Loadcases define the loading condition of the vessel. Static weights that make up the vessel lightship are specified here as well as tank filling levels, expressed as either a percentage of the full tank capacity or as a weight.
To create a load case, switch to the loadcase view by selecting Loadcase from the Loadcase sub-menu in the Window menu. Then select “New Load Case” from the File menu or press Ctrl+N. A new load spreadsheet will be displayed in the Loadcase window. The default loadcase will contain a lightship entry and an entry for each tank (with a default filling of 50%).
The tabs in the bottom of the window can be used to skip through the different loadcases in the design.
To avoid rework, an existing loadcase may be used as a template when creating a new loadcase. To do this,
Ø In the loadcase window, select the Loadcase you wish to use as a template
Bring the loadcase
you wish to use as a template to the front
for example by clicking on the tab on the bottom
Ø select File | New
First, you will be asked for a new Loadcase name after which the following dialog appears:
Ø Select yes
A new loadcase will appear in one of the blank (…) loadcase tabs. If there are no blank tabs left, you will either have to close an existing loadcase, or add more loadcases using the Case | Maxi. Number of Loadcases command.
Note
The template is only used during the creation of the loadcase. Once a loadcase has been created from a template loadcase, changes made in the template are NOT automatically changed in the loadcase derived from it.
A loadcase can be given any name by saving it to a separate file where the loadcase filename will be used as the loadcase name and displayed on the tab in the loadcase window. Alternatively,
Ø Select Edit Loadcase from the Case menu
Ø Changing the name in the Loadcase Properties dialog.
The next time you use the File | Save Loadcase command you will be asked to confirm the loadcase file name.
You can load a saved loadcase into your loadcase window by:
Ø Select an empty tab in the loadcase window that you wish to load the loadcase into
Empty tab.
If there are no empty tabs, you should either increase the maximum number of loadcases (see below), or close an existing loadcase.
Ø Select File | Open Load Case
Ø Select the .hml file you wish to open.
The maximum number of loadcases (up to twenty-five) that can be loaded in Hydromax at any one time is set by selecting “Max. Number of Loadcases” from the Case menu. You may then enter the maximum number of load cases you require.
You must restart Hydromax for this change to take effect. In most cases, you will only need to set this once to the maximum number of loadcases you are ever likely to use. For convenience of use, a sensible number is recommended.
Each loadcase can be selected and used for analysis. Each may be saved and loaded independently, effectively allowing you as many loadcases as you require.
Note:
When loading a design that has more loadcases than the maximum you have currently set in Hydromax, you will receive a warning and the file will not be loaded. You must increase the maximum number of allowable loadcases and restart Hydromax before you can load the design.
Ø Select the tab of the loadcase you wish to close in the Loadcase window
Ø Select File | Close Load Case
To add an extra load to the loadcase,
Ø Select Add Load from the Edit menu or press Ctrl+A.
A new load will be inserted into the table above the currently selected row. You can repeat this process for as many loads as you wish.
If you want to remove a load from the table, simply click anywhere in the row you want to remove, and choose Delete Load from the Edit menu (or highlight the complete row by clicking the grey cell to the left of the row and press the Delete key). If you wish to delete several loads simultaneously, click and drag so that all of the loading rows that you wish to delete are selected, then select Delete Load.
Click on the cell containing the load name and type in a name for this load, for example "Lightship", and press the Tab key to go to the next column in the table (or simply click directly in the cell you wish to edit).
For each item in the list you can specify a quantity. This is used to calculate the total weight of that item. For example: if the item was “crew” with a weight per unit, you could specify the quantity and unit weight, and the total weight of crew would be automatically calculated. The weight of each item should be entered in the next column.
The weight must always be positive. If for some reason you wish to have an upward (negative) load, you can do so by entering a negative quantity – this can be useful if you want to apply a pure moment to the model by applying equal magnitude, but opposite sign loads to the vessel in the loadcase.
Tab to the next column and enter the horizontal lever for the item. After you type in this number, press enter and the total LCG will be automatically re-calculated and displayed in the bottom row of the table. The CG position will also be shown and updated in the View windows if Large Angle Stability, Longitudinal Strength or Equilibrium analysis are selected.
Note:
Levers, as with all other measurements in Hydromax, are measured from the Zero Point.
A number of tools are available for controlling the order in which items and tanks occur in the loadcase. You may move selected items and tanks up and down in the loadcase; you may also sort selected items by name, fluid type (for tanks) etc.
