The document discusses structural dynamics and analysis of multi-degree of freedom systems. It covers key concepts such as dynamic differential equations, natural frequencies, damping, modal analysis, and different analysis methods including direct integration and frequency-based approaches. Linear dynamics allows use of natural modes of vibration while nonlinear dynamics accounts for large motions and changing geometry. Damping dissipates energy through velocity-dependent forces. Analysis can be performed via direct time integration or modal superposition depending on the problem characteristics and dominant frequencies.
The dynamic behavior of structures is an important topic in many fields. Aerospace engineers must understand dynamics to simulate space vehicles and airplanes, while mechanical engineers must understand dynamics to isolate or control the vibration of machinery. In civil engineering, an understanding of structural dynamics is important in the design and retrofit of structures to withstand severe dynamic loading from earthquakes, hurricanes, and strong winds, or to identify the occurrence and location of damage within an existing structure.
The Pushover Analysis from basics - Rahul LeslieRahul Leslie
Pushover analysis has been in the academic-research arena for quite long. The papers published in this field usually deals mostly with proposed improvements to the approach, expecting the reader to know the basics of the topic... while the common structural design practitioner, not knowing the basics, is left out from participating in those discussions. Here I’m making an effort to bridge that gap by explaining the Pushover analysis, from basics, in its simplicity.
A write up on this topic can be found at http://rahulleslie.blogspot.in/p/blog-page.html, though does not cover the full spectrum presented in this slide show.
The results of extensive experimental and numerical simulations illustrate that a TLD can be designed to effectively control the response of a structure subjected to large amplitude broad-banded base excitations, such as those experienced during an earthquake.
The dynamic behavior of structures is an important topic in many fields. Aerospace engineers must understand dynamics to simulate space vehicles and airplanes, while mechanical engineers must understand dynamics to isolate or control the vibration of machinery. In civil engineering, an understanding of structural dynamics is important in the design and retrofit of structures to withstand severe dynamic loading from earthquakes, hurricanes, and strong winds, or to identify the occurrence and location of damage within an existing structure.
The Pushover Analysis from basics - Rahul LeslieRahul Leslie
Pushover analysis has been in the academic-research arena for quite long. The papers published in this field usually deals mostly with proposed improvements to the approach, expecting the reader to know the basics of the topic... while the common structural design practitioner, not knowing the basics, is left out from participating in those discussions. Here I’m making an effort to bridge that gap by explaining the Pushover analysis, from basics, in its simplicity.
A write up on this topic can be found at http://rahulleslie.blogspot.in/p/blog-page.html, though does not cover the full spectrum presented in this slide show.
The results of extensive experimental and numerical simulations illustrate that a TLD can be designed to effectively control the response of a structure subjected to large amplitude broad-banded base excitations, such as those experienced during an earthquake.
Static Indeterminacy and Kinematic IndeterminacyDarshil Vekaria
This ppt is more useful for Civil Engineering students.
I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments.
I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.
What is a multiple dgree of freedom (MDOF) system?
How to calculate the natural frequencies?
What is a mode shape?
What is the dynamic stiffness matrix approach?
#WikiCourses
https://wikicourses.wikispaces.com/Lect04+Multiple+Degree+of+Freedom+Systems
https://eau-esa.wikispaces.com/Topic+Multiple+Degree+of+Freedom+%28MDOF%29+Systems
Design of Reinforced Concrete Structure (IS 456:2000)MachenLink
This is the 1st Lecture Series on Design Reinforced Cement Concrete (IS 456 -2000).
In this video, you will learn about the objective of structural designing and then basic properties of concrete and steel.
Concrete properties like...
1. Grade of Concrete
2. Modulus of Elasticity
3. Characteristic Strength
4. Tensile Strength
5. Creep and Shrinkage
6. Durability
Reinforced Steel Properties....
1. Grade and types of steel
2. Yield Strength of Mild Steel and HYSD Bars
This is an Introductory material for those who want to understand the basic difference between linear and nonlinear analysis in the context of civil and structural engineering.
