PAK BENG HYDROPOWER PROJECT Hydrodynamic Characteristics Research on Valve and Culvert at Valve Section for Pak Beng Ship Lock September 2015
CONTENTS Page 1 FOREWORD... - 1-2 RESEARCH CONTENTS AND EXPERIMENT POINTS... - 1-2.1 RESEARCH CONTENTS... - 1-2.1.1 Unsteady Hydraulic Model Test for Valve Under Normal Pressure...- 1-2.1.2 Steady Hydraulic Pressure-Reduction Model Tests for Valve...- 1-2.2 OPERATION-CONDITIONS OF TESTS... - 2-3 MODEL DESIGN AND LABORATORY TEST EQUIPMENT... - 2-3.1 MODEL DESIGN... - 2-3.1.1 Model Scale...- 2-3.1.2 Model Design of Unsteady Hydraulic Model Test...- 2-3.1.3 Valve Type, Hoist System and Culvert Type...- 3-3.2 TEST EQUIPMENT... - 6-4 HYDRODYNAMIC LOAD CHARACTERISTICS OF UNSTEADY FLOW IN CULVERT AT VALVE SECTION... - 7-4.1 CALIBRATION OF HYDRAULIC PARAMETERS IN MODEL... - 7-4.2 LAYOUTS OF OBSERVATION POINTS... - 8-4.3 RECOMMENDED ELEVATION OF CULVERT AND HYDRODYNAMIC LOAD CHARACTERISTICS OF CULVERT AT VALVE SECTION...- 9-4.3.1 Hydrodynamic Load Characteristics on Culvert at Valve Section When Valve Being in Normal Operation...- 9-4.3.2 Numerical Simulation...- 12-4.3.3 Influence of Valve Opening Speed to Culvert Pressure Characteristics...- 13-4.3.4 Characteristics of hydrodynamic load at culvert under the condition of closing valve in dynamic water...- 13 - i
4.3.5 Analysis of Flow-Induced Vibration of Valve... - 17-4.4 THE HYDRODYNAMIC LOAD CHARACTERISTICS ON CULVERT AT VALVE SECTION AFTER CULVERT ELEVATION RAISED 5M...- 17-4.4.1 Pressure Characteristics on Top of Culvert...- 17-4.4.2 Pressure Characteristics at Bottom of Culvert...- 18-4.4.3 Flow Regime in Culvert at Valve Section...- 19-5 CHARACTERISTICS OF VALVE HOIST LOAD... - 20-5.1 CHARACTERISTICS OF VALVE HOIST LOAD IN OPENING PERIOD...- 20-5.2 THE CHARACTERISTICS OF HOIST LOAD WHEN CLOSING VALVE...- 20-6 ANTI-CAVITATION MEASURES OF EMPTYING VALVE IN PAKBENG SHIP LOCK... - 21-6.1 BASIC IDEA OF SOLVING CAVITATION PROBLEM AT VALVE SECTION OF PAKBENG SHIP LOCK...- 21-6.2 CULVERT TYPE AND ITS FLOW REGIME AT EMPTYING VALVE SECTION OF PAKBENG SHIP LOCK...- 21-6.3 ACHIEVEMENT OF PRESSURE-REDUCTION MODEL TEST... - 23-6.3.1 Test Equipment...- 23-6.3.2 Cavitation Characteristics of Culvert at Valve Section...- 24-6.3.3 Project Measurements to Solve Cavitation Problems of Culvert at Valve Section...- 35-6.4 Valve cavitation under the condition of culvert elevation raised 2m... - 48-7 CONCLUSION... - 49 - ii
LIST OF TABLES Table Title Page Table. 6.3-1 Table. 6.4-1 Relative cavitation number at valve lip, upward slope and downward slope...- 35 - Relative cavitation number at valve lip, upward slope and downward slope...- 48 - iii
LIST OF FIGURES Figure Title Page Fig. 3.1-1 The layouts of upstream lock chamber and valve section...- 2 - Fig. 3.1-2 Abrupt expansion culvert after valve...- 3 - Fig. 3.1-3 Layouts of valve section and downstream reservoir...- 3 - Fig. 3.1-4 Valve type adopted in hydraulic model test (unit: cm)...- 4 - Fig. 3.1-5 Layout of hoist system of reversed tainter valve (unit: m)...- 5 - Fig. 3.1-6 Detail sizes of steps of falling sill (unit: cm)...- 6 - Fig. 3.1-7 Culvert type after valve (unit: m)...- 6 - Fig.3.2-1 Control system of butterfly valve and hoist rod of reversed tainter valve...- 7 - Fig. 3.2-2 Hydrodynamic measurement system... - 7 - Fig. 4.1-1 Data comparison tested from valve model and whole ship lock model (t v =6min)...- 8 - Fig.4.2-1 Observation points of fluctuation pressure... - 8 - Fig. 4.3-1 Layout of water pressure on top of culvert at various open degree... - 9 - Fig. 4.3-2 Fig. 4.3-3 Mean square of pressure fluctuation on top of culvert at various open degrees...- 9 - Time-average pressure distribution on culvert floor at different open degrees...- 10 - Fig. 4.3-4 Fluctuating pressure comparison on culvert floor... - 10 - Fig. 4.3-5 Sketch of flow regime of culvert at valve section... - 11 - Fig. 4.3-6 Flow regime at downward slope after aerating at downward slope... - 11 - Fig. 4.3-7 Flow regime at upward slope after aerating at downward slope (n=0.3)...- 12 - Fig. 4.3-8 Flow regime after aerating at top sealing sill and downward slope... - 12 - Fig. 4.3-9 Flow regime in culvert when valve open degree is n=0.3... - 13 - iv
Fig. 4.3-10 Hydrodynamic load coefficient change curve with various open degree...- 13 - Fig. 4.3-11 Influence of valve opening speed to hydrodynamic load coefficient.. - 14 - Fig. 4.3-12 Influence of water head to hydrodynamic load at valve section... - 14 - Fig. 4.3-13 Fig. 4.3-14 Fig 4.3-15 Fig. 4.3-16 Fig. 4.3-17 Fig. 4.4-1 Fig. 4.4-2 Fig. 4.4-3 Fig. 4.4-4 Fig. 5.1-1 Fig. 5.1-2 Distribution of time-average pressure on culvert top under different water head (tv=6min n=0.4)...- 15 - Minimal value change of pressure on top of culvert with different water head...- 15 - Distribution of pressure-fluctuation intensity on culvert top with different water head (n=0.4)...- 16 - Distribution of time-average pressure at culvert bottom under different water head (tv=6min)...- 16 - Distribution of pressure-fluctuation intensity on and after upward slope (n=0.2)...- 17 - Distribution of time-average pressure on top of culvert in different open degree...- 18 - Distribution of root-mean-square of pressure-fluctuation on top of culvert with different open degrees... - 18 - Distribution of Time-average Pressure at Bottom of Culvert with Different Open Degrees...- 19 - Distribution of root-mean-square of fluctuation pressure at bottom of culvert...- 19 - Change curve of hoist load when opening valve in dynamic water (tv=360s)...- 20 - Relationship of maximal hoist load when opening valve in dynamic water and valve operation speed...- 20 - Fig. 5.2-1 Change curve of valve hoist load in dynamic water...- 21 - Fig. 6.2-1 Recommended culvert type...- 22 - Fig. 6.2-2 Flow regime in culvert recommended...- 22 - Fig. 6.2-3 Flow regime at downward slope...- 22 - v
