34.有關離心式泵（Centrifugal pump）密封環（Sealing ring）的敘述，下列何者正確？ (A)一般以不鏽鋼材質製作 (B)在於使泵殼與葉輪的間距盡可能小 (C)與泵殼一體，無法更換 (D)幾乎不會磨損

10.Longitudinal vibration of propulsion shafting systems is often excited by the variable thrust developed by the propeller due to the non-uniform wake pattern in which it operates. The predominant periodic component of the thrust developed by a propeller occurs at blade-rate frequency, i.e., the number of propeller blades times the rotational frequency of the shaft. For a four-blade propeller running at 60 rev/min, what is the predominant periodic frequency that excites the longitudinal vibration of the propulsion shafting systems? (A)1 Hz (B)2 Hz (C)3 Hz (D)4 Hz

34.有關離心式泵（Centrifugal pump）密封環（Sealing ring）的敘述，下列何者正確？
(A)一般以不鏽鋼材質製作
(B)在於使泵殼與葉輪的間距盡可能小
(C)與泵殼一體，無法更換
(D)幾乎不會磨損

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