30.控制造水機產水量的主要手段是控制下列何者？ (A)給水流量 (B)加熱水流量 (C)冷卻水流量 (D)真空破壞閥開度

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

30.控制造水機產水量的主要手段是控制下列何者？
(A)給水流量
(B)加熱水流量
(C)冷卻水流量
(D)真空破壞閥開度

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