A First-Passage Approximation in Random Vibration

1971 ◽  
Vol 38 (1) ◽  
pp. 143-147 ◽  
Author(s):  
Ronald L. Racicot ◽  
Fred Moses
Keyword(s):  
Random Vibration ◽  
Numerical Technique ◽  
Joint Probability ◽  
Poisson Processes ◽  
Joint Probability Distribution ◽  
First Passage ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Average Size ◽  
Good Agreement

A numerical technique is described for computing approximate first-passage probabilities for single-degree-of-freedom systems. It is applicable to cases where the joint probability distribution of response at two times can be found. From these distributions, the average size of a clump of consecutive failure crossings is computed. Results are compared to previously published simulation first-passage probabilities and good agreement is found. Examples illustrate applications to Gaussian and filtered Poisson processes.

scholarly journals Development of n-DoF Preloaded Structures for Impact Mitigation in Cobots

2018 ◽  
Vol 10 (5) ◽  
Author(s):  
S. Seriani ◽  
P. Gallina ◽  
L. Scalera ◽  
V. Lughi
Keyword(s):  
Three Dimensional ◽  
Impact Loads ◽  
Single Degree Of Freedom ◽  
Impact Mitigation ◽  
Single Degree ◽  
Future Developments ◽  
Core Issue ◽  
Comprehensive Framework ◽  
Peculiar Behavior ◽  
Good Agreement

A core issue in collaborative robotics is that of impact mitigation, especially when collisions happen with operators. Passively compliant structures can be used as the frame of the cobot, although, usually, they are implemented by means of a single-degree-of-freedom (DoF). However, n-DoF preloaded structures offer a number of advantages in terms of flexibility in designing their behavior. In this work, we propose a comprehensive framework for classifying n-DoF preloaded structures, including one-, two-, and three-dimensional arrays. Furthermore, we investigate the implications of the peculiar behavior of these structures—which present sharp stiff-to-compliant transitions at design-determined load thresholds—on impact mitigation. To this regard, an analytical n-DoF dynamic model was developed and numerically implemented. A prototype of a 10DoF structure was tested under static and impact loads, showing a very good agreement with the model. Future developments will see the application of n-DoF preloaded structures to impact-mitigation on cobots and in the field of mobile robots, as well as to the field of novel architected materials.

scholarly journals Blast Simulator Testing of Structures: Methodology and Validation

2011 ◽  
Vol 18 (4) ◽  
pp. 579-592 ◽  
Author(s):  
T. Rodriguez-Nikl ◽  
G.A. Hegemier ◽  
F. Seible
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Detailed Model ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Explosive Materials ◽  
Blast Effects ◽  
Resistance Function ◽  
The University ◽  
Good Agreement

The blast simulator at the University of California, San Diego is a unique tool for conducting full-scale testing of blast effects on structures without the use of explosive materials. This blast simulator uses high speed hydraulic actuators to launch specially designed modules toward the specimen, thereby imparting impulse in a blast-like manner. This method of testing offers numerous advantages over field tests with actual explosives, including cost, turn-around time, repeatability, and a clear view of the progression of damage in the specimen. The viability of this method is established by comparing results obtained in the blast simulator with results obtained with actual explosives. The process by which the impulse is imparted to the specimen is then described by a detailed model based on the equivalent single degree of freedom method. Impulse calculated by the model is found to be in good agreement with the experimentally recorded values. Calculated impulse is found to be relatively insensitive to assumptions made about the specimen's resistance function (often not well known before a test) implying that the model can be used with confidence in designing an experimental study.

Dynamics of a Free Play Type of Nonlinearity System Under Deterministic and Random Excitations

1995 ◽  
Author(s):  
Ismail I. Orabi
Keyword(s):  
Gaussian White Noise ◽  
Harmonic Excitation ◽  
Free Play ◽  
Nonlinear Structures ◽  
Single Degree Of Freedom ◽  
Linearization Technique ◽  
Single Degree ◽  
Nonlinear Responses ◽  
Digital Simulations ◽  
Good Agreement

Abstract The dynamics of nonlinear structures under harmonic and random excitations is studied. The harmonic excitation is modeled by periodic loadings while the random excitations is modeled by segments of stationary Gaussian white noise processes. Transient responses of a single-degree-of-freedom model is studied to illustrate the characteristic of nonlinear responses. A free play type of nonlinearity is considered. The effects of nonlinearities on the overall dynamics of structure is investigated. The linearization technique is used to calculate the response statistics. To check the accuracy of the linearization technique, the results are compared with Monte-Carlo digital simulations and good agreement are observed.

