Posted on

Von Karman Determined That The Added Mass Engineering Essay

In order to happen the maximal force per unit area experienced by the float at initial impact, the empirical equations are derived by Von Karman ( 1929 ) . The theory is based on a prismatic cuneus hull dropped vertically and striking a horizontal H2O surface. The force is derived utilizing the impulse theorem, and can merely be used by presuming a closed system and preservation of impulse. Thus the consequence of diminishing perkiness impulse is neglected.

Von Karman determined that the added mass for the hydroplane float is equal to the mass of the H2O contained in a semi-circular cylinder with diameter equal to the waterplane comprehensiveness in the still H2O status.

This can be assumed if the bottoms are non excessively aggressively inclined. The undermentioned equation predicts the maximal force per unit area moving on the float and includes a dynamic force per unit area parts which corresponds to the impact speed and a term which correlates to the theoretical factor of addition for differing angles of deadrise.

Mayo ( 1945: p.72 ) subsequently trial shows that the flare-off during set downing reduces the perpendicular speed at contact to fraction of the droping velocity of the aeroplane. Furthermore, local force per unit areas may be greater than mean force per unit area. Datas from trials of winging boat, which included measured perpendicular speeds, showed force per unit areas is much greater than those computed by Von Karman expression.

Similarly, Wagner ( 1932 ) assumes in his method related to blunt organic structure impact and the local uprise of H2O. This were based on banging theoretical account of a local little deadrise angle provides simple analytical consequences as where Faltinsen ( 2005 ) so forms Wagner ‘s equations related to lodge bead trials. The trial shows that spray is close to atmospheric force per unit area and therefore is non every bit of import as the big force per unit areas happening at the spray root. In this case, there is green H2O burden, or where the air is n’t assorted with the flow. At the spray, big force per unit area gradients accelerate the H2O at high speeds into a ‘jet flow ” doing a high free surface curvature or wave uprise which so tums into spray under the influence of surface tenseness.

In this equation, Faltinsen ( 2005 ) suggested to cipher the slamming force per unit area, the alteration rate of the wetted surface, and the 2nd term which is considered the added mass force per unit area. After chine submergence, the wetted half beam is changeless, so the slamming force per unit area goes to zero. Therefore, after chine submergence the lone force per unit area moving on the hull is due to the associated added mass of the hull.

On how to find them, several variables in the force per unit area equation need farther insight where Wagner ‘s theory is capable to managing non-prismatic hullforms in which the perpendicular distance of the surface height comparative to the organic structure. nb ( ten ) , can be defined as series which captures the bottom surface geometry and is govern by the equation below.

While to find a map which relates the normal speed to the velocity of extension of the wetted semi-width as the organic structure submerges, Wagner ( 1932 ) defines the map U by expression as follows:

With the map U calculated at a peculiar wetted half beam, the velocity of extension of the wetted semi-width can be determined given an impact speed. This measure can so be substituted into the force per unit area equation to find the hydrodynamic force per unit area on the hull signifier.

Figure 7.3: Definition of parametric quantities to find the impact forces on a hull utilizing Wagner ‘s outer sphere theory ( Faltinsen 2005 ) .

Addition to this, Mayo ( 1945:76 ) based on his experiment said that the bead informations are corrected for the consequence of gravitation by theoretically derived factors and compared with computed values for the instance of flying lift. On this, the spring invariable is modified to suit the information. This alteration is assumed to stand for the snap consequence of the bottom construction. Because of this alteration and other estimates, the exact truth of the theory is non established. However, he argued that the hydrodynamic theory by Sydow ( 1938 ) appears to give about right consequences for perpendicular bead of a triangular prism at zero spare into smooth H2O.

Blundell and Jones ( 1938 ) conducted experiment on force per unit area and entire impact force measurings against a assortment of hydroplane hulls where the

Consequences were so compared with impact theory utilizing the equation below.

The equation given above is derived from V-shape theoretical account trials and shows the relation of the force per unit area, where the changeless K varies depending on the location of impact point and the burden. The K equalled to 68 for a location near to the chine and 47 for a location near the keel. This shows that the impact force per unit area is higher at the keel than at the chine for a V-shape hull. The force per unit area near the chine depends on the burden every bit good as the dramatic speed, whereas the force per unit area near the keel is independent of weight, or the burden, of the hull. It is nevertheless dependent on the slowing through the H2O. It is of import to observe that this equation with the values of K provided is merely for hull signifiers with the same order of lading on the hull underside as the experimental hull signifier.

