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1、Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5
2、.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with A
3、spose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Asp
4、ose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.2.4 2.4 单自由度系统的简谐强迫振动单自由度系统的简谐强迫振动 n简谐强迫振动指激励是时间简谐函数简谐强迫振动指激
5、励是时间简谐函数，它在工程结构的振动中经常发生，它通常是由旋转机械失衡造成的。简谐强迫振动的理论是分析周期激励以及非周期激励下系统响应的基础。通过分析系统所受的简谐激励与系统响应的关系，可以估计测定系统的振动参数，从而确定系统的振动特性（系统识别）。n利用可以产生简谐激励的激振器激励被测结构以分析利用可以产生简谐激励的激振器激励被测结构以分析其振动特性的方法，即所谓正弦激励方法，是测试系其振动特性的方法，即所谓正弦激励方法，是测试系统振动特性最常用的方法之一。统振动特性最常用的方法之一。 Evaluation only.Created with Aspose.Slides for .NET 3
6、.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.2.4.1 2.4.1 系统在简谐激励下的响应系统在简谐激励下的响应典型的受简谐激励的单自由度系统示于图2-13。 图 213Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client
7、 Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.图 214Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only
8、.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.从波形图可以看出： Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.
9、0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.2.4.2 2.4.2 复频率响应复频率响应 幅频特性与相频特性幅频特
10、性与相频特性 n稳态响应的幅值和相角是激励频率的非线性函数稳态响应的幅值和相角是激励频率的非线性函数，在理论分析和实际工作中常引进复频率响应来描述激励频率对响应的影响激励频率对响应的影响。n简谐运动可用复数表示，因而稳态振动也可用复数表示，设有下面两个方程：Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 C
11、lient Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only
12、.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.图 215Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Cop
13、yright 2004-2011 Aspose Pty Ltd.图 215Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.系统稳态振动时，惯性力、弹性力、阻尼力都是与激励同频率的简谐量，分别为：Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd
14、.图216Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.图216Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.图216Evaluation only.Created with Aspose.Slides for .NET 3.5 Cli
15、ent Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.2.4.3 2.4.3 能量关系与
16、等效阻尼能量关系与等效阻尼Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Cli
17、ent Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.说明：说明： 无阻尼系统受简谐激励时，如果激励频率等于系统固有频率，由无阻尼系统受简谐激励时，如果激励频率等于系统固有频率，由于系统无阻尼，因此外力对系统做的功全部转成系统的机械能即振动于系统无阻尼，因此外力对系统做的功全部转成系统的机械能即振动的能量。外力持续
18、给系统输入能量，使系统的振动能量直线上升，振的能量。外力持续给系统输入能量，使系统的振动能量直线上升，振幅逐渐增大。幅逐渐增大。 由此可知，即使是无阻尼系统共振时，也需要一定的时间来积由此可知，即使是无阻尼系统共振时，也需要一定的时间来积累振动能量。这在实际中很重要，有些机械结构在起动或停机时无法累振动能量。这在实际中很重要，有些机械结构在起动或停机时无法避免通过共振区，为避免在共振区给结构造成损坏，可以采用迅速通避免通过共振区，为避免在共振区给结构造成损坏，可以采用迅速通过共振区的办法来解决过共振区的办法来解决。 图 217Evaluation only.Created with Aspos
19、e.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.2. 等效阻尼等效阻尼 n振动时振动能量的耗散有各种的形式，并且与许多因素有关，处理起来比较复杂。在线性振动理论中，通常把其他形式的阻尼等效为粘性阻尼，以使阻尼力线性化，得到等效的线性系统。其方方法是，假定系统做简谐振动，令原系统耗散的能量与粘性阻尼耗法是，假定系统做简谐振动，令原系统耗散的能量与粘性阻尼耗散的能量相同，从而求出等效阻尼系数散的能量相同，从而求出等效阻尼系数。 库仑阻尼和结构阻尼库仑阻尼和结构阻尼Evaluation only.Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0.Copyright 2004-2011 Aspose Pty Ltd.
