Low Noise Collocation on Fluid Pipeline System

HE Tao,SUN Yu-dong,WU Wen-wei,WU You-sheng

(1.National Key Laboratory on Ship Vibration&Noise,China Ship Scientific Research Center,Wuxi 214082,China; 2.Jiangsu Key Laboratory of Green Ship Technology,Wuxi 214082,China)

Low Noise Collocation on Fluid Pipeline System

HE Tao1,2,SUN Yu-dong1,2,WU Wen-wei1,2,WU You-sheng1,2

(1.National Key Laboratory on Ship Vibration&Noise,China Ship Scientific Research Center,Wuxi 214082,China; 2.Jiangsu Key Laboratory of Green Ship Technology,Wuxi 214082,China)

Fluid dynamic and vibration and noise characteristics of pipeline systems are both focused and analyzed as design targets.Cooling pipeline systems of ships are always running during the sail time,outboard noise radiation of cooling pipeline systems is distinct.Low noise collocation method should be proposed in order to control cooling pipeline noise.In this paper,fluid dynamic method of piping systems is established based on one dimensional hydraulic theory,vibration and noise radiation numerical method of piping systems is established based on finite element method under acoustic-vibration and equivalent fluid filled beam model theories.Low noise collocation strategy including principle,fluid collocation method and noise radiation evaluation method is constructed in the end.Finally,typical cooling pipeline system is analyzed and collocation method is elementarily verified experimentally.

fluid pipeline systems;fluid dynamic;vibration;low noise collocation method

0 Introduction

Pipeline systems exist in broad industry fields.Vibration and noise characteristics of pipeline systems are focused and analyzed all the time[1-2].Commonly,there are two controlling methods for vibration and noise of pipeline systems.One controlling method is based on noise source design such as low noise design of equipments[3-4]and the other controlling method is based on noise and vibration isolation&absorption approaches such as vibration isolator, flexible pipes and supports,silencers[5-6],etc.The research results show that noise and vibration of systems can always be reduced by the two control methods,although the noise and vibration level is still unsatisfied.So,combining the hydraulic and noise designs together and matching resistances of pipe and system are necessary to control system noise and realize low noise design object.

Pumps are indispensable equipments in cooling pipeline systems and the main vibration and noise sources.Pumps behave the best effective hydraulic performances under design working points,in the mean time,behave best noise and vibration performances.Guan and Wang[7-8]did sufficient work on hydrodynamic performances and design methods of hydraulic machines. Control valves vibrate and radiate noise under hydraulic inspiriting.The hydraulic and noise& vibration performances are related in nature.The noise level of pipeline system can be lowered by the way of low noise collocation method which make sure that the pumps work under design points matching the system hydraulic resistance.

In this paper,low noise collocation principles are listed as design guidance,the collocation numerical methods are constructed as design methodology,the collocation technology is established in the end.The collocation technology is exercised upon some typical cooling pipeline system,and the collocation principles and methods are verified experimentally.

1 Low noise collocation principles of pipeline systems

Pumps and valves are the main vibration and noise sources in cooling pipeline systems which determine the noise levels of systems.Sufficient researches are done on hydraulic and vibration&noise performances of pumps and valves.The researches reveal that pumps behave the lowest noise levels under designed working conditions.Noise and vibration level increases while flow volume rate of pump increases or decreases.Valves behave the lowest noise levels under states with larger openings and lower flow volume rates which indicates that noise of systems increases with hydraulic powers increase.

Hydraulic performance curves of pumps are illustrated as Fig.1.Shaft powers and hydraulic efficiencies are different under fixed rotating speed with variable flow volume rates and heads. Because of hydraulic efficiency decreasing,mechanical powers turn into vibration powers and transfer through base supports and pipeline,and cause noise radiation to outfield in the end[9].

Fig.1 Hydraulic performance curves of pumps

Fig.2 Working points of pumps related to system

As is illustrated in Fig.2,vibration and noise of pumps vary with hydraulic conditions, main spectrums such as rotating,blade passing,and multiple frequencies of rotating,blade passing frequencies obey the same rules that vibration and noise levels are the lowest under designed working conditions[10].

Synthesizing the above analysis,the low noise collocation principles of pipeline systems areconcluded as:

(1)Reducing the flow powers as low as possible on the premises that flow volume rate needs of users are satisfied;

(2)Making sure that the designed working conditions of pumps match the resistances of pipeline systems;

(3)Reducing additional noise sources such as valves,transitions,elbows et all.

The modulating and adjusting means to realize low noise collocation principles are as follows:

(1)Reducing rotating speeds to match system resistances when fluid powers of pumps are too redundancy;

(2)Control valves should be used to increase system resistances to match design points of pumps if system resistances is lower than head of pumps;

(3)Low noise control valves should be used to adjust system resistance in order to control additional noise sources.

