LM.UiTMPP.FKM(O).09/FYP06 FAKULTI KEJURUTERAAN MEKANIKAL UNIVERSITI TEKNOLOGI MARA mee (Record all FINAL YEAR PROJECT PROGRESS REPORT PROJECT TITLE OPTIMIZATION OF SOLAR PANEL FACING ANGLE AND DIRECTION ON THE PERFORMANCE OF SOLAR PANEL USING RSM MUHAMAD AMIRUL HAFIZ BIN JAILAN NO: 970202015751 STUDENT ID: 2018468796 SEMESTER 08 SESSION 2021 LM.UiTMPP.FKM(O).09/FYP06 FINAL YEAR PROJECT BACHELOR ENGINEERING (HONS) MECHANICAL STUDENT INFORMATION Semester/Session: 8/2021 Student Name: MUHAMAD AMIRUL HAFIZ BIN JAILAN UiTM ID: 2018468796 IC No: 970202015751 Email: amirullhafiz5@gmail.com No Tel/HP: 0177657463 Address: PP93, KG PARIT PULAI, SEROM SUNGAI MATI, 84410, MUAR JOHOR Project Title: OPTIMIZATION OF SOLAR PANEL FACING ANGLE AND DIRECTION ON THE PERFORMANCE OF SOLAR PANEL USING RSM Supervisor(s): Halim Bin Ghafar 019 - 221 6417 LM.UiTMPP.FKM(O).09/FYP06 MEETING DATE BETWEEN STUDENT AND SUPERVISOR Freq. Week 1 1 1 2 1 3 1 4 1 5 1 6 Meeting Date Summary of Discussion Supervisor Signature Present the planning and work progress to the supervisor 12/03/2021 through virtual meeting. Conduct the experiment of PV (Semester break) panel based on DOE for the first trials in Sagil, Johor on 12 March 2021. Presents the experimental progress to the supervisor 15/03/2021 through virtual meetings. Continue conduct the (Semester break) experiment of PV panel for another 3 trials on 15,18 and 19 March 2021. 23/03/2021 Presents the experimental progress with the supervisor (Semester break) through virtual meeting. Continue conducts the experiment for another 3 trials on 23, 24 and 25 March 2021. Present all the data collected to the supervisor through 30/03/2021 virtual meeting. Calculate the value of maximum power by using the equations of fill factor. 05/04/2021 12/04/2021 1 7 19/04/2021 1 8 26/04/2021 1 9 03/05/2021 1 10 18/05/2021 1 11 24/05/2021 1 12 08/06/2021 Discussion session with the supervisor on the procedure/step that need to be carried out on the confirmation runs proposed by the numerical optimization Presents and discuss all the data collected from the experiments to the supervisor. Initially, discuss the step to do the ANOVA analysis and results that need to come out in the Chapter 4 Learn to observe and analyze the response in ANOVA by observing the statistical parameters with the supervisor. Encouragement by overview the writing style from the other papers/journal/article. Discussion on the response model terms. No backward elimination required since the predicted R squared and adjusted R-squared were approximately high and the response models were significant. The supervisor encourages to make some corrections on research background. There were several lacks supporting points especially the research gap. Discuss on the arrangement of subsection analysis results in Chapter 4. Encourage to read other results from journal/paper that related for the significant for lack of fit. The findings must be explained why, how, what The supervisor checks all the explanation methodology in Chapter 3 and give some feedback. There was some correction especially on flowchart of RSM. Submit the 1st draft thesis to supervisor for checking purpose. Comment from supervisor on the 1st draft thesis. A lot of improvement should be made by making the major correction especially in Chapter 4. HALIM BIN GHAFAR Pensyarah Fakulti Kejuruteraan Mekanikal Universiti Teknologi MARA Cawangan Pulau Pinang halim4346@uitm.edu.my 04-3823156 LM.UiTMPP.FKM(O).09/FYP06 LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:12/03/2021 WEEK 1 (Semester Break) Personal Action Taken 1) Find the suitable location to conduct the experiment. 2) Oil palm estate that has been felled near at Gunung Ledang, Sagil Johor has been selected to conduct the experiment of PV panel. 3) Conduct experiment and collect the experiment data of short circuit current, open circuit voltage and the irradiance level based on design matrix experimental plan. Table 1: DOE design matrix Accomplishment 1) Able to take 1 trial only 2) Fill in the data collected into Design Experiment matrix in Design Expert software. Problems encountered 1) Found that one 1 trials insufficient thus some average collected data was needed to minimize the systematic error. 2) Plan to do other experiments trials for the following weeks. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:15/03/2021 WEEK 2 (Semester Break) Discussion topic in Virtual Meeting (Google Meet) 1) Present the work progress to the supervisor. 2) Discussion session about the experiment’s outcome (data collected) from the previous week. Personal Action Taken 1) Continue conduct the practical experiment at Gunung Ledang, Sagil Johor for another trials. 2) Collect the experiment data of short circuit current, open circuit voltage and the irradiance level by based on design matrix experimental plan. Figure 1: Set up PV panel Accomplishment 1) Able to take another 3 trials on 2) Fill the average data collected into Design Experiment matrix in Design Expert software. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:23/03/2021 WEEK 3 (Semester Break) Discussion topic in Virtual Meeting (Google Meet) 1) Present the work progress and further planning to the supervisor. Personal Action Taken 1) Continue conduct the practical experiment at Gunung Ledang, Sagil Johor for another trials. 2) Collect the experiment data of short circuit current, open circuit voltage and the irradiance level based on design experimental plan. Accomplishment 1) Able to take another 3 trials 2) Fill the average data collected into Design Experiment matrix in Design Expert software. 3) Set the criteria in optimization process for confirmation runs. Table 2: Complete DOE Results Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:30/03/2021 WEEK 4 Discussion topic in Virtual Meeting (Google Meet) 1) Discuss on the data collected from the experiment that has been conducted. 2) Seek for opinion and suggestion from the supervisor for the next step taken. What is the governing equation to calculate the maximum power? Personal Action Taken 1) Identify the optimum tilt angle and direction in optimization process which need 2) Calculate the fill factor by observed the specification of solar panel 3) Calculate the maximum power by using Pmax equation and the fill factor value. I use Microsoft excel to ease the calculation tasks for other runs. The equation below is the sample for maximum power for Run 1. Accomplishment 1) Generated full accomplishment value of Pmax for all DOE runs. 2) Successfully completed collect all the experiments data of irradiance level, open circuit voltage, short circuit current and the maximum power Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE: 05/04/2021 WEEK 5 Discussion topic in Virtual Meeting (Google Meet) 1) Present the progress work of practical experimental to the supervisor 2) Discuss on the limitation of PV system practical experiment. How to overcome the problems 3) Discuss on the research background with supervisor. How the results of previous study on RSM towards PV system implementation. This should be discussed in research background in Chapter 1 4) Present the procedure/ steps to conduct confirmation analysis/ runs Personal Action 1) Conduct confirmation runs after the optimization process and take the average by following the confirmation location (proposed by Design Expert) in Table below. 2) Generally, analyze the significant model terms for irradiance, open circuit voltage, short circuit current and maximum power. 3) Set up experiment again in Sagil Johor for confirmation runs 4) Collect all the response data Table 3: Confirmation Runs Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE: 12/04/2021 WEEK 6 Discussion topic in Virtual Meeting (Google Meet) 1) Presents progress and planning for FYP2 journey to supervisor. 2) Presents the experiment data collected to the supervisor for evaluation. 3) Every method in thesis must have flowchart and must be explained. 4) Focus on making result analysis for Chapter 4. Personal Action 1) Observed the complete data collected for analysis of variance 2) Identify modify the suitable flowchart for ANOVA. Accomplishment 1) Updated flowchart of DOE and developed flowchart of ANOVA analysis. 2) Do research findings on analysis of variance from previous paper, journals, article Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:19/04/2021 WEEK 7 Discussion topic in Virtual Meeting 1) Presents work in progress and planning for completing the thesis. 2) Learn how to format the paragraph, heading, sub heading and others for thesis format 3) Learn how to observe and analyze the parameters in ANOVA. Personal Action 1) Perform the analysis of variance (Anova) in RSM. 2) Start writing for Chapter 4 discussion 3) Put all the results graph, figure, and desired information into the thesis report from the Design Expert software results. 