Insert row | Delete row | Sort rows | Move row(s) up | Move row(s) down
Sort selected columns
After moving
loads, subtotals and subsubtotals, you may have to use Analysis | Update
Loadcase (
button) to update the subtotals and
subsubtotals. To ensure data consistency, Hydromax does this automatically
prior to running an analysis.
Hydromax allows you to improve the presentation of the Load Case window by adding blank, heading or sub-total lines in the table.
Adding Component or Heading Lines
Components or headings can be included in a load case by preceding the text with a period (.) character.
A blank line can be added into the load case by placing a dollar ($), apostrophe (‘) or full-stop(.) character in the Item Name field.
A subtotal can be displayed for several loads within a load case. To do this the item name field must commence with the word ‘total’ or ‘subtotal’.
Sub-subtotals
Sub-sub-totals may also be inserted. Sub-subtotals must start with the text “subsubtotal”.
Tanks are listed in the loadcase in the order they are defined in the Compartment Definition table. If you wish to change the order in which tanks appear in the loadcase, it is necessary to reorder them in the Compartment Definition table. See: Compartment and Tank Ordering on page 50.
Different colours can be defined for fixed mass items and tanks; alternatively, tanks may be displayed in the same colour as the fluid they contain (As defined in Analysis | Fluids dialog).
Ø View | Colour menu when Loadcase window is frontmost
Distributed loads can be entered in the Loadcase window in the aft limit and forward limit cells. The aft limit and forward limit columns only appear when Longitudinal Strength analysis is selected and the distributed loads will only have an effect on the results in this analysis mode. The “Long. Arm” column defines the longitudinal position of the centre of the load; the fore and aft limits define the longitudinal extents of the load.
If the longitudinal arm is changed in the Loadcase window, the forward and aft limits will be moved by the same amount.
For an evenly distributed load, the centre of gravity should be midway between the forward and aft limits.
Evenly distributed loads. Red = green and divided in the centre.
For trapezium shaped distributed loads the centre of gravity is not midway between the boundaries, but within the middle third 1/3 of the centre.
Trapezium shaped distributed load. Red = Green divided within middle 1/3 of centre.
Note:
Since the load is
distributed as a trapezium, the centre of gravity should lie within the middle
third between the forward and aft limits of the load, at these extrema, the
load distribution becomes triangular.
Tanks will be automatically treated as distributed loads for the longitudinal
strength calculations.
When you create tanks using the compartment definition, they will be automatically included in the loadcases.
Tanks have a quantity value, expressed as a percentage of the full capacity and a weight column. Tank level can be given as either a percentage of full capacity, a sounding or a weight.
The tank Unit Mass is the tanks mass at 100% filling.
When a tank is changed in the Compartment definition table, question marks may be shown in the loadcase momentarily while the tank’s new volumetric properties are being calculated. To update the loadcase for changes in tank loads, select Update Loadcase from the Analysis menu or toolbar.
Updating tank values in the loadcase
Irrespective of whether you have updated the values in the Loadcase Condition, the Loadcase will be automatically updated as the first step of any analysis using the Loadcase information.
Also see:
Update Loadcase on page 155
If the corrected VCG fluid option has been chosen, the Loadcase will sum the free surface moments, divide by the total displacement to obtain the VCG correction and adjust the VCG accordingly to obtain the corrected fluid VCG.
Fluid simulation
If the Fluid simulation option is selected in the analysis menu, no correction is made to the upright VCG. Instead, at every step of the analysis, Hydromax calculates the actual position of the fluid in the tanks taking into account heel and trim, making the tanks’ free-surface parallel to the sea surface, thus the actual vessel CG is recalculated accounting exactly for the static shift of the fluids in slack tanks.
When the corrected VCG method is selected in the analysis menu, it is possible to choose the type of free surface moment to be applied for each tank in a Hydromax Loadcase. The options available are
Maximum
Hydromax will use the maximum free surface moment of the tank in upright condition for all fluid levels.
Actual
Hydromax uses the free surface moment for the current fluid level of the tank in upright condition.
IMO
Hydromax uses IMO MSC75.(69) Ch 3.3 for the calculation of the free surface moment. This method approximates the movement of fluid due to heeling and is based on the fluid shift in a 50% full rectangular, box-shaped-tank. For other shapes and fillings of tanks it will not correctly approximate the free surface moment.
User specified
A user specified value is used for all levels and heel angles.
Note:
All VCG correction methods, except the user specified method, set the free surface moment to zero for fillings < 0.1% and ≥ 98%. This is allowed by classification societies and is an approximation of reality since the tank is almost empty or full and the shift in fluid mass is negligible.