## 2 Methodology  
### Experimental Methodology  
The experimental work in the SLOWD project followed an incremental development in experimental complexity and cost: single degree of freedom sloshing tests [5], sloshing beam tests [12], scaled wing model and planned full-scale wing sloshing tests. The current experimental campaign is concerned with the experimental demonstrator called \"MiniWoT\" (miniature wing of tomorrow), shown in Figure 1. The model is a 1:5 geometric scale wing structure with some particular features that allow for fuel sloshing investigations. The main structural part is composed of two spars and five torque tubes with spanwise varying cross-sectional properties to match the static and dynamic response of a full-scale research prototype wing specimen, as described in [13]. The structure is approximately 3 m long and is cantilevered at the root to a strong wall using a wedge-bracket configuration that enables the modification of the specimen dihedral angle (shown here in 0\({}^{\circ}\) dihedral configuration). On top of the main structural part, there is a transparent fuel tank with scaled geometry. The tank bears only part of the loads, and it is partially decoupled from the main structural part using two rigid connection points and five flexure-type connections that allow for limited spanwise relative motion between the tank and the underlying structure. This configuration was chosen with multiple aims in mind, among the most important: (1) achieve set natural frequencies and mode shapes, (2) allow for the liquid flow observation inside the tank from the lateral and top directions and (3) the tank should have set scaled dimensions and spanwise position, representative of the full-scale specimen. It can easily be seen how such requirements impose certain design constraints that move the fuel tank vertically up from its natural position inside the wing as well as raise considerable challenges concerning the connection points between the tank and the underlying structure. The fuel tank has a geometry representative of the full-scale prototype with 8 interior cells (numbered in this work from 1 to 8 starting from the inboard position) separated by the baffles. The seven baffles are removable, and multiple baffle geometries can be studied. The individual cells can also be sealed using the solid-section baffles without perforations--this case is considered in this work. The structure is instrumented using 14 accelerometers, one vertical displacement measurement at the tip trailing edge, strain gauges at the root and two high frame rate video cameras for the observation of the sloshing liquid from the side and top of the tank. Three of the accelerometers were placed on the tank in three different spanwise positions, as shown in Figure 1 and labelled \"tank tip\", \"mid\" and \"root\". Two removable eye bolts (labelled as (4) in Figure 1) and a pulley-chain hoist mechanism were used for loading the structure vertically downward, after which it was released into free decaying motion using a pin-release mechanism. The experimental test plan included but was not limited to the following:  
* Ground vibration tests with and without tank attached, part of which was presented in [13],
* Step release tests without liquid (dry tests), with and without additional mass to account for the \"frozen\" liquid,
* Step release tests with tap water as the working liquid, with and without added dye
* Studies with and without the baffles, with the baffles of different solidity ratios,
* Studies with varying filling levels. This work presents an initial assessment and interpretation of the experimental results concerning step release tests at a 0\({}^{\circ}\) dihedral angle, with 50% water filling level in each individual sealed cell using solid-section baffles, and the equivalent dry case with added mass to account for the liquid.