Fig. 6.2-4 Flow regime at upward slope...- 23 - Fig. 6.3-1 Monitory screen of vacuum tank...- 23 - Fig. 6.3-3 Picture of cavitation noise collecting system...- 24 - Fig. 6.3-4 Culvert type and layouts of aeration pipes recommended...- 25 - Fig. 6.3-5 Layouts of hydrophones... - 25 - Fig. 6.3-6 Cavitation pattern at different valve open degrees...- 27 - Fig. 6.3-7 Cavitation pattern at valve section in typical open degrees...- 28 - Fig. 6.3-8 Fig. 6.3-9 Fig. 6.3-10 Changing-curves of noise intensity at typical valve open degrees collected by No.1 hydrophone...- 30 - Changing-curves of noise intensity at typical valve open degrees collected by No.2 hydrophone (n=0.2~0.7)...- 32 - Changing-curves of noise intensity at typical valve open degrees collected by No.3 hydrophone (n=0.2~0.7)...- 34 - Fig. 6.3-11 Top sealing sill shape of Pakbeng ship lock (unit: mm)... - 36 - Fig. 6.3-12 Fig. 6.3-13 Cavitation pattern at gap of top sealing sill and valve plate without aeration (n=0.2)...- 37 - Cavitation pattern at gap of top sealing sill and valve plate with aeration (n=0.2)...- 37 - Fig. 6.3-14 Aeration concentration at gap of top sealing sill and valve plate... - 38 - Fig. 6.3-15 Noise intensity in condition of without and with aeration (different volume of aeration)...- 39 - Fig. 6.3-17 The aeration concentration in culvert of Pak Beng ship lock... - 40 - Fig. 6.3-18 Flow regime at downward slope after aeration... - 41 - Fig. 6.3-19 Flow regime in culvert after aeration at downward slope... - 41 - Fig. 6.3-20 Noise intensity without and with aeration (different aeration volume) at downward slope...- 42 - Fig. 6.3-21 Wave shape of noise without and with different volume of aeration... - 44 - Fig. 6.3-22 Frequency spectrum of No.3 hydrophone without and with aeration (n=0.2)...- 45 - vi
Fig. 6.3-23 Fig. 6.3-24 Fig. 6.3-25 Fig. 6.3-26 Fig. 6.3-27 Cavitation noise intensity collected by No.1 hydrophone with and without aeration (n=0.3)...- 45 - Cavitation noise intensity collected by No.2 hydrophone with and without aeration (n=0.3)...- 46 - Cavitation noise intensity collected by No.3 hydrophone with and without aeration (n=0.3)...- 46 - Sound pressure level of No.2 hydrophone with and without aeration (n=0.3)...- 47 - Recommended culvert type at valve section of Pakbeng ship lock and its arrangement of aeration pipes...- 47 - vii
1 Foreword Pak Beng ship lock is designed as which can transport 500t-class vessels. Its maximal water head is 32.28m and the effective dimensions are 120m 12m 4m. After physical model test research with scale of 1:25 conducted by Nanjing Hydraulic Research Institute, long-culvert dispersed delivery system is proposed. Its main culvert is laid in the wall of lock chamber and the tridimensional diversion port is in the center of lock chamber. The branch culverts under lock chamber are divided into two areas to fill/empty water. Characteristics of Pak Beng ship lock include high water head, large change range of water level and high hydraulic indexes. And valve hydraulic problem is the key technology problem in design of ship lock. In this context, Nanjing Hydraulic Research Institute assumed the task of hydraulic model test research of delivery system and valve for Pak Beng ship lock commissioned by Kunming Engineering Corporation. 2 RESEARCH CONTENTS AND EXPERIMENT POINTS 2.1 RESEARCH CONTENTS 2.1.1 Unsteady Hydraulic Model Test for Valve Under Normal Pressure (1) Model design of unsteady hydraulic model test (2) Shape selection of valve stretch culvert (3) Determination of valve stretch culvert elevation (4) Characteristics of hydrodynamic loads of valve stretch culvert (5) Hydrodynamic loads of valve stretch culvert when valve closing under flowing water (6) Characteristics of valve hoist loads (7) Influences of valve opening speed to culvert pressure characteristics (8) Influences of water head to culvert pressure characteristics 2.1.2 Steady Hydraulic Pressure-Reduction Model Tests for Valve (1) Characteristics of valve lip cavitation (2) Characteristics of drop sill cavitation and rising sill cavitation (3) Characteristics of cavitation at other areas in culvert - 1 -
(4) Comprehensive anti-cavitation measures for valve stretch culvert 2.2 OPERATION-CONDITIONS OF TESTS Water levels of upstream and downstream for testing: (1) upstream maximum navigation water level of 340.00m - downstream minimum navigation water level of 307.62m; (2) upstream minimum navigation water level of 334.00m - downstream minimum navigation water level of 307.62m; (3) Through keeping downstream minimum navigation water level of 307.62m constant and changing upstream water level, characteristics of pressure fluctuation on top and at bottom of culvert at back of valve were studied. Besides, the relationship of hoisting force and water head was also analyzed. 3 Model design and laboratory test equipment 3.1 MODEL DESIGN 3.1.1 Model Scale The object of study is filling and emptying valve of Pakbeng ship lock and model scale is λ L = 10. 3.1.2 Model Design of Unsteady Hydraulic Model Test The sizes of upstream and downstream connecting pipes meet the requirement of inertia length similarity. The layout of valve hydraulic model is shown in Fig. 3.1-1- Fig. 3.1-3. Fig. 3.1-1 The layouts of upstream lock chamber and valve section - 2 -
Fig. 3.1-2 Abrupt expansion culvert after valve Fig. 3.1-3 Layouts of valve section and downstream reservoir 3.1.3 Valve Type, Hoist System and Culvert Type Reversed tainter valve of double faceplate type is recommended in Pak Beng ship lock. The sizes of culvert cross-section are 2.2 2.6m (width height) and the arc radius of reversed tainter valve is 3.8m. The angle between culvert bottom and valve lip is 90 (see Fig. 3.1-4). - 3 -
R340 R380 32.3 20 Fig. 3.1-4 Valve type adopted in hydraulic model test (unit: cm) Layouts of hoist system proposed in model are shown in Fig. 3.1-5. The culvert type of top-abrupt expansion + bottom-abrupt expansion is recommended based on model tests. The bottom-expansion depth is 20m and its falling sill is with steps. The detail sizes of steps can be seen in Fig. 3.1-6, while culvert type is shown in Fig.3.1-7. - 4 -
