Abstract
A Double Tuned Mass Damper (DTMD), which consists of a Tuned Mass Damper (TMD) connected in series with an undamped TMD, has been proven to be more efficient than a traditional TMD in previous studies. To enhance the vibration control performance and robustness of DTMD, an innovative type of DTMD for suppressing structural responses is proposed in this research. This new design includes a DTMD connected to the ground by a linear inerter (abbreviated as DTMDI). After establishing the analytical model of the DTMDI-structure system, the optimal configurations of the DTMDI for different values of inertance are obtained using the Balancing Composite Motion Optimization (BCMO). The effects of the variation in the structural properties as well as the weight and inertance of DTMDI on the performance and robustness of DTMDI are investigated. The present work indicates that an optimal DTMDI is much more effective and robust compared with an optimal DTMD with the same weight. Specifically, the DTMDI configuration with a higher inertance ratio demonstrates increased effectiveness. Moreover, the performance of the DTMDI surpasses that of a TMDI when both have the same mass and inertance, leading to a considerable reduction in the additional weight of the vibration absorber on the primary structure when using the DTMDI instead of the TMDI. While the DTMDI is more robust than both the DTMD and TMD against changes in the structure’s natural frequency, it does not exhibit the same level of robustness as the TMDI when the natural frequency of the structure increases.
Keywords
1. Introduction
Suppressing structural vibrations is a crucial requirement for civil structures under natural hazards (e.g., storms and earthquakes) to ensure comfort for occupants and structural safety (Balendra et al., 1995; Shah and Usman, 2022). Vibration control techniques and strategies have been investigated and successfully applied to worldwide civil structures (Bui et al., 2023a; Chang, 1999; Chang and Hsu, 1998; Di Matteo et al., 2022). One of these techniques is adding one or many vibration absorbers to the primary structure (Araz and Elias, 2024; Cao et al., 2024b; Gao et al., 1999; Pisal and Jangid, 2016; Samali et al., 2004; Tran et al., 2025; Wu et al., 2005). In this way, the most common damper type is TMD (including TLCD), because they are simple and effective dampers (Araz, 2021; Diana et al., 2013; Gao et al., 1999; Momtaz et al., 2017; Vellar et al., 2019; Yalla and Kareem, 2000).
TMDs have been utilized to suppress dynamic responses of structures under different types of loads (e.g., earthquakes, wind, or traffic loads). To enhance control performance of traditional TMDs, researchers have developed advanced types of TMDs (Araz, 2021a, 2024; Araz and Kahya, 2021; Hui et al., 2024; Kahya and Araz, 2019; Wang et al., 2022, 2024; Zuo, 2009). For example, Wang et al. (2024) suggested a novel tuned liquid mass damper for vertical vibration control of a large-span cable-stayed bridge in low-frequency domain, while Araz (2024) used multiple TMDs connected in parallel (MTMD) to reduce of structural vibrations. One of these innovative types of TMDs is inerter-based TMDs which show their noteworthy potential (Baduidana and Kenfack-Jiotsa, 2024; De Angelis et al., 2019; De Domenico and Ricciardi, 2018; Marian and Giaralis, 2014; Pandey and Mishra, 2021; Prakash and Jangid, 2022).
The concept of inerter was first suggested by Smith based on the force-current analogy between the electrical and mechanical networks (Smith, 2002). After that, Marian and Giaralis developed a tuned mass damper inerter to reduce the oscillatory motion of structural systems (Marian and Giaralis, 2014). Pandey and Mishra introduced the inerter-based compliant liquid column damper (TLCDI), proving its effectiveness in reducing dynamic responses for both single-degree-of-freedom (SDOF) and multi-degree-of-freedom (MDOF) structures under the recorded motions (Pandey and Mishra, 2021). Likewise, Wang et al. successfully employed a TLCDI to significantly mitigate the seismic response of SDOF structures (Wang et al., 2020). Moreover, Di Matteo et al. presented an innovative optimization procedure for designing TLCDIs, utilizing a statistical linearization technique that minimizes structural displacement differences, an essential factor for improving performance (Di Matteo et al., 2022). For dynamic vibration absorbers (DVAs), Baduidana and Kenfack-Jiotsa developed a three-element DVA with grounded stiffness and an attached inerter, designed specifically for controlling vibrations in undamped SDOF structures (Baduidana and Kenfack-Jiotsa, 2024). Additionally, Kendo-Nouja et al. proposed a grounded inerter-based DVA that efficiently reduces structural vibrations under both harmonic and random excitations (Kendo-Nouja et al., 2024). The outstanding results from these studies indicate that inerter-based vibration absorbers far outperform traditional ones, offering a robust solution for managing vibrations in various structural applications.
