DYNAMIC CALCULATION OF NON-CONTACT SEALS GAPS AT PULSE PRESSURE CHANGES DURING LEAKAGE FLOW RATING

2015 ◽  
Vol 5 (2) ◽  
pp. 100-106
Author(s):  
Evgeny Aleksandrovich KRESTIN
Keyword(s):  
Channel Wall ◽  
Viscous Friction ◽  
Single Pulse ◽  
Pulse Action ◽  
Stationary Processes ◽  
Leakage Flow ◽  
Hydraulic Systems ◽  
Dynamic Calculation ◽  
Dynamic Studies ◽  
Pressure Changes

Detection of leakage fl ow through slott ed annular gaps in dynamic studies leads to the discrepancy between theoretical and experimental results. This discrepancy is particularly large for non-stationary processes in hydraulic systems. Dynamic characteristics of annular sealing cracks of contactless seals in a typical single pulse action of pressure are found. The velocity profi le in the gap is viewed, leakage fl ow is rated, the force of viscous friction at the channel wall is calculated, the relaxation current is considered, the weight function of the sealing gap is determined.

UNSTEADY HYDRODYNAMIC PROCESSES IN THE SLIT GAPS NONCONTACT SEALS IN A STEP CHANGE IN PRESSURE

2015 ◽  
Vol 5 (1) ◽  
pp. 100-106
Author(s):  
Evgeny A. KRESTIN
Keyword(s):  
Channel Wall ◽  
Weighting Function ◽  
Viscous Friction ◽  
Step Change ◽  
Stationary Processes ◽  
Hydraulic Systems ◽  
Dynamic Studies ◽  
Unit Step ◽  
Hydrodynamic Processes

Determination of leakage of fluid through the slotted annular gaps in dynamic studies leads to the discrepancy between the theoretical and experimental results. This discrepancy is particularly large for non-stationary processes in hydraulic systems. Dynamic characteristics of annular sealing cracks in a typical non-contact seals in stepwise (unit step) change of pressure are found. The velocity profile, the flow of leaks, the force of viscous friction on the channel wall are determined, the relaxation during the defined transition and the weighting function of the sealing gap are viewed.

scholarly journals Modern Modeling of Water Hammer

2017 ◽  
Vol 24 (3) ◽  
pp. 68-77 ◽  
Author(s):  
Kamil Urbanowicz
Keyword(s):  
Side Effects ◽  
Adverse Effects ◽  
Water Hammer ◽  
Hydraulic Systems ◽  
Weighting Functions ◽  
Transient Flows ◽  
Hydraulic Equipment ◽  
Pressure Changes ◽  
The Impact ◽  
Reduced Pressures

Abstract Hydraulic equipment on board ships is common. It assists in the work of: steering gear, pitch propellers, watertight doors, cargo hatch covers, cargo and mooring winches, deck cranes, stern ramps etc. The damage caused by transient flows (which include among others water hammer) are often impossible to repair at sea. Hence, it is very important to estimate the correct pressure runs and associated side effects during their design. The presented study compares the results of research on the impact of a simplified way of modeling the hydraulic resistance and simplified effective weighting functions build of two and three-terms on the estimated results of the pressure changes. As it turns out, simple effective two-terms weighting functions are able to accurately model the analyzed transients. The implementation of the presented method will soon allow current automatic protection of hydraulic systems of the adverse effects associated with frequent elevated and reduced pressures.

scholarly journals Parameters affecting water hammer in metal pipelines

2018 ◽  
Vol 44 ◽  
pp. 00183
Author(s):  
Kamil Urbanowicz ◽  
Mateusz Firkowski
Keyword(s):  
Numerical Modelling ◽  
Method Of Characteristics ◽  
Water Hammer ◽  
Supply System ◽  
Hydraulic Systems ◽  
Wave Pressure ◽  
Hydraulic Machinery ◽  
Metal Pipes ◽  
The Individual ◽  
Pressure Changes

The water hammer related to rapid wave pressure changes in hydraulic systems have been subjected to intensive research for more than a hundred years. Nevertheless, a large number of new papers appear each year. Current literature indicates model differences resulting from the used material of the pipe. In the hydraulic machinery, elastic (metal) pipes are usually used, while water transport in water supply system is currently realized with pipes whose deformation of the walls is viscoelastic. In this paper, the individual and group impact of all parameters influencing the results of numerical modelling of the water hammer occurring in the pipes will be analysed. The method of characteristics will be used to solve partial differential equations describing the flow.