4) Decide the section for chapter 4 discussion Accomplishment 1) All the result being analyze successfully. 2) No transformation was made for all the response model terms. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE: 26/04/2021 WEEK 8 Discussion topic in Virtual Meeting 1) Presents the work progress and planning 2) Discussion on the response model terms. No backward elimination required since the predicted R squared and adjusted R-squared were approximately high. 3) Discussion on comparison between experiment results with predicted results. How much the error difference happens? Research Findings 1) Lack of fit significant- This occur when the pure error is very low compared to the residual. It shows that there are some issues in the model. 2) Try to use narrow ranges of variable if want insignificant Tasks Accomplishment 1) Update and add on several findings on the literature review based on the new findings from article/journal 2) Compare the results obtained with the other papers/journal. 3) Observed the models’ terms for all responses that were significant and insignificant. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:03/05/2021 WEEK 9 Discussion topic in Virtual Meeting 1) Present thesis progress and future planning in completing the thesis draft 2) Discuss on the importance of model fit summary in ANOVA. Abbreviation Irradiance Current Voltage Power Mean St. Dev R2 Adj.R2 Pre.R2 C.V A. P PRESS 1087.49 32.54 0.9806 0.9968 0.8676 2.99 19.5717 50687.29 2.55 0.0167 0.9983 0.9971 0.9899 0.6539 62.5563 0.0116 21.24 0.0391 0.9711 0.9504 0.8873 0.1841 18.1242 0.0418 40.73 0.2610 0.9986 0.9976 0.9913 0.6408 68.4827 2.9 Tasks Accomplishment 1) Do some corrections on research background. There were several lacks supporting points especially the research gap. 2) Import the graph, figure, and other desired results from Design Expert software into the thesis. 3) Do some corrections on citation and formatting equation for the whole chapter. Tasks to do before next meeting 1) Update the discussion writing on Chapter 4 2) Make sure the feedback or outcome from meeting discussion with supervisor has been taking into point and improve the writing skills Signature . LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:18/05/2021 WEEK 10 Discussion topic in Virtual Meeting 1) Present the work progress with supervisor in virtual meeting (google meet) 2) Discuss the workflow subsection in Chapter 4. The subsection arrangement must be neat and orderly. 3) Discuss the other papers/ journals results that related for the significant for lack of fit. The findings must be explained why, how, what? 4) The literature review citation must be properly insert at the end of the sentences Task accomplishment 1) Successfully decide and arrange the section, subsection in Chapter 4 for all the responses. 2) Elaborate the results discussion for irradiance, open circuit voltage, short circuit current and maximum power responses. 3) Changes the unsuitable words/ sentences with the new ones for proper understanding. Tasks to do before next meeting 1) Update and continue writing the results discussion in Chapter 4 2) Paraphrase the sentences/ words in Chapter 2 to reduce plagiarism. 3) Calculate the difference of percentage error of predicted results from RSM and observed results for all the responses. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:24/05/2021 WEEK 11 Discussion topic in Virtual Meeting 1) Present the work progress with supervisor in virtual meeting (google meet) 2) The supervisor checks all the explanation methodology in Chapter 3 and give some feedback. There was some correction especially on flowchart of RSM 3) Discussion on identify the writing errors in thesis by review the student thesis 4) Learn to cross references figure, table and equation properly by following the guidance provided by the faculty. Task Accomplishment 1) Adding the new flowchart of multimeter procedure in Chapter 3 2) Writing discussion results and analysis for irradiance and short circuit current response in Chapter 4 3) Update the logbook weekly Task to do before next meeting 1) Make sure discussion writing on irradiance response has been fully finished 2) Modified and update the major correction 3) Send the first draft thesis to the supervisor for checking and evaluation purpose. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:8/06/2021 WEEK 12 Discussion topic in Virtual Meeting 1) Present the work progress with supervisor in virtual meeting (google meet) 2) Comment from supervisor on the first draft thesis. A lot of improvement should be made by making the major correction especially in Chapter 4. 3) Discuss on how to elaborate the discussion/ point in chapter 4 4) Overview of objective that must related to the objective 5) Overview on how to close the objectives Task Accomplishment 1) Writing discussion results and analysis for open circuit voltage and maximum power response in Chapter 4 2) Develop conclusions and recommendation for Chapter 5. 3) Able to identify the range of critical factors in response surface by overview the darker region 4) Update the logbook weekly. 5) Submit 1st draft thesis to the supervisor via email. Task to do before next meeting 1) Ensure major/ minor correction has been made based on comments provided from the supervisor. 2) Modified and update for the major correction. 3) Submit the 2nd draft thesis to the supervisor via email for checking and evaluation purpose. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE: 14/ 06/2021 WEEK 13 New Research Findings 1) Found the equation of Central Composite Design (CCD) which comprises the axial point, centre point and star point. It has been identified that 13 runs generated by the software were based on 5 centre point, 4 axial point and 4-star point. Task Accomplishment 1) Update the flowchart general procedure for measurement of open circuit voltage and short circuit current. 2) Update the design shape of flowchart process on analysis of variance. 3) Submit the 2nd draft thesis to the supervisor via email. 4) Develop the abstract of the thesis. 5) Make some correction on equation citation numbering. Task plan for next week 1) Make sure all the major corrections have been made perfectly. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE: 21/06/2021 WEEK 14 Task Accomplishment 1) Continue to write and modify the conclusions and recommendation for Chapter 5. 2) Choose the desired results in software to put into the thesis 3) Develop actual format of thesis based on the guideline given. 4) Modify the abstract structure section. 5) Make some correction on equation citation numbering. Task to do for next week 1) Make sure all the writing/ paragraph/ heading/ subheading follow all the guideline provided by the faculty. 2) Make sure the significance of the study section has been completely made the corrections. 3) Prepare correction for 3rd draft thesis. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:29/06/2021 WEEK 15 Task Accomplishment 1) Writing discussion analysis of thesis on maximum power 2) Choose the desired results in Design Expert software to put into the thesis 3) Submit the 3rd draft thesis to the supervisor for checking purpose. Planning for the next task 1) Elaborate more on discussion for the numerical optimization 2) Change the writing style on optimization process Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:5/07/2021 WEEK 16 Task Accomplishment 1) Change the writing style in numerical optimization 2) Update the minor correction especially the grammar words. 3) Update and make some changes on conclusion and recommendation. 4) Ensure minor correction has been made based on comments provided from the supervisor Findings from optimization results 1) Found that the desirability of 0.977 out from 1 on numerical optimization was quite high which illustrate the prediction of RSM on solar engineering field. Signature LM.UiTMPP.FKM(O).09/FYP06 WEEKLY ACTIVITIES RECORD DATE:13/07/2021 WEEK 17 Task Accomplishment 1) Update and make some changes on the conclusion and recommendation in Chapter 5 2) Double check the writing thesis style for all chapter 3) Update the minor/ major correction in thesis 4) Update the logbook weekly. To do next week 1) Submission of Thesis Final Draft and Logbook (softcopy) to the panels and supervisor 2) Prepare the desired form that need to be submitted to the panel and the supervisor. Signature LM.UiTMPP.FKM(O).09/FYP06 Progress Report Week: 1/2/3/1/2/2 Week No: Week 1 (Sem break)-Week2 PLANNING: STATUS: ACTION PLAN: Describe the activities that you have been planned for