528.1-33 information required

528.1-3 NATURAL AND INDUCED ENVIRONMENT AND ASSOCIATED ELEMENTS

NOTE: Annex A contains a list of naturally-occurring “Weather and Climatic Extremes.”

Although climatic conditions during a field test are not likely to be as extreme as the values specified in paragraph 4 and its subparagraphs, there are distinct advantages to conducting tests in real world environments where the combined effects of several climatic factors can cause difficulties not revealed by chamber testing. On the other hand, if natural field environment tests are conducted under conditions that are less extreme than those called for by the system LCEP and requirements documents, additional laboratory tests may be required - particularly when natural field test results are marginal. Data describing climatic conditions prevailing during natural field tests should be recorded at the test site, and documented in the final report to provide a basis for future evaluation.

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METHOD 528.1

• (6) Requirements for combined environments.
• (7) Test schedule(s) and duration of exposure(s).
• (8) Axes of exposure.
• (9) Measurement instrumentation configuration.
• (10) Test shutdown procedures for test equipment or test item problems, failures, etc. (See paragraph 4.3.)
• (11) Test interruption recovery procedure. (See paragraph 4.3.)
• (12) Test completion criteria.
• (13) Assure that test requirements (force, acceleration, velocity, displacement) can be met. Seek approval for variation if required. Document any variation.
• (14) Allowable adjustments to test item & fixture (if any); these must be documented in the test plan and the test report.
• (15) Check bolts and washers before, during (when changing direction of vibration), and after test. Ensure all bolts are proper grip length and that the washers are not rotating.
• (16) Identify potential areas of high stress concentration. Consider composite and cast materials.
• c. Tailoring. Necessary variations in the basic test parameters/testing equipment to accommodate LCEP requirements and/or facility limitations. Tailoring is a function of the ship’s propulsion system and the environment. All tailoring of this test Method must be approved in accordance to the procurement specification before testing.

NOTE: Modal surveys of both test fixtures and test items can be extremely valuable. Large test items on large complex fixtures are almost certain to have fixture resonances within the test range. These resonances result in large overtests or undertests at specific frequencies and locations within a test item. Where fixture and test item resonances couple, the result can be misleading. Similar problems often occur with small test items, even when the shaker/fixture system is well designed. In cases where the fixture/item resonance coupling cannot be eliminated, consider special vibration control techniques such as acceleration or force limit control.

528.1-3.1 Frequency of occurrence

Examples are:

• a. For both worldwide and regional applications, the frequency of occurrence of climatic elements (e.g., temperature) is based on hourly data wherever possible. From hourly data it is possible to determine the total number of hours a specific value of a climatic element is equaled or exceeded. For example, if a temperature occurs, or is exceeded for an average of 7 hours in a 31-day month (744 hours), it has occurred roughly 1 percent of the hours in that month; if it is exceeded an average of 74 hours in the month, it has a frequency-of-occurrence of 10 percent, etc. The value that is equaled or exceeded 1 percent of the time is referred to as the “1-percent value.”
• b. Long-term climatic extremes are values that are expected to occur at least once, for a short duration (≤ 3 hours), during approximately 10, 30, and 60 years of exposure. Therefore, they are rarer climatic events than the 1-percent values.
• c. Values occurring for specified frequencies-of-occurrence during the worst month may also occur in other months, but with lower frequency-of-occurrence.

528.1-3.2 Worldwide surface environment. (Summary of daily cycles) (Paragraph 6.1, reference a, paragraph 5.1.)

Figure 1 provides a general guide as to the location of the four climatic design types described in Table 1. However anomalies may exist within the areas shown, so the LCEP should always be referenced. Table I is a summary table of the daily extremes (highest and lowest values in a 24-hour cycle) of temperature, solar radiation, and relative humidity for the eight daily cycles cited in this document. Details of each cycle, and other atmospheric elements (hydrometeors, wind, blowing sand, blowing dust, ozone, and atmospheric pressure) are given in paragraphs 4 and 5 and their subparagraphs. In most cases, extremes of these other elements do not occur at the same time as the extremes of temperature or humidity. However, with certain severe cold and cold phenomena, two or more elements may occur at the same time, e.g., ice, fog, and low temperatures.

