## 3. Results and Discussion
### Discussion  
The resulting strain contours from all three loading cases studied agree well with expectations. The strain-measuring advantages of the sinusoidal pattern compared to a linear placement pattern can be illustrated by the fact that sinusoidal FOSs can sense different strain components along their paths and obtain distinct strain contours from various loading conditions. Moreover, dual-sinusoidal placement, compared to a single-sinusoidal placement, can effectively further increase monitoring coverage by providing complementary strain-measuring areas. When structures are primarily under in-plane strains, the strains measured along dual-sinusoidal FOSs can be readily related to the corresponding strain components of host materials, while if out-of-plane shear strains become dominant or comparable to in-plane strains, it becomes difficult to do so because the structures are in more complex strain states. In order to more accurately interpret the strains measured by FOSs and reflect the mechanical responses of host materials, further correlations need to be established between numerical and experimental results. They must also include, among others, micromechanical analyses at the interfaces between FOSs and composite constituents [32], as well as the multi-physics (mechanical, thermal, and electrical) implications on real smart structures [33]. These additional aspects to this work can give readers a more comprehensive understanding of how complex the problem is to be solved at the scale of real structures. Last but not least, the current article is focusing solely on the use of optical fibers as strain sensors to monitor strain well below the onset of strain. Other articles that have provided research are using various techniques to monitor damage (for example, [34; 35; 36; 37; 38; 39]) whereas others are using sinusoidal placements of FOSs  
Since dual-sinusoidal placement has the potential for full coverage of a composite structure, it is worth studying its application in increasingly larger specimens. As discussed in Section 3.1, the three in-plane placement parameters have influences on the mechanical behavior and functionality of smart structures; therefore, the key parameters need to be further optimized quantitatively as functions of the length and width of the host composite structures by conducting parametric studies to strike a balance between mechanical influences and sensing functions. For example, if long blades are considered under uniaxial tensile loads only, larger period sizes (V4) of FOSs are desirable because the main target in this case is to more accurately measure longitudinal strains, while alleviating strain concentrations due to embedded sinusoidal FOSs. Under torsion, while smaller period sizes (V4) and larger amplitudes (V3) are required for monitoring shear strains, sufficient edge gaps (V1) need to be guaranteed to avoid initiating premature delamination/debonding. Figure 13: Bending strain measurement carried out with dual-sinusoidal FOSs alignment on a glass-fiber composite specimen [3]. On the other hand, the out-of-plane placement of FOSs also needs attention. For example, an overlap of two sinusoidal FOSs in the thickness direction, which results in stress concentrations, is a main drawback and must be assessed. The concept described in the current article as applied science is new, and let us say, it is at very low TRL (around 1 to 2). The objective upstream is to conduct exploratory deep research that can lead us to TRL 3 to 4, that can be convincing about the potential of offshore engineering to use it, and raise the research issues (analytical and numerical) that have to be solved and the guidelines for future integrated research project that can lead us from the proof of concept (this current article) to the pilot wind-blade that is reliable enough for industrial use in the offshore industry. The pathway toward this goal is very complex and tedious, as the challenges are numerous. So many points need to be worked out, but not at this stage, unfortunately.