Finite Element Investigation of Load Acting on the Hotspot Detector Located inside the Silo Caused by Material Discharge
Round 1
Reviewer 1 Report
The manuscript deals with the load acting on a silo hotspot detector located inside the silo during material discharge. This study includes analytical calculations, experimental data and FEM simulations. The simulations were carried out after previous validation against experimental data reported by other authors (Couto et al.). This research is novel, scientifically sound and provides interesting results. However, some improvements/clarifications are needed before acceptance:
- Although the study is comprehensive and compare different approaches to solve the question, authors have focussed on horizontal pressures acting on the detector. However, other effects are also present that could affect the detector (frictional traction, vertical stress, shakes and vibrations). What would be the effects of these phenomena? Some discussion or mention is expected about the different loads and phenomena.
- The authors should specify if their analytical calculations followed the Eurocode (the Eurocode is only mentioned in Conclusion section). If so, a reference for the Eurocode should be included in Section 2.
- Can the hotspot detector and chain interfere or modify somehow the flow of material in small silos?
- In this study FEM simulations and experimental tests have been developed for a specific silo. However, results could be very different in silos with other geometrical characteristics. Some discussion about this point and future research directions in this sense should be included in secion 4.3.
Other specific comments:
- Lines 29-30: This statement requires a reference.
- Line 76: Place the sentence “This study aims…” in a new paragraph.
- Lines 79-83, use past to state the different tasks developed in this study (confirmed, was analyzed…).
- Section 2.1 should be entitled “Normal pressures on vertical wall” and Section 2.2 “Normal pressures on hopper wall”.
-Material properties in Table 1: Indicate reference or explain how the values were chosen.
- Strenght of detector in Table 2: indicate if the detector was tested by authors or if the value was provided by manufacturer.
-Line 119: the pressure Phf(z) is applied normally to the vertical wall, not vertically.
- Line 124: include reference for AAC2 class.
- Explain “17” in equation 3.
- Line 144: introduce a reference after “steep”.
- Line 229: provide the characteristics of the tensile load measuring device, including model and manufacturer.
-Line 248: “generally identical” should be replaced by an expression like “quite similar” or “the two results match quite well”.
- In Fig. 5, there are significant differences between 3rd and 5th experiments. How was the experimental curve in Fig. 6 drawn from these experimental values? Some further explanation seems necessary.
- Line 265: “Abaqus 2018” requires a reference.
-Indicate the number of cells in the FEM simulations (both in 3.3 and 3.4 sections).
- Include reference [29] in Figure 11 caption to differentiate FEM results obtained by the authors from experimental values previously reported by other researchers.
-Lines 402-403: reword sentence “It can be seen…maximum pressure”.
- Lines 445-451: this information is repeated and can be eliminated.
- Indicate what is the meaning of “t” in Figure 13.
- Table 5: indicate the depth for the tensile forces included in the table.
-Lines 510-515: That paragraph has no relation to this study and should be eliminated.
Author Response
Response to Reviewer 1 Comments
Point 1: Although the study is comprehensive and compare different approaches to solve the question, authors have focussed on horizontal pressures acting on the detector. However, other effects are also present that could affect the detector (frictional traction, vertical stress, shakes and vibrations). What would be the effects of these phenomena? Some discussion or mention is expected about the different loads and phenomena.
Response 1: In the conclusion section, explained the limitations of the interpretation. (Line 536 – 542)
- The limitations in this study are as follows. The silo applied to the analysis and experiment of this study has a geometrically symmetrical shape. However, silos with different geometric properties may differ significantly from the results of this study. In addition, in this study, assuming that the friction traction due to the normal pressure in the regular discharge contributes the most to the silo hotspot detector tensile force, only two cases, from the prediction equation to the analysis result, are considered. However, in reality, phenomena such as shaking, vibration, and voids in the material occur. It is a situation that requires research considering this.
Point 2: The authors should specify if their analytical calculations followed the Eurocode (the Eurocode is only mentioned in Conclusion section). If so, a reference for the Eurocode should be included in Section 2.
