Modelling and Numerical Analysis of De-Icing Sprinkler-Flusher Airport Machine Arms

. Modern and innovative de-icing sprinkler-flusher airport machines are now equipped with special arm system. The vehicle arms are manufactured for removal of ice or frost from the surfaces of the airports runways and areas by pouring designated for that chemicals substances. The paper presents a study of the performance of airport de-icing vehicle's arms, establishes numerical simulation model of the arm system by three-dimensional software and finite element analysis software. Based on the numerical modelling and analysis, the work focuses on study of the strength and stiffness of airport de-icing vehicle's arm and researched the distribution of stress and deformation under the most dangerous condition. The results show that designed double-arm system can be optimized and manufactured from different, light materials and shows dangerous displacement concentration areas of the arm structure. It has important guiding significance to the optimization and manufacturing production of the arm structure.


Introduction
De-icing airport machines are used to remove of ice from airport surfaces. They often works in heavy weather condition performing snow and ice clearance task. These machines are used for spraying airport runaways, where the clearance speed should be high. Commonly used machines, in other market-proposed machines, still have many disadvantages and thus need to be developed and modified [9,10]. The object that need to be improved and developed is spraying apparatus constructed from flexible booms, called also arms, equipped with spray nozzles. The airport de-icing vehicle [10] shows Figure 1. Typical airport vehicles havefront or rear-mounted spray bar and two spraying arms with integrated nozzles situated in one or two rows with maximum working width about25-40 m. The spraying arms cover 20-30 m and the ejection nozzles 3-5 m each, depends on manufacturer. The nozzles, which are arranged side by side, ensure an overlapping spraying result. The spraying process is speed-dependent, it means that the rows of spraying nozzles switch on and off automatically [9,10]. The de-icing process, in the context of effectiveness and accuracy, depends on shape and dimensions of arms. They are the most vulnerable element to mechanical damage and overload. The three most important operating states of the arms are distinguished due to their susceptibility to damage or deformation, related to their mechanical strength of their structure: braking and accelerating, riding on the arc and the impact of their weight. The study design of the spraying arms enables high workingspeeds up to 40 km/h. The scope of this paper is a compilation of results of tests conducted by means of the Finite Element Analysis (FEA) software SolidWorks [7,8]. The comparison is related to the choice of arms model for the analysis of mechanical stress and deformation at steadystate,during braking/accelerating or arc riding.

Methodology
Nowadays, there is many software packages to analyse and simulate real engineering problems thatare well known under the term, Computer Aided Engineering (CAE). The stress and strains distribution, deformations and displacements of the mechanical system can be obtained using SolidWorks Simulation software module. The moduleis a good tool for solving mentioned problems through the application of Finite Elements Method (FEM) [1][2][3].It is well known that FEM consists of a numerical technique to find solutions, where distributed model of the system is describedbyPartial Differential Equations (PDE).In other, FEM is a method for dividing up a very complicated problem into small elements that can be solved in relation to each other. The main features of FEA method are the entire solution domain is divided into small finite segments and over each element the behaviour is described by the displacement of the elements and the material law. All elements are assembled together and the requirement of continuity and equilibrium are satisfied between neighbouring elements while provided that the boundary conditions of the actual problem a satisfied a unique solution can be obtained to the overall system of algebra equation with large and sparse matrices [4][5][6].
In recent years the finite element method has been applied to mechanics problems otherthan those of structural analysis, i.e., fluid flow and thermal analysis. It has been extended topermit the solution of nonlinear as well as linear problems, those of large deformation geometricnonlinearity and/or material property nonlinearity, for example. It is hard to think of any field inwhich finite elements are not extensively used to provide answers to problems which would havebeen unsolvable only a few years ago [5,6]. Briefly describing, the equations in discrete form of the FEM approach are generated from the Galerkin form [1,2,4,5] where b is the vector of external body forces, D is a symmetric positive-definite matrixof materialconstants,t is the prescribed traction vector on the natural boundary Γ , u is trialfunctions, is test functions and ∇ is the symmetric gradient of the displacement field. The approach uses the following trial and test functions where n is the number of the nodal variables of the element, is the nodal displacement vectorand ( ) is the shape function matrix. By substituting the approximations, ℎ ( ) and ℎ ( ), into the weak form and invoking the arbitrarinessof virtual nodal displacements, equation (1) yields the standard discretized algebraic equationsystem where K is the stiffness matrix; f is the element force vector that are assembled with entries of with the strain gradient matrix where integrations (4) and (5) are performed for assumed finite elements with defined interpolation functions, which define the variation of the displacement matrix within the elementand on its surface. Since the displacement vectoru must be continuous over the entire region, itfollows that the displacements at the common nodes of the internal element boundary of two adjoining elements must be the same and that the functional representations of the displacementsover the common boundary must be identical [1][2][3].

