Experimental studies on the dynamic stability of liquid in a spherical tank covered with diaphragm under vertical excitation

• Influence of diaphragm on suppression of liquid sloshing was clarified.
• Influence of diaphragm on the parametric instability region was clarified.
• Influence of liquid volume on the parametric instability region was clarified.

Experimental studies are conducted on the liquid sloshing characteristics in a spherical tank covered with a flexible diaphragm. A spherical acrylic tank with 145.2 mm radius is used as a test tank, and is filled with water. Silicon diaphragms, plane or hemispherical type, with 0.2 mm thickness are used as test diaphragms. The test tank is harmonically excited in the vertical direction by an electro-dynamic exciter. During the test, vibrations due to parametric instability occur when the excitation frequency is twice the natural frequency. Parametric instability regions for some natural modes are measured and are presented in the excitation frequency–excitation acceleration diagram for three cases: liquid surface is uncovered (i.e., free surface), covered with a plane diaphragm, and covered with a hemispherical diaphragm, with the volume of filling water being changed appropriately.