0.33 0.2 0.17 0.1 Hydrodynamic Characteristics Research on Valve and Culvert at Valve Section for Pak Beng Ship Lock 349.520 347.650 342.650 339.920 333.520 327.920 323.520 315.920 313.520 306.650 303.920 8.8 12.0 12.0 12.0 9.52 297.920 2 16.0 2.2 296.620 2.6 1.5 2.0 292.020 3.3 0.5 290.020 1.2 11.23 5.17 4.6 293.320 Fig. 3.1-5 Layout of hoist system of reversed tainter valve (unit: m) - 5 -
0.33 Hydrodynamic Characteristics Research on Valve and Culvert at Valve Section for Pak Beng Ship Lock 17.15 25 200 0.2 0.17 120 Fig. 3.1-6 Detail sizes of steps of falling sill (unit: cm) 297.920 2 16.0 2.2 296.620 2.6 1.5 2.0 292.020 3.3 0.5 290.020 1.2 11.23 5.17 4.6 293.320 Fig. 3.1-7 Culvert type after valve (unit: m) 3.2 TEST EQUIPMENT Control system of butterfly valve and hoist rod of reversed tainter valve can be seen in Fig. 3.2-1. Hydrodynamic measurement system is shown in Fig. 3.2-2. - 6 -
Fig.3.2-1 Control system of butterfly valve and hoist rod of reversed tainter valve Fig. 3.2-2 Hydrodynamic measurement system 4 Hydrodynamic load characteristics of unsteady flow in culvert at valve section 4.1 CALIBRATION OF HYDRAULIC PARAMETERS IN MODEL Under the condition of valve operation time is tv=6min, the water level curve in valve shaft and discharge curve tested from valve model and whole ship lock model are - 7 -
compared in Fig. 4.1-1. (a) Water head with elevation curves in valve shaft (b) Discharge curves of lock chamber Fig. 4.1-1 Data comparison tested from valve model and whole ship lock model (t v =6min) 4.2 LAYOUTS OF OBSERVATION POINTS The layouts of observation points can be referred in Fig. 4.2-1. 14# 16# 2# 3# 4# 5# 6# 7# 8# 9# 10# 11# 12# 13# 28# 15# 298.32 23# 293.52 22# 24# 25# 26# 27# 290.02 17# 18# 19# 20# 21# Fig.4.2-1 Observation points of fluctuation pressure - 8 -
4.3 RECOMMENDED ELEVATION OF CULVERT AND HYDRODYNAMIC LOAD CHARACTERISTICS OF CULVERT AT VALVE SECTION 4.3.1 Hydrodynamic Load Characteristics on Culvert at Valve Section When Valve Being in Normal Operation (1) Pressure characteristics on top of culvert a Water Pressure on Top of Culvert In the duration of opening valve, the minimal water pressure on top of culvert is -2.58m when the open degree is n=0.4 (see Fig. 4.3-1). Fig. 4.3-1 Layout of water pressure on top of culvert at various open degree b Characteristic of Pressure Fluctuation Mean square of pressure fluctuation on top of culvert at back of culvert when valve is in operation with speed of tv=6min (see Fig. 4.3-2). Fig. 4.3-2 Mean square of pressure fluctuation on top of culvert at various open degrees - 9 -
(2) Pressure Characteristics on Culvert Floor a Time-Average Pressure Characteristics Distribute of time-average pressure on culvert floor in typical open degrees is shown in Fig. 4.3-3. Fig. 4.3-3 Time-average pressure distribution on culvert floor at different open degrees b Fluctuating Pressure Characteristics The maximal fluctuating pressure on culvert floor is 4.27m because of jet flow occurred at downward slope. Maximal value at end of upward slope is 1.18m. Fig. 4.3-4 Fluctuating pressure comparison on culvert floor - 10 -
(3) Flow Regime of Culvert at Valve Section Fig. 4.3-5 gives the flow regime of culvert at valve section. It can be departed several regions as following: a. main rolling area caused by flow shrinking and then expanding after valve; b. main flow region; c. rolling area caused by main flow separated from culvert floor after upward slope; d. sub-rolling area at downward slope on account of the jet flow. main rolling area sub-rolling area rolling area main flow region Fig. 4.3-5 Sketch of flow regime of culvert at valve section Specific to cavitation problems at valve section caused by negative pressure on top of culvert and pressure fluctuation, measures of automatic aeration at top sealing sill and forced aeration at downward slope can solve elegantly. When valve open degree is n=0.3, flow regime can be seen in Fig. 4.3-6 under the condition of forced aeration at downward slope. Fig. 4.3-6 Flow regime at downward slope after aerating at downward slope - 11 -
Fig. 4.3-7 Flow regime at upward slope after aerating at downward slope (n=0.3) After aerating at top sealing sill and downward slope, the flow regime in culvert with valve being at typical open degree can be seen in Fig. 4.3-8. Fig. 4.3-8 Flow regime after aerating at top sealing sill and downward slope (4) Spectrum characteristic of pressure at culvert Tests show that dominant frequency focuses on low-frequency areas and dominant frequency is lower than 6Hz. Natural frequency of vibration for ship lock s filling and emptying system is usually high, so flow in culvert would not active resonance. 4.3.2 Numerical Simulation Through two-dimension numerical model, velocity distribution in recommended culvert at valve section is calculated as shown in Fig. 4.3-9. - 12 -
-16-12 -8-4 0 4 8 12 16 20 24 Fig. 4.3-9 Flow regime in culvert when valve open degree is n=0.3 4.3.3 Influence of Valve Opening Speed to Culvert Pressure Characteristics Tests shows that with increase of valve opening speed, the time-average pressure will decline and the pulsating quantity will increase. 4.3.4 Characteristics of hydrodynamic load at culvert under the condition of closing valve in dynamic water In the period of opening valve, maximal coefficient of hydrodynamic load is about 1.25. When closing valve in dynamic water, the maximal coefficient value of hydrodynamic load occurs from n=0.2 to closed fully. But it never bigger than 1.25 (see Fig. 4.3-10). Fig. 4.3-10 Hydrodynamic load coefficient change curve with various open degree The variation of hydrodynamic load coefficient with valve opening speed is shown in - 13 -
