## 3 Results and Discussion  
The static analysis of the mechanical dredger of the Kronstadt port shows the distribution of von Mises stresses, displacements, deformations and the safety coefficient throughout the assembly, but before the static analysis a modal frequency analysis was internally performed in order to detect rigid body modes. If this modal frequency analysis would have obtained the first six frequencies equal or close to 0 Hz, then the model would be a mechanism with which it would not make sense to  
Figure 18: Bucket of the dredger with a very high mesh density. have carried out a static analysis. The frequency obtained were: F1 2.33 Hz, F2 2.34 Hz, F3 2.35 Hz, F4 2.77 Hz, F5 3.10 Hz, and F6 3.10 Hz. Thus, the von Mises stress distribution (Figure 19) shows that in general the mechanism is subject to low stresses. Autodesk Inventor Professional assigns a scale of colors based on the value of the stress reached, establishing the point with the highest value of the von Mises stress with the color red, and with colors close to blue for the surfaces with the least stress. As can be seen, almost the whole machine works with very low stresses, except the point of maximum stress (89.96 MPa), which corresponds to one of the links of the bucket rosary. This piece is a piece of cast iron, and its breaking point (758 MPa) is well above that value (Figure 20). Therefore, it can be said that in general the joins between links are the areas of the machine under the most stress, but as will be explained later always bear this with little fatigue. If we examine other areas of the bucket rosary we can see that the link between the rockers is the other point that presents a higher stress, specifically the place where the metal piece that joins both rocker arms with the rocker arm is attached to the dredge. At a certain point the stress is 54.57 MPa, also below the breaking point, although in this case the surrounding materials have a lower threshold and must be analyzed more closely (Figure 21). These joins are those that will present a lower safety coefficient, as will be explained later. The rest of the elements of the assembly work with very low stresses; therefore, they are not under too mush stress and do not suffer from fatigue. However, one might ask: is it normal for such a  
Figure 21: Von Mises stress on the dredger rocker shaft. Figure 20: Maximum von Mises stress reached in a link of the bucket ro  
Figure 21: Von Mises stress on the dredger rocker shaft. complex transmission to present such low stresses? The answer to this question has to do with the use by the engineer of friction drums instead of gears of straight teeth. A machine like the mechanical dredger runs the risk of being on the seabed with an element that is not capable of moving it. Thus, the chain would suffer a blockage that would affect the transmission. However, as there are no teeth between the axles but rather friction drums, what happens is that these drums roll over one another. Thus, they may heat up or slip, but they will not break. This ingenious procedure avoids a breakage that could become dangerous at sea, since the driving element of the dredger is the bucket rosary itself. Another parameter that helps to distinguish the structural problems that the dredge can present is the analysis of the safety coefficient. The safety coefficient shows, theoretically, the possible points that may be working above their elastic limit. This parameter is calculated as the quotient between the elasticity limit of the material at a given point and the von Mises stress for that same point, establishing a range of values between 0 and 15. A coefficient equal to or less than 1 indicates that that point is worked over the limit of elasticity, and on the contrary an element is considered well dimensioned when the materials work in a range between 2 and 4. With a value above 6, it is usually considered that an element is oversized, and its dimensions are excessive.