DAC File Format Description

Fatigue User’s Guide > Loading Management > DAC File Format Description

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The MSC Fatigue Loading data file has a binary direct access format with a fixed record size of 512 bytes. It is made up of three distinct regions:

• A header region

• A data region

• A footer region

The Format of the Header Region

The file header is contained within the first record, the first 512 bytes, of each data file. Three types of information are stored:

• REAL numbers, floating point values such as 123.16

• INTEGER (16 bit) numbers, 1234

• CHARACTER strings, such as: Seconds

• INTEGER*4 (32 bit) numbers, 1234.

It is convenient to think of the header as being made up of 128, 4-byte elements, making 512 bytes in all. Data can then be stored in each element according to the number of bytes required for each data type; this storage requirement is detailed below:


Data Type	Example	Storage Requirement (Bytes)	Number of Values per Dump Form Element
REAL	150.65	4	1
INTEGER	10	2	2
CHARACTER	A	1	4

In this region, a floating point number will occupy an entire element; an integer will occupy half an element; and a character will occupy a quarter of an element. Broadly speaking, the header is divided into four main areas where data of similar type are grouped. Element numbers 1 to 32 contain exclusively REAL (floating point information), 33 to 65 contain mostly integer information, 66 to 125 textual information and 126 to 128 again contain real numbers. Details of the contents of each of these areas are provided in the following table:


REAL AREA 1:
Dump Form Element No.		Data Type Stored	Contents of Element
1		REAL	Number of data values in file.
2		REAL	Sample rate for time series data, or for HISTOGRAMS: 1/X-axis bins size.
3		REAL	Base for X-axis data.
4		REAL	Increment between data samples, or for HISTOGRAMS; X-axis bin size.
5		REAL	Data mean, (X-axis for paired).
6		REAL	Data standard deviation, (X-axis for paired).
7		REAL	Mean of Y-axis of paired data files.
8		REAL	Standard deviation of Y-axis for paired data files.
9		REAL	Maximum of data, (X-axis for paired).
10		REAL	Minimum of data, (X-axis for paired).
11		REAL	Maximum of Y-axis data for paired.
12		REAL	Minimum of Y-axis data for paired.
13		REAL	HISTOGRAM: the number of bins along the X-axis, for all other data set to 0.0.
14		REAL	HISTOGRAM: Y-axis base.
15		REAL	HISTOGRAM: Y-axis element size.
16		REAL	Multiple set paired data separator.
17		REAL	Number of footer records.
18		REAL	RMS of data.
19 - 32		RESERVED
INTEGER AREA: Notice that some elements of this region contain characters.
Dump Form Element No.	Int. No.	Data Type Stored	Contents of Element
33	1	INTEGER	Data type flag: 1 = Real 2 = Histogram 3 = Complex: data is X-Y paired. 30 = Complex: change pen between sets. 31 = Complex: no change pen between sets.
	2	INTEGER	RESERVED
34	3	INTEGER	RESERVED
	4	INTEGER	Y-axis units validity flag: -2 = Y-axis units strings are valid.
	4	INTEGER	Y-axis units validity flag: -2 = Y-axis units strings are valid.
35	5, 6	CHARACTER	Y-axis units chars. 17 - 20
36	7, 8	CHARACTER	Y-axis units chars. 21 - 24
37	9, 10	CHARACTER	Y-axis units chars. 25 - 28
38	11	INTEGER	X-axis units validity flag: -2 = Y-axis units strings are valid.
	12	CHARACTER	X-axis units chars. 17 - 18
39	13, 14	CHARACTER	X-axis units chars. 19 - 22
40	15, 16	CHARACTER	X-axis units chars. 23 - 26
41	17	CHARACTER	X-axis units chars. 27 - 28
	18	INTEGER	-axis units validity flag: -2 = Z-axis units strings are valid.
42	19, 20	CHARACTER	Z-axis units chars. 17 - 20
43	21, 22	CHARACTER	Z-axis units chars. 21 - 24
44	23, 24	CHARACTER	Z-axis units chars. 25 - 28
45	25	INTEGER	File format flag: 0 = Data represent time series structure. 1 = Data represent a histogram structure.
	26	INTEGER	RESERVED
46	27	INTEGER	Statistics validity flag: 1 = Calculated statistics ARE valid.
	28	INTEGER	RESERVED
47 - 56			RESERVED
57	49	INTEGER	RESERVED
	50	INTEGER	File edited flag.
58	51	INTEGER	File smoothed flag.
	52	INTEGER	Number of smoothing operations.
60-65			RESERVED
CHARACTER AREA:
66		CHARACTER	Original file name chars. 1-4
67		CHARACTER	Original file name chars. 5 - 8
68		CHARACTER	Original file name chars. 9 - 12
69		CHARACTER	Original file name chars. 13 - 16
70		CHARACTER	Original file name chars. 17 - 20
71		CHARACTER	Original file name chars. 21 - 24
72		CHARACTER	Original file name chars. 25 - 28
73		CHARACTER	Original file name chars. 29 - 30
74		CHARACTER	Edited file name chars. 1 - 4
75		CHARACTER	Edited file name chars. 5 - 8
76		CHARACTER	Edited file name chars. 9 - 12
77		CHARACTER	Edited file name chars. 13 - 16
78		CHARACTER	Edited file name chars. 17 - 20
79		CHARACTER	Edited file name chars. 21 - 24
80		CHARACTER	Edited file name chars. 25 - 28
81		CHARACTER	Edited file name chars. 29 - 30
82 - 89		RESERVED
90		CHARACTER	Y-axis title chars. 1 - 4
91		CHARACTER	Y-axis title chars. 5 - 8
92		CHARACTER	Y-axis title chars. 9 - 12
93		CHARACTER	Y-axis title chars. 13 - 16
94		CHARACTER	Y-axis title chars. 17 - 20
95		CHARACTER	Y-axis title chars. 21 - 24
96		CHARACTER	X-axis title chars. 1 - 4
97		CHARACTER	X-axis title chars. 5 - 8
98		CHARACTER	X-axis title chars. 9 - 12
99		CHARACTER	X-axis title chars. 13 - 16
100		CHARACTER	X-axis title chars. 17 - 20
101		CHARACTER	X-axis title chars. 21 - 24
102		CHARACTER	Z--axis title chars. 1 - 4
103		CHARACTER	Z--axis title chars. 5 - 8
104		CHARACTER	Z--axis title chars. 9 - 12
105		CHARACTER	Z--axis title chars. 13 - 16
106		CHARACTER	Z--axis title chars. 17 - 20
107		CHARACTER	Z--axis title chars. 21 - 24
108		RESERVED
109		CHARACTER	Y--axis title chars. 1 - 4
110		CHARACTER	Y--axis title chars. 5 - 8
111		CHARACTER	Y--axis title chars. 9 - 12
112		CHARACTER	Y--axis title chars. 13 - 16
113		CHARACTER	X--axis title chars. 1 - 4
114		CHARACTER	X--axis title chars. 5 - 8
115		CHARACTER	X--axis title chars. 9 - 12
116		CHARACTER	X--axis title chars. 13 - 16
117		CHARACTER	Z-axis title chars. 1 - 4
118		CHARACTER	Z-axis title chars. 5 - 8
119		CHARACTER	Z-axis title chars. 9 - 12
120		CHARACTER	Z-axis title chars. 13 - 16
121 - 125		RESERVED
REAL AREA 2:
126		REAL	Point no. of maximum.
127		REAL	Point no. of minimum.
128		REAL	Point no. of absolute maximum.