Fig. 4.3-11. It shows that valve opening speed has no significant effect on hydrodynamic load coefficient. Fig. 4.3-11 Influence of valve opening speed to hydrodynamic load coefficient It should be noted that a low speed touch link which is frequently used in prototype is applied in this model test. The valve operation procedure can be seen in Fig. 4.3-12. The low speed touch can reduce impact force of valve to culvert floor, extra height of water level in shaft caused by closing valve in dynamic water and hydrodynamic load characteristics. n 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 process of valve operation 0 60 120 180 240 300 360 420 480 540 60 time (s) Fig 4.3-12 Valve operation procedure Fig. 4.3-12 Influence of water head to hydrodynamic load at valve section - 14 -
(1) Influence of Water Head to Pressure Characteristics on Top of Culvert Through Fig. 4.3-13 and Fig. 4.3-14, the conclusion can be got that with the increase of water head, the lowest pressure on top of culvert will decrease. Fig. 4.3-13 Distribution of time-average pressure on culvert top under different water head (tv=6min n=0.4) Fig. 4.3-14 Minimal value change of pressure on top of culvert with different water head The pressure-fluctuation intensity on top of culvert will increase with improvement of water head (see Fig. 4.3-15). - 15 -
Fig 4.3-15 Distribution of pressure-fluctuation intensity on culvert top with different water head (n=0.4) (2) Influence of Water Head to Pressure Characteristics at Bottom of Culvert With increase of water head, the pressure distribution law along the culvert bottom is similar (see Fig. 4.3-16). Fig. 4.3-16 Distribution of time-average pressure at culvert bottom under different water head (tv=6min) The pressure-fluctuation intensity at bottom of culvert will increase with improvement of water head (see Fig. 4.3-17). - 16 -
Fig. 4.3-17 Distribution of pressure-fluctuation intensity on and after upward slope (n=0.2) 4.3.5 Analysis of Flow-Induced Vibration of Valve Through a lot of model tests and prototype observation data, it can be determined that the flow-induced vibration of valve in Pakbeng ship lock is within an acceptable range. 4.4 THE HYDRODYNAMIC LOAD CHARACTERISTICS ON CULVERT AT VALVE SECTION AFTER CULVERT ELEVATION RAISED 5M Considering the issues of diminishing excavated volume and better connecting with outlet downstream, the culvert elevation was raised by 5m to test its hydraulic properties in the model. 4.4.1 Pressure Characteristics on Top of Culvert (1) Characteristics of Time-Average Pressure Distribution The minimal pressure on top of culvert is about -7.68mwc in the process of opening valve with opening speed and open degree of tv= 6min, n=0.4, (see Fig. 4.4-1). - 17 -
Fig. 4.4-1 Distribution of time-average pressure on top of culvert in different open degree (2) Characteristics of Pressure-fluctuation The maximal root-mean-square of pressure-fluctuation in abrupt-expanding body is 1.26mwc occurred at back of valve shaft of 15.6m away, when tv=6min and n=0.3 (see Fig. 4.4-2). Fig. 4.4-2 Distribution of root-mean-square of pressure-fluctuation on top of culvert with different open degrees 4.4.2 Pressure Characteristics at Bottom of Culvert (1) Characteristics of Time-average Pressure There exists a low pressure area behind upward slope, and the minimal value is -0.32mwc when n=0.6 (see Fig. 4.4-3). - 18 -
Fig. 4.4-3 Distribution of Time-average Pressure at Bottom of Culvert with Different Open Degrees (2) Characteristics of Pressure-fluctuation The root-mean-square of pressure-fluctuation at bottom of culvert is relatively big when n=0.2~0.4. The maximal value is 4.10mwc at 18# observation point caused by jet flow at falling sill. The maximal value at end of upward slope is 1.07mwc (see Fig. 4.4-4). Fig. 4.4-4 Distribution of root-mean-square of fluctuation pressure at bottom of culvert 4.4.3 Flow Regime in Culvert at Valve Section The flow regime in culvert at valve section after raising the culvert s elevation of 5m is similar with before. - 19 -
5 CHARACTERISTICS OF VALVE HOIST LOAD 5.1 CHARACTERISTICS OF VALVE HOIST LOAD IN OPENING PERIOD When t v =6min, the maximal hoist load in opening period in dynamic water is 175kN (see Fig. 5.1-1). Fig. 5.1-1 Change curve of hoist load when opening valve in dynamic water (tv=360s) With the increase of valve operation speed, the maximal hoist load when opening valve has an increasing trend (see Fig.5.1-2). Fig. 5.1-2 Relationship of maximal hoist load when opening valve in dynamic water and valve operation speed 5.2 THE CHARACTERISTICS OF HOIST LOAD WHEN CLOSING VALVE The minimal value of hoist load when closing valve in dynamic water is -60kN. The hoist load curve is shown in Fig. 5.2-1. - 20 -
Fig. 5.2-1 Change curve of valve hoist load in dynamic water 6 ANTI-CAVITATION MEASURES OF EMPTYING VALVE IN PAKBENG SHIP LOCK 6.1 BASIC IDEA OF SOLVING CAVITATION PROBLEM AT VALVE SECTION OF PAKBENG SHIP LOCK This research tries to adopt new measure of optimized culvert type +different kinds of aeration which combines active protection and positive protection together to diminish cavitation damage. Through selecting reasonable culvert type, valve lip cavitation can be alleviated. If cavitation still exists at valve lip after optimizing culvert type, automatic aeration at top sealing sill can solve elegantly. Specific to cavitation caused by abrupt-expansion body, aeration measures at different position can be adapted. 6.2 CULVERT TYPE AND ITS FLOW REGIME AT EMPTYING VALVE SECTION OF PAKBENG SHIP LOCK In order to solve cavitation problems at valve section, culvert type with top abrupt-expansion + bottom abrupt-expansion is recommended in the paper. The layouts of culvert shown in Fig. 6.2-1 and flow regime can be seen in Fig. 6.2-2~ Fig. 6.2-4. - 21 -
0.33 0.2 0.17 Hydrodynamic Characteristics Research on Valve and Culvert at Valve Section for Pak Beng Ship Lock 297.920 2 16.0 2.2 296.620 2.6 1.5 2.0 292.020 3.3 0.5 290.020 1.2 11.23 5.17 4.6 293.320 Fig. 6.2-1 Recommended culvert type Fig. 6.2-2 Flow regime in culvert recommended Fig. 6.2-3 Flow regime at downward slope - 22 -
