Design Consideration of Expander Heads for Vibration Systems: Part I: Natural Frequency Equations for Square, Constant Thickness Expander Heads

1991 ◽  
Vol 34 (2) ◽  
pp. 45-55
Author(s):  
Louie Lipp
Keyword(s):  
Natural Frequency ◽  
Test Time ◽  
Constant Thickness ◽  
Reliability Test ◽  
Design Consideration ◽  
Vibration Testing ◽  
Design Considerations ◽  
Simultaneous Testing ◽  
Maximum Utilization ◽  
Truncated Pyramid

Vibration testing, particularly when performed in reliability test chambers, is very costly. Design considerations for vibration expander heads that will accept several test specimens for simultaneous testing are discussed in this report. Well-designed expander heads will provide more meaningful results and reduce test time and costs through maximum utilization of test hardware. This article, the first of a three-part series, discusses natural frequency equations for square, constant thickness expander heads. Parts II and III will cover damping equations for square, constant thickness expander heads and the inverted truncated pyramid expander head. Complete derivations accompany each expander head equation.

scholarly journals Design Considerations for Oligo(p-Phenyleneethynylene) Organic Radicals in Molecular Junctions

2020 ◽  
Author(s):  
Martin Sebastian Zöllner ◽  
Rukan Nasri ◽  
Haitao Zhang ◽  
Carmen Herrmann
Keyword(s):  
Spin Polarization ◽  
Single Molecule ◽  
Fermi Energy ◽  
Organic Radicals ◽  
Stable Radical ◽  
Design Consideration ◽  
Dispersion Interactions ◽  
Electron Transmission ◽  
Design Considerations ◽  
Spin Delocalization

Spin polarization in the electron transmission of radicals is important for understanding single-molecule conductance experiments focusing on shot noise, Kondo properties or magnetoresistance. We study how stable radical substituents can affect such spin polarization when attached to oligo(p- phenyleneethynylene) (OPE) backbones. We find that it is not straightforward to translate the spin density on a stable radical substituent into spin-dependent transmission for the para-connected wires under study here, owing to increased steric interactions compared with meta-connected wires, and a resulting twisting of the radical substituent and OPE π systems. The most promising example is a t-butyl nitroxide substituent, which, despite little pronounced spin delocalization onto the backbone, yields a spin-dependent transmission feature which one might be able to shift towards the Fermi energy by additional substituents. We also find that for bulkier substituents, dispersion interactions with the substituent can lead to twisting of one of the outer OPE rings, reducing the overall conductance. As a further potential design consideration, attaching radicals via linkers might increase the possibilities for spin-dependent intermolecular and molecule-electrode interactions.

Design Considerations for Cold Storage Warehousing

1955 ◽  
Author(s):  
James M. Fiske
Keyword(s):  
Cold Storage ◽  
Mechanical Equipment ◽  
Design Consideration ◽  
Careful Selection ◽  
Professional Advice ◽  
Design Considerations ◽  
General Expansion ◽  
Proper Analysis ◽  
New Facilities

A general expansion of existing Cold Storage Warehousing or a program for construction of entirely new facilities calls for the proper analysis of design considerations and, most important, it requires that management properly establish the design consideration or search-out through study and professional advice, all fundamental considerations for analysis. The high cost per unit of warehouse space plus the fact that, once in use, the building and mechanical equipment cannot be readily and inexpensively repaired, changed, or added to makes careful selection and analysis of all considerations most important. Paper published with permission.

Random Vibration and Accelerated Life Testing

2014 ◽  
Author(s):  
Jon S. Pointer
Keyword(s):  
Random Vibration ◽  
Wide Frequency Range ◽  
Step Test ◽  
Test Time ◽  
Vibration Testing ◽  
Step Method ◽  
Inverse Power Law ◽  
Accelerated Life ◽  
High Degree ◽  
Selection Of

Increasingly random vibration testing is being utilized to validate products that are exposed to high levels of vibration across a wide frequency range when in use. Basic methods utilize the inverse power law and step test to failure to correlate test time at amplified vibration levels to predicted life at in-use conditions. However, many areas of this practice are debated including the selection of a proper exponent for life calculations, selection of test time and test levels, and correlation between dissimilar test and in-use vibration profiles. This paper explores the current literature on the topic and recommends a step by step method for utilizing random vibration testing to validate products that are subjected to a high degree of in-use vibration variability.

Vibration Test Time Compression and MIL-HDBK-781 vs. MIL-STD-810E

1994 ◽  
Vol 37 (1) ◽  
pp. 24-30
Author(s):  
H. Caruso ◽  
E. Szymkowiak
Keyword(s):  
Fatigue Life ◽  
Test Time ◽  
Vibration Test ◽  
Vibration Testing ◽  
Test Program ◽  
Compression Algorithms ◽  
Time Compression

This paper defines test time compression issues associated with vibration testing as described in MIL-STD-810E and MIL-HDBK-781. Differences and similarities associated with the test goals and application of each document are examined. Use of these documents for establishing test time compression algorithms related to fatigue life (durability) and reliability evaluations is discussed. Specific inconsistencies between the vibration models in each document for jet aircraft equipment are identified. Recommendations are offered for bringing these documents into agreement to provide increased uniformity and correlation of results throughout a test program.

