Comparison and Optimization of a Magnetic Lead Screw Applied in Wave Energy Conversions

Round 1

Reviewer 1 Report

The authors propose the Comparison and Optimization of Magnetic Lead Screw Applied in Wave Energy Conversions.

The paper gives positive responses to the following general questions: Does the introduction provide sufficient background and include all relevant references? Is the research design appropriate? Are the methods adequately described? Are the results clearly presented? Are the conclusions supported by the results?

However, I will present here some specific technical comments to improve the paper:

·       In the abstract part, some quantitative results should be included.

·       In introduction section, authors are advised to include the literature review in table format.

·       The main contribution of the proposed study is missing. Authors are advised to add it in the last part of the introduction section.

·       I had a problem on understanding how the algorithm works exactly from the provided description.

·       The font size of equations is not same.

·       Please maintain the uniformity while citing the figures inside the text. Somewhere its written like ‘Figure’ and other places written like ‘Fig.’

·       Figure 15 is not cited inside the text.

·       Please provide some quantitative analysis in the conclusion part.

·       Writing language is also needed to be improved. There are some grammatical and typo errors existing in the text.

 

Author Response

Point 1：In the abstract part, some quantitative results should be included.

Response 1：Considering to the reviewer’s suggestion, we have added some quantitative results in the abstract to " When the moving speed v =0.15m/s, the output power of the MLSHG and outer-PM linear tubular generator are 923W and 87W respectively when the load resistance is 5Ω .The output power of MLSHG is more than 10 times compared to that of the outer-PM linear tubular generator for a fair comparison. It is shown that the power density and output power of are MLSHG increased greatly."

 

Point 2：In introduction section, authors are advised to include the literature review in table format.

Response 2：Under the reviewer’s suggestion, we have included the literature review in Table 1 and added some literature.

Table 1. Different types of wave energy convert system.

Type	Device	Description
Hydraulic	Oyster [4] Waveroller [5]	Hydraulic WEC uses wave energy to drive the hydraulic device to do work on the hydraulic turbine, which in turn drives the traditional motor to generate electricity.
Pneumatic	Limpet [6] Spar buoy [7]	Pneumatic WEC uses air as a medium for conversion. Under the action of wave heave, the wave energy is converted into the pressure energy and kinetic energy of the air.
Gear-box	Columbia Power WEC [8] Wave Dragon [9]	Gear-box WEC uses a sealed drive shaft to convert the energy of wave ups and downs into mechanical energy of a rotating motor through a gearbox, thereby generating electrical energy.
Direct-drive	AWS [10] TE 5 [11]	Direct-drive WEC generally uses linear generators to directly convert the mechanical energy of waves into electrical energy.

The added literature list：

1. Henry A , Doherty K , Cameron L. " Advances in the Design of the Oyster Wave Energy Converter." Proceedings of Marine Renewables & Offshore Wind Conference, RINA HQ, London 2010.
2. T. Whittaker, D. Collier, M. Folley, M. Osterried and A. Henry, "The development of Oyster—a shallow water surging wave energy converter," Proceedings of 7th European Wave Tidal Energy Conference, 2007.
3. J. Lye, D. Brown and F. Johnson, "An Investigation into the non-linear effects resulting from air cushions in the Orecon oscil-lating water column device," in Proceedings of 28th International Conference on Ocean Offshore Artic Engineering, Honolu-lu, 2009, p. 79115.
4. K. UA, "Phase control of floating bodoes fron an on board refernce," Appl Ocean Res, pp. 251-262, 2001.
5. K. Rhinefrank, J. Prudell and A. Schacher, "Development and characterization of a novel direct drive rotary wave energy point absorber MTS-IEEE oceans conference proceedings," OCEANS 2009, 2009.
6. J. Kofoed and P. Frigaard, "Prototype testing of the wave energy converter Wave Dragon. Renewable Energy," 2006, pp. 181-189.
7. H. Polinder, M. E. C. Damen and F. Gardner, "Linear PM Generator system for wave energy conversion in the AWS," in IEEE Transactions on Energy Conversion, vol. 19, no. 3, pp. 583-589, Sept. 2004.
8. P. C. J. Clifton, R. A. McMahon and H. -P. Kelly, "Design and commissioning of a 30kW direct drive wave generator," 5th IET International Conference on Power Electronics, Machines and Drives (PEMD 2010), 2010.

 

Point 3：The main contribution of the proposed study is missing. Authors are advised to add it in the last part of the introduction section.

Response 3：At the end of the introduction section, we have added the main contributions of this research, " This paper proposed and selected a suitable topology of MLS for the wave energy converter. Based on this topology, a magnetic screw compound linear generator is raised and designed as the core device for DD-WEC. The output power of the new generator is more than 10 times compared to that of the general linear generator under some operating conditions, which can significantly improve wave energy conversion efficiency."

 

Point 4：I had a problem on understanding how the algorithm works exactly from the provided description. The font size of equations is not same.

Response 4：We feel sorry for the inconvenience in understanding the algorithm. The working processing is as follows. Firstly, the magnetic field distribution which is established by the PMs of the mover is calculated through Maxwell's equations. After that, the PMs of the rotor are equivalent to the current-carrying coils. Hence, the electromagnetic force of the mover can be calculated using Lorentz's force law. When the force is obtained, the transmission ratio is carried out. This algorithm is merely used to introduce and describe the principle of the MLS, the calculation and optimization are used by Maxwell, one of the business finite element analysis (FEA) software. The font size of the equations was adjusted to the same size.

