{"id":52019,"date":"2023-09-29T04:12:57","date_gmt":"2023-09-29T08:12:57","guid":{"rendered":"https:\/\/blogs.sw.siemens.com\/simcenter\/?p=52019"},"modified":"2026-03-26T06:45:55","modified_gmt":"2026-03-26T10:45:55","slug":"new-dynamic-mount-stiffness-nvh","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/simcenter\/new-dynamic-mount-stiffness-nvh\/","title":{"rendered":"New dynamic mount stiffness characterization – Why get excited about it?"},"content":{"rendered":"\n

My colleague\u2019s new toy<\/h2>\n\n\n\n

Let me tell you why I want to talk today about dynamic mount stiffness characterization. Everything started by discovering my colleague\u2019s new toy in our engineering facility. In fact, I must admit that I was already waiting for it. But in the end, I discovered it on my own, it was standing right there. Working on real objects and being able to bring them physically into the virtual world, are fascinating moments in my work. Let me share one of those with you.<\/p>\n\n\n

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My colleague\u2019s new toy \u2013 let\u2019s see what it really is\u2026<\/figcaption><\/figure><\/div>\n\n\n

And it starts with my colleague\u2019s new toy. This toy is in fact the new test rig and yes new things are making me curious and excited, especially this one. This is as well a story about small parts being difficult to deal with, and this is the case for engine mounts. But the question is why am I talking about a test rig and engine mounts? Engine mounts have been there for a long time. What can this new test rig more than others?<\/p>\n\n\n\n

This is where we start talking about electrification, which has been a hot topic now for a few years in NVH. Even if this topic is already kind of lukewarm. But lukewarm is by the way better to digest. I don\u2019t want to bore you with BEVs anymore. But the new test rig is especially there due to those BEVs and due to an even hotter topic, Component-based Transfer Path Analysis (C-TPA).<\/p>\n\n\n

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Illustration of an electric engine attached to the chassis platform.<\/figcaption><\/figure><\/div>\n\n\n

A dynamic mount stiffness characterization test rig and what?<\/h2>\n\n\n\n

Yes, and there it is, still the test rig. And why I am so excited about it, is the fact that it can characterize high-frequency dynamic mount stiffness, and it can use preload. Well yes, those mounts and the rubber materials and nonlinearities are great for decoupling vibrations, but have you ever modeled them? I have, and engine mounts are a challenge for NVH engineers. Because of so many dependencies, like mounts don\u2019t have a linear stress-strain curve, (Young\u2019s modulus will depend on the preload), their dependency on the load-amplitude, temperature, and of course, the frequency.<\/p>\n\n\n

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Engine mount examples<\/figcaption><\/figure><\/div>\n\n\n

The frequency dependency in particular brings me to another problem, which is the vibration transfer Degrees Of Freedom (DOF). With increasing frequency, we need to consider all DOFs, the translational and rotational DOFs for the mounting. In the end, we have 12×12 stiffness values per frequency to characterize.<\/p>\n\n\n

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Scheme of 6 coupling DOFs for the mount, by the way cross coupling could occur too<\/figcaption><\/figure><\/div>\n\n\n

Am I done? No, additionally there are different mount variants, the hydro-mounts, or the elastomer mounts. Now we allow even multi-levels dynamic stiffness models for multi-preloads to cope even better with the nonlinearities and dependencies.<\/p>\n\n\n\n

Why a new test rig?<\/h3>\n\n\n\n

What is the conclusion, can I do my mount characterization with the classical mount characterization rigs? Whether you use the mount stiffness in C-TPA or in CAE models, there are two things that you will need for accuracy. For sure, you need precise high-frequency results for BEVs electric powertrains, and in many cases, you need all 6 DOF (displacement and rotation) characterized. Sadly, most former test rigs cannot do that. They are lacking either frequency range and\/or the rotational DOFs. The need for rotating DOFs will depend on the mount stiffness. A very soft mount will not transmit a lot of rotations, though. It will depend on the mount itself, but that is another story. If you can do the above already, that is great. I need to use our new test rigs.<\/p>\n\n\n\n

Let\u2019s talk about solutions<\/h2>\n\n\n\n

Let us say now that we want to characterize the mount stiffness, what do we have to do? We will connect two points by the mount stiffness matrix that has 12×12 entries, linking rotations and displacement DOFs to forces and moments.<\/p>\n\n\n

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Example mount to be characterized, with top and bottom attachment.<\/figcaption><\/figure><\/div>\n\n\n

To get the measurement data on precise points, we will use Virtual Point Transformation (VPT). We will do impact testing, measuring accelerations and excite around those virtual points, see below.<\/p>\n\n\n

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Measurement set-up for mount characterization, showing impact and accelerometer positions [1], by the way this not the new test rig.<\/figcaption><\/figure><\/div>\n\n\n

How do we fill the dynamic mount stiffness matrix?<\/h2>\n\n\n\n

Let me show you how this is done in Simcenter Testlab. Simcenter Testlab allows you to create the dynamic stiffness matrix with impact measurements. It creates the full 12×12 dynamic stiffness matrix and thus eases the task for the engineer.<\/p>\n\n\n\n

The impact tests are done on both mount sides. The impact and acceleration locations are transformed into virtual points and the matrix is inverted.<\/p>\n\n\n\n