DI-018_REV_2_VIBRATION_ANALYSIS.pdf

DI-018 Vibration Report Contract 6913G623P800007

Preliminary/Contract Design of Motor Vessel Ranger IV

Submitted by:

Loch Harbour Group

3060 Williams Drive, Suite 510

Fairfax, Virginia 22031

Preliminary/Contract Design of Motor Vessel Ranger IV

Contract No.: 6913G623P800007

CLIN-00100

DI-018 Vibration Report Revision 2

Submittal Date: August 28, 2024

DISTRIBUTION Statement C: Distribution authorized to the U.S. Government agencies and their Contractors. Other request for this document shall be referred to the US Department of Transportation Volpe Center.

DATA RIGHTS: This report, drawing, design, concept, and specification are the intellectual property of Loch Harbour

Group, LLC, and/or R.R.P CONSULTING ENGINEERS, L.L.C and contain information which is proprietary. The rights defined below are reserved by Loch Harbour Group, LLC, and/or R.R.P CONSULTING ENGINEERS, L.L.C.

The United States Government’s rights to use, modify, reproduce, release, perform, display, or disclose these technical data are unrestricted. Any reproduction of technical data or portions thereof marked with this legend must also reproduce the markings.

PZdynamics Website: www.pzdynamics.com Email: info@pzdynamics.com Tel: +44(0)7500478243

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DI-018 VIBRATION ANALYSIS REPORT

Ranger IV

28-08-2024

A report written by PZdynamics Ltd for RRP Consulting Engineers

Dr. P.G. Zoet http://www.pzdynamics.com/

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Contents

1. Summary and conclusions

1. Report content

2. Vibration limit requirements

3. Vibration sources and transmission paths

4. Vibration analysis model

5. Forced Vibration analysis results

Excitation

Response

6. Recommendations for reducing vibration levels

Appendix I: Vibration weighing curves

LIABILITY

PZdynamics has used reasonable endeavours to ensure an accurate assessment of the vibrations and noise investigated in this report, but PZdynamics makes no warranty, expressed or implied, as to accuracy and accepts no responsibility for any use by RRP Consulting Engineers of the Deliverables or PZdynamics Intellectual Property, nor for any reliance placed by RRP

Consulting Engineers, on the Deliverables or PZdynamics Intellectual Property, nor for advice or information given in connection with a Project.

RRP Consulting Engineers will indemnify PZdynamics and keep it fully and effectively indemnified against each and every claim made against PZdynamics as a result of RRP Consulting Engineers use of any of the Deliverables or PZdynamics

Intellectual Property received through this report.

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1. Summary and conclusions

As part of the Work Authorisation subcontract no LA2301-Z0001 the conclusions of the vibration analysis for the passenger vessel Ranger IV are as follows:

Natural frequency and vibration levels have been simulated through finite element modelling.

Simulated vibration levels show the vibration levels meet the requirements at all locations on decks and spaces while running at nominal speed. This resonance caused is within the allowable and it can be much improved by adding stanchions between the decks and running two extra girders below decks on the fly bridge deck (see section 6 for details). These are just the recommendations to further reduce the vibration levels and resonance in some of the spaces to obtain higher comfort notations such as

HAB+.

We are aware that placing these stanchions at exactly these locations will not be possible. Some of these stanchions for instance will end up in the middle of the corridor on the 2nd deck. However, placing them off centre concealed into the cabin panelling will be just as effective.

The report concludes that the vibration levels and resonance is within the allowable requirements and validated to obtain ABS class special notion as “HAB”.

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1. Report content

This report represents the deliverable DI-018 as per Authorisation subcontract no LA2301-Z0001 representing the vibration analysis for the passenger vessel Ranger IV.

This report outlines the vibration requirement in section.

2. Vibration limit requirements Vibration requirements according to the ABS Guide for Crew Habitability on Ships and ABS Guide for

Passenger Comfort on Ships are to be fulfilled. This means that the limit levels apply as shown in Figure

1.

Vibration limit values are presented as total weighted RMS values. This total value is obtained from spectra which have been corrected with a weighting factor, so the total vibration levels also reflect the human’s sensitivity to vibration as a function of frequency (see appendix I for weighing curves).

Therefore, simulated vibration spectra are corrected using the appropriate weighting curves.

Since the vessel needs to fulfil HAB, the level limits apply as shown in

Figure 1 Level limits for vibration.