Thedynamicbehaviourofastructureiscloselyrelatedtoitsnaturalfrequenciesand
correspondingmodeshapes. Awellknownphenomenonisthatwhenastructureissubjectedto
asinusoidalforceandtheforcingfrequencyapproachesoneofthenaturalfrequenciesofthe
structure,theresponseofthestructurewillbecomedynamicallyamplifiedi.e.resonanceoccurs.
Naturalfrequenciesandtheircorrespondingmodeshapesarerelateddirectlytothestructure’s
massandstiffnessdistribution(foranundampedsystem).
Aneigenvalueproblemallowsthecalculationofthe(undamped)naturalfrequenciesandmode
shapesofastructure. Aconcerninthedesignofstructuressubjecttodynamicloadingistoavoid
orcopewiththeeffectsofresonance.
Anotherimportantaspectofaneigenvaluesolutionisinitsmathematicalsignificance-thatis,it
formsthebasisofthetechniqueofmodesuperposition(aneffectivesolutionstrategytodecouple
acoupleddynamicmatrixequationsystem). Themodeshapematrixisusedasatransformation
matrixtoconverttheproblemfromaphysicalcoordinatesystemtoageneralizedcoordinate
system( modes pace).
In general for an FE model, there can be any number of natural frequencies and corresponding
mode shapes. In practice only a few of the lowest frequencies and mode shapes may be required.
Static Indeterminacy and Kinematic IndeterminacyDarshil Vekaria
This ppt is more useful for Civil Engineering students.
I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments.
I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.
What is a multiple dgree of freedom (MDOF) system?
How to calculate the natural frequencies?
What is a mode shape?
What is the dynamic stiffness matrix approach?
#WikiCourses
https://wikicourses.wikispaces.com/Lect04+Multiple+Degree+of+Freedom+Systems
https://eau-esa.wikispaces.com/Topic+Multiple+Degree+of+Freedom+%28MDOF%29+Systems
Design of Reinforced Concrete Structure (IS 456:2000)MachenLink
This is the 1st Lecture Series on Design Reinforced Cement Concrete (IS 456 -2000).
In this video, you will learn about the objective of structural designing and then basic properties of concrete and steel.
Concrete properties like...
1. Grade of Concrete
2. Modulus of Elasticity
3. Characteristic Strength
4. Tensile Strength
5. Creep and Shrinkage
6. Durability
Reinforced Steel Properties....
1. Grade and types of steel
2. Yield Strength of Mild Steel and HYSD Bars
This is an Introductory material for those who want to understand the basic difference between linear and nonlinear analysis in the context of civil and structural engineering.
Thedynamicbehaviourofastructureiscloselyrelatedtoitsnaturalfrequenciesand
correspondingmodeshapes. Awellknownphenomenonisthatwhenastructureissubjectedto
asinusoidalforceandtheforcingfrequencyapproachesoneofthenaturalfrequenciesofthe
structure,theresponseofthestructurewillbecomedynamicallyamplifiedi.e.resonanceoccurs.
Naturalfrequenciesandtheircorrespondingmodeshapesarerelateddirectlytothestructure’s
massandstiffnessdistribution(foranundampedsystem).
Aneigenvalueproblemallowsthecalculationofthe(undamped)naturalfrequenciesandmode
shapesofastructure. Aconcerninthedesignofstructuressubjecttodynamicloadingistoavoid
orcopewiththeeffectsofresonance.
Anotherimportantaspectofaneigenvaluesolutionisinitsmathematicalsignificance-thatis,it
formsthebasisofthetechniqueofmodesuperposition(aneffectivesolutionstrategytodecouple
acoupleddynamicmatrixequationsystem). Themodeshapematrixisusedasatransformation
matrixtoconverttheproblemfromaphysicalcoordinatesystemtoageneralizedcoordinate
system( modes pace).
In general for an FE model, there can be any number of natural frequencies and corresponding
mode shapes. In practice only a few of the lowest frequencies and mode shapes may be required.