2 Low noise collocation evaluation methods of pipeline systems

Collocation evaluation methods include hydraulic evaluation method and vibration and noise radiation evaluation method.One dimensional hydraulic evaluation method is established to carry out low noise collocation schemes satisfying hydraulic requirements of cooling users under low noise collocation principles.Source characteristics of pumps,valves,users under specific hydraulic conditions should be tested and acquired as the input data for pipeline system vibration and noise evaluation.Based on input source data and vibration and noise evaluation method,noise level of different collocation schemes can be evaluated and the collocation schemes can be valued.

2.1 Hydraulic evaluation method of pipeline systems

Pressure drops of hydraulic systems root in turbulent dissipation and inverse pressure gradient.In common industry applications,two mechanisms often appear at the same time. Because of the slightness character of pipeline,invariable pressures and velocities on cross sections can be assumed and hydraulic evaluation method of pipeline systems can be established based on one dimensional theory.The hydraulic evaluation method includes one dimensional fluid control equation,pipeline elements modeling,elements relationship and matrix solving, etc[11-12].

Fluid resistance equation,continuity equation and pressure loss equation are as follows:

where p1and p2are inlet and outlet pressures of component,ξ is fluid resistance coefficient ofcomponent,ρ is density of fluid,u is flow velocity,subscript 1,2 are upwind and downwind positions,u1and u2are flow velocities of two connection points,A1and A2are areas of two connection points,p1and p2are static pressures,are dynamic pressures,z1and z2are head positions.

Cooling pipeline systems commonly contain pumps,valves,heat exchangers,filters, branches,pipes,elbows,etc.

Vane pumps such as centrifugal and axial pumps are often used in cooling systems.Hydraulic performance curves should be provided as input data for system hydraulic solving. Relationship of flow volume rate and head under constant rotating speed can be transferred to Suter dimensionless curves.

Hydraulic performances of discrete losses such as valves,heat exchangers and filters can be expressed as loss coefficients considering effect of low Re on itself.

where ξvis loss coefficients of discrete losses,cReis low Re modified coefficient.

Pressure loss of pipes and elbows increases with distance:

where f is friction coefficient,L is length of pipe or elbow,D is hydraulic diameter.

Pipeline systems are considered as networks based on one dimension theory.Connections of components of pipeline systems are equivalent as serial,parallel and embranchment relationships.Based on serial,parallel and embranchment relationships,hydraulic networks of cooling systems can be constructed as system matrixes.The matrix coefficients are determined by components.In order to solve system matrix equations,flow volume rates are initialized along all network,and fist matrix solution is done to get pressures of nodes of network;based on the pressures solved,the flow volume rates and the matrix coefficients can be updated;in this way,solutions can be iterated;when the residuals of flow volume rate and pressure results are within limited values,the iterative solutions end,and the final system solution is achieved.

2.2 Vibration and noise radiation evaluation method of pipeline systems

Based on equivalent fluid filled beam and acoustic-elasticity theory,finite element models of pipeline system and ship structures are constructed including equipments,pipeline,base and hull,etc.Vibration and noise radiation of ship outboard can be evaluated.The hydraulic collocation schemes can be valued based on the calculation results.

Variation integral equations are obtained based on acoustic-elasticity theory.The spatial domain discrete forms of variation integral equations can be obtained based on FE method. The full coupling structure and fluid dynamic equation is as follows[13-14]:

where Ms,Csand Ksare structural mass,damp and stiffness matrixes;Mf,Cfand Kfare fluid mass,damp and stiffness matrixes;Sfsis fluid and structure coupling matrix;u and p are vectors of displacements and sound pressures of nodes;Psis structural load vector;pfis fluid load vector.

Outboard water field of ships is much more extensive than ships itself,therefore outboard water fields can be assumed as infiniteness.In this paper,sound infinite element technology is used to model far field nonreflecting boundary condition.The far field sound pressure p∞of far field distance r can be extrapolated based on information of sound infinite elements.The noise source level at distance 1 m can be extrapolated based on IFEM results.

Pipelines are chainlike networks,beam elements can be used to model the pipeline for low frequency vibration response evaluation.One benefit of using structural beam element is much less time-consuming than three-dimensional elements.Considering that the compressibility of fluid can be neglected,the fluid filled pipes can be modeled as equivalent fluid beams with fluid inertia influence on beam vibration taken into account[14].

Practical pipeline systems contain pumps,valves,users,flanges,pipes,elbows,vibration isolators,flexible pipes,flexible supports,etc.The inertias and stiffness of discrete elements should be set carefully because that the veracity of discrete elements characteristics determines the precision of system vibration and noise evaluation results[15].

