sections description can be augmented manually provided that all the involved ..... The file is intended for plotting time histories using Tecplot or the special ...
Dynamic Ship Loading Estimation Code: Description of the Program SLAVIB S. Sutulo 2003
The Fortran 90 program SLAVIB computes time histories of the dynamic and equivalent static vertical loads on the hull of a surface ship running at constant speed across an irregular seaway. The program is supposed to be used together with a slightly modiﬁed version of the program STRIP . We shall designate this modiﬁed version as STRIPmod and all the alterations will be described here but most of the description  remains valid and it is supposed to be used together with the present one. Also, an auxiliary program SLAMVORM based on the EUMEDES system  is used for preparing a hull description ﬁle used by SLAVIB.
Used Methods and References
The program SLAVIB performs time-domain simulations of hydrodynamic loads (including nonlinear contributions and slamming), static loads, shear force, bending moment and equivalent statical loads resulting from hull girder vibrations (both springing and whipping). Remarks on the terminology. Throughout this document, the terms “station” and “section” are used as meaning the same (a plane or a contour), as opposed to “strip” or “slice” which mean a piece of ship hull between two neighbouring sections. The program SLAVIB uses transfer functions for relative displacements of sections computed before the simulation by the program STRIPmod. The method is described in .
In the general case, three executable ﬁles must be created: slamvorm.exe (program SLAMVORM), stripmod.exe (program STRIPmod) and slavib.exe (program SLAVIB)1 . First, the preliminary hull discretisation program SLAMVORM must be run. Then, to estimate the loads with account for nonlinear eﬀects and vibration, it is necessary to do the following (it is supposed that all the required input data ﬁles already exist, except for wave length and direction data): 1. The program SLAVIB is run in the preliminary mode (see the description of the input ﬁles). No simulation is then carried out, but the sets of random wave encounter angles and wavelengths, and the sections’ abscissae are obtained as result 2. The arrays of angles and wavelengths contained in ﬁle waves.dat and the array of the sections’ abscissae (ﬁle relmcoor.dat) are copied into the input ﬁle indata.dat for the program STRIPmod at the appropriate locations (angles near to the beginning, wavelengths near to the end, abscissae preceeding the wave lengths) 3. The content of the ﬁle strip sections.dat containing the description of the hull for the program STRIPmod is put in the ﬁle indata.dat replacing the corresponding data already contained in this ﬁle. Also, the number NX of the sections in the preceeding line (preceeding the draught) must also be corrected if necessary. Remark. The sections data produced by Slamvorm can omit some sections if they are not connected (that is consist of more than one part). In the case of need, the sections description can be augmented manually provided that all the involved numbers of sections etc. are corrected accordingly. 4. If necessary, the content of the ﬁle strip absc.dat must be used to replace the list of sections’ abscissae and integer ﬂow separation indicators in the ﬁle indata.dat. 5. The program STRIPmod is run. It produces a ﬁle containing the sectional transfer functions. 6. The program SLAVIB is run in the main mode to perform the simulation. It reads the transfer functions produced by STRIPmod and reproduces the process in the time domain.
Intermediate Files Handling
The ﬁles are only mentioned in this subsection to facilitate data management. More detailed description of all the ﬁles is given in the following sections. 1
e.g. by commands like ‘‘f90 slamvorm.f slamplot.f90 -O -o slamvorm.exe’’; ‘‘f90 stripmod.for -O -o stripmod.exe’’; ‘‘f90 meinslavib.f90 -O -o slavib.exe’’.