Identification of coulomb, viscous and particle damping parameters from the r...ijiert bestjournal
This paper deals with Theoretical and Experimental methods for identification of coulomb ,Viscous and Particle
damping parameters from the response of Single degree of freedom harmonically forced linear oscillator when
system damped with more than one type of damping ,which parameter is responsible for the control of resonant
response of vibrating systems, in experimental method setup have been presented to investigate steady state
response amplitude xi for SDOF system for different values of amplitude Yi of the base excitation from this
relationship of (Xi ,Yi) the values of viscous damping coefficient „c‟ and coulomb friction force F0 ,also
equivalent viscous damping ratios ,have been calculated from frequency response analysis for the systems with
viscous damping ,Viscous and Coulomb friction damping, coulomb friction damping and particle damping by
using half power band-width method and in theoretical studies expression for steady state amplitude X0
obtained is used to study the effect of frequency ratio and coulomb friction parameters on phase angle and
amplitude ratio.
In this study Dynamic property of a structural element which is frequency, damping and mode shapes are described by a process called modal analysis. Structural condition can be monitored by analyzing the changes in frequencies and mode shapes. All materials posses certain amount of internal damping. Similarly steel fibers also produce some internal damping. A system is a combination of elements, for example a structure is a system whose elements are beams, columns, slabs, footings .etc. In all those elements I have selected beam elements. Many research works are conducted on different type of materials under dynamic loading.
Chopra, A.K. Dynamics of Structures – Theory and Applications to Earthquake Engineering. Prentice Hall, 2001
Chen, C. T. Linear System Theory and Design. Oxford University Press, 1999
Soong, T.T. Active Structural Control: Theory and Practice. Longman, 1990
Chapter 1 Review of Structural Dynamics
Chapter 2 Mathematical Description of Structural Systems
Chapter 3 State-space Realizations
Chapter 4 Introduction of Passive Energy Dissipation Systems
Chapter 5 Application of Passive Control
Chapter 6 Controllability and Observability
Chapter 7 State Feedback and State Estimators
Chapter 8 Application of Passive and Active Control
Chapter 9 Application of Semi-active and Hybrid Control
Report on "STRUCTURAL MECHANICAL PERFORMANCE EVALUATION AND HEALTH MONITORING"Abdul Majid
he behaviour of reinforced concrete beams and slabs at service
loads and outlines a reliable method for the calculation of deflection. To satisfy the serviceability
limit states, a concrete structure must be serviceable and perform its intended function throughout
its working life. Excessive deflection should not impair the function or be aesthetically
unacceptable, and cracks should not be unsightly or wide enough to lead to durability problems.
Design for the serviceability limit states involves making reliable predictions of the instantaneous
and time-dependent deformation of the structure.
Structural Health Monitoring of a Cable-Supported Zhejiang Bridge Abdul Majid
The Zhijiang Bridge is a cable-stayed bridge built recently over the Hangzhou Qiantang River. It
has an arched twin-tower space and a twin-cable plane structure. The integrated system of
structural health monitoring and intelligent management for Zhijiang Bridge includes an
information acquisition system, data management system, evaluation and decision-making system,
and application service system. The monitoring components include the working environment of
the bridge and various factors that affect bridge safety. The integrated system also includes a
forecasting and decision-making module for real-time online evaluation, which provides warnings
and makes decisions based on the monitoring information. The monitoring information, evaluation
results, maintenance decisions, and warning information can be input simultaneously into the
bridge monitoring center and traffic emergency center to share the monitoring data. The
installation of long-term structural health monitoring (SHM) systems to long-span cable-supported
bridges has become a trend to monitor loading conditions, assess performance, detect damage, and
guide maintenance. SHM systems can be used to investigate highway loading, railway loading,
wind characteristics, and temperature effects.
It is a high strength, ductile material formulated by combining of cement, silica fume, quartz silica sand , crushed quartz, super plasticizer and metallic fibers
Serviceability Limit State of Two-way Reinforced Concrete Slab Strengthened ...Abdul Majid
The two primary structural design objectives are;
strength and
serviceability.
Serviceability refers to the conditions under which a structure is still considered useful. It refers to conditions other than the structure strength that render the structures unusable.
Structural Health Monitoring of a Cable-Supported Zhejiang BridgeAbdul Majid
Structural Health Monitoring (SHM) aims to give, at every moment during the life
of a structure, a diagnosis of the “state” of the constituent materials, of the different
parts, and of the full assembly of these parts constituting the structure as a whole. The
state of the structure must remain in the domain specified in the design, although this
can be altered by normal aging due to usage, by the action of the environment, and by
accidental events. Thanks to the time-dimension of monitoring, which makes it
possible to consider the full history database of the structure, and with the help of
Usage Monitoring, it can also provide a prognosis (evolution of damage, residual life,
etc.).