The experimental and theoretical consequence shows that at changeless submergence,

Regardless of the impact speed, the maximal impact force will happen. Under this status, the experimental consequences showed that for all three hydroplane hulls, the chine was nowhere nearA· chine wetting when the maximal force was measured. The theory shows and verified by experimental consequences that the force per unit area center of the construction between the keel and the chine is relative to the cotangent of the deadrise angle at a given impact speed which is normal to the keel except when this angle is really little.

Comparing the recorded force per unit area of the three hydroplane hulls and the VA­ form used for experimental survey with the maximal peak force per unit area equation, the consequences showed a good understanding. Since there was good understanding for hydroplanes with curving transverse subdivisions, Blundell and Jones ( 1938 ) imply that the theoretical equation can be applied non merely to level V-sided hulls, but besides to swerve hullforms and to hull signifiers with deadrise varying in longitude. However, the value of changeless K in this force per unit area equation is strictly taken from the listed hull type. Therefore, this method merely applies to these limited types of hulls.

On the other manus, Mayo ( 1945 ) develops an improved theory- by rectifying old impact theory. This theory was used to find the force moving on the hull during impact of a prismatic hull with positive trim. He considered the impact job related to the flow in cross planes, impulse equations, aspect-ratio corrections, consequence of generated moving ridge on the practical mass, distribution of surface force per unit area, and conditions for maximal impact force. On this,

The forward speed of the hydroplane float causes impulse to be passed into the hydrodynamic downwash. For impact with spare the rate of incursion is determined non merely by the speed constituent normal to the keel but besides by the speed constituent analogue to the keel, which tends to cut down the incursion.

The gesture of the hull for oblique impact considers non merely perpendicular, but parallel flow gestures in regard to the keel. The hull passes through these flow planes and when the measure clears a flow plane the flow plane so becomes a portion of the aftermath.

For oblique impact the flow plane comes into contact with all crossA­ subdivisions as the hull degree Fahrenheit ( nm base on ballss through it with clip, whereas for entirely perpendicular impact the flow plane is in contact with merely one cross subdivision.

For an ideal fluid, the growing of the of the intersected hull cross subdivision as it passes a peculiar plane will merely be used to find the flow in that peculiar plane. The full flow procedure for an single plane begins when the keel line penetrates the single plane and ends when the planes slide off the measure or the remA· of the hull.

For perpendicular impact on hull with a spot of spare angle, the accelerated H2O during impact is in the way normal to the plating, therefore the stationnary plane in which the way of unstable moves normal to the keel.

To account for the assorted differences in flow caused by the longitudinal force per unit area differences, an aspect-ratio factor is applied to the force per unit area equation. The entire impact force is calculated by entire alteration rate of impulse. This is equal to summing all the reactions of the single flow planes that the hull brushs and besides the impulse passed on to the downwash along with the flow planes that slide off the measure. The entire hydrodynamic force in the way of the speed normal to the keel is defined by the equation as follows:

In order to use the equation above, the force equation is derived once more with empirical equations for practical mass and aspect-ratio corrections for the distributed burden where the force moving on the hull due to an single transverse flow plane which considers the impulse of the flow in cross program given.

Therefore, to obtain the entire force, the forces moving on the hull from each person flow plane can be integrated over the accomplished length of the hull, where for fixed spare impact a entire force equation is defined by the followers:

Here, the first term is related to the practical mass flow beneath the hull and the rate at which the impulse of the hydroplane is imparted to the downwash. While to account for the practical mass flow in the transverse plane, Sydow ‘s theoretical equation for flow in normal planes of a triangular prism were used along with Pabst ‘s empirical facet ratio factor to rectify the terminal loss. In add-on, to rectify the inaccuracy of Pabt ‘s aspect-ratio factor which were determined by submersed quiver trial, a rectification factor of 0.82 derived from experimental consequences, therefore the resulting equation is,

With farther permutations and cognizing that the entire force equation already stated was derived on the relationship that K = mp/z2ds the mp equation can be substituted into the normal force equation and gives the undermentioned concluding sum force expression.

On this, the proposed theory gives good consequences particularly for hydroplanes which lands with higher spare angles.