this week (Describe the latest status of your project progress) (Describe the steps you should take to achieve your goals) WEEK 1 (Semester Break) Conduct the practical experiments based on experimental design plan (DOE)-13 runs WEEK 2 (Semester Break) Continue conduct the experiments based on DOE at the same place and same time WEEK 3 (Semester Break) Continue conduct the experiments for the final trials based on DOE at the same place and same time. The objectives to take the average data value for 7 days. WEEK 4 Find the maximum power value for all runs (13 runs) by using the fill factor equation. WEEK 5 Conduct the confirmation runs by using the same place and at the same time. This action aim to find the difference effectiveness of predicted optimization by RSM Prepared by: Signature of Student: Muhamad Amirul Hafiz Bin Jailan Completed Completed Completed Choose the suitable locations. Oil palm plantation that has been felled has been selected to conduct the experiment. Collect all the experiments data consist of solar irradiance level, open circuit voltage and short circuit current. Collect all the experiments data consist of solar irradiance level, open circuit voltage and short circuit current. Prepare excel template to record all the data collected. Completed Calculate the fill factor value by observed the specification of PV panel. It has found that the fill factor of PV panel is 0.752. Thus, 0.752 will be used with observed collected data to obtain the maximum power value. Completed Conduct experiment again at the same place by following the optimum tilt angle and direction that been predicted by the RSM on Design Expert software. Tilt angle=17.52 degrees Direction= 179 degree (south) Date Received: Signature of Supervisor: HALIM BIN GHAFAR Pensyarah Kejuruteraan Mekanikal Halim Fakulti Bin Ghafar Universiti Teknologi MARA Cawangan Pulau Pinang halim4346@uitm.edu.my 04-3823156 LM.UiTMPP.FKM(O).09/FYP06 Progress Report No. : 6 / 7 / 8 / 9 / 10 / 10 Week No: Week 6-Week PLANNING: STATUS: ACTION PLAN: Describe the activities that you have been planned for this week (Describe the latest status of your project progress) (Describe the steps you should take to achieve your goals) WEEK 6 Make some corrections on flowchart of DOE, RSM, ANOVA and general procedure for multimeter in Chapter 3. Doing some research findings form other paper that related to ANOVA. WEEK 7 Perform analysis of variance (ANOVA) by observed the statistical parameters value. Import all the figure from Design Expert software into the thesis. WEEK 8 Analyze and compare the predicted results with observed results. Find out the difference percentage of these two results obtained. WEEK 9 Do some corrections on research background after taking the opinion and commenting from the FYP supervisor. Make elaboration on the model fit summary. WEEK 10 Elaborate the results discussion for irradiance, open circuit voltage, short circuit current and maximum power responses in Chapter 4 Prepared by: Signature of Student: Muhamad Amirul Hafiz Bin Jailan Completed Completed Completed Completed Completed Find the specific journal/article/paper from google scholar. Successfully key in the average data collected into the design matrix of DOE. Select the ANOVA section in the software Generate the table of predicted results by RSM versus observed result by DOE. Calculate the percentage difference errors. Find the others references main journal/ article that related to the previous findings on RSM implementation for solar engineering field. Decide and arrange the section, subsection in Chapter 4 for all the responses. Refer to other journal/ paper/ articles for writing style references. Identify which graph should be imported into the thesis. Date Received: Signature of Supervisor: HALIM BIN GHAFAR Pensyarah Fakulti Kejuruteraan Mekanikal Halim Bin Ghafar Universiti Teknologi MARA Cawangan Pulau Pinang halim4346@uitm.edu.my 04-3823156 LM.UiTMPP.FKM(O).09/FYP06 Progress Report No. : 11/ 12 / 13 / 14 / 15 / 115 PLANNING: STATUS: Describe the activities that you have been planned for this week WEEK 11 Writing the discussion results and analysis for irradiance and short circuit current response in Chapter 4. Submit the first draft thesis to the supervisor by email. WEEK 12 Writing the discussion results and analysis for maximum power and open circuit voltage response