Numerical analysis of the machine arms
The arms of the deicer machine are exposed to three main types of forces: gravity forces, centrifugal forces when driving the vehicle on the arc, acceleration and braking forces. In the case of the presented machine, only forces related with braking are important, because the mechanical design of arms unfolding system contains special elements that eliminate forces when vehicle accelerates.
With this assumption the analysis is based on models developed in SolidWorks software package for the stress and deformation computations with the mesh based on tetrahedral elements [1,2].As shown in Fig. 1, each deicer arm consists of two subarms: first fat made from steel S355and second thin made from aluminum AW-5754 [10]. Figure 2 shows meshes of mentioned arm components. a) b)

Fig. 2. Meshes of the arm components a) steel element and b) aluminum element.
For the analysis purpose, three variants of loads are examined computing arms deformation and stress. Firstly, static simulations are performed for gravity forces that acts on arm elements. Next, simulations consisted of finding deformations and stress for both workinggravity and centrifugal forces, Finally, simulations are done for gravity and deceleration forces. From practice, assumed that arm elements works with gravity acceleration g=9,81 m/s 2 , centrifugal 0,5g and deceleration 0,8g as shown in figures 3-5.   Considering static displacement computation for gravity load (presented at fig. 3), figure 6 shows that maximum value of displacement 0,3 mm obtained for aluminum subarm. In case of steel bigger subarm, the value of maximum displacement is significantly lower and results only about 0,1mm. It means that the steel subarm should be optimized with their construction. Next, a static analysis also for both subarms with gravity and centrifugal load is done and presented in figure 7. The mixed load is generated when the deicing machine rides on arc. a) b)

Fig. 7.
Arm elements with gravity and centrifugal loads.
In this case (figure 7), a static displacement computation for gravity and centrifugal, mixed load (presented at fig. 4), shows that maximum value of displacement is the same as in previous case about 0,3 mm obtained for aluminum subarm. In case of steel bigger subarm, the value of maximum displacement is significantly lower and results only about 0,1 mm. It means that the steel subarm should be optimized also when gravity and centrifugal forces are applied on arms mechanicals system during arc riding. Finally, a static analysis is performed for both subarms when gravity and deceleration loads are working. The loads are generated during vehicle braking mode. As shown in figure 7, a static displacement computation for gravity and deceleration load (presented at fig. 5) introduces stronger deformation and displacements than in case of gravity and centrifugal loads. Computation shows that maximum value of displacement results in 0,87 mm for aluminum subarm and 0,29 mm for steel subarm. It means that the steel subarmis more durable and robust on braking forces. But obtained values for aluminum element rises concerns related to dynamic behavior when dynamic or harmonic forces will exist during normal work of the deicing machine.

Conclusions
In this papera static analysis results of spraying arms mechanical system of de-icing airport machine are presented. Compilation of results conducted by means of the Finite Element Analysis (FEA) software SolidWorks, related to the choice of arms model for the analysis of mechanical deformation or material displacement at steady-state, during braking/accelerating or arc riding is examined and discussed.
Presented results shows not only displacements in the arm system and possible deformation but also critical area where the arm geometry can be improved. It is also important information how and where to strengthen the geometry and optimize the structure. This paper and considered results can be helpful in design and manufacturing of de-icing sprinkler-flusher airport machine arms.