In add-on, Crewe ( 1946 ) assumes that the hull has a tangential-to-keel speed relation to the H2O. In this instance, he assumes that the impact gestures have other forces in add-on to the classical impact theory where the extra forces are the same types that occur in steady planing gestures. Crewe refers to these forces as impact-planing forces. On this, the impact-planing forces could be less than the similar forces developed during shaving due to the impact that does non last long plenty for the forces to construct up wholly. Equations were used to foretell the impactA­ planing forces include a ‘time-lag ‘ coefficient to account for this deficiency of full force build-up as compared to the steady planing status. Crewe ( 1946 ) sum up that

The entire H2O force in impact depends on the bill of exchange, attitude, geometry of the hull underside, force per unit area country, and the speed constituents during impact.

The forces considered which affect the impact, includes the classical or pure impact force, impact gliding force, and perchance normal retarding force or a signifier retarding force.

The pure impact is dependent on the practical mass. On this, a hull signifier in gesture has a corresponding mass of H2O that attaches itself with the hull However, the practical mass moves with the normal-to-bottom speed constituent during impact. All H2O effects except the inactiveness forces of the added mass are neglected.

The impact of gliding force is considered when the speed constituent in the perpendicular way is zero and the Froude figure is big. These forces are due to the digressive speed of the H2O relation to the underside and are similar to that in a steady planing instance. The normal retarding force comes from the constituent of flow of the H2O in the way which past the underside of the hull.

Some of the measures could be determined from the design curves in order to use of import design parametric quantities including peak acceleration, clip to make peak acceleration, flying emphasiss, wetted country and bill of exchange. Parameters for frame strength could be determined when the speed constituent perpendicular to the H2O has become. While, mean force per unit area at minute of first contact with H2O would find plating emphasiss.

This method gives an in-depth analysis of the forces impacting the impact status, and allows versatility for assorted impact conditions. However, there is limited experimental grounds to back up the theoretical expression, but the numerical work can be used for a scope of dead rise angles from 10 to 30 grades.

Subsequently, Benscoter ( 1947 ) proposed a measure set downing with an infinite beam and length cuneus get downing at the measure with a flat-bottom without flair and no afterbody. The spare angle is assumed to be remained changeless and the initial speed is in the way of the flight way angle. In most analysis, the speed constituent analogue to the keel is unbroken changeless during the impact period. However, since for stepped landings the spare angle is kept little, so the horizontal speed constituent will be kept changeless. This produces little difference in consequences if the speed constituent analogue to the keel were kept changeless. On this, the hydroplane ‘s reaction reaches a maximal upward acceleration before the point of maximal bill of exchange. This is proven in both experimental and theoretical consequences. Besides it is of import to observe that this bottom reaction, throughout the class of impact period, is merely relative to the perpendicular acceleration when the flying lift peers to burden.

In this case, Benscoter ( 1947 ) concluded that the maximal acceleration is relative to the initial speed squared and reciprocally relative to the bill of exchange at the clip of maximal acceleration. This was achieved by sing several considerations such as:

The of import parametric quantities that affect the burden or gesture of the hydroplane is the deadrise along the hull and the mass of the plane. If the plane is big so snap of the construction may besides be of import, nevertheless in this analysis it is ignored.

The “ unagitated H2O ” intersection of the hull signifier that is non merely plenty to be analysed since H2O pile-up of the spray root and the cross force per unit area distribution must besides be analysed along with the longitudinal force per unit area distribution.

A 3D analysis with a longitudinal distribution that could be merely handled in the proposed province of Benscoter ‘s work via an aspect-ratio factor applied to the force per unit area at all the points along the laden country. On this, to analyze the entire reaction distribution along the length of the hull, unit cross strips of the laden country are analysed at Stationss along the longitudinal loaded country and so integrated along this longitudinal length of burden.

Benscoter ( 1947 ) theory for maximal acceleration gives good understanding with experimental consequences. However, the comparing between bill of exchange in theory and experimental consequences is harder to find and more work should be done on this affair. Overall, the proposed theory gives a good method for finding the longitudinal fluctuation the burden. However, more elaborate work should be done on integrating a more complete theory that includes the cross force per unit area distributions.