SLAMVORM—SLAVIB (preliminary run)
If both programs are located in the same directory, nothing must be done. Otherwise— the ﬁle hullshape.dat must be copied or moved from the SLAMVORM directory to the SLAVIB directory. 3.2.2
SLAVIB (preliminary run)—STRIPmod
The content of the following ﬁles must be copied into the ﬁle indata.dat replacing the corresponding data: 1. File waves.dat 2. File relmcoor.dat 3. File strip sections.dat (or similar ﬁle with the name indicated in slamvorm.dat) 4. File strip absc.dat (or similar ﬁle with the name indicated in slamvorm.dat 3.2.3
STRIPmod—SLAVIB (main run)
If both programs are located in the same directory, nothing must be done. Otherwise, the following ﬁles must be copied or moved from the STRIPmod directory to the SLAVIB directory: 1. File addmass.dat 2. File raos slam.dat 3. File raos hvpt.dat
Program SLAMVORM General Information
Primarily, the program SLAMVORM is aimed at generating a uniform grid discretisation of the ship’s hull with given spacings along the ship’s length and height. It is based on the ship geometry handling system EUMEDES  and is in fact a development and a combination of two similar hull shape preparation programs SLAMVOR  and DITCHVORBEREIT, and of the plotting program DITCHKOERPERPLOT . Also, this program produces the hull description for the program STRIPmod (this part is based on the program STRIPDATA).
The main source code of the program is contained in the ﬁle slamvorm.for and three subroutines belonging to the module Plotting are located in the ﬁle slamplot.f90. 3
All the input ﬁles are read in free format and the data are separated with spaces or line ends. 4.3.1
Input File “slamvorm.dat”
This ﬁle is primary and contains certain conﬁguration information and data to be transfered to some of the output ﬁles although not used by the program itself. text — CHARACTER: a description of the object placed inside single quotes (not longer than 120 symbols including spaces) which will be used throughout all the computations len — REAL: the ship’s length in m drt — REAL: the ship’s draught in m trim — REAL: the ship’s trim in meters (positive by the stern) nx — INTEGER: the last section number (ﬁne grid); the ﬁrst one is 0; 200–400 recommended nz — INTEGER: the last waterplane number; the ﬁrst one is 0; 400–600 recommended dx — REAL: the desired sections spacing in m dz — REAL: the desired waterplanes spacing in m x0 — REAL: the most aft section’s abscissa (section No. 0) in m z0 — REAL: the lowest waterplane’s applicate (waterplane No. 0) in m nx1vib — INTEGER: the last section number (spacing for vibrations calculations); the ﬁrst one is 0; 50 recommended (the program Slavib requires only that nx1vib ≤ nx, but it must also match the capabilities of STRIPmod) nmin — INTEGER: minimum number of segments per section in STRIP calculations smax — REAL: maximum length of a segment in STRIP calculations, m (1 m recommended) infile name — CHARACTER: the name (not longer than 40 symbols) of the input ﬁle containing primary information about the hull’s shape prepared according to the system EUMEDES (a eum-type ﬁle) outfile name — CHARACTER: the name (not longer than 40 symbols) of the main output ﬁle containing the hull form description required by the program SLAVIB. If the file is supposed to be read immediately by the program SLAVIB, its name must be ’hullshape.dat’
stripout name — CHARACTER: the name (not longer than 40 symbols) of the ﬁle containing the hull form description required by the program STRIPmod (the name strip sectons.dat assumed in this description) stripout1 name — CHARACTER: the name (not longer than 40 symbols) of the ﬁle containing the list of the abscissae of the sections described in the previous ﬁle together with corresponding integer ﬂow separation indicators ( 0 is put everywhere; the name strip absc.dat assumed in this description) preplot name — CHARACTER: the name (not longer than 40 symbols) of the postscript output ﬁle representing a plot of the body lines according to the primary EUMEDES description postplot name — CHARACTER: the name (not longer than 40 symbols) of the postscript output ﬁle representing a plot of the body plan created from the ﬁle with the name outfile name (see above) stripplot name — CHARACTER: the name (not longer than 40 symbols) of the postscript output ﬁle representing a plot of the body plan created from the ﬁle with the name stripout name (see above). 4.3.2
Input File “*.eum”
The actual name is deﬁned in the ﬁle slamvorm.dat (ishi.eum in the supplied example for the Ishiguro ship. The description of the content of this ﬁle can be found in .