Discrete elements such as vibration isolators,flexible pipes,flexible supports et al could be modeled as spring and dashpot elements.The complex elasticity coefficients along x,y,z directions are Cxx,Cyyand Czz;the real elasticity coefficients along x,y,z directions are kx,ky, kz;the imagine elasticity coefficients along x,y,z directions are ηx,ηy,ηz:

Discrete elements such as pumps,valves,flanges,etc could be modeled as inertial elements.The mass is m and inertial moments along main axes x,y,z are Ix,Iy,Iz.In local reference frames,the mass matrix of element is diagonal:

3 Low noise collocation on typical fluid pipeline system

Low noise collocation analysis is taken on some typical shaft seawater cooling system. Two types of pumps with different hydraulic performances are tested under five designed hydraulic conditions each.In the mean time,hydraulic and vibration and noise performances of the shaft cooling system are evaluation and the numerical results are compared to experimental results for verification.The purposes of following analysis lay in two objects:firstly,testing on shaft cooling system experimental model provides input and verification data for evaluation methods;secondly,based on evaluation results on outfield noise radiation under different collocation schemes,low noise collocation principles can be validated.

3.1 Experimental and numerical models of shaft cooling system

Design and experiment models of shaft cooling system are illustrated in Fig.3.Cooling users include drive equipment,shaft sealing and controller,etc.Cooling pumps are used to provide cooling water for users.Branch flow volume rates are adjusted and balanced by control valves.Sea water flows in larboard and flows out through starboard and shaft sealing.

Fig.3 Design and experiment models of shaft cooling pipeline system

In experiment,control valves are used as a substitute for cooling users.The fluid resistances of control valves with some specific openings equal that of cooling users.The hull is neglected and outboard water field is modeled as water tank.The inlet and outlet positions are arranged identical to design.The experiment contents hydraulic and vibration tests of system.

Cooling flow volume rates of users,corresponding pressure drop and diameter of pipes are illustrated in Tab.1.Rated and tested hydraulic working conditions of two types of pumps are illustrated in Tab.2.The hydraulic and vibration&noise performances are collected under the corresponding hydraulic states.Pumps provide equal or more cooling water volume rates than cooling needs of users.The particular meanings of testing states are:(P1-1)means full rotating speed,valve full opening,system flow volume rate is much redundancy;(P1-2)means full rotating speed,valve specific opening,system flow volume rate is a little more than cooling water needed;(P1-3)means full rotating speed,valve specific opening,system flow volume rate is near to cooling water needed;(P1-4)means decreased rotating speed,valve full opening,system flow volume rate is a little more redundancy;(P1-5)means decreased rotating speed, valve full opening,system flow volume rate is near to cooling water needed.The meanings of hydraulic testing states of P2 are similar to those of P1.

Tab.1 Characteristic parameters of cooling users

Tab.2 Hydraulic testing conditions of pumps

Hydraulic evaluation model of shaft cooling pipeline system is established based on experiment model.The hydraulic network is illustrated in Fig.4.Total pipeline and hull coupling acoustic-elasticity model is established based on design model.The finite element model is illustrated in Figs.5 and 6.

Fig.4 Hydraulic evaluation model of shaft cooling pipeline system

Fig.5 Acoustic-vibration finite element model

Fig.6 Pipeline system in hull

3.2 Experimental and numerical results

3.2.1 Numerical method verification

The hydraulic states of pumps and systems can be evaluated based on tested hydraulic performances of pump1 and pump2.The hydraulic numerical and experimental results of pump1 are listed in Tab.3.Departures between evaluation and experiment results are within 10%, which means the hydraulic evaluation method is verified by experiment and can be used for engineering applications.

Tab.3 Comparisons of pump1 numerical and experimental hydraulic results

In order to verify vibration evaluation method,only pipeline system is modeled by finite element model based on equivalent fluid beam theory.The pipeline supports is modeled as springs with modular 1e6.Taking P1-1 hydraulic state as example,comparisons of tested and calculated vibration levels at first pump inlet and outlet supports are illustrated in Fig.7.

Fig.7 Comparisons of tested and calculated vibration levels at first pump inlet and outlet supports

The results in Fig.9 indicate that evaluation results undervalued the vibration acceleration levels.This may be caused by neglecting vibration source of valves.The characteristic frequencies of evaluation results are less than those of experiment results,which may be caused by not taking account of frequency dependence characteristics on springs.In despite of some departure,the vibration evaluation method is still verified by experiment and can be used for engineering applications.