Cao and Tran (2023) introduced an innovative model of a DTMD. This device works as a passive control system intended to mitigate structural vibrations. The DTMD consists of a conventional TMD interconnected in series with a larger, undamped TMD. The worthy findings in their research work showed that the DTMD outperforms a conventional TMD with equivalent mass when it is used to reduce dynamic responses in structures. Building upon this foundational work, the present study proposes an upgraded version of the DTMD. This innovation version consists of a DTMD connected to the ground through a linear inerter (denoted as DTMDI). Obviously, DTMDI is not as simple as TMDI from the dynamics and structural viewpoints. However, based on how to connect a DTMDI and a TMDI with the main structure, the DTMDI is more straightforward than the TMDI because the DTMDI only needs a link point on the structure instead of two connection points as the TMDI.
In order to evaluate the structural vibration control performance of the proposed DTMDI absorber under harmonic excitations, a model of a DTMDI integrated into a SDOF structure under an external force is presented in Section 2. The optimal parameters of the DTMDI are then determined using a potential optimization algorithm in Section 3. Numerical simulations, results and discussions are presented in Section 4. Finally, the key conclusions of this work are shown in Section 5.
2. Analytical model of the DTMDI-structure system
An analytical model of a SDOF structure equipped with a DTMDI under an external force excitation is shown in Figure 1(a). This DTMDI consists of a DTMD linked to the ground through a linear inerter with an inertance value of b. It is important to note that the DTMD comprises two components, an undamped Tuned Mass Damper (referred to as TMD1) and a regular Tuned Mass Damper (referred to as TMD2), which are connected in series. The grounded inerter is linked to the DTMD at the TMD1. The reason why the author only uses the undamped TMD1 rather than a regular TMD1 was fully explained in Cao and Tran (2023). The mass and stiffness of TMD1 are (a) Analytical model of the DTMDI-structure system. (b) Simplified model of a linear inerter.
There are many different types of inerters, in which three popular types are based on the inertial amplification mechanism including the rack and pinion type, ball and screw type, and hydraulic type inerters (Konar and Ghosh, 2024; Ma et al., 2021; Pandey and Mishra, 2021). Various inerter devices and their operating principles have been reported in previous works (Konar and Ghosh, 2024; Ma et al., 2021). A simplified model of a linear inerter is presented in Figure 1(b). As presented in the literature (Giaralis and Petrini, 2017; Pandey and Mishra, 2021; Wang et al., 2020), the inerter creates an inertia force
The equations of motion of the system are given by
The natural frequency of the primary structure
As a result, equations (1)–(3) are rewritten in the matrix form as follows:
The dynamic magnification factor (DMF) of the structural response in the steady state is given by (Den Hartog, 1985; Gil-Martín et al., 2012)
The frequency ratio is
The peak dynamic magnification factor of the structural response (
As a result, the structural frequency response is a function of
To facilitate comparisons, the TMDI-structure system is also built, and its equations of motion are presented in Appendix A.
3. Parametric optimization
3.1. Input parameters
Key parameters of the main structure (Cao, 2023; Varadarajan and Nagarajaiah, 2004; Yang et al., 2004).
The lower and upper limits of the parameters of DTMDI.