3.2.1 Acceptable materiel operation

In general, design materiel to operate during all but a small percentage of the time. Once an acceptable frequency-ofoccurrence of a climatic element has been determined, the corresponding climatic value can be ascertained from the available climatic data. Recommend a 1 percent frequency be initially considered for all climatic elements except severe cold temperature, for which a 20 percent frequency is recommended, and rainfall for which a 0.5 percent frequency is recommended.

Consider more extreme climatic values (storage/transit environment and highest/lowest recorded) for materiel whose failure to operate is life-threatening, or for materiel that could be rendered useless or dangerous after a one-time exposure. For such materiel, long-term climatic extremes, or the record extreme, would be more appropriate for design of materiel that is not protected from the environment. Note that highest/lowest recorded extremes depend upon the period of record (POR) and should not be construed as “all time” extremes. The use of these more extreme values, instead of those occurring for a percent of the time during the most severe month each year, should be determined by the agency or department responsible for development. An option for such materiel would be protection from the exposure to these extremes.

Each climatic design type is characterized by one or more daily weather cycles that show the ranges of daily temperatures, humidities, and solar radiation in which materiel must operate if it is intended for use in the areas indicated on the climatic location map (Figure 1). Associated weather elements of paragraph 5 also have worldwide distribution but, unlike the weather elements constituting the climatic design types, they do not have well-defined

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PART THREE

daily cycles. Since these weather elements are associated with irregularly occurring storms and fronts rather than the daily sun cycle, they are described by instantaneous or short term extremes, and by relative frequency of occurrence.

3.2.2 Climatic testing

Materiel under development should be tested in climatic chambers, and undergo natural (i.e., field) environmental tests. Included in this Part is general information on climatic and weather-elements (environmental conditions) that are known to affect the operation, storage, and transit of military materiel.

3.2.3 Laboratory climatic tests

The use of laboratory climatic tests is encouraged, especially under combined (e.g., temperature and humidity) and sequential conditions. In most cases, it is not possible to duplicate exact combined conditions of the applicable climatic design values in these tests. The materiel, however, will be tested to meet the guidelines of the requirements document. Unless otherwise justified, developers conducting laboratory climatic tests should use the daily cycles normally found in nature as their models, rather than chamber testing only at the extreme condition. This daily cycling gives more realistic moisture condensation and temperature response patterns. Test planners and environmental engineering specialists will consult with each other on how the climatic design values apply to testing.

3.2.4 Accelerated and aggravated climatic tests

Accelerated and aggravated climatic tests. Accelerated climatic tests are not addressed in this standard, however, some climatic methods do address the aggravated environment. Aggravated tests involve subjecting materiel to more extreme conditions than are found in nature. The results of accelerated and aggravated tests are evaluated in terms of what they imply for future service performance. Specifically, they give rapid feedback on problems requiring corrective action, as well as statistical data on the margin of safety provided by the design. Comparing results of these tests with the results of field climatic tests of service performance will give a better correlation of results. It also increases confidence in the use of such techniques in subsequent similar situations. In chamber tests, developers are cautioned that subjecting materiel to more extreme conditions than are found in nature may introduce problems that will not occur when testing is conducted in the natural environment. On the other hand, the successful conclusion of chamber tests does not guarantee that materiel will operate satisfactorily in the natural environment, because nature involves complex, synergistic effects that cannot presently be induced in chambers. Such factors must be considered by the developer when evaluating results obtained in chambers. Test planners and environmental engineering specialists will consult with each other to determine the extreme combinations of conditions that occur in nature.

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PART THREE