FOLDING OF A TYPE OF DEPLOYABLE ORIGAMI STRUCTURES

2012 ◽  
Vol 12 (06) ◽  
pp. 1250054 ◽  
Author(s):  
YAO CHEN ◽  
JIAN FENG
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Jacobian Matrix ◽  
Element Analysis ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Element Simulation ◽  
Rigid Plane ◽  
Configuration Changes ◽  
Good Agreement

Some types of rigid origami possess specific geometric properties. They have a single degree of freedom, and can experience large configuration changes without cut or being stretched. This study presents a numerical analysis and finite element simulation on the folding behavior of deployable origami structures. Equivalent pin-jointed structures were established, and a Jacobian matrix was formed to constrain the internal mechanisms in each rigid plane. A nonlinear iterative algorithm was formulated for predicting the folding behavior. The augmented compatibility matrix was updated at each step for correcting the incompatible strains. Subsequently, finite element simulations on the deployable origami structures were carried out. Specifically, two types of generalized deployable origami structures combined by basic parts were studied, with some key parameters considered. It is concluded that, compared with the theoretical values, both the solutions obtained by the nonlinear algorithm and finite element analysis are in good agreement, the proposed method can well predict the folding behavior of the origami structures, and the error of the numerical results increases with the increase of the primary angle.

The Determination of Dynamic Stiffness of Dish-Shaped Metal Corrugated Pipe by Use of Random Vibration Method

2012 ◽  
Vol 468-471 ◽  
pp. 1393-1397
Author(s):  
Li Ming Rui ◽  
Mei Sheng Zheng ◽  
Lian Jun Tian
Keyword(s):  
Random Vibration ◽  
Dynamic Stiffness ◽  
Static Stiffness ◽  
Mass System ◽  
Single Degree Of Freedom ◽  
Vibration Method ◽  
Single Degree ◽  
Wide Range ◽  
Random Vibration Method

This paper simplifies the dish-shaped metal corrugated pipe into a elastic element, constitutes a single degree of freedom spring-mass system, then applicants the random vibration method to measure its natural frequency, further to calculate the dynamic stiffness of dish-shaped metal corrugated pipe. At the same time its static stiffness test is done. By comparison of two results, static and dynamic stiffness values fit well, and dynamic stiffness is closer to the actual working conditions. Random vibration method for dynamic stiffness is convenient, accurate and has application values in a wide range of engineering.

Study of the Random Vibration of Nonlinear Systems by the Gaussian Closure Technique

1978 ◽  
Vol 45 (2) ◽  
pp. 393-399 ◽  
Author(s):  
R. N. Iyengar ◽  
P. K. Dash
Keyword(s):  
Nonlinear Systems ◽  
Random Vibration ◽  
Joint Probability ◽  
Statistical Linearization ◽  
Closure Technique ◽  
Input Variables ◽  
Non Gaussian ◽  
Joint Probability Density ◽  
Gaussian Closure ◽  
Good Agreement

A technique is developed to study random vibration of nonlinear systems. The method is based on the assumption that the joint probability density function of the response variables and input variables is Gaussian. It is shown that this method is more general than the statistical linearization technique in that it can handle non-Gaussian excitations and amplitude-limited responses. As an example a bilinear hysteretic system under white noise excitation is analyzed. The prediction of various response statistics by this technique is in good agreement with other available results.

Response of Linear Systems to Magnitude Limited Random Excitation

1969 ◽  
Vol 91 (4) ◽  
pp. 991-996 ◽  
Author(s):  
P. Y. Hu
Keyword(s):  
Linear Systems ◽  
Gaussian Distribution ◽  
Random Vibration ◽  
Random Excitation ◽  
Experimental Results ◽  
Single Degree Of Freedom ◽  
Physical Systems ◽  
Single Degree ◽  
Random Source ◽  
Instantaneous Values

In many situations, encountered both in the field and in the laboratory, the excitation produced by a broadband random source has many of the characteristics of a signal having a Gaussian distribution of instantaneous values except that the higher values predicted by the theory do not appear. Therefore, in all cases, physical systems are really excited by a magnitude limited Gaussian random vibration rather than a strictly Gaussian random vibration. Analytical as well as experimental results on the response of the single-degree-of-freedom system subject to magnitude limited random vibration are presented.

Sign in / Sign up

Export Citation Format

Share Document