Multifunctional Design of Vibrational Energy Harvesters in a Bridge Structure

Round 1

Reviewer 1 Report

1.      Literature review is quite sparse. Authors are encouraged to use the recent references to strengthen the literature review:

https://0-doi-org.brum.beds.ac.uk/10.1016/j.compscitech.2019.04.020

https://0-doi-org.brum.beds.ac.uk/10.1142/S0219455422500092

2.      make flowchart for optimization

3.      The researchers ought to describe or provide detailed physical justifications for their findings.

4.      In the literature, there is an experiment-based model for energy harvesters (see https://0-doi-org.brum.beds.ac.uk/10.1016/j.enconman.2018.02.054). Authors are encouraged to use these data and talk about the aforementioned study to enhance the application of their research.

5.      It's unclear why natural frequency should be maximized. The deflection can be reduced by optimization. Are they connected? Speculate on it. Cite some academic works that have conducted comparable analyses for structural analysis.

Author Response

1. Literature review is quite sparse. Authors are encouraged to use the recent references to strengthen the literature review:

https://0-doi-org.brum.beds.ac.uk/10.1016/j.compscitech.2019.04.020

https://0-doi-org.brum.beds.ac.uk/10.1142/S0219455422500092

The authors completely agree with the reviewer’s comment as energy harvesting technologies and applications have been investigated extensively. With that said, the authors have tried to summarize and constrain the literature review to recent articles most relevant to the proposed work. The authors thank the reviewer for suggesting the first reference which has been cited in the Introduction section of the revised manuscript in lines 69-71. However, the authors could not find a compelling reason as to why the second reference should be included in the literature review.

“Recently, some researchers have also investigated the effects of multifunctional composite materials combined with energy harvesting for various applications including health monitoring in bridge infrastructure”

2. Make flowchart for optimization

A flowchart for optimization has been included in section 2.1 with Figure 3 to graphically describe the patternsearch algorithm.

3. The researchers ought to describe or provide detailed physical justifications for their findings.

The authors have included a new figure (Figure 10) in the results section along with some discussion to connect the resulting optimal frequencies to the frequency content of the input load considered in this paper.

“To further investigate the behavior of the resulting optimized frequencies, the frequency content of the input load was determined and shown in Figure 10. We can clearly observe that the highest frequency happens around 9.19 rad/s with some high peaks in the vicinity of 12 to 13 rad/s and hence, the tuning of all harvesters in that range.”

4. In the literature, there is an experiment-based model for energy harvesters (see https://0-doi-org.brum.beds.ac.uk/10.1016/j.enconman.2018.02.054). Authors are encouraged to use these data and talk about the aforementioned study to enhance the application of their research.

The authors thank the reviewer for the suggested article. A paragraph has been added in the revised manuscript, in lines 401-406, where some of the relevant experimental study findings to this work are addressed and used to validate the proposed multifunctional vibrational energy harvesting design.

“Recent experimental studies on piezoelectric energy harvesting from vehicle-bridge coupling vibration show that higher energy harvesting efficiency can be achieved when the harvester is installed at the center of the structure [38]. These results validate the approach of implementing the proposed multifunctional vibrational energy harvesting concept at the center of the Bill Emerson Cable-Stayed bridge.”

5. It's unclear why natural frequency should be maximized. The deflection can be reduced by optimization. Are they connected? Speculate on it. Cite some academic works that have conducted comparable analyses for structural analysis.

The optimization problem described in section 2.1 does not aim to maximize frequency, instead, optimal design frequencies are determined by minimizing the negative of the total power generated (equivalent to maximizing the total power generated) of all different harvester configurations considered in the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

I have the following observations regarding the manuscript:-

1. The manuscript is written well and clearly represents the application of Vibrational Energy Harvesters in a  Bridge Structure

2. The abstract part is written in a proper manner

3. The problem formulation qualitatively represents the major contribution of the paper

4. The tables and the figures completely represents the information about the results

5. The conclusion section is written well

Author Response

The authors thank the reviewer for the comments.

Reviewer 3 Report

This paper presents a simulation study to quantify the energy (power) that can be harvested from a large structure, specifically a bridge. A finite element model of a real bridge is used, and a scaled time varying load from seismic data is introduced to reproduce the typical vibrational forcing induced by vehicles transiting. Different distributions of the harvester masses are considered to alleviate the well known power limitations. Simulation results show low power transfer, confirming existing literature. The authors reach the conclusion that this would be enough to power structural health monitoring systems. The paper is completed by a proposed conceptual design of an integrated structure with green elements acting as harvester added masses. 

