Questions related to Structural Vibration
How can I get the second and third natural frequency of a cantilever beam experimentally??
The problem that I am facing is that I got only the first natural frequency.. I can't get other frequencies..
How to represent natural frequencies and mode shapes in same matrix for many cases for damage detection purposes?
I have the following questions regarding vibration-based damage detection of a cantilever beam:
1-What is the purpose of discretizing the cantilever beam by finite element technique?
2-Do the number of discretized elements and their length affect the modal analysis( healthy and damaged natural frequency, mode shapes)?
3- Why do the biggest changes in natural frequency happened when the damage occurred near the fixed end and became smaller if the damage occurred far away from its fixed end?
What is lattice mode in RAMAN vibration mode? In general, can you help me about what the lattice mode is in the RAMAN analysis?
I'm working on Sb2S3 thin films. During the Raman analysis, I saw that there are lattice mode vibrational modes. How is it different from symmetric S–Sb–S stretching or symmetric S–Sb–S bending? In General, can you help me about what the lattice mode is in the RAMAN analysis?
It is recommended to calibrate the measuring instruments before performing any experiment. Ideally, how often do we need to calibrate an accelerometer? Are there any simple and effective methods for calibrating accelerometers in the laboratory without seeking professional assistance?
The FEM discretized (meshed) geometry/domain is considered stiffer than the actual geometry/domain due to the assumption of variation of the displacement within each element. This is analogous to the displacement being constrained to vary in a particular fashion within each of the elements. This results in the stiffness of the discretized domain being greater than the actual domain. As the element size decreases (or the number of elements increases), the constraint on the displacement loosens due to the smaller size of the element and hence, the smaller constraint zone. Thus, the stiffness of the meshed domain decreases and approaches that of the actual domain as the number of elements is increased.
Based on the above reasoning, the natural frequencies (on increasing the number of elements) must converge from above to the actual value (i.e. converge from higher values to the actual value).
- Can this be considered to be strictly true?
- Has any deviation from it been observed (i.e. convergence from below or lower values to the actual value) and if so how can that trend be physically explained/interpreted?
I'm looking for some guidance and advise in the subject of "Machine Learning," which I'll utilize for my research interests in computational mechanics and structural vibration control.
In the article by Yang et al. (2004) , they said the total mass of the structure is 153000 t. However, in another article by Patil and Jangid , they consider the mass of the building to be 150000 t. Moreover, using the matlab files  and calculating the sum of effective modal masses, I found 210862.7 t.
 Benchmark Problem for Response Control of Wind-Excited Tall Buildings. Jann N. Yang; Anil K. Agrawal; Bijan Samali; and Jong-Cheng Wu
 Optimum Multiple Tuned Mass Dampers for the Wind Excited Benchmark Building. Veeranagouda B. Patil a & Radhey Shyam Jangid
Dear Research scholars,
I was doing my MTech thesis on pendulum based TMD and I was having trouble defining the link properties. I even followed the tutorials put on CSI website. still, I wasn't able to properly do that.I would be very grateful if anyone helped me with this.
Despite a few TMD cost models available in the literature, I am searching for more accurate initial and lifetime cost models of translational TMDs for Life Cycle Cost Analysis (LCCA) of TMD-equipped structures.
In fact, the provided cost model affiliated with one of the companies designs and manufactures transitional TMD (such as LeMessurier CO.), which this model consists TMD initial cost (construction and installation of the TMD) and TMD damage cost (maintenance and repair losses of TMD before structural collapse)
In ultrasonic assisted machining, ultrasonic welding etc. systems, transducers are required to vibrate in eigenfrequency . If we vibrate a system at its natural frequency ( eigenfrequency ), won't there be resonance? Why do we want to vibrate in mode shapes ( eigenfrequency )?
In general, the value of modal participating mass ratio (MPMR) for each vibration mode represents the participation of each mode in the structural responses.
when a structure equipped with TMD, a vibration mode is added to the others. MPMR value of the added vibration mode can be significant even when TMD mass is very small and as a result, TMD has no effect on the structural responses.
How can this contradiction be justified?
Can anyone suggest a data compression algorithm to compress and regenerate data from sensors(eg. accelerometer-it consists of time & acceleration) that are used to obtain structural vibration response?I have tried using PCA but i am unable to regenerate my data.Kindly suggest a suitable method or some other algorithm to go with PCA?
Weight drops generates vibrations in the floor they hit. Impulse mdv must be conserved, even if the floor or mass is cushioned with mats. Cushioning leads to less high frequency content in the resulting impulse noise and impact. Does that also lead to a higher content of lower frequency energy in the resulting floor noise and vibrations?