Output Files Output File “hullmon.dat”
1. File hullmon.dat—EUMEDES intermediate results (see ) 2. File striplog.dat—record of forming data for STRIPmod. . 4.4.2
Main Output File
This ﬁle is supposed to have the name hullshape.dat, serves as an input ﬁle for SLAVIB and is described in detail in the section dedicated to this program. However, its name is deﬁned in the ﬁle slamvorm.dat and can be temporarily diﬀerent from the indicated above (it can be then possible to create several hull shape ﬁles with diﬀerent names and to rename then one by one for further use).
Postscript Output Files
The names of these ﬁles are also deﬁned in slamvorm.dat. In the supplied example, the ﬁrst one has the name preplot.ps and produces a plot of body lines according to the input ﬁle *.eum. The second ﬁle (named ishi 400 600 postplot.ps in the example) plots the ﬁne grid control body plan created from the ﬁle hullshape.dat. The third ﬁle (named ishi stripplot.ps in the example) plots the body plan corresponding to the discretisation used by STRIPmod.
Recommendations on Setting Discretisation Parameters
It is recommeneded to set nx=200--400 and nz=400--600 for most hull forms (more detailed guidelines can be found in ). The spacing dx must be chosen in such a way that nx ∗ dx = len − ε where ε is a small distance which can be taken as, say, 5 mm for a 200 m ship. That is, the most forward section must be very small but with non-zero area. The succes of the choice of the parameters can be checked with the help of the post plot and approriate corrections can be introduced if necessary. The waterplanes spacing dz must be deﬁned in such a way that nz ∗ dz = H where H is the height up to which the hull must be described. The maximum possible value of H can also be extracted from the eum-ﬁle.
For the description of the original program STRIP see . Here only the changes of that program and the input and output ﬁles are described.
The part of the program STRIP dealing with the ship in natural seaways does not make sense in connection with slavib. Thus for this application the ﬁrst 3 data values of the input ﬁle should be 1 1 0. Some of the changes made were necessary to adjust the program to the needs of SLAVIB, whereas others were required by one of the used platforms (Microsoft Fortran PowerStation 4.0): 1. The exploitation of the symmetry principle at setting the wave directions was abandoned: the program computes the transfer functions for the indicated wave encounter angles. 2. Transfer functions of the sections’ relative motions are written into a separate ﬁle. 3. Further, heave added masses for the highest frequency are output. 4. OPEN statements deﬁning the ﬁle names given below were added. 6
5. A few changes not aﬀecting the algorithm were introduced to circumvent the used compiler’s deﬁciencies.
The source code of the program is contained in the ﬁle stripmod.for. The input data ﬁle (the stream unit=5) is named indata.dat. See  for its contents. The program creates the following output ﬁles: 1. File hydro_human.dat (original: unit=7) contains the computed hydrodynamic section characteristics including text. 2. File hydro_comp.dat (original: unit=20) contains the same results without text as input for other program parts. 3. File raos_human.dat (original: unit=6) contains the computed transfer functions and response amplitude operators with text. 4. File raos_comp.dat (original: unit=21) contains the same results without text. 5. File raos_spec.dat (original: unit=23) contains other transfer functions (see  for comments). 6. File raos_slam.dat (additional: unit=24) contains the computed relative-motion transfer functions of sections without text to be used by SLAVIB. 7. File raos_hvpt.dat (additional: unit=26) contains the computed heave and pitch transfer functions without text to be used by SLAVIB. 8. File stat_human.dat (original: unit=8) contains statistical results on ship motions in a natural seaway with explaining text if such calculations have been speciﬁed in indata.dat. 9. File addmass.dat (additional: unit=25) contains high-frequency vertical added mass data to be used by SLAVIB.
Program SLAVIB General Characteristics
The program SLAVIB was designed to match as much as possible the program STRIP. It uses the same co-ordinate systems Kξηζ and Kxyz (see ); i.e. the axes are directed respectively ahead, to starboard, and down, and with the origin K lying in the midship plane on the keel. However, the use of Fortran 90 and a somewhat diﬀerent design philosophy resulted in a diﬀerent program structure: all the procedures are organised in modules (which can be contained in separate ﬁles). 7
Due to the use of dynamic allocatable arrays, there are no explicit constraints for the number of sections, wave components etc., although physical memory limits still apply. However, as SLAVIB is supposed to interact with STRIPmod, the latter program’s limitations must be respected. As the program is supposed to be used mainly for full-scale estimations, all the forces are represented and output in kilonewtons and all the masses in tons. However, the program can be also used for model-scale calculations without danger of loosing accuracy as all the real and complex constants and variables are deﬁned with double precision.
