Last-in, First-out (LIFO) cumulative *major* change history & manual errata; 1994-present. Numerous miscellaneous bug fixes, improvements and online help additions have not been listed. >>> Note: Each simulation's on-line documentation contains the most current information and should always be consulted first when questions arise. This is a listing of modifications, many of which are "invisible" to the user (i.e., code changes not reflected by a change in editor/input pages) but that may have an indirect effect on output *values*. This is the first place to look for the "culprit" responsible for any mysterious differences in output values of two simulation versions with the same data file used as input. In general, such differences should be small; code changes which produce significant differences (and their expected effects) will normally be outlined in detail in documentation acompanying the upgrade. Any time significant output changes are noted between a new version and the version it replaces, and these changes are not adequately explained in the acompanying documentation, you should alert SeaSoft. 7/15/96 - Create "buydyn.f" to evaluate quasi-static wave force, mooring force & moment equilibrium in Moorsim/SPMsim/CALMsim. This routine was originally intended as a debugging aid but was incorporated for its potential usefulness to end users. It produces a Catsim-type "OFFSETS" file giving the quasi-static state of the mooring system for 37 instants in a regular wave cycle of the "extreme" anticipated regular wave (in 10 degree phase shift intervals). The "quasi-static state" comprises an instantaneous force & moment balance between the regular wave pressure field and mooring restoring forces, centered about several low-frequency offset points of interest (mean offset point, extreme low-frequency offset point, etc.) When irregular waves have been specified (the most common situation), this "extreme regular wave" is a regular wave whose period equals the spectral peak period and whose *amplitude* is that of the "maximum" expected wave crest (i.e., 1.86 times the significant wave *height* for the specified irregular waves). This feature is currently unsupported in the sense that any errors in implementation will only be corrected on the lowest "time available" priority. ------------------------------------------------------------------------------- 6/15/96 - Implement automatic output of editor input (SHIPIN, MOORIN, etc.) when "E"xecuting any simulation. ------------------------------------------------------------------------------- 5/30/96 - CALMsim code modified to accommodate semisubmersible-type buoys. ------------------------------------------------------------------------------- 5/07/96 - Set Creator to QED1 (QUED/M) for all text output files ------------------------------------------------------------------------------- 5/03/96 - Display "oblique offset definitions" option when continuous equilibrium offset sequences requested in Catsim ------------------------------------------------------------------------------- 05/01/96 - Rework wave-frequency line dynamics algorithms to improve treatment of large wave-frequency fairlead motions in highly nonlinear systems. The modifications were made to correct an inadequacy in the original linearization of static/catenary-type line load variations; basically, the linearization was inadequate in conditions of large w.f. fairlead motions and highly nonlinear catenary conditions (shallow water, high pretension, taut heavy lines, etc.) The main things to notice are: 1. Nontrivially higher wave-frequency individual line loads in the "upper bound" algorithm for "tight" systems sampling a highly nonlinear part of the force-vs-offset curves (e.g., high pretension or large low-frequency motions in shallow water moors) 2. Because wave-frequency line loads are more or less in phase from line to line, net vessel wave-frequency loads are also larger under these conditions. 3. Not much difference should be noticed for "loose" or "nearly linear" catenary systems (elastic lines, deep water systems, etc.). ------------------------------------------------------------------------------- 4/23/96 - Add output line for mean tension value at l.f. offset point for "data at specified low-frequency output point" option in RANOUT ------------------------------------------------------------------------------- 4/17/96 - Catsim-type vertical interpolation level specification added to SPMsim/Moorsim/CALMsim supporting newly implemented finite-amplitude wave-frequency line load algorithms to replace the earlier small-amplitude approximations. See on-line documentation. ================================================================================ >>> 1995 11/1/95 - Catsim now permits "continuous equilibrium" offsets to be applied to buoy/hawser/tanker CALM-type configurations. See on-line documentation. ------------------------------------------------------------------------------- 9/7/95 - Add keel