同濟(jì)大學(xué)結(jié)構(gòu)動(dòng)力學(xué)簡(jiǎn)答題

1、同濟(jì)大學(xué)結(jié)構(gòu)動(dòng)力學(xué)期末考試What are the step-by-step methods for calculating structural dynamic response?(有哪些方法)Interpolation of excitation methodCentral difference methodNewmarks methodWilson- methodState space methodDegree of freedom:The number of independent displacement required to define the displaced positi

2、ons of all the masses relative to their original positions is called the number degrees of freedom(DOFs) (chopra)The number of displacement quantities that must be considered to represent the effects of all significant inertia force is called the number of freedoms of a system. Roy R. CraigEffect of

3、 damping in vibration:Natural frequency of damped systemNatural Period of damped systemExistence of damping will reduce the natural frequencyFor normal structureThe displacement amplitude decays exponentially with timeThe effect of damping is on the rate at which free vibrationdecaysMode Shape: it a

4、ssociates with frequency. And, it is deformed mode of object at that frequency. Example: resonance occurred when,it makes the maximum deformation, different shape (deformation), different frequency.Mode shape is the proportional relationship among the displacement of DOFs.Mode shape is most likely t

5、o occur in the form of the deformation, and the first mode is the easiest one. Therefore, shape functions are selected as close as possible to the mode shape to simplify the analysis.Names of methods for determining the first several vibrations modes of a MDOF system?Superposition methodRayleigh-Rit

6、z methodReyleigh methodMatrix iteration methodJacobi iteration methodSubspace iteration methodStodola iteration methodFor SDOF system under harmonic loading, when the frequency ration一 is very small the amplitude factor is close to 1, when becomes very large becomes very small, explain why? Displace

7、ment response amplification factorr !2婦單自由度系統(tǒng)承受諧波荷載，當(dāng)頻率比很小時(shí)，振幅放大系數(shù) 接近于1，當(dāng)頻率比很大時(shí)，振幅放大系數(shù)較小。請(qǐng)簡(jiǎn)要解釋 原因。The single-degree-of-freedom system bears harmonic load. When the frequency ratio is small, the amplitude amplification coefficient is close to 1. When the frequency ratio is large, the amplitude amplif

8、ication coefficient is small. Please briefly explain why.“具有粘滯阻尼的系統(tǒng)，理論上其自由振動(dòng)永遠(yuǎn)不會(huì)停止”， 這種說(shuō)法是否正確？為什么？Is it true that a system with viscous damping, in theory, will never cease to vibrate freely? Why?什么情況下多自由度體系的動(dòng)力反應(yīng)不能采用疊加法計(jì)算，需 要采用逐步法計(jì)算？Under what circumstances can the dynamic response of a multi-degree

9、-of-freedom system not be calculated by the superposition method, but by the stepwise method.請(qǐng)舉出土木工程領(lǐng)域避免和利用結(jié)構(gòu)振動(dòng)的各兩個(gè)例子。Please give two examples of avoiding and utilizing structural vibration in the field of civil engineering.Civil EngineeringVibrationmonitoringincivilengineeringisatopicthatcoversawid

10、erangeofapplications, includingallthepossiblevibrationsourcesthatcanaffectastructureoraconstructionsite. Itspurposeisdouble:fromonesideitisimportanttoassurethatvibrationsdonotaffect structuresorpeopleandontheothersideitisimportanttoobtaininformationonthe structuredynamicsandonthephenomenaanalyzed.Th

11、etypicalinstrumentationrequiredisusuallytemporaryandincompliancewithregional ornationalstandarddirectives.THEMAINAPPLICATIONSINTHISFIELDARE:CONSTRUCTIONSITESThestructuresinproximityofaconstructionsiteneedatemporaryinstrumentation dedicatedtothevibrationmonitoringinordertoevaluatethestructuraldamagea

12、ndthe humancomfort(onlyincaseofbuildings).Automaticalertsmustbeimmediatelysentin caseofhighvibration,exceedingthresholdlevels.Specificsitealarmsareusefultoforcea reductionoftheworkintensity.RAILWAYMONITORINGTherailwaymonitoringsurveyistypicallya24hoursvibrationmeasurementwiththree mono-axialvelocitysensorsatadistanceofabout10metersbetweentwoconsecutive sensors,wherethemaximumvelocitiesarecollectedandanalyzed.Therelevantfrequency contentisusuallyintherangeof15Hzto80Hz.復(fù)雜結(jié)構(gòu)(超過(guò)十萬(wàn)自由度)求前若千階