Fig. 6.2-4 Flow regime at upward slope 6.3 ACHIEVEMENT OF PRESSURE-REDUCTION MODEL TEST 6.3.1 Test Equipment Pressure-reduction model tests proceeded in vacuum tank. Its monitory screen is shown in Fig. 6.3-1. Fig. 6.3-1 Monitory screen of vacuum tank The cavitation noise wave-shape collecting and analyzing system can be seen in Fig. 6.3-2. Its picture is shown in Fig. 6.3-3. - 23 -
Hydrophone No.1 Hydrophone No.2 High pass filter Amplifier Cavitation noise acquisition device Computer analysis Hydrophone No.n Wave shape output Fig. 6.3-2 Analyzing Principle of Super High-Frequency Collecting System of Cavitation Noise Fig. 6.3-3 Picture of cavitation noise collecting system 6.3.2 Cavitation Characteristics of Culvert at Valve Section (1) Cavitation Pattern at Valve Section The culvert type at back of valve and layouts of aeration pipes adopted in model test are shown in Fig. 6.3-4. - 24 -
Fig. 6.3-4 Culvert type and layouts of aeration pipes recommended The layouts of hydrophones in model can be seen in Fig.6.3-5. Fig. 6.3-5 Layouts of hydrophones The sketch pictures of cavitation pattern at different valve open degrees can be seen in Fig. 6.3-6 and the cavitation pattern at typical valve open degree is in Fig. 6.3-7. - 25 -
- 26 -
Fig. 6.3-6 Cavitation pattern at different valve open degrees (a) Picture of valve lip cavitation, n=0.4-27 -
(b) Picture of valve lip cavitation, n=0.5 Fig. 6.3-7 Cavitation pattern at valve section in typical open degrees The intensity of cavitation noise changing-curves monitored by No.1, No.2, No.3 hydrophones are shown in Fig. 6.3-8~ 6.3-9. noise intensity(pa) 200 150 100 50 0 Hydrophone No.1 n=0.2 0 60 120 180 240 300 360 time (s) Noise intensity(pa) 200 150 100 50 0 Hydrophone No.1 n=0.3 0 60 120 180 240 300 360 time (s) - 28 -
Noise intensity(pa) 200 150 100 50 0 Hydrophone No.1 n=0.4 0 60 120 180 240 300 360 time (s) (a)n=0.2~0.4 Noise intensity(pa) 200 150 100 50 0 Hydrophone No.1 n=0.5 0 60 120 180 240 300 360 time (s) Noise intensity(pa) 200 150 100 50 0 Hydrophone No.1 n=0.6 0 60 120 180 240 300 360 time (s) - 29 -
Noise intensity(pa) 200 150 100 50 0 Hydrophone No.1 n=0.7 0 60 120 180 240 300 360 time (s) (b)n=0.5~0.7 Fig. 6.3-8 Changing-curves of noise intensity at typical valve open degrees collected by No.1 hydrophone Noise intensity(pa) 200 150 100 50 0 Hydrophone No.2 n=0.2 0 60 120 180 240 300 360 time (s) Noise intensity(pa) 200 150 100 50 0 Hydrophone No.2 n=0.3 0 60 120 180 240 300 360 time (s) - 30 -
Noise intensity(pa) 200 150 100 50 0 Hydrophone No.2 n=0.4 0 60 120 180 240 300 360 time (s) (a)n=0.2~0.4 Noise intensity(pa) 200 150 100 50 0 Hydrophone No.2 n=0.5 0 60 120 180 240 300 360 time (s) Noise intensity(pa) 200 150 100 50 0 Hydrophone No.2 n=0.6 0 60 120 180 240 300 360 time (s) - 31 -
Noise intensity(pa) 200 150 100 50 0 Hydrophone No.2 n=0.7 0 60 120 180 240 300 360 time (s) (b)n=0.5~0.7 Fig. 6.3-9 Changing-curves of noise intensity at typical valve open degrees collected by No.2 hydrophone (n=0.2~0.7) Noise intensity(pa) 200 150 100 50 0 Hydrophone No.3 n=0.2 0 60 120 180 240 300 360 time (s) - 32 -
Noise intensity(pa) 200 150 100 50 0 Hydrophone No.3 n=0.3 0 60 120 180 240 300 360 time (s) Noise intensity(pa) 200 150 100 50 0 Hydrophone No.3 n=0.4 0 60 120 180 240 300 360 time (s) (a)n=0.2~0.4 Noise intensity(pa) 200 150 100 50 0 Hydrophone No.3 n=0.5 0 60 120 180 240 300 360 time (s) - 33 -
Noise intensity(pa) 200 150 100 50 0 Hydrophone No.3 n=0.6 0 60 120 180 240 300 360 time (s) Noise intenity(pa) 200 150 100 50 0 Hydrophone No.3 n=0.7 0 60 120 180 240 300 360 time (s) (b)n=0.5~0.7 Fig. 6.3-10 Changing-curves of noise intensity at typical valve open degrees collected by No.3 hydrophone (n=0.2~0.7) - 34 -
(2) Calculation of relative cavitation number The model test gains critical cavitation numbers σ σ at different valve open degrees, seeing Fig. 6.3-11. Obviously, when submerged depth of culvert at valve section is 13m and water head is 32.38m, the minimal critical cavitation number at valve lip is 0.38 which gain excepted goal. Table. 6.3-1 Relative cavitation number at valve lip, upward slope and downward slope n 0.20 0.30 0.40 0.50 0.60 0.7 σ / σ i at valve lip 0.49 0.38 0.42 0.55 0.65 0.85 / i σ / σ i at upward slope 0.60 0.60 0.68 0.90 0.94 >1.00 σ / σ i at downward slope 0.71 0.80 0.85 0.91 0.92 >1.00 6.3.3 Project Measurements to Solve Cavitation Problems of Culvert at Valve Section The abrupt expansion-type culvert is adopted in Pak Beng ship lock to improve cavitation condition at valve lip. Specific to valve lip cavitation residuary, measurement of auto aeration at top sealing sill is taken. Cavitation problem at downward slope can be solved with forced aeration. (1) The Result of Auto Aeration at Top Sealing Sill to Solve Top Sealing Sill Cavitation and Valve Lip Cavitation a The Result of Auto Aeration at Top Sealing Sill to Solve Top Sealing Sill Cavitation The recommended top sealing sill shape and aeration pipe arrangement can be seen in Fig.6.3-11. - 35 -
Fig. 6.3-11 Top sealing sill shape of Pakbeng ship lock (unit: mm) Fig. 6.3-12 and 6.3-13 shows flow regime in gap of top sealing sill and valve plate, n=0.2. After aeration, flow with air can cover the cavitation region of top sealing sill. So aeration at top sealing sill can reduce cavitation intensity effectively. - 36 -
Fig. 6.3-12 Cavitation pattern at gap of top sealing sill and valve plate without aeration (n=0.2) Fig. 6.3-13 Cavitation pattern at gap of top sealing sill and valve plate with aeration (n=0.2) The value of air concentration at gap of top sealing sill and valve plate when tv=6min is shown in Fig. 6.3-14. When n=0.1~0.6, the value of air concentration at gap is bigger than 10%. Lots of research achievements demonstrate that specific to concrete (C15), when air concentration achieves 7%~8%, the cavitation can be suppressed - 37 -
