My doubt is that modal mass coefficient and participation factor as per atc 40 are unitless values. Modes are inherent properties of a structure, and are determined by the material properties and boundary conditions of the structure. How to perform a natural frequency modal analysis in. Depending on industry standards, the minimum number of modes to run in a modal analysis depends on the mass participation percentage. The modal participation factor i for mode i is mo ii li i 26 the modal participation vector is thus.
A free powerpoint ppt presentation displayed as a flash slide show on id. How to calculate the modal mass and modal stiffness. Have you ever wondered how modal analysis is actually working. Help me please ive done modal analysis in ansys on my structure.
You can get that info out of workbench or ansys classic with a snippet. The structures response is based on a subset of the modes of the system, which must first be extracted using an eigenfrequency extraction procedure natural frequency extraction. The modal participation factor is a measure of how strongly a given mode contributes to the response of the structure when subjected to forcedisplacement excitation in a specific direction. Interpreting the modal mass participating ratios table. Nov 18, 2016 why there is no load in a modal analysis. A finite element analysis using the commercial computer program ansys. How can i show model participation factor for modal. The modal participation factors and effective mass will be computed and output to the. A point mass adds mass without additional flexibility to the structure thus reducing the natural frequency km0. Ansys normalizes the mass, so the modal mass matrix is an identity matrix and the modal stiffness matrix is a diagonal matrix of the 1omega2 values, where omega is the natural frequency of each mode in radianssec.
When a horizontal force is acted upon a building, it gets deflected. Sim mech seems to have no problem solving for the modal frequencies the first 6 being the ridged body modes but when i look at the mass participation results file they dont make sense. When i checked the effective mass em for rotational dof, it is very large compared with total mass of the model. Modal analysis is a process of extracting modal parameters natural frequencies, damping loss factors and modal constants from measured vibration data. 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. The captured modal mass is another way of quantifying the importance of the mode and the two are related. I cant however find any useful documentation on how to do this in comsol 4. Ansys modal analysis normal mode eigenvalues and eigenvectors. Ppt modal analysis powerpoint presentation free to. Quantification of uncertainties and model updating master. There are very few documents where they have written the mass participation factor, and its direction, external excitation direction and mode shape determine the no of modes we have to consider. Organizations around the world trust ansys to deliver the best value for their engineering simulation software investment. The participation factor is a measure of the importance of the mode in earthquake type load.
Also, all values of effective mass are very low and the sum of them do not equal total mass of the structure. Modes with relatively high effective masses can be readily excited by base excitation. Aug 21, 2014 as soon as you drag the box, ansys will highlight the geometry and model boxes in the main project. Determine the number of modes for linear dynamic using mass participation. Hi, returning to this unanswered topic because you seem to ask the similar question on react forum. Transient modal dynamic analysis gives the response of the model as a function of time based on a given timedependent loading.
Discuss associated concepts, terminology, and mode extraction methods. How to perform a natural frequency modal analysis in simulation mechanical. Understanding the mass participation factor engineer jau. Modal analysis and participation factors ansys student community. 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. Hi logesh, you can add param,effmas,yes in your input deck bulk part or in hypermesh tool pagecontrol cardsparam,effmass,yes. Understanding mass participation factor results in frequency studies. 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.
How can i view modal participation factor after carrying out. Hello, i am running a modal analysis to find the natural frequencies of a pod and have some questions about. Modal analysis calculates the natural frequencies of the system alone. Modal participation factors structural engineering. The degree of participation of each natural mode in the overall vibration is determined. Allow users to easily view a modal analysis effective mass data without searching through the solver output file.
The modal mass is actually different than the participation factor masses. Tmd r is commonly known as the participation factor. I presume that you have basic understanding of a modal analysis. Dynamics check modal participating mass ratios youtube. Altair simsolid makes it easy to view modal participation factors.
A freefree test requires no fixture and eliminates the impact of fixture modes, friction, and most damping. Xansys view topic xansys struct participation factors. To understand this physically, we must first understand that our structures, not unlike the rest of the universe, are very lazy and tend to take the path involving least work. Its less valuable in any case i can imagine which is why its not readily available. Solidworks simulation finding mass participation factor. Shigeka yoshimoto, in engineering analysis with ansys software second. Participation factors are only available for get,ing from the most recent load step. Topic 6 structural dynamics iii analysis of elastic mdof systems. Jan, 2017 i presume that you have basic understanding of a modal analysis. The reason of big difference in torsional mass participation ratio between robot and etabs may be in different calculation models of slabs used in them rigid diaphragms in. I am surprise there is no clear cut answer to this till now, as far as i know and i got. What is effective mass and modal participation factor. Now lets elaborate whats wrong, the seemingly wrong and the nothing wrong. What are the importance of modal participation factor in.
Modal is the simplest analysis and the only thing it does is telling you what are the resonance frequencies of your geometry. Mass participation factor in each direction x, y, and z a modal analysis will not provide. How many modes should i run in a modal natural frequency. How can i view modal participation factor after carrying out modal. Mode participation factors are seldom directly useful. Modal analysis of a satellite geometry simcafe dashboard. Our new crystalgraphics chart and diagram slides for powerpoint is a collection of over impressively designed datadriven chart and editable diagram s guaranteed to impress any audience.
