Inerter is two-terminal acceleration-dependent mechanical element with amplified inertance. It can adjust the inertance of a structure when intalled between two nodes, just as a spring to adjust stiffness. Meanwhile, only tiny physical mass is needed to obtain expected inertial control force. Inerter can be used to construct enhanced and high-efficient damping system. There are mainly two types of inerter systems: Frequency-Adjustment Inerter System (FAIS) and Tuned Inerter System (TIS). The FAIS can change the frequency of the primary structure and reduce the seismic input energy. The TIS can significantly enhance the damping efficiency of the energy dissipation devices constructionally and mechanically. The diagrams of basic inerter systems can be found in the attached figure.

References:

* Ikago K, Saito K, Inoue N. Seismic control of single-degree-of-freedom structure using tuned viscous mass damper. Earthquake Engineering & Structural Dynamics, 2012, 41(3): 453-474.

* Arakaki T, Kuroda H, Arima F, et al. Development of seismic devices applied to ball screw : Part 1 Basic performance test of RD-series [J]. Journal of Architecture and Building Science, 1999, 5(8): 239 ― 244. (in Japanese)

* Smith M C. Synthesis of mechanical networks: the inerter. IEEE Transactions on Automatic Control, 2002, 47(10): 1648―1662.

* Chao Pan; Ruifu Zhang; Hao Luo; Chao Li; Hua Shen, Demand-based optimal design of oscillator with parallel-layout viscous inerter damper, Structural Control and Health Monitoring, 2018, 25(1).

* Chao Pan; Ruifu Zhang, Design of structure with inerter system based on stochastic response mitigation ratio, Structural Control and Health Monitoring, 2018, 25(6).

* Ruifu Zhang, Zhipeng Zhao, Chao Pan, K. Ikago, Songtao Xue. Damping enhancement principle of inerter system. Structural Control and Health Monitoring. 2020;e2523. https://doi.org/10.1002/stc.2523

* Zhao ZP, Zhang RF, Lu Z. A particle inerter system for structural seismic response mitigation. Journal of the Franklin Institute 2019; https://%20doi.org/%2010.1016/%20j.jfranklin.2019.02.001

* Ruifu Zhang,Yanru Cao,Chao Pan.INERTER SYSTEM AND ITS STATE-OF-THE-ART(In Chinese).ENGINEERING MECHANICS, 2019, 36(10):8-27.

* Qingjun Chen; Zhipeng Zhao; Ruifu Zhang; Chao Pan, Impact of soil-structure interaction on structures with inerter system, Journal of Sound and Vibration, 2018, 433:1-15

* Zhipeng Zhao, Ruifu Zhang, Yiyao Jiang, Chao Pan, Seismic response mitigation of structures with a friction pendulum inerter system, Engineering Structures, 2019, 193 (2019): 110-120

* Qingjun Chen, Zhipeng Zhao, Yuying Xia, Chao Pan, Hao Luo, Ruifu Zhang, Comfort based floor design employing tuned inerter mass system, Journal of Sound and Vibration, 2019, 458: 143-157

You are right to be confused as, indeed, there are many different network layouts that form an inerter-based vibration absorber (IVA) and different research groups use different names/acronyms for the same layout. Attached is a figure with 3-element IVAs (1 spring- 1 damper- 1inerter) most widely studied in the literature for seismic protection taken from:

Taflanidis AA, Giaralis A and Patsialis D (2019) Multi-objective optimal design of inerter-based vibration absorbers for earthquake protection of multi-storey building structures. Journal of the Franklin Institute, 356: 7754-7784.

Intuitively, the interter acts as a (rotational) motion amplified in the TVMD, as a mass amplifier in the TMDI and as a mass replacement in the TID.

More details on the functionality of each of these IVAs can be found

- for TVMD:

Ikago K, Saito K, Inoue N. Seismic control of single-degree-of-freedom structure using tuned viscous mass damper. Earthquake Engineering & Structural Dynamics, 2012, 41(3): 453-474

-for TID:

I.F. Lazar , S.A. Neild , D.J. Wagg , Using an inerter-based device for structural vibration suppression, Earthq. Eng. Struct. Dyn. 43 (8) (2013) 1129–1147 .

-for TMDI:

Marian L and Giaralis A. (2014). Optimal design of a novel tuned mass-damper–inerter (TMDI) passive vibration control configuration for stochastically support-excited structural systems. Probabilistic Engineering Mechanics, 38: 156-164.

As Dr. Giaralis truly mentioned different research groups use different names for inerter-based devices but the simple definition for inerters is as follows:

Inerters are mechanical devices that their resisting force is proportional to the relative acceleration at their end-nodes. This class of response modification devices complements the traditional supplemental damping devices, that their resisting force is proportional to the relative velocity at their end-nodes.

here is useful paper for elastic structures equipped with inerters by Makris and Moghimi 2018.

