经典物控计算题.doc

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1、某车间16*8*3，在侧墙位置台机床，采用吸声降噪的方法，在距机床8米位置噪声降至NR-55，试设计吸声降噪。频率125250500100020004000dB706265605653长m16宽m8高m3体积mmm384384384384384384面积mm400400400400400400倍频程中心频率/Hz顺序项目125250500100020004000说明18米处dB706265605653实测2Nr-55706358555250目标值3需要减噪量Lp007543‘1-24处理前平均吸声系数a10.060.080.080.090.110.11估测5处理后吸声系数a20.060.0

2、80.400.280.280.22a2=a1*10^(0.1*Lp)67处理前吸声量243232364444A1=a1*S8处理后吸声量24.0032.00160.38113.84110.5287.79A2=A1*10^(0.1*Lp)9选材料a0.110.360.790.710.790.75查表，产品资料10所需材料数量m20.000.00203.01160.34139.90117.06S=A/a128+7511实际铺设顶128mm,侧墙24，两侧3*7.5=20212面积SS20220220220220220213计算实际吸声量As22.2272.72159.58143.42159.5

3、8151.5As=a*SS14198198198198198198未铺设剩余面积15未铺设剩余面积吸声量11.8815.8415.8417.8221.7821.7816实际吸声总量34.188.56175.42161.24181.36173.2817实际降噪量dB1.534.427.396.516.155.9518处理后声压级值dB68.4757.5857.6153.4949.8547.05706358555250NR552-11管径100mm的气流通道上，设计一个共振腔消声器，要求125hz有15dB降噪量。截面积m2周长mm管径mm1000.00785314频率hz125降噪量dB15

4、声速m/S340Pi3.14设钢板厚mm2孔径mm51.9625E-055倍孔径间距mm25外径mm400计算过程内容手工取整1确定K3.912976910342求体积V0.026608242990.0273求总传导率G0.143927984430.1444求孔个数n44.025477707445确定长度l0.229299363060.236验算fr125.031268497上限f10378共振频率波长2.729波长/30.90666666667最大几何尺寸小于10波长/120.2266666666711一圈孔分布数12.5612孔排数3.5031847134设排数间距同孔间距13孔分布距

5、离mm62.579617834小于波长/1214某风机，风量60m3/min,风机进气口直径为250mm，在进口2米处测得噪声频谱如表，设计一阻性消声器，消除噪声。直径d流量m3/s流速m/s0.25120.382165605倍频程中心频率序号项目6312525050010002000400080001频带声压级dB108112110116108106100922NR8510397928784828179相当于90dBA3应有消声量5151829242419134P/S16161616161616165选材料吸声系数a00.30.50.80.850.850.860.80.78设定厚度6消声

6、系数0.40.71.21.31.31.31.21.17消声器长度0.781251.33928571430.93751.39423076921.15384615381.15384615380.989583333330.73863636364取为1.4米8消声器长度1.11.21753246750.710227272730.852272727271.26748251751.0489510491.0489510490.899621212120.671487603319高频失效=1.85*C/D2516101.4米消声器消声量8.9615.6826.8829.1229.1229.1226.8824

7、.6411从4000倍频程处消声量算起17.928.2133333333不满足12从8000倍频程处消声量算起16.426666667满足13气流再生噪声声功率114.59099906108.63960979102.6190098796.59840995990.57781004684.55721013278.53661021972.516010306给定r可计算出频带声压级根据Lp=Lw-20lgr-1114也可直接计算