The model used for simulation is not novel as clearly stated and discussed through relevant citations. The authors claim to optimize the distribution of harvester masses in order to mimic the effect of a large mass that would be necessary to transfer sufficient energy for the class of applications considered. However, the paper does not seem to include a formal treatment of the optimization problem, which is instead based on pre defined symmetric distributions of the added masses on the structure. Results confirm well known limitations of energy harvesting in large structures, which would be interesting but it is a quite mature result.

I have serious reservations about the merit of the conceptual design, which is presented in a form that is not mature for a technical publication. Indeed, the concept of using as harvester masses the ones from green elements integrated into the structure is discussed without technical details on how to actually map the elements into harvester. Although the problem formulation is not new, I would still consider a good contribution for this journal a deeper design technical treatment, but unfortunately the paper falls short on this aspect.

In addition, some of the language used is vague and in my opinion attempting to use fashionable but rather vague terms (first sentence of the abstract: "This paper aims to integrate vibrational energy harvesters into structural systems in a 8 holistic fashion to contribute to sustainability") to appeal the journal scope without having the necessary contribution (in the sense explained above).

The abstract should be rewritten more clearly. Equations sometimes introduce term that are not immediately defined, or are defined later in the text. A few examples of unclear sentences that should be improved:

- "As a result, less stiff structures are created which suffer from a secondary, but still of great importance, problem, human discomfort."

- "[...] in the pattern of modification."

Author Response

1. The model used for simulation is not novel as clearly stated and discussed through relevant citations. The authors claim to optimize the distribution of harvester masses in order to mimic the effect of a large mass that would be necessary to transfer sufficient energy for the class of applications considered. However, the paper does not seem to include a formal treatment of the optimization problem, which is instead based on pre-defined symmetric distributions of the added masses on the structure. Results confirm well known limitations of energy harvesting in large structures, which would be interesting but it is a quite mature result.

To make the optimization tractable and also to simulate real-world design constraints of placing harvesters on an existing bridge, the authors considered pre-defined symmetric locations near the center of the bridge which were found to be the most effective location of semi-active dampers in [31] and also in a study on bridge energy harvesting by [38]. A topology/placement optimization is beyond the scope of this manuscript and is more germane to the case of the design of a new bridge structure.  The authors agree that this is an important potential future direction for the research which has been noted by adding text to that effect in the Conclusions.

“Pre-defined symmetric locations were considered in this paper for optimizing the total power generation of all harvesters for the purpose of implementing the multifunctional green garden concept. However, a topology optimization can be performed without alterations to the proposed methodology and is one future direction of the authors’ research.”.

2. I have serious reservations about the merit of the conceptual design, which is presented in a form that is not mature for a technical publication. Indeed, the concept of using as harvester masses the ones from green elements integrated into the structure is discussed without technical details on how to actually map the elements into harvester. Although the problem formulation is not new, I would still consider a good contribution for this journal a deeper design technical treatment, but unfortunately the paper falls short on this aspect.

The authors acknowledge that only a preliminary design of a green element design of the harvester is included in the manuscript but respectfully disagree with the reviewer on the level of contribution of what was presented. Additionally, the authors have added a discussion concerning how the tributary area of each harvester was specified in the revised manuscript for better understanding of how the total garden mass was determined based on technical specifications. 

“Detailed calculations were performed to determine the total required mass for the green gardens, with each harvester tributary area defined by a length of 82.29 meters, considering the spacing between joints, and a width of 3 meters, selected to achieve proportionality within the structure.”

Further research needs to be conducted to investigate different alternatives to physically connect the multifunctional harvester mass to the structure. However, this is beyond the scope of the proposed conceptual preliminary design in this paper.

3. In addition, some of the language used is vague and, in my opinion, attempting to use fashionable but rather vague terms (first sentence of the abstract: "This paper aims to integrate vibrational energy harvesters into structural systems in a 8 holistic fashion to contribute to sustainability") to appeal the journal scope without having the necessary contribution (in the sense explained above).
4. The abstract should be rewritten more clearly. Equations sometimes introduce term that are not immediately defined, or are defined later in the text. A few examples of unclear sentences that should be improved:

- "As a result, less stiff structures are created which suffer from a secondary, but still of great importance, problem, human discomfort."