Step-Stress Accelerated Random Vibration Life Testing

2010 ◽  
Vol 118-120 ◽  
pp. 606-610 ◽  
Author(s):  
Fu Qiang Sun ◽  
Xiao Yang Li ◽  
Jing Rui Zhang ◽  
Tong Min Jiang
Keyword(s):  
Parameter Estimation ◽  
Sample Size ◽  
Stress Level ◽  
Random Vibration ◽  
Normal Operation ◽  
Test Time ◽  
Life Testing ◽  
Vibration Testing ◽  
Testing Method ◽  
Technical Basis

In order to reduce the sample size and test time, a step-stress accelerated random vibration life testing (ARVLT) method is presented. And the method of parameter estimation is also proposed. Through this testing method, the exaggeration factor K can be obtained rapidly, so that the result can be used as the technical basis of conducting an equivalent accelerated vibration testing of the product. In addition, the reliability of the product under the normal operation stress level can be extrapolated.

scholarly journals Design Considerations for Oligo(p-Phenyleneethynylene) Organic Radicals in Molecular Junctions

2020 ◽  
Author(s):  
Martin Sebastian Zöllner ◽  
Rukan Nasri ◽  
Haitao Zhang ◽  
Carmen Herrmann
Keyword(s):  
Spin Polarization ◽  
Single Molecule ◽  
Fermi Energy ◽  
Organic Radicals ◽  
Stable Radical ◽  
Design Consideration ◽  
Dispersion Interactions ◽  
Electron Transmission ◽  
Design Considerations ◽  
Spin Delocalization

Spin polarization in the electron transmission of radicals is important for understanding single-molecule conductance experiments focusing on shot noise, Kondo properties or magnetoresistance. We study how stable radical substituents can affect such spin polarization when attached to oligo(p- phenyleneethynylene) (OPE) backbones. We find that it is not straightforward to translate the spin density on a stable radical substituent into spin-dependent transmission for the para-connected wires under study here, owing to increased steric interactions compared with meta-connected wires, and a resulting twisting of the radical substituent and OPE π systems. The most promising example is a t-butyl nitroxide substituent, which, despite little pronounced spin delocalization onto the backbone, yields a spin-dependent transmission feature which one might be able to shift towards the Fermi energy by additional substituents. We also find that for bulkier substituents, dispersion interactions with the substituent can lead to twisting of one of the outer OPE rings, reducing the overall conductance. As a further potential design consideration, attaching radicals via linkers might increase the possibilities for spin-dependent intermolecular and molecule-electrode interactions.

scholarly journals Design Considerations for Oligo(p-Phenyleneethynylene) Organic Radicals in Molecular Junctions

2020 ◽  
Author(s):  
Martin Sebastian Zöllner ◽  
Rukan Nasri ◽  
Haitao Zhang ◽  
Carmen Herrmann
Keyword(s):  
Spin Polarization ◽  
Single Molecule ◽  
Fermi Energy ◽  
Organic Radicals ◽  
Stable Radical ◽  
Design Consideration ◽  
Dispersion Interactions ◽  
Electron Transmission ◽  
Design Considerations ◽  
Spin Delocalization

Spin polarization in the electron transmission of radicals is important for understanding single-molecule conductance experiments focusing on shot noise, Kondo properties or magnetoresistance. We study how stable radical substituents can affect such spin polarization when attached to oligo(p- phenyleneethynylene) (OPE) backbones. We find that it is not straightforward to translate the spin density on a stable radical substituent into spin-dependent transmission for the para-connected wires under study here, owing to increased steric interactions compared with meta-connected wires, and a resulting twisting of the radical substituent and OPE π systems. The most promising example is a t-butyl nitroxide substituent, which, despite little pronounced spin delocalization onto the backbone, yields a spin-dependent transmission feature which one might be able to shift towards the Fermi energy by additional substituents. We also find that for bulkier substituents, dispersion interactions with the substituent can lead to twisting of one of the outer OPE rings, reducing the overall conductance. As a further potential design consideration, attaching radicals via linkers might increase the possibilities for spin-dependent intermolecular and molecule-electrode interactions.

scholarly journals Structural Dynamic Modification of Cylindrical Shells With Variable Thickness

2020 ◽  
Author(s):  
Farid Mahboubi Nasrekani ◽  
Shymal Shivneel Kumar ◽  
Sumesh Narayan
Keyword(s):  
Natural Frequency ◽  
Variable Thickness ◽  
Cylindrical Shells ◽  
Geometric Parameters ◽  
Constant Thickness ◽  
Geometrical Parameters ◽  
Structural Dynamic ◽  
Significant Difference ◽  
Dynamic Modification ◽  
Classical Shell Theory

Abstract In this paper, the effects of some geometrical parameters on dynamic behavior of cylindrical shells with constant and variable thickness are studied. The equation of motion for the shell with constant thickness is extracted based on classical shell theory using Hamilton’s principle. These equations which are a system of coupled partial differential equations are solved analytically and the natural frequency is determined for cylindrical shells with constant thickness. The natural frequency for cylindrical shells with variable thickness is determined using finite element method by employing ANSYS. The results are compared and the effect of different geometric parameters such as length, thickness, and radius on natural frequency is discussed. The specific ranges for geometric parameters have been determined in which there is no significant difference between shells with constant or variable thickness. Cylindrical shells with variable thickness have better stress and strain distribution and optimum weight, in compare with the shells with constant thickness and it is important to know in which ranges of dimensions and geometrical parameters, there are some significant differences between their mechanical properties such as natural frequency. The results are compared with some other references.

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