Response 2: Section 2 states that the analytical calculations follow the eurocode. (Line 94 – 95)
Point 3: Can the hotspot detector and chain interfere or modify somehow the flow of material in small silos?
Response 3: For silos that are geometrically symmetrical, such as those applied in this study, the material flow also exhibits symmetry, and it is judged that the detector does not interfere with the material flow because it exists only in the vertical wall section. However, in the case of silos that are not geometrically symmetrical, further study is needed because the flow is also not symmetrical.
Point 4: In this study FEM simulations and experimental tests have been developed for a specific silo. However, results could be very different in silos with other geometrical characteristics. Some discussion about this point and future research directions in this sense should be included in secion 4.3.
Response 4: In the conclusion section, we explained the limitations of the interpretation and added a part to discuss future research directions through this. The contents are as follows. (Line 536 – 547)
- The limitations in this study are as follows. The silo applied to the analysis and experiment of this study has a geometrically symmetrical shape. However, silos with different geometric properties may differ significantly from the results of this study. In addition, in this study, assuming that the friction traction due to the normal pressure in the regular discharge contributes the most to the silo hotspot detector tensile force, only two cases, from the prediction equation to the analysis result, are considered. However, in reality, phenomena such as shaking, vibration, and voids in the material occur. It is a situation that requires research considering this.
In future study, this study attempts to compare the stress distribution on the internal stress distribution and the silo wall and silo hotspot detector through an analysis that considers influence factors not considered in this study. In addition, the pressure change acting on silo hotspot detector in the silo having a geometrically different shape from the silo targeted in this study will be compared.
Other specific comments:
- Lines 29-30: This statement requires a reference.
Response : Added reference. (Line 29 – 31)
- Line 76: Place the sentence “This study aims…” in a new paragraph.
Response : Corrected with a new paragraph. (Line 79 - 80)
- Lines 79-83, use past to state the different tasks developed in this study (confirmed, was analyzed…).
Response : Corrected using the past.(confirmed & was analysed) (Line 82 - 86)
- Section 2.1 should be entitled “Normal pressures on vertical wall” and Section 2.2 “Normal pressures on hopper wall”.
Response : Correction was completed. (Line 107 & 146)
- Material properties in Table 1: Indicate reference or explain how the values were chosen. Strenght of detector in Table 2: indicate if the detector was tested by authors or if the value was provided by manufacturer.
Response : The following sentence was added to the text to see where the physical property values in Tables 1 and 2 were referenced. (Line 101 - 103)
- The property values in Table 1 and 2 were set with reference to eurocode [23]. In addition, the tensile strength of the silo hotspot detector shown in Table 2 cited the value provided by the manufacturer.
- Line 119: the pressure Phf(z) is applied normally to the vertical wall, not vertically.
Response : Correction was completed. (Line 127)
- Line 124: include reference for AAC2 class.
Response : It was stated that the eurocode was referenced. (Line 132)
- Explain “17” in equation 3.
Response : "17" in eq 3 is the vertical wall section depth z in Fig 1. Correction was completed. (Line 142)
- Line 144: introduce a reference after “steep”.
Response : It was stated that the eurocode was referenced. (Line 147 – 148)
- Line 229: provide the characteristics of the tensile load measuring device, including model and manufacturer.
Response : Information about the load measuring device was provided as follows. (Line 250 - 252)
- As a load measuring device, a suspension-type scale with a maximum capacity of 5 tons with a model name of 5THB of CAS scale Korea was used.
- Line 248: “generally identical” should be replaced by an expression like “quite similar” or “the two results match quite well”.
Response : Fixed it to "quite similar". (Line 270)
- In Fig. 5, there are significant differences between 3rd and 5th experiments. How was the experimental curve in Fig. 6 drawn from these experimental values? Some further explanation seems necessary.
Response : The amount of material released per hour during the 3rd experiment was different from other experiments. Therefore, data for the 3rd experiment was excluded when creating the graph in Figure 6. (Line 257 - 258)
- Line 265: “Abaqus 2018” requires a reference.