Dear all, i am doing 3d modal analysis using ansys. Sep 06, 2012 i am surprise there is no clear cut answer to this till now, as far as i know and i got. 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. Modal analysis determines modes to better understand the behavior of components and structures under free vibration. Participation factor and effective modal mass altair. Modal mass is independent of directioncoordinate systems as one example. Run simulation upto 90% of em in all dof or only in.
I use to retrieve participation factor after spectrum analysis and i was thinking that i could do the same after a modal analysis. They basically show no mass participation after the rigid body mo. In other words, modal effective mass fraction is the normalized modal effective mass. After an eigenfrequency step has been used to find the eigenvalues of a model, abaqusstandard automatically calculates the participation factor, the effective mass, and the composite modal damping for each mode so that these variables are available for use in subsequent linear dynamic analysis. Each natural frequency is associated with a certain shape, called mode shape, that the model tends. When you want to perform a linear dynamic problem small displacement analysis with linear elastic materials, the technique used in.
Drag and drop the geometry box onto we can now survey the imported geometry by double clicking internal components. Mode shapes mode participation factors how much a given mode participates in a given direction most fundamental of. Modes having a higher mass participation would be the most significant modes to be focused u. Topic 6 structural dynamics iii analysis of elastic mdof.
Definition of modal participation factor typical modal equation. 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. The student community is a public forum for authorized ansys academic product users to share ideas and ask questions. Generally the cumulative effective mass participation factor of around 80 to 90% in any given response direction. Geometry, mass, and constraints are the only factors that can affect modal analysis. Example of how to use the mass participation factor in. The effective mass participation factor represents the percentage of the system mass that participates in a particular mode. They are mostly used as an intermediate step to calculate the modal effective mass. Apr 28, 2006 i use to retrieve participation factor after spectrum analysis and i was thinking that i could do the same after a modal analysis. 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. Fluid effect on the modal characteristics of a square tank. Altair simsolid modal participation factors the altair blog. 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.
Mass participation factor and its role in modal anlysis. 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. Im using ansys to do a modal analysis of a given structure and everything is right, but then when i do the spectrum analysis to observe the response of the structure to an earthquake, i get some negative modal participation factors. I have run a modal analysis for 30 modes using ansys software. Ansys tutorial modal harmonic analysis using ansys me 510499 vibroacoustic design dept. Robot modal analysis torsional mass participation factor. As you said in sap2000 display tables, it gives the participation factors which is true but it. May 29, 2016 the important parts to understand is the mass and the mode. Youngs modulus, poissons ratio, and density are required.
Estimating structural response to random vibration. Getting 80% or better mass participation in all 6 degrees of freedom is important in getting accurate results from a vibration analysis. Chart and diagram slides for powerpoint beautifully designed chart and diagram s for powerpoint with visually stunning graphics and animation effects. Feb 04, 2016 define a coefficient vector l as rmtl 3 the modal participation factor matrix i for mode i is iim. Jamestown, ca introduction for classically damped structures, modal mass, stiffness and damping can be.
The internal components of this satellite have been simplified to reduce modal analysis run time. Introduction every structure has the tendency to vibrate at certain frequencies, called natural or resonant frequencies. Participation factor summary structuralmechanics modal mass participation factor. The effective modal mass provides a method for judging the significance of a vibration mode. Modal mass is now a native feature in ansys mechanical allow users to easily view a. How can i show model participation factor for modal analysis in. Download limit exceeded you have exceeded your daily download allowance. In my post example of how to use the mass participation factor in solidworks you can find a practical example where this methodology is implemented. The modal effective mass fraction is an indirect indication of how well a mode can be excited by basemotion. Ansys offers a comprehensive software suite that spans the entire range of physics, providing access to virtually any field of engineering simulation that a design process requires. Oct 05, 2016 how to simulate a tension test through elastic, platic, and failure using explicit dynamics. Modal mass, stiffness and damping by vibrant technology issuu. Topic 6 structural dynamics iii analysis of elastic mdof systems equations of motion for mdof systems uncoupling of equations through use of natural mode shapes solution of uncoupled equations recombination of computed response modal response spectrum analysis by example use of reduced number of modes.
I presented the results that you can obtain using that software. A spectrum analysis with a specified direction sed,0,1,0 could be used to obtain other values also printed out to the output file is the effective mass. Resoncne will occur if any 15 th modal drequency equal to external. Mode shapes mass participation factor modal effective mass natural frequencies parametric design. Nov 08, 2016 modal analysis of cantilever beam in apdl. How can i show model participation factor for modal analysis. The weighting, often called the modal participation factor, is a function of excitation and mode shape coefficients at the input and output degrees of freedom. Modal mass is now a native feature in ansys mechanical and can be accessed under solution information solution output participation factor summary. She sent me the table below of the modal participating mass ratios extracted from etabs and asked whats wrong with her model. Ansys generates the modal summary results from a dummy load a unit acceleration i think in all 6 degrees of freedom. Ideally the sum of the effective masses in each direction should equal total mass of structure effective mass participation factor 2. Modal mass coefficient and modal participation factor in.
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