Source Files and Modules
SLAVIB’s source code is organised in ten modules which may be and were originally contained in ten ﬁles: 1. File genconst.f90: contains the general constants (including the water density, Young’s modulus etc.) and types deﬁnition module GenConst. 2. File wspecdon.f90 — Donelan’s WaveSpectrumDonelanModule
3. File process.f90 — the irregular sea process modeling module ProcessModeling; uses the module GenConst 4. File geometry.f90 — the module Geometry performs the hull shape input and related preliminary calculations; uses the module GenConst. 5. File auxfuncs.f90 — the auxiliary functions module AuxFunctions; uses the module GenConst. 6. File filters.f90 — the module FiltersV contains the Butterworth ﬁlters code (the vector/array variant); uses the module GenConst. 7. File filtersca.f90 — the module Filters contains the Butterworth ﬁlters code (the scalar variant); uses the module GenConst. 8. File massmode.f90 — the module Vibration supports the vibrations analysis; uses the modules Geometry, AuxFunctions, and ProcessModeling. 9. File impact.f90 — the largest module Impact contains procedures modeling nonlinear hydrodynamic loads (including slamming); it supports the process simulation and most of the output; uses the modules GenConst, Geometry, AuxFunctions, ProcessModeling, FiltersV, Filters, Vibration. 10. File slamtest.f90 — the calling programme SLAVIB; it uses the module Impact. However, in the supplied version, all the listed ﬁles are merged together into the single ﬁle meinslavib.f90. In case of need, the ﬁle can be split back into several ones (not necessarily, identically to the primary partition) but one must be aware that the module structure requires a certain compilation order. 8
The input ﬁles are read using the * (free) format; i.e. the data in there must be separated from each other either by a space or by an end-of-line. 6.3.1
Input File “simulation.dat”
The ﬁle (unit=if_simul=3) is supposed to be created by the user. It contains main parameters determining the simulation process. It is read by the subroutine WaveReadAllocate (module ProcessModeling, ﬁle process.f90). Read are the following variables: irregular — LOGICAL: T for irregular sea, F for a regular wave (auxiliary mode). In the latter case the program simulates not exactly for the wave data speciﬁed in ﬁle spdwave.dat, but for the most similar regular wave used by the program Stripmod. reproduce — LOGICAL: T if the RANDOM_SEED subroutine is not activated, meaning that the same wave process will be simulated at every run; when reproduce=F, diﬀerent sample processes will be generated in each run mode — INTEGER deﬁnes the program mode: 0 at the ﬁrst (preliminary) run to generate random values for wave angles and wave lengths, skipping the simulation; and 1 for a simulation. The latter requires that STRIPmod were run before dt — REAL: “Main” time step in the simulation (in s). 0.005–0.01s was found appropriate for a ship for which L/V = 20 s and the natural heave period about 7 seconds; no adjustment is needed in most cases as the input integration step is automatically modiﬁed by the program in accordance with the actual estimated natural heave period but sometimes smaller steps can be necessary for short and fast vessels pfc — INTEGER: Printing FaCtor; i.e. number of time steps between any two consecutive process outputs vzn — INTEGER: Vibration Zoom Number; i.e. number of time steps dt1 used for the vibration simulation which are contained within a single “main” time step; 20 was found appropriate tm_stop — REAL: Simulation duration (s) thrpar — REAL: Nondimensional slamming threshold ix_first — INTEGER: Smaller station (strip) number for which the processes will be output ix_last — INTEGER: Larger station (strip) number for which the processes will be output
