简介:九十年代初期驱车到过浙江的人们可能都有过这样的感受,当时流传的一句顺口溜叫做“浙江到,汽车跳”,而对于前不见头后不见尾的大堵车的场景可能更是记忆犹新。但是今天,不到十年的发展,尤其是在整个“九五”期间,浙江的公路交通发生了翻天覆地的变化,取得了突飞猛进的发展。截止到2001年底,公路总量已经达到了44005公里,其中高速公路774公里。一级公路1849公里,二级公路5682公里,公路网密度达到43.2公里/百平方公里,公路通乡率达99.6%,通行政村率达96,9%;再过几个月又将有533公里的高速公路建成通车,届时浙江省高速公路总数将达到1307公里,众所瞩目的全省公路“四小时交通圈“(即省会杭州到其余各市四个小时均可到达)的目标也即将成为现实。
简介:Ananalyticalstudywaspresentedonactivecontrolofsoundtransmissionintoavibro-acousticenclosurecomprisingtwoflexibleplates.Twotypesofactuatorswereused,i.e.acousticactuatoranddistributedleadzirconatetitanatepiezoelectric(PZT)actuatorinsteadofpointforceactuator.Usingthemodalacoustictransferimpedance-mobilitymatrices,theexcitationandinteractioninthecoupledsoundtransmissionsystemcanbedescribedwithclearphysicalsignificance.Withthecontrolsystemdesignedtogloballyreducethesoundfield,differentcontrolsystemconfigurationswereconsidered,includingthestructuralactuatorontheincidentplate,actuatoronthereceivingplate,acousticactuatoronthecavity,andtheircombinations.Theeffectivenessandperformanceofthecontrolstrategycorrespondingtoeachsystemconfigurationwerecomparedanddiscussed.Theroleandcontrolmechanismofeachtypeofactuatorwereofparticularinterest.Itwasshownthattheincidentplateactuatoriseffectiveincontrollingthecavity-dominatedmodesandthestructuralmodesdominatedbytheincidentplateandreceivingplate.Twomaincontrolmechanismsareinvolvedinthiscontrolconfiguration,i.e.,modalsuppressingandmodalrearrangement.Forcontrolsystemconfigurationwithonlyacousticactuatorintheenclosure,themechanisminvolvedinthisarrangementispurelymodalsuppression.Desirableplacementsofstructuralactuatorsintermsoftotalpotentialenergyreductionwerealsodiscussed.