3.2. Optimal parameters
The aim of the parametric optimization is to maximize the vibration control capacity of DTMDI. This means that the
It is evident that the objective function, as shown in equation (15), has many variables and constraints. Hence, we need a potential optimization algorithm to solve this problem.
There are many algorithms used to search solutions of optimization problems (Etedali and Rakhshani, 2018; Le-Duc et al., 2020; McCall, 2005), and one can use one of the existing techniques (e.g., Genetic Algorithms, Cuckoo Search Algorithm, Firefly Algorithm, and Moth-Flame Optimization) to optimize the DTMDI. Among the recently developed optimization algorithms, Balancing Composite Motion Optimization (BCMO) is a novel technique introduced by Le-Duc et al. (2020). Basically, the BCMO is a population-based optimization algorithm. The fundamental concept of this algorithm revolves around balancing the composite motion characteristics of individuals within the solution space. By integrating a probabilistic selection model, balancing global and local searches establishes a movement mechanism for each individual. The basic principles of the BCMO method were fully explained, and readers can find them in Ref. (Le-Duc et al., 2020) where the authors provided publicly available MATLAB source codes for this algorithm. The BCMO has demonstrated high efficiency, low complexity, and rapid convergence when compared with different population-based optimization algorithms. One can find those comparisons in the original work of Le-Duc et al. (2020). Additionally, the BCMO is also effective for multi-objective or complex optimization problems involving many variables and constraints (Bui et al., 2023; Le-Duc et al., 2020; Tran et al., 2024). Therefore, the BCMO is chosen to find the optimal parameters for absorbers in this research.
The BCMO algorithm has two main parameters, including the number of generations ( Diagram of the optimization procedure for the DTMDI using the BCMO algorithm.
Optimal configurations of the DTMD and DTMDI with the different values of
Optimal configurations of the TMD and TMDI with the different values of
The data presented in Table 3 offers valuable insights regarding the behavior of various design variables in relation to the importance ratio ( Variation of the DTMDI parameters as the inertance ratio changes from 0% to 5%.
Furthermore, the analysis suggests that achieving an optimal configuration for the DTMDI, particularly as the value of
4. Numerical investigations and discussions
In this section, the author focuses on the effectiveness and robustness of the optimal DTMDI configurations, where effects of structural natural frequency on the vibration control performance of DTMDI and effects of the inerter on the structure response are considered.
4.1. Evaluation criteria
In this study, there are two primary criteria to evaluate the effectiveness of the DTMDI in controlling structural vibrations. The first criterion is
Based on the first criterion, the vibration reduction of each vibration absorber is defined as follows:
Based on the second criterion, the vibrating energy reduction for each device is determined by
4.2. Performance of DTMDI
To assess the vibration reduction effectiveness of an optimized DTMDI, its performance is analyzed and compared against that of the optimal TMDI which has the same weight and inertance ratio as the DTMDI.
As previously discussed, based on the
Based on the same weight and inertance ratio, it is evident that the control effectiveness of optimized configurations of DTMDI is higher than those of TMDI. In particular, the structural vibration reduction achieved from the optimal DTMDI with
For optimized configurations of DTMDI/TMDI, the optimal DTMDI/TMDI configuration with a larger inertance ratio is more effective. This can be explained by the fact that when the inertance ratio (
Figure 4 shows a comparison on the frequency response functions of the main structure equipped with various devices: the optimal TMD, TMDI, DTMD and DTMDI, in which the optimal configurations for TMDI and DTMDI are based on the inertance ratio of A comparison on frequency response functions of the structure controlled by the optimal TMD, DTMD, TMDI with 
With the mass ratio of μ = 2%, Figure 5 depicts DMF response surfaces of the primary structure controlled by the DTMDI and the TMDI as the inertance ratio varies from 1% to 5%. As shown in Figure 5, the DMF response surface of the structure with the DTMDI exhibits a three-peak characteristic, and its peak region remains relatively flat over a broader range of excitation frequencies (refer to Figure 5(a)). In contrast, the response surface of the structure with the TMDI displays a two-peak characteristic, with a peak region that is not flat over a narrower frequency range (refer to Figure 5(b)).