The Zhijiang Bridge is a cable-stayed bridge built recently over the Hangzhou Qiantang River. It
has an arched twin-tower space and a twin-cable plane structure. The integrated system of
structural health monitoring and intelligent management for Zhijiang Bridge includes an
information acquisition system, data management system, evaluation and decision-making system,
and application service system. The monitoring components include the working environment of and application service system. The monitoring components include the working environment of
the bridge and various factors that affect bridge safety. The integrated system also includes a
forecasting and decision-making module for real-time online evaluation, which provides warnings
and makes decisions based on the monitoring information. The monitoring information, evaluation
results, maintenance decisions, and warning information can be input simultaneously into the
bridge monitoring center and traffic emergency center to share the monitoring data. The
installation of long-term structural health monitoring (SHM) systems to long-span cable-supported
bridges has become a trend to monitor loading conditions, assess performance, detect damage, and
guide maintenance. SHM systems can be used to investigate highway loading, railway loading,
wind characteristics, and temperature effects.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
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Online aptitude test management system project report.pdfKamal Acharya
The purpose of on-line aptitude test system is to take online test in an efficient manner and no time wasting for checking the paper. The main objective of on-line aptitude test system is to efficiently evaluate the candidate thoroughly through a fully automated system that not only saves lot of time but also gives fast results. For students they give papers according to their convenience and time and there is no need of using extra thing like paper, pen etc. This can be used in educational institutions as well as in corporate world. Can be used anywhere any time as it is a web based application (user Location doesn’t matter). No restriction that examiner has to be present when the candidate takes the test.
Every time when lecturers/professors need to conduct examinations they have to sit down think about the questions and then create a whole new set of questions for each and every exam. In some cases the professor may want to give an open book online exam that is the student can take the exam any time anywhere, but the student might have to answer the questions in a limited time period. The professor may want to change the sequence of questions for every student. The problem that a student has is whenever a date for the exam is declared the student has to take it and there is no way he can take it at some other time. This project will create an interface for the examiner to create and store questions in a repository. It will also create an interface for the student to take examinations at his convenience and the questions and/or exams may be timed. Thereby creating an application which can be used by examiners and examinee’s simultaneously.
Examination System is very useful for Teachers/Professors. As in the teaching profession, you are responsible for writing question papers. In the conventional method, you write the question paper on paper, keep question papers separate from answers and all this information you have to keep in a locker to avoid unauthorized access. Using the Examination System you can create a question paper and everything will be written to a single exam file in encrypted format. You can set the General and Administrator password to avoid unauthorized access to your question paper. Every time you start the examination, the program shuffles all the questions and selects them randomly from the database, which reduces the chances of memorizing the questions.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
Tutorial for 16S rRNA Gene Analysis with QIIME2.pdf
Structural Dynamics
1. STRUCTURAL DYNAMICS
MULTIPLE DEGREE OF FREEDOM
SYSTEM
Presented By: Abdul Majid (明晢)
Student ID: S32002006W
School of Aerospace and Civil Engineering
Harbin Engineering University
2. OVERVIEW
Dynamic Differential Equation Classic Dynamics versus Nonlinear
Dynamics
Inertial Effects Damping Effects
Natural Frequency Extraction Free Systems Harmonic Systems
Base Motion
Damping Methods
Direct Linear Dynamics
Versus Frequency Based Dynamics
Damping in Direct Linear Dynamics
Controlling Accuracy of Calculations
Nonlinear Dynamics
3. Linear Dynamics allows
effective use of the “natural
modes” of vibration of a
structure.
Example of a Modal shape for
a flat circular disc with
centered circular hole
modeled with shell elements
DYNAMICS
Dynamic analysis differs from static analysis
in three fundamental aspects:
Inertial effects are included
Dynamic loads vary as a function of time.
The time-varying load application induces a
time-varying structural response.
Mass and Density need to be accounted for
Must be in proper (consistent) units
5. DYNAMICS CONCEPTS
Static
- Events in which time parameters and inertia effects do not play a
significant role in the solutions.