completely. 12 11 10 β (%) 9 8 7 340.0m~307.62m 340.0m~313.62m 6 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 n Fig. 6.3-14 Aeration concentration at gap of top sealing sill and valve plate b The Result of Auto Aeration at Top Sealing Sill to Solve Top Sealing Sill Cavitation Model tests shows that valve lip cavitation can be suppressed completely, see Fig. 6.3-15. - 38 -
噪声强度 (Pa) 200 150 100 50 各开度工况 2# 水听器 0.3 开度 0 0 60 120 180 240 300 360 时间 (s) 噪声强度 (Pa) 200 150 100 50 各开度工况 2# 水听器 qa=0.0016m3/s/m 0 0 60 120 180 240 300 360 时间 (s) 噪声强度 (Pa) 200 150 100 50 各开度工况 2# 水听器 qa=0.004m3/s/m 0 0 60 120 180 240 300 360 时间 (s) 200 各开度工况 2# 水听器 qa=0.008m3/s/ 噪声强度 (Pa) 150 100 50 0 0 60 120 180 240 300 360 时间 (s) 噪声强度 (Pa) 200 150 100 50 各开度工况 2# 水听器 qa=0.012m3/s/m 0 0 60 120 180 240 300 360 时间 (s) 噪声强度 (Pa) 200 150 100 50 各开度工况 2# 水听器 qa=0.016m3/s/m 0 0 60 120 180 240 300 360 时间 (s) Fig. 6.3-15 Noise intensity in condition of without and with aeration (different volume of aeration) - 39 -
Obviously, the aeration concentrate in main culvert after aeration at top sealing sill is relatively big which is to advantage of reducing valve lip cavitation, see Fig. 6.3-16~6.3-17. 0.055 0.050 0.045 qa (m 3 /s/m) 0.040 0.035 0.030 0.025 0.020 0.015 340.0m~307.62m 340.0m~313.62m 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 n Fig. 6.3-16 Aeration volume of unit width Fig. 6.3-17 The aeration concentration in culvert of Pak Beng ship lock (2) Measures to Suppress Downward Slope Cavitation Measures of forced aeration at downward slope can solve cavitation there. Besides, the flow with air can protect the bottom of culvert. The flow regime can be seen in Fig. 6.3-18 and 6.3-19 and the noise intensity is shown in Fig. 6.3-20. So the suggestion is arranging two air compressors in both head bay and tail bay to realize forced aeration. - 40 -
Fig. 6.3-18 Flow regime at downward slope after aeration Fig. 6.3-19 Flow regime in culvert after aeration at downward slope - 41 -
Fig. 6.3-20 Noise intensity without and with aeration (different aeration volume) at downward slope - 42 -
(3) Measures of Suppressing Upward Slope Cavitation Cavitation exists at upward slope without aeration. After aeration at downward slope, the impulse of sound pressure wave shape will disappear and the sound pressure level will lower 40dB. Obviously, aeration at downward slope can suppress upslope cavitation effectively. According to comparative experiments with different aeration volume, the required aeration volume to suppress downward and upward slope cavitation completely is very little. Arranging air compressor with capacity of 0.1m3/s and pressure of 1MPa at head bay and tail bay is enough. The wave shape of noise and frequency spectrum of noise is shown in Fig 6.3-21 and 6.3-22. - 43 -
Fig. 6.3-21 Wave shape of noise without and with different volume of aeration - 44 -
SPL (db) 60 40 20 0-20 -40 n=0.2 Hydrophone No.3 n=0.2 downward slope qa=0.004m3/s/m downward slope qa=0.008m3/s/m downward slope qa=0.012m3/s/m aeration -60 1 10 100 1000 f (khz) Fig. 6.3-22 Frequency spectrum of No.3 hydrophone without and with aeration (n=0.2) (4) Effect of Aeration to Suppress Cavitation at Valve Section There exists cavitation at valve section without. And the impulse noise is dense and with big value. After aeration, the curve of noise intensity is flat and without impulse. The sound pressure level lower 55dB. The cavitation noise intensity and frequency spectrum can be seen in Fig. 6.3-23 and 6.3-26. 200 150 Noise intensity(pa) 100 50 0 Hydrophone No.1 n=0.3 0 60 120 180 240 300 360 time (s) 200 150 Noise intensity(pa) 100 50 0 Hydrophone No.1 qa=0.012m3/s/ m at top sealing sill; 0 60 120 180 240 300 360 time (s) Fig. 6.3-23 Cavitation noise intensity collected by No.1 hydrophone with and without aeration (n=0.3) - 45 -
200 150 Noise intensity(pa) 100 50 0 Hydrophone No.2 n=0.3 0 60 120 180 240 300 360 time (s) 200 150 Noise intensity(pa) 100 50 0 Hydrophone No.2 qa=0.012m3/s/ m at top sealing sill; 0 60 120 180 240 300 360 time (s) Fig. 6.3-24 Cavitation noise intensity collected by No.2 hydrophone with and without aeration (n=0.3) 200 150 Noise intensity (Pa) 100 50 0 Hydrophone No.3 n=0.5 0 60 120 180 240 300 360 time (s) Fig. 6.3-25 Cavitation noise intensity collected by No.3 hydrophone with and without aeration (n=0.3) - 46 -
Fig. 6.3-26 Sound pressure level of No.2 hydrophone with and without aeration (n=0.3) The recommended culvert type at valve section of Pakbeng ship lock and its arrangement of aeration pipes can be seen in Fig. 6.3-27. Fig. 6.3-27 Recommended culvert type at valve section of Pakbeng ship lock and its arrangement of aeration pipes - 47 -
6.4 Valve cavitation under the condition of culvert elevation raised 2m Considering that raising culvert elevation can diminish excavated volume, we tested and calculated the relative cavitation number under the condition of culvert elevation was raised 2m, see Table. 6.4-1. Table. 6.4-1 Relative cavitation number at valve lip, upward slope and downward slope Location Valve elevation 0.20 0.30 0.40 0.50 0.60 0.7 Relative cavitation number at valve lip Relative cavitation number at upward slope Relative cavitation number at downward slope Original elevation (emptying valve) Elevation after raised 2m (emptying valve) Original elevation (filling valve) Elevation after raised 2m (filling valve) Original elevation (emptying valve) Elevation after raised 2m (emptying valve) Original elevation (emptying valve) Elevation after raised 2m (emptying valve) 0.49 0.38 0.42 0.55 0.65 0.85 0.38 0.28 0.30 0.39 0.52 0.71 0.65 0.40 0.80 >1.00 >1.00 >1.00 0.54 0.31 0.68 >1.00 >1.00 >1.00 0.60 0.60 0.68 0.90 0.94 >1.00 0.48 0.49 0.57 0.79 0.84 0.71 0.80 0.85 0.91 0.92 >1.00 0.63 0.71 0.75 0.82 0.83-48 -
