:

Easy and fast to use Structured step-by-step approach reduces the number of input errors Reduction in design and stability calculation time

It is important to notice that the input for hold dimensions in the variable definition tables in these Manager applications does not necessarily reflect the hold definitions existing in the database. Therefore, the user should be careful when updating the Manager items as this might result in losing some of the hold definitions. All in all, neither of these Managers do not support editing hold definitions, which have been created without the Manager in question. The use of both Managers requires that the selected compartment arrangement includes the grain compartments. 4.1 GS Manager (MGR*GS)

Figure 15 Screenshot of the GS Manager




This Manager application was originally released in NAPA 2004.1 and it was renewed for NAPA 2006.1. The Manager calculates grain moments according to the International Grain Code.

The main steps of a grain calculation process with this Manager are:

1. Selection of grain holds for a grain moment calculation process 2. Modelling the structures and hatches in the grain space 3. Grain moment calculation and grain load check for the grain holds 4. Creation of permissible grain heeling moment tables for the ship

The creation of the loading conditions and checking the compliance of the grain stability criteria need to be carried outside this Manager.

More about the GS Manager can be found in the NAPA Online Manuals.

4.2 LR SCM Manager (LR_SCM)

Figure 16 Screenshot of the LR SCM Manager




The Lloyds Register Statutory Computational Manager (LR_SCM) has been developed in conjunction with NAPA to allow for checking of ship designs for compliance with statutory regulations from the initial through to the final design stage, providing a seamless integration of plan approval into the design process. The possibility to calculate grain stability will be included in this Manager in NAPA 2008.1. Grain stability can be checked within the IMO Intact Stability calculations, see Figure 16 Screenshot of the LR SCM Manager. The main steps of the calculation process are the following:

1. Setting calculation arguments (freeboard deck edge, relevant openings, etc) 2. Selection of relevant intact and grain stability criteria 3. Selection of grain holds from the compartment arrangement 4. Modelling the structures and hatches of the grain holds 5. Creation of actual grain heeling moment tables for each hold 6. Create allowable grain heeling moment tables for the ship 7. Creating loading conditions 8. Checking the conditions against the grain stability criteria

Hold definition part supports modelling zero to three open tween decks. Each deck may include two hatch openings, which must be set in the longitudinal direction. Most of the vertical hold dimensions can be given from the baseline or from the deck. Compared with the GS Manager, maybe the most significant difference is that in this Manager the grain calculations are fitted into a larger entity. This enables the user to carry out a larger part of the statutory compliance calculations using clear, step-by-step processes within the same application. Furthermore, the functionality used is newer than in the GS Manager, which does not use all the new features of the GS sub-task, such as new plotting functions and checking criteria and allowable heeling moments to both sides. Hold definition can be carried out step-by-step and the outcome of each step can be checked by plotting, whereas the GS Manager requires that hold dimensions are given and run all at one time. The LR Manager uses the hatch included approach which is the preferred method.

5. Relationship between CR, LD and GS tasks In the GS task, we calculate the grain shifting moments, for different fills. To be able to calculate them we have to do some definitions too, to tell the program about the special features of the hold that affect the grain shifts. When we run the CALC command, the program calculates the grain shift moments, volumes, etc for

Partial loads at heights defined by D, ULL or T Filled and trimmed load Filled and untrimmed load Filled with untrimmed ends

These calculation results are stored with the Grain cargo space. In the Loading Conditions task, we load the holds. LD asks the grain task, the user wants to LOAD UTE into this cargo hold, how much is that? The answer is fetched from the grain cargo space description. If the user wants to list the grain heeling moment, the center of gravity or anything like that for a grain load, the question will be asked from the grain subsystem, which will look it up in the grain cargo space. If the values do not exist in the grain cargo space description, GS will try to calculate them. The calculation is also carried out if some object that the grain load is dependent on has changed.




If you load a partial load, and the exact same amount does not exist among the pre-calculated draughts, the result is interpolated from the calculated results. It is important to have enough calculation draughts; otherwise, the accuracy of the interpolated results will suffer. As a rule of thumb, we recommend using 20 heights or more. In the Criteria tasks, you check whether the loading condition passes the grain criteria and any other stability criteria that applies to the ship. Here the connection to grain stability is that the grain heeling moment is fetched from the loading condition. In addition, you create the allowable grain heeling moments list the CR-task. This list is not in any way related to the actual grain heeling moments. The things affecting it are the shape of the hull, the openings, the floating position, the center of gravity of the whole ship, and the freeboard curve. Using these side conditions, the program will iterate to find the biggest moment with which the grain criteria will be passed. Note that there are no free surface moments in this list, so when using it, you will have to correct your KG with a free surface correction. It is possible to do grain criteria checks in both the intact criteria task CR_I and in the grain subtask GCR. This is due to historical reasons; at the time the GCR subtask was created, the general intact criteria task was not as flexible as it is today. The main difference is that limiting the allowable grain heeling moment list with intact criteria is only available in the intact criteria task.