Remark. The parameters ix_first and ix_last vary from 1 to nx1 as deﬁned in the ﬁle massdis.dat. The number of strips used in the vibrations analysis nx1 can be substantially smaller then the corresponding number nx deﬁned in the ﬁle hullshape.dat and used for hydrodynamic loads computations. The ﬁle (unit=if_geometry=10) is created automatically by the program SLAMVORM and normally doesn’t need any manual interference. It contains a description of the hull shape by a large number of half-breadths. The ﬁle is read by the subroutine ShipReadAllocate (module Geometry, ﬁle geometry.f90). It must contain the following data: ship_id — CHARACTER(120): text, e.g. for ship identiﬁcation, placed between quotes len — REAL: ship length between perpendiculars in m drt — REAL: ship draught at midship section in m trim — REAL: ship trim (positive by the stern) in m. nx — INTEGER: last station number; the ﬁrst one is 0 nz — INTEGER: last waterline number; the ﬁrst one is 0. dx — REAL: spacing of stations in m dz — REAL: spacing of waterplanes in m x0 — REAL: x coordinate of station no. 0 in m z0 — REAL: z coordinate of waterplane no. 0 in m (normally 0) nx1vib — INTEGER: last station number in the coarse sectionning used in vibrations and ship motions calculation; the ﬁrst one is 0 ix_strip_start — INTEGER: ﬁrst submerged section number in the coarse sectionning used in vibrations calculation: the aft sections with smaller numbers can stay completely out of the water in the given equilibrium position and these are disregarded in ship motion calculations performed by STRIPmod nx_strip — INTEGER: number of sections involved in the ship motions performed by the program STRIPmod: the spacing is the same as used in vibrations analysis but dropped are sections which are not submerged in equilibrium state and the sections with unconnected contours (i.e. consisting of more than one part that is typical for bulbuous bows) use_input_keel — INTEGER: code for the keel line deﬁning method: 1 if the keel line is deﬁned by the array which then follows; 0 if the keel line is generated by the program automatically (most typical). k_v — REAL(0:nx): array describing the keel line in the used coordinate system (must only be present when use_input_keel==1); y_m — REAL(0:nx, 0:nz): two-dimensional array of halfbreadths of the ship hull in m. The inner loop is over the waterlines, the outer one over the stations. 10
Input File “massdis.dat”
The ﬁle (unit=if_mass=20) is supposed to be created by the user. It describes the ship’s mass distribution over x. It is read by the subroutine MassInitil (module Vibration, ﬁle massmode.f90). It contains the following data: nx1 — INTEGER: this is the same as nx1vib in the ﬁle hullshape.dat i.e. number of strips in vibration calculations and these values must be equal. ms_v — REAL(1:nx1): one-dimensional array of strip masses in t. Their sum must be equal to the ship’s mass. 6.3.3
Input File “addmass.dat”
The ﬁle (unit=if_adms=21) is created by the program STRIPmod. It contains the highfrequency vertical added masses of nx_strip+1 stations starting from the station number ix_strip_start. It is read by the subroutine MassInitil (module Vibration, ﬁle massmode.f90). 6.3.4
Input File “freqshapes.dat”
The ﬁle (unit=if_mode=22) is supposed to be created by the user. It describes the ship girder natural frequencies and mode shapes. It is read by subroutine MassInitil (module Vibration, ﬁle massmode.f90). Read are: nom — INTEGER: number of modes used. Recommendation: 3 or 4. efq_v — REAL(1:nom): one-dimensional array of natural frequencies ω in rad/s mode_m — REAL(1:nom, 0:nx1): two-dimensional array of natural mode shapes in m. Each shape is supposed to occupy at least one line in the ﬁle. The inner loop is over the sections. 6.3.5
Input File “spdwave.dat”
The ﬁle (unit=if_spdwave=1) is supposed to be created by the user. It contains the ship speed and wave data. It is read by the subroutine WaveReadAllocate (module ProcessModeling, ﬁle process.f90). Read are: spd — REAL: ship SPeeD in m/s h13 — REAL: signiﬁcant wave height in m in case of a natural seaway, or wave height in the case of a regular wave t_peak — REAL: wave spectrum peak period in s in the case of natural seaway, or wave period in the case of a regular wave