- "[...] in the pattern of modification."

Some of the unclear sentences have been revised and reworded in the manuscript to facilitate the readers understanding. Some examples can be found in lines 37-38 and 148-149.

The authors thank the reviewer for pointing out the need to improve the written exposition of the article. In response to points #3 and #4, the abstract of the manuscript has been extensively revised. Additionally, the authors have thoroughly reread their previous draft and revised those portions of the text that were unclear to improve the readability of the manuscript. For example, in lines 37-38, 148-149 and 528.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The weaknesses that I pointed out in the first round have not been addressed. Therefore, my recommendation stands. 

Author Response

Dear Reviewer, responses to previous comments were submitted and addressed in the revised manuscript. As previously submitted:

1. The model used for simulation is not novel as clearly stated and discussed through relevant citations. The authors claim to optimize the distribution of harvester masses in order to mimic the effect of a large mass that would be necessary to transfer sufficient energy for the class of applications considered. However, the paper does not seem to include a formal treatment of the optimization problem, which is instead based on pre-defined symmetric distributions of the added masses on the structure. Results confirm well known limitations of energy harvesting in large structures, which would be interesting but it is a quite mature result.

To make the optimization tractable and also to simulate real-world design constraints of placing harvesters on an existing bridge, the authors considered pre-defined symmetric locations near the center of the bridge which were found to be the most effective location of semi-active dampers in [31] and also in a study on bridge energy harvesting by [38]. A topology/placement optimization is beyond the scope of this manuscript and is more germane to the case of the design of a new bridge structure.  The authors agree that this is an important potential future direction for the research which has been noted by adding text to that effect in the Conclusions.

“Pre-defined symmetric locations were considered in this paper for optimizing the total power generation of all harvesters for the purpose of implementing the multifunctional green garden concept. However, a topology optimization can be performed without alterations to the proposed methodology and is one future direction of the authors’ research.”.

2. I have serious reservations about the merit of the conceptual design, which is presented in a form that is not mature for a technical publication. Indeed, the concept of using as harvester masses the ones from green elements integrated into the structure is discussed without technical details on how to actually map the elements into harvester. Although the problem formulation is not new, I would still consider a good contribution for this journal a deeper design technical treatment, but unfortunately the paper falls short on this aspect.

The authors acknowledge that only a preliminary design of a green element design of the harvester is included in the manuscript but respectfully disagree with the reviewer on the level of contribution of what was presented. Additionally, the authors have added a discussion concerning how the tributary area of each harvester was specified in the revised manuscript for better understanding of how the total garden mass was determined based on technical specifications. 

“Detailed calculations were performed to determine the total required mass for the green gardens, with each harvester tributary area defined by a length of 82.29 meters, considering the spacing between joints, and a width of 3 meters, selected to achieve proportionality within the structure.”

Further research needs to be conducted to investigate different alternatives to physically connect the multifunctional harvester mass to the structure. However, this is beyond the scope of the proposed conceptual preliminary design in this paper.

3. In addition, some of the language used is vague and, in my opinion, attempting to use fashionable but rather vague terms (first sentence of the abstract: "This paper aims to integrate vibrational energy harvesters into structural systems in a 8 holistic fashion to contribute to sustainability") to appeal the journal scope without having the necessary contribution (in the sense explained above).
4. The abstract should be rewritten more clearly. Equations sometimes introduce term that are not immediately defined, or are defined later in the text. A few examples of unclear sentences that should be improved:

- "As a result, less stiff structures are created which suffer from a secondary, but still of great importance, problem, human discomfort."

- "[...] in the pattern of modification."

Some of the unclear sentences have been revised and reworded in the manuscript to facilitate the readers understanding. Some examples can be found in lines 37-38 and 148-149.

The authors thank the reviewer for pointing out the need to improve the written exposition of the article. In response to points #3 and #4, the abstract of the manuscript has been extensively revised. Additionally, the authors have thoroughly reread their previous draft and revised those portions of the text that were unclear to improve the readability of the manuscript. For example, in lines 37-38, 148-149 and 528.

Round 3

Reviewer 3 Report

Unfortunately I do not see relevant changes to modify my evaluations. Therefore my recommendation stands.