Mechanical supports for mirrors and other optical components and substrates to maintain their initial undeformed shape is a common engineering problem. Ideally a mirror or similar substrate can be supported on three points if the mirror or substrate is stiff enough. However in many cases, the deflections are too large and more support is required. One of the earliest areas where this problem arose was for the mirrors in early telescopes. Irishman Howard Grubb came up with a novel solution by supporting the mirror on a set of levers known as a whiffletree. For a historical bio of Howard Grubb see Biographical Encyclopedia of Astronomers or the Museum Victoria (Australia) bio or a history of the Armagh Observatory and Grubb’s telescope.
High vacuum systems are becoming more common and a number of semiconductor processes already operate in high vacuum. The following references are ones that I have found useful in performing vacuum system calculations.
Pfeiffer Vacuum, which manufactures vacuum pumps and other components, has a nice PDF handbook which is free to download. It covers the basics of vacuum as well as operating principles of various pumps and as well as a number of practical issues.
The Handbook of Vacuum Technology edited by Karl Jousten is a thorough reference with detailed calculations for wide variety of problems in vacuum systems.
In this article, we compare the performance of a tuned-mass damper mounted at the end of a cantilever beam to the Lanchester damper which was shown in the previous article. The classic single-degree-of-freedom (SDOF) tuned-mass damper is sketched in the figure below. The design approach is to find the equivalent SDOF system for the cantilever beam’s mode of interest and then use the design formulas for an optimal SDOF TMD to determine the stiffness and damping of the absorber.
In this article, we show the robust and broadband performance of a Lanchester damper applied to a cantilever beam and how it achieves good performance without tuning and good performance over a number of modes, not just the primary mode.
This post shows how to set exact view orientation, zoom, pan, and lighting in CFD post. This is especially useful for making consistent figures for reports or presentations.
This picture below is a stream-ribbon visualization of a swirling flow, viewed using the built in “Isometric View (Z up).” The view is centered too low and the lighting angle is not favorable.
We describe how to obtain the constraint equations for a two point pivot and three point pivot. Designing a mechanism which can obtain a desired set of constraints is often an important step in kinematic or exact constraint machine design.
We begin with the simple lever mechanism shown in the figure below constraining the motion of two points A and C using the pivot at O.
Beams are often used in precision engineering applications. One common question is “what are the optimal support locations for a beam?” The answer depends on the desired objective. Below we describe some of the most common support locations: Airy points, Bessel points, minimum deflection, and nodal points. It turns out that these points are relatively close to each other for the uniform beam. The basic problem is sketched in the figure below. A uniform beam is supported on two points and the objective is the determine the placement of the supports in the presence of gravity.
Commonly, we need to save results from an Ansys Workbench study as a text file for post-processing in another program, such as Excel. One can right-click on a desired result and use Export, but that can be tedious if there a lot of results to save. With a snippet one inserts a Commands (APDL) object in the solution and writes APDL code to perform the desired functions.
There is a neat correspondence between the mathematical concept of a constraint and the practice of exact-constraint or kinematic machine design. This leads to some really useful insight for people designing machines with dynamics in mind. The PDF below is the extended abstract for a paper that Justin presented in Austin last week at the ASPE annual meeting.
For a bonded contact, which is the default for models opened in Ansys Workbench Mechanical, the contacts are modeled using elements TARGE170 and CONTA174. The thermal conductivity and stiffness of the contact elements are calculated by Ansys based on the properties of the two bodies. The controls only allow one to change the contact stiffness factor FKN which is a multiplier but not the actual stiffness of the joint (ie with SI units of N/m/m^2). However if one would like to set the value of the contact stiffness or thermal contact resistance, it can be done using Command snippets (also known as the Commands Object) for each contact. Continue reading Setting Mechanical Contact Stiffness and Thermal Contact Conductivity Values in Ansys Workbench using Command Snippets