Article Displacements and Forces in Structures with Inerters when Su...

Inerter is a two-terminal acceleration-dependent control element. The discovery of the mechanism of inerter predates the appearance of the English terminology. The earliest record in the literature is the mass pump in Japanese. Because of the limitation of language and geography, later English scholars renamed it "inerter", which is currently widely used by researchers. However, there is no systematic denominating methods for the inerter systems. Researchers generally give different names according to their own understanding or the convenience of description, resulting in a dizzying variety of abbreviations. In spite of the various denominations, the mechanisms of different inerter systems can be identified clearly according to their topology layouts.

TVMD is an important achievement of the long-term research work on inerter in Japan. It is a kind of efficient and practical inerter system, and the most promising and valuable one in the field of civil engineering. In other languages, in Japanese and in Chinese, it has a broader meaning, including different ways of connecting and installing. In English papers, it is often thought of as a combination of a inerter element, a parallel viscous element and a series supporting spring element. Actually, It has many variants to adapt to different situations in practical application. Until now, inerter systems have already been put into service in some practical projects in Sendai and Tokyo. The inerter systems has been installed between inner-stories, in the isolation story or between the lightweight tuned mass of TMD and the primary structure.

1. Kawamata S. Development of a vibration control system of structures by means of mass pumps, in Institute of Industrial Science. 1973, University of Tokyo: Tokyo

2. Saito K, Toyota K, Nagae K, Sugimura Y, Nakano T, Nakaminam IS, Arima F. Dynamic loading test and its application to a high-rase building of viscous damping devices with amplification system. 2002. Como, Italy.

3. Saito K, Inoue N. A study on optimum response control of passive control systems using viscous damper with inertial mass: Substituting equivalent nonlinear viscous elements for linear viscous elements in optimum control systems. AIJ Journal of Technology and Design 2007; 13(26): 457-462.10.3130/aijt.13.457.

4. Ikago K, Saito K, Sugimura Y, Inoue N. Optimum seismic response control of multiple degree of freedom structures using tuned viscous mass dampers. Proceedings of the Tenth International Conference on Computational Structures Technology. 2010. Valencia, Spain.

5. Ikago K, Saito K, Inoue N. Seismic control of single-degree-of-freedom structure using tuned viscous mass damper. Earthquake Engineering & Structural Dynamics 2012; 41(3): 453-474. DOI: 10.1002/eqe.1138.

6. Garrido H, Curadelli O, Ambrosini D. Improvement of tuned mass damper by using rotational inertia through tuned viscous mass damper. Engineering Structures 2013; 56: 2149-2153. DOI: 10.1016/j.engstruct.2013.08.044.

7. Pan C, Zhang RF. Design of structure with inerter system based on stochastic response mitigation ratio. Structural Control & Health Monitoring 2018; 25(6): e2169.10.1002/stc.2169.

8. Chao Pan; Ruifu Zhang, Design of structure with inerter system based on stochastic response mitigation ratio, Structural Control and Health Monitoring, 2018, 25(6).

9. Ruifu Zhang, Zhipeng Zhao, Chao Pan, K. Ikago, Songtao Xue. Damping enhancement principle of inerter system. Structural Control and Health Monitoring. 2020;e2523. https://doi.org/10.1002/stc.2523

10. Zhao ZP, Zhang RF, Jiang YY, Pan C. Seismic response mitigation of structures with a friction pendulum inerter system. Engineering Structures 2019; 193: 110-120. DOI: 10.1016/j.engstruct.2019.05.024.

@Tianli Chen

Firstly, I am glad that very few researchers are there involved in structural control and you are one of them.

What kinds of inerter systems are included?

So, all the damping components are there in inerter systems. This includes mechanical dampers, viscous dampers and solid damping components.

Which is more useful for structural control in civil engineering?

You can go through my work, since I have worked on many of the topics including structural components and stability improvement techniques

Kindly go through

https://www.researchgate.net/profile/Sagar_Jamle/research

Mahdi Abdeddaim Djedoui Nassim Abdelhafid Ounis

I agree with my colleagues in the above answers, and I want to simplify more.

The inerter as stand alone device is rarely used in civil engineering and vibration control domains.

However, the association of this latter with other control device is widely introduced, the inerter is mainly associated with a Tuned mass damper to enhance it mass (the inerter is well known for it ability to developed a large fictive mass proportional to the relative acceleration between it nodes) [ Agathoklis Giaralis et al. are a reference in this topic].

The inerter also can be associated with spring or dashpot to form what is known as inerto-elastic and inerto-viscous dampers respectively.

* Seismic vibration control using a novel inerto-elastic damper ( M Abdeddaim, AA Kasar, N Djedoui )

* A Novel inerto-viscous damper for seismic vibration control (M Abdeddaim, AA Kasar, N Djedoui and A. Ounis).