Format of the Data Area

The body of a MSC Fatigue loading file contains the actual number to be used in the analysis. As with the header region, this information is stored in fixed length 512 byte records. The numbers themselves are held in a floating point binary format so that each record contains 128 values.

Three generic data structures are currently supported:

• Time series structure

• Histogram structure

• Paired X-Y structure

Format of the Time History (.dac) Structure

The "time series" structure is used to describe single channel data where the increment between samples is constant.

A true time series, where each value represents a sample scaled in physical units and the "gap" between samples represents reciprocal sample rate, is the most common data type normally found in this category. Files of this sort are easily identified by their file extension of ".dac".

As long as the rule of constant increment between samples is obeyed, other types of data can also be represented in time series format; a case in point would be an auto spectrum file with the extension .asd or .psd. In this case each data value represents a power (or amplitude) and the "gap" between values a constant increment in frequency.

A single dimensional histogram representing a time at level (.tlv files) or probability density distribution, (.pdd files) generated by the amplitude distribution module, MADA, also fall into this category.

Within this category of files, the default file extension expected by is .dac.


Note:	MQLD, the quick look display and MMFD, the multi-file display modules are specifically designed to display data files in time series format.

DAC file revision - Larger file capability

Pre V8 DAC files have a problem storing the number of points accurately when the number of points exceeds 16 mega-points. To solve this, the following header values for V8 on:

• The current number of points (CB(1)) is retained and used if the new location is not found.

• The integer control block location ICB(32), or the second element of the real location 48, should be set to 2 for a new file.

• The real area now ends at CB(28) instead of CB(32).

• A new INTEGER*4 area has been created between CB(29) and CB(32), called I4CB.

• I4CB(1) or CB(29) is set to the location of the maximum value

• I4CB(2) or CB(30) is set to the location of the minimum value.