7 Conclusion Pak Beng ship lock is the throat of navigation main line on Mekong. The effective size of the lock chamber is 120.0m 12.0m 4.0m (length width minimal water depth on the sill). The cross section size of recommended culvert at valve section of the filling and emptying system is 2.2m 2.6m (width height) and the maximal water head is 32.38 meters. Its water level amplitude of variation and requirements of hydraulic indexes are close to or in the highest level of built ship locks in the world. Among which the valve hydraulic problem is one of the key technical problems in this ship lock hydraulic design. Through the unsteady hydraulic model tests and steady pressure-reduction model tests with scale of 1:10 at present stage, hydrodynamic pressure on culvert at back of valve, hoist load characteristics, hydrodynamic load on culvert at back of valve during period of closing valve, effect of valve operation speed and water head on hydrodynamic pressure and hoist load etc. are studied. The cavitation characteristics at valve lip, upward slope, downward slope are deeply researched. This report put forward effective measures of automatic aeration at top sealing sill to suppress cavitation at top sealing sill and valve lip, forced aeration at downward slope to suppress cavitation at upward slope and downward slope which are verified by pressure-reduction model test. Characteristics of hydrodynamic pressure on culvert at back of valve under the condition of raising its elevation of 5m and the feasibility are discussed. The cavitation factors are also estimated while culvert s elevation is raised 2m. Main conclusions are as follows: (1) Based on previous research achievements, top abrupt-expansion + bottom abrupt-expansion type is adopted in model test. Height of top expansion is 5m. In order to avoid air collection on top of culvert, the roof of culvert is divergent upward which starting from 2m at back of valve and ending at 2.2m in front of repair gate slot. Its gradient is 1:32. Depth of bottom expansion is 2.0m and the length is 11.23m. Steps are set at downward-slope and upward-slope. The angle between upward-slope and horizontal line is 31. The distance between the end of upward-slope and repair gate slot is 4.6m. Model tests showed that in the period of opening valve, main flow would have effective support action on top of culvert which increases cavitation number and is good for anti-cavitation. Flow regime observation indicates that aerated flow can fit the downward slope with steps. There is no vortex at steps which would adversely affect the structure stability of steps. The aerated flow gradually covers the surface of whole upward-slop until repair gate shaft with valve opening. It not only solves the upward-slope cavitation, but is also to the advantage of anti-cavitation at repair gate. The steps at downward-slope can reduce the turbulence intensity of vertical drop and are convenient for repair. (2) Under different operation condition, pressure variation characteristics on top of culvert are influenced by large-scale vortex roll at back of valve. When the water head is 32.38-49 -
and valve opening time is t v =6min which is recommended, minimal time-advantage pressure occurs at 7.8m away from valve (about three times of culvert height), ie. in center of main vortex roll. Its value is -2.58m of water, when valve open degree is n=0.4. When valve open degree is in range of 0.2~0.6, the root-mean-square of pressure fluctuation is relatively larger for each observation point. Besides, in different open degrees, the largest value of pressure fluctuation in abrupt expansion body occurs at the end of upward-slope (No.18 observation point) which is 15.6m far away from the valve. The largest value is 1.23m of water (n=0.4). The root-mean-square of pressure fluctuation is lower than 0.6m with in 9m downstream range of valve shaft. The maximal pressure fluctuation at downward slope of No.18 point is 4.27m of water caused by jet flow. And the maximal value at upward slope is 1.18m. The model test declares that the area of main vortex roll is restricted in abrupt-expansion cavity of culvert. The location of repair gate is appropriate, 20.2m away from valve (equivalent to 8 times of culvert height). (3) Under the operation condition of that valve opens to different open degrees with speed of t v =6min and then closes with speed of t v =3min, model test indicates the maximal hydrodynamic load coefficient is 1.25. In period of closing valve, water level in valve shaft will rise, but never go up to initial water level which is highest. The hydrodynamic load coefficient should be considered as 1.8 in valve structural design. (4) Characteristics of hydrodynamic pressure on culvert at back of valve under the condition of raising its elevation of 5m and the feasibility are discussed. a b c d In duration of opening valve, the lowest pressure (n=0.4) on top of culvert is -7.68m of water. And it is too low in the process of opening valve, which is bad for anti-cavitation at valve section. When valve open degree is in range of 0.4~0.6, obvious air suction phenomenon will occur at repair gate slot at back of emptying valve. The phenomenon will be more severe in prototype. If the volume of air suction is large enough, it may form repelled downstream hydraulic jump which is unfavorable to emptying valve structure and hoist system. Submerged depth of valve is quite shallow when valve is fully opened. Because of that, the suggestion is remain culvert elevation unchanged which is advised by model test. According to entire filling and emptying system model test, negative pressure on top of culvert at back of filling valve is -1.18m if the elevation of culvert is not raised. It is no doubt that negative pressure will increase in culvert as long as its elevation is lifted. And the cavitation will hard to be suppressed considering the vessels berthing condition. For all these reasons, it's inadvisable to raise the elevation of culvert. - 50 -