option and associated added-mass dynamics modifications for buoys (Discsim); incorporate square-law heave damping to supplement wave damping. ------------------------------------------------------------------------------- 7/1/95 - Change to new ppc development environment using Macintosh Programmers Workshop. No direct effect on end users except output text files have MPW as creator. The new development system produces single, monolithic applications that no longer need access to the "Subroutines" folder as did the last "official" version of SeaSoft (delivered in late 1994 and updated in early 1995). ------------------------------------------------------------------------------- 6/01/95 - The "NSMB '91" current coefficients have been further adjusted to reflect recent changes made in the coefficients by NSMB. These coefficients still may not be in their final form; however, they should be close... ------------------------------------------------------------------------------- 5/1/95 - Moorsim/SPMsim/SALMsim/CALMsim now have completely user-specifiable vessel wave-drift characteristics and vessel RAOs; see on-line documentation and Moorsim/SPMsim Appendix D update. ------------------------------------------------------------------------------- 4/15/95 - Moorsim/SPMsim/SALMsim/CALMsim/Slowsim now have a user-specifiable variable wave drift spectral enhancement factor in addition to the steady wave drift enhancement factor; see on-line documentation. ------------------------------------------------------------------------------- 4/1/95 - Accommodate user specification of "natural" center vs. "cg" for moments/motions reports in Shipsim/Discsim/Semisim; see on-line documentation. ------------------------------------------------------------------------------- 3/1/95 - Moorsim/SPMsim/Catsim/CALMsim have an expanded list of built-in chain and wire rope line types, including Brydon Spiral Strand, Ramnas ORQ, Studless Chain; see on-line documentation. ================================================================================ >>> 1994 8/14/94 - Current Coefficient updates: Slowsim, Moorsim, SPMsim, CALMsim, SALMsim A series of current measurements were taken at NSMB, ending in 1991, which were the source for at least two preliminary NSMB reports (in 1991 and 1993) and one final OCIMF report (in 1994) released to update the original 1977 OCIMF report. The final (1994) OCIMF report contained only a subset of the data contained in the preliminary reports. The SeaSoft implementation of these 1991 measurements is a subjective composite of the data presented in all three (two preliminary, one final) reports. Therefore, slight but noticeable differences exist between the SeaSoft coefficients and those presented in the final (1994) report, and some data, such as that for the "Extreme Cylindrical" bow type, are not to be found in the final OCIMF report at all. Note that the OCIMF/NSMB measurements were made on tankers with L/B ratios between 6.3 & 6.5, while modern tankers have L/B in the 5.0 to 5.5 range. The 1993 OCIMF report notes that the longitudinal coefficients tend higher with decreasing L/B for vessels wider than those measured. Increases of 25% to 30% for small (< 15 degrees) vessel-relative current angles are noted in the report. Adjustments to the head-on current bow areas can be made to accommodate this effect, if desired. The two OCIMF reports (1977 & 1993/4) used different nomenclature and sign conventions for the "attack angles" and Cx, Czz. SeaSoft uses yet a different convention for the scaling of Cx; when comparing Slowsim output with OCIMF data, these differences must be taken into account. Also, the SeaSoft implementation of the later (1991) data is a composite of information, not all published in the final OCIMF 1994 report The later OCIMF report used the FULLY LOADED vessel draft when reporting the water depth/draft parameters (called WD/T in the report) even for the 40% loaded curves. Consider, for example, a tanker with a design loaded draft of 15 meters in a 40% of loaded draft condition (i.e., with simulation draft of 6 m). In 30 meters of water, the ACTUAL depth/draft ratio is 30/6 = 5.0; however the appropriate depth/draft PARAMETER for use with the 1993 OCIMF data would be 30/15 = 2.0; therefore the appropriate OCIMF curves for this example would be the 40% load condition with WD/T = 2.0. Note that with this parameter definition, WD/T parameters < 1.0 will occur whenever a vessel, in a light loaded condition, is in water whose depth is less than that vessel's fully loaded draft. In simulating such a condition, the minimum parameter value (WD/T = 1.1) will be used by the simulation. SeaSoft now documents in the LOWOUT and SLOWOUT streams the OCIMF depth/draft PARAMETER used whenever the NSMB 1991 current database is in use. ------------------------------------------------------------------------------- 6/28/94 - Incorporated individual mooring line and mooring system potential energy calculation into