Old ages subsequently, Hamilton ( 1955 ) conducted a graduated table trial which compares the consequences with Wagner ‘s theory on force per unit area in order to show the full graduated table impact forces and force per unit areas and the magnitude different parametric quantities consequence on the entire results. On this, to find the maximal hydrodynamic force per unit area on a planing underside for local impact, Wagner ‘s equation below was used for the theoretical computations. Although this equation is for a cuneus with flat-sides, Hamilton says it can be used for curving cross-sections since the use of the local deadrise angle in the equation.

Other factors that may impact impact tonss were taken into history such as chine submergence, hull and flying flexibleness, and afterbody effects. Following decisions were made during experimental trials.

Chine submergence is little and takes topographic point after the theoretical clip of maximal acceleration.

Equally far as construction flexibleness, flying quivers were non richly excited to do great differences in maximal acceleration and besides hull flexibleness is negligible.

Last, in order to change over the extremum force per unit areas, or the force per unit areas confined to a little country, to the design force per unit areas, or the force per unit areas over larger countries, for 2D hulls a simple look is derived for the comparative magnitude of extremum and the mean distributed force per unit areas.

Material

Historically, the full wing model of some planes was covered with pasted wood building. This includes propellors, control surfaces, fuselages, the pontoons and hulls of hydroplanes. The gum is used non merely to laminate and construct up big and irregular wooden parts, but it besides used to fix the assorted wooden parts together into the finished construction. On it, the extremely moisture-resistant coatings are used and required to protect the whole building.

The facts, such as articulations, together with fasteners, are, nevertheless, by and large regarded as the weakest portion of the built-up building. Consequently, they control the design in really big portion, despite it is known that the technique of pasting as practiced in aircraft is capable of considerable betterment. Sing on this, the utilizing of gums in aircraft hence require adhesives that retain a big proportion of their strength under moist conditions, even to the extent of staying safe in service after exposure to free H2O.

Now, the procedure used to build an aircraft is Vacuum Assisted Resin Transfer Moulding ( V ARTM ) . This is as a common procedure for the production of aircraft constituents with high quality and low cost aircraft parts. Here, the characteristics incorporated into the design of the constituent can heighten the effectivity of VARTM and do it go a really cost effectual method for bring forthing big graduated table and complex parts. For this procedure, Wood et al. , ( 2011 ) stated that the lone factor impacting the concluding quality of the portion was the inability of the room temperature cured extract rosin system used to defy the hot, wet conditioning trials required for aircraft enfranchisement. The facts, the VARTM procedure specifications and the design characteristics of the parts are applicable to a broad scope of aircraft and high public presentation Marine constructions.

Related to those material, Bellanca et Al, ( 2005:76 ) antecedently commented about the utilizing of complexs which promote laminar flow for hydroplane. This is a enormous advantage because of complexs make possible to fabricate really big structural constituents in one seamless piece without studs, without moving ridges in the tegument surfaces, etc. With such surfaces will enable the aeroplane manufacturer to fabricate an aeroplane that has a drag coefficient of 0.015 and the aircraft which holding more velocity and scope, where its opposite number in aluminum might hold a coefficient of 0.025.

However, Degrigny ( 1995 ) pertinent to hydroplane design and stuffs used, stated that intervention of a composite brand is ever hard when the electrochemical behavior of the different stuffs is incompatible. On this, to handle the whole of a big object incorporating both aluminum metal and Fe metals, he suggested the utilizing chemical and electrolytic methods which involves four stairss: pre-immersion in a chelating solution to fade out the surface corrosion merchandises, electrolytic cleansing of the Fe metal by cathodic polarisation in a solution that inhibits corrosion of the aluminum alloys, dechlorination of the full object by cathodic polarisation and a concluding rinse under cathodic protection.

Simulation

Harmonizing to Ghoreyshi et al. , ( 2009 ) , there is an increasing involvement in utilizing natural philosophies for patterning an aircraft design. For illustration, the design of unstable aircraft constellations would assist on the handiness of high quality theoretical accounts to let control Torahs to be defined. One constituent of the needed theoretical account arises from the aeromechanicss. Stability and control analysis over the flight envelope traditionally uses a look-up tabular array of forces and minutes, measured from air current tunnel trials comparatively towards the terminal of the design rhythm.