Response : Reference was added. (Line 287)
- Indicate the number of cells in the FEM simulations (both in 3.3 and 3.4 sections).
Response : The number of meshes is shown for the numerical analysis model. (Line 382, 410, 496)
- Include reference [29] in Figure 11 caption to differentiate FEM results obtained by the authors from experimental values previously reported by other researchers.
Response : Added reference. (Line 422)
- Lines 402-403: reword sentence “It can be seen…maximum pressure”.
Response : It has been modified with the following new sentence. (Line 426 - 428)
- As a result of comparing the results of the FEM with the experimental values, it can be seen that the results showed quite similar results in the transition section where the maximum pressure occurs.
- Lines 445-451: this information is repeated and can be eliminated.
Response : Since this is a section showing the main results of this study, mentioned it again.
- Indicate what is the meaning of “t” in Figure 13.
Response : The following was added to the text. (Line 482 - 484)
- The pressure profile in Fig. 13 is the result of the analysis at 1, 3 and 5s, the time after which all particles start flowing.
- Table 5: indicate the depth for the tensile forces included in the table.
Response : The corresponding information is added to Table 5 as a tensile force at a depth of 0 to 23.515 m. (Line 480)
- Lines 510-515: That paragraph has no relation to this study and should be eliminated.
Response : Correction was completed.(eliminated that paragraph)
Reviewer 2 Report
Review of the paper “Finite element investigation of load acting on a silo hotspot detector located inside the silo caused by material discharge” by J.H. Rhee, S.I. Kim, Y.M. Lim and M.K. Kim for possible publication in Applied Sciences
This work applies a coupled Eulerian-Lagrangian method to determine the mechanical pressure inside a silo in order to judge whether an inner hotspot detector would be destroyed during material discharge. The work is interesting, because it compares the numerical results with experiments and analytical curves, but it needs a rewriting in several parts before publication.
The title is too complex and with repetition of the “silo” word. Is it really necessary to state that the hotspot detector is “located inside the silo”? Maybe “..on a silo inner hotspot detector…” or similar.
In the Introduction: lines 29-39 are badly written.
In Section 2, the analytical method for silos from Eurocode 1 is described, but you never point out to the corresponding Standard. You should cite there ref. 32 for the reader (it is never cited in the text).
I found the presentation of the analytical method long and confusing. I suggest to rewrite it for better clarity. Why do you need to interrupt the text with the lower/upper characteristic values as in the Eurocode? How do you obtain eq. 3 from eq. 1? What is a silo full and “extreme”? Do you refer to the extreme load conditions mentioned in Eurocode 1? Since you decided to describe the analytical method, then you need a consistent presentation. The symbol ε is not defined in eq. 11. Moreover, you use the same symbol at line 291, but it should be different there. It should be clear also during the discussion of the analytical method where the hotspot detector is placed.
Section 2.3 (experimental). Again, I do not understand where the hotspot detector is placed, when it is put inside the silo. Figure 5 and figure 6 should have the same unit along the vertical axis (I suggest kN). Even better, maybe you can combine the figures.
Section 3. Lines 278 and 280: Sij is the deviatoric stress tensor. Lines 290, 293: ψ is the dilatancy angle (it is correctly named in Table 3). Table 3 collects several geometry and material parameters for the analysis which is actually described in Section 4. Some of the geometry parameters in Table 3 are a repetition from Table 2. Morever, before Section 4, you show other results in Section 3.4 with another Table (Table 4). Provided my interpretation is correct, it is confusing. The captions in the figures 10 and 11 should state clearly that the results there are from a verification analysis (not “to be verified”) described in ref. 28, in order to avoid confusion with respect to the results in Section 4. Cohesion is zero (lines 295) or not (Table 3)?
Section 3.2. It is a coupled Eulerian-Lagrangian analysis, but if the Lagrangian part is rigid, what is the difference with respect to a standard, purely Eulerian analysis with rigid walls?
Figure 11. What is the stress represented here in the map? Is it a horizontal stress as for figures 12 and 14? In the figures 11, 12 and 14 there is no legend; it should include a clear spectrum for the colours.