 

Point 5：Please maintain the uniformity while citing the figures inside the text. Somewhere its written like 'Figure' and other places written like 'Fig.'

Response 5：After reading and checking the full text, we changed "Fig" to "Figure" in the article.

 

Point 6：Figure 15 is not cited inside the text.

Response 6：We have cited Figure 15 in the article. And the sentence is added under Figure 15," When at the position of Z_d = τ_p/2, the air gap flux density of the SMMLS in one lead is shown in Figure 15."

 

Point 7：Please provide some quantitative analysis in the conclusion part.

Response 7：As suggested by the reviewer, we have added a corresponding quantitative analysis " At a constant speed of 0.15m/s, the output power of MLSHG and outer-PM linear tubular generator are 923W and 87W respectively when the load is 5Ω. Assuming that the wave velocity is 0.2sin(πt), which is a sinusoidal velocity, the average output power of MLSHG and outer-PM linear tubular generator are1063.83W and 66.7 W at the load of 10 ." to the conclusion section of the article.

 

Point 8：Writing language is also needed to be improved. There are some grammatical and typo errors existing in the text.

Response 8：Considering your comments, we have checked the words and sentences carefully and fixed some errors, such as:

1. "In which I₀ and K₀ are modified Bessel functions of the first kind. I₁ and K₁ are modified Bessel function of the second kind" changes to" In which I₀ and K₀ are modified Bessel functions of the first kind. I₁ and K₁ are modified Bessel functions of the second kind."
2. "Using Lorentz force law to calculate the force exerted on the mover" changes to "Using Lorentz’s force law to calculate the force exerted on the mover"
3. "The rotor power P_t equals to the mover power P_r." changes to " The rotor power P_t is equal to mover power P_r."
4. "The In addition, the thickness of the back iron is greater than the PMs" changes to " In addition, the thickness of the back iron is greater than the PMs"
5. "The air gap flux density when the QHAMLS magnetic pole position is Z_d = τ_p/2 is shown in Figure 17." changes to "The air gap flux density of QHAMLS at the position of Z_d = τ_p/2 is shown in Figure 17. "
6. "The relationship between the width of the triangle tooth and the width of the PM can be seen from the following formula" changes to "The relationship between the width of the triangle tooth and the width of the PM can be seen in the following formula ", and so on.

Author Response File: Author Response.pdf

Reviewer 2 Report

Good Day!

I would like to let you know that I appreciate the overall quality of the work you've displayed.

There are a few observations in place:

1. Regarding the full model presented up to relation (22), the relationships appear either taken from other published materials. There is nothing wrong with this, whereas the source(s) is/are mentioned in the text right before the relationships. If the relationships are original, one must detail the procedure for obtaining them, not just state them.

2. A short mention of the software package used for FEA may benefit the overall work.

3. The values are not followed by the measurement units in very few places in the text. Please insert the measurement units as well.

4. The values presented in Table 5 contradict the explanation from the text, being reversed. Please, review Table 5.  

5. In line 452, you've mentioned "the previous article." Is this article the one presented as a reference [19]? If yes, please refer it in the text.

Thank you very much

 

 

 

Author Response

Point 1: Regarding the full model presented up to relation (22), the relationships appear either taken from other published materials. There is nothing wrong with this, whereas the source(s) is/are mentioned in the text right before the relationships. If the relationships are original, one must detail the procedure for obtaining them, not just state them.

Response 1: We are so sorry for the carelessness. The original reference [29] has been added at the beginning of the equations. The equations are only used to introduce the basic principle of the MLS. We appreciate your suggestions very much.

 

Point 2: A short mention of the software package used for FEA may benefit the overall work.

Response 2: Under your kind suggestion, we have added a sentence in the Introduction (line 64) to provide information about the software. The sentence is “Maxwell, one of the business finite element analysis (FEA) software, was used to optimize these topologies through 2-D and 3-D analysis.”

 

Point 3: The values are not followed by the measurement units in very few places in the text. Please insert the measurement units as well.

Response 3: We are sorry for our neglect of the measurement units. Under your suggestion, we have checked the values and units carefully. And “a torque peak of 7.35” changes to “a torque peak of 7.35 N·m”.

 

Point 4: The values presented in Table 5 contradict the explanation from the text, being reversed. Please, review Table 5.

Response 4: We have reviewed Table 5 and corrected the mistakes in the table as shown below. Correspondingly, the description in the text has been modified.

Speed (m/s)	Load (ohm)	MLS hybrid generator		Linear generator
		Input power (W)	Output power (W)	Input power (W)	Output power (W)
0.1	5 10	1225 1477	811 1158	52 31		39 26
0.15	5 10	1367 1932	923 1534	118 68		87 58
0.2	5 10	1445 2136	967 1722	205 124		153 104
025	5 10	1492 2278	991 1826	314 189		234 161
0.3	5 10	1508 2356	1003 1889	440 268		330 230

Point 5: In line 452, you've mentioned "the previous article." Is this article the one presented as a reference [19]? If yes, please refer it in the text.

Response 5: We apologize for the inaccurate expression. In fact, what we want to express is according to the previous content (Table 4) in the paper, not “the previous article”. Therefore, we have changed the sentence to “According to the design parameters in Table 4,….”

 

Author Response File: Author Response.pdf