in Chapter 4. Create the conclusion and recommendations WEEK 13 Make some correction based on supervisor’s feedback from first draft thesis. Then, submit again the second draft thesis to the supervisor by email. WEEK 14 Make some corrections based on supervisor’s feedback from second draft thesis. WEEK 15 Update the paragraph format, table citation by follow the guideline provided from the faculty. Submit 3rd draft thesis to the supervisor via email. Prepared by: Signature of Student: Week No: Week 11- Week ACTION PLAN: (Describe the latest status of your project progress) Completed Completed (Describe the steps you should take to achieve your goals) Evaluate and observed the statistical parameters in ANOVA. Refer to other journal/ paper/ articles for writing style references. Understood the trend of the graph, response surface and contour plot. Evaluate and observed the statistical parameters in ANOVA. Refer to other journal/ paper/ articles for writing style references. Understood the trend of the graph, response surface and contour plot. Observed the outcome and make conclusion Update and make corrections based on comment/ feedback from the supervisors. Completed Completed Completed Identify the unclearly discussion statement. Change the unsuitable words to proper words for more understanding and remove unnecessary words/ sentences. Referring to the guideline format of thesis provided by the faculty. Learn from website on how to create the proper format for thesis. Date Received: Signature of Supervisor: HALIM BIN GHAFAR Muhamad Amirul Hafiz Bin Jailan Pensyarah Halim Bin Ghafar Fakulti Kejuruteraan Mekanikal Universiti Teknologi MARA Cawangan Pulau Pinang halim4346@uitm.edu.my 04-3823156 LM.UiTMPP.FKM(O).09/FYP06 Progress Report Week: 16/ 17 Week No: Week 16-Week 17 PLANNING: STATUS: ACTION PLAN: Describe the activities that you have been planned for this week (Describe the latest status of your project progress) (Describe the steps you should take to achieve your goals) WEEK 16 Ensure minor correction has been made based on comments/ feedback from the supervisor WEEK 17 Double check the writing thesis style for all chapter. Modify the minor corrections on the conclusion and recommendation in Chapter 5. Final preparation before submitting the Final Draft on 23/7/2021. Prepared by: Signature of Student: Completed Update minor corrections after getting back the feedback of 3rd draft thesis from the supervisor. Completed Double check all the citations, section arrangement for all chapters, grammar and paraphrase the sentences. Date Received: Signature of Supervisor: HALIM BIN GHAFAR Muhamad Amirul Hafiz Bin Jailan Halim Bin Ghafar Pensyarah Fakulti Kejuruteraan Mekanikal Universiti Teknologi MARA Cawangan Pulau Pinang halim4346@uitm.edu.my 04-3823156 LM.UiTMPP.FKM(O).09/FYP06 Appendix 1.0 THE POSSIBLE RECORD IN LOGBOOK ❖ Sketches/doodling ❖ Customer ❖ ❖ ❖ ❖ ❖ ❖ ❖ ❖ ❖ needs/requirements Class notes Project objectives Meeting notes Action Items Half-baked Ideas Math calculations Work-in-progress Design alternatives Vendor notes ❖ ❖ ❖ ❖ ❖ ❖ ❖ ❖ ❖ Research findings Sources of ideas Evaluation of data/results Design reviews Decision criteria Design process Rationale for decisions Project reflections Professional development The possible question you can ask and answer after several project activities such as Meeting • What were the main outcomes of the meeting? • Was the meeting productive, and why? • What are your personal action items before the next meeting? • Is the team heading in the right direction? Brainstorming • Which ideas seem more feasible, and why? • Are there enough good ideas? • How could better ideas be developed based on this session? Engineering Analysis • What were the governing equations? • What were the most important findings? • What do the results mean and how should they be applied? Visualization • What are the major features/discoveries and why are these significant? • What was learned about the problem or solution possibilities? • What problems were resolved and what still needs to be addressed? • How does this piece integrate with the whole? Searching • What key information did I find? How does it help achieve the project objectives? • Are there other sources that should be pursued? • What new questions were generated? Refer to www.engr.mun.ca/~sbruneau/teaching/.../logbookinstructions.pdf