A Study On The Test Approaches Of Characterization Of Machinery As Vibrational Sources

It is significantly valuable to characterize entirely the noise and vibration (N&V in the following) properties of machinery, including the ability of vibrational energy radiation, the ability of force output in various conditions and the coupling between machines and seatings, for the transmission and sound radiation of vibrational energy. This can provide input data for other projects belonged to N&V study therefore is the base of others. On the other hand, it is feasible to determine the rate of N&V level of machinery after obtaining N&V data of source and the contribution to radiating noise. This is advantageous for optimizing the selection of machines which should be properly treated. In a word, it is urgent to study the characteristics of ship equipments as N&V sources. This will promote the project of N&V control in ships.In this paper, the system of the characterization of machinery exciting properties is stated firstly. Description quantities in various transmission paths have been compared and analyzed, including their relationships. Then, relevant approaches of measurement or calcation have been investigated considering the vacancies in China of measurement criteria of machine exciting force, energy output, transfer of source properties in different engineering installation environments as well as the problem of seating mobility measurement in situ.In the aspect of power flow from machine to its seating, experimental investigations on the measurement of power flow have been done in resilient and rigid mounting conditions. Results of power flow from direct measurement and calculation using Auto-spectrum Method or Cross-spectrum Method have been compared. The accuracy and feasibility in engineering of power flow calculation method have been demonstrated by experiments. It is pointed out that the Cross-spectrum Method is better than the Auto-spectrum Method. It is also pointed out that the power flow attenuation calculated using properties of isolators can be an evaluation quantity for the effect of an isolation system. Power flow injected into seating can be a quantity for limiting machine vibration level.In the measurement and estimation of exciting forces, direct measurement approach by force sensors is stated firstly in this paper. The calculating approach of force transmission correction quantityαis deduced. It is pointed out that there are many problems in the application of direct measurement approach, and it is only recommended to apply the direct approach in the laboratory. To find out feasible approaches in engineering for the measurement of exciting force, two approaches that based on properties of isolators and that based on properties of seating mobilities are investigated in this paper for indirect exciting force estimation. Applying criteria and measurement procedure are concluded and several experiments are done to valid and modify them.It is demonstrated by experiments, that the appoaches of indirect exciting force estimation are accurate and feasible in engineering, and can be employed instead of direct force measurement approach. It is also shown by experiments, that ill-posed problem is generally significant at modal frequencies when using indirect approaches therefore enlarge the estimation error at these frequencies. However, Singular-decomposed technique can be employed to improve the extent of ill-posed problem. It is pointed out to select measuring positions by the transcendent criterion using the inverse of condition number which is been demonstrated in its feasibility. This transcendent criterion gives a rule of selecting and grouping measuring positions, reduces the error of random arrarngement of measuring positions, solves the problem partially that nothing can be done in advance to control the ill-posed error in indirect estimation approaches, avoids measurement repeatedly and reduces labour intensity. All these provide the feasibility of applying indirect estimation approaches extensively in engineering. It is pointed out that Normalized Residue can be employed to evaluate the error as a latterly-checked criterion. This criterion has been validated by experiments in its engineering feasibility. Hence one can control the response residues to keep the accuracy of estimation results. The all-important measure to reduce estimation error in indirect approaches by impoving the Signal-Noise Ratio is pointed out in this paper.To solve the problem in reality that it is difficult to measure mobilities of the seating when the machine is mounted on it, effect of mouted machine to mobility measurement is studied in this paper. The error formula is deduced theorectically about it in one-point contact, multi-point contact, rigid and resilient mounting styles which is the real problem in engineering. It is concluded in this paper that seating mobilities could be measured with the machine rigidly-mounted on it in engineering, if mobilities of machine feet are much larger than mobilities of the seating. Measurement error of seating mobilities can always be neglected in engineering when the machine is mounted resiliently. All these theoerical conclusions are demonstrated by experiments.In the aspect of transferring relationship of exciting properties in various mounting environment, simply and applicatory transferring formulas about force and velocity are deduced in rigid and resilient mouting styles through a bridge of free velocity of machine feet. Different formulas are obtained in one-point contact, single excitation and multi-point contact, multi-excitation conditions. Simplified treatment is done by gloable quantities of isolators in the procedure of theorectical deduction when multi-point mouting style is existed. It is also stated simply about how to solve the problem in Russian documents.At the end of this paper, the measurement approach of Free Velocity is stated. The differences between the measurement of Free Velocity and the measurement of normal acceleration and velocity are focussed on, which can be seen in measurement condition, valid frequency range, machine-mounted condition, isolator selection and the arrangement of measuring positions. The former needs fairly stricter conditions than the latter. It is recommended in paper that Free Velocity can be an evaluation quantity of the vibrational characteristics when ship equipment is tested after being manufactured.