Regards.

Salah Djerouni

Dear Professor Giaralis and Professor Zhang,

Both of you are top researchers in this area and published several high quality papers in this topic. While using inerter for high-rise buildings, it is more effective to linked it to lower floors. However, it is not possible practically to do that, or maybe so far I could not find such realistic solution to answer this doubt. Otherwise, if we connect to top or story below, the performance of a passive tuned mass damper will be better.

Regards

Said Elias Dear Dr. Elias,

What you pointed out is a issue worth studying very much. In the current practical engineering design, the inerter system is installed according to the specific requirements. However, most of the current papers are theoretical research, and the issue you mentioned are of great practical engineering research value. However, such issues are not easy to be accepted and published in scientific papers. In some practical engineering cases using inerter systems in Japan, the inerter systems are installed at different floors according to different requirements. You can find actual engineering examples at the Tohoku University website. https://irides.tohoku.ac.jp/eng/organization/risk/05.html

Dear all

also if it is true that it is not practical/feasible spanning more than one floor with the inerter connectons by using the current technologies, I feel it will be in the near future due to the progress in flooring and facade technologies.

As shown by the literature, spanning one to three floors is sufficient for making the TMDI better than TMD in high-rise buildings.

Professor Ruifu Zhang thank you so much for detailed information.

Dear Professor Petrini,

It works better than TMD if the span is wider and depending upon the acceleration of the floor it is hooked. Therefore it will be depending on physics of the structures. I feel the generalized conclusions in the literature are not so much accurate. They needed to be structures specific conclusions. For every structure we need to design the TMDI differently. I recently found two practical solutions but peer review may not be enough fair to publish them quakely.

Thank you very much for your contribution to the discussion.

Yes, I agree on the fact that TMDI optimal design is structure-specific, but we can say the same for the TMD or other control devices.

I feel the chances of generalizing the conclusions made for the TMDI efficency are not less than for other structural control devices at the same level of development, and specific applications where the device is not good (or also detrimental) for the structural performances exist for sure. If anyone can find such kind of applications, this is a valuable contribution to the advancement of the research in the field, then I really hope to read what you propose.

In addition: the TMDI technology is relatively new in Structural Engineering, then it will need to be adequately tested before reaching the establishment level of competitors.

Thanks.

Thank you. Yes, I agree it requires further detailed understanding. We are working on some specific papers to be published sometime in this year. One such issue we are solving is its practical implications.

Dear Friends, Colleagues, and TMDI enthusiasts:

I agree with all the points you raised. But it is important to realise that the fact that two-points inerter-based vibration absorbers are structure-dependent creates opportunities for research and collaboration with design engineers and (Ruifu Zhang) I do not see why good quality practical solutions are not publishable. An example of how structure-dependency can be exploited to our advantage can be found in our recent paper for wind excited structures (local storey softening):

Article Top-storey softening for enhanced mitigation of vortex shedd...

This trick works for earthquakes as well:

Conference Paper Enhanced optimal tuned mass-damper-inerter performance for s...

Best wishes to all!

Agathoklis Giaralis

Dear Dr. Giaralis,

It is a pleasure to discuss this related issue with you. According to my limited understanding, it may include the following reasons, not limited to papers based on the inerter system : 1. Scientific papers in international journals pay more attention to scientific issues and natural discovery; 2. Practical engineering is mainly a technical problem, and the design of practical engineering involves many factors, not limited to science and technology. As a result, papers focusing on engineering practice do not fall within the scope of topic selection of most journals; 3. The actual project based on the inerter system is mainly located in Japan, and it may be more convenient for Japanese engineers and scholars to publish conference and journal papers in Japanese; 4. The information of practical projects is sometimes limited by the owner and other subjective and objective factors due to commercial contracts and other factors; 5. As a matter of fact, most reviewers are scholars from universities and colleges, lacking experience in actual engineering design and actual device test, so it is easy to make judgments that are not in line with the actual situation when reviewing manuscripts based on limited experience.These are just some of my observations. There may be other factors as well. These thoughts are not limited to the practical engineering based on the inerter system, and similar situations may exist in other engineering papers. At the next World Conference on Earthquake Engineering in Sendai (17 WCEE), maybe can visit some practical projects that use inerter systems.

Dear Dr Ruifu Zhang,

I agree with all the points you make and I understand well where you are coming from. Choosing wisely journals with (some) focus on practical applications may be key to address some of the points you raise. I think a challenging aspect when writing a scientific paper on some practical solution or a case-study is to convincingly draw conclusions with wider applicability and to generalise concepts and results. In any case, I am familiar with some actual recently completed projects in Japan that use inerter systems for seismic protection and the upcoming 17 WCEE is certainly a good occasion to pay a visit to these structures and learn more about them.

Said Elias