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3. Vibration sources and transmission paths

On behalf of RRP Consulting Engineers, PZdynamics has performed a finite element noise and vibration prediction calculations for their design of the Ranger IV passenger vessel.

The analysis consists of the following parts:

- Prediction of vibration levels: Vibration levels are predicted for all listed spaces using the appropriate weighing curves as shown in appendix I. Main sources of vibration considered here are the propellers and diesel engines.

- Natural frequency analysis: Natural frequencies and mode shapes are analysed to obtain information of the reason why simulated vibration levels are over the limit values.

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4. Vibration analysis model

The evaluation of risk of exceeding HAB vibration requirements is based on performing both natural frequency analysis and forced vibration analysis using Finite Element modelling. The entire ship has been modelled using a combination of plate and beam elements at a level of detail deemed relevant for the analysis, focussing on vibration behaviour of decks in the accommodation areas.

Figure 2 Details of the model showing use of plate elements for the deck and hull plating and main girder and beam elements for the pillars and flat plates which come on top of the main girders.

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5. Forced Vibration analysis results

Forced vibration analysis has been carried out of which the results are shown in Figure 5 to Figure 10

(excitation propeller in phase) and Figure 11 (propeller excitation out of phase) .

Excitation Based on the properties of main engines and propellers, the following main excitation frequencies have been identified.

- Main engine 0.5 order at 13.5 Hz

- Engine crankshaft rotation (26.7 Hz)

- Main engine firing frequency at 160 Hz: this frequency is however not considered as it is high enough to obtain descent isolation through application of flexible mounts.

- Propeller shaft rotation frequency (5.4 Hz)

- Propeller blade passing frequency (27.1 Hz)

With the forced vibration analysis, the propeller blade passing pressure pulses have been considered

(at 27.1 Hz). Diesel engine excitation has not been considered for the following reasons:

- Diesel engines are resiliently mounted. The firing frequency is well isolated.

- As the diesel engine shaft rotation frequency is considerably lower than the firing frequency, the resilient mounting will, even though not as effectively as with the firing frequency, still reduce transmission of crankshaft rotation frequency vibration to the ship structure.

However, as the diesel engine shaft rotation frequency is close to the propeller shaft rotation frequency, optimising the ship structure for propeller vibration will also have a beneficial effect on diesel engine crankshaft rotation frequency.

- Propeller shaft and engine 0.5 order vibrations should always be kept a minimum through applying proper maintenance and alignment.

Propeller excitation pressure pulses have been calculated using empirical equations based on the properties of the propeller shown in Figure 3.

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Figure 3 Propeller properties on which the calculation of the pressure pulses is based.

Response Forced vibration analysis has been carried out of which the results are shown in Figure 5 to Figure 10

(excitation propeller in phase) and Figure 11 (propeller excitation out of phase) .

Structural modification recommended based on the analysis results with the propeller in phase will have an equal beneficial effect on the vibrations caused by the propellers excitation out of phase.

A run up has been simulated presenting the maximum vibration levels for each deck for each propeller speed. This helps identifying any relevant resonance frequencies which may need to be addressed. As can be seen in Figure 4 no relevant resonance frequencies were found below 10Hz. Tis means that there is little concern for resonance due to propeller shaft and diesel engine 0.5 order excitation, even though the lowest calculated relevant response frequency at 10Hz may be lower in reality due to added mass effect.

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Excitation SB and PS propeller in phase

Excitation out of phase

Figure 4 Maximum vibration levels as a function of frequency (27 Hz is maximum propeller blade passing frequency).

Double bottom deck

Limit values:

HAB = 5 mm/s HAB+ = 4 mm/s HAB++ = 3 mm/s

All vibration levels are well under the HAB++ limit levels.

Figure 5 Distribution of weighted RMS vibration levels over the top of the double bottom at ship nominal speed and power. Propeller excitation is in phase.

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Deck 2

HAB+ = 4 mm/s HAB++ = 3 mm/s

Local vibration levels are well under the HAB++ limit levels.

Mode shape study:

It is recommended to place a stanchion as shown with the grey line at the centre line between main deck and the double bottom, which will also shift the resonance frequency at the forward section of the main deck.

Figure 6 Distribution of simulated (weighted) vibration levels on the 2nd deck (nominal speed and power, propeller excitation in phase).

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Main deck

HAB+ = 4 mm/s HAB++ = 3 mm/s

Vibration levels inside accommodation under the HAB++ limits.

Vibration levels on outside deck is locally above the HAB limits due to lack of stiffness support related to resonance close to 27 and 29 Hz with the mode shape shown below.