Dynamic
- A significant time dependent behavior exists in the problem because of
inertial forces (d’Alembert forces). Hence, a time integration of the
equations of motion is required.
Linear Dynamic
- The motion or deformation produced by a dynamic behavior is small
enough so that the frequency content of the system remains relatively
constant.
Nonlinear Dynamic
- The motion or deformation produced by a dynamic behavior
of the structure is large enough that we must account for changes in
geometry, material or contact changes in the model.
6. DYNAMICS CONCEPTS (CONT.)
Direct Integration (over time)
- All kinematic variables are integrated through time. It can be used to
solve linear or nonlinear problems.
Natural Frequency
- The frequencies at which the structure naturally tends to vibrate if it is
subjected to a disturbance.
Modal Dynamics
- A dynamic solution is obtained by superimposing the natural frequencies
and mode shapes of a structure to characterize its dynamic response in the
linear regime.
Damping
- The dissipative energy produced by a structure’s motion.
7. NATURAL FREQUENCY
Natural Frequency Solution
The natural frequencies of a structure are
the frequencies at which the structure
naturally tends to vibrate if it is
subjected to a disturbance
When an applied oscillatory load
approaches a natural frequency of a
structure, the structure will resonate.
This is a phenomenon in which the
amplitude of the displacement of an
oscillating structure will dramatically
increase at particular frequencies.
8. The natural frequency solution, or eigenvalue
analysis, is the basis for many types of
dynamic analyses.
The structure may include preload before the
eigenvalues are calculated. This affects the
results.
The natural frequency for a Single Degree
Of Freedom (SDOF) system is given by
The frequency procedure extracts
eigenvalues of an undamped system:
NATURAL FREQUENCY OF
FREE UNDAMPED SYSTEM
9. The structure may include preload before
the eigenvalues are calculated. This affects
the results.
The frequency procedure extracts
eigenvalues of a damped system:
The natural frequency for the Damped
Single Degree Of Freedom (SDOF) system
is given by the same equation of the
undamped system:
NATURAL FREQUENCY OF
FREE DAMPED SYSTEM
11. When the Damped system is loaded with
an exponential function of a single
frequency, the resultant oscillations are
called harmonic:
HARMONIC OSCILLATIONS
17. Example:
Third Modal Shape of a Cantilevered Plate
NATURAL FREQUENCIES,
PRELOADING AND FEM
Preloading changes the structural
stiffness and as a result, changes
the results.
A finite element mesh must be
sufficiently fine enough to
capture the mode shapes that
will be excited in the response.
Meshes suitable for static
simulation may not be suitable
for calculating dynamic response
to loadings that excite high
frequencies.
As a general rule of thumb, you
should have a minimum of 7
elements spanning a sine wave.
18. Example:
Impact Test using Explicit Dynamics
Reaction Force at Wall
FREQUENCY BASED DYNAMICS
When a linear structural
response is dominated by a
relatively small number
modes, modal superposition
can lead to a particularly
different method of
determining the response.
Modal based solutions
require extraction of the
natural frequency and mode
shapes first (i.e. requires
running a Natural Frequency
solution first)
19. DYNAMIC ANALYSIS METHODS IN MSC.MARC
Eigenvalue extractions linear with
preloading
Lanczos method
Power Sweep
Harmonic response linear with
preloading
Real (no Damping)
Imaginary (Damping)
Transient analysis linear and
nonlinear
Explicit
Implicit
Contact
20. DYNAMIC ANALYSIS METHODS IN MSC.MARC
(CONT.)
Modal-based Solutions include:
Steady State Dynamics (i.e.: rotating
machinery in buildings)
Harmonic responses for the steady state
response of a sinusoidal excitation
Modal Linear Transient Dynamics (i.e.:
diving board or guitar spring)
Modal superposition for loads known as a
function of time
Response Spectrum Analysis (i.e.:
seismic events)
Provides an estimate of the peak
response when a structure is subjected
to a dynamic base excitation
21. DYNAMIC ANALYSIS METHODS IN MSC.MARC
(CONT.)
Frequency based dynamics should have the following characteristics:
The system should be linear.
