## 3 Results and Discussion
Figure 6: Safety Factor (SF) maps in different modes: (**a**) “3-10g-R”; (**b**) “3-12g-F”. Objective 3: to consolidate the findings into a practical methodology that ensures R100 compliance during diesel-to-electric bus conversion, without altering certified structures. The problem of converting Europe's huge diesel bus fleet (around 215,000 vehicles in 2023) to electric traction turns out to be quite difficult: changes to the body frame are inadmissible, otherwise the bus will have to be rectified following UNECE R17, 29, 52, 66, 80, 107, etc. In each case, it is necessary to check the indicators of \(\sigma_{max}\), \(\sigma_{ave}\), and especially \(\delta\) of the battery units on the one hand and transmission reactions from bolted connections to the body on the other. Accounting for approximately 40-50% of the cost of the bus, the body is its most expensive part, which is why an individual approach is often used in manufacturing the body in each individual order; there are many modifications with varying complexity. Each such modification must be certified for compliance with R100, because, for example, the body is not a single-cell, and the body is a single-cell, and the body is a single-cell. Figure 7: Total deformation in different modes: (**a**) “1-10g-L”; (**b**) “1-12g-F”. the allowable \(\delta\) values may differ from other modifications, etc. The global scope of the problem of adaptation and certification considered in the work is dramatic. Speaking about the novelty of this study, a comparison should be made with the reviewed academic literature. Thus, the problem of local R100-oriented battery-mount analysis for retro-fits is not sufficiently covered: Most prior works (e.g., [PERSON] et al. [2], [PERSON] et al. [3], [PERSON] et al. [12]) examine the entire bus frame or full-vehicle crash-worthiness under NCAP or R29 conditions. In contrast, the current study isolates battery mounting frames and simulates them locally under UNECE R100 accelerations, while maintaining the constraint of no structural modification to the certified diesel bus body. Another problem is a mathematical attenuation model of acceleration propagation. Unlike studies that apply constant 10 g/12 g loads (e.g., [3; 26]), the current study proposes an exponential decay model of acceleration based on battery location and damping coefficient \(k=0.05\) m\({}^{-1}\), further used to calculate the coefficients in the final Equations (6) and (7). This more realistically represents how actual acceleration differs between front and rear battery units (12.91 g vs. 9.56 g) due to structural damping and wave dissipation. Another problem is UNECE R100 certification for bolt-on electric conversion: Prior studies (e.g., [4; 5]) do not address the specific challenge of retrofitting existing diesel buses with electric powertrains while complying with UNECE R100. The current study is focused on battery mounting designs that meet R100 g-load requirements without triggering re-certification under R66, R80, etc. This is a key step for practical large-scale implementation. In conclusion, it can be noted that, unfortunately, among the analysed modern literary sources that touch on the topic of bus certification UNECE tests, there are no studies on the transformation of buses from diesel to electric traction. This area of engineering and scientific work is only beginning to gain popularity as Europe approaches 2030, when the problem will become relevant. The primary contribution of the study lies in the development of a practical methodology for assessing battery unit integrity and structural behaviour during the conversion of diesel buses to electric propulsion, fully compliant with UNECE R100 regulations. By combining transient structural simulation, mathematical centre modelling of acceleration propagation, and centre of gravity (CoG) prediction, the proposed approach enables engineers to evaluate electric conversions' safety and certification feasibility without modifying the existing bus body.