Understanding mass participation factor results in frequency studies. Understanding mass participation factor results in. I understand the need for a high mass participation factor. Understanding the mass participation factor engineer jau. Xansys struct participation factors hi all, i tried to retrieve participation factors after modal analysis with some get and i saw that its not possible since get,mode,pfact gives only rotz dof i use to retrieve participation factor after spectrum analysis and i was thinking that i could do the same after a modal analysis. What are the importance of modal participation factor in analysis and. Some fea software call the input for modal analysis an eigl card for fea basics. Modal analysis parameters robot structural analysis.
Modal analysis is the study of the dynamic properties of a system in the frequency domain. Example of how to use the mass participation factor in. How can i show model participation factor for modal. For coupled acousticstructural eigenfrequency analyses, an additional. Dec 08, 2012 experimental modal analysis by dr mohit law.
Modal and mass participation factors are highly correlated. Input acceleration will be in this range, dependent on modal mass. But if the first six modes only contribute 60% mass participation, and above 12 th mode also if for mode. In diana all eigenvectors are normalized such that the corresponding generalized mass is equal to one 9. Modal analysis provides an overview of the limits of the response of a. What are the participation factors and the captured. Identification of important modes to use as guides in dynamic analysis. One common rule of thumb is that a mode should be included if it contributes more than 2% of the total mass. Select a modal analysis case in the new case dialog and click ok. Vibration mode vectors from the natural frequency analysis are used. Robot modal analysis torsional mass participation factor thanks pawel i actually suspect the spectra scaling factor to account for spmu was not calculated correctly by robot when i plot the fi.
Modes with relatively high effective masses can be readily excited by base excitation. Mass participation factor and its role in modal anlysis. In a previous post understanding the mass participation factor i have talked about the modal analysis in solidworks and how to make the most of it. For real systems there is often mass participating in the forcing function such as the mass of ground in an earthquake and mass participating in inertia effects the mass of the. I presented the results that you can obtain using that software. The effective mass participation factor represents the percentage of the system mass that. What is the difference between mass participation factor and mode. After that will make a seismic analysis for x, y and z placing the obtained period from modal analysis. The theoretical modal analysis anchors on a physical model of a dynamic system comprising its mass, stiffness and damping properties. Interpreting the modal mass participating ratios table from etabs posted on october 8, 2018 march 14, 2019 by engr dennis mercado i have not been modelling extensively in etabs this. Modal participation factor and modal mass coefficient for the first natural mode in sap 2000 shz7 structural 6 jun 17 02. Feb 15, 2017 modal analysis of centrifugal pump base frame using asnys workbench duration. For real systems there is often mass participating in the forcing function such as the mass of ground in an earthquake and mass participating in inertia effects the mass of the structure itself, m eq. Hello, i am trying to run a random vibration analysis in promechanica and have ran into a question about mass participation factors.
Modal participation factor and modal mass coefficient for the. When i am doing a modal analysis, how many resonant modes should i check. What are the participation factors and the captured modal. A sturm check is not possible for this structure analysis mode. Modal analysis embraces both theoretical and experimental techniques. This application note emphasizes experimental modal techniques, specifically the method known as.
Another is that a cumulative mass participation factor of 0. These properties may be given in forms of partial differential equations. Analytical modal analysis depends on the generation of the. May 11, 20 priestley et al 1996, among other authors, confirm that a sum of all empf known as cumulative effective mass participation factor, cempf of 80% to 90% in any given response direction can be considered sufficient to capture the dominant dynamic response of the structure. The modal mass participation ratio is widely used as the metric to determine the relative significance of modes in a modal response spectrum. On the other hand, regarding the results and if we look at the solution information tap, my main doubt is about participation factors values, as most of them are 0. Effective mass factors the effective mass factors associated with each. The captured modal mass is another way of quantifying the importance of the mode and the two are related. If the option periods with maximal mass participation is off in the seismic analysis dialog, the first.
Finite element simulations are conducted using ansys program to investigate the effect of. Interpreting the modal mass participating ratios table from etabs. The participation factors are, thus, defined for the translational degrees of freedom and for rotation around the center of rotation. Topic 6 structural dynamics iii analysis of elastic mdof systems. Mechanical vibrations overview of experimental modal analysis. I cant however find any useful documentation on how to do this in comsol 4. The modal participation factor i for mode i is mo ii li i 26 the modal participation vector is thus. My doubt is that modal mass coefficient and participation factor as per atc 40 are unitless values. Analytical modal analysis depends on the generation of the equations of motion of a system through a finite element model. But if the first six modes only contribute 60% mass participation, and above 12 th mode also if for mode the mass participation factor is higher should we check with compressor harmonics upto that or not. For seismic loading, mass participation factors are calculated. Modal analysis of centrifugal pump base frame using asnys workbench duration. After spending some time yesterday i discovered that i might be able to use modal analysis and extract the mass participation factors to get a measure of the energy contained within each resonance mode.
Modal analysis provides an overview of the limits of the response of a system. Interpreting the modal mass participating ratios table. On the other hand, modes with low effective masses cannot be readily excited in this. The effective modal mass provides a method for judging the significance of a vibration mode. All the data, from measurement and analysis, is kept in pandas dataframes, which can be read and. The theoretical modal analysis anchors on a physical model of a dynamic system comprising its mass, stiffness and damping. How to calculate the relative contribution of each mode in.
Openmodal accelerating the implementation of your ideas. An example of the use of finite element analysis in the creation of a lowcost, environmentally sensitive structure is itford farm bridleway bridge 2. The modal model modes are inherent properties of a structure, and are determined by the material properties mass, damping, and stiffness, and boundary. The mass participation associated with each mode represents the. Run modal in the way to get 90% mass participation factor, then seismic cases will automatically.
