hours for the pumping station is less than 50 hours
per year.
Alternate 2, Dynamic Analysis, is used when
operating hours are greater than 50 hours per year
and the pump is driven by an electric motor. The
motor described is a vertical shaft type without a
speed reducer. If the decision is made to use a
horizontal shaft motor, then Alternate 2 needs to be
revised to include the speed reducer in the analysis
as described in Alternate 3. Select the first and
second bracketed paragraphs for Alternate 2.
Alternate 3, Dynamic Analysis, is used when
operating hours are greater than 50 hours per year
and the pump is driven by a diesel engine/gear
reduction unit or when an FSI is used. Select the
first bracketed paragraph and the TORSIONAL ANALYSIS
and LATERAL FREQUENCY ANALYSIS paragraphs.
**************************************************************************
[Assembled pumping unit, consisting of [motor][,][engine][,][speed reducer]
and pump shall be free from critical speeds or harmful torsional vibrations
at all speeds encountered within the operating range.]
[Before pump and motor, furnished under Section(s) [_____] are released for
manufacture, pump/motor structure shall be analyzed by pump manufacturer
for harmful natural frequencies in the lateral and torsional directions. A
natural frequency that occurs within 25 percent above or below normal
operating speed is unacceptable. Dynamic analysis model shall be
constructed using a commercially available program such as Ansys, Cosmos/M,
or equivalent, which utilize finite element methods. Incorporate effects
of column pipes, cover pipes, shafts, bearings, mass concentrations, and
other such features as necessary to accurately model pump structure.
Analyze structure in the run (wet) condition and consider the effect of
water mass in the column and damping effect of water in the sump (vertical
units only) at highest and lowest sump water levels. Incorporate Reed
critical frequency and mass elastic diagram information provided by motor
manufacturer. If motor manufacturer cannot demonstrate to the satisfaction
of Contracting Officer (based on impact tests of similar units) that the
Reed critical frequency value is accurate, motor manufacturer shall conduct
a dynamic analysis using finite element methods as described to determine
motor Reed critical frequency for use by pump manufacturer. Submit
complete dynamic analysis report including the following information:
a.
Computer program used.
b.
Schematic diagram of the model depicting nodes and elements.
c.
Input data consisting of node coordinates, element types, material
properties, element characteristics, element connectivities, and
specified displacements.
d.
Motor mass elastic and Reed critical information (or dynamic
analysis, if required).
e.
Analysis results, including significant natural frequencies.
f.
Interpretation of results.
SECTION 15131A
Page 39
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