High Speed Rotary Pulse Width Modulated On/Off Valve

2007 ◽  
Author(s):  
Haink C. Tu ◽  
Michael B. Rannow ◽  
James D. Van de Ven ◽  
Meng Wang ◽  
Perry Y. Li ◽  
...  
Keyword(s):  
High Speed ◽  
Viscous Friction ◽  
Power Input ◽  
Axial Position ◽  
Reverse Direction ◽  
Duty Ratio ◽  
Concept Design ◽  
Hydraulic Systems ◽  
Output Pressure ◽  
Acceleration And Deceleration

A key enabling technology to effective on/off valve based control of hydraulic systems is the high speed on/off valve. High speed valves improve system efficiency for a given PWM frequency, offer faster control bandwidth, and produce smaller output pressure ripples. Current valves rely on the linear translation of a spool or poppet to meter flow. The valve spool must reverse direction twice per PWM cycle. This constant acceleration and deceleration of the spool requires a power input proportional to the PWM frequency cubed. As a result, current linear valves are severely limited in their switching frequencies. In this paper, we present a novel fluid driven PWM on/off valve design that is based on a unidirectional rotary spool. The spool is rotated by capturing momentum from the fluid flow through the valve. The on/off functionality of our design is achieved via helical barriers that protrude from the surface of a cylindrical spool. As the spool rotates, the helical barriers selectively channel the flow to the application (on) or to tank (off). The duty ratio is controlled by altering the axial position of the spool. Since the spool no longer accelerates or decelerates during operation, the power input to drive the valve must only compensate for viscous friction, which is proportional to the PWM frequency squared. We predict that our current design, sized for a nominal flow rate of 40l/m, can achieve a PWM frequency of 84Hz. This paper presents our valve concept, design equations, and an analysis of predicted performance. A simulation of our design is also presented.

Deformation dynamics and spallation strength of aluminium under a single-pulse action of a femtosecond laser

2013 ◽  
Vol 43 (3) ◽  
pp. 242-245 ◽  
Author(s):  
Sergei I Ashitkov ◽  
P S Komarov ◽  
A V Ovchinnikov ◽  
E V Struleva ◽  
Mikhail B Agranat
Keyword(s):  
Femtosecond Laser ◽  
Single Pulse ◽  
Pulse Action ◽  
Spallation Strength ◽  
Deformation Dynamics

Dynamic Model of a Novel Alternating Flow (AF) Hydraulic Pump

2017 ◽  
Author(s):  
Mengtang M. Li ◽  
Ryan Foss ◽  
Kim A. Stelson ◽  
James D. Van de Ven ◽  
Eric J. Barth
Keyword(s):  
Dynamic Model ◽  
High Efficiency ◽  
Check Valve ◽  
Viscous Friction ◽  
Operating Conditions ◽  
Hydraulic Systems ◽  
Displacement Control ◽  
Hydraulic Pump ◽  
Wide Range ◽  
Variable Displacement

High power density and good controllability are the most appealing characteristics that make hydraulic systems the best choice for many applications. Current state of the art hydraulic variable displacement pumps show high efficiency at high displacement while they have poor efficiencies at low displacement. This paper proposes a novel alternating flow (AF) variable displacement hydraulic pump to 1) eliminate metering losses by acting as a high-bandwidth pump for displacement control, 2) achieve high efficiency across a wide range of operating conditions and displacements, and 3) allow multiple units to be easily common-shaft mounted for a compact multi-actuator displacement control system from a single prime-mover. A dynamic model using first principles describes the cylinder pressure, flows between pairs of cylinders, and net inlet and outlet flows as a function of the pump’s phase shift angle. The model captures hydraulic check valve dynamics, the effective bulk modulus, leakage flows, and viscous friction. Piston kinematics and dynamics are discussed and energy loss models are presented and used to guide the design for a first prototype of the AF hydraulic pump. The paper presents simulation results from the model that offer an initial evaluation of this novel pump concept and potential applications.

The Digital Computation of Pressures in Hydraulic Pipes with Small Volume using an Iterative Technique

1990 ◽  
Vol 204 (1) ◽  
pp. 29-36 ◽  
Author(s):  
D E Bowns ◽  
L M Wang
Keyword(s):  
Small Volume ◽  
Digital Simulation ◽  
Computer Time ◽  
Small Computer ◽  
Iterative Technique ◽  
Hydraulic Systems ◽  
First Order ◽  
Forcing Function ◽  
Start Up ◽  
Pressure Changes

This paper describes a mathematical stiffness problem encountered in the digital simulation of hydraulic pipe systems and an iterative technique that may be employed to avoid it. Mathematical stiffness often arises in systems where the compliance of one or more elements is much smaller than the compliance of the majority of elements in the system. In hydraulic systems, pipes are usually described by first-order differential equations, but if the pipe volume for one or more of the pipes is small, the simulation of this equation by digital computer techniques will necessitate the use of very small computer time steps and simulation times may be very long. However, under these conditions, pressure changes are usually very rapid, and for practical purposes can be considered to instantaneously follow the forcing function, that is, behave as though no compliance existed. A very similar set of circumstances arises in the simulation of orifices at start-up of flow or when flow is reversed. In this paper iterative models are proposed for such cases and their effectiveness is demonstrated in simulating two types of system.

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