(5) Reversed tainter valve of double plate type is recommended in this paper which can adapt operation in dynamic flow with high water head and has anti-vibration performance. Under the operation condition of valve opens fully with speed of t v =6min and then closes with speed of t v =3min, the maximal valve hoist load in dynamic flow is 175kN. The maximal value occurs around valve open degree of n=0.25. The minimal value is -60KN which occurs at early stage of closing valve. (6) Culvert type of top abrupt-expansion + bottom abrupt-expansion can improve flow regime and increase pressure at back of valve so to improve the valve s capability of cavitation resistance. When the submerged depth of culvert at valve section is 13.0m and water head is 32.38, the relative cavitation number at valve lip is 0.38 in this recommended culvert type. And the minimal relative cavitation number at upward slope with steps is about 0.6 which means cavitation intensity is relatively weak. The bubble collapse area is on the steps, restricted in abrupt-expansion cavity and will not damage repair gate slot downstream. The minimal relative cavitation number at downward slope is about 0.6 which has lower intensity compared with cavitation at valve lip. The collapse area of downward slope cavitation occurs on culvert bottom is very small. So, the abrupt-expansion culvert type achieves its aim of excellent anti-cavitation capacity. (7) Through model test, automatic aeration at top sealing sill is put forward to solve the cavitation problems at top sealing sill and valve lip. (8) According to the results of section model test of top sealing sill with scale of 1:1 and layouts at valve section of Pakbeng ship lock, the aeration pipe arrangement and top sealing sill shape is recommended. a b The location of water-stop at top sealing sill, horizontal aeration pipe and aeration orifices are mounted with the recommended scheme. In particular, the automatic aeration is sensitive to geometric dimensioning of the gap of top sealing sill. It is necessary to keep h 1 <h 2 <h 3 (see Fig.6.15). Deformation of valve plate under high water head and water-stop preloading should be considered in the installation process, then to guarantee the accuracy of geometric dimensioning of the gap of top sealing sill and high smoothness of valve plate. (9) Pressure-reduction model test indicates that comprehensive engineering measure of top abrupt-expansion + top abrupt-expansion + automatic aeration at top sealing sill (necessary measures)+ forced aeration at downward slope (reserve measures) can solve valve cavitation problem of Pakbeng ship lock with water head of 32.38m. Aerated flow formed by automatic aeration at top sealing sill can protect culvert boundary where main flow passed by and aerated flow formed by forced aeration at downward slope provides good protection to culvert floor. a Valve lip cavitation will occur when valve open degree is in range of 0.1~0.7. When - 51 -
valve open degree is n=0.2~0.5, intensity of valve lip cavitation will become relatively severe. When valve open degree is n=0.8, valve lip cavitation will disappear. In valve open degree of n=0.1~0.7, automatic aeration can be realized at top sealing sill. The aeration volume is larger when n=0.1~0.5and the maximal value is 0.11m 3 /s. Air concentration in flow after automatic aeration at top sealing sill is higher than that in Gezhouba ship lock and Three Gorges ship lock. Model test declares that noise intensity caused by valve lip cavitation decreases significantly. It means valve lip cavitation can be suppressed effectively through aeration at top sealing sill. b Specific to cavitation at upward slope and downward slope of abrupt-expansion culvert, suggestion of mounting aeration pipes on frontend of downward slope to aerate forcedly through air compressor is proposed. ( It will test in prototype if is necessary.) Model test shows very little volume of aeration can solve cavitation at downward slope completely and meanwhile suppress cavitation at upward slope sufficiently. With opening of valve, the aerated flow will cover whole upward slope to the shaft of access door. If necessary, the maximal discharge of recommended air compressor is 6m³/min. (10) Since adoption of recommended culvert type and comprehensive aeration measure in Pakbeng ship lock, the pressure and its fluctuation of flow is in normal range. Besides, the valve cavitation can be suppressed sufficiently. So it don t need steel lining mounted on inner wall of culvert and high-strength concrete as defence. In particular, the culvert s construction quality and flatness at valve section should be controlled strictly. Forced aeration pipes at downward slope are reserved and whether to buy and use the air compressor or not is based on the result of prototype debug. (11) Specific to the valve structure, culvert type at valve section, hydrodynamic load on culvert at back of valve, hoist load characteristics and the effectiveness of anti-cavitation measures, combined with a lot of prototype tests accumulated before, the flow-induced vibration of valve will not occur as long as the installation of suspender and valve are comply with the design specification and this report and prototype tests are carried out before navigation. Suggestions: In view of the complexity of hydraulic problems of Pakbeng ship lock, its relation to whether the international river is unobstructed and its important navigation role, the prototype debug is necessary before the trial operation of ship lock according to the experience of other high water head ship lock. Through prototype debug, the existing technology problems can be resolved, the operation mode of ship lock can be adjusted and optimized and normal operation parameters of ship lock can be determined. Prototype debug can provide basis for operation management procedures of Pakbeng ship lock. Thus operation safety of ship lock can be secured and navigation benefit will be guaranteed. - 52 -