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Flow-induced vibration (FIV) is studied on a horizontal 90-degree elbow in this paper. It was noted that the slugs and pseudo-slugs on the elbow cause the maximum force. Particularly, pseudo-slug flow in gas-liquid systems results in higher force amplitude peaks. These high force amplitudes may potentially cause fatigue in elbows due to the occurrence of flow-induced vibration. Pseudo-slug flow pattern occurs in the transition from slug to segregated flows. It was identified that the magnitude of the force fluctuation is influenced by the change in momentum flux and pressure. Thus, the pressure force can be interpreted as the base from which the hydrodynamic forces create the overall force peaks. Analysis of time-varying quantities of the liquid holdup (slug liquid holdup, 0.18 to 1.00), flow-induced force (force peaks, 10–620 N), and pressure pulsation (pressure fluctuation, 2500–35000 Pa) allowed the study of the separate contributions of momentum and pressure terms on the magnitude of the force fluctuation (force amplitude, 4–180 N). The findings indicate that pressure fluctuations within the elbow play a significant role in estimating force magnitude in pseudo-slug flow, whereas they are not predominant in slug flow. Based on the analysis, a mechanistic model capable of predicting the impacting force as a function of the flow pattern and operational conditions is proposed.

The effects of graded changes in peripheral extracellular volume on heart rate and blood pressure during isometric exercise were studied in 12 healthy male subjects. Each subject performed four calf ergometer tests with each calf. In all tests, static plantar flexion of one foot was performed in a supine body position with the knee joint flexed to 90°. After a pre-exercise period of 18 min, during which the calf volume was manipulated, the subjects had to counteract a spring force of 120 N for 8 min. In the pre-exercise period the peripheral extracellular volume of the calf muscle to be tested was manipulated in four ways. Test 1: 15 min of rest in the exercise position. During the last 3.5 min, the calf volume was increased by venous congestion [80 mmHg (10.67 kPa) applied to the distal part of the thigh by pneumatic cuff]. Test 2: the same protocol as in test 1 but with 7.5-min venous congestion. Test 3: 15 min of venous congestion. Test 4: the calf volume was decreased by a negative hydrostatic pressure for 15 min (calf raised about 40 cm above heart level). To clamp the changed calf volume, the thigh cuff was rapidely inflated to 300 mmHg (40.0 kPa) at the end of the volume manipulation and the subjects remained resting for a further 3 min. In test 4, the leg of the subject was passively brought into the exercise position. The occlusion was maintained until 2 min after exercise. The calf volume manipulation led to changes ranging from +105 ml (test 3) to −134 ml (test 4) as measured by water displacement plethysmography. The blood pressure response to exercise was inversely related to the calf volume changes while the heart rate response during exercise showed no clearcut relationship to the pretreatments.