Figure 13 and Table 5. What is t=1,3,5? A detector number? If so, where are they placed?
Line 491. Elastomer?
Are the numerical analyses dynamical and transient in time? What is the integration scheme? Or are they static with an ordinative time?
Silo discharging is a dynamic problem, with possible void creation for granular materials, vibrations and so on. Your approach seems to work for a “regular” discharge, when the continuum approach is acceptable. You should warn the reader accordingly somewhere in the paper.
Minor issue. FEM = Finite Element Method. Sometimes in your text you should write FE (without “M”).
Author Response
Response to Reviewer 2 Comments
Point 1: The title is too complex and with repetition of the “silo” word. Is it really necessary to state that the hotspot detector is “located inside the silo”? Maybe “..on a silo inner hotspot detector…” or similar.
Response 1: The title has been modified as follows to reflect the opinions. (Line 2 - 4)
- Finite element investigation of load acting on the hotspot detector located inside the silo caused by material discharge
Point 2: In the Introduction: lines 29-39 are badly written.
Response 2: References to the content and some modifications were made. (Line 29 - 34)
Point 3: In Section 2, the analytical method for silos from Eurocode 1 is described, but you never point out to the corresponding Standard. You should cite there ref. 32 for the reader (it is never cited in the text).
Response 3: Section 2 states that the analytical calculations follow the eurocode. (Line 94 - 95)
Point 4: I found the presentation of the analytical method long and confusing. I suggest to rewrite it for better clarity. Why do you need to interrupt the text with the lower/upper characteristic values as in the Eurocode? How do you obtain eq. 3 from eq. 1? What is a silo full and “extreme”? Do you refer to the extreme load conditions mentioned in Eurocode 1? Since you decided to describe the analytical method, then you need a consistent presentation. The symbol ε is not defined in eq. 11. Moreover, you use the same symbol at line 291, but it should be different there. It should be clear also during the discussion of the analytical method where the hotspot detector is placed.
Response 4:
- Some changes were made to section 2. (Line 116 – 119, 160 – 163, 186 – 188)
- The extreme load condition mentioned in Eurocode was applied to find the maximum pressure acting on the detector according to material discharge.
- eq. 3 is the value obtained by multiplying the normal pressure value acting on the vertical wall by eq. 1 multiplied by the flow coefficient to the depth direction. Through this, the tensile force acting on the detector was obtained.
- "Silo full" is a condition where the material is full inside the silo, and this condition is applied to assume the situation where the greatest pressure occurs.
- The ε symbol was explained by adding line 217-219.
- Symbol ε of eq11 was changed to Symbol . (Line 215)
Point 5: Section 2.3 (experimental). Again, I do not understand where the hotspot detector is placed, when it is put inside the silo. Figure 5 and figure 6 should have the same unit along the vertical axis (I suggest kN). Even better, maybe you can combine the figures.
Response 5: (Line 254 & 263)
- Completed additional description and Fig on the installation location of the detector
- Graph is completed using the same unit (in kN)
Point 6: Section 3. Lines 278 and 280: Sij is the deviatoric stress tensor. Lines 290, 293: ψ is the dilatancy angle (it is correctly named in Table 3). Table 3 collects several geometry and material parameters for the analysis which is actually described in Section 4. Some of the geometry parameters in Table 3 are a repetition from Table 2. Morever, before Section 4, you show other results in Section 3.4 with another Table (Table 4). Provided my interpretation is correct, it is confusing. The captions in the figures 10 and 11 should state clearly that the results there are from a verification analysis (not “to be verified”) described in ref. 28, in order to avoid confusion with respect to the results in Section 4. Cohesion is zero (lines 295) or not (Table 3)?
Response 6:
- Symbol name has been modified. (Line 300, 312)
- Tables 2 and 3 are physical properties for the silo to be analyzed.
- To verify the reliability of the applied analysis, we compared the analysis results with the experimental values. Table 4 shows the properties of the silos and materials applied in the experiment.