I am studying the solid-liquid interfaces. I created the solid-liquid coexistence system by combing solid part and liquid part with the same sectional areas together. Then the atoms in the solid were fixed, while the atoms in the liquid were allowed to move freely. The whole system reached equilibrium at a temperature above the melting point of the liquid. Then the system was slowly cooled down to a temperature below the melting point, which caused the liquid solidify. The problem was that the layers in the solidified structure as a whole move forward and backward in a plane parallel to the original solid-liquid interface. Why don't atoms in the solidified structure vibrate around their equilibrium sites? Why do they mainly move forward and backward along a particular direction?
I am currently working on a project which ask me to look for the natural frequency of engine girder structure. This is to ensure that the excited frequency from the engine does not coincide with the natural frequency of the structure. The engine is running at 1900RPM.
However, i am kinda lost because when i run the model using Modal analysis, The range of frequencies for 5 modes are only 1-5Hz, i would have to run around 1000 modes in order to reach 1900 RPM. Am i doing something wrong or is this the case? The structure is made up of around 20 shells.
I appreciate any help. Thanks.
I am looking to start working with the isogeometric method to analyze mechanical behavior such as beam, plate, shell and other structures of complex shapes.
can you help me by giving me simple examples in this method and with articles and books that have explanations and applications?
what do you suggest to me and thank you in advance?
How can I define frequency dependent damping in Ansys ?
it seems to be Damping frequency, but I am told that the value I input here, is used only to calculate the stiffness matrix coefficient, so If I input multiple values for damping , they will get overwritten
I am trying to find the resonant modes of a membrane or plate-like membrane, however, this requires a knowledge of the amount of tension on said membrane, specifically in a 2-d sinusoidal distribution of pressure. The only thing I am finding online is the calculation of surface tension of a fluid, or at least something which has a spherical shape, however, I need it for an initially flat solid.
I have frequency iterations and acoustic amplitude curve. I want to convert it into time vs acoustic amplitude curve. How can I do it using MATLB? Which transfrom required to apply?
Is there a way to find the Eigenvectors and Eigenvalues when there is unknown values in a complex damping matrix , using theoretical methods ?
Is it also possible to be done in MATLAB ?
There are shell theories like Love's, Donnell-Vlasov, Sander's,etc genrally used. Which theory is applicable here based on the limiting ratio mentioned above ?
How can I co-relate the response due to the rectangular rod sliding on plate (movement is made by hand) experiment with the mathematical model. The plate is simply supported. The force of excitation is also moving.
Ideally using both LaGrangian and Newtonian mechanics I need to conduct vibrational analysis on this system.
The system is structured as such:
Wall - SpringDamper - Rotating component 1 - SpringDamper - Rotating component 2 - SpringDamper - Rotating component 3 - SpringDamper - Wall
I have the equivalent mass moment of inertia for all 3 components and the effective spring stiffnesses of each connecting piece. I also have the To value for the system. These are as follows:
Jd1 = 25.5 kg.m2
Jd2 = 12kg.m2
Jd3 = 9kg.m2
Kt1, t2, t3, t4= 7.5E+05Nm/rad
To = 37.5Nm
Anybody have any expertise in this field? Vibrational analysis is something I struggle with and I've never carried it out on a torsional system before.
I am studying the supersonic flutter characterisitcs of rectangular panels. I am new to this domain and have certain fundamental questions that I am unable to answer. I am employing the Piston theory for determining the flutter boundary, i.e. the flutter speed and the corresponding frequency. I have seen several works in which the v-g (velocity-damping) and v-f (velocity-frequency) graphs are plotted and the critical velocity is determined from the v-g curve corresponding to the point where the damping corresponding to a particular mode crosses from negative to positive region. The velocity (is it correct to say free-stream velocity?) is varied from 0 to a particular velocity of interest.
If I am correct, these v-g and v-f curves are plotted for a particular Mach number (M>1 for supersonic) . If this is the case, I am unable to comprehend why the velocity is varied from zero to a higher value? In most of the papers that I have read, M is defined as the free stream Mach number, M=(free-stream velocity/sonic speed). Is the velocity being varied (from vmin=0 to v) while keeping M (>1) constant?
Any help in clearing these misconceptions would be greatly appericiated.
I need to verify my models in ABAQUS, so I need a paper as a reference, what I need is properties of the beam's material, clear thermal loads, and the frequency changes.
thanks in advance.