(but for nonlinear preloading)
Linearized material behavior
No change in contact conditions
No nonlinear geometric effects other than those resulting from preloading.
The response should be dominated by relatively few frequencies.
As the frequency of the response increases, such as shock analysis, modal based
dynamics become less effective
The dominant loading frequencies should be in the range of the extracted
frequencies to insure that the loads can be described accurately.
The initial accelerations generated by any sudden applied loads should be
described by eigenmodes.
The system should not be heavily damped.
22. BASE MOTION
Base motion specifies the
motion of restrained nodes.
The base motion is defined by a
single rigid body motion, and
the displacements and rotations
that are constrained to the body
follow this rigid body motion.
Example: Launch excitation of
mounted electronics packages or
hardware.
Base motion is always specified
in the global directions.
23. Frequency Value
0.0001 0.0000975
0.0005 0.0004875
0.01 0.00975
0.2 0.195
0.3 0.2925
1 0.975
2.5 2.5
3 2.5
4.5 2.5
6.6 2.5
8 2.25
10 2
100 1.1
1000 1.01
This is a typical
earthquake spectrum for
rocklike material with a
soil depth less than 200
ft, as provided by the
UBC
POWER TRANSMISSION TOWER BASE
MOTION EXAMPLE
24. [M]{ü} + [C]{ú} + [K]{u} - P = 0
Where
[C]{ú} - Dissipative forces
[C] - Damping matrix
{ú} - Velocity of the structure
DAMPING
Damping is the energy
dissipation due to a
structure’s motion.
In an undamped structure, if
the structure is allowed to
vibrate freely, the magnitude
of the oscillations is constant.
In a damped structure, the
magnitude of the oscillations
decreases until the oscillation
stops.
Damping is assumed to be
viscous, or proportional to
velocity
Dissipation of energy can be
caused by many factors
including:
Friction at the joints of a structure
Localized material hysteresis
25. Damped natural frequencies are related to
undamped frequencies via the following
relation:
where
wd the damped eigenvalue
wn the undamped eigenvalue
x = c/co the fraction of critical damping or
damping ratio
c the damping of that mode
shape
co the critical damping
2
1
n
d
Damping exhibits three characteristic forms:
DAMPING (CONT.)
Under damped systems (z < 1.0)
Critically damped systems (z = 1.0)
Over damped systems (z > 1.0)
26. MODAL DAMPING
Damping in Modal Analysis
Direct Damping
Allows definition of damping as a fraction of
critical damping.
Typical value is between 1% and 10% of the
critical damping.
The same damping values is applied to
different modes.
27. Direct dynamic solutions assemble the
mass, damping and stiffness matrices and
the equation of dynamic equilibrium is
solved at each point in time.
Direct method is favored in wave
propagation and shock loading problems, in
which many modes are excited and a short
time of response is required.
Since these operations are computationally
intensive, direct integration is more
expensive than the equivalent modal
solution.
Direct dynamic solutions can be used to solve
linear transient, steady state and nonlinear
solutions using Rayleigh damping.
Rayleigh damping is assumed to be made up
of a linear combination of mass and stiffness
matrices:
[C] = [M] + (+gt)[K]
Many direct integration analyses often define
energy dissipative mechanisms as part of the
basic model (dashpots, inelastic material
behavior, etc.)
For these cases, generic damping is usually
not important.
DAMPING IN DIRECT LINEAR
AND NONLINEAR DYNAMICS
28. The damping terms for direct
integration are defined in the
materials form:
DAMPING IN DIRECT LINEAR AND
NONLINEAR DYNAMICS (CONT.)
Mass Proportional
Damping
Introduces damping
forces caused by
absolute velocities in
the model
Stiffness Proportional
Damping
Introduces damping
which is proportional to
strain rate.
29. Nonlinear dynamic procedure
uses implicit time integration,
such as Central Difference or
Newmark-beta methods.
DAMPING IN DIRECT LINEAR AND
NONLINEAR DYNAMICS (CONT.)
Solution includes an
automatic impact solution
for velocity and acceleration
jumps due to contact bodies
including rigid structure.
The high frequency
response, which is important
initially, is damped out
rapidly by the dissipative
mechanisms in the model