Vibration-related Services
Sea-going vessels are often a floating vibration laboratory, and keeping those vibrations at an acceptable level can be a challenge. The solution of vibration problems quite often requires a four-step process:
1. Determine the vibration frequency and vibration mode shape of the item that is vibrating over the vessel speed range, and match the vibration to excitation sources;
2. Determine from the vibration survey if the vibration is forced or resonant;
3. If forced, determine what can be done to repair the source to reduce excitation, or isolate the source;
4. If resonant, determine by analysis if the stiffness across the vibrating system can be changed, and/or the suspended mass of the system can be changed to move the resonance out of the operating speed range.
For example, a high performance tug had an unbearable noise level in the Captain’s stateroom located in the deck house just aft of the bridge. A check of the vessel mast revealed that two diagonal mast stays made from steel pipe and welded to both the mast and the deckhouse top-side corners were vibrating heavily in the fore-aft direction. The stay vibration frequency method matched both the noise frequence and the main engine 3rd order.
An analysis of the pipe stays as fix-ended beams confirmed that the engine 3rd order could excite a stay resonance in the fore-aft direction. The problem was solved by changing the stays from fix-ends (welded), to pin-end (yokes and pins), thereby changing the resonant frequency. The noise disappeared, much to the Captain’s approval.
VIBRATION_SERVICES.PDF
DIEHL_ENGINEERING.PDF
Machinery Vibration Analysis
Diehl Engineering Company has a history of finding practical solutions to shipboard machinery vibration problems. We will perform a vibration survey to determine the strength and frequency of the vibration at the critical locations on the machine, and perform the analysis necessary to determine if the vibration is forced or resonant.
If forced, we will look for the cause internally in the machine. If resonant, we will determine what stiffness or mass changes are necessary to move the resonance outside the excitation range.
Hull Vibration Analysis
Hull vibrations are a special case in which the hull as a beam is often resonant at some excitation frequency, such as a propeller blade passing, or propeller shaft rotational.
We can survey the hull vibratory motions underway and determine the mode shape, either vertical or athwartships, but quite often this is a function of the hull structure and not easily changed. Sometimes, the problem can be solved via changing the number of propeller blades, or isolating the engine on resilient mounts.
In-place Dynamic Balancing
Machinery imbalance is one of the leading contributors to machine vibration and wear, particularly if the forced vibration of the unbalance works in conjunction with a resonant structure.
Diehl Engineering offers comprehensive in-place machinery balancing services. Using the latest in multi-plane, multi-speed balance software and hardware our engineers can provide an accurate, efficient and stable balance solution. From electric ventilation fans to turbine generators of all sizes, we can fill your machinery balancing needs.