As an illustration, LS-Dyna which is used as a Mam tool to imitate the dynamic status of the aircraft during landing and take-off tally. On this, Maimun et al. , ( 2009 ) said that by LS-Dyna, it is possible to mensurate the influence of hull form and land consequence on aeromechanicss by utilizing the Three Dimensional ( 3D ) bundles. Surely, assorted parametric quantities need to be included, such as lift coefficient and lift to drag ratio. Based on the consequences of the CFD simulation indicate a decrease on lift to drag ratio which is caused by hull form every bit good as there are enhancement on lift coefficient and lift to drag ratio when winging in propinquity to the land ( H2O surface ) .

In other surveies for illustration, a survey on impact of stationary for a short continuance of clip during which high local force per unit areas occur on the hull parts of the ship, Das and Batra ( 2011 ) used simulation for banging impact of stiff and deformable hull underside panels. Here, Lagrangian and Eulerian were coupled and formulated utilizing LS-Dyna. Related to hydroplane design, the Lagrangian preparation could be used to depict plane-strain distortions of the hull panel and see geometric nonlinearities, while the Eulerian preparation could be used to analyze distortions of the H2O. On this, distortions of the hull panel and H2O are coupled through the hydrodynamic force per unit area exerted by H2O on the hull, and the speed of atoms on the hull wetted surface impacting distortions of H2O. The considered parametric quantities that should be included to obtain the best consequence such as:

The continuity of surface grips and the inter-penetrability of H2O into the hull are satisfied by utilizing a punishment method.

The force per unit area distributions computed for deformable panels are found to differ from those obtained by utilizing a home base theory and Wagner ‘s banging impact theory.

AERODYNAMICS SIMULATION

Amir and Kontis ( 2007:831 ) said that one of the most ambitious countries of research in aeromechanicss is the decrease of skin clash, particularly for disruptive flows. They added that lower tegument clash is achieved by driving the turbulent boundary bed towards separation. This is accomplished by shooting fluid normal to the wall, determining to bring forth inauspicious force per unit area gradient, surface warming in air, surface chilling in H2O, or any other scheme designed to increase the unstable viscousness at the wall.

On this, computational fluid kineticss ( CFD ) has the prognostic capableness to bring forth the natural information for the look-up tabular array. The job is that, the computational cost involved, peculiarly if this is viewed as a beast force computation for every entry in the tabular array ( Ghoreyshi et al. , 2009 ) . Therefore, the option is to utilize simulation based informations early in the design rhythm in which they emphasizes the representation of the aerodynamic nonlinearities, and is based on trying. Besides, the scenario presuming incremental alteration from an initial geometry, for which a hi-fidelity theoretical account from the first scenario is available. In this instance data merger is used to update the theoretical account where Kriging is used to extrapolate the samples computed utilizing simulation toward the kernel of issues as follows:

First, a scope of modeling degrees is available, from Reynolds Averaged Navier-Stokes down to possible flow theoretical accounts and semi-empirical methods. Each of the degrees has a scope of cogency and cost. Data merger can be used for informations from different methods, with low cost informations bespeaking tendencies and a little figure of high cost simulations rectifying values.

Second, Reconstruction methods that can significantly cut down the figure of informations points which really need to be computed.

Third, the designation of parametric quantity parts where the aeromechanicss is nonlinear, and therefore where information is desperately needed. This is a typical sampling job.

Furthermore, Kokes et al. , ( 2006 ) cleavage of techniques to foretell aerodynamic forces and minutes on a missile in atmospheric flight: empirical methods, air current tunnel testing, computational fluid kineticss simulation, and flicker scope proving. On this, empirical techniques aerodynamically describe the missile with a set of geometric belongingss ( diameter, figure of fives, nose type, nose radius, etc. ) and catalogue aerodynamic coefficients of many different missiles as a map of the characteristics. Therefore, in this undertaking proposal, the aerodynamic forces and minutes will be computed with the computational fluid kineticss solver, while the free flight gesture of the missile will be computed by incorporating the stiff organic structure dynamic ( RBD ) equations of gesture.

