Update figure names with underscore in FINVOL benchmark example.

several hours after initial system operation, the calculated power yield by the different models aligns.

![Fig. 2](images/FINVOL_TU_F_T_SR_ANALYTICAL_TU_A_T_SRtimeplot_Q_b.png)

![Fig. 2](images/FINVOL_TU_F_T_SR_ANALYTICAL_TU_A_T_SR_timeplot_Q_b.png)

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Fig. 2: Timeseries plot of generated power ($Q$) for the Geoloop benchmark with the numerical model.

temperatures in the initial hours of system operation, compared to the analytical model. However, again, the models quickly

align.

![Fig. 3](images/FINVOL_TU_F_T_SR_ANALYTICAL_TU_A_T_SRtimeplot_T_bave_T_fo.png)

![Fig. 3](images/FINVOL_TU_F_T_SR_ANALYTICAL_TU_A_T_SR_timeplot_T_bave_T_fo.png)

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Fig. 3: Timeseries plot of outlet ($T_{out}$) and average borehole wall temperature ($T_{b,ave}$) for the Geoloop benchmark with