wanggen_dg — REAL: wave or seaway encounter angle in degrees (0 for following sea, 90◦ for waves from the starboard) wangm_dg — REAL: maximum deviation of encounter angles of wave components from wanggen_dg, in degrees fq_min — REAL: minimum frequency of wave components in rad/s fq_max — REAL: maximum frequency of wave components in rad/s num_fq — INTEGER: number of components of the natural seaway num_wang — INTEGER, the number of diﬀerent encounter angles in the irregular sea simulation. The total number of wave components num_fq*num_wang is determined by the program. 6.3.6
Input File “raos slam.dat”
This ﬁle (unit=if_raos=2) is produced by the program STRIPmod. It contains the frequency transfer functions (FTF) as a list of complex values: (((raorel_sm(i,j,k),k=0,nx),j=1,num_fq),i=1,num_wang), where i distinguishes encounter angles, j frequencies, and k sections. 6.3.7
Input File “raos hvpt.dat”
This ﬁle (unit=if_raos=4) is produced by the program STRIPmod. It contains the frequency transfer functions of heave and pitch motions as a complex list (((raohv_m(i,j,k),k=0,nx),j=1,num_fq),i=1,num_wang).
Output Files Output File “simustat.dat”
This ﬁle (unit=of_stat=500) is the principle output. It is self-explaining and contains ship data and main results of the computation: maxima and minima of loading, shear force and bending moment and the positions where they occur, as well as maxima and minima of the bending moment amidships for both rigid and elastic hull. 6.4.2
Output File “dynforce.dat”
This ﬁle (unit=of_dynf=100) is generated by SLAVIB. Each of its lines contains the following data: 1. Current time tm in seconds 2. Water surface heights at stations ix_first to ix_last 12
3. Total vertical load per length F (sum of statical and wave-induced part) at stations ix_first to ix_last in kN/m The ﬁle is intended for plotting time histories using Tecplot or the special program dynforceplot. 6.4.3
Output File “staforce.dat”
This ﬁle (unit=of_staf=200) speciﬁes the equivalent static loading of the hull girder by the following data: 1. Current time tm in s 2. Water surface heights at stations ix_first to ix_last in m 3. Equivalent static load Fs at stations ix_first to ix_last in kN/m The ﬁle is intended for plotting time histories using Tecplot or the special program staforceplot. 6.4.4
Output File “vibratns.dat”
This ﬁle (unit=of_vibr=300) speciﬁes the vibratory displacements: 1. Current time tm in s 2. Vibratory displacement z(x, t) at stations ix_first to ix_last in m The ﬁle is intended for plotting time histories using Tecplot or the special program vibratnsplot. 6.4.5
Output File “maxvalue.dat”
This ﬁle (unit=of_maxv=400) speciﬁes maxima (along the ship hull) of the load FRB , the shear force and the bending moment and their longitudinal positions: • Current time tm in s • Maximum rigid body load FRB in kN/m • Station number where the maximum occurs • Minimum load FRB in kN/m • Station number where the minimum occurs. • Corresponding 4 results for the total load Fs in kN/m 13
• Corresponding 4 results for the vibratory displacement z in m • Corresponding 4 results for the shear force of the elastic hull in kN • Corresponding 4 results for the bending moment of the elastic hull in kNm • Corresponding 4 results for the shear force on the rigid hull in kN • Corresponding 4 results for the bending moment of the rigid hull in kNm The ﬁle is intended for plotting time histories using Tecplot. 6.4.6
Output File “midbendm.dat”
This ﬁle (unit=of_midb=600) contains bending moments at the midship section: 1. Current time tm in s 2. Relative water surface height at the midhsip section in m 3. Midship bending moment on the elastic hull in kNm 4. Midship bending moment on the rigid hull in kNm The ﬁle is intended for plotting time histories using Tecplot. 6.4.7