I need to calculate the analytical relation for frequency of a cantilever composite beam, where one beam is prestressed on which an another non-prestressed beam is placed in a way to form the composite system. Can anyone tell if there is any such analtical expression or hint at possible way of derivation of it.
The Elastomeric pads can be used as vibration isolators. I want to know whether there is significant effect of initial compression (pre-loading) of this pads on increasing the dynamic stiffness or it does not worth.
I use Abaqus to model a slender composite structure subjected to dynamic wind actions.
I read in many parts of the literature that Aerodynamic damping exist and could be important for structure which are slender and interact with wind. I am not going into wind-structure interaction at all.
All I need is a convenient and acceptable way of accounting for Aerodynamic damping. From my knowledge on this aspect that the aerodynamic damping coefficient is different from the material/structural damping where a damping ratio is assumed. Instead, it relies on the velocity of the structure and changes with it which is very tedious to incorporate in a Structural Finite Element Analysis procedure.
Please suggest to me from your own experience on how to deal with this issue.
I have been working on the PPF controller for a couple of years, and now I want to start some research on the Saturation Controller. I know that both of them are resonant controllers for active vibration control and they have similarities, but what exactly makes them different from each other?
What special characteristics does the SC have which makes it more or less applicable?
Can you introduce some references that have performed a comparison work between these two methods?
Every time I try, it gives me this error "2 eigenvalues below the shift, Ritz analysis requires all eigenvalues to be above the shift". What can be the problem that makes this error exist?
If a molecule structure is downloaded from chemspider or pubchem, then how to identify point group to do DFT calculations?
Since the identification of point group is very important during the optimization of structure or for vibrational analysis.
Also identification of point group is difficult for long chain molecules.
M Chaitanya Varma
When the continuous systems such as string/beam vibrate in an viscous environment, we know that the natural frequencies of the system become damped natural frequencies and there exists a decay constant associated with each of the mode.
Are these decay constants (or damping factors) different for every mode or same? i.e. given an initial condition corresponding to specific modes, will the system decay down in same amount of period?
The question is raised due to this:
When string vibrates in viscous environment, the equation can be written as,
In this case when we discretize the equation using Galerkin's approach, the damping matrix becomes diagonal with every element same for standard boundary conditions.
I am working on mitigating traffic induced vibrations on buildings. I am looking for measures that can be applied at the RECEIVER side to mitigate vibrations. I did some research and I could find measures such as Free/ constrained layer damping, tuned vibration dampers, changing mass/ stiffness of the structure, base isolation. Can somebody suggest more measures that are practical?
Because I could only use the compression type accelerometer which is more sensitive to the zero shift in the impact test, I cannot obtain the accurate signal, and thus cannot obtain the correct velocity, displacement using common integration approach as well. The velocity and displacement shows unrealistic trend to increase continuously without approaching zero.
So my problem is how to process the acceleration correctly with matlab (preferred) or any other software, the detrend function in matlab seems to be unable to handle this problem.
After reading several relevant literatures I found that the discrete wavelet transform (DWT) method and the empirical mode decomposition (EMD) method may be appropriate to be applied. Have you ever met similar problem during the impact tests? Looking forward to hearing your experiences and thanks in advance.
The brief introduction is enclosed as attachment.
I would like to simulate ambient vibration in a numerical model such as a MDOF shear building. In some cases, the use of random Gaussian white noise can be a solution. Is it a plausible approach?
I have condensed a Finite element model from 8 nodes with 6 dof at each node into 2 nodes with 6 dof at each node using a static condensation method (or Guyan reduction). Now i would like to translate this nodal data (represented in stiffness matrix) into a 3D beam element. So for that i need the beam element properties (like Moment of inertia (Iyy and Izz), Polar moment of inertia (J), Shear modulus (G), Young's Modulus (E), Cross sectional Area and length (L)) from the 12 by 12 stiffness matrix.
What makes it difficult is that the model which i have reduced is made of different material at each sides hence the model does not have a constant Young's Modulus (E) or shear modulus (G).
Can anyone help me in finding out the beam element properties using the beam element stiffness matrix? Well we all know how to do the opposite.
The 3D beam element stiffness matrix definition and Finite element model descriptions are given in the attached .doc. The finite element model shown in figure 1 is before condensation, then the model is condensed into 2 nodes and the condensed stiffness matrix is given by Table 1.
Any help will be appreciated.
After analysis, I want to determined mode shape vectors for linearly elastic vibration modes. PERFORM 3D is announced "There are no Modal Analysis load case in this analysis series". How do you define Modal Analysis load case in PERFORM 3D and export result?
