10:45 AM - 12:15 PM
[SVC29-P06] Preparation for Single Force Measurement Using a liquid jet from a PET Bottle
Keywords:Volcanic eruption, Single force, Eruption earthquake, Model experiment, Jet
Background
When we analyze seismic waves generated during a major volcanic eruption, we sometimes find that the source is a vertical single force (e.g., Kanamori et al., 1984 for the May 18, 1980 eruption earthquake at Mount St. Helens). This single force is thought to be the reaction force, or jet propulsion, of the explosive eruption. Analyzing the single force may allow for estimating the amount and style of the eruption (Brodsky et al., 1999).
Purpose
Fluctuations in the mass discharge rate and the eruption style would modulate the single force F and then should affect the observed seismic waves. The purpose of this study is to investigate how fluctuations in the mass discharge rate and the manner of jetting are affected by the shape of the jet nozzle and source fluid conditions (pressure and properties), and how they affect the relationship between the bulk mass discharge rate and the force F.
Theoretical Consderation
We assume the single force F has a triangular shape (Brodsky et al., 1999) with a time width of 2τ, and the crater area, A, and the jet density, ρ, are constant. The mass discharge rate is ρAv, where v is the jet speed. Brodsky et al. (1999) approximated F by the jet propulsion force, ρAv^2. Then, the mass discharge rate is (ρAF)^ 1/2.
By integrating the mass discharge rate with time to obtain the total ejected mass, M, and multiplying it by the gravity acceleration, g, we can obtain the upward force on the ground by the mass change. If Mg is greater than or equal to the term due to the jet force, the first assumption is violated. We showed that the assumption holds when the peak jet velocity is much larger than τg. Considering the realistic jet speeds, the condition requires τ to be smaller than 10 s.
Preparation and results of a preliminary experiment
We measured the time variation of the pressure inside a PET bottle from which the water jet was being ejected. The bottle was initially filled with 1.5 L of water. We supplied air into the bottle at 5 bars above the atmospheric pressure to push the water out of the nozzle. The pressure in the bottle and images of the water jet are shown in the figure. After the pressure stays at 5 bar for 20 s, it drops at the time (C) when the jet angle narrows. Such change would have some effect on the single force.
Toward Future Experiments
Based on the results of the preliminary experiments, we designed and built an experimental apparatus and prepared to measure the single force associated with the jet using a force sensor. We plan to conduct experiments by changing the gas-liquid mixing ratio and the cross sectional area of the jet.
When we analyze seismic waves generated during a major volcanic eruption, we sometimes find that the source is a vertical single force (e.g., Kanamori et al., 1984 for the May 18, 1980 eruption earthquake at Mount St. Helens). This single force is thought to be the reaction force, or jet propulsion, of the explosive eruption. Analyzing the single force may allow for estimating the amount and style of the eruption (Brodsky et al., 1999).
Purpose
Fluctuations in the mass discharge rate and the eruption style would modulate the single force F and then should affect the observed seismic waves. The purpose of this study is to investigate how fluctuations in the mass discharge rate and the manner of jetting are affected by the shape of the jet nozzle and source fluid conditions (pressure and properties), and how they affect the relationship between the bulk mass discharge rate and the force F.
Theoretical Consderation
We assume the single force F has a triangular shape (Brodsky et al., 1999) with a time width of 2τ, and the crater area, A, and the jet density, ρ, are constant. The mass discharge rate is ρAv, where v is the jet speed. Brodsky et al. (1999) approximated F by the jet propulsion force, ρAv^2. Then, the mass discharge rate is (ρAF)^ 1/2.
By integrating the mass discharge rate with time to obtain the total ejected mass, M, and multiplying it by the gravity acceleration, g, we can obtain the upward force on the ground by the mass change. If Mg is greater than or equal to the term due to the jet force, the first assumption is violated. We showed that the assumption holds when the peak jet velocity is much larger than τg. Considering the realistic jet speeds, the condition requires τ to be smaller than 10 s.
Preparation and results of a preliminary experiment
We measured the time variation of the pressure inside a PET bottle from which the water jet was being ejected. The bottle was initially filled with 1.5 L of water. We supplied air into the bottle at 5 bars above the atmospheric pressure to push the water out of the nozzle. The pressure in the bottle and images of the water jet are shown in the figure. After the pressure stays at 5 bar for 20 s, it drops at the time (C) when the jet angle narrows. Such change would have some effect on the single force.
Toward Future Experiments
Based on the results of the preliminary experiments, we designed and built an experimental apparatus and prepared to measure the single force associated with the jet using a force sensor. We plan to conduct experiments by changing the gas-liquid mixing ratio and the cross sectional area of the jet.