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BR-102021014340-B1 - METHOD FOR OPTIMIZING ANTI-SLOSHING PERFORATED BULKHEADS AND ANTI-SLOSHING PERFORATED BULKHEADS WITH OPTIMIZED SUBMERGED OPENING RATIO

BR102021014340B1BR 102021014340 B1BR102021014340 B1BR 102021014340B1BR-102021014340-B1

Abstract

METHOD FOR OPTIMIZING ANTI-SLOSHING PERFORATED BULKHEADS AND ANTI-SLOSHING PERFORATED BULKHEAD WITH OPTIMIZED SUBMERGED OPENING RATIO. With the aim of mitigating the sloshing phenomenon in tanks of any geometry, including rectangular, prismatic, or horizontal cylindrical tanks, efficiently across wide ranges of fill levels and excitation frequencies, by means of a simple, inexpensive, and easy-to-construct and maintain device, the present invention comprises a method for optimizing the opening ratio in perforated bulkheads and a perforated bulkhead whose submerged opening ratio varies along the height of the bulkhead, with its value being optimized as a function of the fill level. The submerged opening ratio at a given fill level is the ratio between the perforated area of the bulkhead and the total area of the bulkhead that is submerged. The optimized submerged opening ratio at a given fill level is that which results in the lowest value of the maximum sloshing magnitude considering the entire frequency domain between the first and third sloshing resonance modes. Such a bulkhead must be fixed to the inside of the tank so as to divide it into two compartments. Furthermore,(...).

Inventors

  • CEZAR AUGUSTO BELLEZI
  • CHENG LIANG YEE

Assignees

  • UNIVERSIDADE DE SÃO PAULO - USP

Dates

Publication Date
20260317
Application Date
20210721

Claims (12)

  1. 1. Method for optimizing anti-sloshing bulkheads characterized by comprising the following steps: Step 1 - determining the geometry of the tank and excitation movements; Step 2 - determining the number of bulkheads; Step 3 - determining the dynamic sloshing response in tanks with hollow bulkheads with a uniform distribution of the opening ratio for the frequency domain between the first and third resonance modes of the sloshing; Step 4 - determining the optimized submerged opening ratio for each filling level; Step 5 - obtaining the curve of the optimized submerged opening ratio as a function of the filling level; and Step 6 - defining the final geometry of the hollow bulkhead following the optimized submerged opening ratio curve.
  2. 2. Method according to claim 1, characterized in that Step 1 comprises determining the geometry of the vessel, the filling conditions and the excitation conditions.
  3. 3. Method, according to claim 1 or 2, characterized in that Step 2 comprises defining the quantity of perforated bulkheads to be placed in the tank, wherein the quantity n of bulkheads is determined based on the nth resonance mode of the sloshing whose natural frequency is closest to the typical operating frequencies of the tank.
  4. 4. Method, according to any one of claims 1 to 3, characterized in that Step 3 determines the dynamic response of the sloshing in two critical regions, the first associated with the first resonance mode (0.8/m < f < 1.1/m) and the second associated with the second and third resonance modes of the sloshing (0.9/n2 < f < 1.1/ns), and should preferably consider at least 5 aperture ratios and 3 fill levels.
  5. 5. Method, according to any one of claims 1 to 4, characterized in that Step 3 determines the sloshing responses by experiments, computer simulations, such as a series of tests with regular frequency harmonic motion, single tests with irregular frequency harmonic motion ("sweep test") or decay tests.
  6. 6. Method, according to any one of claims 1 to 5, characterized in that Step 4 comprises the following steps: Step 4.1: For each fill, plot the maximum dynamic sloshing response (vertical axis of the graph) as a function of the opening ratio (horizontal axis of the graph); Step 4.2: Obtain the minimum dynamic response point for the fill level and the optimum submerged opening ratio for the fill level; Step 4.3: Repeat this process for all fill levels considered to obtain the optimum submerged opening ratio for all levels considered.
  7. 7. Method, according to any one of claims 1 to 6, characterized in that Step 5 comprises the following steps: Step 5.1: In a graph whose vertical axis is the fill level and the horizontal axis is the optimized submerged aperture ratio, mark the points associated with the values of submerged aperture ratio as a function of fill level obtained in each of the graphs of Step 4; Step 5.2: Interpolate and/or extrapolate a curve of the optimized submerged aperture ratio as a function of fill level;
  8. 8. Method, according to any one of claims 1 to 7, characterized in that Step 5 comprises defining the geometry of the hollow bulkhead, establishing the shapes, dimensions, quantities and distribution of the openings of the hollow bulkhead so that it obeys the optimized submerged opening ratio curve as a function of the filling level found in Step 5.
  9. 9. Perforated anti-slohing bulkhead with optimized submerged opening ratio, characterized by having an optimized opening ratio obtained through the method defined in claims 1 to 8.
  10. 10. Bulkhead, according to claim 9, characterized in that the openings have a plurality of shapes and/or distributions, provided that it complies with the optimized submerged opening ratio.
  11. 11. Bulkhead, according to claim 9 or 10, characterized in that the bulkheads are located longitudinally or transversely to the vessel in which they are installed.
  12. 12. Bulkhead, according to claims 9 to 11, characterized in that the bulkheads are installed in tanks of various geometries, such as rectangular, prismatic or horizontal cylindrical, and in various quantities.