Just as the question.
I've got a detailed and systematical introduction on numerical model of the soil-pile intercation on a sesimic load in the dissertation from the attached link. In figure 3.11 and 3.22 (the atteach picture), page 72, it is reported that real part of the impedance function is obtained from FEA,here Abaqus.
But anyone can tell me how to work it out?
can the analysis be implemented in universal step?
Is this method suitable to a harmonic load uniformly acted at the pile top?
I was simulating the response of a two DoF system with a constant frequency force acting on the second mass. The system was initially at rest. The response obtained through simulation shows that the structure vibrates at three frequencies, the two natural frequencies and the forcing frequency. However the two natural frequencies appear only in the initial part of the response. The system consists of two masses, three springs (one connecting the masses), and two linear viscous dampers. System is fixed on both the sides.
is it possible to represent a flexible body by a multiple of rigide bodies (>10 bodies), this rigide bodies are attached between them by springs and dumpers so they can behave exacly like the flexible body once they are excited at the eigen frequencies of the flexible body. i know some will say try to mesh it, but i don't have a good FEA soft, so i'm trying to represente the meshed body in a non Finite element software.
I'm proposing an upgrade in a Mechanical Vibrations Lab, where some basic experiments will take place. So I'm collecting suggestions of equipment or instruments that could be applied in this lab.
Some of the experiments are listed below:
-Free vibration of spring-mass system
-Free vibration of a cantilever beam
-Logarithmic decrement estimation for a cantilever beam
-Free vibration of a damped, single degree of freedom, linear spring mass system
-Forced vibration of a cantilever beam
-Free vibration of a two-DOF system
-Unbalance response of a rotor-bearing system
-Bearing fault diagnostics by FFT analysis
Rotating bladed disk is modeled as a coupled spring mass system. The spring mass system is represented as 2nd order non homogeneous system of ODEs with time varying oscillating coefficient where stiffness matrix is having a banded structure containing sinusoidal terms. I know for constant stiffness matrix, Newmarks time integration scheme gives stable results. But I wish to know how analytically and numerically time varying stiffness can be handled.
I am looking for a good software to be able to simulate ultrasonic vibrations in glasses. The amplitude of vibrations is in micrometer scale and I'm not sure whether FEM is the right way to deal with this problem or not.
Suppose a 6 story linear building structure with known M,C and K matrices. How is it possible to transfer it to a nonlinear building by adding nonlinear stiffness force calculated by Bouc-Wen model to every story?
How does one accurately measure the effective dynamic load exerted by heavy equipment (huge vacuum pump, multistage centrifugal pump, etc) trasmitted to arbitrary floor without reallocating the equipment?
One method I can think of is to work out the FRF of the floor at a point close to equipment foundation with a force hammer when the equipment is in rest and capture the floor response when the machine is operating. The dynamic load can be then be determined by the relationship of input and out. According to theory it should work for cases with single-toned harmonic excitation, however the equipment is expected to emit multi-toned or non-harmonic excitation.
Is there any other method in dealing with this kind of problem?
I am doing study of stone blocks using impulse response (hitting by hammer at one point and collecting acceleration signal at other point by accelerometer, i.e. impulse response). While going through literature and response plot, I have few questions and looking for guidance: I am looking answer with respect to peaks amplitude and its locations of impulse response frequency plot which has multiple peaks in it.
1. Do these peaks are at natural, damped or resonance frequencies? (all systems have some damping).
2. What is importance of dominant peaks compared to others in a same spectrum?
3. Why do we get some higher peaks compared to others?
4. What will be impact on these peaks' frequency when there is crack between hit and sensing point on same stone block compared to non-cracked pair of hit and sense point, i.e. does peak frequencies will shift to lower or upper side of spectrum or keep old peaks as well introduce new frequencies in spectrum or other way, dominant frequencies will change?
5. Similarly, when material is soft between hit and sense point?
6. Does crack introduce new degree of freedom, i.e. new peak frequencies?
My assumption as per theory, crack reduces the stiffness of material, porosity changes stiffness, mass(density) and increase damping.
Thanks in advance
There is a structure with n degrees of freedom.The structure has forced vibration by cyclic loading. The loading period and its values depends on a parameter. in Ansys workbench how can found this parameter values cause resonance?
I'm going to do dynamic analysis of a vibrating string in ABAQUS. The string is vibrating at a specific frequency and at time t1 boundary conditions are altered in such a way that tension is released while the string is still vibrating. How to model it in ABAQUS?