4.3. Robustness of DTMDI
In practice, the stiffness and mass of the primary structure may be different from the initial calculated values due to errors in measurement progress (Yamaguchi and Harnpornchai, 1993), equipment replacement on the structure (Cao and Tran, 2023), or even environmental factors (e.g., snow accumulation). This leads to the natural frequency of the structure which differs from the initial calculated value (as reported in Table 1). Thus, the DTMDI can be detuned. This is why a survey on the robustness of the DTMDI against changes in the structural natural frequency ( DMF surface of the structure controlled by (a) the DTMDI and (b) the TMDI when the inertance ratio changes from 1% to 5% at 
It is assumed that the change in the structural natural frequency, Effect of changes in the structural natural frequency on the effectiveness of the optimal TMD, DTMD, TMDI, and DTMDI at 
4.4. Effects of the inertance ratio and mass ratio on the structural response
This section investigates the effects of the inertance ratio ( Effects of the inertance ratio and mass ratio on the structure response as 
On the other hand, these
4.5. Vibrations of masses
and
in DTMDI
To further understand how masses DMF curves of the TMD1 and TMD2 masses of the optimal DTMDIs (with 
5. Conclusions
The DTMD has been demonstrated to be more efficient than a traditional TMD (Cao and Tran, 2023). To further improve the performance and robustness of DTMD, an upgraded version of DTMD for structural vibration control was proposed in this research. In the innovative type of DTMD, the DTMD was linked to the ground through a linear inerter. Modeling of the system consisting of a SDOF structure with a DTMDI was established. The optimal configurations of the DTMDI corresponding to various inertance ratios were then found using the BCMO algorithm. Studies on the effects of changes in the structural properties as well as the mass and inertance of DTMDI to the control effectiveness and robustness of DTMDI were conducted. The outstanding findings obtained from this work include: (a) An optimal DTMDI is significantly more effective and robust than an optimal DTMD with the same weight as the DTMDI, in which the optimal configuration of DTMDI with a higher inertance ratio produces higher effectiveness. (b) With the same mass and inertance, the DTMDI yields higher performance compared to the TMDI. Thus, using a DTMDI instead of a TMDI offers a significant reduction in the weight of the device on the main structure. (c) The DTMDI is more robust than both the DTMD and TMD against the variation of the structure’s natural frequency, but the DTMDI becomes less robust than the TMDI when the structural frequency increases. (d) Three-objective optimization surfaces for both DTMDI and TMDI generated in this work provide engineers with a frame to balance design objectives related to the mass, inertance, and performance of each device employed. (e) With a given inertance ratio, vibrations of
The inerter of the DTMDI connected to the ground may be a disadvantage of DTMDI for seismic protection of structures. However, the practical applicability of the proposed damper in civil structures under the other types of loads is very significant. For example, DTMDI can be equipped on offshore platforms to reduce structural responses induced by wave and wind loadings, or it can be integrated into bridges to mitigate vertical vibrations caused by pedestrian and vehicle loads. In addition, DTMDI can be used for base-isolated structures, as mentioned in the previous studies (De Angelis et al., 2019; De Domenico and Ricciardi, 2018).
Although the findings discussed in this work were based on harmonic excitation forces, the proposed device is expected to perform well under random excitations. In future studies, the effectiveness of the DTMDI in controlling the dynamic response of various types of structures subjected to random excitations will be investigated.
Footnotes
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Data availability statement
All data that support the findings of this study are included within the article.
The TMDI-structure system
An analytical model of the system TMDI-structure under an external force excitation is shown in Figure 9. The TMD has the mass Analytical model of the TMDI-structure system.
Here,
The natural frequency of the TMDI is
The damping ratio of the TMD is
The mass ratio between the TMD and structure is
The total mass ratio between the TMDI and the structure is given by
The tuning ratio of the TMDI is