3.2.2 Analysis on vibration transfer and low noise collocation schemes

Based on source excitations of pumps under hydraulic states listed in Tab.2,corresponding source SPLs are evaluated and illustrated in Fig.8.The flow volume rates of pump1 are 8. 9t/h,6.6t/h,5.3t/h under hydraulic states P1-1,P1-2,P1-3,pump1 moves to design point(Q: 8.9t/h,H:27 m)ordinals P1-1,P1-2,P1-3,and source noise level decreases 1 dB and 2 dB.The flow volume rates of pump2 are 9.5t/h,6.3t/h,5.6t/h under hydraulic states P2-1,P2-2, P2-3,pump2 moves away from design point(Q:12t/h,H:17 m)ordinals P2-1,P2-2,P2-3, and source noise level increases 8dB and 7dB.The results indicate that noise of system is the lowest while pump works under design points.The flow volume rates of pump1 are 8.9t/h,6. 1t/h,5.2t/h under hydraulic states P1-1,P1-4,P1-5,the rotating speed of pump1 decreases and source noise level decreases 6dB and 1dB.The flow volume rates of pump2 are 9.5t/h,7. 5t/h,5.1t/h under hydraulic states P2-1,P2-4,P2-5,the rotating speed of pump2 decreases and source noise level decreases 2 dB and 4 dB.The results indicate that noise of system decreases with lowing rotating speed and cutting off hydraulic power redundancies of system. Therefore,low noise collocation principles are validated.The system source noise of this shaft cooling system can be lowered about 10 dB under optimized collocation scheme P2-5 based on low noise collocation principles.

Fig.8 Source SPLs of pipeline systems under working conditions of two type pumps

4 Conclusions

In this paper,low noise collocation principles are concluded,evaluation methods on hydraulic and vibration and noise radiation of pipeline systems are established,the evaluation methods can be used as design tools.Low noise collocation schemes of some typical shaft cooling pipeline system are presented,low noise collocation principles and evaluation methods are validated and verified.These instructive conclusions are achieved:

(1)Based on low noise collocation principles and hydraulic evaluation methods of pipeline network,types and hydraulic performances of pumps can be selected to match system resistances,diameters of pipes and openings of valves can be confirmed to balance cooling water volume rates of users;thus,low noise collocation schemes should be established.The hydraulic evaluation method is verified elementary.

(2)Based on vibration and noise radiation evaluation methods of pipeline and hull coupling system,source noise levels under different collocation schemes can be evaluated andvalued;the study on typical shaft cooling system provides implement approaches.The vibration evaluation method is verified elementary,and the noise radiation evaluation method should be verified in future.

(3)Based on tested and evaluated results on hydraulic and vibration&noise characteristics under different collocation schemes of shaft cooling system,the effects of low collocation design under low collocation principles are shown remarkable.The noise level of the typical fluid pipeline can be lowered about 10 dB by putting pump working states near the design point and reducing rotating speeds of pumps to cutoff hydraulic power redundancies.

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水管路系統(tǒng)低噪聲配置研究

何 濤1，2，孫玉東1，2，吳文偉1，2，吳有生1，2

（1.中國船舶科學(xué)研究中心 船舶振動(dòng)噪聲重點(diǎn)實(shí)驗(yàn)室；2.江蘇省綠色船舶技術(shù)重點(diǎn)實(shí)驗(yàn)室，江蘇 無錫，214082）

管路系統(tǒng)的水力功能和振動(dòng)噪聲性能相互影響皆為設(shè)計(jì)目標(biāo)。艦船領(lǐng)域中冷卻水管路系統(tǒng)長期開啟，管路系統(tǒng)振動(dòng)及船外輻射噪聲受到關(guān)注。為實(shí)現(xiàn)船外輻射噪聲的控制，有必要建立水力和聲學(xué)的協(xié)調(diào)設(shè)計(jì)技術(shù)。文章以低噪聲配置原則為管路系統(tǒng)設(shè)計(jì)指導(dǎo)，基于復(fù)雜水力管網(wǎng)計(jì)算方法進(jìn)行管系合理配置，基于管系等效水梁及管系—船體聲固耦合整體建模方法進(jìn)行振動(dòng)及船外輻射噪聲計(jì)算評(píng)估，形成了水力與聲學(xué)協(xié)調(diào)的管路系統(tǒng)低噪聲配置技術(shù)流程。以典型冷卻水管路系統(tǒng)為對(duì)象，初步測試驗(yàn)證了配置原則和計(jì)算方法。

水管路系統(tǒng)；水力；振動(dòng)；低噪聲配置

U664.5

:A

何 濤（1983-），男，博士研究生，中國船舶科學(xué)研究中心工程師；

U664.5

A

10.3969/j.issn.1007-7294.2015.09.011

1007-7294（2015）09-1149-11

孫玉東（1965-），男，中國船舶科學(xué)研究中心研究員；

吳文偉（1969-），男，中國船舶科學(xué)研究中心研究員；

吳有生（1942-），男，院士，中國船舶科學(xué)研究中心研究員。

Received date：2015-06-09

Foundation item:Supported by Natural and Science Fund of Jiangsu Province-Youthful Fund(BK2012096)

Biography：HE Tao(1983-),male,Ph.D.student,engineer;

SUN Yu-dong(1965-),male,researcher.