Description

Field of invention: [1] The present invention relates to a method for optimizing anti-sloshing bulkheads and an anti-sloshing bulkhead, more specifically, a hollow bulkhead and a method for dimensioning the openings of hollow bulkheads whose distribution of the submerged opening ratio is optimized and varies along the height of the bulkhead. The distribution of the submerged opening ratio in the bulkhead is optimized in order to minimize the sloshing phenomenon at different tank filling levels, considering the frequency domain of the first to third sloshing resonance modes. Fundamentals of the invention: [2] The phenomenon of sloshing consists of the violent flow of fluid in tanks partially filled with fluids. Although not limited to this context, sloshing is especially dangerous in the context of the transport and storage of liquid cargo, such as in the case of liquid cargo vessels, offshore platforms, land or air vehicles, and fixed reservoirs subject to seismic activity. The violent impact of the fluid, in addition to potentially damaging the tanks, also affects the dynamics of the vehicle or vessel and thus impairs its operation. [3] The sloshing phenomenon is usually more violent in cubic and rectangular tanks. Thus, one approach adopted to mitigate sloshing is the use of tanks with different geometries, such as Kvaerner-Moss spherical tanks (NO140686C), cylindrical axisymmetric tanks (US2019-0078735A1) or tanks with unconventional geometries (US8851321B2). Such tanks are generally more complex to construct and maintain. [4] Furthermore, due to their shapes, they have a low rate of utilization of internal vehicle space compared to rectangular tanks, which is a disadvantage in a context where economies of scale are important. [5] Another approach to sloshing mitigation is based on the introduction of a large number of internal structures fixed to the tank, such as giant rings and various other structural elements. Examples of this approach are the SPB-type tanks from IHI Corp. and tanks patented by Exxon Mobil (US 7111750B2 and US 20100083671A1). However, such solutions can considerably increase the weight of the tank structure and, consequently, the cost of their construction. Furthermore, their efficiency in mitigating sloshing is limited, as they are only more effective for a restricted range of fill levels for which they were designed. [6] There is also the possibility of compartmentalizing the tank, dividing it by means of a bulkhead, either watertight (as in US 8235242B2) or perforated; the latter generally with a fairly low opening ratio. This is a simple and inexpensive approach, but whose objective is not actually to mitigate sloshing, but to make it occur for tank movements at higher frequencies, hypothetically outside the typical operating conditions where the tank is installed. In addition, such structures tend to perform worse in mitigating sloshing at low fill levels. [7] With the aim of keeping sloshing mitigation structures close to the fluid surface regardless of the fill level, several floating devices have recently been proposed (EP2062834B1, JP6049084B2, KR101583945B1 and US2019-0031435A1). These devices are effective in mitigating sloshing at different fill levels. However, the addition of moving elements inside the tank creates an additional risk during operation, as well as increasing the cost and complexity of tank construction and maintenance. So much so that, to date, there is no information on the effective practical application of this concept. [8] In view of the limitations of the technologies developed to date, the present invention comprises a perforated bulkhead and a method for optimizing the openings of perforated bulkheads whose submerged opening ratio varies along the height of the bulkhead, wherein its value is optimized as a function of the filling level. The submerged opening ratio at a given filling level is the ratio between the perforated area of the bulkhead and the total area of the bulkhead that is submerged. Such a bulkhead must be fixed to the inside of the tank so as to divide it into two compartments, and more bulkheads can be added to divide very long tanks into more compartments. [9] Thus, the present invention aims to efficiently mitigate sloshing for a wide range of geometries, including rectangular, prismatic or horizontal cylindrical tanks, across wide ranges of fill levels and tank excitation frequencies, by means of a simple, inexpensive and easy-to-build and maintain device. [10] Considering the frequency domain encompassing the first three sloshing resonance modes in the tank without bulkhead (clean tank), the introduction of a perforated bulkhead affects sloshing in two distinct ways. For the first resonance mode, the smaller the opening ratio, the greater the sloshing mitigation. On the other hand, under conditions close to the second and third sloshing resonance modes, the larger the opening ratio, the greater the sloshing mitigation. [11] Ta