Than after that will make a load combination for this to obtain the proper forces. Vibration analysis with solidworks simulation 2015 7 before you start notes on handson exercises and functionality of simulation this book goes beyond a standard software manual. How can i show model participation factor for modal analysis. Till now we are not considering the mass participation factor for targeting the modes.
How do i calculate the fixedmass participation ratio of the model. Priestley et al 1996, among other authors, confirm that a sum of all empf known as cumulative effective mass participation factor, cempf of 80% to 90% in any given response direction can be considered sufficient to capture the dominant dynamic response of the structure. The captured modal mass is another way of quantifying the importance of the mode and the two are. Analytical modal analysis modal analysis is the process of characterizing the dynamic response of a system in terms of its modes of vibration. What is difference between time history analysis and response spectrum analysis. Modal participation factor and modal mass coefficient for. It is important to note that the calculations are referring to the effective mass of the system, not the true mass. Topic 6 structural dynamics iii analysis of elastic mdof.
Modes having a higher mass participation would be the most significant. Modal mass coefficient and modal participation factor in sap2000. Modal parameters estimation of building structures from vibration. The modal model modes are inherent properties of a structure, and are determined by the material properties mass, damping, and stiffness, and boundary conditions of the structure. According to this method you can calculate the exact value for both x and y directions. Each mode is defined by a natural modal or resonant frequency, modal damping, and a mode shape i. Practical dynamic analysis and design for engineers and. For example, asce 705 710 is at home, sorry, section 12. After spending some time yesterday i discovered that i might be able to use modal analysis and extract the mass participation factors to get a measure of the energy contained within. Citeseerx document details isaac councill, lee giles, pradeep teregowda. The captured modal mass percentage shows how much of the response is attributed to a particular mode and also shows the mode orientation x, y or z.
Altair simsolid modal participation factors the altair blog. The modal participation factors and mode shapes are obtained from the. The modal mass participation ratio is widely used as the metric to determine the relative significance of modes in a modal response spectrum analysis. The eigrl card is just a way to enter the parameters for the modal analysis, which are in general. In the modal analysis of plane frames the main aim is to determine the natural mode shapes and frequencies of an object or structure during free vibration. Recall that in a frequency analysis, when we plot the mode shapes, the. Run modal in the way to get 90% mass participation factor, then seismic cases will automatically take all these modes for calculations. If the direction of the load is known, examine the mass participation factor and the direction of each mode. Xansys struct participation factors hi all, i tried to retrieve participation factors after modal analysis with some get and i saw that its not possible since get,mode,pfact.
To define the modal analysis parameters for new dynamic cases in the structure, do one of the following. I understand the need for a high mass participation factor to determine global modes over local modes but i do not understand why an increased number of modes should be used for the random analysis when the frequency range of interest is so much lower than the. The use of finite element analysis in the design of. Nov 18, 2016 some fea software call the input for modal analysis an eigl card for fea basics.
This recommendation was duly noted by my colleague bill reuss, in his blog article from august. Oct 08, 2018 interpreting the modal mass participating ratios table from etabs posted on october 8, 2018 march 14, 2019 by engr dennis mercado i have not been modelling extensively in etabs this recently so this query from a former had my technical engine humming once more. Mod03 lec05 modal response method, modal mass contribution duration. Modal mass coefficient and modal participation factor in.
This program finds the eigenvalues and eigenvectors for a. The modal excitation factors for each vibration mode are calculated. Xansys view topic xansys struct participation factors. Also, all values of effective mass are very low and the sum of them do not equal total mass of the structure.
To develop a preliminary fe model using the commercial software ansys. I want to find out the saspectral acceleration and sd spectral displacement to convert the available pushover. Robot modal analysis torsional mass participation factor. Definition of modal participation factor typical modal equation. This should give you consistent modal participation factors.
I carried out modal analysis in ansys apdl for mode shape upto 100 modes since i wasnot able to obtain modal participation factor more than 90 % with lesser mode. As eigenvibration modes are important for seismic analyses, those which are characterized by a large mass participation factor will be set. Most codes require that at least 90% mass participation factor in each of the lateral directions be obtained for the modeshape extraction used for dynamic analysis. In dynamic analysis, two related topics, resonance and modal. This application note emphasizes experimental modal techniques, specifically the method known as frequency response function testing. The fixedmass participation ratio may be calculated as follows.
Seismic analysis parameters us code asce 710 ibc 2012. Can anyone help with a problem with opensee program. When conducting a frequency or linear dynamics study in solidworks simulation, a highly recommended, bestpractice post processing technique is to investigate both the effective mass participation factor empf and the cumulative effective mass participation factor cempf of the output mode shapes. Conducts a spectral and a seismic analysis using the pseudo modal method. The use of finite element analysis in the design of footbridges. Other areas are treated in a general sense to introduce their elementary concepts and relationships to one another. Naturally, the same goes for dynamic analyses with centers of mass shifted. Random vibration mass participation factors finite. By plotting the mass participation you can see just how important each mode is. The participation factor is a measure of the importance of the mode in earthquake type load.
Openmodal is built using established libraries such as numpy, pandas, pyqtgraph, scipy and others. Several programs such as solidworks are provided with a finite element. Ansys tutorial ansys workbench modal analysis youtube. Sep 06, 2012 till now we are not considering the mass participation factor for targeting the modes.
Quantification of uncertainties and model updating master. Altair simsolid makes it easy to view modal participation factors. Modal analysis is defined as the study of the dynamic characteristics of a mechanical structure. This article what is modal analysis and why is it necessary gives a more detailed answer to your question, but in short. Priestley et al 1996, among other authors, confirm that a sum of all empf known as cumulative effective mass participation factor, cempf of. I have analyzed the frame for the load cases pushover, gravity and modal.