- Reference in the caption in Figure 11 is completed. (Line 422)
- Cohesive force of Table 3 is corrected by typo while writing '0'. (Line 320)
Point 7: Section 3.2. It is a coupled Eulerian-Lagrangian analysis, but if the Lagrangian part is rigid, what is the difference with respect to a standard, purely Eulerian analysis with rigid walls?
Response 7:
There will be differences in interpretation of the two cases on the contact surface. The contact problems involve Eulerian to Eulerian contact and Eulerian to Lagrangian contact. When granular materials interact with each other, the Eulerian to Eulerian contact default produces a sticky behavior, representing a kinematic assumption that a single strain field is applied to all materials within an element. In Eulerian to Eulerian contact, tensile stress is allowed to transmit across the contact interfaces, but no slip occurs at these interfaces. On the other hand, Eulerian material interacts with an Lagrangian element through Eulerian-Lagrangian contact.
Point 8: Figure 11. What is the stress represented here in the map? Is it a horizontal stress as for figures 12 and 14? In the figures 11, 12 and 14 there is no legend; it should include a clear spectrum for the colours.
Response 8: The stresses shown in Figures 11, 12 and 14 are horizontal forces(σxx). (Line 422, 446, 501)
Point 9: Figure 13 and Table 5. What is t=1,3,5? A detector number? If so, where are they placed?
Response 9: The following was added to the text. (Line 482 - 484)
- The pressure profile in Fig. 13 is the result of the analysis at 1, 3 and 5s, the time after which all particles start flowing.
Point 10: Line 491. Elastomer?
Response 10: Corrected typo (Elastomer → Elasto). (Line 518)
Point 11: Are the numerical analyses dynamical and transient in time? What is the integration scheme? Or are they static with an ordinative time?
Response 11: The numerical analysis was dynamic and proceeded until the discharge started and the flow stabilized. Integration scheme is dynamic explicit.
Point 12: Silo discharging is a dynamic problem, with possible void creation for granular materials, vibrations and so on. Your approach seems to work for a “regular” discharge, when the continuum approach is acceptable. You should warn the reader accordingly somewhere in the paper.
Response 12: In the conclusion section, I explained the limitations of the interpretation. The contents are as follows. (Line 536 - 542)
- The limitations in this study are as follows. The silo applied to the analysis and experiment of this study has a geometrically symmetrical shape. However, silos with different geometric properties may differ significantly from the results of this study. In addition, in this study, assuming that the frictional force due to the horizontal pressure at the time of material discharge contributes the most to the silo hotspot detector tensile force, only two cases of force, from the prediction equation to the analysis result, are considered. However, in reality, phenomena such as shaking, vibration, and voids in the material occur. It is a situation that requires research considering this.
Point 13: Minor issue. FEM = Finite Element Method. Sometimes in your text you should write FE (without “M”).
Response 13: Corrected the pointed out. (Line 411, 458, 521, 523)
Round 2
Reviewer 2 Report
The paper improved.
There are still minor issues, indicated below.
Lines 35-40: there are repetitions easily avoidable ("installed"... "installing", "silo" repeated 6 times).
"Number of meshes": you mean number of elements. A mesh is the the full set of nodes and elements.
Put in the caption the units used for the stress maps in figures 11,12,13.
Author Response
Response to Reviewer 2 Comments
Point 1: Lines 35-40: there are repetitions easily avoidable ("installed"... "installing", "silo" repeated 6 times).
Response 1: The sentences containing repeated words were modified as follows. (Line 35 – 40)
- Silo hotspot detector, which can measure the temperature of each level, developed for this purpose, is installed inside the silo and monitors the internal temperature in real time to prevent fires caused by spontaneous ignition.
Point 2: "Number of meshes": you mean number of elements. A mesh is the the full set of nodes and elements.
Response 2: "mesh" was modified to "element". (Line 414, 502)
Point 3: Put in the caption the units used for the stress maps in figures 11,12,13.
Response 3: The stress unit was written in the picture caption. (Line 428, 452, 507)
Author Response File: 
Author Response.docx