6. Relationship between the numbers

6.1 LIST in the grain task

GVOL is the volume calculated from the grain contours, including the voids. GVOLR is the same number but with the steel reduction applied. VOLM is the moulded volume of the compartment, i.e. the room in the arrangement with the same name as the grain cargo space, up to the given height. VNET is the net volume of the compartment For the untrimmed loads, GVOLR is important. For filled and trimmed and partial loads, VNET is the number to look at. DCGY the distance in y-direction that the center of gravity of the load has shifted. GMY/I - the moment of the load initially, i.e. the transverse moment it had before the shift. GMY - the transverse moment of the load after the shift. GRMV - the volumetric grain heeling moment, GRMV = GMY GMY/I. For asymmetric holds, GRMV and GMY will NOT be the same. 6.2 Volumes, weights, centre of gravity, vertical grain shift, etc

According to the grain rule (Part B-1.4), the centre of gravity of untrimmed loads shall be taken to be the volumetric centre of the whole cargo compartment with no account being allowed for voids. When listing the loads in LD, the center of gravity will be that of the compartment in the arrangement, up to the hatch coaming height. The weight of the cargo is however according to the assumption that the grain flows away from the hatch at 30 degrees (i.e. the voids are taken into account). For partial loads, the center of gravity will be that of the load. In these cases, the vertical movement of the center of gravity may be quite large, which makes the stability worse than only the transverse grain shift




would imply. To take this into account, the grain code specifies that the transverse grain heeling moment (GRM) for partial loads is to be multiplied by the factor 1.12. For filled and trimmed holds, the centre of gravity is at the volumetric centre of gravity of the hold. In NAPA that means the centre of gravity of the compartment in the arrangement, measured up to the hatch coaming height. For filled with untrimmed ends loads, the mid part of the section, will be handled like filled and trimmed, i.e. no voids, and forward and aft of the hatch the grain contours are used in the volume calculations. The centre of gravity is at the volumetric centre of the whole cargo compartment. Load Volume VCG GRM Coefficient

Filled and trimmed (F) Cargo hold, up to the coaming height.

Volumetric centre of gravity, up to the coaming height.

1.0

Filled untrimmed (UT) Volume of cargo. Volumetric centre of gravity, up to the coaming height.

1.0

Filled with untrimmed ends (UTE)

Volume of cargo forward and aft of the hatch. Volume of hold abreast of the hatch.

Volumetric centre of gravity, up to the coaming height.

1.0

Partial loads Volume of cargo Centre of gravity of cargo

1.12

The standard methods of calculation are summed up in the table above. For filled and trimmed loads, the rule says that if the administration allows it, you may take the underdeck voids of a filled load into account when calculating the VCG, but you will need to compensate for the vertical shift by using a GRM coefficient. Load Volume VCG GRM Coefficient Filled and trimmed Cargo hold, up to the

coaming height. Cargo with assumed voids taken into account.

1.06

In addition, for these corrective coefficients to the GRM (1.06 & 1.12), the rule allows for any equally efficient method to be used. It is the administration (e.g. classification society) that has the final word in what is equally effective. One such method could be to use the vertical grain shift and correct the heeling arm curve or the GZ curve for the rising VCG. Note When loading grain in LD, capacity (CAP) should be set to 1.0.

7. Changes between Release 2007.2 and 2008.1 During last year, a lot of development has been carried out related to grain calculations in NAPA. In cooperation with some classification societies, we have verified the grain calculations of NAPA against results calculated by hand and results obtained from other software products. In the process, some sources for




inaccuracy were identified, and some interpretations have been changed to be better in line with the interpretations used by the classification societies. As a result of this, there will be differences between the results calculated with 2008.1 compared to older versions of the program. Here are the most important changes; the complete list can be found in the Update Information delivered with the Online Manuals of the new program. 7.1 Changes that may affect calculation results or backwards compatibility

7.1.1 Grain shift moments in LD

NAPA Releases from 2006.1 to 2007.2 contain a bug which causes them to calculate too large grain shift moments in LD for the filled conditions. These programs have incorrectly adjusted the GRM for the volume of the voids in any filled and trimmed part of a load. This has been corrected in Release 2008.1, and it will be visible in the calculation results. 7.1.2 Void depth calculations

When deciding void depths, the standard void depths are selected from a table based on the distance from the hatch to the boundary of the compartment. Previous versions of NAPA have used the distance from the hatch to the void, not to the compartment boundary. In 2008.1, the default method is like the rule says, from the hatch end or hatch side to the compartment boundary. This change will affect void heights. For backwards compatibility reasons, the old interpretation is still available in the program. There is the new command FMODE which can be used to tell how the program determines feeding distances. "FMODE old" will make the void depths act like before while "FMODE standard" will make the program calculate by the book. 7.1.3 Feeding distance and upper stool tanks

The feeding distance in x-direction should be the distance from the hatch beam to the boundary of the compartment. Previously, this has been implemented so that the maximum distance between the compartment end and the beam has been used. Now, the distance is measured just below the deck level. This has an effect on the depth of underdeck voids in cases where there are upper stool tanks.