Thanks for your time
When i solve an eigenvalues and eigenvectors (or frequencies and mode shapes) problem of a multiply degrees of free system. I found frequencies of the system: omega1, ơega2, omega3,....,omega n and corresponding to mode shapes. And, you know that, if structures are excited at what frequency then it will oscillate with corresponding to mode shape. And here, I assumed that, the structure is excited at a frequency range between omega 1 and omega 2 (or any range, such as omega 2 - omega 3, and so on). So, How the structure will oscillate with what mode shape?
By keeping I marker fixed the J marker has displacement and also small rotation. How to manually calculate the result of Spring force with reference to ADAMS. ?
Let us assume linear spring .
According to ADAMS Help.
This gives value in 1D. But I have displacement in 3D space.
For Ex. To calculate total force/reaction by the spring/suspension between chassis and wheel carrier
Note: any axis of I marker at chassis and J marker on wheel carrier are not parallel.
I really appreciate any ones advice and suggestions.
In finite element, I have a cantilever beam (system level) consisting of components A and B joined together (as shown in the figure below). I applied a force of 1N at the free end of the cantilever and I got the x- and y-displacement of each node. Now, I want to isolate component A (component level) and apply boundary conditions to it. My goal is to achieve similar x- and y displacement on each of the nodes of component A, both at the system level and component level. How can I go about it? What boundary condition(s) can I apply to component A only in order to achieve the similar nodal displacements I had when components A and B are combined? I am working in MATLAB.
I am trying to include tuned mass dampers in footbridges. Someone who recommend me how can I calculate the properties for tuned mass dampers in footbridges to minimize the acceleration keeping the TMD relative displacement.
Thanks a lot
I need to build a state space model for a three storey building in Simulink MATLAB: the equation of motion of the building is given by:
Mx'' + Cx' + Kx = Tf - MAx''g
The building is equipped with a damper that produces a force represented by (f).
Goodmorning. I'm trying to model a simply supported beam subjected to a moving sprung mass, as illustrated in Figure 1. Basically, I've modeled the sprung mass as a reference point with a mass of Mv. I've created a reference point as the point where there is going to be the interaction between the sprung mass and the beam. The “Node to Surface Contact” feature of ABAQUS was used to simulate the sliding motion on the frictionless surface of the beam.
I have then created two steps: in the first step the gravity is introduced and in the second step a dynamic analysis is introduced (the sprung mass moves from 0 to L).
Now, the model works but I have a totally bad result. In particular, I don't want that the gravity load is applied also to the beam, I've tried to apply it only to the reference point where the mass is applied but it is not possible. Is there a way to, after the first step (where the gravity is applied to the whole model) to bring the beam at the original position?
I have attached the script of my model if it is needed.
Thanks for any help.
I have done the experiment on a RCC bridge scale modal in laboratory , from that got the natural frquncy as 100Hz, but when im doing the modal analys in ANSYS APDL which value need to consider the naturla frequncy(like if 12 modes are there 12 frequncies will be there)
I am simulating single-mode dynamics (but in various modes) of a micro-beam with modal damping ratios of about 0.001 in Abaqus/standard. The question I have is why Abaqus does not have a simple viscous damping model (zeta) like as what we learn in theory of vibration?
Are there any alternative method of entering modal damping ratios other than calculating coefficients of alpha and beta in Rayleigh damping?
In order to validate a new algorithm, I need reliable reference solutions of the dispersion curves of coupled elastic/fluid acoustic waveguides. These could be either fluid-filled pipes or layered plate-like structures involving fluid layers.
I am looking for either a publication that presents dispersion curves (and gives all relevant parameters that allow reproducing the results) or software (I am using 'disperse' but am not sure the results are correct.)
I would appreciate if someone can point out other sources.
- For study of vibration of cylindrical shell i need to find Governing equation by using energy function with Ritz method.
- Use of Hooks law ,strain vectors ,resultant force and moment relation and strain energy and kinetic energy find the equation for frequency.
Dear engineers, I want to find the normalized stiffness for the machine with unbalanced force Ps_s(t)=P0 sin w0t and also the steady-state transmitted force fs_s(t)= f0 sin(w0-phi). and the given parameters are w0*t0=50*pi.
Then I want to find the analytical expression of the phase angle and angular velocity and unbalanced force.
Also in the attachment, I uploaded the problem.
I really appreciate if somebody can refer me to the relevant example or topic can help to solve this problem or even part of that.
Can anyone provide me with some references presenting exact solution of beam on a Winkler foundation with fixed-fixed (simply support, and cantilever) boundary conditions?