Catsim. This will be used in the future in support of transient analyses of individual line failures. The updated Catsim program permits evaluation of individual mooring line and total system potential energy for requested offset sequences. This capability will be especially useful in visualizing the mooring asymmetry produced by the failure of individual lines and can be used in estimating the transient loads produced by individual line failures in a wide variety of circumstances. The energy units are kip*ft or ton*meter, depending on the system of units (English or metric) in use. The total system potential energy can be used to determine the transient overshoot, assuming zero system damping, when the system is displaced away from equilibrium in one direction and is allowed to swing back and overshoot to the opposite side of equilibrium. The neglect of system damping produces a conservative result that is useful in setting an upper bound to the maximum possible low-frequency transient associated with the failure of a single mooring leg. This information may then be used in conjunction with one of the comprehensive simulations (SPMsim, Moorsim, etc.) in order to estimate the total transient loads (comprising transient low-frequency + environmentally-excited low- and wave-frequency loads). ¥ Known problems: The energy calculation may fail to function properly in some systems containing large buoyant elements. These systems will be characterized by the following warning issued during execution: >>> Buoyant line handling error. Anchor distance in first row ONLY of interpolation table may be slightly in error Even for this class of systems, the energy calculation will be usable for any offset sequences which DO NOT require interpolation on the first row of the affected interpolation table(s) at any offset value. The problematic energy calculation for this small class of systems is currently being reviewed for further possible improvement. ------------------------------------------------------------------------------- 3/21/94 - Modified static interpolation algorithms to accommodate surface-resident buoys of the type commonly found in near-shore terminal installations used for vessel-to-shore crude oil transfers. Affected simulations are: CALMsim, Catsim, Moorsim, SPMsim. Affected support routines are: mrstat.sub, lindrv.sub, qdamp.sub, ldamp.sub, ranlin.sub, dynlin.sub, snpout.sub, CLMTOP.sub, SPMTOP.sub, MORTOP.sub, CATTOP.sub. New assigned version numbers are 3.69 (SPMsim, Moorsim), 1.39 (CALMsim), 1.49 (Catsim). Surface-resident buoy notes: 1. As before, the buoy is treated as a user-definable flexible, buoyant element. The " vertical position" of this distributed element is defined as the AVERAGE of the vertical positions of its two end points. This convention was adopted for algorithmic convenience. In the limit of an extremely short buoyant element, of course, all reasonable conventions (for example, the choice of element midpoint to define the vertical buoy position) lead to identical results. 2. Only the buoyant element closest to the fairlead is constrained to lie on or beneath the surface. Any additional anchor-side buoyant elements are assumed to remain below the water surface under all conditions and are not tested for surface proximity. The vertical end point table in the static interpolation stream (in MOOROUT, SPMOUT, CALMOUT, CATOUT) can be consulted to check that in fact other anchor-side buoys remain below the surface. 3. The surface-resident option applies to Catsim, CALMsim, SPMsim and Moorsim. 4. Statmoor has not been changed in any way by these modifications; Statmoor has always had surface-resident buoy handling capability, although it is implemented in a vastly different way in Statmoor than in the other simulations. For example, the "buoy" option in Statmoor assumes a "point" buoy with no physical size. To compare output for the same system between Statmoor and Catsim, therefore, the surface buoy in Catsim should be simulated by an extremely short buoyant segment; say .01 feet or meters. 5. Choice of surface-resident buoy algorithm occurs on the "General Mooring Information" page (screen page 2 in Moorsim/SPMsim/Catsim). ------------------------------------------------------------------------------- 1/21/94->1/26/94 - Fine-tuned iteration failures in qstat.sub. Prompted by (1) a weakly stable case that had problems finding an equilibrium searching near an UNSTABLE equilibrium point and (2) to better accommodate wharf moorings. 1/14/94 - The quasot.sub file was modified to fix a bug affecting Moorsim/SPMsim data files possessing more than a single line TYPE. 1/12/94 - The vesl2.sub file was modified to correct a bug introduced into CALMsim and Towsim by recent software modifications. The effect of this bug was to produce anomalously low hawser/towline wave-frequency loads and hawser/towline endpoint relative motions. Only the wave-frequency component of the total loads were affected by the bug.