Figure 17 Feeding distance with upper stool tanks

7.1.4 Voids under stools

In previous versions of the program, the hatch end beam has affected the depth of the voids below the upper stool tank, which it should not do in cases where the upper stool is deeper than the hatch end beam. This has been corrected and it will be visible in the calculation results for ships with upper stool tanks.




7.1.5 Void depths in fore and aft hatch configurations

In ships with two hatches on the same deck leading into the same cargo hold, the void depths between the hatches were incorrectly determined by using the distance between the hatches as the feeding distance, and the lesser depth of the girders. According to the grain code, the distance should be the distance to the midpoint between the hatches, and the aft hatch feeds from aft to halfway, and the forward one from halfway to the forward hatch. This has now been corrected. This is a very rare case; the vast majority of ships carrying grain have one hatch per hold. 7.1.6 Hatch coaming height

There is the new possibility to define the height of the hatch coaming when doing hatch definitions. Previously, there has been some confusion about whether ZC is the height of the cover or the coaming; now, there are three heights that can be given: Maximum load height (ZL), Hatch coaming height (ZCOAM) and Hatch cover height (ZC). This is covered earlier in this paper. 7.1.7 Control of alternative calculation methods

Until this release, the type of a grain load should be GRX. Setting it to GR changed the behaviour (center of gravities, volumes, percentages, etc). This caused a lot of confusion, and many users made mistakes when using these settings. From release 2008.1 onwards, any load with a type starting with GR is considered a grain load. The settings for how the load is calculated, i.e. which center of gravity should be used, and what coefficient to use are set in the grain task, using the PARAMETERS command. The PARAMETERS command can be used to get the program to calculate incorrectly, so if you are not sure what you are doing, leave the parameters to the default values. If you want to make sure that the settings are the default ones, run the command GS?>PAR CANCEL This will reset the default settings. 7.1.8 Grain feeding holes compatible with tween decks and multiple hatches

Now grain feeding holes on hatch end beams can be defined also on tween decks. Previously, they could only be set for the highest deck. Note that the feeding hole command must be given after the hatch you want it to affect, while in previous releases it always affected the main deck. 7.1.9 DESCRIBE command (DES)

The DESCRIBE command has changed so that it is generated from the grain cargo hold definition. The code analyzes the grain cargo space and generates the commands that would create such a hold. Previous releases recorded what you wrote in the GCS?> subtask and the DES command repeated it. This change was necessary as grain cargo spaces can now be defined by using service functions. 7.1.10 Assigning variables

Previous release of NAPA has assigned a lot of global NAPA Basic variables when running grain calculations. There has been no way to turn it off. Now there is the ASG command in the grain task for controlling whether to assign these variables or not. This may affect old macros, so that you have to turn ASG ON in the beginning of the macro.




7.2 New features

7.2.1 Permissible heeling moments list limited with intact criteria

The permissible heeling moments list can be limited with intact criteria, so that combinations of KG and draught that do not pass an intact criteria will not get any permissible grain heeling moment. 7.2.2 New alternative layout for permissible heeling moments list

There is a new list command in the GCR task. The LIST PHM command will produce a list with the same kind of information as in the normal permissible heeling moments LIST, but it shows which criteria it is that limits the allowable moment. T DISP ZCG GM 12 deg Area m t m m tm tm 10.000 43889.4 10.00 2.282 23788.2 64779.7 10.000 43889.4 11.00 1.282 14080.5 33990.2 11.000 48623.4 10.00 2.224 25584.7 53616.0 7.2.3 New plotting options

PLOT Z There are lots of new marking options. These can be turned on and off by using the options to the command. Plotting girders in x projection, more markings and improved placement of markings. 7.2.4 Functionality supporting macros

There are new service functions for modifying grain cargo spaces. These come in handy if you are using macros or Manager applications to define the grain cargo space. LD service functions can be used to obtain information about the grain heeling moment and the allowable grain heeling moment for a loading condition. 7.2.5 Miscellaneous

Heeling to port and starboard side when checking the criteria or doing allowable grain heeling moments lists. The updating mechanism has been improved so that the recalculation is done when something has changed. There may still be issues, if in doubt whether the calculation has been carried out, run the CALC command for the hold in the GS task.

8. Acknowledgements The authors would like to thank Brian Parkinson from Lloyds Register for his help in the development of NAPAs Grain Stability sub-task and for providing material for the verification of the results of NAPAs grain stability calculations.

grain (2)

Documents

grain calculations

grain load

actual grain

allowable grain

grain rule

grain cargo space

grain shift moment

mattsson napa user meeting