The remedy would be to place extra stanchions between the decks at the centre line.

Figure 7 Distribution of simulated (weighted) vibration levels on the main deck (propeller excitation in phase, nominal speed and power)

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Passenger deck

HAB+ = 4 mm/s HAB++ = 3 mm/s

Vibration levels were found to be under the HAB limit levels.

Mode shape study:

White circled area shows where levels are likely going to reach close to the HAB limit values due to resonance of the deck.

Figure left shows the mode shape with halve the model cut away. Resonance frequency was found to be at 29.5 Hz and resulting from lack of supporting stiffness in vertical direction on the centre girder.

Placing as many as possible girders around that location will help (as suggested by the grey lines added to the figure).

Figure 8 Distribution of simulated (weighted) vibration levels on the passenger deck (propeller excitation in phase, Email: info@pzdynamics.com

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Bridge Deck

HAB+ = 4 mm/s HAB++ = 3 mm/s

HAB limit levels are exceeded due to lack of support over the main centre girder. Adding pillars will be beneficial.

The exceeding vibration levels are again related to of the main deck, passenger deck bridge and flybridge decks.

Figure 9 Distribution of simulated (weighted) vibration levels on the bridge deck. (propeller excitation in phase, Email: info@pzdynamics.com

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Fly Bridge Deck

HAB+ = 4 mm/s HAB++ = 3 mm/s

HAB limit levels are exceeded due to lack of support over the main centre girder. Adding pillars will be beneficial. The two mode shapes shown below (resonance around 27 Hz)

Figure 10 Distribution of simulated (weighted) vibration levels on the fly bridge deck. (propeller excitation in phase

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Figure 11 Calculation results out of phase excitation from the propellers. All maximum levels were found to be under the HAB++ limits at the main areas where passengers and crew reside.

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6. Recommendations for reducing vibration levels

Addition of support/structure is recommended at the following areas:

- Forward deck extra stanchions (see Figure 12):

o Centre line frame 11, between double bottom, 2nd deck and main deck o Between main deck and 2nd deck, frame 11, 6’ from CL

- Extra stanchions on centre line between 2nd, main, passenger, bridge and fly bridge decks (see

Figure 13). Most urgently at the following locations (or close to) o Centreline, frame 37, from fly bridge down to the main deck o Centreline, frame 41, from passenger deck down to 2nd deck o Also, adding a stanchion at frame 45, and if possible, at frame 49 would further improve the situation in which case the stanchion at frame 45 will be more effective.

- Flybridge deck: add below decks a 8’’x6’’ x1/4’’ stiffener from frame 28 to 13.5, both SB and

PS at approximately 10’ from centreline (see Figure 14).

- Aft deck/engine room: add stanchions of at least 6’’ at the centreline at frame 59, 67 and 75

(see Figure 15).

Figure 12 Extra stanchions at forward deck area (red dots in right hand side drawing).

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Figure 13 Proposed added stanchions at centre line with at least 6’’ diameter.

Frame 41

Frame 45

Frame 49

Frame 37

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Two most dominant mode shapes contributing to the total vibration levels at full speed.

Looking at the most dominant mode shape in the fly bridge deck looking from below. It is proposed to add a 8’’x6’’ x1/4’’ stiffener below decks running from frame 28 to 13.5 shown through two dotted lines both SB and PS at approximately 10’ from centre line.

Figure 14 Additional stiffening on the flybridge deck.

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Mode 98 at 27.1 Hz. Proposed stanchions are shown with red dotted lines.

Mode 99 at 27.6 Hz. Proposed stanchions are shown with red dotted lines.

Figure 15 Proposed extra stanchions at frames 59, 67 and 75.

Stanchion at

Frame 59

Stanchion at

Frame 67

Stanchion at

Frame 75

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Appendix I

Vibration weighing curves.

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Weighing curves are to be applied to the vibration spectra when calcuating the total weighted RMS values aw listed below:

The weighting factors have been applied according to Figure 16, following ISO 8041 (which refers to

ISO 2631-1 for the weighing curves). With the selection of the right weighing curve a distingion is made between weighing factors applied for horizontal vibrations (x and y axis) and vertical axis (z axis).

Where 𝑎𝑤𝑗 is the frequency weighted acceleration in the axis j and T is the duration of the measurement. An additional multiplying factor is used of 1.4 for the evaluation of vibrations in the x and y axis. The value used for assessment is expressed as:

Figure 16 Weighing factors for horizontal and vertical vibrations