• I4CB(3) or CB(31) is set to the location of the absolute maximum value.

• I4CB(4) or CB(32) is set to the number of points (V5 files on).

Program MFILMNP has been modified to auto-correct old files. Old files will work as before ( i.e. accurately to 16 mega-points.).

Format of Histogram Structure

Histogram data files are those which contain a two-dimensional matrix such as might result from a rainflow cycle count. The counts within each element of the X-Y matrix are stored in the form of REAL floating point numbers. The sequence in which the matrix elements are stored can be seen by considering the 16 elements of the, 4 x 4, matrix illustrated below:


x-axis y-axis	Min			Max
Min	1	2	3	4
	5	6	7	8
	9	10	11	12
Max	13	14	15	16

Values from this matrix would be stored within a histogram file starting with element number 1 and proceeding sequentially through to element number 16. In the general case, values within each X-axis column, for each Y-axis row, are stored sequentially, starting at the minimum of both X and Y-axes and ending at the maximum of both the axes.

Numbered among files with this generic format are rainflow (.cyh), range mean (. rmn), Markov (.mkv) and range pair (.rph) files.

Within this category of files, the default file extensions expected are, .cyh, .rmn, .mkv, and .rph.


Note:	MP3D, the two dimensional histogram display module is specifically designed to display these type of data files.

Format of Paired X-Y Structure.

Paired X-Y type data files consist of consecutive pairs of X-Y values stored as REAL floating point numbers. The two parameter creation module, MTPC, can be used to create such files.

Within this category of files, the default file extension expected is .mdf.

An additional subclass of this structure, in which several individual X-Y data sets can be stored simultaneously in the same file, is also supported. The structure is very similar to that described above except that a unique delimiter is inserted between each data set. The value of this delimiter is defined in the header region at dump form element number 16. If for some reason this delimiter ceases to be unique as a result of some manipulation by an MSC Fatigue module, then the offending module will replace it by another value which is again unique.


Note:	MTPD, the two parameter display module is specifically designed to display these type of data files.

Minimum Header Requirement for a Loading Type File

All 128 elements of the header area should be set to zero and then, as a minimum requirement the following elements defined in the REAL area:


Dump Form Element No.	Data Type Stored	Contents of Element
REAL AREA 1:
1	REAL	Set to the number of data values in file.
2	REAL	Set to the sample rate for time series data or reciprocal of the increment between samples.
3	REAL	Set to the X-axis origin.
4	REAL	Set to the increment between data samples.

As a minimum requirement, the following field from the INTEGER area should be set:


Dump Form Element No.	INT. No	Data Type Stored	Contents of Element
33	1	INTEGER	Set to 1.

The X and Y-axis label and units fields can be set, by using the MFILMNP module. As long as the first integer field of dump form element number 46 (INTEGER field number 27) is set to zero, the statistics fields will be automatically calculated by the first MSC Fatigue module to access the file.

Minimum Header Requirement for a Histogram Type File

All 128 elements of the header area should be set to zero and then, as a minimum requirement the following elements defined in the REAL area:


Dump Form Element No.	Data Type Stored	Contents of Element
REAL AREA 1:
1	REAL	Set to the number of data values in file.
2	REAL	Set to 1 / X-axis bin size.
3	REAL	Set to the X-axis origin.
4	REAL	Set to the size of the X-axis bins.
13	REAL	Set to the number of X-axis bins.
14	REAL	Set to the Y-axis origin.
15	REAL	Set to the size of the Y-axis bins.


Note:	The number of bins along the Y-axis is automatically calculated by dividing dump form element number 1 by element number 13 and so this value need not be stored.

As a minimum requirement, the following field from the INTEGER area should be set:


Dump Form Element No.	INT. No.	Data Type Stored	Contents of Element
33	1	INTEGER	Set to 2.
45	25	INTEGER	Set to 1.

Minimum Header Requirement for a Paired Data Type File

All 128 elements of the header area should be set to zero and then, as a minimum requirement the following elements defined in the REAL area:


Dump Form Element No.	Data Type Stored	Contents of Element
REAL AREA 1:
1	REAL	Set to the number of data values in file, X + Y.
2	REAL	Set to 1.
4	REAL	Set to 1.

If multiple X-Y data sets are being stored then element 16 should be set:


Dump Form Element No.		Data Type Stored	Contents of Element
16		REAL	Set to a unique value which will be taken to a delimiter between adjacent data sets within a file containing multiple data sets.

As a minimum requirement, the following field from the INTEGER area should be set:


Dump Form Element No.	INT. No.	Data Type Stored	Contents of Element
33	1	INTEGER	Set to 3 for single data set or 30 for pen changes between multiple data sets or 31 for no pen change pen between multiple data sets.