Output File “detectn.dat”
This ﬁle (unit=of_detec=84) indicates slam times: 1. Current time tm in s 2. Slamming indicator: 1 if, at any station, the slam criterion is satisﬁed The ﬁle is intended for plotting time histories using Tecplot. 6.4.8
Output File “keelline.dat”
This ﬁle (unit=of_keel=108) contains the z coordinate of the keel line as actually used by the program in the form of a real array in the free format starting from the station 0 and ending with the station nx 6.4.9
Output File “relmcoor.dat”
The ﬁle (unit=of_relative=12) contains the coordinates of nx+1 points along the hull at which the relative motion frequency transfer functions must be computed by the program STRIPmod. The ﬁle contains nx+1 lines and each of them contains the coordinates x, y=0, and z=0 corresponding to each section in their natural order. 14
Output File “waves.dat”
This ﬁle (unit=of_waves=10) gives wave data: 1. Number num_wang of encounter angles of the harmonic wave components 2. Array of the wave angles in degree 3. Number num_fq of wave lengths 4. Array of the wave lengths in m 6.4.11
Output File “mon mass.dat”
This ﬁle (unit=of_mamo=25) contains the following data together with explaining texts: 1. Number nx1 of stations in vibration computations 2. Number of modal shapes nom 3. Ship mass in t 4. Ship mass per length at nx1 stations in t/m 5. Vertical inﬁnite-frequency added mass for the whole ship in t 6. Array of the type REAL(0:nx1) of ship vibratory added mass distribution in t/m 7. Array of the type REAL(1:nom) of natural frequencies in rad/s 8. Array of the type REAL(1:nom, 1:nx1) of modal shapes
Several constant parameters deﬁned in the module Impact (ﬁle impact.f90) can be modiﬁed by a competent user although it is recommended to change the default values only in exceptional cases. 1. The boolean parameter auxiliary_output must be set to .TRUE. if additional output like various force components etc. is required. Default: .FALSE.. 2. The integer parameter ix_out indicates the number of “strips” (from 1 to nx) for which the auxiliary output is provided (only meaningful if auxiliary_output = .TRUE.). 3. The boolean parameter piling is normally .TRUE.. If set to .FALSE., the water pile-up is neglected 4. The real parameter fn_thresh is the section’s immersion threshold Froude number at which the fully developed pile-up is supposed to occur. Default: 0.45.
5. The integer parameter max_num_iter is the maximum number of iterations in the pile-up computations. Default: 20. 6. The integer parameter filter_order is the order of the Butterworth ﬁlter used at computing the entry velocity to smooth the computed slamming force. Possible values: 0 to 4; 0 means no ﬁltering. Recommended: 2 or 3. If the parameter is set to another positive integer (≥ 5), a default RC-ﬁlter is activated. 7. The integer parameter filterv_order corresponds to filter_order, but it refers to the ﬁnal ”presentation” ﬁlter. 8. The real parameter t0_cuf is the reference (related to the natural heave period 7 seconds) cutoﬀ period in s for the Butterworth ﬁlters. Default: 1 second. Other typical options could be 0.5, 2, 4. Bigger (than 1) values can lead to overﬁltering while too small values make the ﬁltering insuﬃcient. The actual cutoﬀ period used during the simulation is however adjusted by the program in compliance with the natural period of heave. 9. The real parameter t0_rlx is the same as t0_cuf but corresponds to the default RC-ﬁlter.
References  S¨oding H. Beschreibung des Programms STRIP. — Institut f¨ ur Schiﬀbau der Universit¨at Hamburg: 1994. 7 p.  S¨oding H. Berechnung der Flugzeugbewegung beim Notwassern. — TUHH: 1999. 18 p.  S¨oding H. User Manual of Programs EUMEDES and ARCHIMEDES II. — TUHH: 2001. 59 p.  Zhou Y., S¨oding H. Berechnung von Stoßkr¨aften auf schnelle Schiﬀe. — Manuscript 1999. 11p.  Sutulo S., S¨oding H. Estimation of Ship Dynamic Wave Loads in Irregular Sea. — Manuscript 2003. 46p.