HYDRODYNAMICS SIMULATION

Harmonizing to Szsbehely ( 1960:137 ) , hydrodynamic impact refers to the early entry phases of a organic structure into H2O. The maximal forces are developed really shortly following contact with the free surface of the H2O. These early phases are of extreme importance for the structural design of the outer tegument, back uping construction, and interior ( acceleration-sensitive ) warhead. Based on that, the hydroplane interior decorator, need hydrodynamic impact information in connexion with hydroplane landing. On this, hydrodynamic rules are used to analyze seaplane impact jobs and wave consequence on its or on stable constructions which is closely related. With exclusion on the of import job of really high speed impact ( when the squeezability effects of the H2O go outstanding ) , the incompressible free surface potency flow theory were used. In this case, solutions of the assorted jobs may be reduced to find variable practical multitudes associated with the come ining organic structures.

In add-on, Engle and Lewis ( 2003:180 ) said the development of a first rules approach to foretelling hydrodynamic tonss require interior decorators to hold the tools available to foretell both ordinary moving ridge induced tonss and slamA­ induced floging tonss that result from hydrodynamic impacts. The initial surveies contained herein show encouraging consequences for the anticipation of hydrodynamic impacts. Once a comprehensive proof of these tools is completed, it is believed that these methods will hold the possible to supply interior decorators with a practical and advanced design appraisal capableness.

IMPACT SIMULATION

Physical testing and simulation would be suited to prove the impact while set downing. Based on Smith ( 1950 ) experimental consequences, it shows that the maximal force per unit area measured on a stop depends on the stop size and place and it is non the true maximal force per unit area at that point. The maximal mensural force per unit areas at any given parts of the hull can nevertheless be expressed in footings of the first impact conditions. Based on the experiment conducted, the consequence of the assorted impact parametric quantities of maximal impact force per unit areas on a hull underside encroaching on a H2O surface are measured utilizing D.V.L. mechanical force per unit area recording equipments on three hulls, each of 3-ft. beam, in the hull launching armored combat vehicle. He conducted the experiment as follows:

The dead rise angles of these hulls were 100, 200,300 severally. They were launched with controlled impact conditions of velocity, attitude and acceleration at flight way angles of 80 to 100, but with freedom in heaving and pitch: farther trials were huffy vitamin E by perpendicular beads.

Parallel theoretical surveies have been made to look into the consequence on the maximal force per unit area of:

size of mensurating surface,

beam burden,

freedom to flip,

horizontal speed,

initial perpendicular acceleration,

going from the simple cuneus form

In add-on, other required consideration for this he-man Y is as stated by Peng and Peregrine ( 2000 ) . These considerations are as such:

the value of the pressure-impulse,

speed field at the border of the home base which is non merely remarkable due to they will hard to happen the force per unit areas after the impact, and others relevant belongingss or an impact

Methodology

There are two chief phases m the development of this research undertaking. First, the research will work on the preliminary survey of the undertaking. In this phase, the survey would concentrate on the background of an amphibious aircraft and besides possible development of early construct. This would besides be considered as a feasibleness survey of this undertaking. This is shown clearly in Figure 8.1 below.

PHASE 0:

DATA GATHERING AND PRELIMINARY EVALUATION

PHASE 1:

REFER TO STUDY ON STRUCTURE TO WATER CONTACT

PHASE 2:

PRELIMINARY DESIGN DEVELOPMENT

PHASE 3:

CONCEPT GENERATION

PHASE 4:

DESIGN VERIFICATION

REQUIRE ORIGINAL SHAPE

PROPOSE BASIC SHAPE

STUDY OF CURRENT LANDING PROCEDURE

STUDY OF STRUCTURE TO WATER IMPACT

DESIGN PROPOSAL

PRELIMINARY SIMULATION AND ANALYSIS

CONCEPT DEVELOPMENT

CONCEPT SELECTION

CONCEPT/DESIGN COMPARISON AGAINST CURRENT SETUP ( SHAPE AND FUNCTION )

SIMULATION AND TESTING

PRELIMINARY Phase

DESIGN VERIFICATION STAGE

PHASE 5:

FABRICATION AND VERIFICATION

PHASE 6:

FINALIZING Design

PHASE 7:

FINAL VERIFICATION AND RESULT

Fabrication OF SELECTED DESIGN

VERIFICATION/CORRELATION/SIMULATION/TESTING

FINAL DESIGN MODIFICATION ( STAGE 1-5 )

LS DYNA SIMULATION AND ANALYSIS

FINAL PRODUCT

Confirmation BY SIMULATION AND INDUSTRY EXPERT

Leave a Reply

Your email address will not be published.